Contraction sign
First, the characteristics of defects in injection molded parts
It is usually related to surface marks, which are formed by the contraction and separation of plastic from the surface of the mold.
Second, the causes of possible problems
(1). The melting temperature is too high or too low.
(2) Insufficient plastic in the mold cavity.
(3) During the cooling stage, the surface in contact with the plastic is overheated.
(4) The runner is unreasonable and the gate section is too small.
(5) Whether the mold temperature is compatible with the characteristics of plastics.
(6) The product structure is unreasonable (too high and too thick, with obvious difference in thickness).
(7) The cooling effect is not good, and the product continues to shrink after demoulding.
Three. Relief method
(1). Adjust the shooting pot temperature.
(2) Adjust the screw speed to obtain the correct screw surface speed.
(3) Increase the injection amount.
(4). Make sure to use the correct gasket; Increase the spiral advance time; Increase the injection pressure; Increase the injection speed.
(5) Check whether the check valve is installed correctly, because abnormal operation will lead to pressure loss.
(6). Reduce the mold surface temperature.
(7). Correct the flow channel to avoid excessive pressure loss; According to the actual needs, appropriately expand the section size.
(8) The mold temperature should be properly controlled according to the characteristics of the plastic used and the product structure.
(9) Improve the product structure when conditions permit.
(10). Try to let the product have enough cooling.
summary
First, the characteristics of defects in injection molded parts
It is easy to see in the "air trap" of transparent injection molded parts, but it may also appear in opaque plastics, which is related to the thickness and is often caused by the shrinkage of plastics away from the center of injection molded parts.
Second, the causes of possible problems
(1). The mold is not completely filled.
(2) The check valve runs abnormally.
(3) The plastic is not completely dry.
(4) The preform or injection speed is too fast.
(5) Some special materials should be produced by special equipment.
Three. Relief method
(1). Increase the injection volume.
(2) Increase the injection pressure.
(3) Increase the spiral advance time.
(4) Reduce the melting temperature.
(5) Reduce or increase the injection speed. (such as amorphous plastics, the speed should be increased by 45%).
(6). Check whether the check valve is broken.
(7) The drying conditions should be improved according to the characteristics of plastics, so that the plastics can be completely dried.
(8). Properly reduce the screw speed and increase the back pressure, or reduce the injection speed.
This product has low dimensional accuracy.
Characteristics of defects in injection molded parts
First, the change of weight and size during injection molding exceeds the production capacity of mold, injection molding machine and plastic combination.
Second, the causes of possible problems
(1). The plastic input into the shooting pot is uneven.
(2) The shooting pot temperature or fluctuation range is too large.
(3) The capacity of the injection molding machine is too small.
(4) The injection pressure is unstable.
(5). The screw reset is unstable.
(6) The change of operation time and solution viscosity is inconsistent.
(7) The injection speed (flow control) is unstable.
(8) Using plastic varieties that are not suitable for molds.
(9) Consider the influence of mold temperature, injection pressure, speed, time and holding pressure on the product.
Three. Relief method
(1). Check whether there is enough cooling water flowing through the throat of the hopper to keep the correct temperature.
(2) Check whether the thermocouple is inferior or loose.
(3) Check whether the thermocouple used with the temperature controller belongs to the correct type.
(4) Check the injection quantity and plasticizing capacity of the injection molding machine, and then compare it with the actual injection quantity and the plastic injection quantity per hour.
(5). Check whether there is a stable molten hot material for each operation.
(6) Check whether the backflow preventer leaks, and replace it if necessary.
(7). Check whether the paper feed setting is wrong.
(8). Ensure that the position of the screw is stable in each operation, that is, the change does not exceed 0.4 mm. ..
(9). Check the inconsistency of operation time.
(10). Use back pressure.
(1 1). Check whether the hydraulic system works normally and whether the oil temperature is too high or too low (25-60℃).
(12). Select the plastic variety suitable for the mold (mainly considering shrinkage and mechanical strength).
(13). Re-adjust the whole production process.
There are ripples or silver lines on the surface of the product.
The cause of the possible problem
1) Plastic contains moisture and volatiles;
2) The material temperature is too high or too low;
3) The injection pressure is too small;
4) runner and gate size is too large;
5) The temperature of the insert is too low before preheating;
6) The internal stress of the product is too large.
The gate is stuck.
First, the characteristics of defects in injection molded parts
The nozzle is fixed by the nozzle sleeve.
Second, the causes of possible problems
(1). The nozzle sleeve is not aligned with the nozzle.
(2) There is too much plastic in the nozzle sleeve.
(3) The nozzle temperature is too low.
(4) The plastic is not completely solidified in the nozzle, especially in the nozzle with larger diameter.
(5) The arc surface of the nozzle sleeve and the arc surface of the nozzle are not properly matched, resulting in a "mushroom-shaped" flow channel.
(6). Runners are not enough to pull the slope.
Three. Relief method
(1). Align the nozzle and nozzle sleeve again.
(2) Reduce the injection pressure.
(3) Reduce the spiral advance time.
(4) Raise the nozzle temperature or heat the nozzle with an independent temperature controller.
(5) Increase the cooling time, but it is better to use the nozzle sleeve with smaller nozzle instead of the original nozzle sleeve.
(6) Correct the mating surface between the nozzle sleeve and the nozzle.
(7) Appropriately increase the pull-out slope of the runner.
Warping deformation of plastic parts
First, the characteristics of defects in injection molded parts
The shape of injection molded parts is similar to the mold cavity, but it is a distorted version of the mold cavity shape.
Second, the causes of possible problems
(1). Bending is caused by excessive internal stress in injection molding.
(2) The mold filling speed is slow.
(3) The plastic in the mold cavity is insufficient.
(4). Plastic temperature is too low or inconsistent.
(5) The injection molded parts are overheated during demoulding.
(6) Insufficient cooling or inconsistent temperatures between the moving die and the fixed die.
(7) The structure of injection molded parts is unreasonable (for example, the reinforcing ribs are concentrated on one side, but far apart).
Three. Relief method
(1). Reduce the injection pressure.
(2) Reduce the spiral advancing time.
(3) Increase the cycle time (especially the cooling time). After being pushed out of the mold (especially the thick injection molded parts), immediately immerse them in warm water (38oC) to slowly cool the injection molded parts.
(4) improve the injection speed.
(5). Improve the plastic temperature.
(6). Use cooling equipment.
(7) appropriately increase the cooling time or improve the cooling conditions, so as to ensure that the mold temperatures of the moving mold and the fixed mold are as consistent as possible.
(8) According to the actual situation, improve the structure of plastic parts when conditions permit.
Plastic parts are underfilled.
First, the characteristics of defects in injection molded parts
The injection molding process is incomplete because the mold cavity is not filled with plastic, or some details are missing in the injection molding process.
Second, the causes of possible problems
(1). The injection speed is insufficient.
(2) Plastic shortage.
(3) Leave no screw pad at the end of the trip.
(4). Change of running time.
(5) The shooting pot temperature is too low.
(6) Insufficient injection pressure.
(7) The nozzle part is sealed.
(8) The heater outside the nozzle or shooting pot cannot work.
(9). Injection molding time is too short.
(10). The plastic sticks to the throat wall of the hopper.
(1 1). The capacity of the injection molding machine is too small (i.e. injection weight or plasticizing capacity).
(12). The mold temperature is too low.
(13). The antirust oil of the mold was not cleaned.
(14). The retaining ring is damaged and the melt flows back.
Three. Relief method
(1). Increase the injection speed.
(2) Check the amount of plastic in the hopper.
(3) Check whether the fuel injection stroke is set correctly, and make changes if necessary.
(4). Check whether the check valve is worn or broken.
(5). Check whether the operation is stable.
(6) Increasing the melting temperature.
(7). Increase the back pressure.
(8). Improve the injection speed.
(9) Check the nozzle hole for foreign matter or unplasticized plastic.
(10). Check the outer layers of all heaters, and check whether the energy output is correct with ammeter.
(1 1). Increase the screw advance time.
(12). Increase the cooling capacity of the throat of the hopper, or reduce the temperature at the back of the shooting pot.
(13). Use a larger injection molding machine.
(14). Raise the mold temperature appropriately.
(15). Clean the rust inhibitor in the mold.
(16). Check or change the shift ring.
glitter
The cause of the possible problem
1) The temperature of the bucket, nozzle and mold is too high;
2) The injection pressure is too high and the clamping force is too small;
3) The mold clamping is not tight, there are sundries or the template has been deformed;
4) Poor exhaust of the cavity;
5) The fluidity of plastic is too good;
Melting mark
The cause of the possible problem
1) The material temperature is too low, and the plastic fluidity is poor;
2) The injection pressure is too small;
3) The injection speed is too slow;
4) The mold temperature is too low;
5) Poor exhaust of the cavity;
6) Plastic is polluted.
Sidewall dent
"dent" is caused by local internal shrinkage caused by gate seal or insufficient material injection. The depression or dent on the surface of injection molded products is an old problem in the injection molding process. Dents are generally caused by the local increase of shrinkage of plastic products due to the increase of wall thickness. It may appear near the external sharp corners, or at the sudden change of wall thickness, such as behind bumps, ribs or supports, or sometimes it may appear in some unusual parts. The root cause of dents is the thermal expansion and cold contraction of materials, because the thermal expansion coefficient of thermoplastics is quite high. The degree of expansion and contraction depends on many factors, among which the performance of plastic, the highest and lowest temperature range and the cavity holding pressure are the most important factors. The size and shape of injection molded parts, as well as cooling speed and uniformity are also influencing factors.
The expansion and contraction of plastic materials in the molding process are related to the thermal expansion coefficient of processed plastics, which is called "molding shrinkage". With the cooling shrinkage of the molded part, the molded part loses close contact with the cooling surface of the cavity, and the cooling efficiency decreases at this time. After the molded part continues to cool, the molded part shrinks continuously, and the amount of shrinkage depends on the comprehensive action of various factors. The sharp corners on the molded parts cool fastest and harden earlier than other parts. The thick part near the center of the molded part is farthest from the cooling surface of the cavity and becomes the last part to release heat. After the material at the corner solidifies, the molded part will continue to shrink with the cooling of the melt near the center of the part, and the plane between the sharp corners can only be cooled unilaterally, and its strength is not as high as that of the material at the sharp corners. The cooling shrinkage of the plastic material in the center of the product pulls the relatively weak surface inward between the partially cooled and the sharp corners with greater cooling degree. In this way, the surface of injection molded parts will be dented. The presence of dents indicates that the molding shrinkage here is higher than its surrounding area. If the shrinkage rate of molded parts is higher in one place than in another, then the warpage of molded parts is the reason. The residual stress in the mold will reduce the impact strength and temperature resistance of the molded parts. In some cases, dents can be avoided by adjusting process conditions. For example, during the pressure holding process of molded parts, additional plastic materials are injected into the mold cavity to compensate for molding shrinkage. In most cases, the gate is much thinner than other parts of the product. When the molded part is still hot and shrinking, the small gate has solidified. After curing, holding pressure has no effect on the molded parts in the cavity.
The high shrinkage of semi-crystalline plastic molded parts makes the dent problem more serious; Amorphous materials have low molding shrinkage, which will minimize dents; Filled and maintained reinforcing materials have lower shrinkage and less possibility of dents.
Thick injection molded parts will shrink greatly if they are cooled for a long time, so the big thickness is the root cause of dents. Attention should be paid when designing, and thick-walled parts should be avoided as far as possible. If the thick-walled part is unavoidable, it should be designed as a hollow part, and the thick-walled part will smoothly transition to the nominal wall thickness. Dents near sharp corners can be eliminated or minimized by replacing sharp corners with large arcs.