GB2145503A

GB2145503A - Process of producing protective atmosphere in heat treatment furnaces and ovens

Info

Publication number: GB2145503A
Application number: GB08322680A
Authority: GB
Inventors: Ivor Lawrence Sudney Golding
Original assignee: GOLDING IVOR LAWRENCE SYDNEY
Current assignee: GOLDING IVOR LAWRENCE SYDNEY
Priority date: 1983-08-24
Filing date: 1983-08-24
Publication date: 1985-03-27
Also published as: GB8322680D0; GB2145503B

Abstract

A heat treatment oven or furnace chamber 13 is simultaneously provided with a regulated amount of heat and a sufficient volume of protective atmosphere to protect work pieces from oxidation. Volume and temperature of the products of combustion from burning in burner 4 regulatable quantities of fuel gas and air are controlled by the addition of a measured quantity of clean water from a container 9 which vaporises and passes along a passageway 11 to the chamber 13. The presence of water vapour significantly increases the effective volume of protective atmosphere and serves to adjust the temperature of treatment chamber 13 to that required for processing work pieces. The arrangement serves to utilise the thermal energy which is normally wasted when the protective atmosphere is produced conventionally in a separate generator. Furthermore as the protective atmosphere is composed of a proportion of steam in association with products of combustion the quantity of fuel gas which is required to be burnt is reduced. Additional heat may be supplied to the chamber 13 by a burner 14 with fuel supply 5A and air supply 6A. <IMAGE>

Description

SPECIFICATION Process of producing protective atmosphere in heat treatment furnaces and ovens This invention relates to apparatus (hereinafter referred to as being of the kind specified) and to a method for the generator of protective atmospheres, for example atmospheres suitable for use in furnaces during the heat treatment of workpieces in a non-oxidising atmosphere.

The term 'heat treatment' embraces annealing, tempering, stress relieving, normalising, sintering, brazing, hardening and such operations where it is generally necessary to avoid contact between the work pieces and uncombined oxygen.

Apparatus according to the invention may also be employed to provide a protective atmosphere for other purposes, for example as an inert atmosphere to purge oxygen from chemical or food processing plant.

The protective atmosphere for conventional heat treatment furnaces is generated in apparatus separate from the furnace by burning a fuel gas in an approximately stoichiometric quantity of air (an exothermic reaction), cooling the products of combustion to reduce the water content thereof and feeding this gas to the chamber of the furnace as a protective atmosphere (generally called an exothermic atmosphere) .

One disadvantage of this conventional arrangement is that the heat that is released in the exothermic reaction of fuel when burnt with air is wasted. Cooling equipment must be provided specifically for removing this heat, the heat normally being transmitted ultimately to the ambient atmosphere or to water which is discarded. Furthermore, removing water by condensation reduces the effective volume of the generated exothermic atmosphere by a significant amount.

In a form of generator which has previously been proposed for producing a protective atmosphere for a heat treatment furnace a measured quantity of fuel gas and air is supplied to a burner or reaction tube situated within the furnace chamber. Products of combustion exhausted therefrom are released directly into the furnace chamber as a protective atmosphere.

One disadvantage of this proposal is that whilst a constant volume of protective atmosphere is required to purge the furnace chamber the volume of combustion products generated is dependent on the heat input required by the furnace. Any variation in heat input will result in either an insufficient volume of protective atmosphere to purge the furnace chamber or in the event of maintaining the purge volume, over-heating of the furnace chamber and of work pieces being processed therein.

It is the object of the present invention to provide a combination of heat treatment furnace and apparatus of the kind specified, which is less expensive to manufacture, of more compact form and less expensive to operate than the separate generator and furnace hitherto generally employed. Apparatus of the kind specified also allows a constant and adequate volume of protective atmosphere purge to be maintained within the furnace chamber whilst heat input to the furnace may be varied over a wide range according to requirements of the heat treatment process being performed.

According to one aspect of the invention there is provided in combination with or for combination with a heat treatment furnace or oven apparatus for producing a protective atmosphere and comprising at least one heating burner in which fuel is burnt in a controlled quantity of air. Products of combustion at high temperature are contained in a refractory or heat resisting metallic tube or chamber which is disposed fully or partly within the furnace to form a passageway connecting the burner to the furnace work chamber. Into this passageway is fed a measured and controlled quantity of water which is caused to vaporise by contact with the products of combustion.

Means is provided for varying the quantity of water admitted in order to vary the relative volumes of products of combustion and water vapour and the temperature of the resultant gaseous mixture admitted to the furnace chamber. The temperature to which products of combustion are cooled by vaporised water would be according to the required furnace temperature and the composition and volume of protective atmosphere necessary to protect work pieces and purge the said furnace chamber.

We prefer to provide means to atomise or finely disperse water into the duct, tube or other form of passageway carrying hot products of combustion (exothermic atmosphere).

This passageway communicating, when the burner is installed in a furnace, through a duct or passageway extending into the furnace chamber.

Alternatively, the burner and combustion chamber from which hot gaseous products of combustion (exothermic gas) are discharged may be separate from but adjacent to the furnace. A communicating duct or passageway delivers these gases to the furnace. The said duct or passageway has means provided to introduce and dispense clean water to part cool the products of combustion and increase the total volume of gases by generating steam.

Since the products of combustion (exothermic gas) are mixed with steam the effective volume available for purging the furnace is considerably increased. This is particularly important in certain thermal treatments, for example the heat treatment of copper where the presence of oxygen within the furnace chamber causes discoloration, and an excess of hydrogen over that required to prevent oxidation is objectionable. Dilution of hydrogen present in the exothermic protective atmosphere by steam serves to reduce the partial pressure of the constituent hydrogen to an acceptable level. Furthermore less fuel is consumed in generating a sufficient volume of protective atmosphere including steam than would be the case if the whole volume requirement was composed entirely of the products of combustion.

By varying the rate at which clean water is introduced into the delivery duct or passageway a wide range of controlled temperatures and atmosphere compositions can be produced.

The invention may be applied to apparatus of the kind specified for generating an atmospheric environment which is to be used other than in a metallurgical heat treatment furnace for processes of a non-metallurgical nature.

This is of importance in certain applications, as for example the removal of oil, grease and other surface contaminants of a chemical nature.

According to a further aspect of the invention there is provided apparatus of the kind specified arranged to operate as part of, or in conjunction with, a fuel fired furnace whereby such means that are normally included in the said furnace to provide pressurised air and fuel gas or vapour for combustion are arranged to simultaneously provide a supply of these gases to a burner which forms part of apparatus of the kind specified. This arrangement is of advantage as it permits less expensive manufacture and allows more compact form.

According to a further aspect of the invention there is provided a method of producing a protective atmosphere and simultaneously heating a body which is required to be heated, wherein a fuel is burned with a controlled quantity of air within a first chamber and the products of combustion conveyed through a duct or passageway to a second chamber which serves as the main furnace chamber in which work is processed. The said main furnace chamber may also be provided with one or more burners fed with controlled quantities of air and fuel gas. Clean water is introduced to the said duct or passageway in order to increase the volume of protective atmosphere and control the rate of heat input to the main furnace to an acceptable level.

The invention wili now be described by way of example with reference to the accompanying drawing Fig. 1 wherein is shown a sectional plan view of a furnace according to the present invention The furnace would be of conventional construction in that a preferably gas tight steel casing is lined with suitable refractory materials to form a heating chamber through which workpieces are conveyed and within which heat is supplied to the workpieces. The construction of the chamber and means of conveying the workpieces therein may be substantially conventional. Thus there may be provided a shaker hearth, walking beam, roller hearth, mesh belt, cast link belt, rotary hearth or like conveyor for workpieces.The conveyor may be arranged to discharge work pieces into a quench tank for cooling or arranged to extend through cooling chambers provided with water jackets or other means of removing heat from workpieces. Alternatively the furnace may be adapted for the treatment of workpieces in batches.

The furnace is divided by an internal wall 1 6 to form an anti-chamber 3 and main treatment chamber 13.

Adjacent to the anti-chamber but sealed from it by a refractory or metal wall 1 8 is located the mixing chamber 1 2 in which products from the combustion of a measured and controlled quantity of fuel gas or vapour and air are collected. A burner 4 fed by pipes carrying fuel gas 5 and air 6 discharges the said products of combustion (exothermic gas) through duct 7 into chamber 12. Disposed within chamber 1 2 is a metallic or ceramic dish or bowl 8 which extends to form an interconnecting passageway 11 between the mixing chamber 1 2 and main work treatment chamber 13. The said duct 7, mixing chamber 12, dish or bowl 8 and interconnecting passageway 11 may be arranged conveniently in the form of a single duct.A measured and controlled flow of clean water is fed to container 9, fitted with liquid lock seal 20, and discharges through a tube 10 into dish or bowl 8. There it is evaporated by the heat derived from hot products of combustion (exothermic gas) with which the water vapour so produced mixes in chamber 1 2. The mixture of water vapour and products of combustion (exothermic gas) then pass through passageway 11 to work treatment chamber 1 3.

Additional heat necessary for raising the temperature of workpieces within work treatment chamber 1 3 is provided by a burner 14, which is supplied with measured and controlled quantities of fuel gas or vapour through feed pipe 5A and a proportional quantity of air through feed pipe 6A. Arrangements are included to simultaneously reduce or increase the flow of fuel gas or vapour and air to burner 14 according to the thermal demands of the treatment process being carried out in chamber 13. A partial dividing wall 1 6 may be provided at the junction of antichamber 3 and main treatment chamber 1 3 to slightly restrict the discharge through passageway 1 7 of the mixed exothermic gas and water vapour atmosphere and force part of the flow of this gaseous mixture to discharge point 19.

Heat transmitted through refractory or metallic wall 18 from the products of combustion (exothermic gas) contained in mixing chamber and separated from anti-chamber 3 by the said wall 18 is used to partially preheat ingoing work pieces. At least some part of the hot exothermic gas admixed with water vapour which forms an atmosphere within main treatment chamber 1 3 passes through antichamber 3 and imparts some of its sensible heat to the ingoing work pieces prior to being discharged from the furnace at work entry point 15.

The arrangement illustrated in the accompanying drawing provides for a better atmosphere environment within the furnace treatment chamber compatible with the metallurgical and chemical requirements of copper and its alloys and certain other ferrous and non ferrous metals and alloys. Furthermore, we have found that furnaces as illustrated in the accompanying drawing can achieve a better control of the protective atmosphere within the treatment chamber than is possible with conventional furnaces.

In certain cases, for example where the availability of gaseous fuels is limited, some part of the heating in the treatment chamber may be provided by alternative fuels such as oil or electricity. In the case of oil it is necessary to burn the fuel within radiant tubes which radiate heat to the treatment chamber and exhaust the products of combustion externally. Alternatively electrical heating elements could be disposed within the treatment chamber.

It would also be within the scope of the invention for combustion of the gaseous or vaporised fuel to be carried out in a chamber or passageway outside but adjacent to the main furnace structure. Hot products of combustion (exothermic gas) so produced would be fed through a transfer chamber or passageway to the main treatment chamber. Clean water would be introduced and evaported by and into these gases at any convenient point in the burner, combustion chamber, transfer chamber or passageway, or into the main treatment chamber. It would also be within the scope of the invention for water to be introduced to the products of combustion of fuel burned directly into the main treatment chamber, instead of within a separate chamber communicating with the main treatment chamber.

In certain cases the water could be pumped, sprayed or finely dispersed into the products of combustion without the use of a catchment trough or dish. Such arrangements would incorporate means to ensure near complete evaporation of the water into the products of combustion.

Claims

1. In combination with or for combination with a heat treatment furnace, apparatus for producing a protective atmosphere and comprising at least one chamber or tube within which fuel is burned in a controlled quantity of air, such chamber being disposed at least partly within the furnace so that heat can be transferred from the chamber or tube to workpieces in an anti-chamber or treatment chamber, and clean water entry to a chamber or duct which conveys products of combustion to the treatment chamber, the chamber or duct being arranged to allow contact between the clean water and products of combustion in order to evaporate the water and partially cool the products of combustion. The said chamber or duct conveys the partially cooled mixture of exhaust gases and water vapour to the treatment chamber as a protective atmosphere.

2. Apparatus according to claim 1 comprising a passageway which communicates between a heating burner and treatment chamber, the passageway having provision for water admission.

3. Apparatus according to claim 2 wherein said passageway is disposed at least partly within the treatment chamber.

4. Apparatus according to any of claims 1 to 3 wherein there is further provided means for introducing additional water into said interconnecting duct or into said passageway.

5. Apparatus according to any preceding claim wherein suitable means is provided for controlling the relative rates of supply of air and fuel and water to the burner.

6. Apparatus according to claim 5 as appendant to claim 4 wherein said settable means is also arranged for controlling the rate of supply of water to the interconnecting duct or passageway.

7. Apparatus of the kind specified arranged to supply heat to a body which is required to be heated, such apparatus comprising a heating chamber for containing the said body, a burner in which fuel gas and air are burned which is disposed within or adjacent to said heating chamber, a means of introducing clean water to the burner, interconnecting duct or passageway so that the products of combustion are partially cooled prior to entry into the heating chamber when the apparatus is in use so as to provide a compatible protective atmosphere to workpieces within the heating chamber.

8. Apparatus according to claim 7 wherein additional burners are disposed within the heating chamber.

9. Apparatus according to claims 7 and 8 wherein at least one burner, interconnecting duct or passageway is provided with means of introducing clean water in order to part cool and increase the effective volume of gases for purging a heating chamber in which workpieces are treated under a protective atmosphere.

10. Apparatus according to claim 9 in which the heating chamber in which workpieces are treated receives heat energy and products of combustion from at least one burner disposed within said heating chamber.

The said burner is supplied with controlled quantities of air and fuel gas.

11. A method of heat treating a workpiece wherein the workpiece is conveyed through a treatment chamber, and whilst in the treatment chamber the workpiece is enveloped in a protective atmosphere and receives heat energy from direct contact with hot gases which pass from at least one burner within or adjacent to the heating chamber.

1 2. A method according to claim 11 wherein the protective atmosphere is at a high temperature and composed in part of water vapour, the remainder being hot gases from at least one burner.

13. A method according to any preceding claim wherein free oxygen is excluded from a treatment chamber by hot gases produced by the controlled combustion of a fuel gas with air, the volume of which is enhanced by evaporation of clean water.

14. A method of producing a protective atmosphere and simultaneously heating a body which requires to be heated wherein a fuel gas is burned in air within a burner and the water vapour content of gases exhausted from the burner is increased by direct contact with water in a duct or passageway and heat is transferred from the gaseous mixture to the said body which is required to be heated in an envelope of protective atmosphere.

1 5. A method of heating a body which requires to be heated within a treatment chamber and simultaneously producing a sufficient volume of protective atmosphere to envelope the said body within the said treatment chamber.

16. In or for combination with a heat treatment furnace apparatus for producing a protective atmosphere substantially as herein described with reference to and as illustrated in the accompanying drawing.

1 7. A method of producing a protective atmosphere and simultaneously heating workpieces as herein described with reference to the accompanying drawing.