Injection Molding
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Large creep deformation of homopolymer polypropylene injection 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) Low crystallinity of homopolymer polypropylene; molecular chains easily slip, causing large creep
(2) Insufficient product wall thickness; high stress level accelerates creep
(3) Use temperature too high; creep rate increases near the material glass transition temperature
(4) Material molecular weight too low, poor creep resistance
(5) Product design does not consider long-term creep allowance
Solution
(1) Increase mold temperature to the higher value within the 40-90°C range, increase crystallinity
(2) Increase product wall thickness or ribs, reduce use stress level
(3) Control use temperature within the material 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; leave creep deformation allowance in initial dimensions
Key Takeaway
Creep deformation is an inherent characteristic of crystalline materials under long-term load; it needs to be controlled by increasing crystallinity, reducing stress, and selecting appropriate materials.
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