INJECTION MOULDING & PLASTICS DEFECTS (DEFECTS IN PLASTICS ),injection molding defects ,air bubble in plastics,air bubble in injection moulding ,short shot in plastices,flow mark in injection moulding,silver mark in injection molding

,INJECTION MOULDING 

Injection moulding(molding) is a manufacturing process for producing parts by injecting molten material into a mould. Injection moulding can be performed with a host of materials mainly including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers.

Most important things in injection molding is defects.

• Flash

• Short

• Sink mark

• Warpage

• Silver 

• Flow mark

• Burn mark

• Air bubble

• Flash-

 when molded part dimension increase or excess material  on parting line  after moulding ,its called flash.

cause or reason of  flash  

1.  excess  material volume
2. high injection pressure
3. high  barrel temp.
4. high mould/mold temp.
5. mould/mold wear out .
6. high holding  pressure
7. insufficient clamp pressure  

remedies of  flash in injection molding

1. increase the clamp pressure
2. reduce the injection pressure
3. check the barrel temp. & set it as per material required processing temp.
4.  check mould condition if wear out  then  do the lessor or required welding 
5. reduce the holding pressure
6. reduce the material volume .

• Short -

when the part not  completed or it not take mould shape  after  molding ,then it called short-shot problem .simply we say part not  completed during  injection it called short shot .

cause or reason of  short -shot

1. low injection pressure
2. low melting temperature
3. insufficient shot volume 
4. centering out
5. ring plunger wear out

remedies of  short -shot in injection molding(plastics)

1. increase the  injection pressure
2. increase the melting temperature
3. increase the  material volume
4. check leakage between nozzle & sprue  if centering out then correct it .
5. last option  check the ring plunger may be material go backward through ring plunger during injection . 

• sink mark  in injection molding plastics parts

if we found waviness  or like a miner depth on flat surface of parts after injection in plastics part  its called sink mark or shrinkage .it may  occur where the wall is thicker .

cause or reason of sink mark

1. low injection pressure
2. low holding pressure
3.  low/high mould/mold temperature
4. mould cooling channel block
5. material processing temp. too high
6. thickness of wall

  remedies of  sink mark in injection molding(plastics parts ) 

1. increase injection pressure
2. increase packing /holding pressure
3. set the mould temperature as per required temperature
4. clean mould cooling channel
5. check material processing temperature & reduce as per  required temp.
6. and the last option if problem not control then  reduce the thickness by providing ribs with 7 dgree method. 

• Silver mark or silver  streak

when formed Spatter lines on the surface of the plastics parts after moulding along the direction of material  flow are called silver marks or silver streak.

cause or reason of silver mark

1. raw material contains water
2. excess material temperature (melt decomposition)
3. material containing filler.
4. oil or water in mold surface.
5. injection speed Too fast  (shear decomposition or air entrainment)
6. colour powder has poor temperature resistance.
7. air trapped in barrel

remedies of  silver mark in injection molding or plastics parts )

1.  Dry  raw material in dryer  (within allowed moisture content)
2. reduce the melt temperature
3. reduce the lubricants  filler or replace with other additives.
4. clean the over all mold cavity & runner path with alcohol.
5. reduce the injection speed
6.  use color residence with higher temperature resistance.
7. increase the back pressure .