GB1575350A

GB1575350A - Heat treatment furnaces

Info

Publication number: GB1575350A
Application number: GB2606077A
Authority: GB
Original assignee: Ipsen International GmbH
Current assignee: Ipsen International GmbH
Priority date: 1976-06-25
Filing date: 1977-06-22
Publication date: 1980-09-17
Also published as: DE2628605C3; DE2628605B2; FR2356103A1; DE2628605A1; FR2356103B1

Description

(54) IMPROVEMENTS IN OR RELATING TO HEAT TREATMENT FURNACES (71) We, IPSEN INDUSTRIES IN TERNATIONAL GESELLSCHAFT MIT BESCHRANKTER HAFTUNG, a German Body Corporate, of 52 Flutstrasse, 4190 Kleve 1, Germany, 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: The invention relates to a furnace for heat treating workpieces, for example a singlechamber tempering furnace.

There have been proposed heat treatment furnaces of single-chamber and multichamber construction. Depending on the insulation of the furnace jacket and thus the obtainable furnace temperature, it is possible to perform a wide range of different heat treatments, such as tempering, normalising, and annealing, under a protective gas atmosphere. Such heat treatment involves heating the workpieces in the furnace to the required temperature, maintaining the temperature for a specific time and then cooling the workpieces to a lower temperature.

Depending on the temperature, length of the time over which the temperature is maintained, and the method of cooling, different properties are obtained in the workpiece material. With these previously proposed furnaces the cooling operation is performed either by natural cooling of the furnace or' by transferring the workpiece to another assembly. The furnace cannot be used economically in this manner, or the risk exists of an undesirable oxide formation on the workpieces. Further, the rate of cooling the workpieces cannot be controlled sufficiently accurately to obtain precisely repeatable results in respect of the properties of the workpieces treated.

According to the present invention, there .is provided a batch-type furnace for heat treating workpieces, said furnace comprising an insulated furnace jacket which has a closable loading and unloading opening associated with a charge compartment which is heatable under a protective gas atmosphere which circulates within the furnace, and a cooling system for the protective gas comprising a water-cooled finned tube cooler installed in a housing forming an extension of the furnace jacket, the housing communicating with the charge compartment via an opening, and a closure device for closing the opening, said device being controllable to vary the quantity of gas flowing through the housing and thereby the cooling effect.

The closure device may comprise a closing member which is raised and lowered in a controlled manner and is seated on the inner surface of the furnace jacket in its closed position. The closing member may be arranged at one end portion of a rod led centrally through the cooling system, the other end portion of the rod being connected to a lifting cylinder secured on the cooler housing. Preferably, to control the circulation of the protective gas within the furnace, forced circulation of the gas may be provided by one or more blowers with an associated ducting system. This rod may be hollow to form a conduit for feeding the protective gas centrally into the cooler, the closing member surrounding the end portion of the rod remote from the cylinder; this construction is particularly suitable for carriage bottom chamber furnaces having blowers arranged at the top of the furnace to provide forced circulation.

Further according to the present invention, there is provided a batch-type heat treatment furnace for heat treatment of workpieces under a protective gaseous atmosphere which circulates within the furnace, said furnace comprising a furnace jacket, a charge compartment, a housing mounted on the furnace jacket, the housing opening into the charge compartment via an aperture such that the housing lies on the gas circulation path, water-co6led cooling means within the housing for cooling gas flowing through the housing, and closure means for closing the aperture, said closure means being controllable to vary the quantity of gas flowing through the housing and thereby to vary the cooling effect.

An embodiment of the invention will now be described by way of example only with reference to the accompanying diagrammatic drawing, the sole figure of which is a section of a single-chamber batch-type tempering furnace.

The furnace shown in the drawing comprises a jacket 2 formed of plate material having a lightweight insulation of heatresisting material and supported on legs 1.

The furnace jacket 2 forms a chamber having a charge compartment 3, to which access is provided via a loading and unloading opening 4 in the furnace jacket 2. The opening 4 may be closed by means of an internally-insulated cast door 5 which may be lifted and lowered pneumatically or hydraulically by means of a lifting cylinder 6.

The charge compartment 3 within the furnace jacket 2 is defined by a roller conveyor 7 and bottom and lateral ducting plates 8. The conveyor 7 extends throughout the width of the furnace and into the opening 4 and is journalled at each side within the furnace jacket 2. Below the bottom ducting plates 8 which are spaced above the bottom of the furnace jacket 2 is situated a blower 9 which is driven by a motor 10 via a drive passing through the furnace jacket 2. The bottom ducting plates 8 have an opening 11 to permit circulation of a protective gas as indicated by the arrows.

The lateral ducting plates 8 are spaced from the sides of the furnace jacket 2 to define therewith a space for heating elements 12 which serve the purpose of heating the charge compartment 3 and the charge 13 present in the compartment.

In addition to the motor 10, a source 14 of protective gas is installed on the bottom of the furnace jacket 2 and communicates with the interior of the furnace via an opening 15.

An explosion door 16 for burning off the protective gas, is oppositely situated in the upper side of the furnace jacket 2. The gas is circulated by the blower 9 along flow paths determined by the ducting plates 8, so as to ensure satisfactory gas circulation through the charge compartment 3, the heating and circulating means being arranged below and beside the ducting plates 8, to provide for minimum furnace dimensions for a specified charge compartment size. In this connection it is also advantageous that the heat transfer to the charge occurs'by radiation as well as by convection.

The furnace jacket 2 is outwardly extended at its upper side by a cylindrical housing 17 in which is installed a cooler 18 which comprises a plurality of finned tubes 19 through which cooling water is fed. The housing 17 communicates with the interior of the furnace via an opening 20 which may be closed by means of a closing member 21 arranged to seat against the internal surface 22 of the furnace jacket. The closing member 21 is carried by a rod 23 which is led centrally through the cooler 18 and is connected to a lifting cylinder 24 which controls the opening and closing displacement of the closing member 21. The lifting cylinder 24 is secured on the housing 17. A ducting plate 25 which forces the protective gas to flow through the cooler 18 is situated between the rod 23 and the closing member 21.

In a modified embodiment which is not illustrated, the rod 23 may be hollow to allow the protective gas to be fed into the centre of the cooler 18, the outflow of the cooled protective gas occurring via the opening 20. The different flow pattern produced in this modified embodiment may offer advantages for furnaces which differ from that particularly shown in the drawing.

The chamber furnace is operated by first building up an atmosphere of protective gas in the furnace, whereupon the door 5 is opened for charging, and the charge 13 present for example in a basket or a frame is then moved into the charge compartment 3 on the roller conveyor 7. Following this, the door 5 is closed and the blower 9 is switched on after a scavenging period. Heating of the charge compartment 3 is effected at the same time by means of the heating elements 12. After the required heat treatment temperature (for example 750"C) has been reacted, this temperature is maintained in the charge compartment for a predetermined period. Following this, the heating elements are turned off and the cooler 18 is included in the flow path of the protective gas as indicated by the arrows by slowly lowering the closing member 21. As the closing member 21 is progressively lowered, an increasing quantity of the gas will flow through the cooler 18 in a controlled manner both as regards volume and flow velocity and the protective gas will be cooled down slowly until the charge 13 finally has a desired low temperature of under 100"C.

The door 5 is then opened, and the charge 13 may then be withdrawn from the charge compartment 3 without risk of oxidisation.

The furnace particularly described enables workpieces at high temperature to be cooled in a simple, but accurately controllable, manner to a required temperature (which may be room temperature) while remaining in the atmosphere of protective gas. Consequently the need for charge transfer and the risk of oxodisation, are obviated.

WHAT WE CLAIM IS: 1. A batch-type furnace for heat treating workpieces, said furnace comprising an insulated furnace jacket which has a closable loading and unloading opening associated with a charge compartment which is heatable under a protective gas atmosphere which circulates within the furnace, and a cooling system for the protective gas comprising a water-cooled finned tube cooler installed in a housing forming an extension of the furnace jacket, the housing communicating with the charge compartment via an opening, and a closure device for closing the opening, said device being controllable to vary the quantity of gas flowing through the housing and thereby the cooling effect.

2. A furnace according to claim 1, wherein the closure device comprises a closing member which can be raised and lowered in a controlled manner between an open and a closed position, the closing member being seated against the internal surface of the furnace jacket when in its closed position.

3. A furnace according to claim 2.

wherein the closing member is located at one end portion of a rod which extends centrally through the housing. and the other end portion of the rod is connected to a lifting cylinder secured on the housing.

4. A furnace according to claim 3.

wherein the rod is hollow and forms a conduit for feeding the protective gas centrallv into the cooler.

5. A furnace according to any one of claims 1 to 5. further comprising a blower and ducting system for providing forced circulation of the protective gas.

6. A batch-type heat treatment furnace for heat treatment of workpieces under a protective gaseous atmosphere which circu lates within the furnace. said furnace comprising a furnace jacket. a charge compartment. a housing mounted on the furnace jacket. the housing opening into the charge compartment via an aperture such that the housing lies on the gas circulation path.

water-cooled cooling means within the housing for cooling gas flowing through the housing. and closure means for closing the aperture. said closure means being controllable to vary the quantity of gas flowing through the housing and thereby to vary the cooling effect.

7. A furnace according to claim 6. further comprising means for providing forced circulation of the gas.

8. A furnace substantially as hereinbefore described with reference to the accompanying drawing.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. remaining in the atmosphere of protective gas. Consequently the need for charge transfer and the risk of oxodisation, are obviated. WHAT WE CLAIM IS:

1. A batch-type furnace for heat treating workpieces, said furnace comprising an insulated furnace jacket which has a closable loading and unloading opening associated with a charge compartment which is heatable under a protective gas atmosphere which circulates within the furnace, and a cooling system for the protective gas comprising a water-cooled finned tube cooler installed in a housing forming an extension of the furnace jacket, the housing communicating with the charge compartment via an opening, and a closure device for closing the opening, said device being controllable to vary the quantity of gas flowing through the housing and thereby the cooling effect.

3. A furnace according to claim 2.

4. A furnace according to claim 3.