Showing posts with label plastic processing. Show all posts
Showing posts with label plastic processing. Show all posts
Plastic mold
Mold - The cavity or matrix of cavities into which plastic melt is placed and takes form.
Control Chart and Control Limits
Control Chart - A graphical method for evaluating whether a process is or is not in a state of statistical control (stable). The decisions are made through a comparison of the values of some statistical measurement calculated from the data with control limits.
Control Limits - Limits on a control chart that serve as a basis for judging whether or not a process is in a state of statistical control (stable)
Control Limits - Limits on a control chart that serve as a basis for judging whether or not a process is in a state of statistical control (stable)
Centerline
Centerline - A line drawn down on part drawing that represents the geometrical center of the part in that axis.
Blow Time extrsuion blow molding
Blow Time - The length of time the blow medium is contained in the mold.
Blowing Pressure extrusion blow molding
Blowing Pressure - The pressure in psi of the medium blowing the plastic to the shape of the mold.
SAFETY PRECAUTIONS FOR BLOW MOLDING
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 is 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 tie bars when hydraulic pumps are running.
5. Never disconnect or by-pass safety switches on guards.
6. In order to prevent mechanical hazards such as limbs being drawn into or trapped in the machinery, operators should not wear personal effects such as bracelets, watches, rings or chains during work shifts engaged in operating the blow molding machine.
7. Process only materials that are specified for use with the blow molding machine by the machine manufacturer.
8. Always wear adequate noise protection.
9. Use caution and wear protective gloves when making adjustments on hot die head components and manifolds.
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 the line 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 completed.
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 blow molding resin pressure can reach 4,000 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 mold components and cavity parting line edges.
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.
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 tie bars when hydraulic pumps are running.
5. Never disconnect or by-pass safety switches on guards.
6. In order to prevent mechanical hazards such as limbs being drawn into or trapped in the machinery, operators should not wear personal effects such as bracelets, watches, rings or chains during work shifts engaged in operating the blow molding machine.
7. Process only materials that are specified for use with the blow molding machine by the machine manufacturer.
8. Always wear adequate noise protection.
9. Use caution and wear protective gloves when making adjustments on hot die head components and manifolds.
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 the line 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 completed.
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 blow molding resin pressure can reach 4,000 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 mold components and cavity parting line edges.
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.
Design of experiments, DOX, DOE in extrusion blow molding
A statistical design of experiments, or DOX, is the preferred method to determine an optimum blow molding process and processing window. Initial mold/process evaluations should be completed on a small prototype mold when possible. The mold is normally shipped from the tool builder to the molder's development laboratory. The molder's development laboratory should have the time and resources available to evaluate the molding process for that mold and to perform any initial Design of Experiments.
The objective of a design of experiments is to not only identify an optimum process and processing window, but also to identify the main effects from process variables, interactions between them, and possible curvature effects. Initial experiments are run to determine which combination of process control parameters yields the lowest dimensional variability. Once this is determined, the tool steel can be adjusted to meet the molded container dimensional specifications. It is important NOT to choose process control parameters solely based on the part specifications. If your tool builder constructs the mold using a "Steel Safe" approach, you will be able to easily cut and ‘adjust’ the steel for the most stable and efficient process.
It is recommended that the Design of Experiments be performed on the blow molding machine on which the mold will run on during production or sampling. Only a skilled molding company can accurately translate the process control parameters from one blow molding machine to another. Even if the machines are similar, there are always differences that will affect the attributes of the molded part. The amount of wear on the extruder, the mold clamp system design, hydraulic valves, screw, barrel and timers can differ and can have large effects on process control parameter adjustments. In addition, the molder’s development laboratory often utilizes a different (mold) cooling system than the system used in a manufacturing area. Differences in development laboratory (individual mold temperature control systems) and manufacturing plant (central) coolant system performance can be significant. Careful attention must be given to the actual cooling (heat transfer) variables in the mold.
The objective of a design of experiments is to not only identify an optimum process and processing window, but also to identify the main effects from process variables, interactions between them, and possible curvature effects. Initial experiments are run to determine which combination of process control parameters yields the lowest dimensional variability. Once this is determined, the tool steel can be adjusted to meet the molded container dimensional specifications. It is important NOT to choose process control parameters solely based on the part specifications. If your tool builder constructs the mold using a "Steel Safe" approach, you will be able to easily cut and ‘adjust’ the steel for the most stable and efficient process.
It is recommended that the Design of Experiments be performed on the blow molding machine on which the mold will run on during production or sampling. Only a skilled molding company can accurately translate the process control parameters from one blow molding machine to another. Even if the machines are similar, there are always differences that will affect the attributes of the molded part. The amount of wear on the extruder, the mold clamp system design, hydraulic valves, screw, barrel and timers can differ and can have large effects on process control parameter adjustments. In addition, the molder’s development laboratory often utilizes a different (mold) cooling system than the system used in a manufacturing area. Differences in development laboratory (individual mold temperature control systems) and manufacturing plant (central) coolant system performance can be significant. Careful attention must be given to the actual cooling (heat transfer) variables in the mold.
In Mold Labeling IML setup procedure
The IML system must be adjusted to accommodate the mold cavities, label size, and label position on the container. The adjustments must be done in relation to the molds, with the proper placer arm assembly, vacuum cup heads, and label magazines installed.
Procedure for Shuttle Process:
A. Carriage and Placer Arm Assembly Setup
1. Adjust the carriage and placer arm assembly. Disconnect the actuator links from the front and back sides of the placer arm assembly at the drag links.
2. Check that the angle between actuator arms and the top of the carriage frame is 75 degrees.
3. On the cylinder side only, reconnect the actuator links to the drag link. Check to assure the actuator arm is still in contact with the latch link. Adjust the link as required so that the placer arms are flat against the placer arm bracket and the actuator arm is against the latch link. Adjust the opposite (non cylinder) side, similarly. It is important to ‘balance’ the force on both the front and back side of the actuator links, taking care not to put a
‘jacking force’ on the components.
B. Centering the Placer Arm Assemblies Horizontally Between the Molds
1. Assure adequate daylight opening between mold halves exist on both side A and side B. Back-off the deployment roller (move towards the mold).
2. Move the placer arm assembly between the mold halves to the full in position and set the carriage lock.
3. Loosen the (4) screws that bolt the slide base to the upper frame.
4. Measure the distance from the inside face of the placer arm to the front face of the mold. Repeat the procedure on back face of the mold. If the measurement is not the same turn the adjustment screw located on the upper frame and below the slide base. The placer arm assembly is centered when this distance is the same on both the front and back halves of the mold.
5. Retighten the (4) screws on the slide base.
C. Centering the Vacuum Heads Vertically in the Cavity
1. Back off the deployment roller on the lift-up cam.
2. Move the inserter carriage between the mold halves to the full in position and set the carriage lock.
3. Slightly loosen the (4) screws on the back of the lower frame.
4. Turn the adjustment jackscrew: clockwise to raise, counterclockwise to lower.
5. Check to assure the vacuum cup head is approximately centered vertically in the cavity.
6. Retighten (4) screws.
7. Release the carriage lock and move the carriage out and in by hand to insure that no part of the placer arm interferes with the mold cavities or platen tie rod as it is lifted up into position. Readjust as required, then reset carriage lock to continue.
D. Setting the Tow Bar Length
1. With the placer arm ‘in molds’ and carriage lock engaged, loosen tow bar jam nuts (R.H. and L.H. nuts).
2. While manually extending placer arms, turn the tow bar until vacuum cups are located in the mold cavities as required, usually centered in the label panel area.
3. Tighten the jam nuts.
E. Adjusting the Deployment Roller
1. Assure the carriage lock is engaged.
2. Loosen the lock screw on front of the deployment roller housing.
3. Turn the adjustment screw: clockwise to extend vacuum cups deeper (moves roller away from molds); counterclockwise to retract arms (moves roller towards molds).
4. Check vacuum cup centering, readjust as required.
5. Retighten the lock screw. Placer arm extension should allow for only slight flattening of the vacuum cups against the walls of the mold. Over extension and excessive force may cause excessive wear and premature failure of the placer arm assembly components.
F. Adjusting the Label Magazines
1. Unlock and open the door of the magazine guard.
2. Pull back the pusher plate while holding the remaining stack upright.
3. Load new labels in until desired amount is reached.
4. While releasing pressure on the pusher plate shuffle stack down into and even stack.
5. Close and lock the magazine guard door. Label stacks should be ‘riffled’ several times to eliminate ‘edge welding’ due to die cutting and to allow some air to become entrapped between labels.
6. Set the label stops to allow the labels to be picked easily without double picking or moving the next label out of position. The overlap of the stops onto the label may be different from side to side or top to bottom. The overlap should be about 1/16” initially.
7. Adjust the magazine position (amount of contact force) between the label stack and the vacuum cup heads by moving the magazines in and out. Loosen the lock-down collars and release the lock-down clamp that holds the magazine in place.
8. With the blow molding machine and IML system in ‘Manual’ mode, press the ‘Step/Home’ button to move the first pair of placer arms to the first label pick position. Note how the vacuum cups contact the end label on the stack in the magazine.
9. Adjust the label magazine in or out as required to achieve proper contact. Secure lock-down collars after proper magazine position is achieved.
G. Pick Cylinder Speed
1. Ensure that adequate plant air pressure is available.. Adjust the regulator located on the pneumatic control assembly to 80 psi.
2. Adjust extension speed of the placer arms on valve connected to rod end of cylinder, turn stem: clockwise to slow; counterclockwise to speed up.
3. To adjust retraction speed of the placer arms turn valve connected to other end of cylinder do likewise.
H. Pick and Mold Vacuum
1. The IML system vacuum pumps require 80 psi for optimum performance. Adjust the pick vacuum with the regulator located on the pneumatic control assembly. Settings lower than 60 psi may result in missed picks.
2. Adjust mold vacuum with the regulator located on the pneumatic control assembly. Mold vacuum requirements will vary depending on the number of vacuum ports in the mold, label materials, container shape, etc.
I. Adjusting Label Position on Container
1. The adjustments are side to side, height, and skew (rotation). Adjust the label position by loosening the appropriate clamps and moving the adjustments in direct relation to the container. Retighten clamps to prevent changes in settings due to vibration.
J. Setting Up and Modifying Programs
1. Refer to the IML operating instructions manual for specific program modifications. The number of picks and the position of label picking are normally modified whenever the number of cavities or cavity spacing is changed. No other program modifications are normally required.
Procedure for Shuttle Process:
A. Carriage and Placer Arm Assembly Setup
1. Adjust the carriage and placer arm assembly. Disconnect the actuator links from the front and back sides of the placer arm assembly at the drag links.
2. Check that the angle between actuator arms and the top of the carriage frame is 75 degrees.
3. On the cylinder side only, reconnect the actuator links to the drag link. Check to assure the actuator arm is still in contact with the latch link. Adjust the link as required so that the placer arms are flat against the placer arm bracket and the actuator arm is against the latch link. Adjust the opposite (non cylinder) side, similarly. It is important to ‘balance’ the force on both the front and back side of the actuator links, taking care not to put a
‘jacking force’ on the components.
B. Centering the Placer Arm Assemblies Horizontally Between the Molds
1. Assure adequate daylight opening between mold halves exist on both side A and side B. Back-off the deployment roller (move towards the mold).
2. Move the placer arm assembly between the mold halves to the full in position and set the carriage lock.
3. Loosen the (4) screws that bolt the slide base to the upper frame.
4. Measure the distance from the inside face of the placer arm to the front face of the mold. Repeat the procedure on back face of the mold. If the measurement is not the same turn the adjustment screw located on the upper frame and below the slide base. The placer arm assembly is centered when this distance is the same on both the front and back halves of the mold.
5. Retighten the (4) screws on the slide base.
C. Centering the Vacuum Heads Vertically in the Cavity
1. Back off the deployment roller on the lift-up cam.
2. Move the inserter carriage between the mold halves to the full in position and set the carriage lock.
3. Slightly loosen the (4) screws on the back of the lower frame.
4. Turn the adjustment jackscrew: clockwise to raise, counterclockwise to lower.
5. Check to assure the vacuum cup head is approximately centered vertically in the cavity.
6. Retighten (4) screws.
7. Release the carriage lock and move the carriage out and in by hand to insure that no part of the placer arm interferes with the mold cavities or platen tie rod as it is lifted up into position. Readjust as required, then reset carriage lock to continue.
D. Setting the Tow Bar Length
1. With the placer arm ‘in molds’ and carriage lock engaged, loosen tow bar jam nuts (R.H. and L.H. nuts).
2. While manually extending placer arms, turn the tow bar until vacuum cups are located in the mold cavities as required, usually centered in the label panel area.
3. Tighten the jam nuts.
E. Adjusting the Deployment Roller
1. Assure the carriage lock is engaged.
2. Loosen the lock screw on front of the deployment roller housing.
3. Turn the adjustment screw: clockwise to extend vacuum cups deeper (moves roller away from molds); counterclockwise to retract arms (moves roller towards molds).
4. Check vacuum cup centering, readjust as required.
5. Retighten the lock screw. Placer arm extension should allow for only slight flattening of the vacuum cups against the walls of the mold. Over extension and excessive force may cause excessive wear and premature failure of the placer arm assembly components.
F. Adjusting the Label Magazines
1. Unlock and open the door of the magazine guard.
2. Pull back the pusher plate while holding the remaining stack upright.
3. Load new labels in until desired amount is reached.
4. While releasing pressure on the pusher plate shuffle stack down into and even stack.
5. Close and lock the magazine guard door. Label stacks should be ‘riffled’ several times to eliminate ‘edge welding’ due to die cutting and to allow some air to become entrapped between labels.
6. Set the label stops to allow the labels to be picked easily without double picking or moving the next label out of position. The overlap of the stops onto the label may be different from side to side or top to bottom. The overlap should be about 1/16” initially.
7. Adjust the magazine position (amount of contact force) between the label stack and the vacuum cup heads by moving the magazines in and out. Loosen the lock-down collars and release the lock-down clamp that holds the magazine in place.
8. With the blow molding machine and IML system in ‘Manual’ mode, press the ‘Step/Home’ button to move the first pair of placer arms to the first label pick position. Note how the vacuum cups contact the end label on the stack in the magazine.
9. Adjust the label magazine in or out as required to achieve proper contact. Secure lock-down collars after proper magazine position is achieved.
G. Pick Cylinder Speed
1. Ensure that adequate plant air pressure is available.. Adjust the regulator located on the pneumatic control assembly to 80 psi.
2. Adjust extension speed of the placer arms on valve connected to rod end of cylinder, turn stem: clockwise to slow; counterclockwise to speed up.
3. To adjust retraction speed of the placer arms turn valve connected to other end of cylinder do likewise.
H. Pick and Mold Vacuum
1. The IML system vacuum pumps require 80 psi for optimum performance. Adjust the pick vacuum with the regulator located on the pneumatic control assembly. Settings lower than 60 psi may result in missed picks.
2. Adjust mold vacuum with the regulator located on the pneumatic control assembly. Mold vacuum requirements will vary depending on the number of vacuum ports in the mold, label materials, container shape, etc.
I. Adjusting Label Position on Container
1. The adjustments are side to side, height, and skew (rotation). Adjust the label position by loosening the appropriate clamps and moving the adjustments in direct relation to the container. Retighten clamps to prevent changes in settings due to vibration.
J. Setting Up and Modifying Programs
1. Refer to the IML operating instructions manual for specific program modifications. The number of picks and the position of label picking are normally modified whenever the number of cavities or cavity spacing is changed. No other program modifications are normally required.
Manifold Balance extrusion blow molding
The purpose of the Manifold Balance step is to evaluate the thermal and melt flow balance of the head tooling manifold distribution system and to establish uniform melt flow to each die on multi-head blow molding systems. The melt flow control (normally a choker valve) must adjust freely at normal operating temperature. The valve design must be capable of adjusting material flow to each die head so that the melt flow is stable over a range of extrusion rates.
Both the parison weight and length differences are an indicator of the degree of melt balance control and the quality of the manifold system design. A typical, well-balanced manifold will be balanced to within 5%. It is critical to have the flows balanced to each die or the part-to-part variation may be large and process capability may not be achievable.
Initial manifold control valve balance adjustments should be made during the Parison Centering step to optimize the manifold system flow balance. The Manifold Balance step may have to be repeated at higher extrusion rates, i.e. production rate, as melt flow pressure gradients change with melt flow rate and can affect the manifold melt flow balance.
Proceed to the Verify Mold Operation step if the blow-molding machine is a single die head system.
All the steps during the procedure that involve intimate contact with the bow-molding machine are to be done by a qualified blow molding machine operator.
Shuttle Process Procedure:
Task Description:
1. Verify that the zone temperature controller displays indicate a relatively uniform temperature distribution for the manifold system and head tooling.
2. With the extruder operating at a low rate, cut the parison close to the die face (using the cut device where applicable), extrude a parison and note a reference length for the parison. Typically the reference parison length will be the required parison length for the mold. Shorter parison reference lengths should be used for larger containers to avoid parison sag effects. Use a stopwatch and record a reference parison extrusion time from when the parison was cut until the end of the parison reaches the reference length position. Cut the parison again and record the parison weight for that die head.
Both the parison weight and length differences are an indicator of the degree of melt balance control and the quality of the manifold system design. A typical, well-balanced manifold will be balanced to within 5%. It is critical to have the flows balanced to each die or the part-to-part variation may be large and process capability may not be achievable.
Initial manifold control valve balance adjustments should be made during the Parison Centering step to optimize the manifold system flow balance. The Manifold Balance step may have to be repeated at higher extrusion rates, i.e. production rate, as melt flow pressure gradients change with melt flow rate and can affect the manifold melt flow balance.
Proceed to the Verify Mold Operation step if the blow-molding machine is a single die head system.
All the steps during the procedure that involve intimate contact with the bow-molding machine are to be done by a qualified blow molding machine operator.
Shuttle Process Procedure:
Task Description:
1. Verify that the zone temperature controller displays indicate a relatively uniform temperature distribution for the manifold system and head tooling.
2. With the extruder operating at a low rate, cut the parison close to the die face (using the cut device where applicable), extrude a parison and note a reference length for the parison. Typically the reference parison length will be the required parison length for the mold. Shorter parison reference lengths should be used for larger containers to avoid parison sag effects. Use a stopwatch and record a reference parison extrusion time from when the parison was cut until the end of the parison reaches the reference length position. Cut the parison again and record the parison weight for that die head.
3. Adjust the flow control valve(s) as required to achieve relatively uniform melt flow rates to each die head.
4. Repeat steps 2 through 5 until a satisfactory flow balance is achieved.
5. Calculate the percent imbalance.
4. Repeat steps 2 through 5 until a satisfactory flow balance is achieved.
5. Calculate the percent imbalance.
Parison centering extrusion blow molding
The purpose of the Parison Centering step is to establish a preliminary die position adjustment to achieve stable parison extrusion and uniform, circumferential parison wall thickness distribution.
Die bolts should be free of any degraded material and turn freely over the adjustment range at normal operating temperature for the die bushing. Appropriate repairs should be made for damaged threads on either the die bolt(s) or the die bushing.
Shuttle Process Procedure:
Task Description
1. Switch on the main power to the zone temperature controllers. Set the extruder barrel and head tooling temperature controllers to the material manufacturer’s recommended mid-range melt processing temperature. Verify that there is no error or open thermocouple circuit message on the temperature controller display. If an error or open circuit message is displayed, check all connections, thermocouples, heater bands and replace or repair as required. Allow 90 minutes for the extruder barrel and head tooling heating zones to reach the recommended material processing temperature.
2. Set the mold temperature system controller to the material manufacturer’s recommended mid-range mold surface temperature.
3. Switch on the melt pressure transducer and melt pressure monitor display for the melt distribution manifold and die head(s). Verify that there is no error or open circuit message on the melt pressure monitor display. If an error or open circuit message is displayed, check all connections and replace or repair the melt pressure transducer and/or melt pressure monitor unit as required.
4. Switch on the main power to the blow molding machine control panel. Set the process control mode selector switch to manual. Ensure that the mold(s) are in the open position and/or there is no obstruction in the path of the extruded parison(s) during the centering procedure.
5. Start the extruder at low RPM and monitor the ammeter and/or melt pressure monitor for any significant increase in current (for electric extruder drives) or significant increase in melt pressure, respectively, during start-up. Stop the extruder immediately if a high current or high melt pressure is indicated. Check for degraded material blockage and clean melt flow paths as needed. Increase temperature zone settings as required, allow for thermal soak and restart the extruder.
6. Note the melt pressure during extrusion at low RPM for future reference.
7. Verify that melt is emerging from the die head(s) and allow the material to purge until new material emerges from the die head(s). Note the relative melt strength of the parison(s) and adjust the melt processing temperature as required.
8. For blow-molding machines with multiple die heads, cut each parison close to the die (at the same cut position) during extrusion, measure the rate (length of parison per unit time) and note the results for each die head. Go to the Manifold Balance step 4.2.3 (page 23) if there are significant differences between parison extrusion rates from each die head and ‘balance’ the rate of melt flow to each die head.
9. Observe a parison as it extrudes from a die head and note how the parison drops away from the die. If the parison curls during extrusion (greater melt flow along one edge of the die), then the die bushing must be adjusted and centered.
10. Adjust the die bolts so that the parison drops straight down with minimal curl and melt flow appears stable and uniform. Note that cutting the parison close to the die face and observing the initial parison extrudate allows for the best parison centering evaluation.
11. Repeat the same procedure for each die head as required.
Die bolts should be free of any degraded material and turn freely over the adjustment range at normal operating temperature for the die bushing. Appropriate repairs should be made for damaged threads on either the die bolt(s) or the die bushing.
Shuttle Process Procedure:
Task Description
1. Switch on the main power to the zone temperature controllers. Set the extruder barrel and head tooling temperature controllers to the material manufacturer’s recommended mid-range melt processing temperature. Verify that there is no error or open thermocouple circuit message on the temperature controller display. If an error or open circuit message is displayed, check all connections, thermocouples, heater bands and replace or repair as required. Allow 90 minutes for the extruder barrel and head tooling heating zones to reach the recommended material processing temperature.
2. Set the mold temperature system controller to the material manufacturer’s recommended mid-range mold surface temperature.
3. Switch on the melt pressure transducer and melt pressure monitor display for the melt distribution manifold and die head(s). Verify that there is no error or open circuit message on the melt pressure monitor display. If an error or open circuit message is displayed, check all connections and replace or repair the melt pressure transducer and/or melt pressure monitor unit as required.
4. Switch on the main power to the blow molding machine control panel. Set the process control mode selector switch to manual. Ensure that the mold(s) are in the open position and/or there is no obstruction in the path of the extruded parison(s) during the centering procedure.
5. Start the extruder at low RPM and monitor the ammeter and/or melt pressure monitor for any significant increase in current (for electric extruder drives) or significant increase in melt pressure, respectively, during start-up. Stop the extruder immediately if a high current or high melt pressure is indicated. Check for degraded material blockage and clean melt flow paths as needed. Increase temperature zone settings as required, allow for thermal soak and restart the extruder.
6. Note the melt pressure during extrusion at low RPM for future reference.
7. Verify that melt is emerging from the die head(s) and allow the material to purge until new material emerges from the die head(s). Note the relative melt strength of the parison(s) and adjust the melt processing temperature as required.
8. For blow-molding machines with multiple die heads, cut each parison close to the die (at the same cut position) during extrusion, measure the rate (length of parison per unit time) and note the results for each die head. Go to the Manifold Balance step 4.2.3 (page 23) if there are significant differences between parison extrusion rates from each die head and ‘balance’ the rate of melt flow to each die head.
9. Observe a parison as it extrudes from a die head and note how the parison drops away from the die. If the parison curls during extrusion (greater melt flow along one edge of the die), then the die bushing must be adjusted and centered.
10. Adjust the die bolts so that the parison drops straight down with minimal curl and melt flow appears stable and uniform. Note that cutting the parison close to the die face and observing the initial parison extrudate allows for the best parison centering evaluation.
11. Repeat the same procedure for each die head as required.
Mold certification extrusion blow molding
The purpose of Mold certification step is to verify cavity and mold base dimensions and materials of mold construction. Cavity and neck insert dimensions, mold cooling channel diameter dimensions, cooling line connector diameter dimensions, mold backing plate mounting hole pattern, mounting bolt hole diameter dimension and mounting bolt hole thread type should be verified with the mold and blow molding machine platen prints. Dimensions for the mold mounting bolt holes and the bolt hole pattern in the mold backing plates are verified to help avoid machine scheduling delays during mold installation, initial start-up and process optimization procedures.
The Mold Certification procedure should be performed at the mold builder to expedite any required mold modifications and to help avoid delays during mold installation, process start-up and process optimization procedures. Mold certification documentation must be provided by the mold builder for review before the molds are shipped to the production blow molding plant.
Use of the specified materials in mold construction help to ensure the required level of mold mechanical integrity necessary to meet production run requirements. The specified materials of mold construction also provide the required level of heat transfer characteristics in the neck insert, cavity and pinch-off areas during production.
Mold cooling channel and cooling line connector dimensions should be verified so that heat transfer in the mold is optimized and so that cooling control may be maintained during production. Cavity and neck insert dimensions should be verified to establish the mold dimension ‘base line’ before process optimization procedures are initiated. The ‘base line’ dimension data may be used later in the process optimization procedures and for process centering purposes
The Mold Certification procedure should be performed at the mold builder to expedite any required mold modifications and to help avoid delays during mold installation, process start-up and process optimization procedures. Mold certification documentation must be provided by the mold builder for review before the molds are shipped to the production blow molding plant.
Use of the specified materials in mold construction help to ensure the required level of mold mechanical integrity necessary to meet production run requirements. The specified materials of mold construction also provide the required level of heat transfer characteristics in the neck insert, cavity and pinch-off areas during production.
Mold cooling channel and cooling line connector dimensions should be verified so that heat transfer in the mold is optimized and so that cooling control may be maintained during production. Cavity and neck insert dimensions should be verified to establish the mold dimension ‘base line’ before process optimization procedures are initiated. The ‘base line’ dimension data may be used later in the process optimization procedures and for process centering purposes
SHOT SIZE, SHOT INVENTORY, RESIDENCE TIME
SHOT SIZE, SHOT INVENTORY, RESIDENCE TIME
Sizing your mold to the proper molding equipment may seem obvious but many people don’t do it. If you want to get the best out of your tryout, the clamp tonnage must be enough to keep the mold closed and the shot capacity of the machine sized properly to the amount of plastic it will inject. Each of these three items including a density calculation are outputs of your Setup sheet.
SHOT SIZE:
Shot Size is the volume (usually expressed in grams or ounces) of the amount of plastic injected into the mold. The general Rule of Thumb is to use 50% of the shot capacity + 20%. Machines were originally quoted in Ounces or Grams. However, you had to understand this was in Ounces of General Purpose Styrene. So you had to go back and calculate the density to see if your material could be used in the machine. Today many machines are sized in maximum theoretical injection volume (cubic inches or cubic centimeters). This makes the conversions easier because you simply multiply the density of your plastic (grams per cc) time the volume of the machine of the machine and you get the machine’s capacity (in this case) in grams. Using less than 20% of the machine’s capacity increases the time the material will remain in the barrel (residence time). While some materials are very heat resistant, others will quickly degrade and substantially loose both their physical and chemical properties. Using more than 70% of the machine’s shot capacity overcomes the problem of overheating the material. However, we now encounter the problem of not completely melting all the material we intend to inject.
SHOT INVENTORY
Shot Inventory is the number of shots residing in the barrel. It is used to calculate residence time. Here is how it works: The shot begins in the material hopper. As the screw turns, it is fed into the screw flights. As the molding cycle continues, the screw continues to turn pushing our shot either forward into the barrel, where it is finally pushed into a hot runner system or directly into the mold where it is cooled. Our calculation for shot inventory is how many shots are in the screw flights, barrel, and hot runner system.
RESIDENCE TIME
Residence Time is the amount of time (expressed in minutes or seconds) it takes a theoretical pellet of plastic from the time it enters the barrel to the time it enters the mold. It is probably the most important variable when considering a properly sized machine.
When the material drops from the hopper onto the screw flights, it begins to see heat. The screw then turns mashing the material up against the heated barrel walls, crushing the pellets and pushing it forward. This causes the screw to be pushed backward to where it finally stops. Some of this material remains in the screw flights, merrily cooking. The screw moves forward, injecting the shot. The screw turns again and our shot goes beyond the check ring into the barrel cavity. Again it cooks. As the molding cycle repeats itself, our sample shot is finally injected into the mold. Here it may be directly injected into a conventional sprue and runner system OR it may move into an extension nozzle or hot runner system. If it is residing in either of these heated systems, again it is cooking. Residence time is the time a particular pellet (for our calculations it will be a shot) takes to get from the raw material hopper to be cooled in the mold. Its calculation would be the number of shots residing in a heated system (the shot inventory) divided by the cycle time. Obviously, the two determining factors for this calculation will be the cycle time and shot volume.
SAMPLING:
Random sampling plans tell you about how consistent (precise) the process is. Sequential samples minimize the process component and give an excellent picture of the variation on the mold.
Sizing your mold to the proper molding equipment may seem obvious but many people don’t do it. If you want to get the best out of your tryout, the clamp tonnage must be enough to keep the mold closed and the shot capacity of the machine sized properly to the amount of plastic it will inject. Each of these three items including a density calculation are outputs of your Setup sheet.
SHOT SIZE:
Shot Size is the volume (usually expressed in grams or ounces) of the amount of plastic injected into the mold. The general Rule of Thumb is to use 50% of the shot capacity + 20%. Machines were originally quoted in Ounces or Grams. However, you had to understand this was in Ounces of General Purpose Styrene. So you had to go back and calculate the density to see if your material could be used in the machine. Today many machines are sized in maximum theoretical injection volume (cubic inches or cubic centimeters). This makes the conversions easier because you simply multiply the density of your plastic (grams per cc) time the volume of the machine of the machine and you get the machine’s capacity (in this case) in grams. Using less than 20% of the machine’s capacity increases the time the material will remain in the barrel (residence time). While some materials are very heat resistant, others will quickly degrade and substantially loose both their physical and chemical properties. Using more than 70% of the machine’s shot capacity overcomes the problem of overheating the material. However, we now encounter the problem of not completely melting all the material we intend to inject.
SHOT INVENTORY
Shot Inventory is the number of shots residing in the barrel. It is used to calculate residence time. Here is how it works: The shot begins in the material hopper. As the screw turns, it is fed into the screw flights. As the molding cycle continues, the screw continues to turn pushing our shot either forward into the barrel, where it is finally pushed into a hot runner system or directly into the mold where it is cooled. Our calculation for shot inventory is how many shots are in the screw flights, barrel, and hot runner system.
RESIDENCE TIME
Residence Time is the amount of time (expressed in minutes or seconds) it takes a theoretical pellet of plastic from the time it enters the barrel to the time it enters the mold. It is probably the most important variable when considering a properly sized machine.
When the material drops from the hopper onto the screw flights, it begins to see heat. The screw then turns mashing the material up against the heated barrel walls, crushing the pellets and pushing it forward. This causes the screw to be pushed backward to where it finally stops. Some of this material remains in the screw flights, merrily cooking. The screw moves forward, injecting the shot. The screw turns again and our shot goes beyond the check ring into the barrel cavity. Again it cooks. As the molding cycle repeats itself, our sample shot is finally injected into the mold. Here it may be directly injected into a conventional sprue and runner system OR it may move into an extension nozzle or hot runner system. If it is residing in either of these heated systems, again it is cooking. Residence time is the time a particular pellet (for our calculations it will be a shot) takes to get from the raw material hopper to be cooled in the mold. Its calculation would be the number of shots residing in a heated system (the shot inventory) divided by the cycle time. Obviously, the two determining factors for this calculation will be the cycle time and shot volume.
SAMPLING:
Random sampling plans tell you about how consistent (precise) the process is. Sequential samples minimize the process component and give an excellent picture of the variation on the mold.
Injection molding tryout and qualification
PROCESS
This is the marriage of mold, material, and machine into an on-going process to continuously manufacture a part of consistent dimensions and physical characteristics.
TRYOUT
This is the initial test of a mold to check and repair any mechanical or dimensional defects. Once the mold is proven mechanically, the next tryout’s purpose is to optimize the molding cycle and obtain parts of sufficient quality and quantity for submission for testing and approval. A tryout is never a qualification run.
QUALIFICATION
A qualification run is a sustained run to show the mold and process can consistently produce parts of acceptable quality. This is generally understood to be a sustained run with little or no adjustments after the mold is brought on-cycle for a period of hours. Since this must be done for a sustained time, it can only be done after the parts produced from the tryout have been approved.
STARTUP
This is taking the conditions identical to those approved during the qualification run, translating them to a production machine and beginning a production run.
This is the marriage of mold, material, and machine into an on-going process to continuously manufacture a part of consistent dimensions and physical characteristics.
TRYOUT
This is the initial test of a mold to check and repair any mechanical or dimensional defects. Once the mold is proven mechanically, the next tryout’s purpose is to optimize the molding cycle and obtain parts of sufficient quality and quantity for submission for testing and approval. A tryout is never a qualification run.
QUALIFICATION
A qualification run is a sustained run to show the mold and process can consistently produce parts of acceptable quality. This is generally understood to be a sustained run with little or no adjustments after the mold is brought on-cycle for a period of hours. Since this must be done for a sustained time, it can only be done after the parts produced from the tryout have been approved.
STARTUP
This is taking the conditions identical to those approved during the qualification run, translating them to a production machine and beginning a production run.
Injection molding tryout and qualification
PROCESS
This is the marriage of mold, material, and machine into an on-going process to continuously manufacture a part of consistent dimensions and physical characteristics.
TRYOUT
This is the initial test of a mold to check and repair any mechanical or dimensional defects. Once the mold is proven mechanically, the next tryout’s purpose is to optimize the molding cycle and obtain parts of sufficient quality and quantity for submission for testing and approval. A tryout is never a qualification run.
QUALIFICATION
A qualification run is a sustained run to show the mold and process can consistently produce parts of acceptable quality. This is generally understood to be a sustained run with little or no adjustments after the mold is brought on-cycle for a period of hours. Since this must be done for a sustained time, it can only be done after the parts produced from the tryout have been approved.
STARTUP
This is taking the conditions identical to those approved during the qualification run, translating them to a production machine and beginning a production run.
This is the marriage of mold, material, and machine into an on-going process to continuously manufacture a part of consistent dimensions and physical characteristics.
TRYOUT
This is the initial test of a mold to check and repair any mechanical or dimensional defects. Once the mold is proven mechanically, the next tryout’s purpose is to optimize the molding cycle and obtain parts of sufficient quality and quantity for submission for testing and approval. A tryout is never a qualification run.
QUALIFICATION
A qualification run is a sustained run to show the mold and process can consistently produce parts of acceptable quality. This is generally understood to be a sustained run with little or no adjustments after the mold is brought on-cycle for a period of hours. Since this must be done for a sustained time, it can only be done after the parts produced from the tryout have been approved.
STARTUP
This is taking the conditions identical to those approved during the qualification run, translating them to a production machine and beginning a production run.
Injection molding tryout and qualification
PROCESS
This is the marriage of mold, material, and machine into an on-going process to continuously manufacture a part of consistent dimensions and physical characteristics.
TRYOUT
This is the initial test of a mold to check and repair any mechanical or dimensional defects. Once the mold is proven mechanically, the next tryout’s purpose is to optimize the molding cycle and obtain parts of sufficient quality and quantity for submission for testing and approval. A tryout is never a qualification run.
QUALIFICATION
A qualification run is a sustained run to show the mold and process can consistently produce parts of acceptable quality. This is generally understood to be a sustained run with little or no adjustments after the mold is brought on-cycle for a period of hours. Since this must be done for a sustained time, it can only be done after the parts produced from the tryout have been approved.
STARTUP
This is taking the conditions identical to those approved during the qualification run, translating them to a production machine and beginning a production run.
This is the marriage of mold, material, and machine into an on-going process to continuously manufacture a part of consistent dimensions and physical characteristics.
TRYOUT
This is the initial test of a mold to check and repair any mechanical or dimensional defects. Once the mold is proven mechanically, the next tryout’s purpose is to optimize the molding cycle and obtain parts of sufficient quality and quantity for submission for testing and approval. A tryout is never a qualification run.
QUALIFICATION
A qualification run is a sustained run to show the mold and process can consistently produce parts of acceptable quality. This is generally understood to be a sustained run with little or no adjustments after the mold is brought on-cycle for a period of hours. Since this must be done for a sustained time, it can only be done after the parts produced from the tryout have been approved.
STARTUP
This is taking the conditions identical to those approved during the qualification run, translating them to a production machine and beginning a production run.
Polymer and plastic material
In injection molding there are two major classifications: Thermosets – compounds that go through a chemical reaction when exposed to heat and crosslink into the molded part. The second classification is Thermoplastics – compounds that are only melted, injected and cooled into their new shape of the molded product. Thermoplastics come in two (sometime three) sub classifications: Amorphous – those polymers with no discrete molecular geometry, Crystalline – those with fixed polymer geometry, and Semi-Crystalline – polymers possessing both crystalline and amorphous properties.
Mold polymer processing
A mold is literally the hole into which the plastic is injected to form the part. It must be vented enough to let the air out that is displaced by the plastic, stable enough to not distort under the pressures and heats of processing, have an adequate fill system of sprues and runners, and it must fill evenly.
Molding machine in polymer processing
The molding machine is nothing more than a tool. By analogy what a molding machine is to a molder would be what a table saw is to a cabinetmaker: The saw blade must be sharp with all it’s teeth in alignment and not broken or bent, the motor must have enough power so that the blade can cut, The table must be square and level, and all the adjustments for speed, tilt, and cutting angles must be accurate. While the table saw does not make the cabinet, the cabinetmaker relies on its consistent precision so that his materials are not wasted and his craftsmanship is efficient.
A molding machine MUST deliver a consistent volume of material, at a consistent rate, at a repeatable temperature, and be able to maintain enough pressure to mold the parts. It must also be able to recover a consistent shot of material and open and close with repeatable speed and positions. Without a machine that can deliver the variables in a controlled manner any attempt at molding that will produce useable parts is senseless.
How to determine if your molding machine is fit to produce high quality consistent parts is shown in the section titled “Machine Consistency.”
A molding machine MUST deliver a consistent volume of material, at a consistent rate, at a repeatable temperature, and be able to maintain enough pressure to mold the parts. It must also be able to recover a consistent shot of material and open and close with repeatable speed and positions. Without a machine that can deliver the variables in a controlled manner any attempt at molding that will produce useable parts is senseless.
How to determine if your molding machine is fit to produce high quality consistent parts is shown in the section titled “Machine Consistency.”
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