Injection Molding
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Large Creep Deformation of Polypropylene Injection-Molded Products
Problem Phenomenon
The product undergoes slow deformation under long-term load, and the deformation gradually increases over time.
Creep deformation affects the dimensional stability and service life of the product, and is especially critical in long-term load-bearing products.
Cause Analysis
(1) The crystallinity of polypropylene is low, and the molecular chains easily slip, resulting in large creep
(2) The wall thickness of the product is insufficient, and the high stress level accelerates creep
(3) The service temperature is too high; when approaching the glass transition temperature of the material, the creep rate increases
(4) The molecular weight of the material is low, and the creep resistance is poor
(5) The product design does not consider the long-term creep allowance
Solution
(1) Increase the mold temperature to the higher value within the range of 40-90°C to increase crystallinity
(2) Increase the wall thickness of the product or add reinforcing ribs to reduce the service stress level
(3) Control the service temperature within the long-term temperature resistance range of the material
(4) Select a high molecular weight grade or add reinforcing materials to improve creep resistance
(5) Consider the creep allowance during product design, and reserve the creep deformation amount 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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