Extrusion & Post
4 조회수
Injection molded low density polyethylene products with oversized dimensions exceeding the upper limit
문제 현상
The actual dimensions of the product exceed the upper limit of the drawing tolerance, resulting in excessive clearance or inability to achieve tight fit during assembly.
Oversized dimensions are usually related to insufficient shrinkage, and are likely to occur after changing material batch numbers or adjusting the process.
원인 분석
(1) Holding pressure too high or holding time too long, the product is over-compensated for shrinkage
(2) Mold temperature too low, fast cooling rate and low crystallinity lead to reduced shrinkage rate
(3) Barrel temperature too low, high melt density and small shrinkage rate
(4) Cooling time too long; after the product fully shrinks in the mold the size becomes small, and the shrinkage margin after demolding is small
(5) The shrinkage rate value used in mold dimension design is too large
해결 방법
(1) Appropriately reduce holding pressure or shorten holding time
(2) Appropriately increase mold temperature to the higher value within the 30-60°C range to increase shrinkage
(3) Appropriately increase barrel temperature to the higher value within the 160-220°C range
(4) Verify mold dimensions according to the actual shrinkage rate of 1.5-3.0, and repair the mold if necessary
(5) Establish a process parameter recording system, and inspect the first-piece dimensions at each shift change
핵심 요약
Oversized dimensions are mainly caused by insufficient shrinkage; control the actual shrinkage rate within the tolerance range by adjusting holding pressure and temperature parameters.
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