Engineering plastics shrinkage

One particular feature of PPO is its exceptional dimensional stability amongst the so-called engineering plastics. It has a low coefficient of thermal expansion, low moulding shrinkage and low water absorption, thus enabling moulding to close tolerances. 

Polyamide resins, one of engineering plastics, have several deficiencies such as dimensional instability, high molding shrinkage, and high moisture absorption that severely limit their applications. Blends based on polyamide and ABS have superior chemical resistance, toughness, and heat resistance under low loading. 

Figure 6.4 Dimensions of the substrate for measuring plastic shrinkage cracking using a bonded overlay, from N. Banthia.R. Gupta and S. Mindess, Development of Fiber Reinforced Concrete Repair Materials , Canadian J. of Civil Engineering, Vol. 33, No. 2,2006, pp. 126-1 33 with permssion from NRC Research Press.

Resulting Shrinkage of Plastics A ffect the Shape and Straightness of Extruded Products. Proceedings of the Annual Technical Conference of the Society of Plastics Engineers, May 4-8, 2000. 29. 

Neubert, C., Effect of Colorants on the Shrinkage of Polyester, Society of Plastics Engineers, Tech. P ers ANTEC 94,... 

For example, the calculation of shrinkage and warpage in (long) fiber-rein-forced plastics can be worked out ahead of time and the data can be provided to the processor as well as the structural component development engineers. The same applies to improved integration of anisotropic and viscoelastic material behavior. The generation and expansion of FE calculation models (with rational... 

The Atterberg limits and plasticity index are used in several engineering classification systems to characterise the fine-grained fractions of soils and to specify the fine-grained fraction of construction materials. They are also used to correlate with compressibility, permeability, compactibility, shrinkage and shear strength. 

Of all the thermosetting plastics, epoxies are more widely used than any other plastic, in a variety of applications. There are resin/hardener systems (two-part) that cure at room temperature, as well as one-part systems that require extreme heat cures to develop optimum properties (e.g., 121°C and 177°C). Proper selection of various hardeners, resins, modifiers, and fillers allows the development of desired properties for a particular application. Because of the wide versatility and basic adhesive qualities, epoxies make excellent structural adhesives that can be engineered to widely different specifications. Essentially no shrinkage occurs during polymerization because epoxies are completely reactive producing no volatiles during cure. Epoxy adhesives can be formulated to meet a wide variety of bonding... 

In the event of a dispute, the tolerances indicated on the drawing will determine legal liability. Therefore, it is important for the engineer to understand the establishment of plastics tolerances completely, for they are more complicated than for other materials. Plastics tolerances are divided between the toolmaker (one-third) and the processor (two-thirds). Therefore, a dimensional tolerance of 0.006 in would require the toolmaker to build the tool to within 0.002 in. If it is further presumed that the plastic has a shrinkage rate of 0.005 in/in, it is clear that a 1.000 0.005-in dimension requires a precision mold and very careful molding. 

Kumar and Shit [9] point out that crystalline plastic materials such as PA, which are used to make many engineering components, suffer problems due to shrinkage. The shrinkage occurs because of the crystallisation of the polymer as it becomes solid... 

The values of these limits are used in various aspects. There is a close relationship between the limits and properties of a soil sueh as eompressibility, permeability and strength. Thus the Atterberg limits are not only used to identify the soil s classification, but it also allows for the use of empirieal correlations for some other engineering properties. Liquid limit test is to elassify soils and to find the plasticity index of soil because different soils have various plastie limits. The shrinkage limit is much less commonly used than the liquid and plastic limits. 

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