Engineering applications

The following examples show varied uses of engineering adhesives in industry.

Locking screw threads The liquid is applied to the cleaned thread of a bolt or stud. When the nut is tightened the liquid fills the gaps between mating threads and hardens to form a tough plastic joint which is shock, vibration, corrosion and leak proof. The joint will remain in place until it needs to be undone again using normal hand tools.

Fig. 29.6 Thread locking

Threadsealing pipe fittings The sealant is applied to the clean thread and screwed together as normal. The sealant will not creep or shrink and gives a constant and reliable seal. There is no need to wrench tight and the fitting can be positioned as required.

Shrink Fit Pipe Fittings

Fig. 29.7 Thread sealing

(a) Hydraulic sealant for fine threads in pneumatic and hydraulic systems - particularly those subject to vibration

(b) Pipe sealant used to seal coarse threads of pipes and fittings up to 75 mm outside diameter

Fig. 29.7 Thread sealing

(a) Hydraulic sealant for fine threads in pneumatic and hydraulic systems - particularly those subject to vibration

(b) Pipe sealant used to seal coarse threads of pipes and fittings up to 75 mm outside diameter

Retaining Traditional retaining methods using screws, splines, pins, keys and press fits, etc, do not necessarily seal joints and eliminate the possibility of corrosion. Local stress concentrations may cause cracking. Retaining adhesives can be used to augment these methods. Often, a redesign will give a replacement with substantial cost savings.

These adhesives are supplied in various strengths:

(a) High shear strength adhesives in association with press fits can provide added rigidity.

(b) Maximum strength retainers are used on parts which generally do not need to be taken apart.

(c) Medium strength adhesives suit parts which need frequent disassembly.

Fig. 29.8 Retaining

Sealing with anaerobic gaskets Gaskets are fitted between flanges to provide an effective seal against fluids and gases. It is cheaper to use a gasket than manufacture two perfectly flat mating surfaces with close flatness and surface finish tolerances.

Gaskets can be preformed from materials such as compressed asbestos, paper, fibre or cork. Alternatively, they can be formed where they are required with a liquid.

The principles of liquid gasketing are fundamentally different to preformed gaskets in that they allow metal to metal contact. There are several forms of liquid gasket such as anaerobic, non setting solvent based and moisture curing.

The anaerobic principle Anaerobic gaskets are available in a range of viscosities from thick liquids to non slump pastes. Each can be applied directly from the original container, or by various application methods such as simple rollers, screen printing and computerized robotics. On assembly, the anaerobic gasket spreads between the flanges and is forced into surface irregularities to provide total contact between the two faces. The product then polymerizes at ambient temperaure into a tough thermoset plastic.

The strength of joints from anaerobics can be tailored to suit a specific application. Effective cure requires the absence of air and the presence of metal. At room temperature it takes just a few minutes.

Note. Anaerobic gaskets are thermosetting plastics; the temperature range in service can be from - 50°C up to 200°C at the joint line. They seal against petroleum based fuels and lubricating oils, water/glycol mixtures and many other industrial chemicals. For compatibility of specific chemical environments the designer would be advised to consult the manufacturers.

Although anaerobic gaskets permit metal to metal contact, electrical continuity cannot be assumed.

Figure 29.9 shows the application of an anaerobic gasket to the backplate of a large diesel engine.

The flow of adhesive to the work surface is regulated by manual control of the air supply to a pneumatic cartridge gun.

It often happens during maintenance work that damaged or scored surfaces are found and an adhesive gasket can save the need and cost of remachining.

Engineering adhesives for sealing flat faces have the following characteristics and applications.

(a) They will seal on horizontal, vertical and overhead flanges and accommodate surface irregularities of up to 0.5 mm.

(b) Low strength products are available for close fitting surfaces which will be frequently dismantled.

(c) In the illustrations below (Fig. 29.10) many of the components are manufactured in aluminium alloys. The structural integrity of an assembly can be enhanced by the use of high shear strength adhesives.

Horizontal Structural Irregularities
Fig. 29.10

Engineering adhesives for retaining cylindrical assemblies have the following characteristics and applications:

(a) The retention of shafts and rotors of electric motors, gears, pulleys, sleeves, bushes and oil seals in housings.

(b) The ability to withstand fatigue and augment torsional strength.

(c) Suitable for parts that need easy disassembly, such as bearings on shafts and in housings, bushes and journals in soft metals.

(d) An oil-tolerant adhesive is available that gives high strength retention of parts 'as received', i.e. no cleaning is needed before assembly. Oil impregnated bushes are retained with this grade. They are manufactured by the sintering process.

(e) An adhesive can be recommended for continuous working temperatures up to 175°C. It combines the ability to fill gaps of up to 0.15 mm in diameter with high shear strength and good solvent resistance.

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Responses

  • john
    How adhesive is shown in screw drawing?
    8 years ago

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