GB1580932A

GB1580932A - Induction-heated temperature equalization furnace or zone

Info

Publication number: GB1580932A
Application number: GB24845/77A
Authority: GB
Original assignee: Otto Junker GmbH
Current assignee: Otto Junker GmbH
Priority date: 1976-06-25
Filing date: 1977-06-14
Publication date: 1980-12-10
Also published as: AT356393B; DE2628657A1; ATA426877A; FR2356108B3; JPS617712B2; FR2356108A1; JPS5320141A; DE2628657C2

Description

(54) INDUCTION-HEATED TEMPERATURE EQUALIZATION FURNACE OR ZONE (71) We, OTTO JUNKER GmbH, of 5107 Simmerath, Federal Republic of Germany, a Limited Liability Company registered under the Laws of the Federal Republic of 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 : - This invention relates to an induction-heated temperature equalization furnace or zone for metal workpieces of relatively low thermal conductivity, such as brass, cupronickel or steel and their alloys, which are continuously heated in a heating-up furnace upstream of the equalization furnace or zone.

In the course of the overall heating process a temperature equalization phase of this type is required to follow the phase of "heating up" metal workpieces which are to be continuously heated, particularly when the workpieces for press-forming, forging or rolling proposes must be heated to elevated temperatures at a high rate, as is possible, for example, in the case of inductive heating.

In this case, if the material has relatively poor thermal conductivity, the heat supplied to the marginal zone of a workpiece during the heating-up phase cannot spread fast enough into the interior of the workpiece, and the marginal zone would overheat towards the end of the heating process if the heat input were not reduced. This is particularly true when the workpieces heated are made of brass, cupronickel or steel or steel alloys. For these reasons, therefore, temperature equalization furnaces or zones differ from the heating-up furnaces or zones in that the power expended on the workpiece is substantially lower. The temperature may conveniently be used as a reference variable for controlling the power supply, with the result that the temperature regulating means acquires special significance.

Resistance-heated, fuel-fired or inductionheated furnaces arranged downstream of the heating-up furnaces and often termed soaking chambers have already been used in continuous heating plant.

In resistance-heated furnaces the heat transfer to the workpiece at high temperatures is almost entirely by radiation, and the heating elements must therefore always be somewhat hotter, so that they can transmit thermal energy to the workpiece undergoing temperature equalization. For this reason, particularly at elevated temperatures, the sensitivity of and wear on the heating elements is a disadvantage in such furnaces. Also, it is difficult to arrange the heating elements so that the workpieces are irradiated and heated uniformly on all sides. The temperature regulating process in these turnaces, moreover, is relatively slow, so that the temperatures of individual workpieces are less precise and uniform.

Fuel-fired soaking chambers also suffer from relatively imprecise temperature control, since the flame gases, which burn at high excess temperatures, make if difficult to measure the temperatures of the workpieces accurately for regulation purposes.

An alternative possibility is direct induction heating of the workpieces towards the end of heating, during temperature equalization at reduced power. In this case, however, the problem lies in rendering the temperature control dependent on the actual temperature of the various workpieces in the equalization furnace or zone. This can be done either optically or by means of thermocouples which are pressed on to the workpieces and then removed when the workpieces move on. In the case of optical measurement, any differences in the emission factors of the surfaces of the various ingots may impede accurate temperature measurement.

This occurs especially, for example, in the case of work made of special brass alloys. When heating light alloy work, attempts have been made to render the radiation factor uniform by special measures, for example by painting the measuring area, to overcome this difficulty in optical temperature measurement. A method of this type is described in German Auslegeschrift 1,145,383.

The problem of making the temperature con trol as accurate as possible is accompanied in temperature equalization furnaces by the probelm of conveying the workpieces, which are already at high temperatures, through the equalization furnace or zone, which is also at a high temperature. With the horizontal arrangement generally preferred for intermittent or continuous heating, the workpieces usually slide on rails or slip plates supported on the ceramic lining of the furnace, causing considerable wear due to the forces acting directly on the relatively unresilient ceramic material.

The present invention enables the provision of an induction-heated temperature equalization furnace or zone which is robust and particularly suitable for elevated temperatures, requires little maintenance, and, owing to its special design, permits accurate and reliable regulation of the temperature for maximum uniformity of heating up and heating through in the final phase of heating of the workpieces which are to be continuously heated.

According to the present invention, there is provided a temperature equilization furnace comprising a heating muffle of heat resistant metal having a wall thickness of at least 12 mm, an inductor surrounding the muffle, thermal insultation means between the muffle and the inductor, temperature determining means for determining the muffle temperature, regulating means for regulating the temperature of the equilization furnace in response to the muffle temperature and heat shield means for reducing heat loss from a wokrpiece discharge port. Preferably, the movable heat shield means comprises a movable heat shield at the discharge port of the furnace, which shield can be moved to allow a workpiece to be discharged and can be returned to the original position thereof after each discharge opertaion.

The inductor advantageously comprises a plurality of inductor portions which may be axially aligned.

In a preferred embodiment, only part of the muffle is surrounded by the inductor, the remainder of the muffle being provided with additional thermal insulation means.

The muffle is conveniently divided into axial portions having different wall thicknesses.

It is further preferred that the muffle be of heat resistant steel that the thermal insulation means between the muffle and the inductor be of fibrous ceramic material and that one or more thermocouples connected to a temperature regulator are mounted on the periphery of the muffle.

It will be understood that the term "heatresistant" as applied, for example, to a metal means that the metal is resistant to heat at a temperature at which the furnace is intended to be operated.

The principal advantages which the present invention enables are as follows: 1. Because of the relatively high wall thickness of the heating muffle, so much heat is generated in the muffle by induction that, combined with the heat exchange due to radiation between the workpiece and muffle and the heat generated directly in the muffle, the temperature variation in the muffle is particularly suitable for use as a reference variable in the regulation of the temperature to be produced in the workpiece.

2. The thick-walled muffle acts not only as a heating element, but as a structural element which is resistant to mechanical stresses and which can serve either as a direct support for the workpieces to be pushed through the furnace or as a support for a readily exchangeable slip plate.

3. The workpieces are almost completely enclosed by the muffle ensuring even heating.

4. The invention also has the advantage that even workpieces of substantially small diameter or thickness can be efficiently heated or kept hot, largely irrespective of the inductor diameter.

5. Other advantages of the invention are the rapidity with which it can be prepared for operation and the adaptability of the furnace or zone to intermittent operation.

As described above, in one embodiment of the invention, the inductor may comprise a plurality of inductor portions. The temperatures of different portions of the muffle and hence of the furnace may thus be regulated independently of one another. Since the thermal energy to be transmitted to the workpieces is substantially lower in the equalization furnace or zone than in the heating-up furnace upstream of it, the muffle may, in accordance with another embodiment, be covered by the inductor or inductor portions along only part of its length. The uncovered muffle parts in this case are provided with additional thermal insultaion. In this way the material required for the inductor can be reduced without causing uneven heating of the muffle.

To allow the direct influence of the electromagnetic field of the inductor on the heated workpieces to be varied, the muffle, according to another embodiment, may be subdivided axially into portions of different wall thickness.

One embodiment of the invention has a muffle of heat-resistant steel, with thermal insulation consisting of fibrous ceramic material interposed between the muffle and the inductor, one or more thermocouples connected to a temperature regulator being mounted on the periphery of the muffle.

For a better understanding of the present invention, and to show how the same may be put into effect, reference will now be made to the accompanying drawings, in which: Figure 1 shows a longitudinal section through a temperature equalization furnace embodying the invention and, axially offset relative to this furnace, the discharge end of the associated heating-up furnace; Figure 2 is a longitudinal section through the discharge end of a metal ingot heating-up plant with a temperature equalization zone built on immediately downstream; and Figure 3 is a cross section through a temperature equalization furnace or zone embodying the invention.

Figure 1 shows a temperature equalization furnace 1 which is surrounded by a framework 2. The furnace interior 3 is formed by a heating muffle 4 which is made of heat-resistant metal, for instance steel, and has a wall thickness of at least 12 mm, preferably 20 mm. The muffle 4 is embraced by thermal insulation 5 consisting of ceramic felt mats coiled in one or more plies. The muffle 4 is heated by means of an inductor 6 which can be connected to a current source by busbars 7 and 8. The water to cool the inductor 6 is fed through a manifold 9 (Figure 3) and supply hoses 10 to the water inlet conditions 11 for the inductor and back through the water outlet connections 12, hoses 13 and a manifold 14. The inductor 6 is fixed in position by means of tubular beams 15 to 18 fastened to the end faces of the framework 2 by angle plates 19. Inside the furnace the ingots 20 which are to undergo heating or temperature equalisation lie on a slip plate 21 of heat-resistant steel supported on the muffle 4.

In the embodiment illustrated in Figure 1 heat shields 22 and 23 are provided at the discharge and feed ports and can be pivoted sideways out of the path of the workpieces, for example by means of a pneumatic drive (not shown). A thermocouple 25 can detect the temperature in the muffle 4. The temperture equalization furnace 1 in this embodiment is offset relative to the heating-up furnace 25.

The ingots 20 to be heated are delivered from the heating-up furnace 25 on to a delivery table 26 and thence to a feed table 27 for the temperature equalization furnace, whereupon they are pushed into the furnace interior 3 by a pusher ram 28, the heat shields 23 and 22 having respectively revealed the feed port and discharge port of the equalization furnace 1.

At the same time the ingot 20a at the discharge end is pushed out of the furnace interior and passed by further delivery and conveying means 29 to a forming device for further processing.

In the embodiment shown in Figure 2, the temperature equalization furnace 1 is a temperature equalization zone immediately downstream of and coaxial with the heating-up furnace 25, so that the workpieces 20 in the heating-up furnace 25 and in the interior 3 of the equalization zone form a single ingot column.

In this case the muffle 4 is divided into two muffle portions 4a and 4b, the portion 4a at the delivery end having a greater wall thickness than the portion 4b at the entry end. This ensures that proportionately more thermal energy is supplied by the electromagnetic field to those workpieces which have undergone less temperature equalization than to those at the discharge end which have undergone more equalization. The thermocouple 24 is attached to the muffle portion 4a.

To minimize the effect of the electromagnetic fields of the inductors 6 of the temperature equilization furnace 1 and an inductor 30 of the heating-up furnace 25 on one another, the inductor 6 is spaced from the inductor 30. That part of the muffle not covered by the inductor 6 at this point is provided with additional thermal insulation 31, to keep the heat losses here as low as possible.

WHAT WE CLAIM IS: 1. A temperature equilization furnace comprising a heating muffle of heat resistant metal having a wall thickness of at least 12 mm, an inductor surrounding the muffle, thermal insulation means between the muffle and the inductor, temperature determining means for determining the muffle temperature, regulating means for regulating the temperature of the equilization furnace in response to the muffle temperature and heat shield means for reducing heat loss from a workpiece discharge port.

2. A furnace according to Claim 1, wherein the heat shield means comprises a movable heat shield at the discharge port of the furnace which shield can be moved to allow a workpiece to be discharged and can be returned to the original position thereof after each discharge operation.

3. A furnace according to Claim 1 or 2, wherein the inductor comprises a plurality of inductor portions.

4. A furnace according to Claim 5, wherein the inductor portions are axially aligned.

5. A furnace according to any one of Claims 1 to 4, wherein the temperatures of a plurality of portions of the furnace may be regulated independently.

6. A furnace according to any one of Claims 1 to 5, wherein only part of the muffle is surrounded by the inductor, the remainder of the muffle being provided with additional thermal insulation means.

7. A furnace according to any one of Claims 1 to 6, wherein the muffle is divided into axial portions having different wall thicknesses.

8. A furnace according to any one of claims 1 to 7, wherein the muffle is of heat-resistant steel, the thermal insulation means between the muffle and the inductor is of fibrous ceramic material, and one or more thermocouples connected to a temperature regulator are mounted on the periphery of the muffle.

9. A furnace substantially as herein described with reference to, and as shown in the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. discharge end of a metal ingot heating-up plant with a temperature equalization zone built on immediately downstream; and Figure 3 is a cross section through a temperature equalization furnace or zone embodying the invention. Figure 1 shows a temperature equalization furnace 1 which is surrounded by a framework 2. The furnace interior 3 is formed by a heating muffle 4 which is made of heat-resistant metal, for instance steel, and has a wall thickness of at least 12 mm, preferably 20 mm. The muffle 4 is embraced by thermal insulation 5 consisting of ceramic felt mats coiled in one or more plies. The muffle 4 is heated by means of an inductor 6 which can be connected to a current source by busbars 7 and 8. The water to cool the inductor 6 is fed through a manifold 9 (Figure 3) and supply hoses 10 to the water inlet conditions 11 for the inductor and back through the water outlet connections 12, hoses 13 and a manifold 14. The inductor 6 is fixed in position by means of tubular beams 15 to 18 fastened to the end faces of the framework 2 by angle plates 19. Inside the furnace the ingots 20 which are to undergo heating or temperature equalisation lie on a slip plate 21 of heat-resistant steel supported on the muffle 4. In the embodiment illustrated in Figure 1 heat shields 22 and 23 are provided at the discharge and feed ports and can be pivoted sideways out of the path of the workpieces, for example by means of a pneumatic drive (not shown). A thermocouple 25 can detect the temperature in the muffle 4. The temperture equalization furnace 1 in this embodiment is offset relative to the heating-up furnace 25. The ingots 20 to be heated are delivered from the heating-up furnace 25 on to a delivery table 26 and thence to a feed table 27 for the temperature equalization furnace, whereupon they are pushed into the furnace interior 3 by a pusher ram 28, the heat shields 23 and 22 having respectively revealed the feed port and discharge port of the equalization furnace 1. At the same time the ingot 20a at the discharge end is pushed out of the furnace interior and passed by further delivery and conveying means 29 to a forming device for further processing. In the embodiment shown in Figure 2, the temperature equalization furnace 1 is a temperature equalization zone immediately downstream of and coaxial with the heating-up furnace 25, so that the workpieces 20 in the heating-up furnace 25 and in the interior 3 of the equalization zone form a single ingot column. In this case the muffle 4 is divided into two muffle portions 4a and 4b, the portion 4a at the delivery end having a greater wall thickness than the portion 4b at the entry end. This ensures that proportionately more thermal energy is supplied by the electromagnetic field to those workpieces which have undergone less temperature equalization than to those at the discharge end which have undergone more equalization. The thermocouple 24 is attached to the muffle portion 4a. To minimize the effect of the electromagnetic fields of the inductors 6 of the temperature equilization furnace 1 and an inductor 30 of the heating-up furnace 25 on one another, the inductor 6 is spaced from the inductor 30. That part of the muffle not covered by the inductor 6 at this point is provided with additional thermal insulation 31, to keep the heat losses here as low as possible. WHAT WE CLAIM IS:

1. A temperature equilization furnace comprising a heating muffle of heat resistant metal having a wall thickness of at least 12 mm, an inductor surrounding the muffle, thermal insulation means between the muffle and the inductor, temperature determining means for determining the muffle temperature, regulating means for regulating the temperature of the equilization furnace in response to the muffle temperature and heat shield means for reducing heat loss from a workpiece discharge port.