polymer processing

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...

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...

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!)

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 t...

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 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. I...

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 inter...

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 sli...

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 w...

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...

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. Fil...

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 m...

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 c...

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 ...

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 infl...