Shrinkage examples

Thermoset plastics are almost always processed with fillers and reinforcing materials. This is done to extend and reinforce synthetic resin and especially to minimise shrinkage. Examples of common fillers and reinforcing materials are shown in Table 7.2. 

The purpose of this exercise is to identify what parameters need to be further investigated if the current range of uncertainty in reserves is too great to commit to a development. In this example, the engineer may recommend more appraisal wells or better definition seismic to reduce the uncertainty in the reservoir area and the net-to-gross ratio, plus a more detailed study of the development mechanism to refine the understanding of the recovery factor. Afluid properties study to reduce uncertainty in (linked to the shrinkage... 

In some moulding compositions other special purpose ingredients may be incorporated. For example, naphthalene, furfural and dibutyl phthalate are occasionally used as plasticisers or more strictly as flow promoters. They are particularly useful where powders with a low moulding shrinkage are required. In such formulations a highly condensed resin is used so that there will be less reaction, and hence less shrinkage, during cure. The plasticiser is incorporated to... 

Melamine-formaldehyde condensates are also useful in textile finishing. For example, they are useful agents for permanent glazing, rot proofing, wool shrinkage control and, in conjunction with phosphorus compounds, flameproofing. 

Depending on the type of filter device, additional requirements may be made of the cloth. For example, in a plate-and-frame press, the sealing properties of cloths are very important. In this case, synthetic cloths are more applicable staple cloths, followed by poly filament and monofilament cloths. In leaf filters operating under vacuum and pressure, the cloth is pulled up onto rigid frames. Since the size of a cloth changes when in contact with the suspension, it should be pretreated to minimize shrinkage. 

Fig. 2-62 Example of directional shrinkage in an injection molded product.

As an example the shrinkage and in turn its tolerance of injection molded TPs will be affected as follows. (1) Higher cavity pressures will cause lower shrinkages. (2) Thick sections will shrink more than thin ones. (3) A cooler at the time of the product being ejected from the mold cavity will bring about a lower shrinkage. (4) A melt temperature of the material at the lower end of the recommended... 

Phenolic glass and a diallyl phthalate glass material are available with very low shrinkage. Glass and other mineral fillers minimize the thermal expansion differential problem. Phenoxy and polyphenylene oxides are examples of being low in shrinkage and thermal expansion. 

As reviewed there is much to consider. Examples include cooling as the product sets up results in different shrinkage rates for thicker versus thinner sections in the different processes. This results in either external waviness or sink marks, or warpage and internal voids, as the product contracts. Flat surfaces are difficult to maintain but not impossible to attain using certain processes. High speed of flow to fill the cavity of the mold is impeded going around square corners, so provision for radii and fillets are important. 

For example, TNT shrinks from 11 to 12% on solidification, so that if the melt is too viscous during pouring, the entrapped air may not escape prior to solidification. These bubbles are further enlarged by the volume shrinkage of TNT, resulting in a porous cast of low density... 

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