Lathe Operations: Facing

Facing Operations Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end. Cutting Speeds

If you read many books on machining you will find a lot of information about the correct cutting speed for the movement of the cutting tool in relation to the workpiece. You must consider the rotational speed of the workpiece and the movement of the tool relative to the workpiece. Basically, the softer the metal the faster the cutting. D…

What are the various types of resistant rubbers?

Weather Resistant Rubber

Ethylene Propylene Rubber - These are the fastest growing elastomers because of its outstanding properties such as good weather resistant in ozone environment. It is used in tyre side walls, tank linings, wire and cables, mechanical goods, agricultural equipment and automotive applications.

Modified Polyethylene or Chlorosulphonated Polyethylene - It is unique among elastomers as it is derived from a plastic. It is prepared by dissolving polyethylene in a suitable solvent and passing simultaneously Sulphur dioxide and Chlorine in the presence of a free radical catalyst to bring about chlorination and chlorosulphonation. The rubber is completely saturated and so has excellent resistance to chemicals, weather and ozone. It has flame resistance as well due to the presence of chlorine. It is used for making white tyre side walls after blending with neoprene and neutral rubber and gives a beautiful white colour and a surface free from cracking and ozone attack. It is also used in hoses, electrical applications and reservoir liner construction.

Oil Resistant Rubber

Polychloroprene (Neoprene) - Neoprene is among earliest synthetic rubbers. These are produced from chloroprene by emulsion polymerisation using free radical catalyst. This type of rubber possesses very high tensile strength even without the use of carbon black. It stands well to ageing, resists aliphatic hydrocarbons and is flame proof. Neoprene is better them natural rubber, butyl or SBR as regards oil resistant, but inferior to nitrile rubber. It is used to manufacture industrial hoses, coalmine belts, wire and cable coatings and solid tyres.

Nitrile Rubber - This rubber is obtained by copolymerisation of butadiene and acrylonitrile by emulsion polymerisation using free radical catalyst. Oil resistance is the most important property of nitrile rubber. Because of oil and fuel resistance characteristics, nitrile rubber is used in applications where these properties are required, such as gasoline hoses for automotive, marine, aircraft, industrial air hose, carburettor parts, oil drilling industry, adhesives, cements and brake linings.

Acrylic Rubbers - Acrylic elastomers are obtained by emulsion polymerisation of methyl or ethyl acrylate and chloro ethyl acrylate or chloro ethyl vinyl ether. This elastomer has excellent combination of heat and oil resistance. It also possesses resistance to oxidation and ozone. It is used in hoses, tubing, belting and tank lining.

Polysulphide Rubbers (Thikols) - These types of rubbers are obtained by condensation, polymerisation of aliphatic, dihalids and sodium polysulphide. These types of rubbers have excellent resistance to both aliphatic and aromatic solvents, and have very good low temperature properties, high ozone resistant and low weathering. The main use of these rubbers is in lining of fuel storage tanks, petrol and paint spray hoses etc.

Polyurethane Elastomers (Vulkollan) - This type of rubber contains repeating urethane groups. Other groups such as urea and ester also may be included. The main properties of this class of rubber are high abrasion resistance and tear strength, resistance to aliphatic solvents and non inflammable. They are widely used in various forms, when making thread for elastic garments and sports goods, top lift for ladies high heal soles and also engineering components of resilient type.

Heat Resistant Rubbers

Silicon Rubbers (Silastomers) - These are special purpose rubbers. The outstanding properties of these rubbers are thermal and oxidation stability, retention of flexibility, inertness to weathering, chemicals, oils and solvents, and non-toxicity.

Fluoro Carbon Rubbers (Fluorel/Viton) - These are exciting new group of elastomers. Researches in this field have been carried out mostly by defence department in USA and UK due to military needs for fuel and chemicals resistant rubbers for service under extremely low or high temperatures. The properties of these types of rubbers are heat and chemicals resistance, flame retardance and electrical characteristics. These are the costliest among all the rubbers and have best resistance to heat, chemicals and solvents.


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