Injection Molding
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Large creep deformation of random copolymer polypropylene injection molded products
Problem Phenomenon
The product deforms slowly under long-term load, and the deformation gradually increases over time.
Creep deformation affects product dimensional stability and service life, and is especially critical in long-term load-bearing products.
Cause Analysis
(1) Random copolymer polypropylene has low crystallinity; molecular chains slip easily, causing large creep
(2) Product wall thickness is insufficient; high stress level accelerates creep
(3) Service temperature is on the high side; creep rate increases near the material's glass transition temperature
(4) Material molecular weight is on the low side, with poor creep resistance
(5) Product design does not consider long-term creep allowance
Solution
(1) Increase mold temperature to the higher value within the 40-80°C range to increase crystallinity
(2) Increase product wall thickness or reinforcing ribs to reduce the service stress level
(3) Control service temperature within the material's long-term temperature resistance range
(4) Select high molecular weight grades or add reinforcing materials to improve creep resistance
(5) Consider creep allowance in product design, leaving creep deformation margin in the initial dimensions
Key Takeaway
Creep deformation is an inherent characteristic of crystalline materials under long-term load and needs to be controlled by increasing crystallinity, reducing stress and selecting suitable materials.
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