A method and an apparatus for press tempering

Abstract

 A method of tempering planar metal objects comprises the following steps: first at least one metal object is heated, whereafter the objects are conveyed along a conveyor path (23). Thereafter, the objects are conveyed in between two pressing devices (2, 3) which approach one another until parts of the pressing devices (2, 3) are pressed against one another. At the same time, the objects are retained between the pressing devices (2, 3) and are cooled in a coolant. Finally, the objects are released and conveyed off from the pressing devices (2, 3). When the objects are retained and released, respectively, one of the pressing devices (2, 3) moves vertically through the conveyor path (23).
An apparatus for tempering planar metal objects includes a device for heating the objects, a conveyor path (23), two pressing devices (2, 3) and a cooling device (7) with a coolant. One of the pressing devices (2, 3) is movable in the vertical direction through the conveyor path (23) for retaining and releasing the objects.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method of tempering planar metal objects, comprising the steps that at least one metal object is heated, that the objects are placed between an upper and a lower pressing device, that the two pressing devices approach one another until parts of the pressing devices are urged against one another, at the same time as the objects are retained between the pressing devices, that the objects are cooled in a coolant, and that the objects are released and conveyed off from the pressing devices.

[0002] The present invention also relates to an apparatus for tempering planar metal objects, comprising an upper and a lower pressing device, a device for heating the objects and a cooling device containing a coolant.

BACKGROUND ART

[0003] USPS 1, 457, 772 discloses a method and an apparatus for forming and tempering sheet metal bodies. The tempering takes place in the die which is employed for producing the body, which entails that the method is hardly intended for the rational tempering of large-scale series. Moreover, the capacity in the forming tool or die is limited. Nor is the method principally intended for planar objects. The coolant that is employed is in the liquid phase and is led in through pipes or channels in the die.

[0004] SE 501 685 discloses an apparatus for cooling steel parts on tempering. The patent specification principally relates to the tempering of flat objects. The parts are placed between two grooved press surfaces and the distance between these surfaces is of the same order of magnitude as the thickness of the parts, and preferably 0.05 mm larger. The coolant is a gas which is aspirated in through holes in the troughs of the grooved surfaces. The infeed and discharge of the parts between the surfaces are not described in greater detail.

PROBLEM STRUCTURE

[0005] There is hence a need for a rational method for press tempering large quantities of planar metal objects of thicknesses and configurations that vary between each series. Consequently, it is desirable that the apparatus may readily be adjusted so as to accommodate different material thicknesses, that the infeed and discharge of the objects are rapid and rational, and that, above all, the objects remain flat during the process.

SOLUTION

[0006] The object forming the basis of the present invention will be attained in respect of the method if this is given the characterizing feature that one of the pressing devices moves vertically through the conveyor path when the objects are retained and released, respectively.

[0007] Concerning the apparatus, the object forming the basis of the present invention will be attained if this is given the characterizing feature that one of the pressing devices is movable in the vertical direction through the conveyor path for retaining and releasing the objects.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0008] The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1

is a straight side elevation of the press in the open position when the objects are fed in;

Fig. 2

is a detailed view of the press according to Fig. 1;

Fig. 3

is a view according to Fig. 2 when the press is in the closed position;

Fig. 4

is a view straight from beneath of the upper press plate; and

Fig. 5

is a view corresponding to that of Fig. 2 but seen in the direction of the arrow A.

DESCRIPTION OF PREFERRED EMBODIMENT

[0009] The present invention relates to a pressing and cooling apparatus which is included in a larger plant for tempering. The plant has a furnace for heating the objects which are to be tempered. In the furnace, the objects are surrounded by a controlled atmosphere which, for example, consists of a mixture of nitrogen and methanol. The objects are conveyed through the furnace during a given period of time, whereafter they are fed into a press 1 for cooling, where the press operates at a predetermined pressure. This press 1 constitutes the kernel subject matter of the present invention. Once the objects have been cooled, they are conveyed further through a washing plant and finally through an annealing furnace before being discharged and inspected as regards thickness and flatness.

[0010] The press 1 which is shown in Fig. 1 has a tank 7 for a coolant and a pressing device which is disposed above it. The tank 7 rests on a number of legs 21 which in turn are in contact with the floor. The legs form part of a frame for the apparatus according to the invention. On the upper side of the press, there is disposed a lid 12 fixedly secured in the frame. Through the lid 12, there extend a number of guide rods 11 which are reciprocal upwards and downwards in relation to the frame. The lower ends of the guide rods 11 are connected to a plate 18 which is movable together with the guide rods 11. The plate 18 is connected to an upper pressing device 2. The distance between them is adjustable in order to be able to adapt to the thickness of the metal objects, but is constant during a working cycle. A lower pressing device 3 is movably connected to the plate 18 by the intermediary of a number of rods 17 which extend upwards from the lower pressing device 3 and past the upper pressing device 2 to the plate 18. The lower pressing device 2 moves towards the upper pressing device 3 on retention of the metal objects and away from it on release of them. The objects are conveyed in and out of the press in the direction of the arrow A on a conveyor path which, in the preferred embodiment, consists of a series of rollers 4, a roller path 23.

[0011] Fig. 1 shows the press 1 from the side in its open position. The objects that are to be tempered are conveyed along the roller path 23 in the conveying direction A until they arrive between the upper pressing device 2 and the lower pressing device 3. The objects that are to be tempered are heated during their transport up to the press 1. When the heating has reached a sufficient level, the objects are retained between the two pressing devices 2 and 3, in that parts of them are brought into contact with one another and are cooled, in that the two pressing devices 2 and 3 are lowered, together with the objects, into a coolant in the tank 7 straight beneath the press. When the pressing devices 2 and 3 are once again raised to the original position, the objects are released and conveyed further in the conveying direction A.

[0012] In detail, this implies that the present invention discloses a novel method of tempering flat metal objects. The metal objects are many in number and may have a multiplicity of different configurations, if the only restriction is that their extend in the plane is greater than their extent in the vertical direction, i.e. the metal objects are planar and of a substantially constant thickness. Their thickness is substantially of equal size throughout all objects on one occasion. It is possible to change the permitted thickness, but the objects should be of the same thickness if they are to be tempered at the same time. No adaptation to the outer contour of the objects, above and beyond adjustment of the thickness, needs to be carried out.

[0013] For the metal objects not to arrive partially outside the two pressing devices 2 and 3 on tempering, a certain degree of accuracy is required on the infeed of the objects. In such instance, the objects are placed inside a frame or a zone of predetermined outer dimensions. In the preferred embodiment, the zone is square and its dimensions are 55 x 55 cm. When the zone with these dimensions has been filled with objects, a so-called "batch" has been created. Before the next set of objects, or the next "batch" can be laid out, a predetermined time must elapse. The plant is advantageously provided with clocks and signal lamps which signal to the operator when a new "batch" can be fed in. The time elapsed is determined by the speed of the roller path and by the time which is required for applying the pressing devices 2 and 3, cooling and conveying off one "batch". Thus, the earlier "batch" has been discharged out of the press just before the next "batch" arrives. In order to control when the press is to be closed, there are sensors which sense when the objects in the "batch" have reached sufficiently far forward for pressing and cooling to be both possible and appropriate.

[0014] Before the objects arrive at the pressing devices 2 and 3, they are heated to a suitable temperature for a suitable time. The temperature and heating time are determined by the material employed, the dimensions of the objects, and also by the desired final result. This type of calculation and appropriate measures are previously known in the art and will not be described in greater detail. Typically, the heating time may vary between 5 and 30 minutes.

[0015] The heating time t, the speed of the roller path v and the conveying distance s through the furnace are related to one another in the well-known relationship s = νt. The speed ν of the roller path is thus determined by the desired heating time t, since the conveying distance s is constant for each plant. Correspondingly, the distance between each "batch" is calculated when the speed ν of the roller path and the time for cooling have been established.

[0016] When the objects on the roller path have been conveyed in between the two pressing devices 2 and 3, the lower pressing device 3 is raised towards the upper pressing device 2. The difference between the lowered position and the raised position of the lower pressing device 3 is apparent from a comparison between Figs. 2 and 3. On application, the lower pressing device 3 passes partially through and upwards in the vertical direction past the conveyor device which, in the preferred embodiment, consists of the rollers 4 spaced a short distance from each other. On retention of the metal objects, these are thus only in contact with the upper and lower pressing devices 2 and 3, possibly only with the lower pressing device. The objects are not in contact with the conveyor rollers 4. In the preferred embodiment, the compression force on the lower pressing device lies in the order of magnitude of 7,000 Newton. Also in this stage, the metal objects are surrounded by the controlled atmosphere which, in the preferred embodiment, contains nitrogen and methanol.

[0017] When the pressing devices 2 and 3 have been brought into contact with one another and the objects retained between them, both the pressing devices 2 and 3 and the objects are cooled. The cooling temperature and the time for cooling are determined in the same manner as corresponding parameters in the heating operation. In the tempering method according to the invention, the objects are retained between the upper and lower pressing devices 2 and 3. Already when the pressing devices 2 and 3 close, the objects are directed such that they will be planar. Both of the pressing devices 2 and 3 are subsequently lowered down into the tank 7 with coolant straight beneath the press 1, and the conveyor rollers 4 which are located within the press 1 accompany the pressing devices 2 and 3 down into the coolant. Since the objects are held fixedly clamped between the pressing devices 2 and 3 during the cooling operation, they retain their original configuration and flatness. However, the objects have certain possibilities for movement in the plane, but not in the vertical direction. This implies that objects that are warped are straightened, since the space between the pressing devices 2 and 3 is limited.

[0018] When the cooling is complete, both of the pressing devices 2 and 3 and the rollers 4 are lifted up out of the tank 7 and the objects are released in that the two pressing devices 2 and 3 distance themselves from each other by the press being opened with the aid of hydraulics and forces from a number of spring means 8. In such instance, the lower pressing device 3 moves downwards to a position beneath the conveyor rollers 4. The tempered objects are then free for further transport out of the press 1 along the outgoing roller path 23.

[0019] The apparatus is shown in detail in Figs. 2 and 3. The conveying of the objects that are to be tempered takes place on a conveyor consisting of a large number of rollers 4 placed a short distance from one another. The rollers rotate clockwise in the Figure, so that an object resting on them is conveyed in the direction A, i.e. to the right in the Figures. The rollers 4 are substantially cylindrical. For problem-free conveying of the objects, it is desirable that the rollers 4 are not warped or unintentionally given planar regions along their circumferential surface. The driving of the rollers 4 preferably takes place with the aid of chains. The rollers 4 are disposed in support members 10 on retainer devices 22 which are shown in Fig. 5. The retainer devices 22 extend downwards from the plate 18 on either side of the pressing devices 2 and 3. The retainer devices 22 and the support members 10 accompany in the upward and downward movements of the plate 18, which also implies that the rollers 4 are lowered together with the pressing devices 2 and 3.

[0020] The distance between the rollers is of the same order of magnitude as their diameter. It is essential that the distance between the rollers 4 is not so great that the objects which are to be tempered run the risk of falling down between them or topple downwards and fasten between the rollers 4, with operational stoppage as a result. A large number of rollers with slight diameter in relation to the objects to be tempered is therefore to be preferred.

[0021] The objects are conveyed on the roller path 23 while being heated. During the heating operation, the objects are, as was mentioned above, preferably surrounded by a mixture of nitrogen and methanol. The heating takes place advantageously in a closed tunnel-like space. When the objects are ready-heated and have arrived at the press 1, they are conveyed further on the conveyor rollers 4 in between the upper pressing device 2 and the lower pressing device 3. The lower pressing device 3 is provided with a row of elongate support members or bars 5 whose width or thickness corresponds to or is slightly less than the distance between the rollers 4 in such a manner that the bars 5 may pass up between the rollers 4. When the lower pressing device 3 moves upwards, passage of the support members 5 is permitted between the rollers 4. Thus, the upper edge of the support members or bars 5 will, on pressing, be located above the upper defining surface of the conveyor rollers 4, which implies that the objects to be tempered are no longer in contact with the conveyor rollers 4. The advantage with this is that the risk that the rollers be flattened or warped in the pressing operation is eliminated. The upper pressing device 2 is provided with a number of downwardly directed elongate ribs 6 which are intended for contact with the objects to be tempered.

[0022] The lower pressing device 3 is moved towards the upper pressing device 2 and holds the objects therebetween. Along two opposing edge portions on the upper pressing device 2, once spacer element 24 is disposed on each. The spacer elements 24 are elongate and replaceable. A replacement of the spacer elements 24 implies that spacer elements 24 of different, but pairwise equal, height are disposed on the upper pressing device 2. On contact between the lower 3 and the upper pressing device 2, the spacer elements 24 are those parts which determine how close to one another the two pressing devices 2 and 3 are moved. The spacer elements 24 are selected such that the distance between the two pressing devices 2 and 3 inside the spacer elements 24 is always slightly larger than the maximum permitted thickness of the objects. As a result, full compression pressure is not applied on the metal objects. When the objects are warped and must be straightened, they are subjected to a certain pressure until they have been straightened out sufficiently. Their total extent in the vertical direction then lies within the maximum permitted. In order to support the lower pressing device 3 and manoeuvre it up and down, a number of rods 17 are provided which extend upwards from the lower pressing device 3 past the upper pressing device 2 to the plate 18 which in turn is connected to the guide rods 11. The clamping force of the lower pressing device 3 is given by a number of spring means (six in number in the preferred embodiment) which draw the lower pressing device 3 upwards until a number of arrest devices 9 stop the upwardly directed movement. In the preferred embodiment, the arrest devices 9 are in the form of rings which are disposed on the rods 17 which interconnect the lower pressing device 3 with the plate 18. The arrest devices 9 stop the movement when they come into contact with sleeves 19 which are disposed on the underside of the plate 18.

[0023] In detail, the procedure for moving the pressing devices 2 and 3 towards one another is such that the plate 18 is moved downwards by a number of hydraulic cylinders (not shown). When the springs 8 lose contact with the lid 12, the two pressing devices 2 and 3 are moved into contact with one another with the aid of spring forces from the springs 8. Conversely, the two pressing devices 2 and 3 will be separated from one another when the springs 8, with the aid of the hydraulics, once again come into contact with the lid 12.

[0024] The upper pressing device 2 and the lower pressing device 3 are not only movable in relation to one another, but may also be displaced as a unit in the vertical direction. This takes place on the cooling of the objects to be tempered. In such instance, the conveyor rollers 4 in the support members 10 also accompany into the coolant. The coolant is disposed in the tank 7 and, for example, consists of an oil. The coolant circulates in the tank 7, and also outside it in order to be cooled. The volume of the tank 7 is of the order of magnitude of 1 m³ and the circulation system (not shown) disposed outside the tank 7 is of the order of magnitude of 2 m³. By such means, an almost constant temperature can be maintained in the coolant. If necessary, for example when the plant has been inoperative for a period, the coolant may also be heated to a suitable temperature. In order for the pressing devices 2 and 3, and the conveyor rollers 4 to be lowered and raised vertically, the guide rods 11 are disposed from the upper pressing device 2 and up to the upper side or lid 12 of the press 1. By such means, a linear movement will be ensured. The guide rods 11 consist, in the preferred embodiment, of four tempered shafts which run through ball bushings 16 in the upper side or lid 12 of the press 1. In order to arrest the upwardly directed movement of the pressing devices 2 and 3, one or more mechanical arrest members 20 are disposed on the upper side of the plate 18. When these come into contact with the upper side 12 of the press 1 from beneath, the movement is arrested.

[0025] In order to permit the coolant to completely surround the objects that are to be tempered, the upper pressing device 2 (which, in the preferred embodiment, is a press plate) is provided with a large number of holes 13 through which the coolant passes. This is most clearly apparent from Fig. 4 where the upper press plate 2 is shown from beneath. In this Figure, the ribs 6 in the upper press plate 2 are also visible. The plate 2 is meticulously machined, polished and nitrocaburated in order to keep it planar despite repeated heating and cooling.

[0026] After the cooling, the lower pressing device 3 is, as was previously described, released from the upper pressing device with the aid of hydraulic cylinders, compressed air or other suitable prime movers which counteract the force of the spring means 8. Such prime movers are not shown on the Drawings. The two pressing devices 2 and 3 are separated and the elongate support members 5 sink down between the conveyor rollers 4 and the objects to be tempered once again come into contact with the conveyor rollers 4. Thereafter, the objects are conveyed on the conveyor rollers 4 out of the press. In order to inspect the flatness and outer dimensions of the objects, it may be advantageous to cause the objects to pass through a gap acting as a gauge, a so-called letterbox, whose height corresponds to the maximum permitted height of the objects, including any possible warps. The parts which have become warped or which are excessively high will, in this operation, be entrapped in the gap and can be sorted off.

[0027] The upper pressing device 2 is spherically suspended in the centremost guide rod 14. The centremost guide rod 14 is also provided with a handle or spindle 15 for setting the height of the pressing position, i.e. the distance between the two pressing devices 2 and 3 on pressing. To this end, a section of the guide rod 14 is threaded, like its passage through the plate 18. The guide rod 14 extends further through a bushing in the lid 12. Thus, the guide rod 14 is movable through the lid 12.

DESCRIPTION OF ALTERNATIVE EMBODIMENT

[0028] The present invention may be modified so that the two pressing devices 2 and 3 are not wholly closed until the objects to be tempered are located a short distance down in the coolant. In practice, this is realised in that two hydraulic rams are provided so that they counteract or delay the release of the springs 8. The pressing devices 2 and 3 will then have time to be lowered a short distance down into the coolant before the spring forces move them into contact with each other. A complete contact between the objects and the coolant will be obtained, since the compression pressure does not prevent the coolant from penetrating in between the pressing devices 2 and 3 and the objects. A very brief period of time after the objects have been lowered down into the coolant, the pressing devices 2 and 3 are applied. This implies that the objects are not cooled excessively without compression pressure. Instead, the predominant part of the cooling cycle takes place, as previously, under pressure.

[0029] The present invention may also be modified for practical application in which the metal objects on average are subjected to a considerably higher pressure. This takes place in that use is made of spacer elements 24 which are as high as or lower than the maximum permitted thickness of the objects. However, this procedure may result in marks in the tempered metal objects, and the method is therefore only suitable when lower standards are placed on surface finish.

Claims

1. A method of tempering planar metal objects, comprising the steps that at least one metal object is heated, that the objects are conveyed along a conveyor path, that the objects are conveyed in between an upper (2) and a lower (3) pressing device, that the two pressing devices (2, 3) approach one another until parts of the pressing devices (2, 3) are urged against one another, at the same time as the objects are retained between the pressing devices, that the objects are cooled in a coolant, and that the objects are released and conveyed off from the pressing devices (2, 3), characterized in that one of the pressing devices (2, 3) moves in the vertical direction through the conveyor path when the objects are retained and released, respectively.

2. The method as claimed in Claim 1, characterized in that both the conveyor path between the pressing devices (2, 3) and the pressing devices (2, 3), and the objects are moved down into the coolant while the pressing devices (2, 3) hold the objects.

3. The method as claimed in Claim 1 or 2, characterized in that the pressing devices (2, 3) are urged against one another before the cooling in the coolant is commenced.

4. The method as claimed in Claim 1 or 2, characterized in that the cooling in the coolant is commenced before the pressing devices (2, 3) are pressed against one another.

5. The method as claimed in any of Claims 1 to 4, characterized in that the conveying of the objects takes place with the aid of rotating rollers (4).

6. The method as claimed in Claim 5, characterized in that parts of the pressing devices (2, 3) pass between the rollers (4).

7. An apparatus for tempering planar metal objects, comprising a device for heating the objects, a conveyor path for conveying the objects, an upper (2) and a lower (3) pressing device and a cooling device (7) containing a coolant, characterized in that one of the pressing devices (2, 3) is movable in the vertical direction through the conveyor path for retaining and releasing the objects.

8. The apparatus as claimed in Claim 7, characterized in that the conveyor path between the pressing devices (2, 3) and the pressing devices (2, 3) may be immersed in the coolant together with the retained objects.

9. The apparatus as claimed in Claim 7 or 8, characterized in that the conveyor path includes a large number of rotatably disposed rollers (4).

10. The apparatus as claimed in Claim 9, characterized in that the rollers (4) are disposed in such spaced apart relationship from one another that passage of parts of the pressing devices (2, 3) is permitted.

11. Use of an apparatus as claimed in any of Claims 7 to 10 for tempering planar metal objects.

Drawing