GB2082299A

GB2082299A - Continuously Operated Heat- treatment Furnace for Pipes

Info

Publication number: GB2082299A
Application number: GB8123310A
Authority: GB
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 1980-08-08
Filing date: 1981-07-30
Publication date: 1982-03-03
Also published as: GB2082299B

Abstract

An apparatus for heat-treating pipes comprising a furnace chamber A for accommodating a plurality of pipes P as arranged in parallel, a chain conveyor 15 disposed in the furnace chamber for transporting the pipes P in a direction at right angles to the axes of the pipes, and a plurality of stopper means 20 for stopping the pipes intermittently at suitably spaced- apart positions in the path of transport by the chain conveyor 15 and causing each of the pipes to rotate about its own axis in cooperation with the chain conveyor 15. Since the pipe is intermittently stopped and rotated about its own axis during heat treatment, the pipe is free of thermal deformation to an elliptical shape. Pipes can be heat-treated in succession in a small space, therefor with a very high efficiency. The force of transport of the chain conveyor 15 is utilized for rotating the pipe without necessitating any additional device for the rotation, hence advantageous in cost. <IMAGE>

Description

SPECIFICATION Apparatus For Heat-Treating Pipes The present invention relates to an apparatus for heat-treating pipes, such as cast-iron pipes.

It is known to heat-treat cast-iron pipes by heating the pipes to a predetermined temperature after the pipes have been spontaneously cooled once and subsequently cooling the pipes slowly at a specified rate to obtained the desired ferrite structure. For this heat treatment, continuous annealing furnaces are generally used in which the pipes are passed through a heating zone, soaking zone and slow cooling zone while being transported. However, the slow cooling of pipes requires a considerably long distance and a large space. The large space results in great heat losses, while energy losses are also involved in heating the pipes to the predetermined temperature after spontaneous cooling. On the other hand, batch furnaces, although used, are inefficient.

The main object of the invention is to overcome these problems and to provide a heattreating furnace by which pipes can be treated efficiently in a small space while being prevented from deforming to an elliptical cross section due to the high treating temperature.

To fulfill this object, the invention provides an apparatus for heat-treating pipes comprising a furnace chamber having an inlet and an outlet and capable of accommodating a plurality of pipes as arranged in parallel at a suitable spacing, a plurality of main chains disposed in the furnace chamber and drivingly movable in a direction at right angles to the axes of the pipes for providing a path of transport of the pipes, and a plurality of stopper means for stopping the pipes intermittently at suitably spaced-apart positions in the path of transport and causing each of the pipes to rotate about its own axis in cooperation with the main chains.

According to the arrangement described above, the pipe is brought into engagement with the stopper means at each of its stopped positions, where the pipe is rotated about its own axis by the movement of the main chains. This prevents elliptical deformation of the pipe during the heat treatment. Further since the force of movement of the main chains (generally the conveying force thereof) is utilized for rotating the pipe about its own axis, there is no need to separately supply a power only for the rotation of the pipe.

In addition to the foregoing problems, the heattreating of pipes involves the following problem.

For example, because the weight of the pipe per unit length is not uniform axially thereof, the pipe is liable to move axially thereof while being rotated about its own axis in engagement with the stopper means or the like. Such axial movement or displacement of the pipe may be corrected, for example, by a pusher for pushing the pipe in the axial direction, but if the pipe has a large diameter, the pusher requires a great force.

Furthermore, when pushing the pipe in a red-hot state, the pusher is likely to deform the pipe. The pushing method is therefore infeasible.

Accordingly it has been practice to use a furnace of increased width for avoiding the possible damage to the furnace wall by the collision of pipes and to provide an additional chain for preventing the pipe from running off the path.

This entails increased heat losses and renders the equipment costly.

According to a preferred embodiment of the present invention, the apparatus further comprises sensor means provided in corresponding relation to each of the stopper means for detecting axial movement of the pipe, and an expedient provided for the stopper means and operable in response to the sensor means for correcting axial displacement of the pipe.

With this arrangement, the axial displacement of the pipe can be corrected at each of its stopped positions, consequently eliminating the necessity of increasing the width of the furnace or providing an additional chain and therefore assuring savings in heat energy and a reduction in the equipment cost.

Various features and advantages of the present invention will become apparent from the following embodiments described with reference to the accompanying drawings, in which: Fig. 1 is an overall side elevation in vertical section showing an apparatus which is a first embodiment of the invention; Fig. 2 is a side elevation showing stopper means thereof; Fig. 3 is a plan view showing a modification of the stopper means; Fig. 4 is a side elevation of the same; Fig. 5 is a block diagram showing a system for controlling the stopper means; Fig. 6 is a front view showning another modification of the stopper means; Fig. 7 is a side elevation showing the same partly in section; Fig. 8 is a side elevation partly in section and showing another modification of the stopper means;; Fig. 9 is an overall side elevation in vertical section showing a second embodiment of the invention; Fig. 10 is a side elevation showing modified engaging portions of stopper means thereof; and Fig. 11 is an overall side elevation in vertical section showing a third embodiment of the invention.

With reference to Figs. 1 and 2, a furnace 1 has a furnace chamber A capable of accommodating a plurality of (e.g. five as illustrated) pipes P as arranged in parallel at a suitable spacing. The chamber A has an inlet 2 for the pipe P at one end of the parallel arrangement of pipes and an outlet 3 for the pipe at the other end thereof. A chamber 4 for feeding the pipe P is adjacent the inlet 2. A pipe P as withdrawn in a red-hot state from the rotary die of an unillustrated centrifugal casting machine is brought into the feed chamber 4 and retained therein while being prevented from cooling before being fed into the furnace chamber A. A liftable door 5 is provided between the inlet 2 and the feed chamber 4, and a liftable door 6 is disposed at the outlet 3. The furnace chamber A further has an intermediate liftable door 7 at an intermediate location of the parallel pipe arrangement.The furnace chamber A is divided by the intermediate door 7 into a heating chamber Al at the inlet side and a slow cooling chamber A2. Heat-insulating curtains are usable in place of the doors 5 to 7.

Mounted on the upper wall of the furnace 1 are burners 8a and 8b positioned in the heating chamber Al above the arrangement of pipes P for directly heating the top of the pipe P with a hightemperature gas to a predetermined temperature.

Cooling pipes 9 are disposed in an upper portion of the slow cqoling chamber A2 closer to the heating chamber Al for efficiently cooling the pipe P at a rate within a predetermined range.

Through a damper 11 and a distributing header 12, cooling air is supplied to the cooling pipes 9 from a blower 10 mounted on the furnace 1. The air is heated while passing through the cooling pipes 9 and sent via a collecting header 13 and an air duct 14 to the burners 8a and 8b as combustion air.

At a lower portion of the furnace chamber A, a chain conveyor 1 5 travels for transporting pipes P from the inlet 2 to the outlet 3 and rotating each of the pipes P about its own axis. The chain conveyor 1 5 comprises a plurality of endless main chains 1 6 arranged side by side axially of the pipe P at a suitable spacing for transporting pipes P on their outer peripheries. Indicated at 1 7 are drive sprockets at the outlet 3, at 18 driven sprockets at the inlet 2 and at 19a, 19b upper and lower chain guide rails, respectively.

Stopper means 20 are arranged at a suitable spacing in the direction of transport of pipes by the chain conveyor 1 5. Each of the stopper means 20 has a set of rollers 21 arranged as spaced apart axially of the pipe P and upwardly movable into the path of transport of pipes by the chain conveyor 1 5 of engage the pipe P, the set of rollers being downwardly movable from the engaging position to a retracted position below the path. Thus each of the illustrated pipes P is rotatably supported at its engaged position on the chain conveyor 1 5 by the set of rollers 21 at the corresponding engaging position. With the travel of the main chains 1 6, the pipe P is rotated about its own axis in the stopped or engaged position.

As shown in Fig. 2, each of the stopper means 20 comprises a pivotable frame 25 turnably supported at its lower end by horizontal pivots 24 on bearings 23 at one end of a fixed base 22, the above-mentioned rollers 21 rotatably mounted on the upper end of the pivotable frame 25, and a cylinder assembly 26 interconnecting an intermediate portion of the pivotable frame 25 and the other end of the base 22 for turning the pivotable frame 25. The rollers 21 are moved into or out of the path of transport of the pipe P by the extension or contraction of the cylinder assembly 26.

A lifter 27 of the pantograph type disposed at a lower portion of the feed chamber 4 includes a lifting support 27a and a tiltable frame 27b on the support 27a. A pipe P withdrawn from the rotary die is placed onto the tiltable frame 27b in its lowered position. To feed the pipe P into the furnace chamber A, the tiltable frame 27b is raised by the support 27a to the level of the path of transport on the chain conveyor 1 5 as shown in broken lines in Fig. 1 and is thereafter tilted to cause the pipe P to roll into the chamber A.

Indicated at 28 is a delivery guide adjacent the outlet 3. When the path of transport provided by the chain conveyor 1 5 is slightly inclined as illustrated, the pipe P will roll along the path during transport.

The apparatus operates in the following manner. For the heat treatment of pipes P, the chain conveyor 1 5 is driven in the direction of arrow shown at all times. With the rollers 21 of the stopper means 20 projected into the path of transport on the chain conveyor 1 5, the liftable door 5 is raised, and the pipe P in the feed chamber 4 is fed to the furnace chamber A through the inlet 2 by the lifter 27, whereupon the door 5 is closed. The pipe P is transported by rolling by itself and also by the chain conveyor 15, and is stopped by engagement with the set of roller 21 in a first engaged position. In this stopped position, the pipe is rotated about its own axis by the travel of the main chains 1 6 while being heated at its top portion to a specified temperature directly by the burners 8a thereabove.Although the pipe P becomes easily deformable by the rise of temperature due to the heating, elliptical deformation of the pipe P is prevented by the rotation.

Upon lapse of a predetermined period of time, the stopper means 20 are operated to retract the rollers 21 from the path of transport for a short period of time. The rollers 21 are thereafter projected to the engaging position again. In the meantime, the pipe P is transferred to a second engaged position into engagement with the rollers 21 of the stopper means 20 in this position by the travel of the chain conveyor 1 5 and also by rolling. In the same manner as above, the pipe P, while rotating about its own axis, is heated by tne burners 8b and maintained at a specified temperature for a specified period of time.

The intermediate door 7 is thereafter lifted, and the rollers 21 are retracted from the path for a short period of time again. The pipe P is transported from the heating chamber Al to a third engaged position in the slow cooling chamber A2, where the pipe is engaged by another set of rollers 21 and cooled for a specified period of time while rotating about its own axis.

Subsequently the pipe P is similarly cooled at fourth and fifth engaged positions while rotating about its own axis and is thereafter delivered from the outlet 3 onto the delivery guide 28 on completion of heat treatment. Although the heat treatment has been described above stepwise only for one pipe P to simplify the description, a plurality of pipes are of course heat-treated continuously in succession in practice.

Figs. 3 and 4 show a modification of the stopper means provided with an expedient for correcting the axial displacement of the pipe. In this modification, the pivotable frame 25 is supported by horizontal pivots 24 on a second frame 29 which is slidable on a fixed base 22. The second frame 29 is turnably mounted on a vertical rod 30 upstanding from the fixed base 22 and positioned closer to one of the main chains 1 6. A second cylinder assembly 31 is attached at its base end to the fixed base 22 and has a piston rod 31 a with its forward end attached to the second frame 29. When the piston rod 31 a of the second cylinder assembly 31 is stretched or retracted, the second frame 29 turns about the vertical rod 30 in a horizontal plane.Sensors 32a, 32b for detecting the axial movement of the pipe P are electrically connected to a circuit c (Fig. 5) for controlling the second cylinder assembly 31.

Throughout Figs. 1 to 4, et seq. like parts serving the same functions despite some differences are referred to by like reference numerals.

The axial displacement of the pipe is corrected by the modified stopper means 20 in the following manner. When the pipe P in one of the engaged or stopped positions moves more than a distance axially thereof, the pipe P comes into contact with the sensor 32a or 32b to actuate that sensor. Assuming that the pipe P has moved, for example, rightward in Fig. 3, actuating the sensor 32b, a signal from the sensor 32b is fed to the control circuit c, which controls the second cylinder assembly 31 to stretch its piston rod 31 a, turning the second frame 29 about the vertical rod 30 in the direction of arrow A in Fig. 3 through a specified angle. This shifts the position of the contact of a roller 21 b with the pipe P toward a direction opposite to the direction of transport of the pipe to correct the axial displacement of the pipe P.If the pipe P moves leftward in Fig. 3, the piston rod 31 a of the second cylinder assembly 31 retracts, shifting the position of the contact of the roller 21 b with the pipe P toward the pipe transport direction to correct the axial displacement of the pipe P.

While the axial displacement of the pipe is corrected by turning the second frame 29 about the vertical rod 30 in the case of the modified stopper means 20 described, the first pivotable frame 25 may be replaced by a plurality of (usually two) pivotable arms which are each provided with a roller at the free end and which are turnable by separate cylinder assemblies individually for adjustment to correct the axial displacement of the pipe.

Although the rollers 21 of the stopper means 20 shown in Figs. 1 to 4 are movable into or out of the path of transport all by turning, Figs. 6 and 7 show another modified stopper means 20 having rollers which are linearly movable. In this case, each of rollers 21 a, 21 b is mounted on th'e forward end of a support member 35 fitting in a guide member 33 and upwardly or downwardly movable along a direction inclined with respect to the vertical by a drive assembly 34, such as an electric jack. The drive assemblies 34 are coupled via a control circuit c (Fig. 5) to sensors 32a, 32b for detecting the axial displacement of the pipe.

The axial displacement of the pipe is corrected by the stopper means 20 substantially in the same manner as by the one shown in Figs. 3 and 4. When the pipe P touches the sensor 32b with the rollers 21 a, 21 b in engagement with the pipe P, the roller 21 b is further projected by the corresponding drive assembly 34 for correcting the axial displacement. When the pipe touches the sensor 32a, the roller 21 a is similarly moved for correction. The position of the pipe can be course be corrected by lowering one of the rollers 21 a, 21 b, or by lowering one roller and raising the other roller, instead of raising one of the rollers.

Since the arrangement of the lower portion of the furnace chamber is not shown in detail in Figs.

1 to 4, the arrangement will be described with reference to Figs. 6 and 7. A slot 36 is attached to the endless main chain 16 by unillustrated members. The slat 36 actually provides a surface for transporting the pipe thereon. The main chain 16 travels by being guided with a guide 37, and the slat 36 with guides 38, 39. The furnace chamber A is divided into upper and lower two portions by a partition wall 40 made of refractory bricks or the like, whereby heat losses in the furnace chamber can be prevented.

Fig. 8 shows still another modification of the stopper means which has the same construction as the one shown in Figs. 6 and 7 except that rollers 21 a, 21 b are vertically movable instead of being obliquely movable. This modification is advantageous in that the space in the partition wall 40 around the stopper means 20 can be sealed easily.

A second embodiment of the invention will now be described with reference to Figs. 9 and 10. With this embodiment, stopper means 20 comprise projections 42 attached to a plurality of auxiliary chains 41 extending in parallel to main chains 16, the projections 42 being arranged in the direction of transport of pipes at a suitable spacing. Each of the stopper means 20 includes a set of projections 42 aligned axially of the pipe.

Each of the auxiliary chains 41 is reeved around a drive sprocket 43 disposed in the vicinity of a furnace chamber inlet 2 and a driven sprocket 44 provided close to a furnace chamber outlet 3, and is driven in the direction of transport of the pipe P intermittently at a predetermined time interval.

The auxiliary chain 41 is moved at a time by a distance corresponding to the pitch of the projections 42. The projections 42 are of course replaceable by rollers 45 as shown in Fig. 10 to reduce the frictional resistance involved.

In the case of the present embodiment, pipes P are transported by driving the main chains 1 6 and auxiliary chains 41 in the direction of arrows. The pipe P can be rotated about its own axis by continuously driving the main chains in the direction of arrow while holding the auxiliary chains 41 in a stopped position, i.e. holding the pipe P in engagement with the aligned projections 42 or rollers 45. Conversely it is possible to drive the main chains 1 6 from the outlet 3 toward the inlet 2 and transport the pipe P by the auxiliary chains 41, with the projections 42 or rollers 45 thereon in engagement with the pipe P on the rear side thereof with respect to the direction of transport. In this case, the auxiliary chains 41 must have a length equal to or larger than the length of the main chains 16.

Fig. 11 shows a third embodiment of the invention which is characterized by a furnace chamber A inclined downward from inlet to outlet, and main chains 16 and auxiliary chains 41 which are similarly inclined. Preferably the angle of inclination of the furnace chamber A is 5 to 200. Adjacent the outlet 3 of the furnace chamber A, there is a delivery chamber B having an upper delivery outlet 46 which is provided with a shutoff door 47. Only when either one of a liftable door 6 and the shutoff door 47 is held closed, the other door is openable so that the interior of the furnace chamber A will not directly communicate with the atmosphere when the pipe P is delivered. Flexible curtains 48, 49, which are knitted of heat-insulating material, are suspended from the top wall of the furnace 1.The curtain 49, corresponding to the liftable door 7, has a simpler construction than the door.

The present embodiment somewhat differs from the foregoing embodiments in the cooling and air supply system. Air supply-discharge ducts 50,51 having shut-off valves 50a, 51a are disposed close to the inlet 2 and outlet 3 of the furnace 1. An inlet portion of the furnace chamber and an outlet portion thereof are held in communication with each other by an air duct 52 which is provided with a fan 53 for supplying air selectively in one of opposite directions and a shutoff valve 54.The shutoff valves 50a, 51 a, 54 and fan 53 on these ducts 50, 51, 52 are operatively connected together to adjust the rate of cooling as desired, for example, by forming an air stream from heating zone Al to slow cooling zone A2 in the furnace chamber A for reducing the cooling rate, or by forming an air stream from slow cooling zone A2 to heating zone Al for increasing the cooling rate. Between the fan 53 and the valve 54, an air supply pipe 55 having a shutoff valve 55a extends from the duct 52 to burners 8a, 8b, such that air heated in the furnace chamber A can be used for combustion.

A lifter 56 is disposed in the lower portion of the delivery chamber B. The pipe P sent out from the furnace chamber A is placed on the lifter 56, the liftable door 6 is closed, the shutoff door 47 is opened, and the pipe P is raised to above the outlet 46. The pipe P is thereafter placed onto a delivery guide 28 adjacent the outlet 46.

The present embodiment is characterized in that the furnace chamber A is inclined. This assures the advantage of reducing convection from heating zone at the inlet side to slow cooling zone at the outlet side, readily affording a temperature gradient needed for heating and slow-cooling pipes in the furnace chamber.

Furthermore since the path of transport of pipes is also inclined in corresponding relation to the inclination of the furnace chamber A, the pipes can be transported by gravity, with the result that the main chain 16 can be driven in the direction of arrow, i.e. from outlet to inlet, solely for rotating the pipe P about its own axis.

Although the furnace chambers A of the foregoing embodiments are divided into a heating chamber Al and a slow cooling chamber A2 which have two and three stopped positions, respectively, the furnace chamber A need not always be so divided depending on the composition of the pipe, casting conditions, etc., while the number of stopped positions is variable as desired.

Claims

1. An apparatus for heat-treating pipes comprising a furnace chamber having an inlet and an outlet and capable of accommodating a plurality of pipes as arranged in parallel at a suitable spacing, a plurality of main chains disposed in the furnace chamber and drivingly movable in a direction at right angles to the axes of the pipes for providing a path of transport of the pipes, and a plurality of stopper means for stopping the pipes intermittently at suitably spaced-apart positions in the path of transport and causing each of the pipes to rotate about its own axis in cooperation with the main chains.

2. An apparatus as defined in claim 1 wherein each of the stopper means comprises a pivotable frame supported at its base end by horizontal pivots, a plurality of rollers mounted on the free end of the pivotable frame, and means for moving the pivotable frame into or out of the path of transport by turning the frame.

3. An apparatus as defined in claim 2 wherein the horizontal pivots are attached to a frame member turnably supported by a vertical rod on a fixed base and slidable on the fixed base.

4. An apparatus as defined in claim 3 which further comprises sensor means provided in corresponding relation to each of the stopper means for detecting axial movement of the pipe, and means coupled to the sensor means for turning the frame member about the vertical rod, whereby axial displacement of the pipe in transport is corrected.

5. An apparatus as defined in claim 1 wherein each of the stopper means comprises a plurality of rollers spaced apart axially of the pipe, and means for moving the rollers linearly into or out of the path of transport.

6. An apparatus as defined in claim 5 wherein the roller moving means are provided for the rollers individually and each comprises a guide member disposed below the path of transport, a slider fitting in the guide member and supporting the roller on its one end, and a drive assembly connected to the other end of the slider.

7. An apparatus as defined in claim 6 which further comprises sensor means provided in corresponding relation to each of the stopper means for detecting axial movement of the pipe and wherein the amounts of projection of the rollers of each stopper means are individually controlled in response to the corresponding sensor means to correct axial displacement of the pipe in transport.

8. An apparatus as defined in claim 1 wherein each of the stopper means comprises a set of engaging portions arranged axially of the pipe and mounted on a plurality of auxiliary chains drivingly movable in a direction parallel to the main chains.

9. An apparatus as defined in claim 8 wherein the engaging portion is a roller.

10. An apparatus as defined in claim 1 wherein a feed chamber is opposed to the inlet for accommodating the pipe to be fed to the furnace chamber.

11. An apparatus as defined in claim 1 wherein partition means is provided for dividing the furnace chamber into a heating zone and a slow cooling zone.

12. An apparatus as defined in claim 11 wherein the partition means is a liftable door provided between the inlet and the outlet.

13. An apparatus as defined in claim 11 wherein the partition means is a heat-insulating curtain provided between the inlet and the outlet.

14. An apparatus as defined in claim 1 or 11 wherein each gf the inlet and the outlet is provided with closure means.

1 5. An apparatus as defined in claim 14 wherein the closure means comprises a liftable door and/or a heat-insulating curtain.

1 6. An apparatus as defined in claim 1 wherein burners are provided at the inlet side of the furnace chamber for radiating heat toward the top of the pipe.

1 7. An apparatus as defined in claim 1 6 wherein means is provided for supplying to the burners air subjected to heat exchange at the outlet side of the furnace chamber.

1 8. An apparatus as defined in claim 1 wherein means is provided for adjustably supplying to the inlet side of the furnace chamber air subjected to heat exchange at the outlet side of the furnace chamber.

1 9. An apparatus as defined in claim 1 wherein the furnace chamber is inclined from inlet to outlet, and the path of transport is similarly inclined.

20. An apparatus as defined in claim 19 wherein the furnace chamber and the path of transport are inclined at an angle of 5 to 20 .

21. Apparatus for heat-treating pipes substantially as described herein with reference to and as illustrated in Figures 1 to 8, or 9 and 10, or Figure 11 of the accompanying drawings.