GB2054330A - Microwave heat treatment apparatus - Google Patents

Abstract

The heat treatment of articles on an industrial scale has been delayed for lack of suitable equipment. Apparatus is now provided for this purpose, which comprises a series of bases 11 arranged in carousel form so as to step successively through a loading and unloading stage 26, a treatment stage 27 and first and second cooling stage 33 and 34 respectively. At the treatment stage a cover 13 is lowered over the base to form a treatment chamber, with a microwave seal between the base 11 and cover 13. The cover 13 carries microwave generators 38 and also motors 39 for rotating randomising reflectors. The seal comprises a flange 43 on the base, bridging pieces 44, 45 on the cover and beryllium copper contacts 48, 49. The top of the flange engages an elastomer 51 having embedded conductor wires. <IMAGE>

Description

SPECIFICATION Heat treatment apparatus This invention relates to heat treatment apparatus.

Our co-pending application No. 7924783 claiming priority from application 7830117, and entitled "Improvements in or relating to Grinding Products, was filed simultaneously with our application 7924782 from which the present application claims priority. Application 7924783 describes and claims the use of microwave heating for the drying, vitrification and curing of vitreous or organic grinding wheels and other grinding products.

Microwave heating has been known for a long time but its application to large scale industrial production methods has been delayed by lack of suitable applicators adapted for the needs of industry.

The present invention relates to equipment which, although primarily designed for use in the heat treatment of grinding products for drying, firing or curing, is also applicable in a wide range of industries to which batch or semi-continuous production techniques may be applied, while maintaining safety standards for the operatives.

According to the present invention, there is provided apparatus for carrying out heat treatment by the application of microwave energy; comprising a base member adapted for the reception of articles to be heat treated, a cover member adapted to fit over the base member, a microwave seal around the junction of the base member and cover member and microwave generators mounted on the cover member to provide sources of microwave energy.

Preferably, a plurality of base members are located on a carousel for successive engagement by the cover member so that a semicontinuous treatment may be achieved.

Preferably, also, the microwave seal comprises resilient conductive contact strips, e.g.

of beryllium copper, located between the base member and the cover member so as to make electrical contact therebetween and arranged in close lateral proximity with adjacent similar strips.

The seal is conveniently located where a flange of the base member extends between two portions of the cover member and includes a row of contact strips between each portion of the cover member and the flange.

In addition the flange may extend close to a bridge portion between the said two portions of the cover member and a further seal to microwave energy may be located in the gap therebetween, e.g. an elastomer with embedded conductor wires. The spacing of the various seal elements may be half the wavelength of the energy to be used. This energy is preferably of approximately 2450MHz frequency, giving a wavelength of about 1 2.2 cm.

The cover may also include a false ceiling of insulating material, e.g. polypropylene.

The invention will be further described with reference to the.accompanying drawings, in which Figure 1 is a plan view of a form of apparatus according to the invention; Figure 2 is an isometric view of the apparatus of Fig. 1 with some parts omitted for clarity of illustration; Figure 3 is a side elevation of a cover member shown in the apparatus of Figs. 1 and 2; and Figure 4 is a sectional view of a microwave seal.

Figs. 1 and 2 show a carousel arrangement for carrying out batch-type or semi continuous heating followed by appropriate cooling. Four separate bases 11 are formed by carriages running clockwise on rails or guides 23 and 24 (omitted from Fig. 2). The carriages are connection to a central drive arrangement 25 for intermittent stepwise movement on the rails or guides 23, 24. At a first station 26, the products are loaded onto the base 11 and then pass to the heat treatment station 27 at which a cover 1 3 is lowered over the base 11 to form an enclosure.A control console is indicated at 28 and suspension means 29 are shown for the cover 1 3. The cover is thus suspended from an appropriate gantry 31 by means of an arm 32, and raising or lowering of the cover 1 3 by a motorised drum 35 is controlled from the console 28, as is the supply of microwave energy. Appropriate interlocks are provided to ensure against application of microwave energy while the cover is up, and appropriate cut outs are also provided to ensure that the energy is switched off in the event of failure.

Where the arrangement is primarily for drying of vitreous products an air supply has to be circulated through the enclosure. By comparing the moisture content of the input and output air, the state of drying can be monitored, and when the output moisture content has been reduced substantially to the input moisture content, drying may be deemed complete.

At the completion of heat treatment, the microwave input is switched off and the cover lifted and the carousel stepped round once more so as to put a fresh load of products into the heating position. From the heating position, the base 11 passes to a first cooling station indicated by the reference 33 and on the next step it passes through a second cooling station indicated by the reference numeral 34. From the second cooling station 34, the base 11 returns to the loading station 26 where the products are first unloaded and then a fresh batch is loaded on during the course of a single heating cycle.

Figs. 2 and 3 show some further details of the cover or hood 13, and in particular Fig. 3 shows an induction fan 36 for the supply of air to the enclosure formed between the hood and the base 11, and an exhaust line is shown at 37. On the roof of the cover or hood 13, there are shown mounted a number of microwave generators 38, preferably for microwave energy at 2450 MHz, and interspersed over the area of this roof there are also motors 39 which rotate deflectors 40 within the enclosure so as to provide further random reflections of the microwave energy.

These rotating parts and the waveguides leading from the microwave generators 38 are concealed by a false ceiling 41, e.g. of a material such as polypropylene which has a low dielectric constant and therefore absords only a negligible amount of the energy fed into the enclosures. This ceiling thus acts as a protection for these parts when the hood or cover 1 3 is raised, and it separates the hot and cold regions of the over.

When the apparatus is used for curing of organic or rubber matrix articles such as grinding wheels or other grinding products, it has been found that it is advantageous to heat the air in the enclosure under the cover 13, since if the products are cured in a cold air ambient they tend to take on a white appearance. Accordingly, it is preferred that an air heater is provided to preheat the air e.g. to 90"C, and also to ensure that any air entering the chamber during curing is also preheated to maintain substantially that air temperature.

A lower part of the cover 13, as iliustrated by reference 42, is arranged to extend over an upturned flange 43 on each base member 11 so as to provide a seal against the microwave energy within the enclosure. Details of this sealing arrangement are shown in Fig. 4. The upturned flange 43 is shown as extending between a lower marginal portion 44 of the cover 1 3 and an additional plate member 45 welded to the cover. The lower marginal portion 44 is cranked outwardly at 46 to form a bridge portion. The member 45 is terminated by a lower inwardly extending flange 47.

Each of the members 44 ano 5 carries a line of closely laterally adjacent contact strips 48 and 49 e.g. of beryllium copper) which are held by rivets 50 at one end and bow outwardly to make resilient electrical contact with the flange 43 and then bow back to make further contact with the supporting member.

In addition, at the point where the upper edge of the flange 43 approaches the bridge portion 46, a silicone elastomer pad 51 extends the length of the bridge portion so as to form a cushion to receive the upper end of the flange 43, and also has embedded therein wires, e.g. of monel metal, to form a further seal against the microwave energy. In order to give the seal the optimum effect, it is preferred that the dimensions marked X, Y and Z are each substantially one-half of the wavelength of the microwave energy so that the seal elements are located substantially at nodes. It will be seen that the seal is substantially in three parts, namely the strips 49, the cushion 51 with its embedded wires, and the strips 48.

in this way, the leakage of microwave energy from the enclosure, even at very high power dissipations, will be kept to extremely low levels, thereby ensuring the safety of personel working in the vicinity of the apparatus.

Automatic control of the overall microwave heat treating process may be achieved by using a pre-programmed micro-processor to achieve a series of treatments at required energy levels, and in particular the various stages may be controlled by infra-red and other detectors to monitor the progress of the treatment and to input their readings to the microprocessor. The cutouts and interlockd may also be controlled by the microprocessors.

Various modifications may be made within the scope of the invention.

Claims (11)

1. Apparatus for carrying out heat treatment by the application of microwave energy, comprising a base member adapted for the reception of articles to be heat treated, a cover member adapted to fit over the base member, means for raising and lowering the cover member off and onto the base member, a microwave seal around the junction of the base member and cover member and microwave generators mounted on the cover member to provide sources of microwave energy.

2. Apparatus as claimed in claim 1, in which a plurality of base members are located on a carousel for successive engagement by the cover member so that semi-continuous treatment may be achieved.

3. Apparatus as claimed in claim 1 or 2, in which the microwave seal comprises resilient conductive contact strips located between the base member and the cover member so as to make electrical contact therebetween and arranged in close lateral proximity with adjacent similar Strips.

4. Apparatus as claimed in claim 3, in which the contact strips are of beryllium copper.

5. Apparatus as claimed in claim 3 or 4, in which the contact strips are attached to one of the cooperating parts, bowed onto contact with the other and then bowed back into contact with the part to which they are attached.

6. Apparatus as claimed in claim 3, 4 or 5, in which the seal is located where a flange of the base member extends between two portions of the cover member and includes a row of contact strips between each portion of the cover member and the flange.

7. Apparatus as claimed in claim 6, in which the flange extends close to a bridge portion between the said two portions of the cover member and a further barrier to microwave energy is located in the gap therebetween.

8. Apparatus as claimed in claim 7, in which the further barrier consists of an elastomer with embedded conductor wires.

9. Apparatus as claimed in claim 7 or 8, in which the spacing between the successive seal elements is substantially one half of the wavelength of the energy to be used.

10. Apparatus as claimed in any of the preceding claims, comprising a false ceiling of insulating material.

11. Apparatus as claimed in any of the preceding claims, comprising a heater for the air in the enclosure formed by the cover and base.

1 2. Apparatus for heat treatment by the application of microwave energy substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.