Hardening induction heating of wire mandrels with tails. When drawing thick-walled pipes, there was a massive failure of hollow mandrels for cracking. To prevent cracking used mandrel solid section with shanks, which are designed for mounting the mandrel to the boring bar. Mandrels with shanks, as well as hollow ones, were cemented, hardened and tempered. However, when testing the tail part of the mandrel burst on the thread to its wear. Replacing volumetric hardening by surface hardening with induction heating eliminates damage to the tail section.
Mandrels were made from forgings of ZOHGSA steel with a diameter of 40 mm and a length of 160 mm. Machined mandrel cemented in a solid carburizer to obtain a layer of 1.3-1.7 mm on the working surface; then the mandrel was quenched from 830-850 ° C in running water.
Hardened mandrel released at 180-200 ° C, subjected to grinding the working surface, chrome and leave
at 150-200 ° C. During operation, the mandrel collapsed along the thread. Volumetric hardening has been replaced by surface hardening, since at surface hardening only the working part of the mandrel can be hardened.
A high-frequency station with a MGZ-102 machine generator, designed for surface heating of steel parts with a diameter of 35-100 mm to a depth of 2-6 mm, consists of a 100 kW high-frequency motor-generator with a frequency of 2500 Hz; heating station with control equipment; transformer and inductor; the lathe, in the centers of which the hardened part is installed.
In the process, short mandrels with shanks experience stress when drawing pipes, therefore the fatigue limit of the mandrels is reduced. It is known from  that the ratio between the thickness of the hardened layer and the core determines the magnitude of the fatigue limit. The greatest fatigue limit is achieved with the same stiffness of the outer layer and core – with the hardened layer equal to 0.1 of the diameter of the part; The thickness of the hardened layer for short mandrels with shanks with a diameter of 30-40 mm should be 3-4 mm.
Determined the strength and durability of the mandrels. Mass testing of the mandrels showed that the mandrels failed due to wear and not damage. Therefore, surface hardening dramatically increases the strength of the tails of the mandrels.
Mandrels were tested when drawing thick-walled pipes (wall thickness 6-6.5 mm) on beds with different speeds of movement of chains. The stability of the mandrels with shanks averaged 220 pipes. Shanks failed by wear.
Findings. 1. Short mandrels with shanks for drawing thick-walled pipes do not crack and have greater durability than hollow ones.
2. The use of surface hardening with induction heating made it possible to exclude cases of mandrel failures along the threaded portion.
3. Surface hardening with induction heating provides a layer with a depth of 3-4 mm, hardness HRC 58-64.
A. V. NIKOLENKO
Lyudinovsky Locomotive Plant
ISSN 0026-0819. “Metallurgy and heat treatment of metals”, No. 4. 1963
1. Lozinskiy M. G. Surface hardening and induction heating of steel. Mashgiz, 1949.
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