Injection molding process defect handling manual (65 kinds)

65 kinds of process defect analysis and solution methods, after years of experience accumulation, summarized the following defects: insufficient injection molding, depression, fusion seam, material flow pattern, poor gloss, air hole, black spot, overflow, warping deformation, silver text, poor demoulding, cloud, rough punching, horseshoe shape, small central hole, large central hole, too thick substrate, too thin substrate, large birefringence, small birefringence, substrate fracture, runner fracture, radial stripe Record groove, halo, pitting gas, body scorch, cold material, spray line, craze, uneven embossing, slip mark, flash, whisker pattern, surface peeling, bubble, discoloration, cavity, ripple, mold scale, wire drawing, crack, poor gate cutting, poor measurement, unstable injection volume, main channel adhesion, salivation, streamline, etc.
Causes of the above defects: mold temperature, punching knife, runner temperature, injection speed, injection pressure, pressure holding, pressure holding time, conversion point, mold locking force, cooling time, barrel temperature, plasticizing time, plasticizing speed, back pressure, etc
Product defects and causes overcoming methods
Phenomenon and solutions of various defects in injection molding
（1） Weldline
The fusion mark is caused by the cooling of the front part of the molten resin from different directions and the incomplete fusion at the junction. Fusion occurs at the confluence of resins. Fusion occurs when two resin streams meet. At this time, the lower the temperature of the two, the more obvious the fusion.
Because the two resin streams at the fusion point do not mix with each other (because they advance while semi-curing in the jet), if the temperature is low, the surface layer will become thicker, the lines are obvious, and the strength will also be reduced. This is due to the weakening of the adhesion between the two. On the contrary, if the temperature of the two resin streams is higher, the adhesive force will be enhanced and the appearance will become less obvious. At the fusion point, the two melted resins are squeezed, and the bonding condition here depends on the pressure applied there.
The lower the holding pressure, the more obvious the fusion and the lower the strength. If it is necessary to consider not only the setting of pressure maintaining, but also the pressure actually applied at the fusion point will reduce this condition, the above (i) to (iv) are almost equally applicable. This is because the pressure transfer will become more difficult with the curing process. In addition, if the gate size becomes smaller and the gate position becomes worse, the appearance and strength of the fusion will deteriorate. Fusion is the confluence point of resin, and may also be the flow end. At this time, if an exhaust port is not properly set at this position to exhaust gas, the appearance and strength of the fusion will deteriorate.
Generally, it mainly affects the appearance, painting and electroplating. In serious cases, it will affect the strength of products (especially in the case of fiber reinforced resin).
The following items can be referred to for improvement:
l) Adjust molding conditions to improve liquidity. For example, increase the resin temperature, mold temperature, injection pressure and speed.
2) It is also beneficial to exhaust by adding an exhaust slot and setting a push rod at the place where the weld line is generated.
3) Minimize the use of release agent.
4) Set up the process overflow and use it as the place where the weld line is generated, and then cut off and remove it after forming.
5) If it only affects the appearance, it can change the position of the burn four to change the position of the weld line. Or, the part where the weld line is produced shall be treated as a dark glossy surface for modification.
（2） Radial stria
Jetting
1. Apparent jet from the gate, a dark gray stream of molten metal is immediately wrapped by the subsequently injected molten metal after slightly contacting the mold wall. This defect may be partially or completely hidden inside the product.
For physical reasons, the radial pattern often occurs when the molten material enters the mold cavity and the front end of the fluid stops developing. It often occurs in the mold with large cavity, and the molten flow does not directly contact the mold wall or encounter obstacles. After passing through the gate, some hot molten materials contact the relatively cold mold cavity surface and then cool down, which cannot be closely combined with the subsequent molten materials during mold filling.
The obvious surface defects are removed, the radial pattern is accompanied by non-uniformity, the molten material is frozen and stretched, and the residual stress and cold strain are generated, all of which affect the product quality.
In most cases, it is impossible to improve only by adjusting the forming parameters, and only by improving the gate position and geometry size can it be avoided.
The causes and improvement measures related to processing parameters are shown in the following table:
1. The injection speed is too fast to reduce the injection speed
2. Injection speed Single stage adopts multi-stage injection speed: slow-fast
3. If the melting temperature is too low, the barrel temperature will be increased (only in the metering area for heat-sensitive materials).
The reasons and improvement measures related to the design of increasing low screw back pressure are shown in the following table:
1. The transition between gate and mold wall is not good, providing arc transition
2. The gate is too small to increase the gate
3. The gate is located at the center gate reset position of the section thickness. The overflow of the barrier injection process means that a deeper exhaust slot is manually opened on the mold. The slot generated during production (batch peak), also known as the process batch peak, is mainly used to improve the glue burning or welding mark. The glue burning or welding mark can be adjusted to this batch peak, and it can be removed after production.
2. Burn four position refers to the position where the glue burning or welding mark is not easily seen by the process, so as not to affect the appearance of the product.
3. Increasing the low screw back pressure means adjusting the back pressure
4. Obstacle injection refers to adding a block in front of the water. Change the flow direction of the injection gate. In order to change the flow direction of the rubber during injection. This method is helpful for solving the spray pattern.
（3） Greyor black clouding
1. The apparent gray and black markings may occur near the gate, in the middle of the runner and in the part far away from the gate. It can only be seen in transparent parts, and it is often found in products made of PMMA, PC and PS materials.
Physical causes
If the metering process starts too early, the air wrapped in the particles in the screw feeding area does not overflow the feeding mouth, and the air will be squeezed into the melt. However, the pressure in the feeding area is too low to move the air to the rear. The air squeezed into the molten material in the material barrel will cause gray and black spots in the product.
Like what happens in the compression ignition diesel engine, the coking phenomenon caused by the air squeezed into the cylinder is sometimes called "diesel engine effect".
The coking phenomenon can explain the high temperature at the junction of the molten material and the squeezed bubbles due to compression, and the oxygen in the air causes the molten material to fracture through oxidation.
The process commissioning should start the melting process in the middle of the feeding area, where the melting pressure has been high, forcing the air between particles to move backward and overflow the material port.
The causes and improvement measures related to processing parameters are shown in the following table:
1. Too low screw back pressure increases screw back pressure
2. The barrel temperature in the feeding area is too high to reduce the barrel temperature in the feeding area
3. Screw speed is too fast to reduce screw speed
4. The cycle time is short, that is, the residual time of molten material in the barrel is short, and the cycle time is extended
The reasons and improvement measures related to the design are shown in the following table:
1. Unreasonable screw geometry selects the screw with long feeding section, and the screw groove in the feeding section is deep
It is necessary to find out whether it is water spots or other spots. There are also water spots that will not occur if the rubber material is not dried thoroughly. Other factors will also form water spots, such as mold freezing water, dew due to temperature difference effect, mold mixing water, material mixing and so on.
（4） There is a dark area near the material head
Dullareas nearsprie
1. It is apparent that there is a discernible ring around the material head - if the central gate is used, it is a central circle, if the side gate is used, it is a concentric circle, because the ring size is small, it looks like a halo. This is mainly due to this phenomenon when processing high viscosity (low fluidity) materials, such as PC, PMMA and ABS.
Physical causes
If the injection speed is too high, the melt flow speed is too fast and the viscosity is high, some materials on the surface near the material head are easy to be dislocated and infiltrated. These dislocations will appear faint in the outer layer.
Near the feed head, the flow velocity is particularly high, and then gradually decreases. With the injection velocity becoming constant, the front end of the flow body expands into a gradually widened circle. At the same time, in order to obtain a low flow velocity near the feed head, multistage injection must be used, such as slow - fast - fast. The purpose is to obtain uniform melt flow velocity throughout the filling cycle.
It is generally believed that the halo is caused by the dislocation of the molten material during the pressure maintaining stage. In fact, the role of the forward flow effect is to move the molten material into the product during the pressure maintaining stage.
The causes and improvement measures related to processing parameters are shown in the following table:
1. The flow rate is too high. Multistage injection: slow - fast - fast
2. If the melting temperature is too low, the barrel temperature will increase and the screw back pressure will increase
3. Too low mold wall temperature increases mold wall temperature
The reasons and improvement measures related to the design are shown in the following table:
1. The gate forms a sharp angle with the product and forms an arc between the gate and the product
2. The gate diameter is too small to increase the gate diameter
3. Gate position error Gate relocation
（5） Void
1. Apparent
The gap inside the product is in the form of round or elongated bubbles. Only transparent products can see the gap inside from the outside; Opaque products cannot be detected from the outside. Voids often occur in products with relatively thick walls and in the thickest places.
Physical causes
When bubbles are produced in the product, they are often considered as bubbles, which are caused by the air in the mold being wrapped by the molten material flowing into the mold cavity. Another explanation is that the moisture and bubbles in the barrel will try to enter the interior of the product. Therefore, such "bubbles" have many sources.
At the beginning, the products produced will form a layer of hard skin, and will develop rapidly or slowly depending on the degree of mold cooling. However, in the thick-walled region, the central part still remains sticky for a long time. The skin has sufficient strength to resist any stress shrinkage. As a result, the molten metal in the product was stretched outward, and the plastic center part in the product still formed voids. The reasons and improvement measures related to processing parameters are shown in the following table:
1. The pressure maintaining pressure is too low to increase
2. The pressure holding time is too short to increase the pressure holding time
3. The mold wall temperature is too low to increase the mold wall temperature
4. Melt temperature is too high to reduce melt temperature
The reasons and improvement measures related to the design are shown in the following table:
1. The gate cross section is too small to increase the gate cross section and shorten the gate
2. Nozzle hole is too small to increase nozzle hole
3. The gate is opened in the thin wall area. The gate is opened in the thick wall area
（6） GranulesUnmelted
1. There are unmelted particles near the apparent material head. It is impossible to obtain smooth surface for thin-walled products.
Physical causes
Due to the short production and molding cycle of thin-walled products, it is necessary to plasticize at a high screw speed to shorten the residual time of molten material in the screw barrel. When it comes to the production of thin-walled products, usually including PE, PP, PC, etc., the mold union tries to reduce the melting temperature to shorten the cooling time, and the incompletely melted particles will be injected into the mold.
The causes and improvement measures related to processing parameters are shown in the following table:
1. Too low melting temperature increases barrel temperature
2. Screw speed is too high to reduce screw speed
3. Too low screw back pressure increases screw back pressure
4. The cycle time is short, that is, the residual time of molten material in the barrel is short, and the cycle time is extended
The reasons and improvement measures related to the design are shown in the following table:
1. Unreasonable screw geometry Select appropriate screw geometry (including metering shear zone)
（7） Colorstreams
The apparent color difference is the color difference of the product surface, which can occur near and far from the material head, and occasionally in the material flow area with sharp edges.
Physical causes
Uneven color is caused by uneven distribution of pigments, especially when adding color through color masterbatch, toner or liquid pigment.
When the temperature is lower than the recommended processing temperature, the masterbatch or color cannot be completely homogenized. When the molding temperature is too high or the residual time of the material barrel is too long, it is also easy to cause the thermal degradation of pigment or plastic, resulting in uneven color.
When the material is plasticized or homogenized at the correct temperature, if the injection is too fast when passing through the cross section of the material head, friction heat may be generated, resulting in pigment degradation and color change.
Generally, when using color masterbatch, it is necessary to ensure the compatibility of chemical and physical properties of the resin to be colored by the pigment and its solution.
The causes and improvement measures related to processing parameters are shown in the following table:
1. Uneven mixing of materials reduces screw speed; Increase barrel temperature and screw back pressure
2. If the melting temperature is too low, the barrel temperature will increase and the screw back pressure will increase
3. Too low screw back pressure increases screw back pressure
4. Screw speed is too high to reduce screw speed
The reasons and improvement measures related to the design are shown in the following table:
1. If the screw stroke is too long, use the material barrel with larger diameter or larger length-diameter ratio
2. The molten material stays in the barrel for a short time. Use the barrel with larger diameter or larger length-diameter ratio
3. The screw L: D is too low, and the barrel with large length-diameter ratio is used
4. Screw with low compression ratio adopts screw with high compression ratio
5. No shear section and mixing section provides shear section and/or mixing section
（8） Diesel effect away from sprue
1. Silver or black lines appear on the surface of the apparent products with the gate or a nearby point as the center. If low viscosity (high fluidity) materials and high molding temperature are used, the grain is mostly black, and if high viscosity (low fluidity) materials are used, the grain is mostly silver white.
Physical causes
This is another kind of bubble squeezed and compressed by. If the screw depressurization amplitude is too high (screw retraction), the depressurization speed is too fast, and the molten material in front of the screw head is released too much, negative pressure will be generated in the molten material, and it is easy to form bubbles in the molten material when the temperature of the molten material is too high.
These bubbles will be compressed again in the later injection stage, resulting in the formation of black lines in the product, and finally become "diesel engine effect".
If the gate is a central gate, the grain will radiate from the material head. In the case of injection with hot runner, the grain will only appear after a certain section of the runner, because the material in the hot runner does not contain any bubbles, so the material will not produce scorch marks. Only the molten material at the head of the re-feeding cylinder will produce scorching marks.
If it is a low-viscosity melt, the grain is darker and larger than that of high-viscosity material, because the former is easy to produce vacuum and voids during the screw pressure reduction process.
The causes and improvement measures related to processing parameters are shown in the following table:
1. The screw pressure drop is too high to reduce the screw pressure drop amplitude
2. The screw pressure reduction rate is too high to reduce the screw pressure reduction rate
3. If the melting temperature is too high, lower the barrel temperature, lower the screw back pressure, and lower the screw speed

（9） Moisturestrreams
Apparent water mark is a long silver thread on the surface of the product. The opening direction of the water mark is along the material flow direction. At the place where the product is not fully filled, the front end of the fluid is very rough.
Physical causes
Some plastics such as PA, ABS, PMMA, SAN and PBT are easy to absorb water. If the plastic storage conditions are not good, moisture will enter the particles or attach to the surface. When the particles melt, the moisture will be converted into steam to form bubbles. During injection, these bubbles will be exposed to the surface of the fluid front, burst and produce irregular lines
The causes and improvement measures related to processing parameters are shown in the following table:
1. The residual moisture in the particles is too high. Check the storage conditions of the particles, shorten the time of the particles in the hopper, and provide sufficient pre-drying for the materials
（10） Gramophone rippie
1. It is apparent that deep grooves can be seen in the whole material flow direction and even to the end of the flow passage. This phenomenon occurs when high viscosity (poor fluidity) materials and thick wall products are used for production. These grooves look like the lines on the record. It is very clear on the products made of PC material, but it is larger on the ABS products, and it is gray.
Physical causes
If during the injection process, especially under the condition of low injection speed, the condensation speed of the melt contacting the mold surface is too fast and the flow resistance is too high, it will cause distortion at the front of the fluid. The solidified outer material will not completely contact the mold cavity wall and form a wave shape. These wavy materials will freeze, and pressure retaining will no longer be able to flatten them.
The causes and improvement measures related to processing parameters are shown in the following table:
1. The injection speed is too low to increase the injection speed
2. The melting temperature is too low to raise the barrel temperature and increase the screw back pressure
3. The mold surface temperature is too low to increase the mold temperature
4. Pressure maintaining is too low to increase pressure maintaining
The reasons and improvement measures related to the design are shown in the following table:
1. The gate cross section is too small to increase the gate cross section and shorten the gate
2. Nozzle hole is too small to increase nozzle hole
（11） Cold plug
(1) What is cold material?
1. Cold material refers to the phenomenon that the cured resin at the front end of the nozzle is mixed with the molding product.
2. The cold material shows poor gloss or spray lines on the surface of molded products. Although it looks similar,
3. However, due to different countermeasures, attention needs to be paid.
(2) Reasons for cold material generation
(2-1) Low nozzle temperature
In order to prevent salivation (resin flowing out of the hole at the front of the nozzle), the resin temperature should be properly reduced at the front of the nozzle. Therefore, the initial part of the resin injected into the mold will become cured or semi-cured resin. This is called cold material.
In order to prevent the resin from entering the mold cavity, the resin accumulator is generally made at the root of the main channel and the branch channel on one side of the mold to serve as the receiving container for cold materials. However, if the resin temperature is too low, the amount of cold material will increase, which may enter the mold cavity. These will show spray lines or poor gloss appearance.
(3) Countermeasures for cold materials
(3-1) Increase nozzle temperature
It is very effective to prevent cold material and increase nozzle temperature. But the appearance of salivation must be considered In order to avoid salivation, the set temperature of the barrel and nozzle should be gradually increased. If the nozzle is fixed to the mold, it is also effective to increase the mold temperature
(3-2) Expand the cold material trap (resin storage)
Expanding the cold material trap can prevent the cold material from entering the formed product. Generally, it is recommended to use a cold material trap with a length of about 1.5 times the diameter of the main runner root.
(3-3) Backward the barrel once per cycle
When the nozzle is fixed to the mold, it is also a very effective method to make the barrel back once every cycle and make the nozzle come out of the mold. But we must also pay attention to salivation. Since salivation also depends on the viscosity and fluidity of the resin, nozzle model and aperture, you must repeat the actual test (including the above temperature adjustment). According to the situation, methods such as reducing nozzle aperture (i.e. changing to another nozzle) to suppress salivation and increasing temperature to suppress cold material should also be considered in advance.
1. Apparent means that a piece of cold material is stuck or stuck on the surface near the material head. Cold material head will cause traces on the surface of the product, and seriously reduce the mechanical properties of the product
Physical causes
When the molten material can be cooled near the nozzle or hot runner of the machine, it often produces a cold head. Since the molten metal injected first always gathers near the gate, defects will occur in this area. The reason is that the temperature control around the machine nozzle or hot runner nozzle is unreasonable.
The causes and improvement measures related to processing parameters are shown in the following table:
1. Too low hot runner temperature increases heating runner temperature
2. If the nozzle temperature is too low, measure the nozzle temperature, increase the nozzle temperature and reduce the nozzle contact area
The reasons and improvement measures related to the design are shown in the following table:
1. The nozzle cross section is too small to increase the nozzle cross section
2. The geometric size of the gate is changed unreasonably, leaving the cold material head in the channel
3. The geometric size of hot runner nozzle is changed unreasonably
（12） Plastic molding and processing methods
Plastic products are usually made of polymers or mixtures of polymers and other components, which are molded into a certain shape under certain conditions after being heated
It is formed by cooling, shaping and trimming. This process is the molding and processing of plastics. If the performance of plastic and thermosetting plastics after heating is different, their molding and processing methods are also different. There are dozens of plastic molding methods, the most important of which are extrusion, injection, calendering, blow molding and molding. The weight of the products they process accounts for more than 80% of all plastic products.
Extrusion molding - Extrusion molding, also known as extrusion molding or extrusion molding, is the most important molding method for thermoplastics, and about half of plastic products are extruded. Almost all thermoplastics can be formed by extrusion, and the products mainly include continuous production, equal-section pipe, plate, film, wire and cable coating and various special-shaped products. Extrusion molding can also be used for plasticizing, granulating, coloring and blending of thermoplastics.
After the thermoplastic polymer and various additives are mixed evenly, they are subjected to the action of mechanical shear force, friction heat and external heat in the plastic cylinder of the extruder, making it plasticized and melted, and then under the push of the screw, they enter the molding mold through the filter plate and are extruded into products.
Injection molding - Injection molding is also known as injection molding or injection molding. This molding method is to heat and melt the plastic (generally granular material) in the barrel of the injection molding machine. When it is in a flowing state, the molten plastic is compressed and moved forward under the pressure of the plunger or screw, and then injected into the closed mold with low temperature at a very fast speed through the nozzle at the front of the barrel. After a certain time of cooling and shaping, the mold is opened to obtain the product.
Injection molding is developed according to the principle of metal die-casting. Because injection molding can produce products with complex shape, precise size or metal inserts at one time, it is widely used, accounting for more than 20% of the total molding processing.
Injection molding process usually consists of five stages: plasticizing, mold filling (i.e. injection), pressure maintaining, cooling and demoulding.
Generally, injection molding products have sprues, runners and other waste materials, which need to be trimmed and removed. This not only consumes labor, but also wastes raw materials.
The sprueless injection molding developed in recent years not only overcomes the above drawbacks, but also helps to improve production efficiency.
（13） Paste spots (full or partial discoloration)
Cause: The temperature setting of the barrel is unreasonable. Local material storage occurs in the barrel. The resin intrudes into the joint between the barrel and the nozzle (long-term storage). A backflow valve or backflow ring is installed. Hydrolysis due to insufficient drying. The capacity of the injection molding machine is too large.
Treatment method: reduce the temperature of the barrel. Avoid * angle structure. Try to eliminate the gap at the joint. Avoid using backflow valve and backflow ring. Pre-dry according to the specified conditions. Select the injection molding machine with appropriate capacity.
（14） Warping and deformation
Warping and deformation of injection products are very difficult problems. It should be solved mainly from the mold design, while the adjustment effect of forming conditions is very limited. The causes and solutions of warpage and deformation can refer to the following items:
1) When the deformation is caused by the residual stress caused by the molding conditions, the stress can be eliminated by reducing the injection pressure, increasing the mold and making the mold temperature uniform, increasing the resin temperature or adopting the annealing method.
2) When the stress deformation is caused by poor demoulding, it can be solved by increasing the number or area of push rods and setting the demoulding slope.
3) If the cooling method is not suitable and the cooling is uneven or the cooling time is insufficient, the cooling method can be adjusted and the cooling time can be extended. For example, the cooling circuit can be set as close to the deformation as possible.
（15） Color stripe, color line, color flower
This is a common problem for plastic products that use color masterbatch coloring. Although color masterbatch coloring is superior to dry powder coloring and dye paste coloring in terms of color stability, color purity and color mobility, but the distribution, that is, the mixing uniformity of color particles in dilute plastic is relatively poor, and the finished product naturally carries
(1) Increase the temperature of the feeding section, especially the temperature of the rear end of the feeding section, so that its temperature is close to or slightly higher than the temperature of the melting section, so that the color masterbatch will melt as soon as it enters the melting section, promote the uniform mixing with dilution, and increase the chance of liquid mixing.
(2) When the screw speed is constant, increasing the back pressure will increase the melt temperature and shear effect in the barrel.
(3) Modify the mold, especially the pouring system. If the gate is too wide and the melt passes through, the turbulence effect is poor and the temperature rise is not high, so it is uneven. The color band cavity should be changed to have regional color differences.
（16） Finished mucosa (difficult to demould)
It refers to the phenomenon that molded products cannot be taken out of the mold.
According to the size, temperature and other conditions of the molded product, the poor demoulding will occur when the demoulding resistance increases. Although it is also affected by the resin characteristics and molding conditions, the main reason is still the shape of the molded product and the structure of the mold. Special attention should be paid to the situation when it is closely associated with slender stiffeners, hubs and plastic hole bolts.
When the molding shrinkage around the plastic hole bolt is too large, the holding force of the plastic hole bolt will become larger, which is easy to cause poor demoulding. In terms of molding conditions, the mold temperature is low and the pressure holding is too high, which is easy to cause poor demoulding.
When the long stiffeners or hubs are filled in the vertical molding products, these stiffeners or hubs will become difficult to fall off, resulting in poor demoulding. In terms of molding conditions, the mold temperature is low and the pressure holding is too high, which is easy to cause poor demoulding. This is the opposite of the plastic hole bolt.
The demoulding angle of the mold cavity part is too small, and the demoulding resistance is too large, so it is easy to cause demoulding defects. The position of the ejector pin also has a great influence (it is better to set the ejector pin at the place where the stripping resistance is too high). In addition, the surface finish or damage of the mold cavity also has an impact on the release resistance, resulting in poor release.
During injection molding, there will be mucous membrane in the finished product. First of all, consider whether the injection pressure or pressure retaining pressure is too high. Too high injection pressure will cause the finished product to be oversaturated, making the plastic filled into other voids, making it difficult for the finished product to be stuck in the mold cavity for demoulding, and it is easy to have mucous membrane when taking out.
When the temperature of the material pipe is too high, there are usually two kinds of scene. One is that the temperature is too high, which causes the plastic to decompose and deteriorate, and loses its original characteristics; In the process of demoulding, it will break or tear, causing mucous membrane. Second, it is difficult to cool the rubber after filling the mold cavity, and it needs to prolong the cycle time, which is not economic. Therefore, it is necessary to properly adjust its operating temperature according to the characteristics of the rubber. As for the problem of mold, if the feeding port is not balanced, it will make the finished product easy to have mucous membrane when demoulding.
Possible causes and treatment measures of finished mucosa:
Troubleshooting
(1) Excessive filling reduces the injection dose, time and speed
(2) The injection pressure or barrel temperature is too high to reduce the injection pressure or barrel temperature
(3) Pressure holding time is too long to reduce pressure holding time
(4) The shooting speed is too fast to reduce the shooting speed
(5) The uneven feeding makes the part too full to change the size or position of the overflow
(6) Insufficient cooling time increases cooling time
(7) If the mold temperature is too high or too low, adjust the mold temperature and the relative temperature of both sides
(8) There is undercut in the mold. Repair the mold and remove the chamfer
(9) Unbalanced feeding ports of multi-cavity die or unbalanced feeding ports of single-cavity die restrict the flow of plastic, and close to the main channel as much as possible
(10) Poor design of demoulding exhaust of probe barrel provides sufficient escape passage
(11) The screw advance time is too long to reduce the screw advance time
(12) The mold center is misaligned to adjust the mold center and locked with the "backset" angle
(13) The mold surface is too rough to polish the mold cavity surface and spray release agent
4-3 sprue bonding (difficult to demould)
Troubleshooting
1、 The sprue is too large to modify the mold
2、 The runner cooling is not enough to extend the cooling time or reduce the material pipe temperature
3、 The demoulding angle of runner is not enough. Modify the mold to increase the angle
4、 The fitting of the runner concave arc and the nozzle is not correct. Re-adjust and fit
5、 The inner surface of the runner is not smooth or has demoulding chamfer to repair the mold
7、 The outer hole of the runner is damaged and the mold is repaired
8、 Grab lock added without sprue
When the demoulding resistance caused by the clamping of the plastic hole bolt is too large, it is also effective to control the molding shrinkage by increasing the pressure holding and mold temperature.
On the contrary, if the size is increased and embedded into the mold cavity due to overfilling, the pressure holding and mold temperature should be reduced to increase the molding shrinkage. When the demoulding resistance caused by the clamping of the plastic hole bolt is too large, it is also effective to control the molding shrinkage by increasing the pressure holding and mold temperature.
Increase the demoulding slope at the periphery of the mold cavity, hub and stiffener. Especially if it has been embedded firmly, the ejector pin should be configured for the part that needs to increase the ejector strength by adding ejector pin and other methods.
（17） Air wrap
Air traps means that the air in the mold cavity is covered before the glue is melted, which occurs when the air converges from different directions before the glue is melted, or when the air cannot escape from the exhaust hole or the gap of the embedded part. The wind-blowing usually occurs in the last filling area. If the exhaust hole in these areas is too small or there is no exhaust hole, it will cause the wind-blowing, causing voids or bubbles inside the plastic parts, short shot of the plastic parts or surface defects. In addition, when the thickness of plastic parts varies greatly, the melt glue tends to flow to the thick zone, resulting in the race-tracking effect, which is also the main reason for the wind,
In order to eliminate the blast, the injection rate can be reduced to change the filling mode; Or change the position of the exhaust hole and increase the size of the exhaust hole. The air bag caused by the racing effect can improve the exhaust problem by changing the thickness of the plastic part or changing the position of the exhaust hole. The improvement methods of air bag are described as follows:
(1) Change the design of plastic parts: reduce the proportion of meat thickness, which can reduce the competitive flow effect of melt adhesive.
(2) The mold design should be changed: the exhaust can be improved by setting the exhaust hole at the proper position. The vent hole is usually located in the last filled area, such as the junction between the mold and the mold, the parting surface, the position between the embedded parts and the mold wall, the ejector pin and the mold slider. Re-design the gate and the glue conveying system can change the filling mode, so that the final filling area falls at the appropriate exhaust hole position.
In addition, it should be ensured that there is enough exhaust hole to allow the air to escape during filling; But also be careful that the vent hole is not too large to cause burrs. The recommended vent size is 0.025 cm (0.001 inch) for crystalline plastic and 0.038 cm for amorphous plastic

（18） Sore: (silver stripe)
The surface of the finished product, centered on CATE, has many silvery stripes, which are basically produced along the flow direction of raw materials. This phenomenon occurs after many bad conditions have accumulated, and sometimes it is difficult to grasp the real reason.
1.1 If there is water or other volatile components in the raw material and it is not fully dried, a lot of silver bars will be produced on the surface.
1.2 When other raw materials are accidentally mixed into the raw materials, they will also form sores, which are in the shape of mica or needle-point, and are easy to be separated from sores caused by other reasons.
1.3 This is also easy to happen when raw materials or material pipes are not clean.
1.4 The injection time is long, the temperature of raw materials injected into the mold cavity at the initial stage is low, and the volatile components will not be eliminated as a result of curing, especially for temperature-sensitive raw materials, which often occurs.
1.5 If the mold temperature is low, the raw material will solidify quickly and easily (1.4), so that the volatile components will not be discharged.
1.6 When the mold exhaust is poor, the gas is not easy to be discharged when the raw material enters, which will cause sores. In this case, the top of the finished product will often burn black.
1.7 If moisture is attached to the mold, the heat brought by the filling material will evaporate and melt with the molten material, forming a sore, which is albumen fog.
1.8 The cold material nest of the rubber duct has cold material or small. When it is ejected, the cooled raw material is brought into the mold cavity, and part of it will quickly solidify to form a thin layer. When the mold temperature is low at the beginning of production, it will also cause sores.
1.9 During the filling process of raw materials, due to the rapid cooling of the contact part of the mold cavity surface, a thin layer is formed, which is melted and decomposed by the following raw materials, forming white or smudge-like, which is commonly seen in thin-shell products.
1.10 During filling, the raw material is turbulent, which makes the flow path of the raw material longer, and the friction is caused by the influence of the structure in the mold cavity. In addition, the filling speed is faster than the cooling speed of the raw material. The GATE position is located at the tendon or small position, which is easy to produce sores, and the place where the meat thickness of the finished product is sharply increased is also easy to produce sores.
1.11 The GATE and the flow channel are small or deformed, and the filling speed is fast, and the friction is generated instantly, which causes the temperature to rise sharply and causes the raw material to decompose.
1.12 The raw material contains recycled material, which is not fully dried and decomposed when it is ejected, causing sores.
1.13 The raw material stays in the material pipe for a long time, causing partial overheating and decomposition.
1.14 The back pressure is insufficient and the air is drawn in (the compression ratio is insufficient).
Sore:
Molding machine
The plasticizing ability is insufficient. Resin overheat decomposition (material pipe temperature) The raw material in the material pipe stays for a long time, causing partial overheating. The injection pressure is too high. The screw is drawn into air (insufficient back pressure).
mould
Poor exhaust in the mold. The mold temperature is low. The storage of the cold material nest of the rubber channel is small. GATE is too small or deformed.
There is moisture on the mold surface. The shape of the mold cavity is poor (the cross section or wall thickness changes more rapidly).
raw material
The raw material consists of water and volatile components. Insufficient drying of raw materials. Mix with other raw materials.
（19） Dimension difference of injection parts
1. Characteristics of defects of injection molded parts
The change of weight and size during the injection molding process exceeds the production capacity of mold, injection molding machine and plastic combination.
2. Possible causes of problems
(1) . Input the uneven plastic in the injection cylinder.
(2) The temperature or fluctuation range of the injection cylinder is too large.
(3) The capacity of the injection molding machine is too small.
(4) The injection pressure is unstable.
(5) Screw resetting is unstable.
(6) The change of operation time and solution viscosity are inconsistent.
(7) The injection speed (flow control) is unstable.
(8) The plastic varieties that are not suitable for the mold are used.
(9) Consider mold temperature, injection pressure, speed, time and pressure holding
Etc.
3. Remedies
(1) Check whether there is sufficient cooling water flowing through the hopper throat to maintain the correct temperature.
(2) . Check for poor quality or loose thermocouple.
(3) Check whether the thermocouple used with the temperature controller is of the correct type.
(4) Check the injection quantity and plasticizing capacity of the injection molding machine, and then compare with the actual injection quantity and hourly injection
Compare the amount of plastic.
(5) Check whether there is stable molten hot material in each operation.
(6) Check the backflow prevention valve for leakage and replace it if necessary.
(7) . Check for incorrect feeding settings.
(8) Ensure that the screw is stable at the return position of each operation, that is, no more than 0.4mm change.
(9) . Check the operation time for inconsistency.
(10) . Use back pressure.
(11) Check whether the hydraulic system operates normally and whether the oil temperature is too high or too low (25-60oC).
(12) Select the plastic variety suitable for the mold (mainly considering the shrinkage and mechanical strength). (13) Readjust the entire production process.
（20） Craze (including surface bubbles and internal pores)
The main reason for the defect is the interference of gas (mainly water vapor, decomposition gas, solvent gas and air). If the screw speed is too fast and the back pressure is too low, the amount of air involved in the resin being plasticized will increase. The result is that the strip-like bubbles appear on the surface of the molded product, and the craze is easy to form. Resin belongs to chemical substances, so it will decompose gradually with the increase of temperature.
The higher the temperature of the resin, the more it decomposes, and the easier the craze appears. If the pre-drying of the material is insufficient, the moisture and the original gas components in the resin will be brought into the molding product intact, which is easy to form craze. When the gas is not completely discharged, bubbles will remain on the surface of the molded product, which is prone to craze. If different components from the original resin are mixed due to insufficient cleaning and other reasons, and the temperature of the resin is low, sometimes gas will be generated and craze will be induced.
1. Machine:
(1) The material barrel and screw are worn or there is a material flow * angle in the rubber head and rubber ring, which is decomposed due to long-term heating.
(2) If the heating system is out of control and causes decomposition due to excessive temperature, check whether there is any problem with the heating components such as thermocouples and heating rings. The screw is improperly designed, which may lead to individual breakdown or easy to bring in air.
2. Mold:
(1) Poor exhaust.
(2) The friction resistance of runner, gate and cavity in the mold is large, resulting in local overheating and decomposition.
(3) Unbalanced distribution of gates and cavities, and unreasonable cooling system will cause uneven heating and local overheating or blocking of air channels. (4) The cooling passage leaks into the cavity.
3. Plastic:
(1) Due to high humidity of plastics, excessive proportion of recycled materials added or harmful scraps (scraps are easily decomposed), the plastics should be fully dried and scraps should be eliminated.
(2) If moisture is absorbed from the atmosphere or from the colorant, the colorant should also be dried. It is better to install a dryer on the machine.
(3) The amount of lubricant and stabilizer added in the plastic is too much or mixed unevenly, or the plastic itself contains volatile solvent. The mixed plastic will also decompose when the degree of heating is difficult to take into account.
(4) The plastic is contaminated and mixed with other plastics.
4. Processing:
(1) When the set temperature, pressure, speed, back pressure, and the rotational speed of the glue melting motor are too high to cause decomposition, or the pressure and speed are too low, the injection time, pressure holding is not sufficient, and the back pressure is too low, and the gas cannot be melted due to the failure to obtain high pressure, the density is insufficient, and the craze appears, the appropriate temperature, pressure, speed and time should be set, and the multi-stage injection speed should be used.
(2) Low back pressure and fast rotation speed are easy to make air enter the material barrel and melt into the mold. If the cycle is too long, the melt will decompose due to too long heating in the material barrel.
(3) Insufficient material quantity, too large feeding buffer pad, too low material temperature or too low mold temperature will affect the material flow and molding pressure, and promote the formation of bubbles.
Bubble
According to the causes of bubbles, the countermeasures are as follows:
1) When the wall thickness of the product is large, the cooling speed of its outer surface is faster than that of the center part. Therefore, with the cooling process, the resin in the center part shrinks and expands to the surface, resulting in insufficient filling in the center part. This condition is called a vacuum bubble. The main solutions are:
a) Determine reasonable gate and gate size according to wall thickness. Generally, the gate height shall be 50%~60% of the product wall thickness.
b) Until the gate is sealed, a certain amount of supplementary injection material is left.
C) The injection time should be slightly longer than the gate sealing time.
d) Reduce the injection speed and increase the injection pressure.
e) Use materials with high melting viscosity grade.
2) The main solutions to the bubbles caused by the generation of volatile gases are as follows:
a) Pre-dry fully.
b) Reduce the resin temperature to avoid decomposition gas.
3) Bubbles caused by poor fluidity can be solved by increasing the temperature of resin and mold and increasing the injection speed.
Gas bubbles
1. Apparent
There are many bubbles on the surface and inside the product - mainly near the material head. The place in the middle of the flow path and away from the material head - not only the place where the product wall thickness occurs. Bubbles have different sizes and shapes.
Physical causes
Bubbles mainly occur in heat-sensitive materials that must be processed at high temperature. If the necessary molding temperature is too high, the material will decompose through molecular splitting, and the molten material will be in danger of thermal degradation, and bubbles will be easily generated during the molding process.
If the cycle time is long, it may usually be the cause of too long residual time and insufficient travel utilization. It is also possible that the molten material in the barrel is overheated.
The causes and improvement measures related to processing parameters are shown in the following table:
1. Too high melting temperature reduces barrel temperature, screw back pressure and screw speed
2. The residual time of molten material in the barrel is too long. Use a smaller barrel diameter
The reasons and improvement measures related to the design are shown in the following table:
1. Unreasonable screw geometry using low compression screw
（21） Gate area defect
1. Light line
In the design of the point gate perpendicular to the direction of the part, a radiation system consisting of different color depth and gloss with the gate as the center appeared on the surface of the part during injection molding, called the ray line. Generally, there are three kinds of performance, namely, dark lines on the dark bottom, dark lines on the dark bottom and dark lines around the gate are dense and white.
Most of these defects occur during the injection of polystyrene and modified polystyrene mixture, and are related to the following factors: the two materials have differences in rheology, coloration, etc., and the flow rate and heating conditions of the stratosphere and turbulent layer of the gating system are different; The charred wire is formed due to the thermal decomposition of plastics; Interference of gaseous substances during plastic injection molding.
Solution:
(1) When mixed plastic is used, the plastic shall be mixed well, and the particle size of plastic shall be the same and uniform.
(2) The plastics and colorants should be mixed evenly. If necessary, appropriate dispersants should be added and mixed mechanically.
(3) The plasticization shall be complete, and the plasticization performance of the machine shall be good.
(4) Reduce the injection pressure and speed, shorten the injection and holding time, increase the mold temperature, increase the nozzle temperature, and reduce the front furnace temperature.
(5) Molten materials and coking substances that can prevent the degradation of plastics and increase viscosity: for example, pay attention to the screw and barrel
There is no wear and tear, or the heating system is out of control, or improper processing operation causes the plastic to decompose due to long-term heating. The inner surface of the screw and the front end of the barrel can be polished.
(6) Improve the gate design, such as enlarging the gate diameter, changing the gate position, changing the gate into a fillet transition, trying to heat the gate locally, and adding a cold well at the runner end.