Device for heat treatment

Abstract

Known devices for heat treatment comprise a process space surrounded by a furnace lining made of quartz glass, a heating facility, and a reflector. In order to provide, on this basis, a device for heat treatment having a furnace lining that can be manufactured easily and in variable shapes and enables rapid heating and cooling of the material to be heated and short process times and is characterized by its long service life, the invention proposes that the furnace lining comprises multiple wall elements having a side facing the process space and a side facing away from the process space, and that at least one of the wall elements comprises multiple quartz glass tubes that are connected to each other by means of an SiO.sub.2-containing connecting mass.

Claims

1. A device for heat treatment, comprising: a furnace lining made of quartz glass, surrounding and defining a process space within; a heating facility; and a reflector; wherein the furnace lining comprises multiple wall elements having a side facing the process space and a side facing away from the process space, at least one of the wall elements comprising multiple quartz glass tubes connected to each other by means of an SiO.sub.2-containing connecting mass; and wherein at least two of the wall elements are connected to each other in a log house manner, whereby a first and a second wall element alternately project beyond the other at a corner of the furnace lining, thereby interlocking the first and second wall elements.

2. The device according to claim 1, wherein the SiO.sub.2-containing connecting mass serves both as reflector and as connecting means.

3. The device according to claim 1, wherein the SiO.sub.2-containing connecting mass is applied to the side of a wall element facing the process space.

4. The device according to claim 1, wherein the SiO.sub.2-containing connecting mass is applied to the side of a wall element facing away from the process space.

5. The device according to claim 1, wherein the quartz glass tubes have a round cross-section and in that the outer diameter of the quartz glass tubes is in the range of 4 mm to 50 mm.

6. The device according to claim 1, wherein a heating element, which is part of the heating facility, is arranged in at least one of the quartz glass tubes.

7. The device according to claim 6, wherein all quartz glass tubes of a wall element are configured with heating elements.

8. The device according to claim 6, wherein the heating element is an infrared radiator comprising a radiator tube and a heating filament.

9. The device according to claim 8, wherein the quartz glass tube is the radiator tube of the infrared radiator.

10. The device according to claim 6, wherein the heating element is designed to emit medium-wave infrared radiation.

11. The device according to claim 1, wherein the wall elements form a cuboidal hollow body.

12. The device according to claim 11, wherein the cuboidal hollow body comprises a wall element that forms a floor plate, a wall element that forms a cover plate, and four wall elements that form side walls of the hollow body.

13. The device according to claim 1, wherein the projecting wall elements, for fixation thereof, are connected to a furnace shell surrounding the furnace lining.

14. The device according to claim 12, wherein the floor plate and/or the cover plate comprise(s) multiple quartz glass cylinders that are connected to each other by means of the SiO.sub.2-containing connecting mass.

15. The device according to claim 1, wherein the at least two wall elements are dovetailed on corners of the body.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

EXEMPLARY EMBODIMENT

(2) In the following, the invention is illustrated in more detail by means of exemplary embodiments and a drawing. In the figures showing schematic views:

(3) FIG. 1 shows a spatial view of a first embodiment of a wall element of the device for heat treatment according to the invention;

(4) FIG. 2 shows a side view of a second embodiment of a wall element of the device for heat treatment according to the invention;

(5) FIG. 3 shows a top view onto four wall elements according to FIG. 1 that are connected to each other;

(6) FIG. 4 shows a spatial view of four wall elements that are connected to each other; and

(7) FIG. 5 a temperature-time course of a sample positioned in the device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a schematic view of a wall element of the device for heat treatment according to the invention, which, in toto, has reference number 1 assigned to it. The wall element 1 consists of four quartz glass tubes 4a-4d made of transparent quartz glass. The dimensions of each quartz glass tube 4a-4d are lengthwidthheight (LWH) 350 mm34 mm14 mm. In order to build-up a two-dimensional wall element, the quartz glass tubes 4a-4d are arranged adjacent to each other and are connected to each other by means of a SiO.sub.2-containing connecting mass 5. The quartz glass tubes 4a-4d are arranged in planar and alternating manner in wall element 1, offset by 50 mm, such that the quartz glass tubes 4a and 4c on the one hand and the quartz glass tubes 4b and 4d on the other hand project from the composite. The whole wall element 1 is 140 mm in width and 400 mm in length.

(9) The production of the wall element 1 is illustrated in more detail in the following: For connecting the quartz glass tubes 4a-4d, a suspension of quartz powder and water is used as SiO.sub.2-containing connecting mass 5 to coat one side of each of the four quartz glass tubes 4a-4d one after the other. The suspension is applied to the surface of the quartz glass tubes 4a-4d at room temperature using an automated spraying method. The coating is approximately one millimeter in thickness. Prior to drying, the quartz glass tubes 4a-4d, which are coated on one side, are placed with the coated side up on a temperature-resistant level holder plate made of quartz glass. Right after coating, the quartz glass tubes 4a-4d are pressed against each other axially such that a successive build-up generates a substance-to-substance level composite in the form of a plate.

(10) The quartz glass tubes 4a-4d, which are being pressed against each other, are in the fragile green compact state after coating; therefore, they are then transferred to a sintering furnace together with the holder plate. The green compact is then sintered at 1,240 C. for two hours in an air atmosphere. After sintering, the quartz glass tubes 4a-4d are connected to each other in mechanically stable manner such that a wall element 1 is obtained that consists of more than 99.9% quartz glass (SiO.sub.2). The coating in the finished wall element 1 is applied to the side 3 of the wall element 1 facing the process space; it is opaque and also serves as reflector layer 6.

(11) In as far as the same reference numbers are used in FIGS. 1 to 4, these denote components and parts that are identical in design or equivalent as illustrated in more detail above by means of the description of the embodiment of the wall element 1 according to FIG. 1.

(12) A second embodiment of a wall element is shown schematically FIG. 2 depicting a side view of the wall element 20. The wall element 20 comprises four quartz glass cylinders 21a, 21b, 21c, 21d that are connected to each other by means of an SiO.sub.2-containing connecting mass 5. The quartz glass cylinders are arranged adjacent to each other and are alternately offset by 50 mm with respect to each other. The side 22 as well as the opposite side (not shown) of the wall element 20 are coated with the SiO.sub.2-containing connecting mass 5 only in the region where they are connected. The dimensions of the individual quartz glass cylinders 21a, 21b, 21c, 21d are as follows: (LWH) 350 mm34 mm14 mm; the whole wall element 20 is 140 mm in width and 400 mm in length.

Example 1

(13) In the first embodiment, the device for heat treatment (not shown) comprises a furnace lining in the form of a cuboidal hollow body; the furnace lining comprises multiple wall elements 1 made of quartz glass, a floor plate, and a cover plate.

(14) FIG. 3 shows a top view of four wall elements 1 that are stood up vertically and are connected to each other by means of a joined connection. The composite, in toto, has reference number 30 assigned to it. The wall elements 1 are assembled appropriately such that the ends of the wall elements 1, which are alternately offset by 50 mm with respect to each other, are nested inside each other and are connected to each other in a log house design. Each wall element 1 comprise a side 2 facing away from the process space 31 and a side 3 facing the process space 31. The side 3 facing the process space 31 is coated with the SiO.sub.2-containing connecting mass 5. A spatial view of the wall elements 1 connected in a log house design is shown in FIG. 4.

(15) The composite 30 is covered by a rectangular cover plate (not shown) consisting of eleven tubes made of quartz glass. The tubes have a length of 400 mm, a width of 34 mm, and a height of 14 mm; they are connected to each other by means of a SiO.sub.2-containing connecting mass 5. The connection is effected in the same manner described for wall elements 1 in FIG. 1. The individual tubes of the cover plate are arranged adjacent to each other. Unlike the wall elements 1, the individual tubes of the cover plate are not arranged at an offset with respect to each other. The side of the rectangular cover plate facing the process space is coated with the SiO.sub.2-containing connecting mass, whereas the side facing away from the process space is not coated. The dimensions of the rectangular cover plate are as follows: LWH 40040014 mm. The surface area of the cover is 0.16 m.sup.2.

(16) The floor plate (not shown) is also fabricated from round tubes made of quartz glass that are connected to each other by means of the SiO.sub.2-containing connecting mass 5. In order to produce the floor plate, ten round tubes with an outer diameter of 10 mm and a length of 400 mm are connected to each other. The round tubes are arranged adjacent to each other in a plane, but with no offset with respect to each other. The width of the floor plate is approximately 100 mm and its surface area is 400 mm100 mm.sup.2=0.04 m.sup.2.

(17) A heating wire (filament) with a length of 350 mm is inserted into each of the ten round tubes of the floor plate. The ends of the round tubes are closed by means of a ceramic mount. The electrical power of each filament is 400 watts, the total power is 4 kilowatts (kW). Since the surface area of the heating field of the floor plate is 350100 mm.sup.2 in size, the resulting power per unit area is 4 kW/0.035 m.sup.2=114 kW/m.sup.2.

(18) The difference in surface area (0.12 m.sup.2) between floor plate and ceiling [JT1] plate is covered with tube sections. The tube sections are coated on the top with opaque, highly diffusely reflecting quartz glass. The coating consists of very many small quartz beads with a diameter of approx. 10 nanometers to 50 micrometers. The firmly sintered and correspondingly porous SiO.sub.2 material, whose pores are filled with air, has an enormous surface area of approx. 5 m.sup.2 per gram of the material due to the tiny structures. In the design described presently, approximately 670 grams of the opaque material are applied such as to be fixed such that the surface area on the inside of the furnace is approximately 3,350 m.sup.2. The surface being this large promotes rapid indirect heating of the air in the pores via the direct heating of the quartz glass by the infrared radiation.

(19) The furnace lining is surrounded by a single-layer thermal insulation. The insulation consists of a refractory high temperature mat based on aluminium oxide and silicon oxide and comprises a thickness of 25 mm. The outside of the thermal insulation is surrounded by a sheet metal jacketing. In order to allow the furnace to be loaded from the top, the cover can be opened. Altogether, the irradiation device weighs approx. 10 kg and is well-suited for mobile use.

(20) The material to be heated is introduced into the process space 31 that is surrounded by the furnace lining. The process space 31 has a length of 320 mm, a width of 320 mm, and a height of 145 mm.

(21) FIG. 5 shows the temperature-time profile of a sample that was positioned in the middle of the process space 31 of the device according to the invention. The sample is a round quartz glass tube having an outer diameter of 10 mm and a length of 50 mm. In order to measure the temperature of the sample to be measured, a NiCrNi thermocouple affixed with ceramic adhesive is provided inside the round quartz glass tube. In order to prevent the measuring result from being falsified by the direct radiation from the heating filaments into the inside of the quartz glass tube, the outside of the round quartz glass tube comprises an all-around gold coating. The sample was placed on a quartz glass goods holder situated at a distance of 30 from the heating field.

(22) For determination of the sample temperature, the device was started up at room temperature (so-called cold start) at full electrical power (4 kW). The temperature of the material to be heated reached 260 C. after 2 minutes and 540 C. after 4 minutes. A temperature of 900 C. was reached after approx. 17.5 minutes and the maximal temperature of 950 C. was reached after 22 minutes.

(23) In order not to endanger the quartz glass components, the maximal temperature was limited to 950 C. and the heating phase was terminated once this temperature was reached. If the quartz glass components and the heating wires are operated at less than 1,000 C. in the long-term, the maintenance-free service life can be up to 10,000 operating hours and more.

(24) In order to set a holding temperature of 800 C. subsequently, the electrical power was lowered to and kept at 1.6 kW. Said temperature is well-suited, for example, for the application of directed reflectors onto substrates made of glass, i.e. metallic layers such as, for example gold. Due to the set-up being closed, not only is the radiation energy used, but the convective heat of the heated air thus generated contributes to the total heating. The temperature gradient in the linear range (260 to 560 C.) is approx. 2.3 K/min during the heating phase and the requisite heating times are minimised.

(25) After the heating process and immediately after the electrical power was switched off, the cover of the set-up was taken off and the sample was removed with tongs. The temperature of the sample still exceeds 600 C. at this time. Due to the excellent heat shock resistance of the internal lining of the furnace made of pure quartz glass, no time-consuming cooling phase is needed such that the total process time is reduced by several hours as compared to conventional muffle furnaces, see reference example 1. The sample can be changed instantaneously such that the process can be repeated right away.

(26) Since the novel internal lining of the furnace consists of quartz glass and the material and the radiators withstand temperatures of almost 1,000 C. in the long-term, there is no need to cool the individual components by means of fans or coolant liquids.

Example 2

(27) The design of the device differs from the design of the device from exemplary embodiment 1 in that it eliminates two wall elements 1 situated opposite from each other. The openings are preparations for continuous introduction of the material to be heated. The furnace having the novel internal lining, in the form of the remaining two walls with cover and floor, is loaded in the middle in warm and switched-on condition (electrical power kept at 1.5 kW). The goods holder is situated at a distance of 60 mm from the heating field (floor).

(28) The sample made of quartz glass, as described in exemplary embodiment 1, is heated up from room temperature, initially at a gradient of approx. 9 K/min, and reaches the temperature of 600 C. after only three minutes and a maximal temperature of 740 C. after 14 minutes. The difference to the maximal temperature of 800 C. as in example 1 is related to convective losses due to the two side openings and the somewhat larger distance between the material to be heated and the radiation source.

Example 3

(29) The design of the furnace according to example 3 corresponds to that of the device from example 2. The furnace is operated in warm and switched-on condition (permanent electrical power of 1.5 kW) and used for a continuous sintering process. For this purpose, a component coated on the upper side with gold, for example a quartz glass tube having dimensions of LWH=1,0003414 mm, is guided appropriately through the furnace to burn-in the coating such that the component moves through the hot process chamber of the furnace at a speed of 200 mm/min and is guided out on the opposite side. The component is moved through the furnace using a holder situated outside the furnace. The tube is moved keeping a distance of 60 mm to the heating field of the floor plate.

(30) Downstream of the furnace, the coating on the tube has a visually homogeneous surface with very good surface adhesion. The adhesion of the gold to the surface was determined using the adhesive tape tear-off test. Said test encompasses applying a commercially available adhesive tape, for example a Scotch adhesive tape made by 3M, onto the gold-coated surface and then tearing the tape off suddenly in one motion. If the adhesive strength of the gold is insufficient, metallic residues will be seen to remain on the adhesive surface of the tape. The metal-coated surface shows no imperfections due to particles or foreign substances, since the novel furnace lining made of SiO.sub.2 is free of contamination and works without generating particles.

Reference Example 1

(31) A conventional muffle annealing furnace comprises an installed electrical power of 24 kW, a furnace lining in the form of a brick lining, and a process chamber of the following useful space dimensions: LWH=1,000 mm500 mm300 mm. A quartz glass tube that was metal-coated on one side and had a length of 300 mm, a width of 34 mm, and a height of 14 mm was introduced into the muffle annealing furnace in order to burn-in the coating, and the temperature-time profile of the sample was determined. The heating curve (not shown) shows a gradient of 6.6 K/min between 700 and 1,000 C.; the furnace temperature is maintained at maximally 1,000 C. After switching off the furnace, it takes 5.5 hours for the temperature to reach 600 C., which is the earliest time the sample can be removed. In order to ensure a long service life for the brick lining (>1 year) without crack formation, the furnace should be opened only below 400 C., since the lining bricks do not possess high heat shock resistance.

Example 4

(32) The design of the device differs from the one in example 1 in that three floor plates arranged next to each other are provided as two-dimensional radiators. Each floor plate comprises 10 round tubes which each are provided with a heating filament with a power of 400 watts. The total electrical power of the device is 12 kW. Ceramic mounts are provided on the ends of the round tubes. The three two-dimensional radiators (floor plates) cover a total surface area of 400300 mm.sup.2=0.12 m.sup.2. The difference to the opposite surface of the cover (0.16 m.sup.2) is covered with individual tube sections that are coated on one side on their upper surface.

(33) The heating is directed at a steel plate (LWH=200 mm120 mm0.75 mm), whose surface is slightly oxidised. The shortest distance between plate and two-dimensional radiator is 30 mm. The target temperature of 800 C., starting from room temperature of 20 C., is reached after four minutes. The heating gradient in the linear range is approx. 4.5 K/s.

Reference Example 2

(34) A steel plate according to example 4 having the same dimensions and quality is being heated from one side in a conventional infrared module with nine short-wave radiators. The infrared module has a power per unit area of 100 kW/m.sup.2 and a total electrical power of 38 kW. The surface area of the heating field of the infrared module is LW=700 mm500 mm. The distance between the heating field and the material to be heated is 120 mm.

(35) The heating gradient is approx. 14 K/s initially and then falls off strongly. The maximal temperature of 640 C. is reached after approx. 2 min. Due to the high convective losses towards all sides and the high reflectivity, the temperature of the steel plate cannot be made higher through heating by means of radiation, it is not feasible to reach the target temperature of 800 C. It is not expedient to have a smaller distance between plate and heating field, since the surroundings including the radiator heat up to a non-permissible degree in this temperature range despite cooling.

Reference Example 3

(36) A steel plate of the same dimensions and identical quality as the one from reference example 2 is being heated from two sides using two conventional infrared modules with short-wave radiators. The power density of each of the infrared modules is 100 kW/m.sup.2 and the total electrical power is 75 kW. The surface area of each heating field of the modules is LW=700 mm500 mm. The distance between the heating field and the material to be heated is 120 mm.

(37) The heating gradient is approx. 25-30 K/s initially, the maximal temperature of approx. 680 C. is reached after approx. 1.5 minutes, the target temperature of 800 C. is not attainable. Marked heating (production of smoke) of the surroundings is observed from 500 C.

Example 5

(38) In an alternative embodiment, a wall element is designed appropriately such that it works as a heating radiator and simultaneously heats the material to be heated from multiple sides. Five individual twin tubes made of quartz glass and having a length of 875 mm, a width of 34 mm, and a height of 14 mm are bent into the shape of a ring and are then coated on the outside and connected to each other. The inner radius of the process chamber thus obtained is approx. 120 mm. The circular arc is open by a gap (approx. 30 mm) through which the electrical connections for power supply are guided into a zone outside the process space. The five twin tubes are each fitted with two heating coils with a length of 70 cm each; they are assembled perpendicular above each other in direct contact to form a composite. The power of each heating coil is 0.9 kW. The total power of the device is 9 kW. The floor plate and the cover plate consist of joined individual tubes with no heating elements, as described in exemplary embodiment 1.

(39) A steel plate as described in exemplary embodiment 4 or reference examples 2 or 3 is placed vertically in the middle of the chamber. The mean distance between the steel plate and the inner wall is approx. 120 mm. Starting from a starting temperature of approx. 65 C., more than 1,000 C. are reached after approx. 35 seconds at a heating gradient of approx. 30 K/s. For a holding temperature of approx. 800 C., the electrical power is reduced to 1.6 kW.

Example 6

(40) The furnace lining in another embodiment differs from the furnace lining according to exemplary embodiment 1 in that one wall element 1 is removed. As a result, loading of the process space through the open side is favoured and is effected by means of an automatic robot arm. The robot keeps the component to be heated in the hot zone for a defined period of time until the target temperature is reached. Then, the component is placed in a forming tool. Lastly, the next component is heated to the target temperature in the infrared furnace.

(41) A carbon fibre-reinforced plastic material (CFRP), with the thermoplastic material PPS (polyphenylsulfide) in the present case, is heated. The dimensions of the CFRP plate are LWH=180 mm85 mm4 mm. The distance between the two-dimensional radiators and the plate is 55 mm.

(42) The two-dimensional radiators are switched on and operated at an electrical input of 4 kW. The process space is heated for five minutes initially before the CRFP material is held into the hot zone. The heating gradient in the linear heating range on the side of the CRFP facing away from the radiator is approx. 4.8 K/s. The electrical heating is switched off some 10 seconds after introduction of the material to be heated into the heating zone in order to avoid premature over-heating of the CFRP surface. Due to the internal lining of the furnace, the emission from the walls, supported by warm air (convection) causes the temperature on the inside to keep increasing despite the side being open such that the target temperature of 260 C. is reached on the side facing away from the radiator approx. 85 seconds after introduction of the CFRP. In the subsequent 100 seconds of recording, the temperature increases up to 280 C. at a gradient of approx. 0.2 K/s and the temperature is maintained at this level for the next minute. Due to the homogeneous heating to 260 C., the PPS softens such that the material is easy to form.

(43) It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.