Main Reasons for Severe Sink Marks on the Outer Surface of Column Positions During Injection Molding

Main Reasons for Severe Sink Marks on the Outer Surface of Column Positions During Injection Molding

During injection molding, severe sink marks sometimes appear on the outer surface of cylindrical positions of the injection molded parts. Even after multiple adjustments of machine parameters, it is difficult to solve, and flash may even occur. There are two main reasons for severe sink marks at the ejector pin position:

• Ejector Pin Design Issues:

  
  

• Ejector pin too short or too thin: This results in excessive plastic thickness at the root of the ejector pin position. Due to plastic cooling and shrinkage, thicker areas are more prone to sink marks. In this case, simply adjusting machine parameters may not be effective.

  

• Ejector pin too long: When the injection molded part is demolded, an excessively long ejector pin is pulled outward, which may create a vacuum inside the ejector pin hole. The external atmospheric pressure will press the surface of the injection molded part inward, resulting in sink marks.