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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