Which of the following lapping abrasives is used for obtaining high quality finish?

Explanation:

Lapping:

• It is an abrading process for refining surface finish and the geometrical accuracy of flat cylindrical and spherical surfaces
• It is a process or removing surface roughness, tool marks, surface cracks from grinding, slight distortions and other minor – defects from previous operations
• Lapping produces geometrically true surfaces, corrects minor surface imperfections, improves dimensional accuracy and provides a very close fit between two contact surfaces
• Very thin layers of metal (0.005 to 0.01 mm) are removed in lapping.

Lapping abrasives:

Abrasives of different types are used for lapping. The commonly used abrasives are:

• Silicon Carbide
  • This is an extremely hard abrasive. Its grit is sharp and brittle.
  • While lapping, the sharp cutting edges continuously break down exposing new cutting edges.
  • Due to this reason, this is considered as very ideal for lapping hardened steel and cast iron, particularly where heavy stock removal is required.
• Aluminium Oxide
  • Aluminium oxide is sharp and tougher than silicon carbide. 
  • Aluminium oxide is used in un-fused and fused forms.
  • Unfused alumina (aluminium oxide) removes stock effectively and can obtain a high-quality finish.
  • Fused alumina is used for lapping soft steels and ferrous metals.
• Boron Carbide 
  • This is an expensive abrasive material that is next to a diamond in hardness.
  • It has excellent cutting properties. Because of the high cost, it is used only in specialized applications like dies and gauges.
• Diamond
  • This being the hardest of all materials, it is used for lapping tungsten carbide.
  • Rotary diamond laps are also prepared for accurately finishing very small holes which cannot be ground.