Shrinkage processing

Mixtures of methyl methacrylate and methacrylic acid or butyl methacrylate are also used. Polymer-monomer mixtures are often used in the production process. This allows reduction of the total exothermic effect of the process, shrinkage, and production time. These mixtures are obtained by two methods ... 

Fig. 15.20. Registration marks on PEN after a full OTFT process. Shrinkage can be determined by measuring the offsets.

Fig. 11 Degree of crystallization a as a function of crystallization time during an isothermal crystallization process. Shrinkage V = const, (memory effect), not to confuse with volume contraction where V / const...

Fig. 12 Schematic course of processing shrinkage and aftershrinkage in relation to mold temperature [4]...

Figure 76 shows the qualitative dependence of process shrinkage on process... 

Figure 5-88. The influence of the flow angle on processing shrinkage. 

Plastics shrink in molds during the cooling process. Shrinkage for amorphous plastics is less than for semi-crystalline plastics. Shrinkage is larger in the thickness direction than other directions. Orientation of plastic occurs in the direction of flow. 

F abrikationshilfsmittel processing shrinkage Verarbeitungsschwindung procuring/ procurement/supply Beschaffung produce vb (manufacture/make) produzieren, erzeugen, herstellen producer... 

When manufacturing the mold, the process shrinkage of the thermoplastic material has to be taken onto account. 

Values for the process shrinkage of hot forming are similar to the values for injection molding. Values for the process shrinkage from the material manufacturer are always averaged values. 

When a material is sufficiently heated and the drawn part has everywhere the same demolding temperature, the drawn part will have equal process shrinkage. However, this is a problem because of the different demolding temperatures, mainly because of the different wall thicknesses of the drawn part. 

For molded parts with tight dimensioning tolerances, prototype parts using test molds have to be manufactured to determine the process shrinkage in different positions and in different directions. A uniform quality of the material has to be maintained. 

For the most part, the edge and the bottom areas are thicker and the side wall thinner. The different demolding temperatures have different process shrinkages. The thicker areas have a higher process shrinkage. 

Polyesters are very w idely used because of their wide property range and ease of handling and processing. Shrinkage on moulding can be a problem and reinforcing with fibres (and/or fillers) will reduce the shrinkage values of the cast resins appreciably. 

Processing shrinkage 0.2-0.6% Practically no aftershrinkage. If lifting tapers are too shght on external contours difficulties in ejection possible. 

Processing shrinkage Unplasticised PVC 0.2-0.5% Plasticised PVC 1-2.5% Practically no aftershrinkage with unplastieised PVC... 

Processing shrinkage 0.2-0.5-0.7% Lower values with lower wall thickness. Practically no aftershrinkage, but dimensions change due to absorption of moisture... 

Processing shrinkage 0.7-0 8% in direction of flow and almost the same transversely (low tendency to orientation) practically no aftershrinkage. 

Shinkage Processing shrinkage 0.7-0.9%, independent of the flow direction Aftershrinkage almost 0... 

Processing shrinkage 0.7-0.5-0.1% reinforced with fibre glass... 

Shrinkage Processing shrinkage in direction of flow 1.3-2%, crosswise to direction of flow 0.8-1.8%. 

Shrinkage Processing shrinkage 0.2-2.5%, depending on type and component. Post shrinkage decreases as processing shrinkage increases. 

Shrinkage Processing shrinkage 1-2%. Postshrinkage with semi-crystalline PET only becomes negligibly small at mould temperature of 140 °C. 

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