Zhengzhou Gou's induction heating equipment manufacturer tells you how to conduct heat treatment inspection on guide rails?

The machine tool bed, columns, beams, turntables, etc. all have guide rails. The guide rail type of the machine tool bed is an important workpiece base surface of the machine tool and is also the basis for the accuracy of the machine tool workpiece. Therefore, the quality of the guide rail has a very important impact on the machine tool itself. The adoption of reasonable heat treatment process is crucial to the quality of the guide rail. Therefore, it is necessary to inspect the heat treatment quality of the guide rails.

The quenched guide rails should be inspected item by item according to the material and heat treatment technical requirements specified in the drawing.

(1) Surface inspection

There should be no cracks or burns on the quenched surface.

(2)Crack detection

The overall hardened alloy steel guide rails are cooled by oil or nitrate. As long as the process is correctly operated, they will generally not be quenched and cracked. Induction heating surface quenching is prone to overheating and cracking due to the sharp corner effect.

Cast iron guide rails are prone to fire cracks due to casting defects (such as blisters, subcutaneous pores, shrinkage porosity, etc.). During the quenching process, heating is often stopped midway for some reason. When quenching is restarted, cracks are likely to occur near the joint. If quenching is interrupted, quenching should be restarted from the beginning. Tempering between two quenchings is more likely to occur. Quenching crack.

The detection of cracks is generally carried out one by one with the naked eye or a low-power magnifying glass. When the cracks are difficult to distinguish, the coloring method can be used for inspection.

(3)Hardness check

The hardness of the light steel-inlaid guide rail plane can be measured directly on the Rockwell hardness tester. When measuring both ends of the guide rail, a height-adjustable bracket can be added to the extended end to keep the workpiece being measured horizontal.

For heavy-duty steel-inlaid guide rails and cast iron guide rails, the hardness before quenching is generally carried out after rough machining and aging. Brinell hardness test is carried out according to the national standard metal Brinell hardness test method. The surface hardness should be ≥190HBW. The hardness of the guide rail after quenching For measurement, Shore hardness tester or Leeb hardness tester is generally used.

When performing Shore hardness measurement, the guide rail plane should be in a horizontal position. The hardness at each location is the measured value based on the average of 5 consecutive readings. The center distance between two adjacent indentations should be greater than twice the diameter of the indentation. . Start testing the hardness 4mm from the edge of the guide rail quenching area. When the guide rail width is <50mm, the guide rail should be measured at at least three transverse places; when the guide rail width is >50mm, the hardness can be measured every 15 to 30mm, at least in four places. In the longitudinal direction of the guide rail, when the guide rail length is ≤1000mm, the hardness can be measured every 100mm; when the guide rail length >1000mm, the hardness can be measured every 100-500mm.

There shall be no soft spots or soft zones in the hardening area specified in the drawings and processes, if the average hardness value measured within the range of 10mm × 10mm is lower than the specified hardness. This is the soft spot. The hardness difference on the same workpiece should not be greater than 4HRC.

(4) Contact resistance heating surface quenching quality inspection

The quality assessment after quenching is carried out in accordance with JB/T 6954 "Quality Inspection and Rating of Contact Resistance Heating Quenching of Gray Cast Iron Materials". The main inspection items are: the depth of the hardened layer after manual or mechanical grinding or fine grinding with oilstone is ≥0.18mm, the hardness is ≥550HV, the hardened area should be no less than 25% of the surface to be quenched, and the microstructure is grade 2 to 4. , which is cryptocrystalline martensite and a small amount of retained austenite or fine needle-like martensite and a small amount of retained austenite. The quenching stripes should be arranged neatly, with few broken lines and few burned pits. Longitudinal soft strips are not allowed on the quenching surface.

(5) Detection of metallographic structure before quenching (or nitriding)

The original structure of steel-inlaid guide rails made of non-alloy steel or alloy steel should be normalized (spheroidized annealing), quenched and tempered state, and should be based on its corresponding metallographic grade.

The chemical composition of steel should comply with the standards of the Ministry of Metallurgy. The P content of cast iron is generally ≤0.15%, and the combined carbon content should be controlled between 0.6% and 0.8%. These two indicators are crucial to the quality after quenching. When exceeding this number, the guide rail is prone to cracks when quenched.

(6) Inspection of the depth of the hardened layer

This quality index is very important for cast iron guide rails or steel-inlaid guide rails that undergo induction heating surface quenching, flame heating surface quenching, and chemical heat treatment. Because it directly affects the load-bearing capacity of the guide rail, the depth of the hardened layer of the finished product is generally specified on the drawing. 

1. The effective depth of the carburizing and quenching layer of the carburized guide rail should be within the range of 1.1 to 1.5mm.

2. The depth of nitriding layer of nitrided guide rail should be >0.5mm.

3. The effective hardened layer depth of induction heating surface quenching and flame heating surface quenching must be ≥0.8mm for high-frequency quenching, ≥1.5mm for ultrasonic quenching, and ≥2mm for medium-frequency quenching.

The inspection method is: the carburized and quenched guide rail is measured according to the national standard steel parts carburizing and quenching effective hardened layer depth measurement and verification; the nitrided guide rail is measured according to the national standard steel parts nitriding layer depth and metallographic structure inspection; induction quenching and flame Quenching is measured according to the determination of the effective hardened layer after induction quenching or flame quenching of national standard steel.

(7) Deformation detection of guide rails

1. For deformation detection of steel-inlaid guide rails, the surface of the workpiece should be cleaned and placed on the measuring surface. Use a feeler gauge to measure its gap, measure its highest and lowest points, and determine its curvature; a more accurate measurement method is to use a measuring platform. Place three measuring columns of equal height on the workpiece to support the workpiece, use a dial indicator to move horizontally on the surface of the guide rail, and observe the changes in the needle. At this time, attention should be paid to the bending deformation caused by the weight of the guide rail. While measuring the bending deformation of the steel-inlaid guide rail, attention should also be paid to measuring the twisting deformation of the guide rail. The V-shaped steel guide rail always has a concave surface after quenching, because the cross-section is asymmetrical.

2. Detection of deformation of cast iron bed guide rails. Due to the thermal stress and structural stress during the quenching process of the bed guide rails, the guide rails are deformed concavely. The maximum value of the concavity is in the middle of the guide rail length direction, while the sides of the guide rails have little deformation. . To measure the deformation of the cast iron guide rails of the bed, a large flat ruler or long test rod is generally placed on the upper surface of the guide rails, and a feeler gauge is used to measure the gap. It can also be placed on the workbench of a guide rail grinder or a gantry planer (milling) machine (or a large Measurements are taken on a flat surface.

This article briefly introduces the heat treatment quality inspection method of guide rails. Zhengzhou Gou's is a manufacturer specializing in the manufacturing and sales of high-frequency induction heating equipment, high-frequency welding machines, medium-frequency smelting furnaces and other induction heating equipment. It has knowledge of quenching and annealing of workpieces. If you still have questions about the heat treatment detection method of guide rails, you can call us for consultation.