Common problems and solutions in PC material processing

1, silver

The silver streaks are mainly caused by the moisture absorption of the resin, and therefore, the resin should generally be dried at a temperature 10-15 ° C lower than its heat distortion temperature. Especially when using the automatic drying hopper, it is necessary to select a reasonable capacity according to the molding cycle (forming amount) and the drying time, and it is also necessary to start the baking before a few hours before the start of the injection. In addition, the stagnation time of the resin in the cylinder is too long to produce silver streaks. Different types and grades of materials should not be mixed. Secondly, during the filling and condensation process, due to the influence of internal stress anisotropy, the stress generated in the vertical direction causes the resin to flow and the non-flow oriented portion produces different refractive index and flash filaments appear. When it expands, it may Crack the product. In addition to the attention paid to the injection molding process and the mold, it is preferable to anneal the product. For example, the PC material can be heated to 160 ° C or above for 3-5 minutes, and then naturally cooled.

2, bubbles

Mainly because the water vapor and other gases in the resin are not discharged or due to insufficient filling, the condensation surface is too fast to condense to form a "vacuum bubble". According to the cause of the bubble, it can be divided into the following types: (1) When the wall thickness of the product is large, the outer surface is cooled faster than the central portion, so as the cooling progresses, the resin portion of the central portion is expanded toward the surface. To make the center part insufficiently filled. This condition is called a vacuum bubble. The solution is to determine the proper gate and runner size based on wall thickness. Generally, the height of the gate should be 50%~60% of the wall thickness of the product; until the gate is sealed, a certain amount of supplementary injection material is left; the injection time should be slightly longer than the gate sealing time; the injection rate is lowered, and the injection pressure is increased. ; use a material with a high melt viscosity grade. (2) The bubbles caused by the generation of volatile gases are solved by fully pre-drying the raw materials and using an injection molding machine with a drying hopper; reducing the melt temperature and avoiding decomposition gas. (3) Bubbles caused by poor fluidity can be solved by increasing the temperature of the resin and the mold and increasing the injection rate.

3, the surface gloss is poor

Due to the large surface roughness of the mold or the premature condensation, the resin cannot be copied to the surface of the mold, all of which causes slight irregularities on the surface of the product, thereby tarnishing. The solution is to polish the mold forming surface; extend the cooling time; appropriately increase the melt temperature, injection pressure, injection rate, mold temperature.

4, the earthquake

The seismic pattern refers to the dense corrugation formed around the gate. The main reason is that the melt viscosity is too large, the front end material has been condensed in the cavity, and then the material is broken through the condensation surface, and the surface is damaged. The solution is mainly to improve the fluidity and adjust the molding conditions, such as increasing the resin temperature, mold temperature, injection pressure and injection rate; adding a venting groove; minimizing the use of the release agent; if it does not affect the appearance, the gate can be changed. The position is changed by changing the position of the seismic pattern, or treating the part produced by the seismic pattern as a dark glossy surface.

5, whitening, halo

It is mainly caused by dust falling into the resin in the air or the water content of the resin is too large. The solution is mainly to remove resin impurities and pollution; to fully dry the resin, and to use an injection molding machine with a drying hopper; to precisely control the melt temperature and production cycle; to increase the injection pressure and mold temperature.

6, white smoke, black spots

Mainly due to the decomposition or deterioration of the plastic melt in the barrel due to local overheating. The solution is mainly to remove resin impurities and pollution; to minimize the melt temperature; to minimize the residence time of the resin in the barrel.

7, wrinkles and pockmarks

The main reason is that the resin capacity is insufficient, the pressure in the cavity is insufficient, the resin fluidity is poor, and the exhaust effect is not good. Mainly can be improved from the following aspects: (1) prolong the injection time, to prevent the resin from flowing back before the gate is solidified due to the short molding cycle, it is difficult to fill the cavity. (2) Increasing the injection rate, mold temperature, resin temperature, and injection pressure. (3) Expand the gate size. Generally, the height of the gate should be 1/3~1/2 of the wall thickness of the product. (4) The gate is placed at the maximum wall thickness of the product.

(5) Set the exhaust groove (average depth 0.03mm, width 3~5mm) or the exhaust rod. It is more important for smaller parts. (6) A certain buffer distance is left between the screw and the injection nozzle. (7) Select a resin with a low viscosity grade.

8, shrink pit

The reason for the shrinkage pit is the same as the wrinkle and the pockmark. In principle, it can be solved by excess filling, but there is a danger of stress. Therefore, the wall thickness should be evenly designed in the design, and the reinforcing ribs, studs, etc. should be reduced as much as possible. The thickness of the wall.

9, weld line

The weld line is caused by the front end portion of the molten resin from different directions being cooled and not being completely fused at the joint. Under normal circumstances, it mainly affects the appearance, and in severe cases, it affects the strength of the product. The solution is mainly to improve the fluidity and adjust the molding conditions, such as increasing the resin temperature, mold temperature, injection pressure and injection rate; adding a venting groove, and setting the ejector rod at the place where the weld line is generated is also advantageous for exhausting; The use of the release agent; if it only affects the appearance, the position of the gate can be changed to change the position of the weld line, or the portion where the weld line is produced can be treated as a dark glossy surface, etc., and modified.

10, warping, deformation

Warpage and deformation should be mainly solved from the mold design, and the adjustment effect of molding conditions is very limited. The causes of warpage and deformation and the solutions are mainly as follows: (1) When deformation is caused by residual stress caused by molding conditions, it can be eliminated by reducing the injection pressure, increasing the mold temperature, uniformizing the mold temperature, and increasing the resin temperature or by annealing. stress. (2) When the stress is deformed due to poor mold release, it can be solved by increasing the number or area of ​​the push rod and setting the draft angle. (3) Since the cooling method is not suitable, and the cooling is not uniform or the cooling time is insufficient, the cooling method and the cooling time can be adjusted. If possible, set the cooling circuit close to the deformation. (4) For the deformation caused by the molding shrinkage, the design of the mold must be corrected. The most important of these should be to make the wall thickness of the product consistent. Sometimes, in the case of a last resort, the mold can only be trimmed in the opposite direction by measuring the deformation of the product.

11, burns

The solutions adopted are different depending on the burn caused by mechanical, mold or molding conditions. (1) Reasons for the injection molding machine. Due to abnormal conditions, the barrel is overheated, causing the resin to decompose at high temperature, injection molding after burn, or the resin is stagnant, decomposed and discolored after being brought into the product due to the nozzle and screw thread in the barrel, the check valve, etc., so that the product is in the product. With dark brown burn marks. The nozzle, screw and barrel should be cleaned. (2) Reasons for the mold. Mainly due to poor exhaust. This type of burn usually occurs in a fixed area and is easily distinguished from the first case. Attention should be paid to measures such as adding a venting groove and a venting rod. (3) Reasons for molding conditions. Excessive back pressure will cause overheating of the barrel and cause burns. If the screw speed is too high, it will also generate overheating, generally 40~90r/min. When the venting groove is not provided or the venting groove is small, the injection rate is too high, which may cause burns of the superheated gas.