Ebonites hardness

Both linear and branched polymers are thermoplastics. However, cross-linked three-dimensional, or network-polymers are thermoset polymers. The cross-linked density may vary from the low cross-linked density in vulcanized rubber to high cross-linked density observed in ebonite (hard rubber highly cross-linked natural rubber). 

Establishes a system for designating cellular elastomeric materials based on natural, synthetic, or reclaimed rubber, or rubber-like materials, alone or in combination. Cellular ebonite (hard rubber) and rigid cellular plastics are not included. Revision B was issued 30 January 1968. Notice 1 makes this standard inactive for new design, which would thereafter refer to the applicable portions of ASTM D 1055, D 1056, D 1505, D 1667 and D 3574. Cross reference tables are given. 

Hartgummi/Ebonit hard rubber, vulcanite, ebonite... 

Abrasion resistance A ebonite hardness A ebonite hardness B-C ebonite hardness B... 

In extensions of this work on vulcanisation, which normally involved only a few per cent of sulphur, both Goodyear and Hancock found that if rubber was heated with larger quantities of sulphur (about 50 parts per 100 parts of rubber) a hard product was obtained. This subsequently became known variously as ebonite, vulcanite and hard rubber. A patent for producing hard rubber was taken out by Nelson Goodyear in 1851. 

Ebonite, or hard rubber as it is often known, is black in colour and has a specific gravity, in the absence of mineral fillers, of about 1.18. 

The terms ebonite and hard rubber are now extended to cover hard produets made from synthetic rubbers. SBR is now replacing the natural materials in many ebonite applications whilst nitrile rubber ebonites are of interest where oil resistance is required. 

Hard products may also be made by vulcanising rubber (natural or synthetic) using only about two parts of sulphur per 100 parts of rubber. In these cases either the so-called high-styrene resins or phenolie rubber compounding resins are ineorporated into the formulation. These compounds are processed using the methods of rubber technology but, like those of ebonite, the produets are more akin to plastics than to rubbers. Examples of the usage of these materials are to be found in battery boxes, shoe heels and ear washer brushes. 

Soft rubber is obtained by adding 2-4% sulfur by adding extra sulfur (25-40%), the rubber can be made into ebonite, which is a hard, brittle material, having a wider range of chemical resistance than soft rubber. Soft ordinary rubber is chemical and erosion resistant, but its thermal resistance is not high (about 80 C). 

Unless test coupons are produced alongside the lining, the only method of testing the vulcanisation state is with a hand hardness meter. A Shore A or IRHD meter is used for soft rubber linings and a Shore D meter for ebonites. The usual specification is that the hardness has to conform to 5° of the specified hardness. There is no quantitative non-destructive test for the strength of the bond between the lining and the substrate and so such tests are usually carried out in the laboratory on a sample prepared from the materials used. 

A much more heavily crosslinked material can be obtained by increasing the amount of sulfur in the mixture, so that it represents about a third of the mass of the product. Heating such a mixture of raw mbber and sulfur at 150 °C until reaction is complete gives a hard, thermoset material that is not at all elastic. This material is called ebonite and is used to make car battery cases. 

Initially, vulcanization was accomplished by heating elemental sulfur at a concentration of 8 parts per 100 parts of rubber (phr) for 5 h at 140°C. The addition of zinc oxide reduced the time to 3 h. Accelerator in concentrations as low as 0.5 phr have since reduced time to 1-3 min. As a result, elastomer vulcanization by sulfur without accelerator is no longer of commercial significance. An exception is the use of about 30 or more phr of sulfur, with httle or no accelerator, to produce molded products of hard mbber called ebonite. 

Butyl Rubber and Halo-Butyl Rubber Ethylene Propylene Rubber (q) Hard Rubber (Ebonite) (h) Soft Natural Rubber (h) Neoprene (i) Nitrile Rubber Chlorosulphonated Polyethylene Polyurethane Rubber (v) Silicone Rubbers (k)... 

Also known as vulcanite and (mainly in the USA) hard rubber . The hard, horn-like product obtained when natural rubber and some synthetic rubbers such as nitrile (NBR) are vulcanised with a high proportion of sulphur or organic nonsulphur vulcanising agent. Butyl rubber and polysulphide rubber do not form ebonites. Ebullioscopy... 

NR can yield a hard rigid thermoplastic with excellent chemical resistance when cured with over 30 phr of sulphur. Such a product is termed ebonite. 

ISO 868, Plastics and ebonite - Determination of indentation hardness by means of a durometer (Shore hardness), 1985. 

Usually a mono- or disulfide cross-link occurs but larger numbers of sulfur atoms are possible. If the total percentage of sulfur in the material is <5%, it is usually very elastic. If >5% of sulfur is added, it produces a very hard, dark, nonelastic material called ebonite, sometimes used for things like combs and buttons. 

The properties of a rubber are determined essentially by the number of crosslinks (degree of crosslinking) assumed Tg is sufficiently low, weakly crosslinked rubbers are highly elastic and have a low elastic modulus. Upon increasing the crosslinking density, the elasticity decreases and the elastic modulus rises. Highly crosslinked rubbers lose their elasticity almost completely (hard rubbers, ebonite). 

Rubber lining Rubber roll covering Tyre carcass Tyre tread Moulded tubes Footwear Soles and heels Mechanical goods Ebonites or hard rubber... 

The reduction of rubber-sulphur ratio gives an advantage of bloom-free products in soft rubber goods. But this is an exception in the case of hard rubber or ebonite. 

Accelerators are second in importance only to sulphur. Their function is to accelerate the normally slow rubber-sulphur reaction, increase the rate of vulcanization, and increase productivity. Accelerators are classified into two main classes by types, namely organic and inorganic. The inorganic accelerators such as lime, litharge and other lead compounds and magnesia were employed extensively before the introduction of organic accelerators. They are still used mainly to produce hard rubber or ebonite products. Litharge is used in rubberized fabrics, insulated wires and cables and shoe compounds as well as chemical resistant rubber products... 

However, for construction purposes, solid ebonites were chosen. As is known from rubber chemistry, solid ebonite, commonly known as hard rubber, is a polymer material with sulfur content used for vulcanization. Ebonite, like elastomeric or flexible rubber, is made from a combination of sulfur with polydienes (unsaturated rubbers containing double bonds). The sulfur and polydienes are combined with some auxiliary additives and heated to produce vulcanization. Typical mass ratios of sulfur to rubber are 2 100 for elastomeric rubber and 40 100 for hard rubber. Due to the large degree of sulfide cross linking formed in the vulcanization process, solid ebonite is a hard, non-flexible, plastic-like material possessed of... 

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. 

AR Kemp and F.S. Malm Bell Telephone Laboratories NY "Hard Rubber (ebonite)". 2. C. Davis T. Blake "The Chemistry and Technology of Rubber" -1937. 

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