Solve the twenty difficult problems of injection molding

Solve the twenty difficult problems of injection molding


1.The setting of loose back

The right position of loose back= moving position of over rubber ring+ the screw moving distance


2.The importance of loose back position setting

The loose back position setting too big, it will cause O2 into the recycle material. The position setting too small, the inner pressure of material barrel big, the shearing too high let the rubber material break down, injection nuzzle will salivate. The position mistake can not over 0.4mm. 

3.The melting posting setting
The melt positing= product weight/(max stroke/max melt quantity)

4.The main advantage of gas auxiliary injection molding(GAM)
It can pumping the thick material core part and makes the hollow pipe and save the material and shorten the cycle time.

It can make the pressure uniform distribution if use the gas in injection molding, the gas can be compensated by the expansion of the plastic shrinkage. Decrease the internal stress of mold plastic product then improve the shape stability, to eliminate the deformation and warping phenomenon.

5.The problems : the outer diameter of the piston rod is smaller in the middle, two hands is bigger
it cause the outer diameter of the piston rod is smaller in the middle, two hands is bigger because middle hole needle too hot, the contraction is not balanced. The middle hole needle can use the fast radiating copper materials, mold can exhaust in the middle part of the products.


6.Problems: After screw printing, the ball surface craze

There is the stress on product surface, it cause the craze after screw printing. Increase the mold temperature, decrease the stress, use the way of annealing to remove the stress.

7.Problems: the runner edge of glasses frame product is easily broke
There is the inner stress on the big runner, it will cause the product easily broken, try to decrease the injection pressure and holding pressure, appropriate improve the mold temperature.


8.Problem: it is easy to burst while installing the screw on the four columns of electric applicant 
Because there is clip waterline on columns, it is easy to burst when assemble columns, the mold increase the exhaust, appropriate improve the mold temperature, increase the injection speed to decrease the clip waterline.

9.The problem: product deformation
The product deformation is mainly caused by thermal shrinkage imbalance or product self inner stress.

10. The problem: transparent PC housing bubble
The raw material dry not enough, product products are uneven phenomenon, mold exhaust gas not well, raw material easily decompose will cause the product bubble. Full dry, increase the mold exhaust, decrease the phenomenon of uneven thickness of glue.

11.The problem of magnetic material injection molding
It should adopt the high mold temperature, fast inject way. 

12. Question: Rubber coating glue water gap shrink

Mold exhaust bad, injection speed slow, holding pressure and holding time not enough, it might cause the water gap shrink. Increase the mold exhaust, appropriately improve the injection speed, increase the holding pressure and holding time.

13. Product inner stress, the product burst after a period of time
Because of product inner stress, the product burst after a period of time. Increase the mold temperature to decrease the injection pressure to remove the product stress, product can remove the stress by annealing method.

14.The ABS mix the black color Master batch, it will cause the product easy to break and peeling,

The black color master batch included too much toner, it cause the product peeling. Change the color of color master batch.

15.One set 180ton injection molding machine, four cavity CD box total 120 gram, good appearance, no burr, but the one weight of 2 gram more than others, why?

Four cavity product, because of mold glue inlet imbalance it cause the one of the products injection full, high density, the weight of 2 gram more than other products. 

16.One set 100 ton full hydraulic joint machine has used for three years. it often can not open after clamping.
The machine joint wear, it causes the mold opening imbalance, so the mold can not open after mold clamping.

17.One set machine has used for two years, the injection unstable, one cavity product with burr one cavity lack the material, even change the oil seal and glue head, the system pressure also stable but the injection unstable.

The recycle material uneven because of the screw wear or damage, so the injection unstable. 

18. One set 150 ton new machine to produce the PP material a half year, the fastest melt time is three seconds before, but now is six seconds.

It cause the material recycle slow because of the screw wear.

19.A technician is testing a product, the product lack the rubber, increase the speed and pressure, still no response, If continue to rise, it will produce the burr.
The machine clamping mechanism will cause the clamping clearance, so it will produce the burr and so on. 

20. One machine for two years only, the barrel temperature higher, no use even turn off the power

The screw get rough after wear, the recycle material friction heat, it will cause the middle of barrel temperature higher.


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