![]() ![]() I (DRHJ), being an engineer, change the oil and filter on my car myself, and always reuse the copper washer (it saves me money, and I can't be bothered to go to the garage and buy a new one). Comment on the practical significance of your answer. At this level of torque, estimate the ratio of the tensile stress in the shank to the yield stress of the steel. The drain plug is torqued up until the copper yields. The drain plug has a shank 15 mm in diameter, and is made from steel with a yield strength of 280 MN m –2. 29.7Ī washer for an oil drain plug has an outside diameter of 22 mm, an inside diameter of 15 mm, and is made from soft copper with a yield strength of 50 MN m –2. Explain the principle involved in selecting a soft metal for such applications. Examples are the use of soft copper washers under the heads of drain plugs in car engine sumps, or indium gaskets between bolted stainless steel flanges in high-vacuum equipment (indium melts at only 156☌, and is one of the softest metals known). Soft metal gaskets are often used for gas-tight or liquid-tight seals between steel surfaces. The number of links in the chain is currently 110. ![]() Estimate the radial wear on the pins and holes, assuming all contacting surfaces wear at the same rate. I (DRHJ) find that I need to shorten my bicycle chain by 25 mm (two chain pitches) every five years or so. The stretch is in fact caused by wear between the links and the pins. Referring to Example 13.4, this cannot be due to plastic extension or creep, because the material is hardened steel, with a factor of safety of 8.5 against yield. Give examples, from your own experience, of situations where wear is (a) desirable, and (b) undesirable 29.5īicycle chains often “stretch” during use. Give examples, from your own experience, of situations where friction is (a) desirable, and (b) undesirable. The axial load on the joint is p wπ r 2 and the radial pressure applied to the outside of the pipe by the olive is P = σ y t/ r. Comment on your answer in relation to typical hydrostatic pressures in water systems. P w = 2 μ σ y ( t r ) ( L r )where μ is the coefficient of friction between the olive and the outside of the pipe.Ĭalculate p w given the following information: t = 0.65 mm, L = 7.5 mm, r = 7.5 mm, μ = 0.15, σ y = 120 MN m -2. ![]() The loading method and compression load required will need careful consideration in liaison with the packing supplier. The selection of a suitable load and loading method is therefore more difficult and it can often cause a situation where continuous wear occurs and packing life is reduced.įor large rotary machines with slow rotational speed, such as driers and some mixers, again live loading can be a benefit, especially if access for adjustments is difficult or not possible. The packing load is much lower and can be critical to individual applications. The use of live loading on pump packing where the speed is higher is comparatively rare. A further claimed advantage of this arrangement is that it is then tamperproof. ![]() With a matched packing-set and spring combination, the enclosure can be tightened to give a prescribed loading to the packing. Some suppliers offer a system with an enclosure, or contained unit. The selection of springs and the spring force required will involve consideration of the operating environment and information from the packing supplier on the recommended packing stress for the type of packing to be used. They come in a wide variety of materials from the relatively standard 17-7 PH stainless steel, to alternative stainless and alloy steels, phosphor bronze, and high-nickel alloys, depending on application. Source: Latty.īelleville washers offer a number of benefits for this type of application, including compactness, high spring force at low deflection, absence of set or fatigue under normal loads, a straight-line load/deflection curve, and simple adjustment by the addition or removal of individual springs. ![]()
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