Pressure contact

The application of liquid couplants is not only inconvenient, but the results obtained tend to be sensitive to contact pressure, and there is always a danger of losing coupling. 

Ultrasonic Welding. Ultrasonic welding has been appHed to Tefzel with weld strength up to 80% of the strength of the base resin. Typical conditions include a contact pressure of 172 kPa (25 psi) and 1—2 s cycle time. The two basic designs, the shear and butt joints, employ a small initial contact area to concentrate and direct the high frequency vibrational energy. 

Mating surface AISA 1018 steel, Rc 20, 16AA contact pressure 689 kPa at 20°C in air no lubricant. 

Cl Velocity of steam flow m/s ft/s Pmax Contact pressure, N/m ibftft ... 

Generally, the rolling elements ride on an internal race, installed on the shaft, and an external race, installed in the machine housing. The races and the rolling elements are made of hardened alloy steels, because the contact pressure caused by the radial (or thrust) forces can be eiv high. 

Only high tensile (HT) fasteners must be used for busbar Jointing and their interconnections or links not only to take care of the fault level but to also maintain the recommended contact pressure over a long period of operation as noted in Table 29.1. An ordinary fastener may not be able to withstand or sustain this torque for long. Similarly, the busbar supports, which are mounted on only two or three fasteners, should also be fitted with these fasteners. 

For busbar joints, however, use of high tensile fasteners alone is recommended with a view to ensure adequate contact pressure per unit area, as discussed in Section 29.2 and noted in Table 29.1 which an ordinary fastener may not be able to maintain over long periods. 

The contact resistance can be minimized by increasing the pull of the fasteners. Increasing the area of overlap may not reduce the contact resistance, unless the number of fasteners is also increased. It is mandatory to maintain a certain minimum contact pres.stire per unit area of the joint overlap. An average contact pressure at around 40-55 kg/cm is considered adequate. For the purpose of easy application, it is expressed in terms of bolt torque, depending upon the area of overlap and the number of fasteners, as specified in Table 29.1. 

Where the contact pressure is of utmost importance, it is recommended to use conical washers (some call them Belliville washers) to counteract the loosening of a bolt and nut assembly, caused by setting or indentation. The last column of Table 29.2 indicates the vital dimension h for such washers as in DIN-6796,... 

Molding, contact pressure Method of molding or laminating whereby... 

This type of lubrication provides the answer to why many mechanisms operate under conditions that are beyond the limits forecast by theory. It was previously thought that increasing pressure reduced oil film thickness until the aspirates broke through, causing metal-to-metal contact. Research has shown, however, that the effect on mineral oil of high contact pressure is a large increase in the viscosity of the lubricant. This viscosity increase combined with the elasticity of the metal causes the oil film to act like a thin solid film, thus preventing metal-to-metal contact. 

Table 7.27 Effect of lime and lemperaiure on ihe visible penetration of carburisation in nickel alloys under contact pressure (l-79N/mm ) with graphite ...

Contact molding Also called open molding or contact pressure molding. It is a process for molding RPs in which the reinforcement and plastic are placed in a mold cavity. Cure is either at room temperature using a catalyst-promoter system or by heating... 

The temperature rise in the contact region can be evaluated based on Eq (14), and sufficient heat would gasify the liquid him when the boiling point is reached. Moreover, it is to be noted that a relatively high contact pressure would cause an increase in the boiling point, and it is known that the pressure py in the contact region is nonuniform with a distribution, which can be written as... 

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