Inadequacies and defects in the processing of acrylic products

Acrylic Products PlusInjection molding various defects and Solution Acrylic products generally have defects such as warpage, deformation, bubbles, cracks, wrinkles, and pitting, shrinkage, overflow, weld lines, burns, silver lines, and jet lines during processing injection molding. What kind of solutions should we adopt when these defects occur? Below we share the experience with you based on the years of experience of coral aquarium in the processing of acrylic products.

        Insufficient filling The main reasons for insufficient filling are the following: insufficient resin capacity. Insufficient pressure in the cavity. The resin has insufficient fluidity. The exhaust effect is not good. As an improvement measure, we can mainly start from the following aspects:

1) Increase the injection time to prevent the resin from flowing backward before the gate is solidified due to the short molding cycle, which makes it difficult to fill the cavity.

2) Increase the speed of injection.

3) Increase the mold temperature.

4) Increase the resin temperature.

5) Increase the injection pressure.

6) Expand the gate size. Generally, the height of the gate should be equal to 1/2 to l/3 of the wall thickness of the product.

7) The gate is placed at the maximum wall thickness of the product.

8) Set the exhaust groove (average depth 0.03mm, width 3 to smm) or the exhaust rod. It is more important for smaller workpieces. 9) A certain (about smm) buffer distance is left between the screw and the injection nozzle. 10) Use low viscosity grade materials. 11) Add lubricant. Fourth, wrinkles and pockmarks The reason for this defect is essentially the same as filling, but to a different extent. Therefore, the solution is basically the same as the above method. Especially for resins with poor fluidity (such as polyoxymethylene, PMMA resin, polycarbonate and PP resin), it is necessary to pay attention to the proper increase of the gate and the appropriate injection time.

  V. The reason for the shrinkage pit is also the same as the filling deficiency. In principle, it can be solved by excess filling, but there is a danger of stress. The design should pay attention to the uniform wall thickness. The wall thickness of the reinforcing ribs, studs, etc. should be reduced as much as possible.  

      VI. Overflow The focus of the treatment of overflow should be mainly on the improvement of the mold. In terms of molding conditions, it is possible to reduce the fluidity. Specifically, the following methods can be employed:

1) Reduce the injection pressure.

2) Lower the resin temperature.

3) Use high viscosity grade materials.

4) Reduce the mold temperature.

5) Grinding the mold surface where the overflow occurs.

6) Use a harder mold steel.

7) Improve the clamping force.

   8) Adjust the joint surface of the accurate mold.

9) Increase the mold support column to increase rigidity. Ll) Determine the size of the different vents according to different materials.

VII. Albino The phenomenon of whitening mainly occurs in the introduction of ABS resin products. The poor release effect is the main reason. It can be improved by reducing the injection pressure, increasing the draft angle, increasing the number or area of the push rod, and reducing the surface roughness of the mold. Of course, the spray release agent is also a method, but care should be taken not for the subsequent process. Such as hot stamping, painting, etc. have adverse effects.

VIII. Weld marks Weld marks are caused by the front end portion of the molten resin from different directions being cooled and not fully fused at the joint. Under normal circumstances, it mainly affects the appearance and affects the coating and plating. In severe cases, it has an effect on the strength of the product (especially in the case of fiber reinforced resins). It can be improved by referring to the following items: adjusting the molding conditions and improving the liquidity.

1. Increase resin temperature, increase mold temperature, increase injection pressure and speed.

2.) Adding a venting groove, and setting the ejector rod at the place where the weld line is generated also facilitates venting.

3) Minimize the use of release agents.

       4) Set the process flash as the place where the weld line is formed, and then cut and remove after molding.

5) If only the appearance is affected, the four positions can be changed to change the position of the weld line. Alternatively, the portion where the weld mark is generated may be treated as a dark glossy surface or the like.

IX. Burns The solutions adopted are different depending on the burn caused by mechanical, mold or molding conditions.

1) Mechanical reasons, for example, due to overheating of the barrel due to abnormal conditions, pyrolysis of the resin, injection into the product after burns, or threading of the nozzle and screw in the material, check valve, etc. The part causes the stagnation of the resin, which is disintegrated and discolored, and then brought into the product, with black-brown burn marks in the product. At this time, the nozzle, screw and barrel should be cleaned.

2) The reason for the mold is mainly due to poor exhaust. This type of burn usually occurs in a fixed place and is easily distinguished from the first case. At this time, attention should be paid to measures such as adding a venting groove to the exhaust rod. 3) In terms of molding conditions, when the back pressure is above 300 MPa, the barrel is partially overheated, causing burns. When the screw speed is too high, overheating will also occur, generally in the range of 40 to 90 r/min. When there is no venting groove or the venting groove is small,