WO2007073707A1

WO2007073707A1 - Furnace, particularly for thermal and chemotermal treatment of metal products

Info

Publication number: WO2007073707A1
Application number: PCT/CZ2005/000100
Authority: WO
Inventors: Radim Ledl; Ivo Biskupic
Original assignee: Lac S.R.O.
Priority date: 2005-12-29
Filing date: 2005-12-29
Publication date: 2007-07-05

Abstract

A furnace intended particularly for large-sale thermal and chemothermal treatment of metal products using e.g. cementing, nitrocarburizing, nitriding, carbonitriding, annealing, hardening, tempering, and similar processes. The furnace is arranged to enable its upper location while it is transferred above the individual baths using the side travel. A charge is inserted in the furnace from below. The furnace can be turned round its axis that enables inserting of the grate assembly together with the product charge into the furnace and locking by its back turning motion where the edges of the lowest grate are clamped by the lock in the furnace retort to enable locking of the charge in the furnace. Said arrangement eliminates the negative effect of thermal distortion of the furnace retort that could disturb charge locking or unlocking.

Description

Furnace, Particularly for Thermal and Chemotermal Treatment of Metal Products

Field of the Invention

The present invention relates to a furnace intended particularly for thermal and chemothermal treatment of metal products using cementing, nitrocarburizing, nitriding, carbonitriding, annealing, hardening, tempering, and similar processes.

State of the Art

Thermal and chemothermal treatment of metal products is usually performed in shaft or bell furnaces and related units being usually baths of various compositions whereas individual operations and units are arranged generally into lines enabling successive batch performance of thermal or chemothermal treatment of charges.

Several variants of furnace arrangement are known: a) Furnaces are located in the upper half of a structure of a line frame while hardening baths and washers are located in its lower half. Furnaces are laterally movable, they are traversed above hardening or other baths, and a charge is put into baths using chargers. b) Furnaces are located in the upper half of a structure while hardening baths and washers are located in its lower part. Baths are movable and they are transferred under each furnace where charges intended for hardening are put into them. Several variants of a charge transfer from a furnace into baths are also known:

1) According to the first variant, a furnace moves a charge (using a slip plane being formed by the furnace bottom and an upper plate of a hardening bath) up to a bath charger; the latter takes over the charge and transports it into the bath. The furnace then returns to its operating position and is ready to handle with the new charge (e.g. EP 0 533 615^"A1).

2) According to the second variant, a charge located on a grate is locked in the furnace so that a retort is turned in the furnace and the grate is clamped using protrusions arranged in the retort (e.g. EP 0 295 207 A1). After the chemothermal treatment is completed, a furnace cover moves down and the charge is transported by moving the entire furnace above the bath where said charge is taken over by the bath charger. The latter is pushed forward, takes the charge being unlocked by turning the retort; the latter is then turned back to its original position in the furnace and the charger transports it into the bath. The furnace is then returned back into its operating position and is ready to handle with the new charge.

3) According to the third variant, the charge is locked in the furnace using three rotary holders that are controlled by rods passing through the entire furnace and leaving it at its top part.

The disadvantage of the second and the third variants is the fact that the movable parts of the furnace are subjected to heat stress. E.g. in case of the second variant, problems with charge locking or unlocking in the furnace may occur.

The problems as mentioned above are eliminated by the solution according to this invention enabling safe operation of the furnace including charge locking, unlocking and removing even if the retort shows certain distortion.

Summary of the Invention

A furnace according to the invention intended particularly for thermal and chemothermal treatment of metal products using e.g. cementing, nitrocarburizing, annealing, hardening, etc., is arranged so that a charge may be inserted from the bottom of the furnace, whereas said furnace is fitted with a side travel enabling its movement together with the charge above the individual units and baths being located under the furnace. The furnace has advantageously a circular plan and its jacket serves simultaneously as a bearing frame for the unit. Except of several inlets intended e.g. for a propeller drive, measuring probes and a supply of process media, a top part of the furnace is sealed. Its bottom part is sealed with a vertically movable cover bearing a multi-stage grate with the charge on posts. The entire outer jacket of the furnace is fitted with thermal insulation. Electrical heating elements encircling the entire inner working area - a circular retort - are located in a heating chamber located in the area between the thermal insulation and the furnace retort. A cylindrical metal jacket, and a circulation insert which both the upper and bottom ends are opened, are located concentrically inside the inner circular area of the furnace. The insert divides the inner area to two axially aligned parts. A circulation propeller is located close to the upper end of the circulation insert in its centre line, said propeller exhausts hot gas from the inner area of the insert and forces it via the area outside the circulation insert, along the heated retort down where the flow direction is turned and gas turns back to the exhaust of the circulation propeller through the inside area of the circulation insert. The circulation propeller is driven by an electromotor through a spindle which bearing is water-cooled. A distribution duct distributes cooling air intended for the controlled cooling into the air-distributing duct and the heating chamber.

The heating chamber of the furnace is cooled with air, which is forced by a fan through the distributing duct into the heating chamber of the furnace from where hot air is exhausted from the heating chamber through the second and the third duct into an exhaust bleeder. Flaps enabling regulation of the proportion of the air entering the furnace, and mixing of the fresh air with the hot exhaust air are located in a body of the distribution duct. Said arrangement enables the controlled cooling of the furnace.

The thermal insulated furnace cover can be vertically moved by means of a mechanically controlled hoisting unit representing the charge charger. The bottom open edge of the retort, when being in its closed position, is extended into an annular trough being arranged round the perimeter of the furnace cover; said trough is filled with silica sand or other suitable fireproof material. The trough with silica sand forms a seal capable to compensate thermal dilatation of the furnace and prevent leak of the internal atmosphere. The top side of the furnace cover is fitted with pins onto which a multi-stage grate assembly is put on in order to fix its position. Outlet pipes intended for the alternative atmosphere burnup, a control foil test and, if necessary, a thermocouple, are conducted out through the cover centre. According to the currently available known solutions, the charge is locked so that the retort fitted with the protrusions is turned inside the stationary furnace whereas the grate with the charge is clamped by the protrusions inside the retort and locked. The disadvantage of the solution mentioned consists in that the retort may be distorted which causes problems with charge locking or unlocking due to the effect of the temperature differences, particularly in large furnaces. According to this invention, the charge located on the grate is locked so that the entire furnace is turned whereas the retort in the furnace is stationary, and its distortions have a minimum effect. The advantageous and sufficient angle of rotation necessary for charge locking is about 30°. The furnace may be turned because it is arranged on an axial bearing being inserted between the sole plate and the furnace body. The mechanism intended for driving of furnace turning is advantageously derived from the electromotor fitted with a gear-box by means of sprockets engaged into link chains that transfer movement to the furnace jacket. One of the sprockets controls the furnace movement at the clockwise direction while the second one controls it at the opposite direction. During turning, the relevant, pulled, link chain, which remoter end is fixed to the furnace jacket, is taken up onto the relevant sprocket while the link chain is uncoiled from the second sprocket. The motor with the gear-box is advantageously located in the upper part of the furnace and is connected with a shaft, being advantageously located outside the furnace, with the drive itself being located on the sole plate.

The first - the lowest - grate intended for location of metal parts forming simultaneously the base of the all-grate assembly has approximately the shape of a polygon, preferably octagon, with a honeycomb grating. The shapes of the second and the next stages of the grate assembly are limited only by the demand relating its passage ability through the profile of the furnace lock. Orifices for posts supporting the individual stages of the grate assembly are located at the distance of about two thirds of the radius from the centre of grates. The first, the lowest - stage is, in addition, fitted with orifices enabling mounting the assembly onto the pins of the furnace cover. The outer dimensions of the lower grate having the polygonal, advantageously octagonal, shape forming the lowest stage of the grate assembly shall be smaller than the inside profile of the lock which shape corresponds to that one of the lowest grate and passes through it freely. The charge is charged and locked in the furnace so that the products being ready for treatment are put onto the stages of the grate assembly that is then mounted onto the pins of the furnace cover. The hoisting unit lifts the cover with the grate assembly and the relevant charge into the heating chamber of the furnace, the latter being turned by about 30° so that the grate may pass freely above the upper level of the polygonal, advantageously octagonal, lock; the furnace is then turned back and the hoisting unit is let down. This results in that the second locks of the grate assembly are clamped by the straight parts of the first locks of the furnace so that the grate assembly is locked. The furnace cover is then moved into its operating position and the entire furnace is simultaneously sealed by its cover.

A side travel of the furnace is enabled by means of a prismatic support located in the rear part of the sole plate. The shaped support fixes the furnace both in the axis of the furnace travel and in the axis perpendicular to the travel. On the front side, the furnace is travelled along pulleys being supported on the line frame to enable thermal expansion of the furnace. The electromotor and the gear-box of the side travel of the furnace are advantageously located at the upper part of the furnace and are connected by the shaft with the travel mechanism being located close to the sole plate whereas said shaft is advantageously located outside the furnace, similarly to the turning mechanism. The side travel of the furnace may be provided using the known manners, e.g. by means of a tooth wheel being engaged into a rack that is clamped to the line frame.

Brief Description of Figures on Drawings

Fig. 1, in its broken-out section, is the general diagram of one of the possible solutions of the furnace intended for thermal and chemothermal treatment of metal products according to the present invention.

Fig. 2 is the horizontal projection of the furnace. Fig. 3 is the first grate.

Fig. 4 is the grate lock.

Fig. 5 is the first grate engaged into the lock.

Fig. 6 is the first grate locked in the lock by its turning.

Fig. 7 is the detail of the mechanism intended for furnace turning. Fig. 8 is the detail of the mechanism intended for the side travel of the furnace. Description of the Exemplary Embodiment

One of the possible solutions of a furnace intended for thermal and chemothermal treatment of metal products according to the present invention will be described below using the preferred embodiment. An arrangement of a furnace intended for thermal treatment of metal products according to the present invention enables inserting of a charge from beneath, locking of the charge in a retort by turning the entire furnace, and side travel enabling transfer of the furnace together with the charge above individual units and baths located underneath the furnace. The furnace has the circular plan and its outer jacket (1) serves simultaneously as a bearing part for unit. Except of several inlets intended e.g. for a spindle (2), a propeller (3), measuring probes (4) a supply of a cooling medium (5) for a bearing (6) and a supply of process media, a top part of the furnace is sealed. Its bottom part is open and is sealed with a cover (7) by means of a vertically travelling hoisting unit. The outer jacket (1) of the furnace is fitted with a thermal insulation (8). Twelve stages of electrical heating elements (10) being arranged at a hexahedron shape and encircling the entire operating area and a circular retort (11) are located in a heating chamber (9). A cylindrical circulation metal insert (12), which both the upper and bottom terminals are opened, is located at the centre line of the circular retort (11). The circulation insert (12) divides the inner area to two parts in which heating or, if necessary, cooling gas circulates. The propeller (3) is located at the centre line of the upper opened end of the circulation insert (12), said propeller exhausts hot gas through the centre and forces it via the area outside the circulation insert (12), along the retort (11) down where the flow direction is turned, and gas flows through the inside area of the circulation insert (12) along grates (13 through 15) forming together a grate assembly, and turns back to the exhaust of the circulation propeller (3). The propeller (3) is driven by a first drive (16) by means of a gear-box and the spindle (2), which bearing (6) is cooled with water fed via the supply (5). At the point where the jacket (1) is opened, a first duct (17) is arranged distributing the cooling air from a fan (20) into the heating chamber (9) from which it passes via a second (18) and a third (19) duct into an exhaust bleeder (21) of the air distribution system. Flaps (22) enabling regulation of the mixing proportion between the fresh and hot air entering the furnace and thus enabling its controlled heating are located in a body of the first duct (17).

The thermally insulated cover (7) of the furnace travels vertically by means of the mechanically controlled hoisting unit that forms a charger for a charge. The charge is put onto a multi-stage grate assembly comprising the first (13), the second (14) and the third (15) grate being mounted on posts (23) whereas said assembly is mounted onto four pins (24) of the furnace cover (7) by a base being the first grate. Tubes (25) fitted with ball valves intended for an alternative atmosphere burnup, a control foil test and, if necessary, a thermocouple, are conducted out through the cover centre (7).

The bottom open edge of the retort (11) of the furnace, when being in its closed position, is extended into an annular trough (26) being arranged round the perimeter of the furnace cover (7) and is filled with silica sand. The bottom edge of the retort (11), when being in its lowest position, extends into the trough (26) with silica sand and forms a seal capable to prevent leak of the internal atmosphere from the retort (11) and thus to compensate thermal dilatation of the furnace whereas the bottom edge of the retort (11) does not come into contact with the trough (26) bottom.

The mechanisms intended for driving of the unit enabling furnace turning (27) and its side travel (28) are mounted on individual posts (29, 30) being fixed to a sole plate (31) located outside the furnace. The drive intended for furnace turning is derived from a second drive (27) fitted with the electromotor, a gear-box and a first shaft (32) by means of two sprockets (34) mounted on the common first shaft (32) into which link chains (35) mounted on a part of a perimeter of the furnace jacket (1) are engaged. One of the sprockets (34) controls the clockwise furnace travel while the second one controls its counter-clockwise travel. When the furnace is turned, the relevant link chain (35), which remoter end is fitted to the furnace jacket (1), is winded up to the relevant sprocket (34) while it is pulled off from the second sprocket (34). The furnace is arranged on an axial bearing (36) located on the sole plate (31) and it turns round its axis through the angle of 30°.

A guide of the furnace travel during its side movement is provided by a prismatic support (37) where two first pulleys (38) are located at the rear bottom side of the sole plate (31) whereas, at the front part, the sole plate (31) is supported onto two second pulleys (39) being freely rolled along a frame (40) of the unit. The prismatic support (37) fixes the furnace position both in the direction of its travel and in the axis perpendicular to the direction of its travel. Said method of mounting enables furnace thermal expansion. The furnace travel drive is ensured by a third drive (28) via the gear-box by means of a second shaft (33) with a gear wheel (41) and a rack (42) being clamped to a line frame (40).

The first grate (13) intended for placing of metal components has the octagonal shape whereas its outer dimensions enable its freely passing through a profile between the first locks (43) formed inside the furnace retort (11). The second (14) and the third (15) grade have the circular shape. In the incircle being at about one half of the width of the first grate (13), first orifices (44) for posts (23) are located; the individual stages of the grate assembly comprising further the second (14) and the third (15) grates are mounted on the latter. The first grate (13) is fitted with the second orifices (45) enabling mounting the first grate (13) onto pins (24) of the cover (7). When the furnace is turned round its vertical axis by the angle of 30°, the first grate (13) passes freely through the inside profile of the orifice between the first locks (43) provided at the bottom end of the retort (11). When the furnace is turned by the angle of 30° into its initial position, the second locks (46) of the first grate (13) and the straight parts of the first locks (43) are overlapped and so the grate is locked in the furnace. The furnace cover (7) can be thus lowered whereas the grate assembly with the charge remains to be engaged in the furnace. After the charge is locked in the furnace, the latter can be transferred above the next equipment (bath) of the line intended for thermal treatment while the cover (7) is open.

Industrial Applicability

The furnace is intended particularly for large-scale thermal and chemothermal treatment of metal products using e.g. cementing, nitrocarburizing, nitriding, carbonitriding, annealing, hardening, tempering, and similar processes. List of Reference Characters

1 Jacket

2 Spindle (of a propeller)

3 Propeller (circulation)

4 Measuring probe

5 Supply (of a cooling medium)

6 Bearing

7 Cover (of a furnace)

8 Insulation

9 Heating chamber

10 Heating element

11 Retort

12 Insert (circulation)

13 1^st grate

14 2^nd grate

15 3^rd grate

16 1 ^st drive (of a propeller)

17 1^st duct

18 2^nd duct

19 3^rd duct

20 Fan

21 Bleeder (exhaust)

22 Flap

23 Post

24 Pin

25 Tube (exhaust)

26 Trough

27 2^nd drive (furnace turning)

28 3^rd drive (side travel)

29 1^st stand (turning)

30 2^nd stand (travel)

31 Sole plate

32 1^st shaft (turning)

33 2^nd shaft (travel)

34 Sprocket

35 Link chain

36 Axial bearing (turning)

37 Prismatic support

38 1^st pulley

39 2^nd pulley

40 Frame (of an equipment)

41 Gear wheel

42 Rack

43 1^st lock (on a retort)

44 1^st orifice (of a grate)

45 2^nd orifice (of a grate)

46 2^nd lock (on a grate)

Claims

PATENT CLAIMS

1. A furnace intended particularly for thermal and chemothermal treatment of metal products fitted with a bottom filling of a charge, locking of the charge and a side travel characterized in that a furnace is pivoted on an axial bearing 36, whereas a first grate 13 forming together with a second grate 14 and a third grate 15 an assembly being mounted on posts 23 of a cover 7, which is inserted into the previously turned furnace, where the latter then turns back into its initial position and the cover is let down, is locked in the furnace so that second locks 46 provided on the first grate 13 are clamped by first locks 43 provided on the inside wall of a retort 11.

2. The furnace according to Claim 1 c h a r a c t e r i z e d in that an angle of 30° is advantageously used for the furnace turning during inserting and locking of the charge.

3. The furnace according to Claims 1 and 2 c h a r a c t e r i z e d in that the furnace is turned so that at least one sprocket 34 on which a link chain 35 is taken up is turned whereas said link chain 35 is at least partially located on a jacket 1 of the furnace and its remoter end is fasten to the jacket 1

4. The furnace according to Claim 1 characterized in that the jacket 7 of the furnace is fitted with at least three pins 23.

5. The furnace according to Claim 1 characterized in that the first grate 13 has a polygonal shape.

6. The furnace according to Claim 1 characterized in that the first grate _,13 has advantageously the shape of a symmetrical octagon having the sides of the unequal length whereas the shapes of a second .14 and a third 15 grate are such as to pass freely through a profile between the first locks 43.

7. The furnace according to Claim 1 c h a r a c t e r i z e d i n t h a t the side travel of the furnace is provided by turning a gear wheel 4J. being engaged into a rack 42 being clamped to a frame 40 of the equipment.