Methods of preventing matrix crack of circular saw blade

The diameter thickness ratio of circular saw blade is generally more than 120, which is a typical ultra-thin part. In the process of sawing, the circular saw blade is easy to appear obvious cracks and cracks in the root of the back of the cutter tooth or the expansion joint area under the action of the centrifugal force, sawing force, sawing heat and other alternating loads. Based on the analysis of the crack area, the factors to prevent the cracks in the design process of circular saw blade matrix structure are described.

As an important product of superhard materials, cemented carbide circular saw blade is a powerful emerging industry in the field of new materials. It is a high-quality and efficient tool for processing wood, man-made panels and other materials. In the process of sawing, the saw blade bears the alternating loads such as centrifugal force, sawing force and sawing heat. In the process of research, we explored the causes of matrix cracks from the aspects of matrix material, laser cutting, heat treatment and matrix structure design. In laser cutting, hardness and heat treatment, through a lot of test work. It is found that although these three aspects will have a certain degree of influence on the matrix crack, but the influence is not significant when controlled within a certain range. From the analysis of the matrix with cracks, the matrix with cracks in the small radius expansion joint accounts for a larger proportion, followed by the root of the cutter tooth back. Therefore, we focus on the area and structure form of the matrix with cracks, analyze the causes of cracks, and carry out the corresponding tests.

1. Base material and heat treatment factors

Currently, the spring steel 65Mn is widely used as the base material of cemented carbide circular saw blade. Because of its good hardenability and high strength, it is used as the base material of professional products. The theoretical quenching hardness can reach hrc58-60. Because the content of Mn is between 0.90% and 1.2%, the plasticity decreases and the cracking tendency increases with the increase of hardness. Therefore, the matrix hardness of cemented carbide circular saw blade should be controlled between hrc42 and 48. Through the special blade with a diameter of 300mm, we have trial produced hrc46-50 saw blade samples, and the products have no cracks in the process of use. However, in the process of making the matrix, not only the waste rate of heat treatment is high, but also it is not easy to be leveled manually and mechanically. In the market, there have been accidents that the saw blade matrix cracked and the fragments flew out to hurt people, so there is no further test that the hardness requirement is above HRC50. Considering that most of the existing professional products have no matrix cracking phenomenon, we can not easily reject and replace 65Mn material. We can only study the structure of products with matrix cracks and find out the causes of cracks.

2. Causes of laser cutting

The principle of laser cutting is to melt the base material with high temperature laser beam and blow off the residual slag with high pressure air flow. The laser beam cuts straight line or arc according to the step set by the program. Through microscopic observation, it is found that the cross section of the material to be cut is gully shaped. When the arc is smaller, the micro cracks formed by laser cutting are more likely to cause excessive stress concentration in the process of heat treatment and mechanical leveling, which will increase the possibility of micro cracks developing to depth and lead to macro cracks under complex cutting conditions.

3. Adjustment of expansion joint of product structure

In the research process, taking 305mm diameter, 120 teeth plywood special blade as an example, through the analysis of the matrix crack position, the crack source is from the two fillet transition of the saw blade expansion joint, extending to other parts of the saw blade, some 1-3mm, even up to 5mm long cracks. Through analysis, the common characteristics of this kind of saw blade expansion joint are: the two transition fillet radii are r1.4 and R1.0 respectively. It is precisely because the two transition fillet radii of the expansion joint are too small, which leads to excessive stress concentration in the process of laser cutting, heat treatment and leveling machine, resulting in micro cracks in the matrix, which lays a hidden danger for the generation of macro cracks in the matrix during the sawing process. According to the above analysis, the technical scheme of adjusting the structure of the expansion joint and increasing the radius of the two transition fillets of the expansion joint of this kind of saw blade to r1.8 is determined to reduce the stress concentration at the transition fillet and prevent the matrix from cracking. After adjustment, after batch product testing, the matrix of this series of circular saw blades did not crack along the two transition fillets of the expansion joint.

4. Tooth back structure and air hole

The 305-36t multi blade saw in Yunnan market has the phenomenon of matrix cracking from the air hole to the center and paste matrix deformation, which leads to the product can not be used. The original matrix is in diameter φ 210 and φ The diameter of 230 is 4- φ 12, 8 air holes in total; The radius of the original chip holding groove is R5, and the back angle of the base tooth is 20 °。 Through analysis, it is considered that the back angle of the base tooth is 20 °, The radius of the chip holding groove is R5. Because the chip holding groove is small and the tooth back angle is small, the chip holding volume of the saw blade is insufficient. In the cutting process, the chip is easy to fill the chip holding groove and can not be discharged in time, resulting in adverse chip removal and chip accumulation in the chip holding groove; Because there are 8 holes in the matrix φ 12 air hole, the chip containing glue will gradually fill φ With the high-speed rotation of the saw blade, the chips in the air hole generate heat due to the friction between the plate and the matrix, so the heat is not easy to be dissipated. When the heat reaches or approaches the chip's spontaneous combustion temperature, it will slowly form a burnt state, resulting in a sharp increase in the temperature in this area. The artificial glue or natural resin in the chips melts and adheres to the matrix, forming a ring-shaped adhesive area, resulting in the paste matrix. This causes too much cutting resistance and axial deflection of the matrix. When the strength limit of the matrix material is exceeded, the matrix will fracture and the product can not be used normally.

We think that it is because of the matrix tooth back angle of 20 °, The radius of R5's chip holding groove is too small, and the chip is filled because of the bad chip removal φ When the air hole is 12, the cutting resistance is too large due to the heat generated by friction, which leads to the matrix cracking along the air hole, or paste the matrix and deviate. According to these conditions, the radius of chip holding groove of this kind of saw blade is increased to r5.5, and the back angle of base tooth is increased to 30 °, Remove it at the same time φ 12 technical scheme of air hole. After batch trial production and market cutting test, there is no matrix crack or paste matrix phenomenon, and the cutting quality and use effect are acceptable to users. Up to now, there is no similar phenomenon of matrix cracking and paste matrix in the market.

5. Summary

Based on the analysis of the material, heat treatment, laser cutting and structure design of the matrix of the circular saw blade, the expansion joint structure and tooth back structure which are easy to produce matrix cracks are adjusted to prevent the generation of matrix cracks.