Frequently Asked Questions about Plastic Injection Molding

Some problems often occur during the first mold trial of plastic parts after injection molding. Common problems include defects such as shrinkage, strain, deformation, too much glue, too little glue, water lines, and sharp edges.

  1. Shrinkage is the phenomenon of local depressions and holes forming on the surface of plastic parts. It often occurs in places where the glue is relatively thick, such as bone locations and screw posts.
  2. The edge is commonly known as burr. A small amount of material overflows on the parting surface, forming flash. The places where it often occurs include the parting surface, the line clamping position, the inclined top position, the insert position, etc.
  3. Plastic deformation. When plastic parts are injection molded, the plastic in the mold is subjected to high pressure, causing internal stress. After demoulding, deformation, bending, warping, etc. may occur. Flat products are most susceptible to deformation.
  4. More glue and less glue. Too much glue means that there are too many glue positions that are not needed during the design, and too little glue means that the glue positions that are needed during the design are not made. Especially where there is a thimble, it is easy to get too much glue.
  5. Ejection white refers to the white marks on the outer surface of the plastic parts that are ejected by the ejection pin.
  6. Drag and strain on plastic parts refers to the phenomenon that the rubber parts rub against the mold during the demoulding process, leaving traces on the appearance of the plastic parts along the direction of demoulding.
  7. Scorching is due to poor mold exhaust, which causes the polymer in the plastic to carbonize due to high temperature or long heating time, resulting in product discoloration (yellow brown, black), surface damage (rubber carbonization), etc.
  8. Water lines, also known as weld lines, refer to the weld lines caused by the combination of multiple nozzles or flows in more than two directions when plastics pass through slots, holes, etc. during injection molding.
  9. Poor nozzle removal refers to the unevenness, cracking and leakage of the rubber material that occurs when the nozzle material is removed.

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