Bumper molding trouble shooting

 1.  How to solve the jointing lines on the bumper when bumper moulding? 

When the bumper injection moulding, it is very easy
that there will be some jointing lines occurs on the
moulded bumper. In order to solve this problem,
normally we use timing controlled hot runner valve
gate to adjust the jointing line, but the jointing
area will still be some differece due to the two
melted material’s temperature difference. We can try
to increase some hot nozzle’s temperature or plastic
filling speed to reduce the jointing line. We cann’t
avoid the jointing line completely, but we can reduce it.

The timing controlled hot runner valve gate also can
reduce the effects of the jointing line to the moulded
bumper
strength.

2. Shorten bumper moulding cycle time.

The bumper moulding cycle time included the mechanical
action time, plastic moulding machine’s plasticizing time,
bumper mould opening or clamping time, bumper mould side
actions time, bumper moulds cooling time and ejection time.
Normally the cooling time should be less then 25 seconds.
If the bumper moulds steel are well selected and the harden
treatment is well done, also the bumper moulds components are
accurated machininged. Then you can use high speed filling
system injection molding machines with high speed mould
clamping system. Alos please be sure that the cooling water
temperatuere should be low then 12 centigrade degree. 

3. Gas venting and shrinkage during the bumper moulding.

Due to the bumper wall thickness is normally more than 3.5mm,
in order to reduce the air will be compressed inside of the
moulding material, normally we choose edge fan shape filling
gates. In the same time, this gate can make easily help the
pressure holding,by this we can solve the shrinkage marks also.   

 4. Deforming of the moulded bumper

Due to the length of the bumper, also because of the bumper
material physical funtion (good flexibility), the adjustment
to the deforming is by when the bumpers were assembling.

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This is post by Mr. Kai Liu SINO MOULD Vice Cheif Engineer