See how experienced driver can easily solve pre-molding failure of injection molding machine!
Time：2025-07-02 10:29:12 / Popularity： / Source：
Molten glue does not move back! Material does not go down at discharge port. Screw does not move back\pre-molding motor keeps turning. I have checked everything I can think of and everything is good. Pre-molding does not move back. Material is nylon plus glass fiber. What is reason?
1 Take screw out and take a look. Material is carbonized and it will be like this inside.
2 Change other materials and wash them first to reduce temperature at the end of screw and flow of circulating water.
3 There is a gap between screw and barrel
4 Check if it is "wrapped screw" or "carbonized" material. "Fix it before installing it, adjust temperature and melt speed.
5 There are problems with screw; rubber ring; check ring
6 The lightest powder material overhead is used
2 Change other materials and wash them first to reduce temperature at the end of screw and flow of circulating water.
3 There is a gap between screw and barrel
4 Check if it is "wrapped screw" or "carbonized" material. "Fix it before installing it, adjust temperature and melt speed.
5 There are problems with screw; rubber ring; check ring
6 The lightest powder material overhead is used
Machine dissolves very slowly. After removing screw, it is found that check ring has a crack. Why does rupture of check ring lead to no material discharging
1 It is understood that sealing is not possible after rubber ring breaks. Although we may think that it is not in sealing position when melting, it will be in sealing state or in the position where force that makes screw pushed backward by expansion of front rubber material is the largest after force exceeds balance point
2 Slow dissolution and no material discharging should not be the problem of check ring. Check ring is used to seal glue during injection to prevent material from returning to barrel and ensure that all contained glue is injected into mold
3 When check ring is broken, reverse glue will be generated during injection (plasticized plastic will run to feed port), causing plastic at the feed port to agglomerate or temperature to be too high, resulting in slow feeding.
2 Slow dissolution and no material discharging should not be the problem of check ring. Check ring is used to seal glue during injection to prevent material from returning to barrel and ensure that all contained glue is injected into mold
3 When check ring is broken, reverse glue will be generated during injection (plasticized plastic will run to feed port), causing plastic at the feed port to agglomerate or temperature to be too high, resulting in slow feeding.
Company currently has a machine that makes PVC sewer pipes. Melt motor will rotate during injection. In addition, injection is unstable, sometimes injection is not full, and sometimes mold expands. Solenoid valve and melt motor have been replaced, and melt solenoid valve plug has been unplugged during injection. It has not been solved yet. I understand that it may be too big and temperature is still too high, especially last paragraph
1 Is replaced valve new? Is model correct? Valve problem is solved
2 Check screw check ring!! Rubber ring is not well sealed. If PVC special screw does not pass rubber ring, change nozzle. Remember that nozzle hole should be larger than conventional one.
3 Is screw reverse or forward? If it is reverse, you can add a one-way valve to oil return pipe to limit oil. If it is forward, directional valve is more likely to be cause
4 Spring of sol valve is broken.
5 You should check one-way valve behind sol motor!
2 Check screw check ring!! Rubber ring is not well sealed. If PVC special screw does not pass rubber ring, change nozzle. Remember that nozzle hole should be larger than conventional one.
3 Is screw reverse or forward? If it is reverse, you can add a one-way valve to oil return pipe to limit oil. If it is forward, directional valve is more likely to be cause
4 Spring of sol valve is broken.
5 You should check one-way valve behind sol motor!
There is an old machine, melt speed is very slow, and pressure always fails to reach set value. After checking, it is found that melt solenoid valve is very hot. Is there a problem with solenoid valve, or is valve core leaking?
1 Solenoid valve should be fine.
2 Check whether sol oil motor has internal leakage.
3 Check whether there is any sound when rotating, and suspect that there is a problem with oil motor bearing.
4 If speed is low, you need to find flow problem.
2 Check whether sol oil motor has internal leakage.
3 Check whether there is any sound when rotating, and suspect that there is a problem with oil motor bearing.
4 If speed is low, you need to find flow problem.
Oil temperature is high, melt speed is fast and slow. What is problem? Melt speed is normal, sometimes it retreats quickly, sometimes it does not retreat, and it is still turning.
1 Speed of melt is fast and slow, which is basically a problem of barrel screw.
2 High oil temperature is because cooling water is not good or pressure is set too high or oil cooler is blocked.
3 Screw, check ring is seriously worn, or it does not cooperate well with meson. You have to change a set of glue components.
4 Screw is wrapped, that is, temperature of feed section is high. You have to lower temperature of feed section.
5 It is also possible that raw materials are bridging, no material is fed in, material is too large and blocked in feed port.
6 Comprehensively speaking, if machine occasionally retreats and sometimes does not retreat, 80% of time it is due to high temperature of feed section and 20% of wear gap of screw barrel is too large.
1 See how other actions work? Try to see if the total pressure can reach system pressure! What is pressure of large pump?
2 If other actions are normal, you need to replace a melt motor. Motor is leaking and unloading pressure, so it is powerless. Replaced oil seal is just to prevent oil from leaking to outside.
3 Screw has not been cleaned up from last decomposition of raw materials, causing friction.
4 Check whether set temperature is normal and actual temperature difference.
2 High oil temperature is because cooling water is not good or pressure is set too high or oil cooler is blocked.
3 Screw, check ring is seriously worn, or it does not cooperate well with meson. You have to change a set of glue components.
4 Screw is wrapped, that is, temperature of feed section is high. You have to lower temperature of feed section.
5 It is also possible that raw materials are bridging, no material is fed in, material is too large and blocked in feed port.
6 Comprehensively speaking, if machine occasionally retreats and sometimes does not retreat, 80% of time it is due to high temperature of feed section and 20% of wear gap of screw barrel is too large.
1 See how other actions work? Try to see if the total pressure can reach system pressure! What is pressure of large pump?
2 If other actions are normal, you need to replace a melt motor. Motor is leaking and unloading pressure, so it is powerless. Replaced oil seal is just to prevent oil from leaking to outside.
3 Screw has not been cleaned up from last decomposition of raw materials, causing friction.
4 Check whether set temperature is normal and actual temperature difference.
There is a 250T injection molding machine, which was used since 2000. Last year, due to large wear of clamping part, it was returned to factory for repair. After repair, it can be used normally. In the past half month, in the case of semi-automatic production, screw sometimes does not rotate when storing materials, system shows that there is flow and pressure. Manual, storing materials, and screw rotates normally. Sometimes it stops when opening mold.
1. Check oil motor. When screw does not rotate, remove oil motor and turn it on to see if it rotates normally.
2. Check electrical control to see if computer 5V power supply is normal. It may be that 50V 15000uF filter capacitor of power board fails. Voltage is sometimes present and sometimes absent.
3. Check if hydraulic oil is clean and if pressure and flow output of P and Q valves are normal.
2. Check electrical control to see if computer 5V power supply is normal. It may be that 50V 15000uF filter capacitor of power board fails. Voltage is sometimes present and sometimes absent.
3. Check if hydraulic oil is clean and if pressure and flow output of P and Q valves are normal.
Preform is being punched. If back pressure is small, product is abnormal and has bubbles. If back pressure is increased, product is normal, but screw retracts very slowly. When I just bought a new machine, I only added a little back pressure and product was normal and screw retracted quickly. After using it for a few years, is back pressure valve broken or pre-plastic motor problematic? Please advise!
1. If sol is very slow, what about screw speed?
2. If you separate screw and motor and check them without load, you will know if there is any problem with barrel.
3. When screw is melted, carefully check if screw retracts slowly when back pressure is increased. Is speed also slow? You can solve it with corresponding method according to observation and conclusion. B: If screw speed does not slow down significantly, it proves that there is a problem with injection component.
① If clearance between screw and barrel is too large or worn, molten material will retract slowly when screw reflows.
② Three small parts of glue head (check ring) have poor check effect (check ring and meson are damaged, cannot seal glue or matching gap of barrel is too large to seal glue), which means that screw retreats slowly when melting glue.
A: If screw speed is also very slow, it proves that pre-plastic motor is not strong enough. It is a problem with hydraulic valve oil circuit.
2. If you separate screw and motor and check them without load, you will know if there is any problem with barrel.
3. When screw is melted, carefully check if screw retracts slowly when back pressure is increased. Is speed also slow? You can solve it with corresponding method according to observation and conclusion. B: If screw speed does not slow down significantly, it proves that there is a problem with injection component.
① If clearance between screw and barrel is too large or worn, molten material will retract slowly when screw reflows.
② Three small parts of glue head (check ring) have poor check effect (check ring and meson are damaged, cannot seal glue or matching gap of barrel is too large to seal glue), which means that screw retreats slowly when melting glue.
A: If screw speed is also very slow, it proves that pre-plastic motor is not strong enough. It is a problem with hydraulic valve oil circuit.
Everything is normal during pre-plasticization. Screw reverses during injection. Check check ring and pre-plastic solenoid valve. Oil seal behind five-star motor is intact. May I ask if it is a problem with five-star motor? How to repair it?
1. Barrel is flared, and there is a problem with screw! Material pipe group is severely worn.
2. One-way valve is broken and there is a problem with oil circuit and there is leakage!
3. Replace one-way throttle valve at motor inlet, which can be dealt with temporarily.
4. This is a problem with oil circuit. It may be that there is a sealing problem with five piston rings of oil motor.
5. Install core in oil motor in reverse, and it will be OK.
6. If screw is checked, add a one-way valve to oil inlet of hydraulic motor, and pay attention to direction.
2. One-way valve is broken and there is a problem with oil circuit and there is leakage!
3. Replace one-way throttle valve at motor inlet, which can be dealt with temporarily.
4. This is a problem with oil circuit. It may be that there is a sealing problem with five piston rings of oil motor.
5. Install core in oil motor in reverse, and it will be OK.
6. If screw is checked, add a one-way valve to oil inlet of hydraulic motor, and pay attention to direction.
Barrel is always agglomerated. What are causes of failure?
1 It may be caused by setting temperature of rear section being too high or actual temperature being too high.
2 Screw and barrel are worn. Check ring or check ring and retaining ring seat are uneven, resulting in material return. When material returns to the rear section, it will also agglomerate.
3 Exhaust at the tail of screw is not smooth, which will also agglomerate. The most likely thing is that material cannot go down, and screw will break when torque is large.
4 Cooling water circulation in rear section of barrel is blocked, resulting in too high temperature.
5 Water inlet material and powder material in raw material are too much.
2 Screw and barrel are worn. Check ring or check ring and retaining ring seat are uneven, resulting in material return. When material returns to the rear section, it will also agglomerate.
3 Exhaust at the tail of screw is not smooth, which will also agglomerate. The most likely thing is that material cannot go down, and screw will break when torque is large.
4 Cooling water circulation in rear section of barrel is blocked, resulting in too high temperature.
5 Water inlet material and powder material in raw material are too much.
When melting glue, screw rotates but does not retreat, and always stops at the position when injection is completed, but it returns to normal after a few minutes. Please help analyze it! This is an old machine, from the 1980s! <I suspect that spring in valve controlling sol is broken. I haven't disassembled it yet! Because this spring was broken before and was replaced! >
1. Main reason is that material is not discharged. Screw retreats by material.
2. Is back pressure not adjusted properly (is discharge of nozzle large when screw rotates)?
3. Check temperature of discharge port, proportion of water added and crushing condition. Is barrel temperature suitable? Is there any sticky material block or foreign matter on screw?
4. Screw is likely to be worn.
5. There may be agglomeration! This will happen if agglomeration wraps around screw!
6. Remove screw and check whether rubber ring of screw is broken.
2. Is back pressure not adjusted properly (is discharge of nozzle large when screw rotates)?
3. Check temperature of discharge port, proportion of water added and crushing condition. Is barrel temperature suitable? Is there any sticky material block or foreign matter on screw?
4. Screw is likely to be worn.
5. There may be agglomeration! This will happen if agglomeration wraps around screw!
6. Remove screw and check whether rubber ring of screw is broken.
An old 1600T machine, system pressure cannot go up during sol, sol is too slow, pressure gauge shows 60 when set to 100, other actions are normal, and set pressure can be reached. Temperature is normal, ammeter; pressure gauge are normal, why can't pressure go up during sol?
1. This problem needs to be discussed separately. If sol pressure cannot be increased, but feeding is normal, there is no problem. If sol pressure cannot be increased and screw speed cannot be increased, working efficiency of oil motor may be reduced, and internal leakage has occurred.
2. According to description, machine is normal, but understanding is wrong. Melt pressure is not set to 100, and pressure gauge can display 100. Pressure is determined by melt resistance. If screw speed is slow, it is necessary to check flow setting or actual flow of oil pump.
2. According to description, machine is normal, but understanding is wrong. Melt pressure is not set to 100, and pressure gauge can display 100. Pressure is determined by melt resistance. If screw speed is slow, it is necessary to check flow setting or actual flow of oil pump.
There is a small device. During process of screw rotation during sol, screw moves back in a straight line and then sols again, like ejection, but ejection valve seems to be not energized. What is reason?
1 Normal melt should rotate and retreat at the same time. Check glue extraction valve (valve core) or try another glue extraction valve.
2. Check settings. There are two types of loosening and retreating: loosening and retreating before melting, loosening and retreating after melting. If both are set, above action will appear.
3. Check whether back pressure valve is faulty or back pressure is adjusted too low or no.
2. Check settings. There are two types of loosening and retreating: loosening and retreating before melting, loosening and retreating after melting. If both are set, above action will appear.
3. Check whether back pressure valve is faulty or back pressure is adjusted too low or no.
Machine melts glue very slowly, and other actions are normal. There is material unloading, screw has been checked, melt motor has been replaced, and oil circuit has been blown with air. Now the most likely possibility is that there is a problem with oil valve plate, but according to old employees, machine has had this problem since it was bought.
1. It is very likely that there is a problem with pre-plastic valve and circuit output, or first disassemble melt motor without removing oil pipe, and use oil motor to run idle to see if speed can be fast or slow?
2. Has current output been tested? Set pressure and speed to large and small, and use a meter to measure proportional output of current size.
3 Replace same type of machine and try it. It is easy to see that pressure, flow and current output are directly reflected by ammeter on machine!
4 Set melt speed to 10 and pressure to 99, then remove melt solenoid valve socket to prevent oil from entering oil motor. Press melt to see if pressure is maximum to judge whether oil motor is good or bad.
5 Is there any wear between barrel and screw that causes speed to slow down?
2. Has current output been tested? Set pressure and speed to large and small, and use a meter to measure proportional output of current size.
3 Replace same type of machine and try it. It is easy to see that pressure, flow and current output are directly reflected by ammeter on machine!
4 Set melt speed to 10 and pressure to 99, then remove melt solenoid valve socket to prevent oil from entering oil motor. Press melt to see if pressure is maximum to judge whether oil motor is good or bad.
5 Is there any wear between barrel and screw that causes speed to slow down?
1250T equipment screw, making PC material, screw makes a loud noise when adding material, it feels loud and quiet. After producing several products, screw will stop rotating, and pressure gauge will continue to be high pressure. Screw has been disassembled, and screw parts are normal
1 Choose large, medium, small, or which type of screw? Melt motor is too small.
2 Pay attention to check whether each heating ring is intact and whether temperature setting is too low.
3 Are raw materials used now same as raw materials used before? You can try to increase temperature appropriately!
4 What kind of screw is used? Screw eats too deep. Use a stainless steel screw for PC material!
5 Please loosen screw and apply high-temperature oil to the back of screw.
2 Pay attention to check whether each heating ring is intact and whether temperature setting is too low.
3 Are raw materials used now same as raw materials used before? You can try to increase temperature appropriately!
4 What kind of screw is used? Screw eats too deep. Use a stainless steel screw for PC material!
5 Please loosen screw and apply high-temperature oil to the back of screw.
An injection molding machine is very unstable in making products. There are always flashes! Many related process parts have been adjusted but there is no effect. It is observed that position where screw rotates back during sol is different every time. This position does not refer to position where pre-plastic stops, but position where screw stops rotating when it withdraws. I don’t know if screw is broken.
1 When adjusting machine, first adjust end position of melt. Method to ensure that melt position will not deviate is: adjust melt speed slowly, give a little position when ending, and do not turn wire too fast. If end position of melt is a contact, control will not be very stable. It is best to replace it with an inductive proximity switch.
2 It is very likely that screw's rubber ring is broken or worn. If it is a problem with rubber ring, it is very easy to find in production. There is often a lack of glue. After adjustment, it will not be stable. Flash, lack of glue, shrinkage and other phenomena often occur. If this is case, only rubber ring has been replaced.
3 A higher back pressure will be better. If cycle time allows for a finer speed adjustment, back pressure will hold up and plasticized position will be same.
4 Electronic ruler failure will also occur.
5 Appearance of flash is related to mold, clamping mechanism, mold matching, process settings, etc.
2 It is very likely that screw's rubber ring is broken or worn. If it is a problem with rubber ring, it is very easy to find in production. There is often a lack of glue. After adjustment, it will not be stable. Flash, lack of glue, shrinkage and other phenomena often occur. If this is case, only rubber ring has been replaced.
3 A higher back pressure will be better. If cycle time allows for a finer speed adjustment, back pressure will hold up and plasticized position will be same.
4 Electronic ruler failure will also occur.
5 Appearance of flash is related to mold, clamping mechanism, mold matching, process settings, etc.
Plasticizing pressure hits plasticizing switch, and plasticizing action does not stop
1 Switch failure, computer problem..
2 Plasticizing stop switch line is broken, and signal is not added to IO board. Check input and output screen and voltage.
3 Check plasticizing valve
2 Plasticizing stop switch line is broken, and signal is not added to IO board. Check input and output screen and voltage.
3 Check plasticizing valve
I have bought a machine for 4-5 years. This year, melting of glue has been very slow. It takes about 30 seconds to melt 160 grams of ABS material. Now I suspect it is a problem with screw. I would like to ask if there is another problem? When melting glue, no material comes out of nozzle
1 If speed is normal, it should be problem of screw!
2 If speed is normal, back pressure is reasonable, and cooling temperature of inlet is normal, then there is a problem with screw or distributor.
3. After screw and barrel are worn, clearance becomes larger, resulting in slow melting. It is time to replace screw and barrel.
4. Internal leakage in melt motor can also cause this failure;
Judgment method:
① Remove connection between screw and rear part, then start machine. If speed is normal, it is a screw failure.
② If speed is still very slow, remove melt motor. If speed is normal, then connection bearing is faulty, otherwise it is a melt motor failure or oil circuit failure;
2 If speed is normal, back pressure is reasonable, and cooling temperature of inlet is normal, then there is a problem with screw or distributor.
3. After screw and barrel are worn, clearance becomes larger, resulting in slow melting. It is time to replace screw and barrel.
4. Internal leakage in melt motor can also cause this failure;
Judgment method:
① Remove connection between screw and rear part, then start machine. If speed is normal, it is a screw failure.
② If speed is still very slow, remove melt motor. If speed is normal, then connection bearing is faulty, otherwise it is a melt motor failure or oil circuit failure;
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