cbn abrasive sanding belt

Why do CBN sanding belts can replace conventional sanding belts in precision grinding?

CBN sanding belts

Brief

1 Test conditions

1.1 Specifications of CBN sanding belts and fused alumina sanding belt

1.2 Grinding Parameters of Machine Tools

2Contrastive analysis of grinding test results

2.1 Comparison of wear resistance between CBN and fused alumina sanding belts

2.2 Contrastive Analysis of Surface Roughness of Workpiece

2.3 Analysis and comparison of grinding efficiency and wear mode

Conclusion

Brief

Compared with wheel grinding, belt grinding has the advantages of high grinding efficiency, low grinding heat, the good surface quality of workpiece and low cost. For used alumina, silicon carbide abrasive belt, because of low hardness of abrasives, they are difficult to process hard and brittle workpieces and have a low grinding ratio and serious dust pollution. Superhard material sanding belt features large grinding ratio, high grinding efficiency, and low grinding cost. They have diamond sanding belts and CBN sanding belts.

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 The hardness of diamond is higher than that of CBN, but it has a great advantage in processing hard and brittle materials such as ceramics, glass, carbide, etc. In the process of grinding materials containing iron group elements, there will carbonization reaction for diamond. So it is not suitable for machining steel materials. With strong chemical inertia, CBN is suitable for machining hard and tough iron-based alloys.

We will compare the performance of fused alumina abrasive belt and CBN sanding belt with the same specification for grinding 45# steel.

1 Test conditions

  • 1.1 Specifications of CBN abrasive belt and fused alumina sanding belt, 

Belt Type Abrasive size

d/μm

Abrasive hardness GPa Dimension w/mm Bond
Fused alumina 75-106 21.57-22.55 152 Resin
CBN 90-106 46.94-86.01 152 Metal

1.2 Grinding Parameters of Machine Tools

Machine tool speed: 1600r/min

Contact wheel size: 152mm *38mm

Shore hardness of sponge wheel: 22

Workpiece:

Workpiece: 45# steel, Size: 13 mm x 11 mm x 50 mm

Grinding and cooling methods: constant feed grinding, coolant is water.

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2 The contrastive analysis of grinding test results

2.1 Comparison of wear resistance between CBN and fused alumina sanding belt

Grinding ratio is that the ratio of removal of workpiece mass Mw to the belt wears mass Mo. It is an important parameter for the wear resistance of the sanding belt. It reflects the relationship between sanding belt wear and material removal. It is also an important basis for guiding sanding belt grinding technology.

The actual formula is G=Mw/Mo

When grinding 45# steel with the same specification, the fused alumina abrasive belt basically loses grinding ability after 60mins, but CBN sanding belts still keep good sharpness after 180mins. After grinding, weigh the wear of 2 kinds of sanding belts and the removal of a workpiece.

sanding Belt Wear Before & After Grinding

Belt Type Mass before grindingm0/g Mass after grindingmt/g Belt wear mass(M0/g)
CBN sanding belt 47.9 47.4 0.5
Fused alumina sanding belt 11.0 10.1 0.9

 

Removal Rate of Workpiece for 2 Kinds of Abrasive Belt

Belt Type Grinding time (t/min A total removal rate of a workpiece (Mw/g)
CBN sanding belt 180 105.2
Fused alumina sanding belt 60 17.0

Removal Rate of Workpiece for 2 Kinds of Abrasive Belt

 

The grinding ratio of CBN sanding belts calculated by G=Mw/Mo is 210.4, and that of fused alumina sanding belt is 18.9. The wear resistance of CBN sanding belts is much higher than that of fused alumina abrasive belt. So CBN sanding belts have a longer service life.

Analysis: CBN abrasives have a compact crystal structure, high hardness, and good wear resistance. But the fused alumina abrasives crush and fall off easily, and the cutting effect of abrasives is smaller, which reduces the removal rate of the workpiece. Also, because of the resin bond of fused alumina abrasive belt with poor heat resistance, bad wear resistance and much wear loss, the fused alumina sanding belt has a low grinding ratio.

2.2 Contrastive Analysis of Surface Roughness of Workpiece

2.2.1 Surface Roughness of Workpiece Comparison

Test the surface roughness of the workpiece every 30 minutes. In the early stage of sanding belt use, because there is big height deviation for the abrasive grains on the belt surface, CBN and fused alumina abrasive belt have poor surface quality. As the grinding process continues, CBN sanding belts are in the stable stage for wear by friction.

The abrasive wear improves the height of abrasive on the belt surface, and the surface roughness decreases linearly.

Changes of surface roughness with time

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At the end of grinding, the surface morphology of the workpiece is as follows: The surface texture of workpiece processed by CBN sanding belts are clear and complete, and there is no iron chip adhesion basically. The main reason for this situation is that CBN abrasive belts are orderly arrangement working layers that can form a good chip space, which is good for coolant into the grinding interface. Thus quickly radiate the heat, and improve the chip removal ability and machining quality.

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Conclusion: Under the condition of the same grinding speed and feed speed, the surface roughness of workpiece is mainly related to the size of abrasive, but the types of abrasives and sanding belt have little effect on it. From the above table, it can be seen that the abrasive grain size ranges of 2 belts are the same, and the peaks and valleys of abrasive scratches are similar. The surface roughness of workpiece machined by CBN sanding belt is 0.127μm and that of fused alumina sanding belt is 0.128μm.

2.3 Analysis and comparison of grinding efficiency and wear mode

2.3.1 Grinding efficiency

The changes of grinding efficiency of CBN and fused alumina sanding belt with time are shown in the following figure. In the early stage of grinding, the belt has a sharp edge, more abrasive grains, strong cutting ability, and high material removal rate. When grinding for 30mins, the grinding efficiency of the CBN sanding belt is 43.4 g/h and that of fused alumina sanding belt is 29.6 g/h.

 

Changes of grinding efficiency with time

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2.3.2 Wear mode

Observe the surface morphology of abrasive belts with different grinding time. Before grinding, the abrasive edge height of CBN sanding belt is 20%-30%. At this time, the alumina abrasives in the belt are in the resin bond. When grinding, the abrasive grains of CBN sanding belts are exposed and the sharpness is better.

60mins later, fused alumina abrasive belt basically lost its grinding ability. The grinding efficiency of CBN sanding belt is still 40.2g/h and decrease small. This is because CBN sanding belts are metallic nickel bond, and the hardness of bond is much higher than that of resin bond, and the fused alumina abrasive belt applies resin bond. The abrasive wear mode is mainly grinding flat and blunt. But the surface abrasives of fused alumina belt have fallen off.

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 120mins later, we continue to observe the surface of CBN sanding belts and found that there were a few pits left by abrasive falling. The number of abrasive grains for grinding decreased, and the grinding efficiency decreased to 30.6 g/h, and it is not much different from the initial grinding efficiency of the fused alumina sanding belt. It still showed a good sharpness, and then into a stable stage.

The grinding efficiency of CBN sanding belt at 180mins is 28.2 g/h. It is also predicted that the service life is much longer than 180mins.

Conclusion:

Use the same grain size and specification CBN and fused alumina sanding belt for grinding 45# steel,

The grinding ratio, grinding efficiency, the service life of CBN sanding belts are much higher than that of fused alumina sanding belts. Also, the surface roughness of workpiece processed by 2 kinds of sanding belt is the same.

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