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The Rejection of Perfection
Published in Sharon Ann Holgate, Understanding Solid State Physics, 2021
While synthetic rubber is manufactured from petroleum, natural rubber is the latex of the rubber tree (Hevea brasiliensis) from South America. Although it can be used in its natural state, rubber can be made much more elastic and less sticky by adding sulphur to it. The process of adding sulphur to rubber is known as vulcanisation and was invented by Charles Goodyear in 1839. Some of the sulphur atoms form cross-links between chains, which then make the rubber harder. If more and more sulphur is added, rubber eventually becomes a hard solid known as ebonite.
Basic Materials Engineering
Published in David A. Hansen, Robert B. Puyear, Materials Selection for Hydrocarbon and Chemical Plants, 2017
David A. Hansen, Robert B. Puyear
Very hard rubber (called ebonite) is considerably more corrosion resistant to organic solvents as well as to oxidizing environments. Ebonite will swell and crack when in contact with the more effective rubber solvents such as benzene, chlorobenzene and carbon disulfide. Also, ebonite is much less resilient and is subject to mechanical damage from impacts, dents in metal backing, etc., which can occur during shipping and handling. Because of its brittleness, ebonite should not be used in applications involving thermal cycling and/or thermal stresses.
Relaxation transitions in some polymers
Published in Maxim Arzhakov, Relaxation in Physical and Mechanical Behavior of Polymers, 2019
A similar situation is observed when the linear polymers are crosslinked by chemical and radiation methods. For example, the vulcanization of 1,4-cis-polyisoprene (rubber with a glass transition temperature Tg = −72°C) is used to produce ebonite (glassy resin with Tg = 80°C). Obviously, this process is accompanied by the glass transition of the product due to the formation of a complex topological structure, namely a three-dimensional chemical network.
Modified fine blanking of cam-shaped profile using a double-action hydraulic press
Published in Materials and Manufacturing Processes, 2019
U. Aravind, C. Uday, P. Venugopal
Ebonite rubber pads of 25 mm thickness and Shore A hardness 100 that were precompressed were used for generating the counter-force. Ebonite rubber is a variant of vulcanized natural rubber with approximately 30% sulfur by weight. The mechanical behavior of the rubber pads was characterized by uniaxial compression tests (Fig. 9). Suitable diameter of pad was chosen based on the required counter-force for each material. As can be observed in Fig. 8, rubber is not constrained from lateral expansion during the modified fine blanking operation and so the boundary conditions are same as in uniaxial compression. Thus, the data generated by uniaxial compression tests (Fig. 9) was used to determine the diameter of rubber to be used. Choice was made such that rubber pad generates the desired counterforce value at a stroke position of 1.5 mm which is half the total cutting stroke of 3 mm. A pre-compression of around 0.5 mm was given to the rubber in order to ensure that the working region on the force-stroke curve is shifted away from the initial non-linear regime. Further, in-setup trials were conducted to fine tune the working range of rubber by giving it the desired pre-compression. Also, counterforce from rubber was quantified by in situ measurement made by load cell 2 (Fig. 8). Thereby, it was ensured that the force generated by rubber during operation was within the desired range. Once the diameter of rubber pad and pre-compression was set, fine blanking was carried out without any interruptions. Blank holder force was controlled by varying the hydraulic pressure in the press actuator. Fine blanking trials with conventional tooling in the same experiment set-up were carried out for a fair comparison. Table 2 lists the forces applied and corresponding rubber pad diameters for fine blanking each of the four materials. Five trials were conducted for each material. Table 3 shows the process parameters. In order to understand the effect of counterforce application, a few trials were also conducted without using any counterforce.