Threaded fasteners

Plate thickness is an important factor in electroplating, in terms of both performance and economics. Corrosion resistance, porosity, wear, appearance, and several other properties are proportional to plate thickness. Minimum plate thicknesses are, or should be, specified as should the location, or check-point, where the thickness is to be measured. In some appHcations, such as threaded fasteners, maximum thicknesses should be specified. Root diameters of finer machine threads can be adversely affected by as Htde as 10 p.m of plating. 

Threaded fasteners coupled heaters to the basins of cooling towers. (The heaters were used to prevent freezing of cooling towers during the winter.) Failure of the fasteners was extensive, affecting every coupling in each of several towers. 

To protect clamping system, use dissimilar metals to prevent galling on threaded fasteners... 

The bearing housings and supports required extensive repair. All of the housing bores were pounded out, partieularly the bearing bores, whieh were pounded out up to one-quarter ineh. Ninety pereent of the threaded fasteners had been ripped out of their respeetive threaded holes and the dowel holes were all oval. The sealing steam ehamber of tlie bearing support was ripped away from the main support struemre. 

As can be seen in Figure 7.48, the pipe clamp consisted of two U-shaped half-shells, with two 1 Vi-inch threaded studs at each end, used to tighten the two half-shells together around the nubbin ends of the pipe. The failure involved the complete fracture of the bottom half-shell, as it was positioned on the pipe. All four of the threaded fasteners were still intact, with no evidence of cracking, although the studs had been bent as a result of the failure. 

J429—Mechanical and Material Requirements for Externally Threaded Fasteners... 

Vernon Krieble, then a professor at Trinity College in Hartford, Connecticut. Their first use was as threadlocking sealants, to lock nuts on threaded fasteners as a replacement for metal lock washers, and to lock threaded fasteners in tapped holes in metal parts. They were the first products termed sealants to have a viscosity lower than that of water. Today, such anaerobic adhesives and sealants are used in almost all mechanical equipment that is subject to vibration. 

Thread locking. The first applications for anaerobic adhesives were for locking threaded fasteners. Filling the inner space between a nut and bolt with a hard, dense material prevents self-loosening. 

The International Organization for Standardization (ISO) has finalized an International Standard (ISO/DIS 10964 1993) Adhesives Anaerobic Adhesives— Determination of Torque Strength of Anaerobic Adhesives on Threaded Fasteners. This standard describes testing procedures for liquid and preapplied sealants using manual and graphical procedures. 

With plastic materials, the designer also has a greater choice of bonding techniques than with many other materials. Thermosets must be adhesively bonded or mechanically joined, but most thermoplastics can also be joined by solvent or heat welding. Additionally, plastic parts can be designed for assembly by means of molded-in, snap-fit, press-fit, pop-on, and threaded fasteners so that no additional adhesives, solvents, or special equipment is required. 

Many different threaded fasteners can be used with plastics. (These are described in the following section.) Sometimes threads must be machined into the part to provide for fasteners. Threads can be cut in thermoplastics and thermosets by the same methods used with metals and generally with the same ease of operation. Plastics may also be tapped and threaded on conventional lathes and screw machines. 

Threaded fasteners are occasionally supplied pre-coated with a locking medium in the form of a band of microencapsulated epoxy or anaerobic adhesive around the appropriate section of the screw thread. This ensures that the adhesive application is not overlooked. While microencapsulation is attractive and useful, its chequered history indicates limited potential any one of the following major drawbacks may be encountered in practice ... 

Weaker anaerobics should be used with soft alloy nuts and other threaded fasteners to prevent thread stripping during disassembly. Soft alloy and plastics fasteners exhibit a lower removal torque than their steel equivalents, because less hoop stress is generated as the adhesive is crushed during removal. Despite this apparently lower performance (remember removal is only a test method ranking) the parts will still be effectively locked and resistant to vibration. 

Figure 2.38 The developed form of the butt joint. Ultimately the lowering and widening of the column in Figure 2.37b results in the truncated form above (a ). This structure is so inflexible that an extremely strong joint is formed. Derivatives of this are used to attached threaded fasteners or may serve as stiffners in the form shown in b, which is not necessarily recognised as a butt joint - though its origins are clear.

Case 4 Permanent locking of threaded fasteners ( G in Table 3.1)... 

The mounting of a trolley castor is a perfect example of the permanent locking of a threaded fastener. 

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