RU2842362C1 - Hardening vacuum furnace with heated retort - Google Patents

Abstract

FIELD: furnaces.

SUBSTANCE: invention relates to hardening vacuum furnaces with heated retort. Furnace with a heated retort located vertically consists of a movable electric furnace with lining, one vacuum pump, a heated retort with a cover plate and a retort cooling system for hardening outside the furnace. Furnace is made with a space between the furnace and the retort filled with argon, helium or nitrogen by displacement, the furnace lining is made with a protrusion for the bottom of the retort to rest on, retort cooling system for tempering consists of one or several sections cooled from inside by running water and pressed against retort heated part.

EFFECT: simplicity, reliability of the device; one vacuum pump is enough for operation of the furnace; due to vertical arrangement of the retort it is possible to temper and perform other thermal treatment of long-length thin-walled items in a suspended state with minimum deformation, for example, those produced by methods of an additive technology.

2 cl, 4 dwg

Description

The proposed technical solution applies to vacuum furnaces, mainly intended for hardening parts made of high-alloy steel, as well as sintered materials or obtained by additive technology. Such parts after hardening and tempering are subjected to only minimal mechanical processing - grinding and finishing of the most accurate dimensions.

The design of furnaces with a heated retort (muffle) has long been known. The parts are loaded into the retort, which is evacuated and placed in an electric furnace, in which the retort is heated to the desired temperature while continuing the evacuation, then removed from the furnace and cooled.

Close to the proposed technical solution is the utility model CN 207147233 Laboratory with an external hot-type vacuum furnace, filing date 09/07/2017, publication date 03/27/2018, publication type B, IPC F27B 2/17. In this device, in order to minimize resistance to the gas flow, the vacuum system is connected to the front part of the retort by a short wide pipe, the retort is stationary, and the heating electric furnace moves to accelerate the cooling of the retort, but this device is not intended for hardening, the retort is cooled in air, and the vacuum is created by a system of two pumps: a forevacuum and a jet pump.

The closest to the proposed technical solution is invention RU 2006773 C1 PORTABLE VACUUM FURNACE FOR CHEMICAL-THERMAL TREATMENT OF SMALL-SIZED TOOLS AND STRUCTURAL PARTS (EXPERIMENTAL DESIGN BUREAU "FAKEL"), 30.01.1994, IPC F27B 5/05 (1990.01). Disadvantages of this design: low-speed quenching by cooling the retort in still air and violation of vacuum technology requirements - evacuation is performed through a small-diameter pipe and a vacuum hose, while it is impossible to create a vacuum of sufficient depth at a high temperature (1000°C) and protect parts from oxidation, high-temperature quenching in the furnace is not performed separately, but is combined with chemical-thermal treatment using substances containing carbon (monoethanolamine, triethanolamine); in addition, the furnace has small dimensions and is used to process small-sized parts.

The proposed technical solution sets the task of simplifying a vacuum furnace with a heated retort, while obtaining the necessary cooling rate of parts (charge), sufficient for hardening high-alloy steel, with simultaneous protection of the charge from oxidation, and also reducing warping of parts during hardening. A scheme is proposed in which a vertically located retort is stationary and connected to a vacuum pump by a short wide branch pipe, and the electric furnace moves along the retort for its heating and subsequent cooling, shown in Fig. 1,

where 1 is a movable electric furnace,

2 - oven cover,

3 - vacuum pump,

4 - retort,

5 - retort lid,

6 - water cooling of the retort lid,

9 - retort cooling system.

The load (parts in the device) rests on the bottom of the retort or is suspended in a vertical position inside the retort. The bottom of the retort rests on a strong projection of the lining, the retort pressure force can be adjusted from the full weight of the retort with the load to a smaller value, for example 0.5-0.8 of its weight, in order to achieve minimal warping of the retort walls during long-term operation.

When heating the retort in the furnace to a high temperature, 800-1000°C and more, the air leakage into the retort increases several times, oxidizing the charge inside the retort. To protect the charge, as well as the surface of the retort and the furnace heaters, it is proposed to fill the space between the retort and the inner surface of the furnace insulation with inert gas or nitrogen, as shown in the diagram in Fig. 2,

where 1 is a movable electric furnace,

4 - retort,

7 - heaters,

8 - hole for supplying inert gas or nitrogen.

Filling with nitrogen, argon or other inert gas is done by displacing air through a small hole in the casing and lining of the furnace, the displaced air is removed through the gap between the retort and the lining in the upper part of the furnace. Ceramic tubes can be inserted into the holes to prevent the lining from crumbling. There can be several holes for supplying protective gas, their location can also be different to create the maximum possible ratio of the volume of protective gas to the residual volume of air with optimal consumption of protective gas. To protect against oxidation, it is sufficient to contain about 90% of the volume of inert gas or nitrogen in the atmosphere between the lining and the retort.

The specified protection against oxidation will allow the use of only one vacuum pump for vacuuming the retort, for example, a standard two-stage vane-rotor vacuum pump with a residual pressure of 0.2 Pa and a capacity sufficient for the volume of the retort.

The retort cooling system is shown by position 9 in Fig. 1 and the diagram in Fig. 3,

where 1 is a movable electric furnace,

2 - oven cover,

9 - retort cooling system.

The retort is cooled by several sections having a cavity inside into which water is supplied at a temperature of about 15-30°C and a pressure of about 2-4 atm, which is typical for cooling purposes; after circulation inside the cavity, the water is removed. Figs. 1 and 3 show a variant with six sections; at the heating stage (Fig. 1), the furnace is raised, the sections are moved apart; at the cooling stage (Fig. 3), the furnace is lowered down, the sections are pressed against the retort with the required force; the pressing can be carried out, for example, electromechanically, hydraulically or pneumatically. It is also possible to use one flexible, for example corrugated, cooling section that completely envelops the retort during cooling. The sections can be made of corrosion-resistant steel, a combination of steel and copper, or other materials, provided that there is no melting of the surface of the section in contact with the retort heated to a high temperature.

When cooling the retort in sections, even a small air gap of 0.01 mm or more sharply reduces the cooling rate due to the low thermal conductivity of air. A variant of filling the air gap with a melt of a low-melting metal or alloy is proposed, as shown in the diagram in Fig. 4, where 9 is the retort cooling system (one section is shown). The inner surface of the section, pressed against the retort, is covered with round depressions of approximately 5-10 mm in diameter and about 1 mm in depth, filled with a low-melting metal (alloy) with a melting point of about 200-400°C and a high boiling point, such as tin. The shape and size of the depressions may be different, based on the condition of no melt flowing off the surface of the section and a sufficient cooling rate. Also required is high wettability of the section surface by the melt and low wettability of the retort surface, for which purpose the section surface at the recess can be plated with a metal with high wettability by the melt, for example, copper in the case of using tin.

The proposed vacuum furnace can be used for hardening parts up to several meters long.

The proposed technical solution will allow:

- simplify the design of a vacuum furnace to achieve the required cooling rate of parts (charge), sufficient for hardening high-alloy steel while simultaneously protecting the charge from oxidation;

- reduce warping of parts during hardening;

- increase the reliability of the vacuum furnace by using one vacuum pump.

Claims (2)

1. A quenching vacuum furnace with a heated retort located vertically, consisting of a movable electric furnace with a lining, one vacuum pump, a heated retort with a lid and a retort cooling system for performing quenching outside the furnace, wherein the furnace is made with a space between the furnace and the retort filled with argon, helium or nitrogen by displacement, the lining of the furnace is made with a projection for resting the bottom of the retort on it, and the retort cooling system for performing quenching consists of one or more sections cooled from the inside by running water and pressed against the heated part of the retort. 2. A quenching vacuum furnace according to item 1, characterized in that the surface of one or more sections pressed against the heated part of the retort is covered with a low-melting alloy.

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