Shore D Scale

Commercial products have hardnesses from 28 on the Shore A scale (which is very soft) to 45 on the Shore D scale (almost leathery). Specific gravities usually range from 0.9 to 1.20 some products intended for soundproofing have specific gravities as high as 1.95. Properties of representative grades are given in Table 9. 

The polyetherimide—polysdoxane multiblock copolymers are relatively hard (about 70 on the Shore D scale). Their main appHcation is flame-resistant wire and cable covering (24), where they combine very low flammabiUty with a low level of toxic products in the smoke. This unusual and vital combination of properties justifies their relatively high price, about 37/kg, at a specific gravity of about 1.2. 

Compression sets after 22 h at 70°C, which are not severe conditions, for some grades with hardnesses in the Shore D scale are in the 30-50% range. 

Hardness Measurements. Hardness was measured on two scales, the Rockwell R scale, and the Shore D scale. The Rockwell test measures nonrecoverable deformation after a %-inch sphere has been pressed into a molded sheet of the plastic and the load released. In the Shore... 

Durometer hardness, Shore, D scale Heat-distortion temperature, °C At 0.455 MPaa At 1.82 MPaa... 

A general rule is that natural rubbers have better mechanical properties than the synthetic rubbers but the latter have better corrosion resistance. Natural rubbers are superior in certain applications such as with wet chlorine and hydrochloric acid. Natural rubber-based ebonite provides good resistance for such application at higher temperatures up to 90 °C. Corrosion resistance increases with increasing hardness, from a range of 60 on the Shore A scale to 80 on the Shore D scale. Higher proportions of sulfur increase the hardness range in the Shore D scale. 

The Shore A scale, or as it is sometimes called, durometer hardness, enjoys considerable success in North America and in particular is widely accepted by the automotive industry the scale is an integral part of the classification system for elastomeric materials used in automotive applications (ASTM D2000). Shore hardness has also become the industry standard for the rapidly growing thermoplastic rubber sector, where advantage can be taken of the complementary Shore D scale for harder grades and for rubber-modified plastics. Seven Shore scales are described in ASTM D2240, while Shore A and D hardness are also detailed in the international standard for pocket hardness meters. ISO 7619 (BS903. Part A57). The latter also specifies a pocket meter based on the IRHD scale. 

Shore D scale was used to determine the hardness values of all samples. The tests were carried out Zwick/Roell apparatus of out at the room temperature and 76 cm Hg pressure hardness... 

Shore hardness. Durometer hardness is a property that, as apphed to elastomers, measures resistance to indentation. Shore A scale is used for soft elastomers, with shore D scale for harder materials. 

Even though vulcanized EPDM has some oil resistance, in contrast to unvulcanized EPDM which has virtually none, a rubber with inherent oil resistance should be even better. For this reason, more polar rubbers have replaced EPDM in applications where oil resistance is critical. Dynamic vulcanizates of nitrile rubber with polypropylene are the most important example. Commercial grades are somewhat harder than EPDM equivalents (between 70 on the Shore A scale to 40 on the Shore D scale) and are also more dense (about 1.0-1.1 specific gravity) (26,49). 

Hardness Hardness measurements are performed according to ASTM D 2240-05 Standard Test Method for Rubber Property-Durometer Plardness), using two Durometers (Shore D scales) for the composites. The dimensions of the specimens are 16 mm x 16 mm x 6.5 mm. The measurements were performed at room temperature (25 °C). 

The hardness of plastics (and coatings may be considered to be very thin plastics) is most commonly measured by the Shore (durometer) test or Rockwell hardness test. Both of these hardness methods measure the resistance of plastics toward indentation. This provides an empirical hardness value. Shore hardness most often uses either the Shore A or the Shore D scale. These methods are best used for rubbers or elastomers and are also commonly used for softer plastics such as polyolefins, lluoropolymers, and polyvinyls. The Shore A scale is used for softer rubbers while the Shore D scale is used for harder ones. This method works better for thicker coatings, as with all hardness tests on coatings. The hardness of thin coatings can be influenced by the substrate, that is, an artificially hard measure may be measured. A picture of a durometer is shown in Fig. 2.23. 

Thermoplastic elastomers usage has increased significantly in recent years and is expected to continue to rise. Worldwide, consumption was estimated at 1,400,000 metric tonnes/year in 2000. Some examples of common thermoplastic elastomers are shown in Table 2.5. As well as adhesion considerations, the suitability of a TPE will also depend on properties such as its hardness and compression ratio. Hardness can be defined as the resistance of the material to indentation and is usually measured on a durometer using a Shore Hardness scale. TPEs tend to be rated on a Shore A scale, the softest materials ranging from around 3 Shore A and the hardest to 95 Shore A. Out of interest, thermoplastic materials are measured on a different. Shore D scale. This gives an indicator of the differences in properties. TPE material grades are available with a range of hardness levels, however it must be considered that hardness is also a function of the thickness of the material and the substrate... 

PVC is a substantially amorphous, thermoplastic material which does not exhibit a sharp melting point. With a density of approximately 1.4gcm-3 (0.81 oz/cu.in.) the material (solid, non-filled material) will sink in both water and in saturated, magnesium chloride. The density of commercial compounds may range from 1.34 to 1.45gcm-3 (0.78 to 0.84 oz/cu.in.). The natural color of the material is clear when it is unfilled and stabilized with appropriate stabilizers, for example, tin stabilizers. If the material is stabilized with lead stabilizers, and /or filled, then the natural color is usually an off-white. In either case this means that a wide color range is possible. Many compounds have a hardness, on the Shore D scale, of about 80 and a Vicat softening point (SON) from 65 to 90° C (149 to 194° F). 

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