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Analysis of the basic theory of steel ball lapping plate

In the lapping disk, there may be A, D, E type, spherical graphite, ferrite, pearlite, sorbite and hard phase. Embedded abrasive size is generally 0.8 ~ 1.8um, the limit of 0.3 ~ 3um. The role of the organizations in the grinding process varies. Graphite is soft, easy to fall off. Rough grinding effect of the plate, graphite thin, a width of 2 ~ 6um (pearlite graphite film), and abrasive size similar.

Rough pieces of graphite, such as A-type graphite, lapping effect is poor. First of all show the difference in micro-hardness, graphite hardness only a few HB. Graphite stored too much abrasive, local grinding ability is too strong, and uneven distribution; followed by large abrasives in the graphite is difficult to break the refinement, once with the ball out, easy to scratch the ball; , Resulting in rolling steel ball instability, the formation of an instant stagnation or slippage, cementite (Fe3C) skeleton edge scratches the sphere directly, Ma Hang larger, the greater the impact.

In addition, steel ball rolling, the impact of the continuous impact under the action of the skeleton, causing the skeleton fragmentation, forming a secondary hard phase, the size is much larger than the abrasive, such as rupture, resulting in a large hard phase, with the abrasive movement Scratched steel ball surface, so A-type graphite has great harm. D-type and E-type graphite, the practice proved lapping better.

Ferrite is a solid solution formed by dissolving a small amount of carbon in the α-iron phase, having a body-centered cubic lattice with low strength. Grinding process, the abrasive can be embedded therein, but on the other hand cause body-centered cubic lattice distortion hardening, and on the other hand, embedded abrasive solid, abrasive can not be purified, resulting in late polishing of steel ball surface scratches, and the lines chaos . Further study found: But in the ultra-fine grinding, the use of oil grinding fluid, which does not have abrasive, very low pressure, ferrite and showed excellent polishing performance.

Pearlite is cementite and graphite sheet-like distribution of the microstructure. Sorbite is a fine pearlite, more evenly distributed. Graphite pearlite spacing of 0.5 ~ 4um, graphite sheet width of 0.5 ~ 12um (maximum 20um), so the abrasive embedded in pearlite graphite sheet, the abrasive by both sides of the rigid cementite sheet extrusion and protection, Good sex, stable role. If the distribution of cementite in the pearlite is small, and the sheet is short, intermittent, and not strengthened, then the cementite can also be abrasive grinding, does not form a secondary hard phase. Ensure the mirror surface quality steel ball. The substrate of the lapping plate is a uniform pearlite with the proper sorbite microstructure, but the body of the plate is also slightly worn.

Hard point phase, including binary, ternary phosphorus eutectic, cementite and metal complexes, characterized by high hardness. Due to the high compressive strength, the hard phase is easy to break, the hard phase size is much larger than the abrasive, which can easily scratch the spherical surface, so it must be avoided.

Steel ball lapping plate material is cast iron range. Gray cast iron contains C content and Si content, and C and Si are all elements that strongly promote graphitization. The carbon equivalent CE% = C% + 0.33 × (Si + P)%. Improve CE%, prompting the graphite tablets thicker, the number increased, the strength and hardness decreased. Reduce the CE%, can reduce the number of graphite, refined graphite sheet, increase the amount of primary austenite dendrite, strength and hardness increased. Lowering the CE% also leads to a decrease in casting performance, an increase in the sensitivity of the fracture of the casting, an increase in the stress in the casting and an increase in the hardness after the lattice dislocation. Therefore, the CE grinding plate should be sub-eutectic gray cast iron matrix, according to the specific steel ball material, hardness, size to make a reasonable choice.

Improper final amount of Si, the quality of the rig grinding disk instability, the bearing steel steel ball and large steel ball may be appropriate to increase the carbon steel ball and small steel ball, refined research and development recommended low-Si disk.

When the content of P in molten iron is slightly higher, the binary and ternary P eutectics appear again in the microstructure. These P eutectic grains are large in size and high in hardness, especially in the grain boundary. The quality of the lapping plate is poor. Therefore, Strict research disk drive P The same should be strictly controlled S.

Graphite graphite in ductile iron is spherical, the role of the metal cut is greatly reduced, the stress concentration should be basically eliminated due to graphite, so that the metal matrix strength, ductility, ductility, mechanical properties were significantly improved. Steel ball lapping machine selection of pearlite ductile iron, fatigue strength has been greatly improved. It is found that the grinding efficiency of ductile iron lapping plate is lower than that of gray lapping lapping plate, but it has more excellent polishing performance in the stage of lapping and superfine lapping.

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