Detailed explanation of injection molding problems of plug products

1. What are wire pressing, wire bursting, material shortage, shrinkage, deformation, wrong mold, biased mold, crooked head, terminal height, scorching, impurities, terminal damage, blurred markings, fusion lines, flow lines, plugging, bubbles, and cracks?

Answer: Wire pressing: refers to incorrect placement of wire in cavity or wire groove, causing it to be crushed during mold closing. In mild cases, insulation or sheath is damaged; in severe cases, conductor will be exposed.
Wire bursting: refers to incorrect placement of wire in cavity, and PVC rubber material will be crooked during injection, so that wire is exposed on the surface of plug.
Glue flushing: refers to wire being punched out and broken due to excessive injection pressure, high material temperature, or outer diameter of wire is too small and mold is not clamped tightly, even PVC is punched out along wire to burn wire, and wire is pulled back too much to break copper wire.
Material shortage: refers to phenomenon of less plastics caused by PVC rubber material not filling cavity and wire tail during injection.
Shrinkage: refers to situation that although PVC rubber fills cavity during injection, surface shrinks and sinks too much after plug cools due to poor injection conditions, and size will also cause deviation.
Deformation: refers to situation that cooling time is too short, and product is forced out of mold when it is still very soft, resulting in deformation due to force, or cooling time is sufficient, but mold removal method is incorrect (such as grabbing wire with one hand very close to mold, etc.), too many local hanging wires squeeze each other, etc., resulting in deformation due to force.
Head tilt: It is a kind of deformation, specifically referring to terminal and plug terminal surface are not perpendicular.

Terminal height: refers to incorrect terminal position caused by failure of mold to position correctly, failure to place terminal in correct position, short cooling time, etc., and size exceeds tolerance.

Burning: refers to discoloration, bubbles, and even solidification of PVC rubber caused by long-term heating without injection or less injection, which blocks material pipe.
Impurities: refers to phenomenon that there are impurities on the surface of product due to incomplete material replacement or impurities in rubber.
Damage to terminal: refers to improper operation when placing terminal into mold, scratching electroplating layer or scratching terminal during molding due to mismatch between mold and size of terminal.
Blurred marking: refers to various marks or contours on the surface of product are blurred.
Fusion lines: refers to joint lines caused by two strands of rubber in different directions meeting and welding during injection. A deep fusion line is a crack.
Misalignment: refers to phenomenon of left and right or front and back misalignment caused by misalignment of upper and lower cavities or tail of wire.

Deflection: refers to deviation of terminal, wire engraving, etc. caused by incorrect position of letter plate, wire groove, cross pin or positioning

Flow lines: refers to traces of rubber flow on the surface of product, generally in a curved spiral shape (fusion lines are generally straighter).
Plug material: refers to phenomenon of rubber flowing from terminal orifice due to improper molds, terminals or operation methods.
Bubbles: refers to bubbles and looseness on the surface and inside of product caused by water vapor in rubber material not being dried, too many volatiles in rubber material, too high heating temperature causing decomposition, or poor mold exhaust.
Flash: refers to phenomenon that product has obvious mold line and glue overflow at terminal position due to reasons such as too high mold temperature, too high material temperature, too high pressure, too fast shooting speed, too large mold gap, and too small clamping force.
Mold lifting: refers to phenomenon that upper mold is lifted up, mold line is too large or even connected together due to reasons such as too high pressure, too small clamping force, or sudden blockage of a certain hole. It is often accompanied by occurrence of glue flushing.

2. Why must 100% confirmation be made before molding after stripping? What is standard for confirmation? What is main reason why molding cannot be performed immediately after stripping?

Answer: Pay attention to: a. Terminal or inner mold must not be damaged, and exposed part must not be injured.
b. No more than three copper wires are broken, and terminal must be cut off if more than three are broken.
c. If inner insulation is damaged, please keep a certain distance from other wires and damaged insulation, otherwise it will be easy to fail during high-voltage testing.
d. If copper wire is exposed, it must be cut off at the root and insulation layer must be pushed as far as possible to terminal riveting point.
e. Damaged insulation and sheath must be cut off, otherwise it will be easy to be exposed on the surface of product after molding.
f. When pushing insulation layer or sheath, start from a little distance from wire tail and wire groove, otherwise PVC at wire tail wire groove will be thinned, outer diameter will become smaller, wire tail and wire groove will not be clamped tightly during injection, resulting in glue punching.

Reasons why it cannot be molded immediately after stripping are:
a. It is very easy to cut or pull off more than three copper wires when stripping.
b. It is very easy to cut insulation layer when stripping, and high-voltage test after molding will fail.
c. Outer skin is damaged when stripping, and it will burst out of product surface without trimming.
d. Outer skin is stretched or not pushed back.

3. What are consequences of using PVC incorrectly? Hardness, color, performance, N.M. vulcanization resistance, N.M. UL temperature, W-A.

Answer: a. Hardness: Different plugs, SR, etc. require different hardness of rubber materials to match them, so as to achieve corresponding performance requirements. For example, some plugs require SA95 (35P) PVC to meet standard (terminal will not be pulled out), but some plugs require SA80 PVC to meet requirements of swing test; generally SR uses softer materials, but sometimes hard materials are used to achieve a certain purpose. Therefore, hardness is not given at will, and must be used according to product engineering drawings or other technical documents. If you are unclear, please ask development department.
b. Color: Color is the most easily criticized by customers. There are many ways to express color, and each supplier has different regulations. Our company uses YJ´´´ to express color. In addition to number, you must also use your eyes to check whether color is correct. Comparison should be done in daylight or in sufficient sunlight to avoid errors.
Note: Colored PVC will darken slightly after injection.
c. Temperature resistance: PVC often has 60℃, 105℃, etc., which indicates different temperature resistance. Obviously, 105℃ rubber has higher temperature resistance than 60℃ rubber, mechanical and electrical properties at high temperature are better, so they cannot be mixed.
d. N.M.: N.M. is abbreviation of "non-migratory", which means that this PVC will not corrode plastics such as ABS and PS. However, general PVC will corrode ABS, PS, etc. in long-term contact with them. ABS and PS are common electrical product shell materials.

e. UL: Indicates plastics that meet UL standard requirements. Its various comprehensive properties are very good, while general PVC does not meet all UL requirements.
f. Sulfur resistance: Sulfur resistance means that PVC will not change color in a sulfur-containing atmosphere.
g. Cold resistance: W-A is generally used to indicate that PVC is outdoor cold-resistant, which means that it is not easy to bend and crack at low temperatures.

4. Why should remaining material in material tube be ejected before stopping machine (by hand or other methods)?

Answer: a. Ejecting remaining material can prevent PVC in material tube from burning and clogging nozzle.
b. Ejecting remaining material while it is hot can make material tube clean. It is easier to start machine again to change other types of rubber, which is fast and not easy to have impurities.
c. Material tube heats up quickly again.

5. Why close mold before stopping machine?

Answer: Closing mold before stopping machine has following benefits:
a. Prevent upper mold from falling off and injuring people when machine is turned on when it fails.
b. Prevent accessories, tools, etc. from being forgotten on mold due to negligence, and mold is crushed when machine is restarted.
c. Prevent foreign matter or dust from falling into mold.

6. When can pin of horizontal pin be pulled out?

Answer: Pin should be pulled out between time of starting to add material and before opening mold. If it is pulled out too early, terminal will be pushed by injection, and glue is still very soft, which makes it difficult to fix terminal, so terminal height will still appear; if it is pulled out too late, pin will still fix terminal during ejection, which will cause plug to deform and terminal size will be difficult to guarantee.

7. Why should temperature of material tube be reduced by 100℃ when leaving machine due to a device failure? Even turn off power supply and motor.

Answer: Because PVC rubber is a heat-sensitive material, it will decompose and discolor at a slightly higher temperature or a slightly longer heating time. In severe cases, it may even carbonize (i.e. burn). Discoloration can be eliminated by punching empty mold, but if it burns, it must be repaired by a specialist. Do not force pressure to pull out or rotate material to pull out material tube. Even if burnt material tube is repaired, it is very easy to hide carbonized particles, etc., which will bring inconvenience to future production. Turning off motor is to save power.

8. Why do we need to blow clean mold cavity before each mold closing?

Answer: Because sometimes terminal will be scratched during production operations, leaving electroplating layer or copper layer; sometimes wire will be crushed to leave copper foil or rubber layer; sometimes slip in double-coated wire will fall into mold; sometimes there is moisture in cavity and too much mold release agent, debris, etc. If it is not blown off, it will be attached to surface of product during molding or cause other effects on molding.

9. What is role of mold release agent? How can it be used correctly?

Answer: It helps to demold. Sometimes product is still stuck in mold after mold is opened and it is not easy to remove. It will cause deformation when forced to remove or eject. Mold release agent can also be used to achieve purpose of keeping product in lower mold or upper mold. When using mold release agent, pay attention to following points:
a. Shake up and down before spraying to fully mix liquid inside.
b. Do not spray at close range to avoid excessive concentration. Distance should be about 300mm.
c. Do not spray excessively. Excessive or distant spraying will cause excessive local release agent, gasification during closed exhaust groove molding, poor exhaust and lack of material, shrinkage, or too long and too deep fusion line.
d. Excessive unevenness between upper and lower molds will cause obvious differences in the surface finish of two sides of product.

10. What is role of rust inhibitor? How to use it correctly?

Answer: It plays the role of rust prevention on the surface of cavity. When using, please pay attention to:
a. Shake up and down before spraying to fully mix liquid inside.
b. Do not spray at close range to avoid excessive concentration, and distance should be about 200mm.
c. Do not spray excessively. A protective film is enough, because there is some wax in rust inhibitor. If there is too much, it will be difficult to clean it up next time.

11. Why should mold cooling water be turned off after shutdown?

Answer: Mold cooling water is different from machine cooling water. Machine cooling water is water that has been radiated, while mold cooling water is water that has been chilled by a water chiller. Water temperature is usually below 20℃, which is very different from room temperature. Therefore, after shutdown, condensed water droplets will form on mold, which will cause mold to rust. It will also cause unnecessary waste of electricity.

12. Why can't font be wrong?

Answer: Font is a mold accessory, but it forms a mark on the surface of product, representing product's certified country model, voltage, current, etc. Some fonts, although above contents are same, will be considered inconsistent with customer's approval, will be returned due to different arrangement positions and individual marks. Therefore, font errors are serious shortcomings and must be taken seriously. Product engineering drawings must be checked before molding.

13. What should I do if I find wrong polarity before molding?

Answer: If wrong polarity is found before molding, it should be picked out and marked immediately, and handed over to relevant personnel for processing. Never continue molding and let inspector to measure electricity. Because inspector may be negligent, tester may also fail, and it is possible that defective products will flow out.

14. What should I do if copper leakage is found before molding?

Answer: If copper leakage is found before molding, it depends on situation. If copper leakage is less than 3 pieces (including 3 pieces, it can be torn off or cut off and continue molding; if it exceeds three pieces, it should be picked out or marked immediately, and handed over to relevant personnel for processing. Never mold, inspector may be negligent, tester may also fail, and it is possible that defective products will flow out).

15. What is metering and how to measure correctly?

Answer: So-called metering refers to preparatory action that can ensure that molding machine can use screw to eject plasticized melt at a constant temperature, constant pressure, and constant quantity. In layman's terms, metering is distance screw retreats when adding materials, which controls how much new material is added. Accuracy of metering directly affects whether injection volume is sufficient. Generally speaking, metering is controlled by "material end" stroke. The farther switch is from nozzle, the more material is added. To ensure accuracy of metering, following points should also be noted:
a. Switch should be firmly fixed, otherwise frequent collisions or vibrations will cause changes in position to cause metering changes.
b. Back pressure should be appropriate. If back pressure is too small, rubber material is loose and has a low density, which can easily cause inaccurate metering.

16. What are primary pressure and secondary pressure?

Answer: Injection filling refers to process in which screw starts from metering position in material tube and applies high pressure through cylinder to inject plasticized rubber into mold through nozzle. Filling is divided into three stages: flow filling, pressure holding and shrinkage compensation, and backflow.
a. Flow filling is what we often call "primary pressure" or "first pressure" stage. Pressure in this stage is relatively high, purpose is to overcome resistance of injection and inject most of rubber (about 90%) into mold in a short time. If pressure is too low, injection is very slow, which will cause material shortage or poor fusion. If pressure is too high, injection speed may be too fast (of course, injection speed can be adjusted separately), which may cause wire to be offset, or wire to be broken or there will be traces of injection. High pressure may also cause glue flushing.
b. Pressure maintenance and shrinkage compensation is what we often call "secondary pressure" or "secondary pressure" stage. Pressure in this stage is relatively low, and purpose is to make up for glue that was not fully injected in the first pressure. At the same time, when product cools and shrinks, add a little more material to avoid shrinkage. Time of second pressure is enough for nozzle to cool and solidify, and glue will not flow back. Too long time is meaningless to avoid shrinkage, but will cause surface quality near nozzle to deteriorate and demolding difficulties. Second pressure should not be too high, otherwise it will cause glue flushing and mold lifting, and too low will cause material shortage or shrinkage.
c. Backflow means that when screw starts to rotate and feeds material, then retreats, unsolidified rubber in cavity flows in opposite direction toward sprue and runner. The entire backflow process starts from elimination of second pressure and ends when rubber at sprue solidifies. Main reason for backflow is that after injection pressure (second pressure) is removed, pressure in mold cavity is greater than pressure of the runner, and back pressure of feed is very small, which is not enough to hold rubber in runner. If sprue has solidified when injection pressure is removed, there will be no backflow.
Here we emphasize again: 1. The first pressure must be greater than the second pressure. 2., you cannot use only the first pressure or the second pressure when injecting. 3. Stroke of first press must reach more than 90%. 4. Although stroke of second press is only about 10%, it must not reach the end of material tube. There should be some rubber left in material tube after second press is full. Only in this way can second press be effective and there will be no shrinkage or material shortage.

17. What is principle of setting pressure?

Answer: As long as normal molding can be maintained, the smaller the better. Because:
a. The smaller pressure, the less power consumption and energy saving.
b. Hydraulic valve and mold of machine are subjected to less force, less deformation, and less prone to damage.
c. Hydraulic oil generates less heat and is not easy to become thin, so pressure is stable. Oil has a long life and is not easy to leak.

18. Why do you need to close mold with both hands?

Answer: Closing mold with both hands is entirely for safety reasons. In other words, as long as mold is closed, it is impossible for any hand to be placed in mold. Therefore, you must never jam a button for convenience and close mold with only one button, which will lead to lifelong regrets.

19. What does ejection (loose withdrawal) mean? What is its function?

Answer: "Ejection withdrawal" means that after feeding is completed, screw will retreat a distance. Its function is to shrink cold material generated by contact between nozzle (material nozzle) and mold into material tube for heating, so as to prevent cold material from blocking gate (water outlet) during cast injection, causing a hole to lack material and a hole to be flushed. Cold material squeezed into cavity will also cause other poor appearance. However, ejection withdrawal cannot be excessive, otherwise there will be too much air in material tube, and poor exhaust during injection, resulting in poor molding. Ejection withdrawal is not suitable when injection volume is small.

20. Why can't you just go to oil tank to get oil?

Answer: There are following harms:
a. Oil level in oil tank continues to drop, causing oil to circulate too quickly, heat up and become thinner, affecting oil life, causing unstable pressure and leakage.
b. When it drops to a certain position, oil pump will inhale air, causing vibration of oil pump and pipeline, unstable pressure, noise, etc., and even damage to machine.
c. If oil extraction tool is not clean or oil tank cap is not covered, dirt will fall into oil, causing various oil valves to wear more and even get stuck. If oil valve is worn, it will cause unstable pressure due to leakage, and if it gets stuck, it will fail to work.

21. What should I do if I encounter an emergency during molding?

Answer: In an emergency, such as foreign matter in mold, line is not placed properly, material head is not torn off, hand is pressed on mold, etc., you should immediately press red "Emergency Fixing" button in the middle of lower part of workbench, so that upper mold will open. For new workers, they should be allowed to practice repeatedly to form a conditioned reflex so that they will not panic when encountering problems.

22. Why should we develop habit of not putting parts on mold?

Answer: A mold costs at least 4,000 to 5,000 yuan, and at most 20,000 to 30,000 yuan. It is a very expensive tool. If you leave parts on mold at will, when you close mold without paying attention when starting machine, parts will be crushed, and mold itself will also be damaged.

23. Why should pinhole of mold be aligned with ejector?

Answer: For vertical machines, ejector and nozzle are generally concentric, mold feed port and ejector hole of mold are generally concentric. Therefore, as long as mold feed port is aligned with machine nozzle, mold ejector hole and machine ejector will naturally be aligned. For horizontal machines, since nozzle can move back and forth, if its position is not appropriate, ejector and ejector hole may not be concentric. This has following disadvantages:
a., Eccentricity will cause uneven force on push rod and bottom plate of reset rod of mold, which is easy to get stuck during ejection or reset, causing ejector to break or not return.
b., Eccentricity will cause ejector to rub against wall of ejector hole and cause damage, causing ejector oil seal to wear out and leak oil when ejector retracts.

24. Why should mold's pressure plate be reliably locked? How to lock it?

Answer: Failure to lock it is very harmful, mainly for following reasons:
a. Mold will gradually move during use, causing upper and lower molds to be out of center. When closing mold, guide pins and guide sleeves may be crushed at best, and the entire mold may be crushed or even hurt.
b. When opening mold, upper and lower molds will tilt, break guide pins and clamping screws, and pull mold plate screw holes out of shape. When locking mold plate, pay attention to following points:
1. Whether screws are correct. Because we generally use metric threads, if imperial threads are used incorrectly, mold plate's threads will be damaged.
2. When tightening, tighten diagonally and gradually. Do not tighten one first and then second, otherwise mold will warp.
3. Do not tighten only a few turns for the sake of saving trouble, because this will not lock tightly and will easily damage threads.
4. It must be locked after upper and lower molds are pressed tightly.

25. Why do we sometimes need to shoot an empty mold?

Answer: Because plastic material in material tube is not plasticized evenly when machine is just turned on, or material temperature is too high and fluidity changes due to not shooting for a long time, or rubber material changes color due to heat, etc., it is necessary to shoot an empty mold once or even several times to remove bad rubber material and achieve predetermined molding conditions.

26. Why is it required to add cyclohexanone, butanone (MEK) or PVC glue when making products?

Answer: Sometimes customers require that adhesion between product and wire must reach a certain level, sometimes customers require that product has a certain degree of sealing and waterproofing. At this time, we will require some solvents or glue to be added to wire. Principle is that solvent melts outer skin of wire to form glue (PVC glue itself is glue). It is then bonded to PVC during molding to enhance adhesion and sealing. Be careful when using it. Never use too much, otherwise it will easily cause poor appearance, such as too large fusion lines, etc.; do not apply it to wire groove, otherwise it will easily cause glue rush (because electro-fusible wire is dissolved and wire groove cannot clamp wire tightly). Characteristic of cyclohexanone is that it dries slowly and needs to be slightly dried before molding. Same is true for PVC glue; while butanone dries quickly and can be molded after application. Remedy for solvent leakage is to use a needle to inject a small amount of solvent into seam of product, and wire tail must not be moved, otherwise wire tail will crack.

27. Why do guide pins of mold and molding machine need to be frequently oiled?

Answer: Guide pins and guide sleeves are often rubbed. If there is no oil lubrication, they will quickly wear and lose precision, which will not only affect product quality, such as misalignment and flash, but also cause parts between upper and lower molds to collide with each other and cause damage.

28. Why do we need a stable molding cycle?

Answer: Molding cycle refers to the time required to complete an injection molding process, including injection time, feeding time, mold opening, wire removal, inspection and application of release agent, wire laying, mold closing, etc. If, due to various reasons, time difference of each cycle is too large, it will cause a large change in temperature of rubber in material tube. If cycle is short, actual temperature of rubber may be lower than set temperature; if cycle is long, it may be higher than set temperature, or even discolor or burn.

29. Why do we need to tighten screws in mold?

Answer: If screws in mold are not tightened, parts will loosen and shift under influence of mold closing force and vibration, which may cause poor quality, such as mold deviation, wrong mold, terminal damage, wire pressing, etc.; in severe cases, product will be scrapped and mold will be crushed.

30. What is basis for determining color of wires and PVC?

Answer: Basis is a. Color number on product engineering drawing. b. Color plate kept in file room. c. Compare wires and PVC. Because in addition to supplier's numbering, our company has numbered each color (except black), represented by YJXXXXXX, where XXXXXX represents sequence number, such as YJ010. At the same time, supplier will provide color plates for our company to recognize as quality basis for both parties. However, there will be a large error in comparing color plates, because of difference in light and personal, so plug rubber and wire must be compared again in the end.

31. What is back pressure and screw speed? How to adjust?

Answer: Back pressure (plasticizing pressure) refers to counter pressure generated by molten glue collected at the front end of screw when screw is plasticizing molding rubber, referred to as back pressure. Increasing back pressure is effective in improving plasticizing effect, metering stability, density of molten glue (reducing shrinkage), and preventing air from mixing. However, if screw speed is not increased accordingly after increasing back pressure, molten glue will flow back in screw, thereby reducing plasticizing capacity, and it looks like screw is turning but moving slowly (small machines do not have a speed adjustment mechanism). Pay attention to following points when adjusting back pressure:
a. Too much back pressure will cause nozzle to flow easily (i.e. rubber will flow out of feeding nozzle).
b. Too much back pressure will cause friction between screw and rubber to generate a lot of heat, causing rubber to lose heat.
c. Too much back pressure will cause screw to retreat slowly, rubber in screw will flow back, and plasticizing time and molding cycle will be extended.
d. Too little back pressure will cause air to enter front end of screw, dark brown cloud-like stripes (silver streaks) and tiny bubbles (air sores) will appear after molding.
e. Too little back pressure will cause density of rubber to be too low, which is easy to cause shrinkage.
Therefore, back pressure should be selected at minimum limit that can maintain normal production. Screw speed refers to rotation speed of screw during plasticization and gelation. As speed increases, plasticizing capacity increases, and temperature of molten glue also increases. However, too high a speed will also cause rubber inside screw to flow back, increase energy consumption, and cause rubber to lose heat.

32. How to judge whether there is a problem with temperature sensing line (thermoelectric) or thermostat?

Answer: During operation, when it is found that although temperature is not high, there are always bubbles, burning and discoloration, or thermostat is always in "ON" heating position, and corresponding ammeter pointer also indicates, it is necessary to consider whether there is a problem with temperature sensing line or thermostat. Reasons are as follows:
a. Temperature sensing line is broken and cannot measure temperature of material tube. Therefore, thermostat thinks that set temperature has not been reached, and it keeps notifying heating tube to heat, resulting in excessively high material temperature.
b. If thermostat is broken, although temperature sensing line has measured temperature, thermostat always thinks that temperature has not been set, so it keeps heating.

33. Why does rubber material need to be dried before it can be formed? Why can't it be dried in a sealed plastic bag?

Answer: Particles of rubber material are very small, surface area is large, and it has strong hygroscopicity. In addition, rubber material factory generally needs to cool it in a water tank when making rubber material, and surface also absorbs a lot of moisture (of course, it is invisible to naked eye). If moisture is not dried, bubbles and silver streaks will appear on product during molding. Large machines with drying hoppers generally do not need to be dried in advance; while small machines do not have drying hoppers and must be dried in advance. Some people think that rubber material that has just been opened does not need to be dried in advance, which is wrong. Drying temperature is generally 70℃ for PVC. Too low will have no effect, too high will soften PVC and stick it together, affecting feeding. Too long drying time and too high temperature will also affect performance of PVC. In addition, some people are greedy for saving trouble and put PVC in a sealed plastic bag and put it in hopper. In this way, although rubber material is very hot, it cannot be dried at all because moisture cannot evaporate. You can use a good woven bag (that is, outer packaging bag for PVC) to put PVC in for drying. Use dried PVC as soon as possible. When not in use, it can be packaged in a sealed bag, especially in humid seasons. In addition, hopper must be thoroughly cleaned during drying, and dark-colored rubber particles must not be mixed with light-colored rubber particles. It is not a big problem if light-colored particles are mixed with dark-colored particles.

34. Why must working temperature be reached before injection or feeding?

Answer: If working temperature is not reached, fluidity of rubber is very poor. If injection or feeding is performed at this time, machine and screw will be heavily loaded; if pressure is increased to inject or feed, machine may even be damaged and screw may be broken. Generally, injection or feeding should be performed 5 minutes after working temperature is reached.

35. What is plasticization?

Answer: After rubber is heated, compacted and mixed in material pipe, it is transformed from a loose granular solid to a continuous homogenized melt. This process is called plasticization. So-called homogenization includes four aspects, that is, after material is plasticized, melt must have uniform components (sometimes some mixed materials are used), uniform density, uniform viscosity and uniform temperature distribution. Only in this way can we ensure good fluidity during molding process and obtain high-quality products.

36. What is residual material? How to determine it?

Answer: When each injection action is completed, there must be some residual material at the front end of material tube, which is residual material. Role of residual material is to transmit and buffer pressure of screw to prevent screw from hitting nozzle when injection action is completed. If there is no residual material or residual material is too small, there will be no pressure-transmitting medium in material tube when injection action is completed. At this time, no matter how high injection pressure is, how fast injection speed is, and how long pressure holding (second pressure) time is (in fact, pressure holding has lost its meaning), product will be short of material, shrink or hollow, etc. Residual material is also called a buffer pad, and its thickness can be selected according to following principles:
a. If injection volume is small each time (such as making a small SR, etc.), residual material should be very small. Otherwise, rubber will be heated for a long time and discolor and burn.
b. If molding cycle is very long, especially when time between mold opening and mold closing is very long, amount of residual material should be small, otherwise rubber material will be heated for a long time and discolor and burn.
c. If injection volume is large and molding cycle is short, amount of residual material can be appropriately increased, purpose is to make rubber material that was not injected last time fully heated in material tube to avoid defects such as lack of material.

37. How to judge whether heating tube is broken?

Answer: During operation, when it is found that there is always a lack of material, surface of injected rubber material is dull, or temperature and pressure are increased but effect is not great, or a certain hole is short of material while other holes are flushing, or thermostat is always in "ON" heating position, but corresponding ammeter needle does not move, it is necessary to consider whether there is a problem with heating tube. Reasons are as follows:
a. If heating tube of rear section or middle section is broken, material temperature will definitely not reach working temperature, fluidity is poor, plasticization is uneven, surface is dull, and there is a lack of material during injection.
b. If heating tube of nozzle is broken, although temperature inside tube is very high, nozzle is in contact with mold and heat dissipation is fast. Therefore, temperature of material here is low. After being squeezed into mold, a piece of cold material will block water outlet of a certain hole and cannot be injected into cavity, causing material shortage. At this time, hot material behind will be injected into other holes, causing glue flushing.
c. If heating tube is broken, temperature is low. Temperature sensing wire (thermocouple) will tell thermostat to power on for heating, but heating tube can no longer be powered, so ammeter reflects no current.
In addition to notifying electrician, you can also touch heating tube with a section of material head. If it melts and smokes, it means it is good; if there is no big reaction, it means it is broken (of course, it may also be caused by circuit that good heating tube does not heat).

38. What should I do if machine makes an abnormal sound?

Answer: Machine should be stopped immediately to report to team leader and engineering department should be notified for inspection. Machine should not continue to work because abnormal noise is often an early sign of machine failure. Timely repair can avoid damage. If it is used forcibly, it will cause extremely serious damage.

39. Why should mold accessories be handled with care?

Answer: I often see people knocking the mold with cross pins; cross pins are very rough when they are put into mold, and they are very bad habits. Mold is a very expensive tool and a very precise tool. Random knocking will produce burrs, which will not fit together during assembly. Frequent collisions will cause deformation, loss of precision, jamming, glue leakage, etc., and in severe cases, mold will be damaged.

40. Why should the guard plate be tightened?

Answer: Some lower molds have a guard plate on each side. Some people often do not tighten guard plate after changing line groove, tail of line, and letter plate, so guard plate is loose and useless. Main function of guard plate is to:

a. Guide cross pin to be put into mold smoothly and accurately.

b. When cross pin is put in, it will not wear sharp corner of lower mold cavity. There will be no flash when molding here.
c. Some guard plates have springs to tilt the cross pin backwards, so that the upper cavity will not crush the cross pin when the mold is closed. In summary, guard plate must be locked correctly and firmly.

41. Why can't hard metal, iron rods, or screwdrivers be used to push wires or terminals in cavity?

Answer: It often takes a lot of force to push wires or terminals. Once they slip, iron will directly hit cavity, causing scars in cavity, which will be scrapped in long run.

42. How to deal with mold problems?

Answer: Stop operation, report to team leader immediately, protect site, and notify engineering department to repair it. Do not return defective mold to engineering department and conceal facts.

43. There are many kinds of materials for inner mold. Even if appearance is exactly same, can they be mixed at will?

Answer: There are many kinds of materials for inner mold, and colors are different. They cannot be mixed at will because:
a. Different materials have different properties, such as temperature resistance, fire resistance, resistance to leakage and tracking.
b. Same material may have different colors. Therefore, you must read instructions of product engineering drawing before using inner mold.

44. What is shooting speed and how to adjust it?

Answer: It refers to speed of screw's injection movement. It can also be expressed by amount of injection per unit time. In short, it indicates speed of injection. Shooting speed is closely related to injection pressure and complements each other. When other conditions (such as material temperature, mold temperature, rubber, etc.) are constant, the higher injection pressure, the faster injection. Of course, we hope that shooting speed is as fast as possible, which can at least improve production efficiency. But high shooting speed also has adverse consequences. Now introduce selection method of shooting speed:
a. At high shooting speed, due to friction, rubber temperature is higher and viscosity is lower, so flow resistance is small, and pressure in mold cavity will also increase, so product must be dense, weld mark strength will also increase, size and quality errors of each cavity product are also smaller.
b. When shooting speed is too high, rubber causes jet flow in mold cavity, resulting in poor product quality. At the same time, too high a shooting speed will cause poor exhaust, air in mold cavity will be compressed and heated, which will burn product, cause material shortage (because air cannot be exhausted), and cause bubbles in product.
c. Too low a shooting speed is also not good, which will cause surface of product to cool quickly, easily cause material shortage, delamination, and obvious weld marks.

45. Why should pressure and stroke of ejector be as small as possible while ensuring operation?

Answer: Purpose of ejector is to eject product out of cavity after mold is opened. Ejector stroke is to ensure that height of product is ejected appropriately. When choosing pressure, please pay special attention. Start with a very small pressure and gradually increase it. As long as it can be ejected, it is fine. Do not increase it too much, and stroke should be as short as possible. In production, ejector in mold is often broken, spring is damaged, ejector bottom plate is deformed, and mold is loose because of excessive pressure or too long stroke.

46. Why does XYP-001 (P) type mold letter plate, which has been used for a long time, suddenly damage terminal?

Answer: There are several possibilities:
a. Terminal supplier has been changed, so size and shape are not same.
b. Although supplier has not been changed, size of terminal may be different, especially the place where letter is pressed on terminal is thicker.
c. Mold is not installed well, position of letter plate and cross pin is misaligned.
d. Cross pin's core letter plate is crushed and deformed.
e. Core is worn, terminal is not clamped tightly, it will shake left and right.
Operator forcibly presses letter plate in.

47. What are consequences of water vapor in cavity?

Answer: Temperature of rubber material during injection is above 100℃, and following problems will occur when it meets water in cavity:
a. Rubber material and water meet and cool down, and fusion line increases.
b. High-temperature rubber material meets water and vaporizes, and exhaust is not smooth, resulting in material shortage.

48. What should I do if rubber material is accidentally burned?

Answer: Power must be turned off and engineering department must be notified immediately. Never increase pressure to perform injection, ejection, feeding, etc. without permission, because this will break screw and damage other accessories and machines.

49. How to clean material tube?

Answer: If type or color of plastic needs to be changed during production, or rubber material changes color or burns, material tube must be cleaned. Usually, it is cleaned by air injection. When cleaning, pay attention to following:
a. When molding temperature of rubber material to be replaced is higher than molding temperature of residual material in material tube (generally speaking, the higher hardness, the higher molding temperature), temperature of nozzle and material tube should be raised to the lowest molding temperature of material to be replaced, then add material to be replaced or secondary material of same specification, defective material, etc., and continuously inject into air until all residual material is removed.
b. When molding temperature of rubber material to be replaced is lower than molding temperature of residual material in material tube, temperature of material tube and nozzle should be raised to the highest molding temperature of material to be replaced, then material to be replaced or secondary material of same specification, defective material, etc. should be added, and continuously injected into air until all residual materials are removed.
c. When molding temperatures of two materials are not much different, there is no need to change temperature.