Grinding and hardening method for conical surface of center hole of roller

Abstract

The invention relates to a method for grinding and hardening the conical surface of a center hole of a roller made of C3 or Cr5, which comprises the following steps of: machining the center hole meeting the grinding and hardening requirements on the roller made of the Cr3 or Cr5 material, adjusting the precision by clamping and erecting a product by using a lathe, and pre-grinding an outer circle at a frame position; the hard alloy tip is put into a tailstock, the rotating speed of a workpiece is 125 r / min, and the tail position ratio is adjusted to 1: 20; the center is forcibly jacked into the center hole for grinding, jacking force grinding continues to be kept after jacking does not move, and after it is observed that a dark red heat affected zone appears on the periphery of the center hole, the center is withdrawn; after the workpiece is stopped stably, the alloy tip is jacked into the center hole again, an ultrasonic hardness meter is used for checking that the hardness of the ground surface of the center hole reaches 52 HRC or above, the length is 12 mm or above, and a coloring agent is used for detecting that the conical surface has no visible cracks and extrusion damage defects; the method is suitable for roller products of 10 tons or below, and the quality requirements that in the grinding process of the roller products, product jumping is within 0.0015 mm, the surface hardness requirement is larger than or equal to 50 HRC, and the hardening layer depth reaches 2-3 mm are met.

Description

Technical Field

[0001] The present invention belongs to the field of heat treatment technology and relates to a method for grinding and hardening the conical surface of the center hole of a roll made of C3 or Cr5. The method is applicable to roll products with a capacity of less than 10 tons and meets the quality requirements of product runout within 0.0015 mm, surface hardness requirement ≥50HRC, and hardened layer depth of 2-3 mm during the grinding process of the roll products. Background Art

[0002] As roll products continue to evolve, demands for greater stability during use are becoming increasingly stringent. Some high-precision rolls, such as battery rolls, have extremely stringent form and position tolerances compared to standard rolls. Runout, cylindricity, and coaxiality are all required to be within 0.002mm. Because the accuracy of live-center grinders (where the center rotates with the workpiece) relies on the precision of the machine's internal bearings, and bearings exhibit play and runout, the external runout of the product after reversing can range from 0.02mm to 0.04mm, completely failing to meet the requirements for high-precision rolls.

[0003] To ensure product quality, only a grinding machine with a dead center (non-rotating center) can be used for processing. During the processing, the grinding machine relies on the hard contact between the grinding center and the center hole of the product and rotates to grind the product to complete the product processing. During the grinding process, because the hardness of the workpiece is lower than that of the center, and the processing error causes the cone surface of the center hole to be inconsistent with the center, resulting in an excessively small contact surface. Over a long processing period, the center hole of the workpiece is scratched during processing, reducing the center hole accuracy and ultimately rendering it unusable. Therefore, it is necessary to improve the hardness of the center and the accuracy of the cone surface. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for grinding and hardening the conical surface of the center hole of a roller to meet the accuracy requirements of the product adjustment by a clamp and a stand, in which a center hole of a certain size is pre-processed on an ordinary lathe. By adjusting the dead center and the center hole under certain rotation speed, tightening force, grinding time, temperature and insulation requirements, the surface hardness of the center hole is ≥50HRC and the depth of the hardened layer reaches 2-3mm.

[0005] The technical solution of the present invention is achieved as follows: A method for grinding and hardening the conical surface of a roller center hole, wherein a roller made of Cr3 or Cr5 material is subjected to friction heat working to harden the center hole. The roller is then clamped and machined using a common lathe to adjust the accuracy requirements. The roller center hole is subjected to a certain rotational speed, clamping force, grinding time, temperature, and insulation requirements to achieve the technical requirements for the accuracy of the roller center hole and the depth of the hardened layer. The specific steps are as follows: Step 1) Process a center hole of a Cr3 or Cr5 roller that meets the grinding and hardening requirements, with the bottom hole of the center hole not larger than Φ16mm and the major diameter of the cone surface not larger than Φ40mm; Step 2) Use a lathe to clamp and mount the product to adjust the accuracy. Pre-grind the outer circle of the mount to a roundness of within 0.01mm. Under the condition of workpiece rotation at 80r / min, align the workpiece runout to within 0.025mm at the chuck end and within 0.02mm at the mount. Step 3) Place the carbide tip into the tailstock, rotate the workpiece at 125 rpm, and adjust the tailstock ratio to 1:20. Step 4) Push the center hole with force to grind. Continue to grind with force when it stops. The grinding time is 4-6 seconds. When a dark red heat-affected zone of 2-3mm appears around the center hole and the infrared temperature reaches 860℃, immediately withdraw the center hole and stop the workpiece rotation. Step 5) After the workpiece stops, push the alloy tip into the center hole again to keep it warm for 6-8 minutes; Step 6) Use an ultrasonic hardness tester to check that the hardness of the center hole grinding surface reaches 52HRC or above, and the length is more than 12mm. Use a colorant to inspect the cone surface to see if there are any visible cracks or extrusion defects.

[0006] The present invention has the following advantages: 1) The pre-processing center is easy to achieve by using ordinary lathe and carbide top processing.

[0007] 2) The processing method is simple and easy to operate.

[0008] 3) This method has high processing precision, high pass rate and low risk. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Schematic diagram of the center hole of the present invention. DETAILED DESCRIPTION

[0010] Example 1: The process results were verified by grinding and hardening a Cr3 roller with a diameter of 750*950*2570. The Cr3 roller hardens its center hole through frictional heat working. Using a conventional lathe with a single clamp and a single stand, the precision requirements were adjusted. The technical requirements for the roller's center hole accuracy and hardened layer depth were achieved by grinding the die center and the center hole under certain speed, clamping force, grinding time, temperature, and insulation requirements. The specific steps are as follows: Step 1) Design the size of the pre-processed center hole as required; Step 2) Pre-grind the outer circle of the frame and use a micrometer on the machine tool to check that the runout roundness is within 0.01mm; Step 3) Align the roller on the lathe with one clamp and one rack. When the workpiece rotates at 80r / min, the runout should be less than 0.025mm at the chuck end and less than 0.02mm at the rack position. Step 4) Place the carbide tip into the tailstock and adjust the tailstock ratio to 1:20; Step 5) Adjust the roller speed to 125r / min, push the top into the center hole with force to grind the hole. After it stops moving, continue to grind with the top force for 4s. When a 2-3mm dark red heat-affected zone (infrared temperature measurement is above 860℃) appears around the center hole, immediately withdraw the top and stop the workpiece rotation. Step 6) After the workpiece stops, push the alloy tip into the center hole again to keep it warm for 6-8 minutes; Step 7) Use a hardness tester to check that the hardness of the center hole grinding surface reaches 54-57HRC, the length is 17mm, and use a colorant to detect the cone surface to see if there are any visible cracks, extrusion defects, etc. Step 8) The double top grinding roller is tested for runout. After grinding, the runout of the micrometer is 0.0008, which meets the requirements. Step 9) After turning the hardened center hole, a destructive test was performed to detect that the depth of the hardened layer reached 3.7 mm.

Claims

1. A method for grinding and hardening the conical surface of the center hole of a roller, characterized in that: The center hole of the Cr3 or Cr5 roller is hardened by friction heat working. The precision requirements are adjusted by using a common lathe with one clamp and one stand. The technical requirements of the roller center hole precision and hardened layer depth are achieved by grinding the die center and the center hole under certain speed, clamping force, grinding time, temperature and insulation requirements. The specific steps are as follows: Step 1) Process a center hole of a Cr3 or Cr5 roller that meets the grinding and hardening requirements, with the bottom hole of the center hole not larger than Φ16mm and the major diameter of the cone surface not larger than Φ40mm; Step 2) Use a lathe to clamp and mount the product to adjust the accuracy. Pre-grind the outer circle of the mount to a roundness of within 0.01mm. Under the condition of workpiece rotation at 80r / min, align the workpiece runout to within 0.025mm at the chuck end and within 0.02mm at the mount. Step 3) Place the carbide tip into the tailstock, rotate the workpiece at 125 rpm, and adjust the tailstock ratio to 1:

20. Step 4) Push the center hole with force to grind. Continue to grind with force when it stops. The grinding time is 4-6 seconds. When a dark red heat-affected zone of 2-3mm appears around the center hole and the infrared temperature reaches 860℃, immediately withdraw the center hole and stop the workpiece rotation. Step 5) After the workpiece stops, push the alloy tip into the center hole again to keep it warm for 6-8 minutes; Step 6) Use an ultrasonic hardness tester to check that the hardness of the center hole grinding surface reaches 52HRC or above, and the length is more than 12mm. Use a colorant to inspect the cone surface to see if there are any visible cracks or extrusion defects.

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