Weld line
Encyclopedia
In manufacturing
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

, the Weld line or Knit line or Meld line is the line where two flow
Fluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...

 fronts meet when there is the inability of two or more flow fronts to "knit" together, or "weld
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

", during the molding
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

 process. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. . Knit lines are considered molding defects, and occur when the mold or/and material
Material
Material is anything made of matter, constituted of one or more substances. Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term "material" is used more narrowly to refer to substances or components with certain physical properties that are used as inputs to...

 temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

s are set too low: thus the materials will be cold when they meet, so that they do not bond perfectly.

Causes

Knit lines could be caused by different causes:
  • Low temperature of molding machine barrel
  • Inadequate back pressure
  • Injection pressure or injection speed is too low
  • Low mold temperature
  • Small injection gates and/or runners
  • Improper location of injection gate
  • Excessive gate land length
  • Improper flow rate of injected materials
  • Inconsistent process cycle
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK