3 examples – the problem of brittle injection moulded parts

injection moulded parts

3 examples – the problem of brittle injection moulded parts

1、brittle defects performance
Embrittlement refers to the easy cracking or fracture of the part in some parts. Brittle is mainly due to the degradation of the material and lead to macromolecular chain breakage.

reducing the relative molecular mass of macromolecules, thus reducing the overall physical properties of the polymer

injection moulded parts

Second, the causes of brittle plastic products
 A large part of the brittle products is due to internal stress. There are many reasons for brittle products, mainly:

1. Equipment
(1) There are dead solutions or obstacles in the barrel of the machine, which can easily cause degradation of the melt.

(2) The plasticizing capacity of the machine is too small, the plastic is not fully plasticized in the barrel;

the plasticizing capacity of the machine is too large, the plastic is heated and sheared in the barrel for too long, the plastic is easily aged and the products are brittle.

(3) The ejector device is tilted or unbalanced, and the cross-sectional area or distribution of the ejector rod is improper.

2. For mold
(1) The gate is too small, consider adjusting the size of the gate or adding auxiliary gates.

(2) The manifold is too small or not properly configured, try to arrange the balance reasonably or increase the size of the manifold.

(3) Poor mold structure causes abnormal injection cycle.

(1) The temperature of the barrel and nozzle is too low and should be adjusted high. If the material is easily degraded, the temperature of the barrel and nozzle should be increased.

(2) Reduce the screw pre-molding back pressure and speed to make the material slightly looser and reduce the degradation of plastic caused by shear overheating.

(3) mold temperature is too high, difficult to demold;

mold temperature is too low, the plastic premature cooling, poor integration of fusion joints, easy to crack, especially high melting point plastics such as polycarbonate is more so.

(4) The cavity core should have an appropriate release slope.

When the core is difficult to release the mold, to increase the cavity temperature, shorten the cooling time you love; cavity difficult to release the mold, to reduce the cavity temperature, extend the cooling time.

(5) minimize the use of metal inserts, want to polystyrene, such as brittle cold and heat than the large capacity of the plastic, more can not join the insert injection molding.

4. For raw materials
(1) The raw materials are mixed with other impurities or adulterated with inappropriate or excessive solvents or other additives.

(2) Some plastics such as ABS, etc., heated in the case of moisture will be catalytic cracking reaction with water vapor, so that the parts undergo a large strain.

(3) The number of plastic regeneration or recycled material content is too high, or in the barrel of the heating time is too long, will promote the parts brittle cracking.

(4) the quality of the plastic itself is not good, such as the relative molecular mass distribution, containing rigid molecular chains and other inhomogeneous structure of the components occupy too much;

or by other plastic adulteration pollution, bad additive pollution, dust and impurity pollution is also the cause of brittle.

5. Product design
(1) The product has sharp corners, notches or parts with great difference in thickness that are prone to stress cracking.

(2) The design of the product is too thin or too much hollowing.

3、Improvement methods are shown below
Material – Set proper drying conditions before injection molding.
Plastic if continuous drying for several days live drying temperature is too high,

although it can remove volatile components and other substances, but also easy to lead to material degradation, especially heat-sensitive materials.

Reduce the use of recycled materials and increase the proportion of virgin materials:
Choose high strength plastic, mold design, increase the size of the main flow channel,

manifold and gate, too small main flow channel, manifold or gate can easily lead to excessive shear heat, which leads to the decomposition of the polymer.

Injection Molding Machine – Selecting a well-designed screw:
It makes the temperature distribution more uniform when plasticizing.

If the material temperature is not uniform, it tends to accumulate too much heat locally, which leads to the degradation of the material.

Process conditions – lower barrel and nozzle temperatures.
Reduce the back pressure, screw speed and injection speed to reduce the generation of excessive shear heat and avoid polymer decomposition.

If the brittleness is caused by insufficient melt trace strength, the melt trace strength can be improved by increasing the melt temperature and increasing the injection pressure.

Thank you for watching and if you still have questions. Or if you would like to know more, please contact us by email or phone!


Tel:+86 13823302586

Grandshine Website:Shenzhen Grandshine Technology Co.,Ltd / ISO9001 ISO14001 (grashine.com)

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