EP0225432A2

EP0225432A2 - Heat treatment method and heat treatment apparatus

Info

Publication number: EP0225432A2
Application number: EP86111599A
Authority: EP
Inventors: Ono Takashi; Ishimoto Takashi
Original assignee: Daido Steel Co Ltd
Current assignee: Daido Steel Co Ltd
Priority date: 1985-11-11
Filing date: 1986-08-21
Publication date: 1987-06-16
Also published as: EP0225432A3; JPS62112717A

Abstract

In a furnace (2) having an inlet (8a, 8b, 8c) and an outlet (9a, 9b, 9c), a plurality of conveying components (a, b, c) for conveying materials to be heated from the inlet toward the outlet (8a to 9a, 8b to 9b 8c to 9c) are provided in parallel. A plurality of the materials are continuously loaded on the conveying components at the inlet of the furnace, subjected to heat treatment during the conveying process performed by the conveying components in the furnace, and successively reach the outlet. In this process, the conveying components are driven at conveying speeds which are different from each other. Among a plurality of the materials to be heated, these materials which are required to be heated for a long time are loaded on conveying components which are driven at low speed. As a result, they are conveyed and heated in the furnace for a long time. On the other hand, the materials which are only required to be heated for a short time are loaded on the conveying components driven at a high speed and consequently, they are conveyed and heated in the furnace for a short time.

Description

Background of the Invention

1. Field of the Invention

The present invention relates to a method of heating materials to be heated (called simply "materials" hereinafter) and an apparatus therefor, particularly to a heat treatment method and apparatus therefor in which a plurality of materials are heated by being continuously passed through a furnace.

2. Description of the Prior Art

There are known methods and apparatus for this type of heat treatment in which a plurality of materials are continuously sent into a furnace from an inlet provided on one side of the furnace, conveyed in succession toward an outlet provided on the other side of the furnace while being heated in the conveying process, and then sent out of the outlet in succession. For example, a method and apparatus is disclosed in the description appearing in the passage from line 18 of the right column on page 211 to line 17 of the left column on page 212 in "Industrial Furnace Handbook" issued by the Tokyo Technocenter in Japan on July 20, 1978. The method as described above is suitable for production of a small variety of goods in large quantities. This method, however, involves some inconvenience when heating a large variety of materials in small quantities. Namely, in the above-described method, it is necessary to reduce the conveying speed for certain kinds of materials which are required to be heated for a long time in the heating process, while it is necessary to increase the conveying speed for other kinds of materials which only need to be heated for a short time. Under such conditions, when a plurality of materials required to be heated for a long time are sent into a furnace and heated at a slow conveying speed, and materials which only need to be heated for a short time are then sent into the furnace and heated therein, there is a problem in that the latter materials following the materials sent into the furnace at a slow conveying speed tend to be heated for an excessive length of time. Thus, there is a problem since it is necessary to wait for a certain period after the materials transferred at a slow conveying speed have been sent out of the furnace before the materials which need to be sent at a high conveying speed can be sent into the furnace. Thus the furnace remains empty for this period of waiting time and the operating efficiency and throughput is thus decreased.

Summary of the Invention

It is an object of the present invention to provide a heat treatment method and apparatus which is capable of sending a plurality of materials into a furnace from an inlet of the same, conveying the materials in the furnace toward the outlet and heating them continuously during the conveying process, and sending out the materials in succession from the outlet of the furnace.
It is another object of the present invention to provide a heat treatment method and apparatus in which a variety of materials in several groups each of which requires a heating time which is different from the materials belonging to the other groups can be dealt with by continuously sending each of the groups into a furnace wherein all of the materials can be respectively heated for an appropriately selected time and sent out from the furnace thereafter.
It is a further object of the present invention to provide such a heat treatment method and apparatus as is described above in which the materials belonging to the groups which are required to be heated for a long time are passed through a furnace at a slow speed, while the materials belonging to the groups which are required to be heated for a short time are passed through the same furnace at a fast speed, so that the materials in all groups can be heated for a suitably selected time.
It is still further object of the present invention to provide such a heat treatment method and apparatus as is described above wherein, when it is desired that the materials to be conveyed at a slow speed due to the necessity to heat them for a long time are previously sent into a furnace and the materials to be conveyed at a high speed due to the necessity to heat them for a short time are thereafter sent into the same furnace and heated therein, it becomes possible to send the latter materials into the furnace and to heat them without being affected by the presence of the materials which are being conveyed at a low speed which had been previously sent into the furnace by enabling the fast moving materials to pass quickly alongside the slow moving materials.
Such heat treatment method and apparatus according to the present invention obviates the need for a waiting time such as is required with a conventional method and apparatus and allows the throughput ratio of a furnace to be maintained at a high level.
Other objects and advantages of the invention will become apparent during the following discussion with reference to accompanying drawings.

Brief Description fo the Drawings

Fig. 1 is a longitudinal sectional schematic drawing of a heat treatment apparatus;
Fig. 2 is a horizontal sectional view of the heat treatment apparatus shown in Fig. 1 which also shows the heat curves of the respective materials conveyed by three conveying components in a furnace;
Fig. 3 is a schematic drawing of the conveying system in the apparatus shown in Fig. 1; and
Fig. 4 to 6 are longitudinal sectional views which show embodiments of conveying systems having different structures.

Description of the Preferred Embodiments

In Figs. 1 to 3, reference number 1 denotes a heat treatment apparatus, reference number 2 denotes a furnace formed as a hollow body and provided with an inlet 8 at one end thereof and an outlet 9 at the other end. The furnace is formed such that its width comprises a plurality of longitudinal spaces (three in this embodiment) through which materials can be passed from the inlet 8 toward the outlet 9. The inside of the furnace 2 is divided in the longitudinal direction thereof into a heating and heat-maintaining chamber 3 and a cooling chamber 4. The furnace wall of the heating and heat-maintaining chamber 3 is lined with fireproof and heat insulating materials. The heating and heat-maintaining chamber 3 is provided with a heat source 5 such as a radiant tube, a burner, or an electrical heating wire, and an agitation fan 6 which together form a heating means. Reference number 7 denotes a driving motor for the fan 6. As for the heat source 5 and the fan 6, wide ones extending over the whole width of the furnace 2 are in some cases used, while in some cases narrow ones are separately provided over each of the plurality of longitudinal spaces. The inlet 8 and the outlet 9 are formed to be wide and are provided with longitudinally movable doors 8a, 8b, 8c, 9a, 9b, 9c, which can be individually opened and closed, respectively. A front chamber 11 extends backward from the inlet side of the furnace and a rear chamber 13 extends forward from the outlet side thereof. The front chamber 11 and the rear chamber 13 are provided with longitudinally movable doors 11a, 11b, 11c, 13a, 13b, 13c, which can be individually opened and closed, respectively. A loading table 12 and a discharging table 14 are provided ahead of the front chamber 11 and beyond the rear chamber 13, respectively.
Reference number 15 denotes a conveying system which comprises in this embodiment three lines of conveying components 15a, 15b, 15c. The respective components are constructed as a roller hearth and disposed in parallel with each other so that the conveying loci of the materials conveyed by the components are parallel with each other in the furnace. The above-described conveying components 15 include a great number of roller shafts 16a, 16b, 16c. These roller shafts are provided such as to cross the conveying loci of the materials at right angles and both ends of the shafts are rotatably supported by bearings 22 provided on both side walls 2a, 2b of the furnace 2. The bearings on the right and left sides are sometimes provided on the outside of the furnace. Many of these roller shafts are provided in parallel with each other under the conveying loci of the materials through the full length of the furnace 2. Each roller shaft is provided with one of the conveying rollers 17a, 17b, 17c. These conveying rollers have a larger diameter than those of the roller shafts and are formed such as to have a length which does not extend over a plurality of the conveying loci. Each of the conveying rollers 17a, 17b, 17c are provided such that the rollers shown by the same attached letters (a, b, c) show the same conveying loci. Each of the conveying components 15a, 15b, 15c is constructed by a plurality of the conveying rollers 17a, 17b, 17c which show each conveying loci. In this embodiment, the distances at which the rollers 17a, 17b, and 17c are arranged with respect to each other are equal, but they may be different from each other in other embodiments. For example, the distances at which the rollers of one conveying component are arranged may be long so as to be suitable for mainly conveying materials having a relatively great length while those of the other component may be small so as to be suitable for mainly conveying relatively short materials. Next, in the driving mechanism of the conveying system 15, reference numbers 18a, 18b, 18c denote chain sprockets provided at one end of the roller shafts 16a, 16b, 16c, respectively. Reference numbers 19a, 19b, 19c denote chains which are placed over the chain sprockets shown by the symbols 18a, 18b, 18c having the corresponding letters (a, b, c) attached. Reference numbers 20a, 20b, 20c are driving means separately provided for the respective conveying components, so that the conveying speeds of the respective conveying components can be separately determined.
In the conveying system 15 comprising such a structure, the conveying rollers 17a, 17b, 17c are rotated by the separated operation of the driving means 20a, 20b, 20c respectively, and materials 21a, 21b, 21c loaded on the conveying rollers are separately conveyed.
Furthermore, conveying systems having the same structure as the above-described conveying system are provided on the loading table 12, the front chamber 11, the rear chamber 13, and the discharging table 14. In general, these conveying systems are separately driven by individual driving mechanisms which are separate from the those of the above conveying system 15.
Next, description will be made of the heat treatment of many different materials by the above-described heat treatment apparatus. In this embodiment, the group comprising materials which need to be heated for the shortest time is shown by reference symbol 21a, a group comprising materials which need to be heated for a medium length of time is shown by reference symbol 21b, and a group comprising materials which need to be heated for the longest time is shown by reference symbol 21c. The materials of each of the groups are conveyed and subjected to heat treatment independently of the other groups. Description will be made of the materials 21a as an example, but the other materials are subjected to the same treatment.
The materials 21a provided on the table 12 are sent into the front chamber 11 by opening the door 11a by means of the operation of the conveying systems of the table 12 and the front chamber 11. The door 11a is then closed. The materials 21a sent into the front chamber 11 are then sent into the furnace 2 by opening the door 8a by means of the operation of the conveying systems of the front chamber 11 and the conveying components 15a of the furnace 2. The door 8a is then closed. The materials 21a are conveyed toward the outlet by the conveying components 15a in the furnace 2. The conveying may be carried out by a continuous method or an intermittent method. As described above, during the conveying process of the materials 21a, the materials 21a are heated to a predetermined temperature, are maintained at this temperature (heat-maintaining treatment) in the heating and heat-maintaining chamber 3, and are then cooled in the cooling chamber 4. When a vacant space is created in the furnace adjacent to the inlet 8 with the movement of the materials 21a, the door 8a is opened and the materials 21a in the front chamber 11 are sent into the furnace. When the materials 21a are completely cooled in such a manner as described above, the door 9a is opened, the materials 21a are sent into the conveying system in the rear chamber 13, and the door 9a is closed. The door 13a is then opened, the materials 21a are transferred onto the table 14 by the conveying systems of the rear chamber 13 and the table 14, and the door 13a is closed.
When the materials 21a, 21b, 21c of each of the groups are respectively conveyed by the conveying components 15a, 15b, 15c in the furnace 2, the conveying components 15a, 15b, 15c are driven at conveying speeds which are different from each other. The speeds are so selected that the time required for the materials conveyed by the conveying components to pass through the heating and heat-maintaining chamber 3 is equivalent to the predetermined time for heating of each of the materials. More specifically, the conveying speed of each of the conveying components is so selected that the materials belonging to each of the groups are heated for a time sufficient for them to reach a predetermined temperature and then exposed to heat for the predetermined time for heat maintenance therefor. An example is shown in Table I.
As seen from the table, the materials of each of the groups are conveyed at a suitable speed by the independent conveying components. As a result, the materials 21a, 21b, 21c which are subjected to heat treatment display, for example, heat curves which are suitable for these materials as shown by the graphs (A), (B), (C) in Fig. 2, respectively. The transverse axis in Fig. 2 shows the time the materials are present in the furnace and corresponds to the position at which the materials are conveyed in the furnace 2 in Fig. 2.
When the conveying components 15a, 15b, 15c convey the materials in the furnace 2, as described above, since many roller shafts 16a, 16b, 16c are supported by the bearings 22 at both ends, heavy materials can be stably supported and conveyed thereby. In addition, the roller shafts of a certain conveying component are placed between the conveying rollers of another conveying component and if the conveying speeds of the conveying components 15a, 15b, 15c are different from each other, the conveying rollers 17a∼17c of each of the components 15a, 15b, 15c are of such a dimension as to have the above-described thickness. Thus, the materials can be stably conveyed independently of the presence of the above roller shafts.
Fig. 4 shows another embodiment of a conveying system. Conveying rollers 23, 24 are provided such as to pass through one side wall 2ae and another side wall 2be of a furnace 2e, respectively. The ends of the rollers are free ends on furnace side, while the ends on the outside of the furnace are rotatably supported by bearings 25 provided on a frame (on which the furnace is also mounted) of a heat treatment apparatus. The ends of the rollers 23, 24 on the outside of the furnace are provided with chain sprockets 26. Many of these rollers 23, 24 are disposed in parallel with each other along the conveying loci of the materials. The portions of the rollers 23, 24 within the furnace form conveying components 15ae, 15ce for conveying materials 21ae, 21ce, respectively.
The sprockets 26 provided on the rollers 23 on one side are connected to a driving means 20ae through a chain and the sprockets 26 provided on the rollers 24 on the other side are connected to another driving means 20ce in a similar manner.
In the conveying system constructed as described above, the distances between each of the rollers 23 and between each of the rollers 24 can be made smaller than those in the structure shown in Fig. 3. Thus, it becomes possible to convey short materials. The portions of the conveying system which can be considered as having the same structure as that shown in Figs. 1 to 3 from the viewpoint of their function are indicated by corresponding symbols with the letter e added and a duplicated description of such portions is omitted.
(Furthermore, the same portions in following drawings are also shown by symbols with the letters f, g, in that order, respectively added thereto from the same viewpoint; duplicated descriptions of these portions are also omitted.
Fig. 5 shows a conveying system in a furnace provided with three lines of conveying components. In this conveying system, conveying rollers 23f, 24f on the right and left are formed as hollow cylinders and are provided on the same axis. The ends of each of the conveying rollers 23f, 24f on the inside of the furnace are separated from each other by sufficient distances to allow the conveying loci of the materials 21bf to be formed therebetween. Other conveying rollers 27 having a small diameter are inserted into the right and left conveying rollers 23f, 24f and the right and left ends of the rollers 27 are supported by bearings 28 provided on the outside of the furnace. Many of the above-described conveying rollers 27 are provided along the conveying loci of the materials and conveying component 15bf is formed by the center portions of the rollers 27. Chain sprockets 29 are provided on the rollers 27 and connected to a driving means 20bf.
In the conveying system constructed as in the above, the rollers forming the center conveying component 15bf should be of a considerable length. However, even if the rollers are long in this way, both ends are supported by the bearings and it thus becomes possible to stably support and convey the materials.
Fig. 6 shows another conveying system provided with two-line conveying components. Conveying rollers 23g are formed into hollow cylinders. Conveying rollers 31 which have a smaller diameter than that of the conveying rollers 23g and which are provided on the same axes as the rollers 23g pass through the conveying rollers 23g. Both ends of these rollers 31 are supported by bearings 32 provided on the outside of a furnace and they are provided with chain sprockets 33 on one of their ends. Many of conveying rollers 31 as described above are provided in correspondence with the rollers 23g and each of the chain sprockets 33 of each of the rollers 31 is connected to driving means 20cg.
In this specification, a roller hearth is shown as an embodiment of the conveying component, but a mesh belt, a chain conveyer, a pusher, or a cast link may be used as other embodiments of the conveying means.
As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Claims

1. A method of heating materials to be heated in a plurality of groups, the heating times of which are different from each other, by using a heat treatment apparatus comprising a hollow furnace having an inlet at one end and an outlet at the other end, said furnace being provided with a heating means for heating said materials passing through said furnace, and a plurality of conveying components which are provided in parallel with each other in said furnace for conveying said materials from said inlet to said outlet, said method comprising the steps of operating a plurality of said conveying components at conveying speeds which are different from each other so that the times required for conveying said materials from said inlet to said outlet are different from each other, loading in succession a plurality of said materials in said groups which are required to be heated for a long time on said conveying components which are driven at a low conveying speed to thereby convey them toward said outlet, and loading in succession a plurality of materials of those groups which are required to be heated for a short time on said conveying components which are driven at a high speed to thereby convey them toward said outlet.

2. A heat treatment apparatus comprising a hollow furnace (2) having an inlet (8) at one end and an outlet (9) at other end, said furnace being provided with a heating means (5, 6) for heating materials (21a, 21b, 21c) to be heated while passing through said furnace, and a conveying system (15) provided with a plurality of conveying components (15a, 15b, 15c) for conveying said materials from said inlet toward said outlet, said plurality of conveying components being provided in parallel so that the conveying loci of a plurality of said materials conveyed from said inlet toward said outlet are formed in parallel, wherein said conveying system comprises a plurality of roller shafts (16a, 16b, 16c) which are provided in parallel so as to cross said conveying loci and which are supported by bearings (22) provided on both sides of said furnace at both ends of said shafts, a plurality of conveying rollers (17a, 17b, 17c) which are respectively provided on a plurality of said roller shafts and which have a larger diameter than that of said roller shafts and a length which does not extend over a plurality of said conveying loci, and a plurality of driving means (20a, 20b, 20c) the number of which corresponds to that of said conveying loci, the axial position of each of the roller shafts of said plurality of conveying rollers is determined such that said plurality of conveying rollers are placed along each of said conveying loci, each of said conveying components is formed by said plurality of conveying rollers placed along each of said conveying loci, and each of said plurality of driving means is connected to said plurality of conveying rollers placed along each of said plurality of conveying loci so that said plurality of conveying rollers can be rotated at the same speed.

3. A heat treatment apparatus comprising a hollow furnace (2) having an inlet (8) at one end and an outlet (9) at the other end, said furnace being provided with a heating means (5, 6) for heating materials (21ae, 21ce) to be heated while passing through said furnace, and a conveying system provided with two conveying components (15ae, 15ce) for conveying said materials from said inlet toward said outlet, said two conveying components being provided in parallel so that a plurality of the conveying loci of a plurality of said materials conveyed from said inlet toward said outlet are formed in parallel, wherein said conveying system comprises a plurality of conveying rollers (23) which are provided so as to pass through one side wall (2ae) of said furnace in a state of crossing said conveying loci and supported by bearings (25) at one end on the outside of said furnace, the portions within said furnace forming one of said conveying components, a plurality of conveying rollers (24) which are provided so as to pass through the other side wall (2be) of said furnace in a state of crossing said conveying loci and supported by bearings (25) at one end on the outside of said furnace, the portions within said furnace forming the other conveying components, and two driving means (20ae, 20ce), said pluralitiy of conveying rollers on one side being connected to one of said driving means so as to rotate at the same speed as said driving means and said plurality of conveying rollers on the other side being connected to the other driving means so as to rotate at the same speed as said other driving means.

4. A heat treatment apparatus according to claim 3, in which all of said conveying rollers (23f, 24f) on both sides are hollow cylinders, said conveying rollers on one side and on the other side are respectively placed on the same axes, and the ends of said conveying rollers on each side within said furnace are separated at intervals sufficient to form another conveying locus therebetween, said apparatus comprising a plurality of conveying rollers (27) having a small diameter which are inserted into said conveying rollers (23f, 24f) placed on the same axes and supported at both ends thereof by bearings (25f) provided on the outside of said furnace (2f) which are different from said conveying rollers, another driving means (20bf) being additionally provided separate from said driving means (20af, 20cf), and said plurality of conveying rollers (27) having a small diameter being connected to said another driving means (20bf) so as to rotate them at the same speed.

5. A heat treatment apparatus according to claim 3, wherein said conveying rollers (23g) on one side and those (31) on the other side are respectively placed on the same axes, all of said conveying rollers (23g) on one side are hollow cylinders, all of said conveying rollers (31) on the other side have a smaller diameter than that of said conveying rollers on the one side and extend at the other ends so as to pass through said conveying rollers (23g) on one side, said conveying rollers (31) being supported by additional bearings (32) which are separated from said bearings (25g) and are provided on the outside of said furnace.