The introduction of the reason which influence of grinding

Writer: Eric Bearing Limited

According to FAG bearings working surface grinding badness layer formation

mechanism, influence FAG bearings grinding badness layer is the main factor

grinding heat and grinding force.
1. Grinding heat
In grinding machining, grinding wheel and the contact area, and consume large

amounts of can, have a lot of grinding heat, causing the grinding local

instantaneous heat. Using the linear motion heat source heat transfer theory,

calculation formula or application infrared method and thermocouple measurement

method under the condition of the instantaneous temperature, can be found in 0.1 ~

0.001 in the transient temperature ms grinding can be as high as 1000 ~ 1500 ℃.

Such instantaneous heat, enough to make a work surface of certain depth surface

layer produce high temperature oxidation, amorphous organization, high temperature

tempering, secondary quenching, even burn cracking and so on many kinds of

changes.
(1) surface oxidation layer
Under the action of instantaneous heat to the surface of steel and the oxygen in

air role, rise into the very thin (20 ~ 30 nm) iron oxide thin layer. Note the

oxidation layer thickness and surface grinding badness layer thickness test

results is a total corresponding relationship. It shows that the oxidation layer

thickness and grinding process directly related, is an important symbol of

grinding quality.
(2) the amorphous organization layer
The instantaneous heat the grinding surface to melt condition, molten metal

molecules flow and is uniformly apply to the work surface, and metal matrix at

tremendous speed cooling, formed a very thin layer of the amorphous organization

layer. It has high hardness and toughness, but it only about 10 nm, very easy in

precision in grinding process has been removed.
(3) high temperature tempering layer
The instantaneous heat can make grinding surface certain depth (10 to 100 nm) in

higher than to the heating temperature of heating the tempering. Do not meet

austenitic transition temperature, as the heating temperature rise, the surface

will produce step by step and heating temperature corresponding to the tempering

or high temperature of tempering organization transformation, hardness is then

drop. The higher the temperature of heat, hardness and more severe decline.
(4) second quenching layer
When the instantaneous heat the workpiece grinding surface layer heated to

austenitic transition temperature (Ac1) above, the layer of austenite organization

in subsequent cooling process, and to be hardened into martensite organization.

Anyone with a second quenching burns workpiece, the second time under quenching

layer must be very low hardness of high temperature tempering layer.
(5) grinding crack
Secondary quenching burns will make workpiece surface layer stress changes.

Secondary quenching area in compression state, under which the high temperature

back there is the biggest sand materials tensile stress, here is the most likely

place of core crack. The most easy to crack the original along austenite grain

boundaries spread. Serious burns will cause the whole grinding surface crack (a

cracked) caused the crash.
2. Of the formation of the grinding force badness layer
In the grinding process, workpiece surface layer will be grinding wheel cutting

force, compression force and friction role. Especially after both action, to make

the work surface layer formation of plastic deformation, the direction of strong

layer and processing hardening layer. These metamorphic layer will inevitably

affect surface layer residual stress changes.
(1) cold plastic deformation layer
In the grinding process, and every moment grits is equivalent to an cutting edge.

But in many cases, cutting edge horn before negative, grits in addition to cutting

function besides, is to make the surface of workpiece under extrusion action (the

plough role), make the surface layer of plastic deformation left obvious. The

deformation of the deformation degree of as grinding wheel grinding blunt degree

and grinding increases feed.
(2) thermoplastic deformation (or high temperature sex deformation) layer
In a work surface grinding heat of the formation of the transient temperature,

make certain depth of workpiece surface layer elastic limit fell sharply, even to

the extent of the elastic disappear. At this time in surface grinding force,

especially compression force and friction force, under the action of the free

extend caused by the limits of the metal matrix, the surface be compressed (more

plough), in the surface layer caused the plastic deformation. High temperature

plastic deformation in the grinding process under the condition of invariable, the

surface with the increase of temperature increase.
(3) processing hardening layer
Sometimes use microhardness method and metallographic method can be found that,

because of the machining deformation caused by increased surface hardness.
In addition to outside grinding, casting and heat treatment caused by heating the

decarburization layer surface, after again if the machining process of is not

completely place to remain in the surface will also cause surface softening

metamorphism, facilitates the bearing early failure.