Anaerobic adhesives applications

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). 

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. 

ORIGIN/INDUSTRY SOURCES/USES not a natural product formed by the anaerobic biodegradation of trichloroethylene and by the hydrolysis of 1,1,1-trichloroethane manufacturer of polyvinylidene copolymers and methyl chloroform flexible films for food packing (Saran and Velon wraps) flame retardant coatings for fiber and carpet backing in pipes coating for steel pipes adhesive applications... 

Interest and activity in a field is often a reflection of the number and variety of papers that have appeared of a topical or review nature. This last year has seen over twenty articles to date. An extensive review has appeared on the function of different types of photoinitiators and their future development as well as a large number of overviews and advances in terms of developments in the different types of application systems. A number of articles have targeted interest in photosensitive emulsion polymers, novel highly catalytic systems, anaerobic adhesives and liquid crystalline materials. ... 

The first anaerobic adhesives were made at the General Electric Company by aeration of a polyethylene glycol dimethacrylate. This Anaerobic Permafil required continuous aeration to prevent hardening [7]. Although a number of internal applications had been identified, the problems associated with shipping and storage made the product so impractical that the company decided to discontinue its manufacture. 

Vernon Krieble, chairman of the Chemistry Department at Trinity College in Hartford, Connecticut, learned about the product through his son, Robert Krieble, who was employed at General Electric. Vernon Krieble found a chemical solution to the problem by using cumene hydroperoxide (I) (see Section XII for all structures) as the initiator and packaging in half-filled oxygen-permeable polyethylene bottles [8]. He licensed the GE patent and in 1954 founded the American Sealants Corporation, which later became Loctite Corporation [9]. At the present time anaerobic adhesives and sealants are manufactured or sold on every continent by more than a dozen companies. Applications in virtually every industry, and technological iimovation, as measured by patent activity, continue unabated. 

The wide variety of applications of anaerobic adhesives and sealants is made possible by the modifications that make the viscosity appropriate to the application. An application that requires penetration into close-fitting parts should have very low viscosity, while a produet used with large, loose-fitting parts should have a high viscosity. A styrene aerylate eopolymer could be used to increase the viscosity [59]. Polymethacrylates, eellulose esters, butadiene-styrene eopolymers, acrylonitrile-butadiene-styrene copolymers, poly(vinyl ehloride), copolymers of vinyl chloride and vinyl acetate, poly(vinyl aeetate), eellulose ethers, polyesters, polyurethanes, and other thermoplastic resins have also been used to eontrol the flow eharacteristics of anaerobic sealants [60]. The flow eharaeteristies of anaerobic formulations can also be controlled by the addition of fumed siliea and other solid additives whieh can impart thixotropic properties [61]. 

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. 

These anaerobic adhesives fill all surface irregularities and tolerance gaps and effectively seal clearances up to 0.76 mm. They can be applied by high-speed applications in moving production lines. The cured film has excellent chemical resistance to most liquids and gases within an operating temperature range of -54°C to 232°C. 

Properties of cured anaerobic adhesives are related to the formulation chosen for a given application area. For example, anaerobic threadlocking formulations cure to very hard materials for studlocking applications and to relatively soft solids for locking precision screws. Usually, cured anaerobic prodncts are highly cross linked and form strongly adhesive, but somewhat, brittle solids. They are resistant to water and solvents and perform well under extremes of temperatnre (—50°C to -I-150 °C). 

Fig. 1. Applications for anaerobic adhesives in an automotive final drive...

Figure 1 shows a series of uses for anaerobic adhesives in the final drive of an automobile as examples of application areas (see also Automotive applications). 

Further examples are given in Anaerobic adhesives. Industrial applications of adhesives and Joint design - cylindrical joints. 

The following calculations apply to Anaerobic adhesives and use of a computer-aided design program called RETCALC. The program could be modified for application to other adhesives provided that appropriate data for their properties were inserted. 

Anaerobic adhesives D P MELODY Chemical constitution, applications... 

Adhesives may also be classified by the way they are applied or cured. Hence, anaerobic adhesives are adhesives that set only in the absence of air, for instance, when confined between plates or sheets. A contact adhesive is one that is apparently dry to the touch but will adhere to itself instantaneously on contact (also called contact bond adhesive and dry bond adhesive). A heat-activated adhesive is a dry adhesive film that is made tacky or fluid by application of heat or heat and pressure to the assembly. A pressure-sensitive adhesive is a viscoelastic material that in solvent-free form remains permanently tacky. Such materials will adhere instantaneously to most solid surfaces with the application of very slight pressure. Room-temperature setting adhesives are those that set in the temperature range of 20-30°C. These are usually two-component adhesives that must be mixed before application. A solvent adhesive is an adhesive that has a volatile organic liquid as a vehicle and sets or becomes tacky after the solvent has evaporated. A solvent-activated adhesive is a dry adhesive film that is rendered tacky just before use by applicafion of a solvent. 

Although there is, as might be expected, a grey area between structural and mechanical applications of adhesives, it helps understanding to consider them separately. Generally, structural adhesives are used in some form of overlap joint, as distinct from the co-axial joints formed from turned parts, where anaerobic adhesives (see Chapter 3 and Section 5.1.2) are normally employed. However, structural adhesives may be used in co-axial configurations when maximum performance is required. 

Anaerobic adhesives are not generally stringy in nature and contain no solid catalysts, so they are suited for application on many relatively small parts -particularly co-axial assemblies where they can be placed with ease. Their characteristics ensure that they readily fill the minute gaps always found in interference-fitted joints. Thus, they can be used both to seal and supplement the overall performance of such joints. 

An anaerobic adhesive is the best choice for these applications and only under extreme environmental conditions is it necessary to resort to the toughened variants or - in the final resort - the toughened, single-part epoxies (see p.33 Splines, keys and set screws and p.71 Co-axial - splined). 

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