GB1582438A

GB1582438A - Heat treatment

Info

Publication number: GB1582438A
Application number: GB42315/76A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1976-10-12
Filing date: 1976-10-12
Publication date: 1981-01-07
Also published as: ZA775735B; DE2745725A1; AU2921777A; ATA729177A; JPS5353506A; CH626656A5; FR2367830A1; AU510708B2; AT359104B; SE7711419L

Abstract

Arranged within a frame construction formed by horizontal upper bars (3) and vertical side bars is a refractory wall with a cavity (2) for accommodating a bath. The lateral areas of the frame construction are closed off by means of screening plates (5) and the upper side of the wall is closed off by means of a cover plate with a central opening. A hood (7) is placed on the upper part of the frame construction. The hood opens into an extraction duct (8) and, at its front side, has a window (9) which can be moved up and down. The upper bars (3) are hollow and each upper bar located in the vicinity of the window has a number of holes (12) in its upper side. Air or gas is passed into the interior of the upper bars via a pipe (10), and the air or gas emerging from the holes (12) forms a protective air or gas curtain when the window is open. This design renders unnecessary any additional pipes for the supply of air or gas and, as a result, access to the duct is unhindered. <IMAGE>

Description

(54) HEAT TREATMENT (71) We, IMPERIAL CHEMICAL INDUS TRIES LIMITED, Imperial Chemical House, Milibank, London SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to plant for the treatment of metals, especially for the heat treatment of metals, and in particular it relates to molten salt bath heat treatment plant.

Various metal heat treatment processes are known. For example, it is known to im prove the surface properties of metal articles, especially articles of iron or of ferrous alloys, by treating the articles in a bath of molten salt. Such known treatments include carburising and nitriding of metal parts, for example, by heating the parts in a molten salt bath containing an alkali metal cyanide.

Other known processes include heating metal articles in molten salt baths in order to bring about phase changes in the articles treated; treating metal articles in molten salt baths, for example, in a salt bath containing a mixture of an alkali metal nitrate and an alkali metal nitrite, in order to clean the articles, for example, in order to remove paint from the articles or to remove sand from metal castings; and treating articles in aqueous media, e.g. in solutions of salts at high temperature, in order to wash the articles.

The plant in which such heat treatment processes may be carried out generally comprises a bath for containing the molten salt or aqueous medium surrounded by a refractory material and positioned within an outer framework, and means for heating the bath.

Some of the salts used in such processes are toxic, and in some cases extremely toxic.

In particular this is the case with alkali metal cyanides which are widely used in molten salt bath heat treatment processes. Some of the salts used are also corrosive, especially at elevated temperatures. Furthermore, at the elevated temperatures at which such heat treatment processes are often operated, for example, temperatures in the range 4000 C to 800"C and even up to 1000"C, noxious fumes may be evolved and it is often necessary to enclose the top of the bath by a canopy and to provide a fume extraction system associated with the canopy in order to protect the operator from the noxious fumes. However, the operator must be able to gain access to the bath and for this purpose the canopy may be provided with an opening.

It is convenient to provide a curtain of an inert gas, that is a gas which is not harmful to the operator of the bath, e.g. air, in the region of the opening in the canopy in order to protect the operator by preventing noxious fumes from escaping.

A curtain of inert gas has previously been provided by means of a pipe connected to a suitable supply of inert gas and positioned in the opening in the canopy between the operator and the bath. The positioning of the pipe has proved to be inconvenient for the operator as it has generally projected above the level of the bath and has obstructed access to the bath making inspection of the bath and the transfer of metal articles to and from the bath inconvenient.

This inconvenience may be overcome by the present invention which provides a heat treatment plant which includes a framework, positioned within the framework an assembly of refractory material containing a bath in which metal articles may be heat treated, and a canopy enclosing the top of the plant and through which fumes from the bath may be extracted, at least part of the framework itself being in the form of a pipe having one or more apertures therein and from which a curtain of inert gas may be directed towards the extraction part of the canopy, and the canopy being provided with a movable part which may be moved to permit access to the bath.

As the curtain of inert gas issues from the framework of the plant itself it can be seen that the provision of this curtain of inert gas does not depend upon additional pipework being provided on the plant. As the top of the bath will generally be on about the same level as the top of the framework it can be seen that the inconvenience previously associated with the provision of additional pipework is eliminated.

In use the framework is connected to a source of inert gas, e.g. air. The aperture(s) in the framework are so positioned that, when the supply of inert gas is turned on, the curtain of inert gas is positioned at least between the operator and the bath and is directed towards the extraction part of the canopy thus protecting the operator from the noxious fumes associated with the plant when in use. The framework comprises a plurality of apertures so as to provide the curtain of inert gas.

The canopy encloses the top of the plant and is provided with a movable part, e.g.

a window, which may be moved to permit access to the bath and which may be closed when access to the bath is not required.

If desired, the means for controlling the supply of inert gas may be operatively connected to the canopy. Thus, when a part of the canopy is moved so as to create an opening in the canopy the supply of inert gas may be caused to be turned on, and conversely that when a part of the canopy is moved so as to close the opening in the canopy the supply of inert gas may be caused to be turned off. For example, the movable part of the canopy may be operatively connected to a valve which controls the supply of inert gas.

The heat treatment plant will generally comprise a bath in which metal articles may be heat-treated, for example a bath of steel or of other metal, e.g. a titanium bath or a titanium-lined bath, surrounded by a refractory material which serves to reduce heat losses. The refractory material may be an assembly of refractory brickwork or of refractory inorganic fibrous material positioned within the framework and having a cavity in which the bath may be placed.

Alternatively, the bath may be provided merely by a cavity in the assembly of refractory brickwork.

The framework may, for example, define a box-like shape having horizontal top members and vertical side members, and optionally horizontal bottom members, the top members of the framework including one or more apertures through which a curtain of inert gas may be directed towards the extraction part of the canopy.

Means for heating the bath may be provided by a suitable burner, for example, a gas burner or an oil burner. Where the heat treatment plant comprises an assembly of refractory brickwork the brickwork may also contain a passageway leading to the bath and in which the heater for heating the bath may be placed, and also a passageway leading from the bath and through which combustion gases formed by burning of the gas or oil may be conducted to a suitable flue.

Alternatively, and especially in the case where the bath is provided by a cavity in an assembly of refractory brickwork, electrical heating means may be provided for example a pair of electrodes.

Plates, for example, of sheet metal, may be fastened to the framework of the heat treatment plant in order to protect the refracory material from damage which may occur in use.

An embodiment of the invention will now be described with the aid of the following diagrams in which Figure 1 shows a view in perspective of a heat treatment plant of the invention and Figure 2 shows a perspective view, partly cut away, of a part only of the heat treatment plant shown in Figure 1.

The heat-treatment plant comprises an assembly of refractory brickwork (1) containing a cavity (2) which may itself provide the bath in which metal articles are to be treated or which may receive a separate bath. The assembly of refractory brickwork (1) is positioned within a framework comprising horizontal top members (3), vertical side members (4), and optionally horizontal bottom members (not shown). The framework carries facing plates (5) to protect the refractory brickwork and a top plate (6).

On top of the framework there is positioned a canopy (7) which leads to a flue (8) and the front of the canopy is provided by a window (9) which can be slid vertically upwards to permit the operator of the plant to gain access to the bath. The top members of the framework are hollow and are connected to a pipe (10) containing a valve (11), the pipe being connected to an air supply (not shown). The top member of the framework at the front of the plant, that is the member adjacent to the window (9), comprises a plurality of holes (12). Not shown in the accompanying figures are the means for heating the bath which is positioned at the rear of the assembly of refractory brickwork and which may be, for example, an oil burner or a gas burner, and the means for introducing into the bath the metal pieces which are to be treated. The metal pieces may be introduced by means of a travelling hoist through an aperture in the side of the canopy, and removed from the bath by similar means after treatment.

WHAT WE CLAIM IS:- 1. A heat treatment plant which includes a framework, positioned within the framework an assembly of refractory material containing a bath in which metal articles mal be heat treated, and a canopy enclosing the top of the plant and through which fumes

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. being provided on the plant. As the top of the bath will generally be on about the same level as the top of the framework it can be seen that the inconvenience previously associated with the provision of additional pipework is eliminated. In use the framework is connected to a source of inert gas, e.g. air. The aperture(s) in the framework are so positioned that, when the supply of inert gas is turned on, the curtain of inert gas is positioned at least between the operator and the bath and is directed towards the extraction part of the canopy thus protecting the operator from the noxious fumes associated with the plant when in use. The framework comprises a plurality of apertures so as to provide the curtain of inert gas. The canopy encloses the top of the plant and is provided with a movable part, e.g. a window, which may be moved to permit access to the bath and which may be closed when access to the bath is not required. If desired, the means for controlling the supply of inert gas may be operatively connected to the canopy. Thus, when a part of the canopy is moved so as to create an opening in the canopy the supply of inert gas may be caused to be turned on, and conversely that when a part of the canopy is moved so as to close the opening in the canopy the supply of inert gas may be caused to be turned off. For example, the movable part of the canopy may be operatively connected to a valve which controls the supply of inert gas. The heat treatment plant will generally comprise a bath in which metal articles may be heat-treated, for example a bath of steel or of other metal, e.g. a titanium bath or a titanium-lined bath, surrounded by a refractory material which serves to reduce heat losses. The refractory material may be an assembly of refractory brickwork or of refractory inorganic fibrous material positioned within the framework and having a cavity in which the bath may be placed. Alternatively, the bath may be provided merely by a cavity in the assembly of refractory brickwork. The framework may, for example, define a box-like shape having horizontal top members and vertical side members, and optionally horizontal bottom members, the top members of the framework including one or more apertures through which a curtain of inert gas may be directed towards the extraction part of the canopy. Means for heating the bath may be provided by a suitable burner, for example, a gas burner or an oil burner. Where the heat treatment plant comprises an assembly of refractory brickwork the brickwork may also contain a passageway leading to the bath and in which the heater for heating the bath may be placed, and also a passageway leading from the bath and through which combustion gases formed by burning of the gas or oil may be conducted to a suitable flue. Alternatively, and especially in the case where the bath is provided by a cavity in an assembly of refractory brickwork, electrical heating means may be provided for example a pair of electrodes. Plates, for example, of sheet metal, may be fastened to the framework of the heat treatment plant in order to protect the refracory material from damage which may occur in use. An embodiment of the invention will now be described with the aid of the following diagrams in which Figure 1 shows a view in perspective of a heat treatment plant of the invention and Figure 2 shows a perspective view, partly cut away, of a part only of the heat treatment plant shown in Figure 1. The heat-treatment plant comprises an assembly of refractory brickwork (1) containing a cavity (2) which may itself provide the bath in which metal articles are to be treated or which may receive a separate bath. The assembly of refractory brickwork (1) is positioned within a framework comprising horizontal top members (3), vertical side members (4), and optionally horizontal bottom members (not shown). The framework carries facing plates (5) to protect the refractory brickwork and a top plate (6). On top of the framework there is positioned a canopy (7) which leads to a flue (8) and the front of the canopy is provided by a window (9) which can be slid vertically upwards to permit the operator of the plant to gain access to the bath. The top members of the framework are hollow and are connected to a pipe (10) containing a valve (11), the pipe being connected to an air supply (not shown). The top member of the framework at the front of the plant, that is the member adjacent to the window (9), comprises a plurality of holes (12). Not shown in the accompanying figures are the means for heating the bath which is positioned at the rear of the assembly of refractory brickwork and which may be, for example, an oil burner or a gas burner, and the means for introducing into the bath the metal pieces which are to be treated. The metal pieces may be introduced by means of a travelling hoist through an aperture in the side of the canopy, and removed from the bath by similar means after treatment. WHAT WE CLAIM IS:-

1. A heat treatment plant which includes a framework, positioned within the framework an assembly of refractory material containing a bath in which metal articles mal be heat treated, and a canopy enclosing the top of the plant and through which fumes

from the bath may be extracted, at least part of the framework itself being in the form of a pipe having one or more apertures therein and from which a curtain of inert gas may be directed towards the extraction part of the canopy, and the canopy being provided with a movable part which may be moved to permit access to the bath.

2. A heat treatment plant as claimed in claim 1 in which the movable part of the canopy is operatively connected to means for controlling the supply of inert gas.

3. A heat reatment plant as claimed in claim 1 or claim 2 in which the framework defines a box-like shape having horizontal top members and vertical side members, one or more of the top members having one or more apertures therein.

4. A heat treatment plant as claimed in claim 1 substantially as hereinbefore described and as shown in Figures 1 and 2.