Differential shrinkage Warpage

Overpacking excessive costly part weight. Overpacking warpage due to differential shrinkage. Underflow structural weaknesses. 

To reduce the risk of warpage occurring on molded components, the blending of two different grades of BDS is often carried out. However, as the differential shrinkage is relatively low, warpage is not such a problem as compared to other thermoplastics materials. 

Fill pattern Weld line position. Air trap position. Position of vents. Overpacking excessive costly part weight. Overpacking warpage due to differential shrinkage. Underflow structural weaknesses. 

The FTIR method is based on the ratio of certain absorbances [17, 18]. It is especially useful for mapping the crystallinity of surfaces but it is unable to penetrate to any great depth within a sample. Measurement of local crystallinity variations can help assess variation in cooling rate and in the analysis of differential shrinkage and warpage. 

Specific heat and enthalpy control the cooling of an article in a mould and predominantly the design of the cooling channels in a mould. The cooling system should balance the heat flow from the part to ensure uniform part cooling and minimise residual stresses, differential shrinkage, and warpage. 

Because LLDPE exhibits lower differential shrinkage values the problem of component warpage is considerably reduced compared to HDPE and LDPE. As a result of this the design of the mold cooling circuitry for LLDPE is not as critical as it is for LDPE and HDPE. The increased stiffness of LLDPE also allows the molding to be ejected from the mold at elevated temperatures without the risk of distortion. 

Warpage It is the dimensional distortion in a plastic part after processing. The most common cause is variation in shrinkage of the part. The major processing factors involved are flow orientation, area shrinkage, and differential cooling. 

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