Leak Detection Systems - Extrusion Blow Molding

>> Friday, 1 April 2011

The leading container leak detection systems are manufactured as a complete functional package with self-calibrating microprocessor and adjustable stand-strand conveyor or indexing rotary table. Leak detection systems may be equipped with one or up to four leak detection heads and require specific adjustments depending on the container design and production rate requirements. Most systems are programmable allowing the fill value and inspection time to be tailored and can accommodate a wide range of container sizes. Additional programmable functions allow the inspection cycle to be adjusted to Trimmer speeds or Blow Molding machine cycle time. The systems include an LCD display that indicate accepted and rejected containers in total and accepted containers as a percentage.

Initial adjustment procedures include centering the leak detector nose cone assembly over the opening of the container, adjustment of the relative height of the nose cone assembly on the column stand and adjustment of the conveyor height.

Nose cones have two ports on them. One port is for the fill line and is used to fill the container with air. On certain nose cones, the two ports are different sizes. If the ports are different, the fill line should be connected to the larger of the two ports. The second port is for the sensing line. The sensing line is used to track the pressure in a container during the inspection cycle. This line is connected to the bottom of the control panel, which then goes to the pressure transducer on the printed circuit board.

Set-Up

1. Disconnect the air and turn the power off to the leak detector.
2. Remove the gasket from the nose cone.
3. Extend the cylinder to full stroke.
4. Raise or lower the nose cone assembly, so that the surface of the nose cone just meets the opening of the container.
5. Center the nose cone by moving the arm the desired direction.
6. Reconnect the air and turn the power on.

Note: The printed circuit board uses the input from the photo-eye to start the leak detector. The timing of the nose cone comes from the position of the photo-eye. The photo-eye needs to be positioned so that the nose cone comes down in the center of the container opening.

7. Run some containers past the leak detector. Adjust the photo-eye so when the leak detector is cycled the nose hits the center of the container opening.
8. After the timing is set, switch the leak detector to the maintenance mode. Run a couple of containers through the leak detector. Monitor the four test parameters found in the maintenance mode.

Note: After any adjustments are made, the leak detector should be put into the maintenance mode. The test parameters should be monitored to determine if the chances were correct.
8. After the timing is set, switch the leak detector to the maintenance mode. Run a couple of containers through the leak detector. Monitor the four test parameters found in the maintenance mode.

Note: After any adjustments are made, the leak detector should be put into the maintenance mode. The test parameters should be monitored to determine if the chances were correct.


Sequence Of Operations

The following is the sequence of operations for a Single Head Inline Leak Detector. Special applications may cause slight variations from this description. The steps are as follows:

1. A container enters the leak detection area and breaks the photo-eye beam.
2. After the printed circuit board receives the cycle start input from the photo-eye, the fill and nose cone solenoids will energize. The fill solenoid will stay energized until the starting pressure is reached or the Max. Fill Time has elapsed. The nose cone solenoid will stay energized for the total leak test period.

Note: If the inline system is equipped with an index cylinder it will be programmed slightly different. The cycle start signal will energize the index/brake solenoid first. This is so the index cylinder can extend and stop the container before the nose cone meets the container opening. This output is controlled by a programmable timer and is referred to as the Stop Lead Time. After the index/brake solenoid times out, the fill and nose cone solenoids will energize as stated before.

3. As long as the preprogrammed Fill Value was reached, the leak detector will complete its test cycle. If the Fill Value was not reached, the leak test cycle will be aborted and a No Fill condition will occur. This may be do to a large air leak in the system or a large hole in the container. If no leak can be found, the Max. Fill Time may need to be increased.
4. After the pressure in the container has reached its Fill Value, there is a short delay . This delay is to allow for the valve response and to let the air settle in the container before the leak test takes place. If an air flow is present during the leak test, a false pressure loss will be measured. If this pressure is great enough to make the loss negative, the container will be rejected. This delay is typically set a t .050 msec. And can be increased or decreased to meet the particular needs of the container being leak tested.
5. Next, the microprocessor takes a pressure measurement, waits for a period of time, and then takes another pressure measurement. The period between the two pressure measurements is called the Check Time. This time determines how small of a hole the Leak Detector can detect. The longer the time is between the two measurements means the more air pressure that will be lost. It should be noted that the longer Check Time is, the larger the normal Loss will be on a good container. This is due to system air leakage. If the Check Time is increased significantly, the Initial Average Loss will have to be increased also. The Initial Average Loss should be equal to the average loss of several containers. The difference in PSI between the two pressure measurements is displayed as the Loss. If the Loss is smaller in value than that of the Loss Limit, the container is considered good. This container will then advance, allowing another container to enter the test area. If the Loss is greater than the Loss Limit, the container will be failed. At this point, the eject contact will close and the eject solenoid will be energized. The bad container will be ejected of the conveyor by the means of a blow-off or a pusher. The eject solenoid will stay energized until the Blow-Off Time has elapsed.

Note: The blow-off has to be completed before the next container enters the leak detection area.
The Blow-Off Time should be programmed as short as possible, so that this can be accomplished.

Test Conditions

The leak detector has 3 possible test conditions:

1. PASS (good container) - When the loss of the container being tested is lower than that of the Loss Limit (LMT), the test condition will become pass. The eject contact will stay in its de- energized state.

2. FAIL (bad container) - When the loss of the container being leak tested exceeds the value of the Loss Limit (LMT), the test condition will become a fail. The eject contact will go to its energized state. It will stay energized until the Blow-Off Time has elapsed. The Blow-Off Time can be increased of decreased by the use of a hand held programmer.

3. NO FILL (bad container) - A no fill condition is the same as a fail and the container will be rejected. This condition may be the result of either a large air leak of the absence of a container.

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Power Up of Extruders/PLC - Wheel Blow Molder

Following is a extruder startup procedure for a wheel blow molding machine:

1. Turn on the plant chilled or tower water supply to the extruder heat exchanger and extruder feedthroat.
2. Turn on the power at the PLC wheel drive cabinet by raising up the handle in the top right corner. An audible alarm will sound.
3. Push the reset button that is located in the middle of the cabinet door. The button will illuminate.
4. Go to the PLC monitor and wait momentarily for the computer to boot up.
5. Press the ACK and the RESET touch button on the screen . This will silence the alarm.
6. Press the touch button that reads HYD. WATER HEATS in the lower left corner. A start screen will appear.
7. Press the start touch buttons for the pump heats only.
8. Press the MAIN touch button in the top right corner to return to the main screen.
9. Verify that the green lights below the water and heats label on the screen are illuminated. This indicates an “on” condition.
10. Press each individual extruder touch button located in the top right corner of the main screen to access each extruder screen one at a time. Press the AMP on/off touch button in the lower left corner of the extruder screen to observe the current draw.
11. Repeat the above instruction for each extruder to check current draw for each zone.
12. Push the Main touch button to return to the main screen.
13. Wait for a minimum of two (2) hours for the heats to arrive at their set points and soak.
14. After the heats have reached their setpoints and sufficient soak time has expired the extruders can be started.
15. Press the HYD WATER HEATS touch button in the lower left corner of the main screen. The start screen will appear.
16. Press the START touch button for the hydraulic pump. The pump will start momentarily.
17. Return to the main screen by pressing the MAIN touch button.
18. Press each individual extruder touch button located in the top right hand corner of the main screen to access each extruder one at a time. Press the ON touch button directly under the enable label to enable that extruder.
19. Go to the main screen by again pressing the MAIN touch button in the top right corner.
20. Repeat this enabling process for each extruder.
21. Check all heats once again.
22. Go to the main screen and press the EXTRUDERS touch button to initiate. The main speed control potentiometer must be at the zero (0) setting.
23. At this time proper face shields and gloves must be worn.
24. Slowly rotate the main speed pot to the #20 position closely observing the extruder amps and PSI for each extruder. Note: Quickly rotate the main speed potentiometer to the “0” position at the first indication of high amps or PSI while keeping the maximum extruder pressure under 6,000 PSI.
25. Increase extruder speeds by turning the pot to #100 (100% extruder speed) and purge for 30 seconds or until all entrained air in the plastic is removed.
26. Stop extruding by rotating the speed potentiometer to #0 position.

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Control Chart Interpretation – Three Basic Rules – C, P, R

C - If any data points are outside the control limits, treat them as a special cause.
Caution: with 3 sigma limits, 3 out of 1000 times will not be a special cause,
but 997 times out of 1000 it will be!

P - Since the data should be normally distributed about the mean, look for any non-normal patterns.
The easiest way to do this, is to divide the distance between the UCL and the mean or the LCL and the mean into 3 equal parts or zones.
- If about 68% of the data points fall within the first zone above and below the average, then there are no special causes.
- If there are more than 68% (say 90%) or less than 68% (say 45%) then there are special causes acting on the process.


R - If there is a consecutive run of 7 points in a row above or below the mean,
treat the 7 or more points as a special cause, i.e., the process has "shifted".
Think of it as flipping a coin and getting 7 heads in a row.
A very unlikely event!! (Actually, only 8 chances out of 1000!)

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Qualification (Process Capability Study) - Validation procedure for injection molds

The tenth step in validating a injection mold with the overall process shown in injection mold validation flow chart is Qualification (Process Capability Study). The steps before:
1. Mold certification
2. Dry cycle mold
3. Process stability test
4. Gage repeatability & reproducibility (R&R) test
5. Mold viscosity test
6. Balance of fill analysis
7. Gate Freeze Test
8. Commissioning (multi-cavity analysis)
9. Design of Experiments (DOE or DOX)

Purpose:
The purpose of the qualification study is to determine if the process can meet the specified key part tolerance ranges. The first mold being manufactured to produce a molded part might be made “metal safe”. In this case, the qualification step will determine how much metal needs to be modified in the mold. Resin and colorant properties also need to be evaluated so that process capability may be determined.

Once a process has been selected from performing the Design of Experiments (DOE or DOX), the qualification study needs to be performed to determine the amount of variation of each key dimension (via control charts). This variation is compared with specified key part tolerances to estimate percent out of specification and product quality measures (Cr, Tz & Cpk). A solid understanding on creating and interpreting statistical control charts is necessary to perform the process capability study.

Material and Colorant Variation
Resin differences and the addition of colorants effect molded part performance. The rate of the shrinkage changes depending on the resin properties and type of colorant used. This will effect molded part dimensions and mechanical performance. In many cases, there is variation from one resin lot to the next, i.e., lot to lot variation. This lot to lot variation in resin properties is inherent. The resin variation must be evaluated to determine if the material specification range will drive the molded part to be out of the specification. In addition, the Qualification study must properly evaluate each colorant, while including the lot to lot variation in the base resin. Understanding the effects of different colorants is imperative since the same part must be produced in multiple colors from the same mold. The information obtained from the qualification study results can be used to properly modify the mold.

To quantify base resin, and resin to colorant blend properties, a reliable test method must be selected. Equipment such as the gel permeation chromatograph (GPC), differential scanning calorimeter (DSC) and capillary rheometer are reliable tools for quantifying the lot to lot range. However, it is sometimes difficult to obtain the data from these tools. Material suppliers in all regions generally provide data from the melt flow index (MFI) apparatus. The disadvantage of using the MFI unit is it only provides one data point on the shear rate versus viscosity curve. And, more importantly for qualification purposes, the accuracy of the test is poor. When data from the GPC, DSC or capillary rheometer is not available, regress to the MFI data as a means to quantify the upper, lower, and mean specification of the base resin.

While the mold is being designed, a lot to lot variation representing the maximum expected variation in the resin should be requested from the material supplier. Three lots of the base resin representing the upper, lower and mean specifications from the supplier will deliver an accurate indication of the capability ratio achievable in a production environment. Couple this together with an investigation of all colorants and the percent regrind to capture the remaining sources of inherent variation. Multiple options of the procedure for the qualification study were created to allow for a variety of different circumstances. A description of when to use each option is provided with the procedure. Review these descriptions to find an option which best meets the needs of your qualification study. It may be necessary to edit these options to identify the best qualification possible. Be sure to capture the intent of the qualification which is to examine all the sources of variation by means of an extended molding run. The qualification provides the confidence to make proper metal modifications to the mold and to provide the go ahead to move into the verification stage.

Option 1 Description:
This is the best option to study the inherent material and colorant variation. It requires representative virgin resin lots of the upper, lower and mean specifications. In addition, it requires adequate amounts of all colorants which will run on the mold.

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Option 1 Procedure:
1. Run a qualification study at the selected process conditions with the mean specification resin lot appropriately mixed with primary colorant for a period of 8 hours.
2. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
3. Switch to the resin lot representing the upper specification. This resin lot should be appropriately mixed with the primary colorant. Run for a period of 8 hours.
4. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
5. Switch to the resin lot representing the lower specification. This resin lot should be appropriately mixed with the primary colorant. Run for a period of 8 hours.
6. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
7. For each additional colorant, appropriately mix the colorant with the resin representative of the mean specification. Run each additional colorant blend for a period of 8 hours.
8. During each additional run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
9. After proper conditioning, measure and record all critical dimensions of all the parts.
10. Develop an and R Chart (n=4).
Note: in the course of a day, you may have several measurements from each cavity to repeat the multi-cavity analysis (within cavity/between cavity variation), if needed.
11. Both the and R charts should show control, otherwise investigate the sources of variation (root cause.)
12. Proceed to determine percent out-of-spec. and calculate the appropriate Product Quality Measures1 (Cr, Tz & Cpk).
13. Compare results to the results from the DOX process. Also, compare to the target and develop a histogram of sample population with and to assess normality of the parent.

Option 2 Description:
This option does not evaluate the inherent material variation. It does investigate the differences attributed to molding the same part in a number of colorants. It requires a representative virgin resin lot of the mean specification. In addition, it requires adequate amounts of all colorants which will run on the mold.

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Option 2 Procedure:
1. Run a qualification study at the selected process conditions with the mean specification resin lot appropriately mixed with primary colorant for a period of 24 hours.
2. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
3. For each additional colorant, appropriately mix the colorant with the resin representative of the mean specification. Run each additional colorant blend for a period of 8 hours..
4. During each additional run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
5. After proper conditioning, measure and record all critical dimensions of all the parts.
6. Develop an and R Chart (n=4).
Note: in the course of a day, you may have several measurements from each cavity to repeat the multi-cavity analysis (within cavity/between cavity variation), if needed.
7. Both the and R charts should show control, otherwise investigate the sources of variation (root cause.)
8. Proceed to determine percent out-of-spec and calculate the appropriate Product Quality Measures2 (Cr, Tz & Cpk).
9. Compare results to the results from the DOX process. Also, compare to the target and develop a histogram of sample population with and to assess normality of the parent population.

Option 3 Description:
This option evaluates the inherent material variation along with the complication of using regrind. This Qualification study investigates the variation attributed to molding the same part in a number of colorants. It requires a representative virgin resin lot of the upper, lower and mean specification. In addition, it requires adequate amounts of all colorants which will run on the mold and regrind.

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Option 3 Procedure:
1. Run a qualification study at the selected process conditions with the mean specification resin lot appropriately mixed with primary colorant and percent regrind for a period of 8 hours.
2. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
3. Switch to the resin lot representing the upper specification. This resin lot should be appropriately mixed with the primary colorant and percent regrind. Run for a period of 8 hours.
4. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
5. Switch to the resin lot representing the lower specification. This resin lot should be appropriately mixed with the primary colorant and percent regrind. Run for a period of 8 hours.
6. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
7. For each additional colorant, appropriately mix the colorant with the resin representative of the mean specification and percent regrind. Run each additional colorant blend for a period of 8 hours.
8. During each additional run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
9. After proper conditioning, measure and record all critical dimensions of all the parts.
10. Develop an and R Chart (n=4).
Note: in the course of a day, you may have several measurements from each cavity to repeat the multi-cavity analysis (within cavity/between cavity variation), if needed.
11. Both the and R charts should show control, otherwise investigate the sources of variation (root cause.)
12. Proceed to determine percent out-of-spec. and calculate the appropriate Product Quality Measures3 (Cr, Tz & Cpk).
13. Compare results to the results from the DOX process. Also, compare to the target and develop a histogram of sample population with and to assess normality of the parent population.

Option 4 Description:
This option does not evaluate the inherent material variation. It does investigate the differences attributed to molding the same part in a number of colorants along with the complication of using regrind. The Qualification study requires a representative virgin resin lot of the mean specification. In addition, it requires regrind and adequate amounts of all colorants which will run on the mold.

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Option 4 Procedure:
1. Run a qualification study at the selected process conditions with the mean specification resin lot appropriately mixed with primary colorant and percent regrind for a period of 24 hours.
2. During the run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
3. For each additional colorant, appropriately mix the colorant and percent regrind with the resin representative of the mean specification. Run for a period of 8 hours.
4. During each additional run, take a reading from a single cavity (selected at random) once every 15 minutes. More than one reading may be necessary for destructive test methods or to keep additional parts on hand.
5. After proper conditioning, measure and record all critical dimensions of all the parts.
6. Develop an and R Chart (n=4).
Note: in the course of a day, you may have several measurements from each cavity to repeat the multi-cavity analysis (within cavity/between cavity variation), if needed.
7. Both the and R charts should show control, otherwise investigate the sources of variation (root cause.)
8. Proceed to determine percent out-of-spec. and calculate the appropriate Product Quality Measures4 (Cr, Tz & Cpk).
9. Compare results to the results from the DOX process. Also, compare to the target and develop a histogram of sample population with and to assess normality of the parent population.

The further steps are required in validating a injection mold according to injection mold validation flow chart is dry cycle mold:

11. Mold metal Adjustments - centering process
12. Verification (30-day run)

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Safety precautions for injection molding

>> Saturday, 12 March 2011

Safety is everyone's responsibility in the workplace. Safety is most often related to good maintenance and good housekeeping. Safety needs to be an attitude that if always present in your daily activities. Employees should not be hesitant to voice safety concerns in the workplace. Management is just as committed to safety as the operators on the floor; the primary difference is that the operators are usually the closest to unsafe conditions; keep management advised of unsafe conditions.

The following list includes items which should be maintained to assure a safe working environment:

1. Floor and machine should be kept free of oil
2. Floor and machine should be kept free of pellets.
3. Never reach over or under machine guards.
4. Never climb between the bars when pumps are running.
5. Retract injection. unit before entering the bar space.
6. The front gate should have an electrical, hydraulic and mechanical safety device preventing clamp from closing when the front gate is open.
7. The rear gate should have an electrical interlock preventing clamp from closing when rear gate is open (there is often a hydraulic interlock here also).
8. Readjust mechanical safety each time the mold open daylight space is adjusted.
9. The purge shield should prevent injection forward if the purge shield limit switch is not made.
10. Catwalks or platforms with railing should be present if hoppers such as drying hoppers stand tall enough whereby access requires climbing onto machine.
11. Know location of portable fire extinguishers; there should be an extinguisher no farther than 75 feet.
12. All electrical outlets should be marked as to voltage.
13. Never reach into the throat of an operating granulator. Unplug granulators before working on.
14. Always wear suitable foot and eye protection; safety glasses should be worn and steel toed shoes are recommended; soft soled shoes should not be worn.
15. Doe not operate any equipment unless suitable training has been supplied.
16. All employees should be advised of any chemicals in the facility which are considered hazardous; read further about "Right To Know" laws for each particular state.
17. First aid kits should be available.
18. Advise operators that injection molding resin pressure can reach 30,000 psi and that hydraulic line pressure can reach 2500 psi. Clamp tonnage developed equals 2000 lbs of force for each ton; operators be advised.
19. Be conscious of sharp square corners on ejector pins; many cuts result from protruding ejector pins.
20. Razor knives also require extreme caution as their use results in many cuts.
21. NEVER use steel tools on the mold cores, cavities or parting line... Use brass, copper or aluminum. Brass can scratch highly polished steel, so use caution.
22. Do not stick fingers or rods into the barrel/screw feed throat area.
23. Examine air hoses and electrical cords to verify condition is proper; do not use cords with damaged insulation. Be especially observant when working near nozzle heater bands as these wires are easily
24. damaged.
25. Use only swivel type safety eyebolts; screw eyebolts far enough in such that thread engagement is 1.5 times the diameter.
26. Never stand directly below a mold suspended in air.
27. Avoid back injuries; lift properly with the back upright and straight; know your limitations and do not exceed them; use proper tools and get help when needed.

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9. Design of Experiments (DOE or DOX) - Validation procedure for injection molds

The ninth step in validating a injection mold with the overall process shown in injection mold validation flow chart is Design of Experiments. The steps before:


1. Mold certification
2. Dry cycle mold
3. Process stability test
4. Gage repeatability & reproducibility (R&R) test
5. Mold viscosity test
6. Balance of fill analysis
7. Gate Freeze Test
8. Commissioning (multi-cavity analysis)

Purpose:
The purpose of the Design of Experiments (DOX or DOE) is to identify the optimum mold process and the mold process window. A solid statistical understanding of DOX is necessary. There are many different types of software that can be used to assist you in performing design of experiments properly. Use the software that you are most comfortable with.

The DOE can require a large amount of time to perform depending on the number of variables selected to test. In some cases a properly conducted DOX can require 2-3 days to perform as well as additional time to measure part attributes. It is best to perform an extensive DOE on the pre-production tooling (Pilot Tool) which replicates the production tooling. This will give a good representation as to which key variables will effect the critical attributes of the molded part from the production tool. It is also recommended the DOX be performed immediately after the commissioning test. Especially is you are confident with the skill and precision of your mold builder to produce a mold which has minimal variation between cavities.

It is recommended that a fractional factorial be performed to study the main effects. Variables that do not have a significant effect on critical part dimensions can be eliminated by performing the fractional factorial first. Significant variables for a full factorial experiment are determined from the fractional factorial, eliminating guesswork. The information from the full factorial as well as the fractional factorial analysis can then be used to perform Statistical Process Control (SPC).
Fractional Factorial Description:
This step should be performed when it is not clear which variables will effect key dimensions and attributes of the part. In some cases, it may be necessary to perform the fractional factorial DOE to determine the main effects for the aesthetics of the part. This will ensure that a full factorial DOX for the critical dimensions can be run while achieving aesthetically pleasing parts. The fractional factorial is to be used as a screening devise for identifying significant processing variables and not for process optimization.

Caution: The fractional factorial will not determine interaction effects.

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Fractional Factorial Procedure:

1. The multi-cavity analysis has been successfully completed, i.e., there is no difference between cavities on the critical part dimensions.
2. Set up fractional factorial experiment to include all significant molding variables.
3. Typical mold process variables to include in DOX are:
Melt Temperature, Hold Pressure, Hold Time, Cooling Time, Mold Coolant Temperature, Cavity Pressure at Injection Cutoff, Peak Cavity Pressure (Packing), Screw Speed, Back Pressure.
4. Test extreme conditions (corners) of the DOE to verify you are within the molds processing window.
5. If a test "Fractures" then stop the DOX and rerun the experiments with acceptable degrees of variation for each factor.
6. For each change in processing conditions, allow time for system to equilibrate for changes in machine set up. For example, changes in mold temperature may require the mold running for 1 hour before it reaches steady state conditions.
7. Collect 5 shots for each process conditions. Attach a process set-up sheet and test code to samples.
· For each destructive test method, collect one additional shot.
8. Condition parts for 24 hours at 23C (73.4F) and a relative humidity of 50% with a standard tolerance of 2.0C (3.6F) and 5% relative humidity, respectively, for 2 days.
9. Measure and record all key attributes for one cavity, representative of the mold (see multi cavity analysis).
10. Analyze the data using any statistical software with a DOX option. Use coded units for the analysis.
11. Identify significant processing variables to be evaluated in the full factorial DOX.

Full Factorial DOX Description:
The full factorial is to be used to determine the optimum processing conditions based on key part dimensions. When it is unclear which variables are significant, the fractional factorial should be performed first.

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Full Factorial Procedure:

1. The multi-cavity analysis has been successfully completed, i.e., there is no difference between cavities on the critical part dimensions.
2. Set up full factorial experiment using significant variables determined from the fractional factorial (if applicable).
3. Typical mold process variables to include in DOX are:
Melt Temperature, Hold Pressure, Hold time, Cooling Time, Mold Coolant Temperature, Material Lot (different lot of same resin), Colorant, Cavity Pressure at Injection Cutoff, Peak Cavity Pressure (Packing), Screw Speed.
4. Test extreme conditions of the DOE to verify you are within the molds processing window.
5. If a test "Fractures" then stop the DOX and rerun the experiments with acceptable degrees of variation for each factor.
6. For each change in processing conditions, allow time for system to equilibrate for changes in machine set up. For example, changes in mold temperature may require the mold running for 1 hour before it reaches steady state conditions.
7. Collect 5 shots for each process conditions. Attach a process set-up sheet and test code to samples.
· For each destructive test method, collect one additional shot.
8. Condition parts for 24 hours at 23C (73.4F) and a relative humidity of 50% with a standard tolerance of 2.0C (3.6F) and 5% relative humidity, respectively, for 2 days.
9. Measure and record all key attributes for one cavity, representative of the mold (see multi cavity analysis).
10. Analyze the data using any statistical software with a DOX option. Use coded units for the analysis.
11. Perform the optimization of the process based on the various critical dimensions and most efficient cycle time.
12. Identify upper and lower control settings for each processing variable evaluated (create a mold processing window).

The further steps are required in validating a injection mold according to injection mold validation flow chart is dry cycle mold:

10. Qualification (process capability study)
11. Mold metal Adjustments - centering process
12. Verification (30-day run)

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8. Commissioning (multi-cavity analysis) - Validation procedure for injection molds

The eight step in validating a injection mold with the overall process shown in injection mold validation flow chart is Commissioning (multi-cavity analysis). The steps before:


1. Mold certification
2. Dry cycle mold
3. Process stability test
4. Gage repeatability & reproducibility (R&R) test
5. Mold viscosity test
6. Balance of fill analysis
7. Gate Freeze Test

Purpose:
The purpose of commissioning is to ensure that all cavities in the mold deliver the same quality, i.e., there is no difference between cavities in the mold on the critical dimensions. The time required to perform this analysis is a function of the number of cavities and number of critical dimensions. The time on the injection molding machine is minimal compared to the time required to measure the parts. However, by performing this analysis it will significantly reduce the number of parts required to test and measure for future experiments on the multi-cavity tool. A solid understanding of creating and interpreting statistical control charts is necessary to perform the multi-cavity analysis.

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Procedure:
1. Set melt temperature at resin manufacturer's recommended mid-range.
2. Set mold temperature at resin manufacturer's recommended mid-range.
3. Set fill rate and transfer method (position, time or pressure) based on result of the 5. Mold viscosity test.
4. Set hold time based on result of the 7. Gate Freeze Test
5. Set cooling time long enough so that parts eject without being distorted.
6. Allow the mold to run at least 1 hour, which should be long enough for the system to reach thermal equilibrium and for the process to stabilize. Longer stabilization time may be necessary for higher cavitation tooling like 128 cavity stack molds.
7. Ensure the measurement technique is stable and measurement sigma is known. The measurement technique must be accurate and precise enough to capture small amounts of variation in part dimensions and attributes.
8. Take one all-cavity shot every 15 minutes for an hour (n=5) with each cavity identified. (Base your choice of time on capturing most of the variation that is present.)
Caution: For destructive test methods, additional all-cavity shots will be required - to sample every 15 minutes. For every destructive test method, collect one additional shot.
9. Group all the parts from a particular cavity together to get samples of 5 observations each. The number of samples corresponds to the number of cavities.
10. Condition parts for 24 hours at 23C (73.4F) and a relative humidity of 50% with a standard tolerance of 2.0C (3.6F) and 5% relative humidity.
11. Measure and record all critical dimensions, attributes and variables for all parts.
12. Construct an and R Chart where the Range Chart will capture the variation within a cavity over an hour and the Chart will capture the variation between cavities. Calculate the Cp, CpK and target Z. This information will be used as a flag if the mold is considered off specification. For constructing an and R Chart use a spreadsheet Commissioning (multi-cavity analysis) which should be modified for your specific requiment.

13. Interpret the Range Chart.
• If the Range Chart is in control (pass C, P, and R), all the cavities deliver the same variability which can be calculated by , where d2=2.326 for n=5 (See Factors for constructing variables control chart on page 45), and is the average of the range measured within each cavity.
• If the Range Chart fails, and #7 was done, there is a particular cavity that is different from the others relative to the variability it produces. When the upper control limit (UCL) and the lower control limit (LCL) are not statistically meaningful, in comparison to the upper specification limit (USL) and lower specification limit (LSL), continue with the validation process.
14. Interpret the Chart (if the Range chart is in control ONLY)
• If the Chart is in control (pass C, P, and R), all the cavity averages are statistically not different. All the variability in the mold occurs within one cavity and all cavities are statistically not different.
• If the Chart fails, the special cause cavity must be investigated and corrected, i.e., is it because of mold, material, process, or people? When the upper control limit (UCL) and the lower control limit (LCL) are not statistically meaningful, in comparison to the upper specification limit (USL) and lower specification limit (LSL), continue with the validation process.
15. Upon completion of the molding run for the multi-cavity analysis, explore the molds processing window to determine key parameters (factors) to be varied during a design of experiments and the amount of variation (levels) of each.

A multi-cavity analysis curve shown in figure.

1. The range chart is in control (pass C, P, R): The variation (range) within any cavity is not significantly different than the mold average-range of 0.0027" (.0068 cm).
2. The average chart fails C (cavities 2, 9, 13): Cavity 2 is consistently bigger than the rest of the mold while cavities 9 and 13 are consistently smaller than the rest of the mold. All other cavities are not significantly different than the average inside diameter of 2.1728" (5.52 cm).

The cause for these out-of-control cavities should be investigated and identified. Root causes may be measurement errors, different steel dimensions, imbalanced runner system (small/large gates, different probe tip temperatures, etc.), different cooling conditions, etc. Use your investigative skills to identify the special cause. When the upper control limit (UCL) and the lower control limit (LCL) are not statistically meaningful, in comparison to the upper specification limit (USL) and lower specification limit (LSL), continue with the validation process.

A multi-cavity analysis curve shown in figure.

1. The range chart is in control (pass C, P, R): The variation (range) in weight within any cavity is not significantly different than the mold average-range of 0.121 grams.
2. The average chart is also in control (pass C, P, R): All weights are not significantly different than the average preform weight of 29.024 grams, i.e., any one cavity is representative of the quality (weight) of the 16 cavity tool.
Since there is no significant weight difference between cavities, on-going monitoring of the weight (as an overall process stability indicator) can be achieved by sampling ONLY one cavity randomly from the 16 cavities in the mold. Remember to spread the observations within samples to capture the "true" process variation.

The further steps are required in validating a injection mold according to injection mold validation flow chart is dry cycle mold:

9. Design of experiments
10. Qualification (process capability study)
11. Mold metal Adjustments - centering process
12. Verification (30-day run)

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7. Gate Freeze Test - Validation procedure for injection molds

The seventh step in validating a injection mold with the overall process shown in injection mold validation flow chart is Gate Freeze Test. The steps before:


1. Mold certification
2. Dry cycle mold
3. Process stability test
4. Gage repeatability & reproducibility (R&R) test
5. Mold viscosity test
6. Balance of fill analysis


Purpose:

The purpose of the gate freeze test is to identify the hold conditions necessary to freeze the gate. The extent and duration of hold pressure has a large effect on the dimensional stability and outer appearance of the molded part. If the hold time is too short, the gate will not have had enough time to freeze off and sink marks could appear on the part. This is especially true of larger parts and when higher hold pressures are employed. After the mold gates "freeze", hold pressure has no effect and should be terminated at that point. It is typically better to be a little high on the hold pressure timer setting. This will cause a slight wear increase on the hydraulics of the injection press but the molder will be able to ensure higher dimensional accuracy.

Hold pressure is set at a pressure which allows no plastic melt to enter or leave the gate as the part solidifies. A high hold pressure setting could pack the part excessively, beyond dimensional tolerances. A low hold pressure setting will allow the melt to exit through the gate causing sink marks and voids in the part.

The gate freeze test is designed to achieve minimal dimensional variation by ensuring no plastic leaves the cavity before the gate is frozen. Hold times in the sharply rising part of the weight curve introduce additional variation. The gate freeze can be accurately determined via flow analysis programs which utilize the cooling circuitry layout, mold geometry, tool steel and hot/cold runner configuration. A predominant amount of the flow analysis programs assume isothermal conditions in the mold. This would produce best case results and typically the gate will never freeze off in this short of time. Properly interpreted, the flow analysis results serve as a good starting point.

Notes: 1) When using a valve gated system, no hold time is required. Once the valve is closed, no material will enter or leave the cavity. The valve is held open long enough to properly pack the part, and then closed. At this point, no pressure needs to be applied. 2) Having poor shot size control on your molding machine and an imbalanced mold will lead to less than desired results (lack of precision).

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Procedure:

1. Set melt temperature to resin manufacturer's recommended mid-range.
2. Set mold temperature to resin manufacturer's recommended mid-range.
3. Set cooling time long enough so that parts eject without being distorted.
4. Set fill rate from results of mold viscosity test and if desired, profile the injection stroke to have velocity controlled pack. At this moment, record the dosing stroke and change over position. For the remainder of the validation process this will remain constant.
5. Set hold time based on the machine operators experience, take their estimate and multiply by 1.5. Use this as the starting point for hold time. If after running the test you do not identify a point at which the gate freezes off, increase the hold time incrementally. Caution: On some molds, high hold pressure and hold times can cause ejection issues. Pay heed to the advice of the mold builder and do not increase the hold pressure and time to the point the parts are difficult to eject off the cores. If you see this issue on your pilot mold, you may want to modify the mold or part design to make your part ejection more robust.
6. Set hold pressure so that there are no visual sink marks.
7. Collect and weigh 3 consecutive shots to 0.01 grams or better.
8. Subtract one second from hold time.
9. Add one second of time to cooling in order to maintain a consistent molding cycle.
10. Begin a table similar to Table: Gate Freeze Test.
11. Graph the shot weight versus the hold time Figure 1: Gate Freeze Test.
12. Repeat steps 7 - 9 until the part weight begins to decrease.
13. Repeat the test with a high mold temperature and high melt temperature to document the worst case scenario for hold time.

A typical "gate freeze test" curve is shown in Figure 1: Gate Freeze Test. There is a region on the left side of the graph where small changes in hold time result in large changes in part weight. These large changes in part weight may result in part quality variation with regards to dimensions or mechanical performance. The region on the right side levels out at 3.5 seconds indicating that the part weight is more stable and that the gate has frozen off, i.e., no polymer melt enters or leaves the cavity.

Table: Gate Freeze TestTable: Gate Freeze Test
Figure 1: Gate Freeze TestFigure 1: Gate Freeze Test

Figure displays a gate freeze test when the gate never froze. This is typical for hot tips directly gated onto the part. The thicker the part, the more likely this will occur. When such a curve is graphed, identify the region on the curve where a change in slope is evident. In figure 2, this area is at 1.0 seconds. A hold time of at least 1.5 seconds is recommended.
Figure 2:  Gate Freeze TestFigure 2: Gate Freeze Test

It is possible the part will become over-packed and either flash or stick in the core, causing ejection problems, before obtaining a level curve. The above test had to be stopped at 4.0 seconds due to the part sticking in the core at longer hold times. Therefore, the hold time could be set anywhere between 1.5 & 4.0 seconds. If cycle time is not limited by hold time, a design of experiments could be performed using hold time as a variable. This will help to select the optimum hold time.

The further steps are required in validating a injection mold according to injection mold validation flow chart is dry cycle mold:

8. Commissioning (multi-cavity analysis)
9. Design of experiments
10. Qualification (process capability study)
11. Mold metal Adjustments - centering process
12. Verification (30-day run
)

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Increase Injection Velocity

>> Monday, 28 February 2011

Raising the injection velocity will reduce the time taken to fill the cavity and it is therefore possible to achieve faster cooling of the preform. However, it will also increase shear in the material. Shear is a major factor affecting overheating of the material, A.A. Generation and I.V. reduction, therefore increasing velocity will damage the PET resin.
When working with hot preform method, the injection velocity will also make a significant difference to the material distribution in the finished container. Filling faster means that the preform will be colder when the mold opens and its temperature balance will also have changed. Typically, the shoulder area will become relatively cooler than the base area giving less stretch at the top of the preform.

When working with warm / cool / cold preform method the temperature related effects of increasing the velocity are either greatly reduced or non-existent

Oil flow into the injection cylinder must be increased.

For machines fitted with electronic injection control, increase the velocity percentage value on the injection screen of the electronic injection control system. Maximum allowable setting is 99%.
For machines without electronic injection control, increase the setting of the valve found on the operator side of the injection unit.

In most cases, the five steps of injection control can be set to the same value. Different values may be advantageous in cases of complicated preform design or technically difficult bottles.
Increasing the injection velocity too far may cause other preform defects such as lowered I.V., increased A.A., silver streaks and internal sink marks.

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Reduce Injection Velocity

Keeping the injection velocity low will reduce the shear that occurs in the material. Shear is a major factor affecting overheating of the material and I.V. reduction, therefore reducing velocity will protect the PET resin from excessive damage.
When working with hot preform method, the injection velocity will also make a significant difference to the material distribution in the finished container. Filling slower means that the preform will be hotter when the mold opens and its temperature balance will also have changed. Typically, the shoulder area will become relatively hotter than the base area giving more stretch at the top of the preform.

Excessive injection velocity can also disturb the alignment of the injection core, especially if the design is long and thin.

Reducing the injection velocity will also have the effect of making the holding time shorter since the V/P time will increase.

When working with warm / cool / cold preform method the temperature related effects are either greatly reduced or non-existent.

Oil flow into the injection cylinder must be reduced.

For machines fitted with electronic injection control, reduce the velocity percentage value on the injection screen of the electronic injection control system. Minimum usable value is typically around 15~17% but beware of making a short shot at very low settings.
For machines without electronic injection control, reduce the setting of the valve found on the operator side of the injection unit. Beware of making a short shot at very low settings.

In most cases, the five steps of injection control can be set to the same value. Different values may be advantageous in cases of complicated preform design or technically difficult bottles.
Reducing the injection velocity too far may cause other preform defects such as specks of crystal in the gate area.

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Ensure Correct Preform Temperature Balance

Hot PET stretches more easily, cooler PET is more difficult to stretch.
Therefore the primary method of adjusting the positioning of material in the finished container is to use relative temperature in various parts of the preform.

If the temperature is balanced, the wall thickness of the container can be optimized and the overall strength of the container can be improved.

If the balance is incorrect, some areas may become thick leading to a mottled or grainy appearance while the thin, overstretched areas such as the corners may show pearlescence or crystallization.

Balance the temperature of the material within the preform to give the most equal strength in the finished product.

There are two major methods of doing this.
In the first method, injection velocity is used to control the temperature balance of the preform. Since most of the retained heat from the injection process is used in the blowing of the container, this method can have dramatic effects on the finished container.

Filling the injection cavity faster will have the effect of making the shoulder portion of the preform relatively cooler resulting in a container having a thicker shoulder area and a thinner heel.
Filling the injection cavity more slowly will allow less cooling time for the shoulder area of the preform (relative to the base) leading to thinner shoulders and a thicker heel.
This method is more critical where the preform is relatively long. Shorter preforms show less response.

The second method uses temperature adjustment at the conditioning station. The method of adjusting preform temperature depends on the type of conditioning system fitted.

Conditioning Systems
Oil / Water Conditioning Core With Electric Heating Pot
Electric Heating Core With Electric Heating Pot
Electric Heating Core With Oil / Water Conditioning Pot
Electric Heating Core With Split Type Oil / Water Conditioning Pot


Note that strength does not only come from wall thickness, it also comes from good bi-axial orientation of the material and physical design of the container. Therefore a container having equal wall thickness may not always have the best overall strength.
Thicker, unstretched areas of the container may have a mottled body or grainy shoulder appearance.

The conditioning station is not intended to re-heat the preform so the power and control is limited (in most container designs). The main purpose of this part of the machine is to provide a balancing function across multi-cavity molds and in some cases it actually provides additional cooling.

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6. Balance of fill analysis - Validation procedure for injection molds

>> Sunday, 27 February 2011

The sixth step in validating a injection mold with the overall process shown in injection mold validation flow chart is balance of fill analysis. The steps before:


1. Mold certification
2. Dry cycle mold
3. Process stability test
4. Gage repeatability & reproducibility (R&R) test
5. Mold viscosity test

Purpose:

The purpose of the balance of fill analysis is to evaluate the thermal and flow balance of the plastic distribution system in the mold. The plastic distribution system encompasses the hot or cold runner system, as well as the core and cavity. Only a naturally or symmetrically balanced manifold should be specified.

The cavity-to-cavity weight difference is an indicator of the quality of the hot runner system. It is critical to have the flows balanced to each cavity or the part-to-part variation may be large and process capability may not be achievable. Recall, the purpose of the mold validation procedure is to reduce variation throughout the injection mold. A typical mold is generally within +/- 10%. If the mold you are qualifying exceeds these values it should not cause you to cease the qualification process. Do investigate for possible causes such as, blocked gates, hot tip controller malfunction, hot tip failure, and non-uniform cooling. If the issue is not identified, document the data and continue. This data will be of use while analyzing the data collected during commissioning (multi-cavity analysis).

All the steps during the procedure that involve intimate contact with the injection molding machine are to be done by a qualified injection molding machine operator.

Caution: This test is part geometry dependent. The part may stick in mold and need to be removed manually.

Procedure:

1. Set melt temperature to resin manufacturer's recommended mid-range.
2. Set manifold and probe tip temperatures to resin manufacturer's recommended mid-range.
3. Set mold temperature to resin manufacturer's recommended mid-range.
4. Set hold time and hold pressure to zero.
5. If the machine is equipped, set pack time and pressure to zero.
6. Set cooling time long enough so that resin has cooled and parts eject consistently.
7. Set fill rate using the results from the mold viscosity test.
8. Transfer from injection to hold phase by screw position.
9. Have sufficient cushion to prevent the screw from bottoming out against the barrel during injection.
10. Adjust feed stroke so that the heaviest part is approximately 90% filled by weight.
Note: To achieve accurate results it is imperative none of the parts be completely filled.
11. Add adequate hold time and pressure, as well as pack time and pressure (if the machine is equipped with pack time and pressure) so no sink marks appear and cycle for five shots.
12. Remove hold time and pressure, as well as pack time and pressure.
13. Collect one all cavity shot.
Note: With certain mold designs it is difficult to perform a manifold balance test because of ejection issues with short shots. For example, some parts are designed with a slight undercut to ensure the part will stay on the side of the mold with the ejection action. If this is the situation, the undercut might not be filled during a short shot and the part will stick on the wrong side of the mold. In this case, you should evaluate the number of samples to be collected. In addition, study the parts to verify the balance of fill is not a result of poor venting. Lack of venting can artificially make the mold appear in balance.
14. Repeat steps 11-13 until 3 full shots have been collected.
Note: It is necessary to cycle five shots before each collection of shots to ensure each collection is subjected to the same thermal conditions.
15. Weigh all the parts and average the data per cavity.
16. Chart the weight by cavity.
17. For each cavity, use the following formula to calculate % imbalance:
%Im balance = (Wf-Wn)*100/Wf, where Wf = Weight of heaviest cavity, Wn = Weight of cavity n, where n = cavity number
18. Graph and interpret results.
Figure Balance of Fill Analysis depicts typical results for a mold which is not properly balanced, i.e., cavities 9, 10, and 12 are not within 5% of the weight of the full cavity #7.
Balance of fill analysis

Plotting the data relative to a mean weight is also a good method of identifying problem cavities. The 0.00% level of imbalance is based on the mean weight of all cavities in the mold. Cavity to cavity imbalance calculated against the mean part weight. Showing the data in this manner helps to highlight cavities to both extremes - higher than normal, or lower than normal. The formula below shows the calculation for calculating the imbalance using this method. %Im balance = (Wa-Wn)*100/Wa, where Wa = Average Weight of all the cavities, Wn = Weight of cavity n, where n = cavity number
It is also recommended the data be plotted in other ways. Doing so will make it easier to trouble shoot molds when necessary. Figure Balance of Fill Analysis shows the cavities in “clusters” according to their position in the mold. This is a good method to identify problems in a runner system, cooling system, one face of a stack mold, or inadequate clamp tonnage across the entire face of the mold. The “cluster” method of plotting the data according to mold construction is probably the best method. This method is very useful when plotted using average part weights for calculated imbalance.
On a hot runner system if you plot the imbalance and find that the majority of the cavities are reasonably well balanced but you have one or two obvious deviations (i.e. on a 32 cavity mold 30 cavities are 4 % imbalanced and 2 are 20% imbalanced) it is evident there is an issue with those two cavities. Steps you could take are:
1.Ensure correct hot tip operation, read power usage and temperature setting/variation on display unit.
2.Check for a foreign particles which may be blocking the gates of the suspect cavities
3.Measure gate size/shape (i.e. circularity) in cavity. Measure hot tip height in relation to the gate.
If one or two cavities have substantially (over 10%) higher imbalance than others the above analysis should highlight the reasons.

The further steps are required in validating a injection mold according to injection mold validation flow chart is dry cycle mold:

7. Gate freeze test
8. Commissioning (multi-cavity analysis)
9. Design of experiments
10. Qualification (process capability study)
11. Mold metal Adjustments - centering process
12. Verification (30-day run)

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Optimize Secondary Blow Delay (Start)

The purpose of the Secondary Blow air is to make the final shape of the container with all details. The Secondary Blow air should NOT be controlling or influencing the inflation of the preform.
As with the Primary Blow Delay timer, there is no "correct" setting for Secondary Blow Delay. The optimum setting will depend on many other factors upstream of the stretch blow process and will include the setting of the Primary Blow Delay. Therefore, adjusting the Secondary Blow Delay time should be the last processing adjustment to be made when setting up a machine.

As a general rule, the Secondary Blow Delay timer should be set as short as possible to get the best definition in the container, but without upsetting the blow-up of the preform. Having the Secondary Blow Delay set too short is likely to cause off center gates and neck rings.

If there is too much delay between the introduction of the primary air and the secondary air, it may cause pearlescence in the corners of the container.

Before setting up the Secondary Blow Delay time, the Primary Blow Delay setting should be finalized. Then, adjust the Secondary Blow Delay to the earliest possible setting without upsetting the blow-up of the preform.

After the Primary Blow Delay time has been set to give the best blown bottle using Primary Air only, the machine should be re-started.
Reduce the Secondary Blow Delay setting from its long setting to a setting of about 0.5~0.8 seconds.
While blowing bottles, decrease the Secondary Blow Delay setting in steps , this should be about 0.1 second per step. Collect a sample container at each step, mark it and place it on a table. At first, there will appear to be no or very little difference in the containers but on close inspection you should be able to see improvements in the definition of ribs, logos and corners. At some point, the container quality will go bad, typically this will be an off center gate or a neck ring. There is no point in going any further once this happens and it is possible that a preform will split leaving fragments of PET in the mold if you continue.
Once the quality has turned bad, slightly increase the Secondary Blow Delay setting a little until the container quality comes good again. This is the optimum setting for the Secondary Blow Delay timer.

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Optimize Primary Blow Pressure

The purpose of the primary blow air is to inflate the preform as much as possible to the final shape of the container. The setting of the primary blow pressure can be extremely critical with containers having flat panels although it is not normally so important for round containers.
If there is insufficient inflation in the primary blow, the extreme high pressure of the secondary blow may cause damage to the inflating preform such as pearlescence in the corners or splitting in the base.

Too much primary air pressure can cause uncontrolled inflation of the preform leading to splitting preforms or buckling of flat panels.

Turn off the Secondary Air and test the inflation of the preform at varying Primary Pressures.

Referring to Optimize Primary Blow Time, increase the time delay of Secondary Air to the same as the blow time. This will prevent the secondary air from starting so that the Primary Air inflation can be more easily observed.
Reduce the Primary Air Pressure to around 0.3~0.4 MPa (3~4 Kg/cm²), then start the machine.
Wait for the preform temperature to stabilize, then turn on the blow mold.
Collect a sample bottle, make a note of the pressure used, then increase the pressure by 0.1 MPa (1kg/cm²) and repeat the sample collection.
Continue this until the pressure has reached around 2.5 MPa (2.5 kg/cm²) or the inflation of the preform becomes uncontrolled.

If any other parameters such as injection or conditioning settings are changed, it may be necessary to re-optimize the pressure.

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Optimize Primary Blow Delay (Start) for ISBM

The purpose of the Primary Blow Air is to inflate the preform as much as possible to the final shape of the container. The setting of the Primary Blow Delay time is one of the most critical processing adjustments that can be made in the molding process. Very small changes can have a significant effect on the container quality. There is no "correct" setting for Primary Blow Delay. The optimum setting will depend on many other factors upstream of the stretch blow process and it is also important to understand that the optimum setting will change if one of those upstream conditions changes. Therefore, adjusting the Primary Blow Delay time should be one of the last processing adjustment to be made when setting up a machine.
If Primary Blow Delay is too early, the container may suffer from neck rings or off center gates. If it is too late, the shoulder may show a grainy appearance, there may be a constriction or the preform may split in the body.
If there is insufficient inflation in the primary blow, the extreme high pressure of the secondary blow may cause damage to the inflating preform such as pearlescence in the corners, splitting in the base.
It is nearly impossible to judge the effect of the Primary Blow air on the inflation of the preform if the Secondary Blow air is also operating normally. Therefore, the first step is to disable the Secondary Blow air, after which the primary air time setting can be adjusted to various settings to find the optimum.

Optimize Primary Blow Delay (Start) for Injection Stretch Blow Molding
1. Increase the setting of the Secondary Blow Delay timer to the same or more than the Blow timer. This will prevent the Secondary Blow from taking place.
2. Reduce the Primary Blow Delay time to 0.0 seconds.
3. Start the machine, allow the preform temperature to stabilize, then turn on the blow mold. Take a sample then increase the Primary Blow Delay setting, this should be about 0.05~0.1 seconds per step. Collect a sample container at each step, mark it and place it on a table. At some point, the container quality will go bad, typically this will be a constriction mark around the shoulder area. There is no point in going any further once this happens and it is possible that a stretch rod tip may be broken if you continue.
4. Stop the machine and study the sample bottles produced, it is likely that the quality will have gone through a range as shown by the red curved line, somewhere around the middle setting, the best formed bottle will be seen. This is the optimum setting for the Primary Blow Delay timer.
5. After the Primary Blow Delay has been optimized, you should then optimize the Secondary Blow Delay setting.

The technique used here can also be applied to the Primary Blow pressure and Primary Blow flow settings.
Some container designs, notably square and flat-oval shapes are very sensitive to these adjustments, whereas round simple shapes may not be.

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