Warpage formation

A preliminary study shows that the onset of part warpage at different degree of part solidity is independent of the total cycle time for the rotational moulding process with external-internal cooling. For the external cooling process, this warpage formation for thicker parts does have a considerable influence on prolonging the total... 

Carbon formation is a very real problem, leading as it does to deposits (4,27). These may cause poor acceleration characteristics, uncertain ignition and spark-plug operation because of carbon accumulation in the dome areas, and decreased liner life caused by warpage resulting from uneven temperature profiles across the combustor liner when carbon deposits are present (37). 

The formation of thick walled sections of a molding can be easily achieved by introducing gas in the desired locations. The gas channels thus formed also effectively support the flow of resin, allowing the molding pressure to be greatly reduced, wbicb in turn reduces internal stresses, allows uniform mold shrinkage, and reduces sink marks and warpage. 

The aspect ratio of nucleant particles induces preferential crystal orientation and contributes to the formation of superstractures (e.g., shish-kebab, etc.). This has negative effect on shrinkage of the parts during and after molding. Shrinkage anisotropy may also cause warpage of the parts. ... 

In the DSC cooling of PP from the melt, crystallization occurs. The minimum of the exothermic peak defines the crystallization temperature. This temperature is an indication of how rapidly the PP crystallizes. The higher the temperature, the more rapid the crystallization. Nucleating agents added to PP increase the crystallization rate of PP, resulting in a higher crystallization temperature. PP crystallizes such that crystalline structures called spherulites are formed. Nucle-ation results in the formation of smaller spherulites than would otherwise have been formed. This, importantly, results in increased clarity and stiffness but also imparts some possibly undesirable features, such as warpage or brittleness. 

Eom et al., 2001). As a result, it may cause premature composite failure due to stress-induced cracks, debonding and delaminations, insufficient fiber—matrix bonding, warpage, and void formation. 

Kaolin is primarily used in the rubber industry as a filler and is frequently used in the calcined form. It is being widely used in innerliner compound in the tubeless tire industry. Use of kaolin in glass fiber reinforced thermosets improves surface quality, reduces warpage, and lowers crack formation. Kaolin is used in polyvinyl chloride (PVC) wire coating because of its good electrical insulating properties. Surface-treated calcined kaolines are used for tire wheel cap made from polyamides (PA) and greenhouse films from LDPE [7[. 

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