Loaded ebonite

Loaded Ebonite In this class a mineral filler is added for green strength and to reduce deformation at higher temperatures. 

ISO 75-2 2004 Plastics - Determination of temperature of deflection under load - Part 2 Plastics and ebonite... 

Do not yield ebonite rubbers with high sulphur loadings. 

The choice between materials for a particular application may be determined by a combination of technical economic and aesthetic considerations. Ebonites have a great dimensional stability in moist conditions with freedom from deterioration caused by oxidation and excellent resistance to various chemicals. The temperature of use is limited where the material is under mechanical load, owing to its comparatively low softening point. This can be overcome by suitable compounding to some extent. A further weakness in appearance is the tendency of ebonite to develop an acid surface and to... 

Flexible Ebonite This can be called semi-ebonite usually loaded with mineral fillers with a lower proportion of sulphur, say 15 phr, and by incorporating into the compound synthetic rubbers like polychloroprene, polyisobutylene or butyl rubber. This ebonite will have good resistance to impact. A sheet made of flexible ebonite will look like a hard flexible leather. 

The load-bearing properties of polyurethanes are superior to that of conventional rubbers. The properties of the harder polyurethanes are superior to that of a rubber with the same hardness. To reach the 60 D to 70 D range, the conventional rubbers have to be very highly loaded or in the form of an ebonite (25% sulfur). Polyurethanes can be produced in this high range while maintaining the elastic properties that are also present in the lower-hardness materials. 

ASTM, D648 describes the determination of temperature of deflection under load for plastics and ebonite. ISO 75, BS 2782 Method 121 A and 121 B are equivalent. DIN 53461 is similarly related to the ISO method. Since these standards are similar, only the ASTM method will be described. 

ISO 75, Plastics and Ebonite Determination of the Temperature of Deflection Under Load, Switzerland (1974). 

A very popular test method for measuring the softening point of plastics is the temperature of deflection under load test, also known as the heat distortion or HDT test, standardized in ISO 75 [138]. The standard is now published in three parts. Part 1 covering general principles. Part 2 for plastics and ebonite, and Part 3 for reinforced plastics. Part 3 will not be considered further in this chapter. 

The heat distortion temperature (HDT) is standardized in ISO 75 1-3. Here the test specimens are loaded in a flatwise three point bending device. The heating rate is 120 K h . Plastics and ebonite are loaded with a maximum flexural stress of 1.8 MPa (procedure A), 0.45 MPa (procedure B) or 8 MPa (procedure C). The specimens dimension is 80 x 10 x4 mm, the support span is 64 mm (Fig. 3.5). 

Plastics—Determination of Temperature of Deflection under Load—Part 2 Plastics and Ebonite... 

UNI EN ISO 75-2, Plastics - Determination of Temperature of Deflection Under Load - Part 2 Plastics, Ebonite and Long-Fibre-Reinforced Composites, 2004. 

DIN EN ISO 75-2, Plastics—Determination of temperatnre of deflection under load— Part 2 Plastics and ebonite, 2004. 

Apparent density of material that can be poured from a specified funnel Apparent density of molding material that cannot be poured from a specified funnel Determination of water absorption Plastics and ebonite—Determination of temperature of deflection under load Determination of bulk factor of molding materials... 

For a polymer to be strongly elastic it must not only have a somewhat tangled molecular structure, but those molecules must also be joined together at the points where they most closely fit in order to prevent any sliding under load. This is called cross-linking whereby chemical links are formed across from one chain to another at selected points. In rubber it is known as vulcanisation and the cross-linking chemical is sulphur. If too many cross-links are formed the material loses its elasticity and becomes hard and brittle. When too much sulphur is added to natural rubber the hard plastic ebonite is formed, which was made in large quantities before the discovery of modern polymers. 

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