Breakaway torque

Refer to Figure 2.1 where r, = starting torque or breakaway torque. 

For cases in which such secured screw connections have to be loosened again, adhesives with different adhesive-layer strengths (initial breakaway torques) are available. 

Furthermore, the rotational impulse overcomes the breakaway torque and the linear impulse reduces pre-tension in order to ease loosening. The loosened screw is now unscrewed by a pneumatic drive and the impact mass is pushed to the starting position (Seliger and Wagner 1996). In case a screw cannot be released due to influences in the use phase (e.g., corrosion or dirt), the end effector can be used as a hollow drill with wide edges in order to remove the screw head. 

To illustrate their effectiveness as anaerobic adhesives several combinations of the adduct, with or without added filler, reactive diluents, or peroxide, were screened using nut/bolt combinations. The results in terms of breakaway torque are listed in Table 2. The strengths obtained, although none of the systems were optimized, demonstrated the use of the methacrylated polyester compounds as anaerobic curing or thermal curing adhesives. 

Table VII lists threadlocking anaerobics and gives a general description of popular grades it is not comprehensive. This product type represents the majority of anaerobic business. Once cured in a nut and bolt or screw assembly, anaerobics prevent loosening due to vibration or impact. Data demonstrating these properties are voluminous. Threadlocking products come in different strengths and viscosities, required because of the variety of bolt and screw sizes. Smaller screws, for instance, require a lower strength product to allow nondestructive removal. Viscosities vary to accomodate thread density and the need to wick into preassembled fasteners. Threadlocking performance is measured in terms of the torque required to loosen the fastener after cure (breakaway torque) and the torque required to turn the nut or screw after breakaway (prevailing-out torque).

Locked-rotor torque (also called starting torque, static torque, breakaway torque) The minimum torque developed at rest for all angular positions of the rotor with rated voltage applied at rated frequency. 

Torque is the turning effort developed by the motor or the resistance to turning exerted by the load. Usually torque is expressed in ft-lb however, the usual expression is as a percentage of the full load torque. Synchronous motors usually offer several types of torque. Starting or breakaway (called locked rotor) torque is developed at the instant of starting, see Figure 14-12. 

The torque after breakaway for acceleration to full speed must be considerably greater than the torque required by the driven machine. The greater the margin, the shorter will be the time to accelerate the inertia (Wk ) of the driven equipment and of the motor rotor to full speed. The Wk of the driven equipment must be obtained from the equipment manufacturer and given to the motor manufacturer. 

In Germany, standards have been published describing the Compression Shear Test (DIN 54452), Dynamic Viscosity Determination of Anaerobic Adhesives by Rotational Viscometer (DIN 54453), Initial Breakaway Test at Bonded Threads (DIN 54454), and Torsion Shear Test (DIN 54455). DIN 54455 is particularly interesting since it is one of a very few tests in which a nut and bolt (MIO) are seated to a measured torque before the anaerobic sealant is allowed to cure. 

Remote actuated valves must be chosen to match process requirements. Design decisions include materials of construction, valve seat material, valve t q)e, actuator type and controls characteristics. The design must match utility supply levels (air pressure, hydraulic pressure, flow capacity) and tolerances with actuator design to provide the correct torque/thrust to the valve. The torque/thrust must be above breakaway requirements and must be below stress limits of the drive train. With some valves, the ratio of these values may limit the available operating safety factor. 

Consider torque or force limiting devices for any part-moving device such as turntables, carriages and slide assemblies, etc. (For instance, magnetic couplings used for emergency breakaway on linear shuttle assemblies.)... 

Description Viscosity (cp) Torque breakaway/ prevailing (inch-lb) Cure time (fixture) with primer/ without primer (min)... 

Viscosity, mPa S (mean) Torque, N-m, Breakaway/ Prevailing Cure Speeds at Room Temperature ... 

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