Injection Molding
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Insufficient Rigidity of Polypropylene Injection-Molded Products
Problem Phenomenon
The product deforms greatly when stressed, and the rigidity modulus is lower than the design requirement.
Insufficient rigidity causes the product to deform excessively in use, affecting function and safety, and is especially critical in structural parts.
Cause Analysis
(1) The crystallinity of polypropylene is low, and the rigidity modulus is insufficient
(2) The product wall thickness is too thin or the reinforcing rib design is unreasonable
(3) The mold temperature is too low, the cooling is too fast, and crystallization is insufficient
(4) The barrel temperature is too high, the material degrades, and the molecular weight decreases
(5) The material grade is selected improperly or the reinforcing material addition is insufficient
Solution
(1) Increase the mold temperature to the higher value within the range of 40-90°C to increase crystallinity
(2) Optimize the product design, increase the wall thickness or reinforcing ribs, and increase the section moment of inertia
(3) Control the barrel temperature at a reasonable value within the range of 200-280°C
(4) Extend the cooling time to ensure full crystallization
(5) Select a high-rigidity grade or add a nucleating agent, and use reinforcing materials when necessary
Key Takeaway
Insufficient rigidity is caused by low crystallinity or unreasonable structural design, and needs to be solved from two aspects: process parameters and product design.
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