Mechanical cleaning consists of physically disturbing the contaminants by wire or fibre brushing, abrasive blasting, tumbling or steam jets, belt sanding, buffing and polishing. These processes are mostly effective in removing rust, scale and other solid contaminants.
1. Power brushing:
The process utilizes both fibre and wire wheels (power operated) for removing weld flux, heat-treatment scale, burns, etc. Some typical power wire brushes are shown in Fig. These brushes operate at very high speed. When used with fine abrasive compounds, they can produce fine finish on metal surfaces.
Power brushing is also used to blend sharp contours left by grinding so that uniform plating can result. Fibre brushes are also used which consist of natural fibres, horse hair, cord materials, etc. Synthetic fibres are also used. Manual wire brushing is commonly used for cleaning weldments, castings, forgings, etc.
Different types of power brushes.
These are (a) wheel brush. (b) cup brush. (c) end brush,(d) side-action brush and (e) wide-face brush
2. Abrasive blasting:
The dry abrasive blasting consists of drawing abrasives through a hose to join the high-velocity air stream at a nozzle and impinge on the metal surface. The abrasive used may be shot, steel grit, or coarse sand. Dry abrasive blasting machines are used to clean stubborn and hard to remove heavy scales, corrosion and welding slag. The process provides clean surface with teeth to hold protective coatings properly.
The operation of abrasive blasting is carried out in a closed chamber. In wet abrasive blasting machines, the abrasive slurry is kept in suspension by an agitator and the abrasive is fed to the blasting gun by a centrifugal pump. The gun forces the abrasive at extremely high velocity (with compressed air) on the metal surface. The abrasive used are silica, quartz, garnet or aluminium oxide. Usually dry abrasive blasting is used for cleaning whereas wet abrasive blasting is used for finishing.
Tumbling is mainly used for removing burrs, scale, fins, flash and brightening or polishing. The operation consists of placing the components in a drum or barrel along with steel balls, granite chips, sand, aluminium oxide pallets, slag, etc. The loaded barrel is rotated slowly (as fast rotation may damage the component). The rubbing of abrasives with the components results in cleaning action.
4. Vibratory cleaning:
The components are loaded with abrasive media in containers which are vibrated in the range of 900-3600 cycles per minute. Both amplitude and frequency of vibration are selected based on the shape and size of components to be cleaned, the abrasive media used, noise level, etc. 5. Belt sanding and buffing: Belt sanding is a simple method of obtaining smooth finish on metal parts using a belt sander in which an endless abrasive coated belt moves on two pulleys and the components are held against it.
Buffing gives a reflective and lustrous surface. Buffing wheels are made of very soft materials such as felt, muslin or linen and are charged with very fine abrasive particles mixed in wax. When components are held against the rotating buffing wheel, a lustrous surface results.
See More: Wire Drawing
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See More: Sheet Metal Forming:(Press Working)