Лако-красочные материалы — производство

For securing or locking, joining and sealing in the manufacture of internal combus­tion engines, and in transmission manufacture, the use of anaerobic diacrylate-based adhesives is virtually self-evident today. Anaerobic adhesives remain liquid as long as they remain in contact with oxygen from the air (see Section 5.7).

When a screw is tightened in a thread, the adhesive sets via a radical mechanism initiated by metal ions. Excess adhesive escaping at the screw thread end can easily be removed. Screw locking by using anaerobic adhesives provides very good resistance to vibrations and reliable sealing against different

media such as oils or fuels. Extensive tables on the resistance of anaerobic adhesives to solvents are available that allow the reliable selection of a correct adhesive [48].

Fast-setting anaerobic adhesives also allow the caps of core holes of motor and cylinder head closings to be reliably sealed, so that the heads can be subjected to an on-road test shortly after bonding. When replacing a flywheel, high functional strength is rapidly achieved by using a screw-locking anaerobic adhesive. In tests performed with a setting time of 20 min, M10 screws stressed with 50 Nm withstood 104 loadings [47].

Another example is the bonding of camshafts. Rather than using forged parts, the cams are bonded to tubular shafts, allowing the free choice of materials for both parts. The same applies to crankshafts that can be bonded instead of being forged or cast. Sometimes, this can be less expensive or even mandatory in terms of structural design. The bonding of shaft-hub connections has been thoroughly investigated in a joint project funded by the former German Federal Ministry of Research and Technology BMFT (now Federal German Ministry of Education and Research BMBF) [49].

Bonding cams made from gray cast iron, or sintered material, and applied onto hollow steel shafts, require a shear strength of 10 N mm~2, or more. The key parameters of investigation were defined as: (i) a torsional fatigue strength during 15 years of service; (ii) resistance to a temperature of up to 160 °C; and (iii) resistance to motor oil containing fuel, combustion residue and water. Another important parameter was creeping strength at a temperature of 80 °C or more during several hours because, when a motor is very hot and then switched off, it is always assumed that a cam opens a valve, and the adhesive joint is continuously exposed to stress. The cam then must not change position on the shaft at all.

These investigations showed that anaerobic adhesives are well suited for shaft — hub connections for the following reasons: (i) they are easily applied; (ii) nonset adhesive residues can be removed without the need to rework the camshaft; (iii) the setting of thin adhesive layers takes place rapidly and completely at room tempera­ture; and (iv) the thermosetting adhesives have good resistance to media and elevated temperatures.

Shaft-hub connections (Figure 8.63) have higher fatigue resistance than keyway assemblies or gearings. Therefore, the large-dimensioned, long-life drive trains of steel mills can only be manufactured using bonded shaft-hub connections.

Shrinkage is a well-known, reliable method of joining elements. The strength obtained with the shrinkage of differential ring gears used in the automobile industry, however, does not allow exposure to elevated temperatures. Shrink-bonding by means ofanaerobic adhesives is the solution, providing a strength which is three — to fourfold as high as that of joints produced by shrinkage alone. At the same time, contact and fretting corrosion is avoided. The increase in strength is mainly due to the fact that the contact area increases from 30% to 100% of the real surface owing to material joining, provided that the application and setting of the adhesive are accurately adjusted to the prevailing manufacturing conditions. Shrink-bonding is performed at around 170 °C.

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Figure 8.63 Application of anaerobic adhesive for fixing the shaft in a small direct current (DC) motor. (Photo courtesy of Dorel Verlag).

8.9.4