Burnish
Introduction
burnishing is a circular process with hard chip removal that is carried out on a previously ground piece, with the aim of increasing the precision and surface quality in addition to improving the macro geometry (cylinder, plasticity, roundness,...). It is generally used in most cases to grind internal diameters; This type of work consists of smoothing and improving the surface with reliefs and/or one-dimensional grooves using stones. It is widely used in the manufacture of engine sleeves, connecting rods, internal diameters of gears, etc. Burnishing is a surface finishing operation, not a rough geometry modification operation.
The tools used in honing are called abrasive stones or tools. Burnishing is a process widely used in the finishing of cylinders for internal combustion engines, connecting rods, inner diameters of gears, etc.
Other similar processes are superburning and lapping.
Stones or abrasive tools
Burnishing uses a special tool, called an abrasive stone or bar, to obtain a precision surface and remove any grinding marks. The abrasive stone or bar is mounted on an expandable head with a rotation from left to right and a feed with a vertical upward and downward stroke equal to the length of the material to be polished. It is composed of abrasive grains and binder.
The grain size is obtained by the number of sieve meshes per inch. Fine abrasive is used in honing. Therefore, the grain size is between 80 and 600. The higher this number, the finer the abrasive grain. Additionally, small grain sizes produce smoother surfaces on the piece being worked.
The choice of abrasive material depends on the characteristics of the material of the piece. The most commonly used abrasive materials are corundum or alundum (AlO), silicon carbide or carborundum (CSi), cubic boron nitride and natural or sintered diamond. To increase profitability and extend the life of the tool it can be treated with wax or sulfur, preferably wax for environmental reasons.
The binder is responsible for retaining the abrasive grain in the stone or bar until it has been blunted by the cutting process. The binder will break away from these spent grains, causing new grains to appear below the missing ones; This is called self-sharpening.
The honing bars are identified as HON3 shape, where the measurements are indicated by the dimensions. B= width x C=height x L=length.