Thread sealing applications

Tape may be made by a similar process. In this case the lubricant selected is a non-volatile oil. The preform is placed in the extruder and a rod extruded. The rod is then passed between a pair of calender rolls at about 60-80°C. The unsintered tape is often used for lapping wire and for making lapped tube. Sintering is carried out after fabrication. The current most important application of unsintered tape is in pipe-thread sealing. 

Major applications of unsintered polytetrafluoroethylene are as tape in thread sealing and wrapping electrical cables, and as rod and tape in packings. Important properties of PTFE like chemical resistance, broad service temperature, low friction, flexibility, high machine direction strength, and deformability in the cross direction make unsintered fine powder PTFE ideal for these applications. 

Fluoropolymers possess excellent thermal stability and are nearly completely inert to chemical attack. Polytetrafluoroethylene (FIFE), discovered in 1938 by Roy Plunkett at I.E. du Pont de Nemours and Company, is the world s most used fluoropolymer. PIPE accounts for 59% of the fluoropolymers market and its production amounted to some 79,000 metric tons in 2004 [1], Applications exploiting the extraordinary properties of the material are wide-ranging and include gaskets, thread-seal tape, pipe liners, bearings, gears, slide plates, filter bags, medical prosthetics, and architectural material [2,3]. 

Activation by a metal surface also takes place in the commercially important anaerobic adhesives. These one-part adhesives are stable in the package, but cure quickly in an oxygen-free environment such as a tightly controlled bond line. Important applications include thread-locking, sealing, retaining, and some structural bonding [111]. A representative model formulation has recently been described [112] (Fig. 3). 

B. Pipe Joints. Good joints suitable for vacuum or pressure applications can be made by means of tapered pipe thread joints in heavy-walled tubing. Unlike all of the joints discussed so far, the seal is made in the threads of this joint. The threaded portions of both the male and female pipe joint are tapered, and as a result the inner and outer threads are wedged into each other when they are screwed together (Fig. 10.9). To achieve a good seal the male pipe threads are wrapped with two layers of Teflon pipe tape, which serves the role of sealant and... 

The threads of the bungs must be cleaned after material has been decanted from the container to prevent sealing of the bung. If the bung cannot be opened, the gentle application of heat around the bung is often sufficient to soften the partially cured polyurethane and to allow the reopening of the container. Excessive heat must not be applied and any seals must be checked after this method is used. 

Screw thread connectors. These have many applications but are not suitable for high vacuum work. Two examples of these connectors are shown in Fig. A.4, with silicone mbber seals and a. Teflon washer. 

Anaerobic adhesives mainly serve the purpose of protecting threads from undesired loosening as a consequence of vibrations or dynamic stress and represent a preferred alternative to mechanical locking devices. Furthermore, they enable shaft-hub connections, for example, when mounting a gear wheel on a shaft (Figure 11.6). They have also delivered optimal performance as liquidly applied surface seals alternatively to the solid seals required in the respective dimensions. Figure 4.6 shows these application possibilities. 

Screw closures based on single (continuous) or multi-start thread constitute the most widely used form of closuring. Prethreaded closures made from metal or plastic rely on achieving an adequate torque which is measured as N m or lb force inch to effect a seal. In general the unscrewing torque is 50-75% of the application torque, but variations occur according to the materials, time elapsed, temperature conditions and, in the case of thermosetting closures, humidity. 

One common application of fluoropolymers is in gaskets and seals. This sec-I tion presents a case study of a threaded con-... 

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