Common problems in injection molding processing

Analysis and solutions to uneven product color in medical injection molding products The main reasons for uneven color of injection molding products and their solutions are as follows: (1) Poor diffusion of colorants, which often causes patterns to appear near the gate. (2) Plastics or colorants have poor thermal stability. To stabilize the color of the parts, the production conditions must be strictly fixed, especially the material temperature, material quantity and production cycle. (3) For crystalline plastics, try to make the cooling speed of each part of the part consistent. For parts with large differences in wall thickness, colorants can be used to mask the color difference. For parts with relatively uniform wall thickness, the material temperature and mold temperature must be fixed. (4) The shape and gate form of the part have an impact on the plastic filling situation, causing color differences in some parts of the part. If necessary, modifications should be made.

For some polystyrene parts, a thin layer of white frost-like substance will be found attached to the local surface near the parting surface during demolding. Most of them can be removed after polishing. These white frost-like substances will also adhere to the surface of the mold cavity. This is because the volatile substances or soluble low-molecular-weight additives in the plastic raw materials become gaseous after being heated, and are released from the plastic melt. After entering the mold cavity, they are squeezed to the parting surface near the exhaust function, and precipitate or crystallize. These white frost-like powders and grains adhere to the mold surface, which will not only scratch the next demolding part, but also affect the smoothness of the mold surface if it happens too many times. Insoluble fillers and colorants are mostly irrelevant to the appearance of white frost.

Solutions to white frost: Strengthen the drying of raw materials, reduce molding temperature, strengthen mold exhaust, reduce the proportion of recycled materials, etc. When white frost appears, pay special attention to frequent cleaning of the mold surface. Analysis and solutions to the causes of uneven product color in injection molding processing The main causes and solutions for uneven color of injection molding products are as follows: (1) Poor diffusion of colorants, which often causes patterns to appear near the gate. (2) Plastics or colorants have poor thermal stability. To stabilize the color of the parts, production conditions must be strictly fixed, especially material temperature, material quantity and production cycle. (3) For crystalline plastics, try to make the cooling speed of each part of the product consistent. For products with large differences in wall thickness, colorants can be used to mask the color difference. For products with relatively uniform wall thickness, the material temperature and mold temperature should be fixed. (4) The shape and gate form and position of the product have an impact on the plastic filling situation, causing color differences in some parts of the product. If necessary, they should be modified.

When the molten plastic in the cavity encounters inserts, holes, areas with discontinuous flow rates, areas where the filling material flow is interrupted, and when the gate injection molding occurs, it cannot be completely fused and produces linear weld marks. The existence of weld marks greatly weakens the mechanical strength of the product. The method to overcome weld marks is basically the same as the method to reduce product dents. 1. Equipment: Poor plasticization and uneven melt temperature can extend the molding cycle to make plasticization more complete. If necessary, replace the machine with a larger plasticization capacity. 2. Mold (1) The mold temperature is too low. The mold temperature should be appropriately increased or the local temperature at the weld seam should be purposefully increased. (2) The runner is too small, too narrow or too shallow, and the cold well is small. The runner size should be increased to improve runner efficiency and increase the volume of the cold well. (3) The gate section should be enlarged or reduced, and the gate position should be changed. When opening the gate, try to avoid the melt flowing around the inserts and holes. The gate that occurs injection filling should be corrected, moved or buffered with a block. Try not to use or use multiple gates as little as possible. (4) Poor exhaust or no exhaust holes. The exhaust channel should be opened, expanded or unblocked, including exhaust through the gaps of inserts and ejector pins. III. Process (1) Increase the injection pressure and extend the injection time. (2) Adjust the injection speed: high speed can make the molten material reach the confluence before it has time to cool down, and low speed can allow time for the air in the cavity to be discharged. (3) Adjust the temperature of the barrel and nozzle: high temperature makes the plastic viscosity small, the flow is smooth, and the weld mark becomes thinner; low temperature reduces the decomposition of gaseous substances. (4) Use as little release agent as possible, especially silicone-containing release agents, otherwise the material flow will not be able to merge. (5) Reduce the clamping force to facilitate exhaust. (6) Increase the screw speed to reduce the viscosity of the plastic; increase the back pressure to increase the density of the plastic. IV. Raw materials (1) The raw materials should be dry and the liquid additives in the formula should be minimized. (2) For plastics with poor fluidity or high heat sensitivity, add lubricants and stabilizers appropriately. If necessary, use plastics with good fluidity or high heat resistance. V. Product design (1) If the wall thickness is small, the product should be thickened to avoid premature solidification. (2) The position of the insert is improper and should be adjusted. Causes and solutions for delamination of products in plastic processing I. Process: (1) Low barrel and nozzle temperature. (2) Low back pressure. (3) For PVC plastics, too fast injection speed or low mold temperature may also cause delamination. II. Raw materials: (1) Raw material contamination or mixing of foreign matter. (2) Mixing of different plastics. After some plastic products are molded and demolded, swelling and blistering will soon appear on the back of the metal insert or in the particularly thick parts. This is because the plastic that has not been completely cooled and hardened releases gas and expands under the action of internal pressure. Solution: (1) Reduce mold temperature and extend mold opening time. (4) Improve the situation where the product wall is too thick or the thickness varies greatly. (2) Reduce the drying temperature and processing temperature of the material; reduce the filling rate; reduce the molding cycle; reduce flow resistance. (3) Increase the holding pressure and time.