Vacuum quenching furnace with heated retort

Abstract

The invention relates to a vacuum quenching furnace. A vertically arranged retort is immobile and is connected by a short pipe to a single vacuum pump. The space between the retort and a lining is filled with a protective gas by displacement. During quenching, the furnace is lowered and the retort is rapidly cooled by sections containing cold running water, which are tightly pressed against the retort. To eliminate an air gap between the surfaces of the sections and the retort, the surface of the sections may be coated with a low-melting alloy; during quenching, liquid alloy fills the air gap. The technical result includes a simple and reliable device in which a single vacuum pump is sufficient for the operation of the furnace, and the possibility of carrying out quenching and other thermal treatment of long thin-walled articles, such as articles produced by additive manufacturing, in a suspended state and with minimal deformation.

Description

Vacuum quenching furnace with heated retort

[0001] The invention relates to vacuum furnaces primarily designed for hardening parts made of high-alloy steel, as well as sintered materials or those produced using additive manufacturing. After hardening and tempering, such parts undergo only minimal mechanical processing—grinding and finishing to the most precise dimensions.

[0002] The design of furnaces with a heated retort (muffle) has long been known. Parts are loaded into the retort, which is evacuated and placed in an electric furnace, where the retort is heated to the desired temperature while continuing the evacuation, then removed from the furnace and cooled. Utility model CN207147233 "Laboratory with an External Hot-Type Vacuum Furnace" is close to the proposed technical solution, 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 gas flow, the vacuum system is connected to the front of the retort by a short wide nozzle, the retort is stationary, and the heating electric furnace moves to accelerate the cooling of the retort. However, 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 TOOLS AND STRUCTURAL PARTS (EXPERIMENTAL DESIGN BUREAU "FAKEL"), 30.01.1994, IPC F27B 5 / 05 (1990.01). The disadvantages of this design include: low-speed quenching by cooling the retort in still air and a violation of vacuum technology requirements – evacuation is performed through a small-diameter pipe and a vacuum hose, making it impossible to create a vacuum of sufficient depth at high temperatures (1000°C) and protect the parts from oxidation. High-temperature quenching in the furnace is not performed separately, but is combined with chemical-thermal treatment using carbon-containing substances (monoethanolamine, triethanolamine). Furthermore, the furnace has small dimensions and is used for processing small parts.

[0003] The proposed vacuum furnace design features a vertical heated retort, protected externally by an inert gas during heating, and water-cooled sections. The components (loads) are positioned vertically, sometimes suspended, inside the retort. The water-cooled sections are offset from the retort during heating and do not interfere with heating. During quenching, the water-cooled sections tightly enclose the retort to ensure rapid cooling.

[0004] The goal is to simplify a vacuum furnace with a heated retort, while achieving the required cooling rate of parts (charges), sufficient for hardening high-alloy steel, while simultaneously protecting the charge from oxidation, and also to reduce warping of parts during hardening.

[0005] It is proposed: - to make a heated retort in the form of a vertically located closed metal tube, wherein the long parts inside the retort will be in a vertical state, including suspended, to reduce their deflection (warping); - to make the retort stationary and connect it to a single vacuum pump by a wide short pipe for minimal resistance to the gas flow in accordance with the requirements of vacuum engineering; - to make the electric furnace heating the retort movable vertically in order to free the surface of the retort after heating for its rapid cooling; - to make holes in the lining of the electric furnace heating the retort for filling the space between the heaters and the retort with an inert gas or nitrogen, by displacing air, to protect against oxidation of parts inside the retort, the surface of the retort and the electric heaters; to reduce deformation of the retort during heating, it can rest on a protrusion in the lining;– hardening of parts is carried out by rapid cooling of the retort, for which several sections, cooled from the inside by running water, are pressed with force against the outer surface of the retort; one flexible section can also be used.

[0006] The proposed technical solution: - simplifies the design of the vacuum furnace while simultaneously increasing reliability, as a single vacuum pump is sufficient to create a vacuum in the retort; - ensures a cooling rate sufficient for hardening high-alloy steel; reduces warpage of long parts; and increases the service life of the retort and electric heaters of the furnace. Furthermore, the proposed furnace allows for hardening parts up to several meters long without significantly increasing costs. Figure 1

[0007] Describes the arrangement of vacuum furnace components during heating of the charge prior to quenching. Figure 2

[0008] describes the location of the retort inside the furnace during heating, as well as the location of the electric heaters and the diagram for supplying inert protective gas (or nitrogen) inside the furnace. Figure 3

[0009] Describes the arrangement of vacuum furnace components during charge quenching. Figure 4

[0010] is an example of the implementation of a low-melting alloy coating of the retort cooling system.

[0011] An example of the proposed vacuum furnace design: a vertically positioned retort is stationary and connected to a vacuum pump via a short, wide pipe, while an electric furnace moves along the retort. The charge is placed inside the retort, the retort is closed with a water-cooled lid, and then the retort is heated. The arrangement of the vacuum furnace components during charge heating is shown in Fig.

[0012] Where 1 is a movable electric furnace, 2 is a furnace lid, 3 is a vacuum pump, 4 is a retort, 5 is a retort lid, 6 is a water cooling system for the retort lid, 9 is a retort cooling system. The charge (parts in the fixture) rests on the bottom of the retort or is suspended in a vertical position inside the retort. The retort bottom rests on a strong lining projection, and the retort pressure force can be adjusted from the full weight of the retort with the charge 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 the retort is heated in a furnace to a high temperature, 800 - 1000 C or more, 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 furnace heaters, the space between the retort and the inner surface of the furnace insulation is filled with an inert gas or nitrogen, as shown in the diagram,

[0013] Where 1 is the movable electric furnace, 4 is the retort, 7 are the heaters, and 8 is the inert gas or nitrogen inlet. Nitrogen, argon, or another inert gas is filled by displacing air through a small opening in the furnace shell and lining. The displaced air is removed through a gap between the retort and the lining at the top of the furnace. Ceramic tubes can be inserted into the openings to prevent lining shedding. There may be several inlet openings for the protective gas, and their locations can also vary to create the highest possible ratio of protective gas volume to residual air volume with optimal protective gas flow rate. To protect against oxidation, an inert gas or nitrogen content of approximately 90% by volume in the atmosphere between the lining and the retort is sufficient.The specified protection from oxidation will allow the use of only one vacuum pump for evacuating 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 retort volume. The retort cooling system is shown in position 9 of the diagram, where 1 is a movable electric furnace, 2 is a furnace cover, 9 is a retort cooling system. Cooling of the retort is carried out by several sections having a cavity inside, into which water is supplied at a temperature of about 15 - 30 C, typical for cooling purposes, and a pressure of about 2 - 4 atm. After circulating inside the cavity, the water is removed. A variant with six sections is shown in Fig.; at the heating stage, the furnace is raised, the sections are moved apart, at the cooling stage, the furnace is lowered downwards, the sections are pressed against the retort with the required force; pressing can be carried out, for example, electromechanically, hydraulically or pneumatically.It is also possible to use a single flexible cooling section, such as a corrugated one, that completely encircles the retort during cooling. The sections can be made of corrosion-resistant steel, a combination of steel and copper, or other materials, provided that the surface of the section in contact with the retort, heated to a high temperature, does not melt. When cooling the retort in sections, even a small air gap of approximately 0.01 mm or more dramatically reduces the cooling rate due to the low thermal conductivity of air. An option is to fill the air gap with a melt of a low-melting metal or alloy, as shown in the diagram, where 9 is the retort cooling system (one section is shown). The inner surface of the section, pressed against the retort, is covered with circular depressions approximately 3-10 mm in diameter and approximately 1 mm deep, filled with a low-melting metal (alloy) with a melting point of approximately 200-400 C and a high boiling point, such as tin.The shape and size of the depressions may vary, subject to the condition of preventing melt flow from the section surface and sufficient cooling rate. High wettability of the section surface by the melt and low wettability of the retort surface are also required. To achieve this, the section surface at the depression can be clad with a metal with high wettability by the melt—copper, if tin is used.

[0014] The proposed vacuum furnace can be used for hardening parts made of high-alloy steel, such as corrosion-resistant 30X13, 40X13 (1.4031, 1.4034, AISI 420S), heat-resistant 15X11MF, 15X12VNMF (AISI 4340, AISI 440C), tool-grade Kh12MF (D2), and others. This vacuum furnace is particularly suitable for hardening long, thin-walled parts, such as those 1 meter or longer, where subsequent machining with significant metal removal is unacceptable. This is particularly promising for parts produced using powder metallurgy and additive manufacturing. Patent literature

[0015] CN207147233 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.

[0016] RU 2006773 C1 PORTABLE VACUUM FURNACE FOR CHEMICAL-THERMAL TREATMENT OF SMALL TOOLS AND STRUCTURAL PARTS (EXPERIMENTAL DESIGN BUREAU "FAKEL"), 30.01.1994, IPC F27B 5 / 05 (1990.01).

Claims

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. A vacuum quenching furnace according to claim 1, characterized in that the surface of one or more sections pressed against the heated part of the retort is coated with a low-melting alloy.