GB2197347A

GB2197347A - Heat-treatment of small parts

Info

Publication number: GB2197347A
Application number: GB08725066A
Authority: GB
Inventors: Karl Heinz Edler
Original assignee: Ipsen International GmbH
Current assignee: Ipsen International GmbH
Priority date: 1986-11-14
Filing date: 1987-10-26
Publication date: 1988-05-18
Anticipated expiration: 2007-10-26
Also published as: GB2197347B; FR2606790A1; FR2606790B1; ES2007744A6; GB8725066D0; DE3639052A1

Abstract

Small parts are heat-treated in a protective atmosphere and then immersed in an oil bath (5) in which they are quenched. The protective gas enriched with oil vapour, from above the oil bath is extracted, the oil is subsequently separated from the extracted gas and returned to the oil bath and the protective gas, which is now free of oil vapour, is also returned to the heat-treatment chamber (1). <IMAGE>

Description

SPECIFICATION Heat-treatment of small parts The present invention relates to a method for the heat-treatment of small parts, in which the parts are heat-treated in a protective atmosphere and then immersed in an oil bath, in which they are quenched. The invention also relates to apparatus for carrying out the method.

Heat-treatment furnaces for the heat-treatment of small metallic parts are known. The small parts are carburized in a protective atmosphere in these furnaces. The small parts which are thus treated are subjected to an aftertreatment in a subsequent oil quenching chamber comprising an oil quenching bath in which the carburized small parts are immersed and thus quenched. For this purpose the furnaces may either be operated continuously with an open quenching shaft or on a batch process basis with an attached oil quenching chamber. In both cases the operation is carried out in a protective atmosphere.

The known apparatus and methods for the heat-treatment of small metallic parts have the disadvantage that the oil vapours produced by the oil quenching bath in the oil quenching chamber diffuse into the heat-treatment chamber. Large amounts of oil vapour escape particularly when the hot parts are immersed in the oil quenching bath. These oil vapours contaminate the protective atmosphere in the heat-treatment chamber and the small parts which are to be heat-treated. This is caused by the drops of oil settling on the latter. The entire heat-treatment result is therefore impaired.

In order to condition or to keep the oil vapours out of the furnace chamber, the protective gas was previously pumped in large quantities through the chambers, so that the oil vapours arising in the oil quenching chamber are kept away from the heat-treatment chamber by the protective gas flow and can be burnt off. As the protective gas is therefore used used as a circulation gas, a quantity is constantly required which is greater than that needed for the actual heat-treatment. This entails considerable expense. Furthermore, fresh oil has to be continuously supplied to the oil quenching bath due to the burning-off process.

The present invention provides a method for the heat-treatment of small parts, comprising heat-treating the parts in a protective gas atmosphere and then immersing them in an oil bath, in which they are quenched, extracting the gas enriched with oil vapour from above the oil bath, separating from the extracted gas, the oil and the protective gas atmosphere, and recycling the oil to the oil bath and the gas to said protective atmosphere.

The advantage of the above defined method is that the protective gas and the oil are circulated in separate circuits with, on the one hand, cleaned protective gas being returned to the protective atmosphere of the heat-treatment chamber and, on the other, the separated oil also being returned to the oil bath.

This reults in a flow circulation of the protective gas which prevents the oil vapours rising above the oil bath from entering the heattreatment chamber, as these are immediately extracted. Furthermore, as the protective gas is recycled, only a small amount is consumed.

The oil consumption is similarly reduced by recycling the oil. The overall result is therefore faster conditioning of the protective gas.

The extraction operation preferably starts before the small parts are immersed in the oil bath, as considerable quantities of oil vapour, which contaminate the protective atmosphere, are particularly produced when the hot small parts are first immersed in the oil quenching bath.

It is also preferable to monitor and, if necessary, adjust the composition of the recycled protective gas. This enables the protective atmosphere in the heat-treatment chamber to be continuously monitored in a simple manner, without further discharge or feed pipes being required.

The invention also provides apparatus for carrying out the heat treatment of small parts, comprising a heat-treatment chamber for containing a protective gas atmosphere, and a quenching chamber comprising an oil bath adjacent said heat treatment chamber, an extraction device opening into the quenching chamber for extracting gas enriched with oil vapour from above the oil bath, a separating device for separating the oil from the extracted gas, and respective return pipes leading from the separating device to the heat-treatment chamber for the protective gas, and to the oil bath for the separated oil.

The extraction device is preferably a fan which is preferably arranged in the return pipe leading to the heat-treatment chamber. A fan of this type enables the gas enriched with oil vapour in the oil quenching chamber to be extracted in a technically simple manner. Oiling up of the fan is prevented by arranging it in the return pipe leading to the heat-treatment chamber.

In a preferred embodiment the separating device comprises condensing coils through which a coolant, for example water, flows and past which the extracted gas is guided. A separating device of this kind with condensing coils is technically very easy to construct and operates reliably.

If a door is provided between the heat-treatment chamber and the oil quenching chamber, the operation by which the door- is opened is preferably linked with the actuation of the extraction device. In this case advantage is taken of the fact that no oil vapour can dif fuse into the heat-treatment chamber from the oil quenching chamber when the door is closed. This means there is no danger of contamination and therefore no need to carry out an extraction operation and an appropriate cleaning operation. It is only when the door is opened that there is a risk of the oil vapours entering the heat-treatment chamber from the oil quenching chamber.This risk is particularly great if the small parts are immersed in the oil quenching bath immediately after heat-treatment, in which case large quantities of oil vapour, which can very easily enter the heattreatment chamber, are produced due to the rise in temperature of the oil. However by linking the actuation of the extraction device with that of the door, the rising oil vapours are immediately extracted.

According to a further preferred feature of the apparatus, it is proposed that the oil quenching chamber be provided with a funnel in its extraction area, in order to improve the extraction operation in the flow guideway.

Finally, according to a development of the apparatus, it is proposed that a device for monitoring and adjusting the composition of the gas of the protective atmosphere be provided in the return pipe of the heat-treatment chamber. This enables the composition of the protective gas to be monitored and, if necessary, adjusted without any great extra cost or additional auxiliary devices. As the protective gas is constantly circulating due to the extraction operation, it is also possible for the composition to be constantly monitored and adjusted. This means that the heat-treatment of the small metallic parts can be continued in a very consistent manner over a long period.

An embodiment of the heat-treatment method and apparatus will now be described, by way of example only, with reference to the accompanying diagrammatic drawing which is a side view of the apparatus with a heattreatment chamber and an oil quenching chamber for the heat-treatment of small metallic parts.

The drawing shows a heat-treatment chamber 1 which (on the left-hand side of the drawing) has a door 2 through which small metallic parts are fed into the heat-treatment chamber 1, where they are subjected to heattreatment. This heat-treatment takes place in an atmosphere of protective gas, and an inlet 3 for the protective gas can be seen in the upper area of the heat-treatment chamber. The direction of flow of the protective gas through the heat-treatment chamber 1 is represented by the arrows.

An oil quenching chamber 4 with an oil bath 5 adjoins the heat-treatment chamber 1 (on the right-hand side in the drawing). This oil quenching chamber 4 is separated from the heat-treatment chamber 1 by a door 6. A further door 7 is provided for removing the small parts from the oil quenching chamber 4. The carburized small metallic parts are subjected to an aftertreatment in the form of quenching in this oil bath 5 in the oil quenching chamber 4.

The oil quenching chamber 4 has a burningoff device 8 at the top.

The oil quenching chamber 4 is also connected to an extraction device and an oil separating device 11. The function of these is to extract the protective gas which is enriched with and contaminated by oil vapour from above the oil bath 5 and to separate the oil contained in the gas. For this purpose a fan 9 is provided which extracts the protective gas enriched with oil vapour in the oil quenching chamber 4 via a pipe 10 and feeds it to the separating device 11. This device 11 may, for example, comprise condensing coils through which a coolant (for example water) flows, past which the extracted gas is guided and on which the oil in the oil gas mixture condenses.

This condensed oil is returned to the oil bath 5 in the oil quenching chamber 4 by means of a return pipe 12. In order to improve the flow of the gas enriched with the oil vapour from above the oil quenching bath 5 into the pipe 10, the latter opens into the oil quenching chamber 4 via a funnel 13.

As the contaminated extracted gas is freed from the oil vapour in the separating device 11 and is therefore pure again, it is returned to the heat-treatment chamber 1 through a return pipe 14. The fan 9 is also connected in this return pipe 14.

The actuation of the fan 9 can be linked with the actuation of the door 6 between the heat-treatment chamber 1 and the oil quenching chamber 4, so that, when the door 6 is opened for a batch of carburized small parts to be conveyed from the heat-treatment chamber 1 into the oil quenching chamber 4, the fan 9 is also started.

A device for monitoring and adjusting the composition of the cleaned protective gas may also be provided in the return pipe 14 between the separating device 11 and the heattreatment chamber 1. The composition of this gas is preferably monitored and adjusted by the furnance control system.

The described apparatus creates a circuit for the protective gas which is formed by the heat-treatment chamber 1, the oil quenching chamber 4, the pipe 10, the separating device 11, the return pipe 14 and the fan 9. This prevents oil vapours rising above the oil bath 5 from entering the heat-treatment chamber 1 and thus contaminating the latter's protective atmosphere and the small parts which it contains. The oil vapours which are produced are immediately removed by the extraction circuit and returned to the oil bath 5 via the return pipe 12.

Claims

1. A method for the heat-treatment of small parts, comprising heat-treating the parts in a protective gas atmosphere and then immersing them in an oil bath, in which they are quenched, extracting the gas enriched with oil vapour'from above the oil bath, separating from the extracted gas, the oil and the protective gas, and recycling the oil to the oil bath and the gas to said protective atmosphere.

2. A method according to claim 1, wherein the extraction operation starts before any parts have been immersed in the oil bath.

3. A method according to claim 1 or 2, wherein the composition of the recycled protective atmosphere is monitored and, if necessary, adjusted.

4. A method according to claim 3, wherein the adjustment is carried out in conjunction with a furnace control system.

5. Apparatus for carrying out the heat treatment of small parts, comprising a heattreatment chamber for containing a protective gas atmosphere, and a quenching chamber comprising an oil bath adjacent said heat treatment chamber, an extraction device opening into the quenching chamber for extracting gas enriched with oil vapour from above the oil bath, a separating device for separating the oil from the extracted gas, and respective return pipes leading from the separating device to the heat-treatment chamber for the protective gas, and to the oil bath for the separated oil.

6. Apparatus according to claim 5, wherein the extraction device is a fan.

7. Apparatus according to claim 6, wherein the fan is arranged in the return pipe leading to the heat-treatment chamber

8. Apparatus according to any one of claims 5-7, wherein the separating device comprises condensing coils through which a coolant flows and past which the extracted gas is guided.

9. Apparatus according to any one of claims 5-8, wherein a door is provided between the heat-treatment chamber and the oil quenching chamber, the operation of the door being linked with the actuation of the extraction device.

10. Apparatus according to any one of claim 5-9, wherein the oil quenching chamber is provided with a funnel in the area from which the gas is extracted.

11. Apparatus according to any one of claims 5-10, further comprising a device for monitoring and adjusting the composition of the protective gas in the return pipe leading to the heat treatment chamber.

12. A method for the heat-treatment of small parts substantially as herein described with reference to the accompanying drawing.

13. Apparatus for the heat-treatment of small parts substantially as herein described with reference to the accompanying drawing.