Shrinkage on cooling

For installation, care should be used to install the hub at the proper location on the shaft taper to provide the interference needed. A jig should be used and allowance made for hub shrinkage on cooling. 

Distortion in mouldings can be worse in crystalline polymers than in amorphous plastics. This is because additional stresses may be set up as a result of varying crystallinity from point to point in the moulding so that the shrinkage on cooling from the melt also varies from point to point. This uneven shrinkage sets up stresses which may lead to distortion. 

The expansion at the die is not the sole determinant of final product specific volume. Guy and Horne (1998) also report the extent of shrinkage on cooling of extruded maize grits (Figure 18.7). 

The differences in thermal expansion coefficients of the individual phases and also their anisotropies result in non-uniform shrinkage on cooling. Tf this non-uniform shrinkage cannot be met by deformation, stresses arise restricted to short distances (microstresse.s). This phenomenon is characteristic for ceramics and influences their mechanical properties. High tensile stresses may even result in the formation of ciacks visible under the microscope, for example iji fireclay or porcelain. These cracks arc usually situated at phase boundaries. 

The high degree of crystallisation, which leads, among other things, to a high shrinkage on cooling. 

The maximum shrinkage on cooling in a mullite single crystal will occur along [010]. True or False ... 

Polymer Sp.Ht. kJ/kg/ C Latent Ht. of Fusion kj/kg Process Temp C Total Ht. to Process Temp. kJ/kg % Shrinkage on Cooling Solidifying... 

These materials have higher stiffness than PAEK between Tg of the PAEK and Tg of the sulfone or etherimide. The performance of the PAEK can be improved by adding reinforcing fibres but there remain some applications in which this performance window is critical. Since they are amorphous they undergo less shrinkage on cooling and this leads to better dimensional tolerance and stability. They are also relatively transparent. However, amorphous resins tend to have much lower chemical resistance, inferior fatigue performance and will lose useful properties immediately above Tg. These limitations of amorphous resins mean that it is usually obvious when a PAEK is required. 

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