NEWS

2021-06-29

The common used fillers in resin bond grinding wheels

In resin bond superabrasive wheels, filler is also an indispensable part. Its main function is to improve the heat resistance, hardness and strength of the bond, and the ultimate goal is to improve the durability of the grinding wheel. There are many kinds of fillers for resin bond diamond grinding wheels. Cr2O3, ZnO and Cu powder are common fillers for phenolic resin bond; Except Cu powder, The common used fillers in polyimide binder are Zr, Co, CaCO3, etc when dry grinding; When wet grinding, quartz powder (SiO2), alumina powder (A12O3) and other ceramic materials can be added.

 

For resin bond CBN wheels, metal powder and metal oxide powder, such as Cu and Cr2O3, are commonly used as fillers in bond. The dry grinding effect is better when using Green Silicon Carbide(GC) and White Alumina(WA) as fillers, but it is not convenient for CBN recovery. The other used fillers in imported grinding wheels are electroplating MoS2 and some metal salts, such as BaSO4 and MgSO4. The amount of abrasive has an obvious influence on the grinding effect, especially in dry grinding.

 

The purpose of adding fillers is to improve the grinding performance and mechanical properties of abrasive tools. Under the premise of a certain abrasive content, the filler also plays an insufficient part in the filling unit volume. Metal powder as filler can improve the hardness and strength of grinding wheels, which is conducive to the conduction and diffusion of grinding heat. However, too much filling will make it difficult for the bond to fall off, and the abrasive is not easy to get out of the edge. In serious cases, it will cause blockage, burn the workpiece, carbonize the diamond grits on the surface of grinding wheel and increase the consumption; In addition to improving the strength, hardness and thermal conductivity of grinding wheels, oxides can also be used as fillers to obtain polishing performance and improve the water absorption of grinding wheels.

 

In addition, in order to improve the grinding performance and mechanical properties of grinding wheels, some solid lubricant materials(like graphite) can be added appropriately, especially for dry grinding, which plays a particularly prominent role in reducing friction. Too much such filler will reduce the strength of abrasive tools.

 

Characteristics and functions of the common used Fillers:

 

  1. Cu

 

Cu has high melting point (1 083 ℃) and good thermal conductivity. The instantaneous high temperature produced in grinding process can be quickly transmitted to the metal body of the grinding wheels through Cu; The heat dissipation is fast,  which  reduces  the  local overheating phenomenon  in the

 

grinding area and improves the heat resistance of the bond. The chemical adsorption between Cu and resin has good adhesion, and the thermal expansion coefficient of Cu is close to that of resin. The strength of resin bond grinding wheel is greatly improved by using Cu as filler. Cu itself has good wear resistance. All the above properties are beneficial to improve the wear resistance of the grinding wheel. The tool life of grinding wheel with Cu powder is several times longer than that without Cu powder. However, Cu is a tough material with high ductility, and the grinding wheel is easy to stick with workpiece chips if the amount of Cu is too much. The grinding ability is reduced Generally, the volume fraction is 15% ~ 20%.

 

Because of its excellent electrical conductivity, Cu powder (or mixed with graphite powder) is used as filler to make ECG grinding wheel. ECG grinding can shorten the processing time and improve the work efficiency. This is also used in common resin abrasive tools.

 

  1. Cr2O3 and ZnO

 

Cr2O3 is a dark green hexagonal crystal with a density of 5.1 ~ 5.2g/cm3 and a melting point of 2435 ℃. ZnO is a white hexagonal crystal or powder with density of 5.6 g / cm3, melting point of 1975  ℃, amphoteric compound. These

metal oxides have high melting point and mechanical properties, which can significantly improve the strength, hardness and heat resistance of grinding wheel. The test shows that the hardness and strength of the grinding wheel with Cr2O3 are slightly higher than those with ZnO, but the wear ratio is slightly

smaller. The effect of the two is very close, and they are often mixed used. Generally, Cr2O3 ∶ ZnO = 1 ∶ 1 ~ 2 ∶ 1. The former is  used  for external grinding, internal grinding and edge sharpening, while the latter is

used for dry grinding and fine grinding.

 

Fe2O3 can also improve the strength and hardness, but the effect is obviously lower than that of ZnO and Cr2O3. Fe2O3 is generally used as a transition layer.

 

  1. Other fillers

 

The grinding performance can be improved by adding quartz powder, aluminum oxide powder, WA, GC and other abrasive fillers.

 

Table

Function of various fillers

 

 

 

Filler

Density

g/cm3

Melting Point

/

 

Main function

 

Cu

 

8.93

 

1083

Improve the bonding strength, electrical conductivity

and heat dissipation of grinding wheel

 

Al

 

2.7

 

660

Compared with Cu, it can reduce weight, but has

poor heat resistance

 

Ag

 

10.5

 

960

The conductivity is better than that of Cu, can be

used for ECG grinding wheel but more costly

 

Cr2O3

 

5.2

 

2435

 

 

 

Improve the bonding strength, hardness, heat resistance. With polishing performance

 

ZnO

 

5.6

 

1975

 

Fe2O3

 

5.24

 

1565

 

Zr

 

6.49

 

1852

The melting point and hardness are higher than that of Cu, and the thermal conductivity is better than that of oxide, which can improve the wear resistance,

hardness and strength of grinding wheel

 

Co

 

8.9

 

1492

 

SiO2

 

2.65

 

1710

 

Improve the heat resistance and hardness of grinding wheel

 

Al2O3

 

3.96

 

1850

 

SiC

 

3.2

 

1627

Reduce the blocking of grinding wheel and play the

role of auxiliary grinding.