IE904330A1

IE904330A1 - A cylindrical high temperature induction furnace

Info

Publication number: IE904330A1
Application number: IE433090A
Authority: IE
Inventors: Dietmar Bolsch
Original assignee: Euratom
Priority date: 1989-11-30
Filing date: 1990-11-30
Publication date: 1991-06-05
Also published as: PT96040B; DE59003236D1; LU87628A1; ES2045727T3; PT96040A; EP0430138B1; IE64252B1; DK0430138T3; EP0430138A1

Abstract

The invention relates to a cylindrical high-temperature induction furnace for uniaxial tests in air and above 1000 DEG C on electrically insulating materials, having a radio-frequency generator for generating an RF field and having a cylindrical susceptor made of an electrically conductive material, which is heated by the induction field and, for its part, heats the test materials arranged in it by radiation. According to the invention, the furnace can be split into two identical halves along the furnace axis and contains an RF coil (5) in each half. In consequence, it is possible to mount the furnace around a sample which has already been clamped into a test set, which results in a very compact construction. <IMAGE>

Description

The invention relates to a cylindrical high temperature induction furnace for uniaxial tests in air and above 1000°C for electrically insulating materials, comprising a high frequency generator for generating a high frequency field and a susceptor in the shape of a cylindrical tube made from an electri10 cally conductive material, which is heated by the induction field and which itself heats by radiation the test materials to be disposed therein.

High frequency induction heating has been used for years for heating metallic materials. It allows the quick upheating of a specimen. If, however, the specimen consists of electrically insulating materials such as ceramics like aluminium oxide or silicium nitride, a direct heating from room temperature upwards is not possible because of the high electric resistance.

In this case, an electrically conductive transmitter or susceptor is used, which itself surrounds the specimen to be heated and heats it by heat radiation.

For uniaxial test, such as for example fatigue tests or creep tests, the specimen is brought into the tube-shaped susceptor and then clamped with its two ends in a test apparatus which produces the desired mechanical stresses. To this end, the specimen must protrude at both ends out of the suspeceptor and out of the whole furnace so that it can be connected to the test apparatus.

It is the aim of the invention to conceive a furnace as cited above so that the specimen needs not be mounted any more together with the furnace in the test apparatus, but that the furnace can be mounted in the test apparatus after the latter - 2 has been supplied with the specimen, and this without requiring an additional free space on both sides of the furnace for mounting purposes .

This aim is attained by the furnace as characterized in claim 1. For preferred embodiments of this furnace, reference is made to the sub-claims.

The invention will now be explained more in detail by means of 10 the drawings.

Figure 1 shows in perspective the elements of a furnace according to the invention.

Figure 2 shows a test apparatus in which one half of the furnace according to the invention has already been mounted.

The furnace, whose elements are shown in Figure 1, uses the principle of an indirect high frequency heating of a specimen {not shown), in which is disposed a susceptor tube consisting of two half-tubes 1, 2. The susceptor is for example made of silicium carbide or (for even higher temperatures) of zirconium boride ZrB^· As Figure 1 shows, the furnace can be mounted from two identical halves, one half being shown assembled in the upper part to the left of the Figure, i.e. ready for mounting in a test apparatus, whereas the elements of the other half are shown in detail. The basic concept of the invention consists in arrang30 ing the furnace and all of its elements divisibly along a plane which extends through the axis of the susceptor tube 1, and through the axis of the specimen to be disposed therein. With this concept it is possible to firstly mount the specimen in the test apparatus and then to mount the furnace from both sides around the specimen. - 3 The furnace is mechanically held by a chassis which consists of two half-chassis 3 and 4, which comprise each a semicircular base plate and a top plate connected by bars to the base plate. The active elements of the furnace are mounted in the interspace between the two plates and all interstices between these elements are filled with a resilient felt of ceramic fibres, so that different expansions of the elements do not lead to their breaking. The elements are slightly pressed by the felt layers so that they are held in the chassis without additional measures such as screws or gluing.

As shown in the right half of Figure 1, the elements of one half-furnace comprise a susceptor half-tube 2, an entire high frequency coil 5 and two coil carrier half disks 6 and 7. The coil 5 is fed by a high frequency generator 16. It extends along a half circular cylinder and has, in the mounted state, an axis which extends perpendicularly to the axis of the tube 2. The coil consists of a water-cooled copper tube and is introduced into a cavity 8 in one of the coil carrier halfdisks, for example 6. The cavity 6 is arranged in such a way that also the coil feeds can be placed laterally therein. The carrier also has a recess along the furnace axis in which the half susceptor tube is loosely disposed.

The coil carriers have a honeycomb structure and withstand as well the high inner furnace temperature as the high temperature gradients to the outside without requiring forced cooling. Furthermore, there is no risk of cracks in the structure due to the high heating speed, since the honeycomb walls are very thin.

Next, thin felt mats 9 are placed on the coil carrier half disks 6. These felt mats are arranged in such a way that there remains space for the coil and the susceptor. The thickness of - i the felt layer depends on the desired length of the furnace, i.e. of the susceptor tube, such that the arrangement tightly fits into the half chassis 4 when the second coil carrier half disk 7 is mounted on top.

The left half of Figure 1 is ready for mounting in a test apparatus. Figure 2 shows a detail of this apparatus which is not part of the invention. A stress specimen 10 is clamped between two clamp heads of the test apparatus which are sup10 plied with cooling heads 11, 12 and hidden by the latter. As can be seen in figure 1, the half-furnace is provided with a support arm 13 projecting upwards, which allows to fix the furnace by suspending it at the upper cooling head 11 and which further permits the adjustment of the longitudinal fur15 nace axis with respect to the longitudinal specimen axis.

The second half of the furnace is fixed in the same way after its assembly via a corresponding half arm 14 (Figure 1) to the cooling head 11 and secured by screws to the first half. It can be seen in Figure 2 that an access to the clamping head in which the specimen is clamped is not possible and not even necessary, since the furnace is only added after the mounting of the specimen. After the mounting of the furnace, the coil ends are coupled to a high frequency generator 16 and a cool25 ing circuit.

It is further possible to introduce thermocouples through the honeycomb structure into the furnace or also to provide channels for the insertion of measuring arms of an extensometer 15 (figure 2) or even an observation channel for a pyrometer or for a direct opto-microscopic observation of the specimen surface (for example fatigue crack growth tests).

The invention is not limited in all details to the described embodiment. This applies in particular to the kind of the test apparatus and the instrumentation of the furnace. The suscep tor tube can have cylindrical shape, as shown, or else have variable inner diameter which is specially conceived for con stant temperatures. In addition, the furnace is not only appropriate for isothermal tests, but also thermocyclical or combined thermomechanical tests are possible.

Claims

1. A cylindrical high temperature induction furnace for uniaxial test in air and above 1000°C for electrically insulating 5 materials, comprising a high frequency generator for generating a high frequency field and a susceptor in the shape of a cylindrical tube made from an electrically conductive material, which is heated by the induction field and which itself heats by radiation the test materials to be disposed therein, 10 wherein the high frequency generator feeds two mutually indepe'Sent coils which are electrically parallel-connected and are each disposed in a half-cylindrical plane which is coaxial to the cylinder axis, and also the susceptor is made of two half tubes, the intersection planes of the half-cylindrical 15 plane and of the half-tubes coinciding and including the furnace axis .

2. A high temperature furnace according to claims 1, wherein the coil axes run perpendicularly to the intersection planes 20 and through the furnace axis.

3. A high temperature furnace according to one of claims 1 and 2, wherein the coils are embedded each in fitted cavities of at least one honeycomb-type carrier made of ceramic material.

4. A high temperature furnace according to one of claims 1 to 3, wherein the elements of the furnace are mounted in a metal chassis consisting of two halves which are joined along the intersection plane of the susceptor.

5. A high temperature furnace according to one of claims 1 to 3, wherein in the interstices between the different elements of the furnace felt layers of ceramic fibres are provided for compensating size changes due to thermal effects. - 7

6. A high temperature furnace according to any preceding claim substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.