GB1561337A

GB1561337A - Chain conveyors

Info

Publication number: GB1561337A
Application number: GB3650676A
Authority: GB
Original assignee: Buehler AG
Current assignee: Buehler AG
Priority date: 1975-09-05
Filing date: 1976-09-02
Publication date: 1980-02-20
Also published as: JPS5249580A; DE2639789A1; NL7609626A; CH585139A5

Description

(54) IMPROVEMENTS RELATING TO CHAIN CONVEYORS (71) We, GBBRUEDER BUEHLER AG, of CH 9240 Uzwil, Switzerland, a Swiss Body Corporate, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to improvements to chain conveyors and more particularly to drag chain conveyors (also termed trough and chain conveyors) having a reversal shaft adjustable in position: it also relates to a method of operating such a conveyor.

Conveying chains of trough and chain conveyors are usually tensioned to about the equivalent of the frictional resistance of the return run. A suitable force is provided for acting on the reversal shaft so as to adjust automatically the position of the reversal shaft and to prevent the chain from becoming loose and sagging excessively.

If a relatively small adjustment travel is expected, the force of a preloaded compression spring can be used successfully for tensioning. The useful force of a spring is used up upon elongation of the chain, so that after relatively long spring travel the tensioning force may become too small and no longer able to compensate for further elongation of the chain.

To cater for long adjustment travel in chain conveyors, nowadays weights tend to be used for preloading. The reversal shaft is tensioned by a weight and rope-pulley system, the weight being appropriate to the necessary adjustment or tensioning force.

The use of weight represents a very good solution since the force remains constant over the entire tensioning distance. On the other hand, it is a disadvantage that the constructional outlay involved is relatively large, since not infrequently a tensioning force of several thousand kg and a corresponding weight are required.

As is known, in a chain conveyor serious consequences could result if the adjusting device fails. Particularly in the case of an enclosed trough and chain conveyor, the sagging portion of the chain running off the driving wheel could accumulate greatly so that a large part of the conveyor would be damaged without the possibility of detecting what is happening at a sufficiently early stage to try to prevent it. It does happen too often that such conveyors are damaged in this way.

The invention has as its object to provide an improved trough and chain conveyor and a method of operating it.

According to one aspect the invention provides a drag chain conveyor having a reversal shaft adjustable in position by a hydraulic adjustment piston and cylinder assembly, comprising a pump for delivery of hydraulic fluid under pressure to the adjustment cylinder by way of a pressure conduit, a non return valve intermediate the cylinder and the pump to check return flow of fluid, a first pressure limiting means upstream of the non return valve to limit to a selected first pressure value the pressure of the fluid presented by the conduit to the non return valve for onward transmission, a second pressure limiting means downstream of the non return valve to relieve the pressure of the fluid whenever it reaches a selected second pressure value higher than the first pressure value, the arrangement being such that as tension in the conveyor varies in course of normal operation the working pressure of the fluid can fluctuate between the said first and second pressure values and when it reaches the said second pressure value the conveyor can continue to operate with hydraulic pressure in the cylinder relieved to the said second pressure value.

The first pressure limiting means can be formed of a first pressure relief valve, and the second pressure limiting means can be formed of a second pressure relief valve which is set to a higher pressure than the first pressure relief valve.

The pump may be constructed as a gear pump and between the shaft and the gear pump a slip clutch may be arranged for limiting the maximum delivery pressure.

However the pump is preferably constructed as a piston pump and movement in one direction of the piston is caused by an eccentric disc arranged on the shaft and movement in the other direction by a spring.

Great operational reliability is obtained if (in accordance with a subsidiary feature of the invention) the spring is effective for actuating the pump in the oil delivery direction. In a further development of the invention the spring may be preloaded and by varying the preload the pump pressure can be adjusted. The maximum delivery pressure of the pump can then be determined by the maximum force of a spring and cannot exceed a predetermined value.

This construction is very advantageous particularly when the suction travel of the pump piston is brought about by an eccentric disc.

For if in this case the pressure in the hydraulic system has reached the maximum value the pump spring is completely compressed by the oil pressure and the pump is no longer operated. In this way the pump is only brought into operation when necessary so that, apart from the saving in energy, the mechanical parts of the pump are subjected to less wear and the working life can be considerably prolonged, so that in this way a further contribution is made to the operating reliability of the entire system. Because of the elastic behaviour of the spring, shock-like or jarring movements of the chain are not transmitted directly to the adjusting device.

A very advantageous and compact solution constructionally is obtained if the piston pump and the spring are arranged in a unit at one side of the eccentric disc.

Particularly in chain conveyors whose chain is driven by a polygon wheel, it is very advantageous to provide a hydraulic accumulator in the hydraulic system. The oscillations of the chain do not then apply detrimental forces to the tensioning device and back to the chain. Stress peaks from oscillation build-ups do not occur such as might be expected in extreme cases in hydraulic systems not provided with an accumulator.

According to another aspect the invention provides a method as set forth in claim 14.

Several embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 shows in a diagrammatic manner a drag chain conveyor with the adjusting and conveying forces belonging thereto, Fig. 2 shows a first constructional form of the adjusting device, Fig. 3 shows a second constructional form of the adjusting device, Fig. 4 shows a third constructional form, and Fig. 5 shows a fourth constructional form.

In Fig. 1, 1 is a drag chain conveyor shown diagramatically, with a driving shaft 2 having a polygon wheel, a driving motor 3, a reversal shaft 4 and a chain 5. The chain conveyor 1 is of closed construction, because of the provision of a housing 6.

Bulk material (represented by dots) enters at an inlet 7 and issues again at an outlet 8 after being conveyed longitudinally by transverse scrapers or flights (not shown in Fig. 1 but see description of Fig. 3). In the illustrated example the chain 5 moves in the clockwise direction. Directly after the driving shaft 2 there is a section of chain slack 9. The chain 5 is tensioned by an adjusting device 10 which acts on the reversal shaft 4. The forces which act on the upper chain part are represented by a triangle 11 which is drawn above the conveyor and which increase linearly from the driving shaft 2 where they have a value of nil to half the tensioning force P/2 upstream of the reversal shaft 4.Half the tensioning force P/2 is taken up by the lower chain run and gives the rectangle 13 which together with half the tensioning force P/2 represented by the lower triangle 14, gives the complete tensioning force P which when idling has to be applied on the one hand as chain tension by the driving shaft 2 and on the other hand as preloading of the reversal shaft.

The tensioning force P is maintained when conveying a product also, except that here the chain tension at the driving shaft must be increased by a suitable amount Z for conveying (triangle 15).

Fig. 2 shows the first constructional form of the adjusting device. 20 designates the shaft or reversal shaft of a continuous conveyor, this shaft being mounted in a sliding frame 21 by way of bearings 22 and 23.

The reversal shaft 20 supports at one of its ends 24 a disc 26 which is secured eccentrically with a fixing screw 25. A yoke 27 which is adapted to be displaced at right angles to the axis of the reversal shaft 20 is arranged about the disc 26. The yoke 27 bears by way of a transmission plug 28 against a compression spring 29 which in turn obtains purchase from an adjusting screw 31 and is disposed in a spring housing 30. At the opposite side the yoke 27 is connected with a pump piston 32 of a hydraulic pump 33. Arranged on the disc 26 is a ball bearing 34 to lessen friction when force is transmitted. Instead of the ball bearing a conical roller bearing or a plain bearing could be used.The hydraulic pump 33 is connected on the one hand to an oil tank 35 by way of a conduit 36 including a non-return valve 37 and on the other hand is connected with a working cylinder 40 by way of a pressure conduit 41 which also includes a non-return valve 42. The pressure conduit 41 is also connected to a pressure indicator 43, an accumulator 44, and by way of a further conduit 45, a pressure relief valve 46. The pressure relief valve 46 and the working cylinder 40 are connected with a return flow conduit 47 to the oil tank 35. The working cylinder 40 acted upon by way of the pressure conduit 41 from the hydraulic pump 33 bears against a fixed structural part 48 and by way of a piston rod 49 and the sliding frame 21 can adjust the position of the reversal shaft 20. The working cylinder 40 and piston rod 49 form part of an adjustment piston and cylinder assembly.

The pressure relief valve is adjusted to a value 50% higher than the pump pressure for example, depending on the particular use of the apparatus.

Upon resuming operation, it can be assumed that there is already sufficient pressure available in the pressure conduit 41 from the last preceding period of operation. However, the pressure can be more readily maintained by an additional pressure accumulator which is connected to and shut off from the conveyor with a shutoff device. The return flow from the working cylinder to the oil tank can also be inhibited.

However when setting up the conveyor for operation for the first time or when the requisite pressure is not available already the following procedure may be adopted.

The disc 26 is turned with the reversal shaft 20 into the illustrated position, so that the yoke can move freely relatively to the disc 26 against the action of the spring 29. The adjusting screw 31 is replaced by a pump handle and by several pressing actions on the pump piston 32 by way of the transmission plug 28 and yoke 27 the necessary pressure is pumped by hand.

The constructional form shown in Fig. 2, which is illustrated in a very greatly simplified way, operates as follows. When the chain conveyor 1 (Fig. 1) is started, the reversal shaft 20 rotates, with the chain 5 tensioned by the said shaft. The disc 26 and the ball bearing 34 arranged thereon act by way of the yoke 27 on the side remote from the pump piston 32, directly against the spring 29. This movement draws oil into the hydraulic pump 33 by way of a conduit 36 and the spring 29 is subjected to initial preload. At the next half revolution of the eccentric disc the yoke 27 is no longer supported, and the full spring force acts on the pump piston 32 so that oil is pumped and the pressure in the hydraulic system is increased.This operation is repeated whilst the piston rod 49 adjusts the position of the reversal shaft and applies the necessary tensioning force for preventing the reversal shaft from being drawn back and as a result causing the chain to be de-tensioned.

The pumping force is determined by the spring 29, and this can be preselected within wide limits by turning the adjusting screw 31. Thus the oil pressure can be adjusted directly with the adjusting screw 31. When the maximum oil pressure is reached, the yoke 27 is pressed into the uppermost position by the oil pressure acting on the pump piston 32. Oil pressure and spring force are in equilibrium and the pumping operation is cut out. The disc just touches the outermost region of the yoke until the oil pressure falls below the preselected value, either by leakage losses or by stretching of the conveying chain 5.

Thus the spring 29 between the reversal shaft 20 and the hydraulic pump 33 acts in a special way as a mechanically elastic force-transmitting element which ensures the adjusting and tensioning of the reversal shaft 20 with very great reliability, and the spring acts as the first pressure limiting means. If the resistance at the return run of the conveyor chain increases, the position of the reversal shaft still has to be maintained. This is achieved by adjusting the pressure relief valve 46 to a value substantially higher than the pump pressure, so that only when that higher pressure is reached is oil discharged. The pressure indicator 43 can have a control connection with the driving motor 3 (Fig. 1) so that the chain conveyor can be switched on only when there is sufficient tension and is switched off when there is overpressure in the cylinder.

More particularly in the case of chain conveyors, often no visual supervision of the chain within the closed housing 6 is possible. The constructional form shown in Fig. 2, therefore, allows, more particularly in closed chain conveyors, very rapid operational control to be carried out and any sources of trouble detected.

Chains 5 (Fig. 1) in bulk material conveyors are usually driven by means of a chain wheel, and the reversal shaft is constructed as a polygon wheel. This gives a fluctuating mechanical stressing of the chain 5 (polygon effect). Corresponding oscillations can be absorbed and rendered harmless by the accumulator 44 as a further elastic force-transmitting element for the chain tension, and have no longer any adverse effect on the chain 5.

Fig. 3 shows the second constructional form. At the end of a chain conveyor 50 the entire adjusting and tensioning device with the shaft or reversal shaft 51 is secured on a sliding frame 52 in order to make it possible to achieve the necessary tension for the chain 53 (which is here shown with its transverse scrapers or flights 53'). Two plunger pistons 54 abut against abutments 55 connected securely with the chain conveyor 50. Apart from a pump 56 and the plunger piston 54 all the other hydraulic elements are combined in a unit 62, vlz filter 65, non-return valves 57, discharge cock 58, pressure relief valve 59, pressure indicator 60 and accumulator 61. The unit 62 is secured together with the pump 56 and the two plunger pistons 54 on the sliding frame 52 and they all move with the frame over the extent of the tensioning distance or travel.

In basic construction the second constructional form corresponds to the first constructional form. Of special interest here is the pump 56 which in Fig. 3 is also shown in a section A-A. A spring 60, a pump piston 61 and a transmission plug 62' are assembled to form a single unit at one side of an eccentric disc 63. Apart from disturbances caused by foreign bodies, which result in sudden changes in the length of the conveying chain 53 and are taken up by the accumulator 61, the necessary tensioning operations proceed very slowly.

Therefore, in most cases a relatively small delivery quantity of oil is sufficient. The spring 60 and thus the pump pressure can be preselected here again with an adjusting screw 64 in accordance with the first constructional form.

The third constructional form shown in Fig. 4 in contrast represents a very advantageous solution for less demanding applications.

Here there is simply shown the axis 70 of a rotating shaft or reversal shaft 71 with an eccentric disc 73 secured thereon. A piston 74 at one end supports a follower wheel 75 which rolls on the periphery of the disc 73 and at the other end bears directly on a spring 76 which is arranged in the pump housing 77. Oil delivery in this case is effected by the disc 73, through the agency of follower wheel 75 and piston 74. A safety spring 78 is also built into the piston 74 as an overload safety means or mechanically elastic element, and this spring when a specific pressure is reached yields and cuts out the pumping operation so that the piston 74 is shortened instead of carrying out a longitudinal displacement.

The pump 77 is connected directly by way of a non-return valve 79 to a working cylinder 80. The shell of the working cylinder 80 is connected with fixed structural parts 81 and the piston 82 by way of a partly indicated holding frame 83 with the shaft 71 which is to be tensioned. The pressure relief valve 84 and an oil tank 85 have corresponding functions to those in the previous examples. In broken lines there is shown a hand lever 86 which is pivotably connected to the pump 77 and which can be operated by moving to and fro when the oil pressure is first produced. For this purpose here again the disc 73 can be rotated through 1800 relatively to the position illustrated so that it does not hinder pump movements.

The safety spring 78 in this constructional form provides a safety factor also for the operation of the hand lever to avoid the shaft becoming over-tensioned, if the pressure relief valve is incorrectly set or blocked for any reason.

As Fig. 1 also shows, all constructional forms of the invention allow better utilisation of the allowable chain or belt tension (Z max). Since P can be adjusted to the necessary value, there remains a maximum possible value Z res up to which the tensioning force can be increased or to which it is possible to adjust the pressure of the second pressure limiting means for the working cylinder.

Fig. 5 shows a further constructional example. A hydraulic pump 100 feeds pressure into the hydraulic system which comprises on the one hand a first pressure limiting means or element 101 for keeping a constant value, this element defining the lower pressure value limit, and on the other hand a second pressure limiting means or element 102 which sets an upper limit for the pressure. In order to make it possible with this simple system to adjust an effective working pressure, a non-return valve 103 is arranged between the hydraulic pump 100 and the second (pressure-limiting) element 102, but after the first element 101 (which keeps the pressure constant). The pressure in the working cylinders 106 can thus adjust itself effectively between the pressure values set at the elements 101 and 102.

Between the working cylinders 106 (of which two are provided, each cylinder acting on one end of the reversal shaft of the chain conveyor) and the second element 102 a pressure accumulator 105 is provided and also an oil release cock 104. During servicing all the oil can be drained off into the oil tank 108.

The drive of the pump is only shown diagrammatically by a drive 110 in Fig. 5.

But preferably in this constructional form also the pump is driven directly by the reversal shaft of the chain conveyor. However, this solution is particularly suitable also for independent drive for example by an electric motor. In this way the same pump can be used for two or more chain conveyors. It is also convenient to provide a pressure gauge 107 in the hydraulic system.

Particularly in the case of independent drive, electrical interlock with the driving motor of the chain conveyor itself is very important in order to prevent it from being brought into operation without the necessary tension.

In trough and chain conveyors or transporters it is often very difficult to calculate the frictional resistance between chain and floor, not least because in many cases pieces of the material being conveyed may wedge between the chain and the slide walls of the trough. In order to make it possible to prevent sagging of the chain, in trough and chain conveyors the adjusting device has to overcome these operational resistances in addition to the friction which occurs when the conveyor runs empty (or for that matter additional friction present in a newly installed conveyor which is not yet run in) since they occur in the return run of the chain likewise. The several constructions described above deal with these aspects very adequately.

It will be appreciated that the constructions described above also take account of the fact that more particularly in trough and chain conveyors hydraulic adjustment must operate in an interplay between the pressure applied by the hydraulic pump and the forces which occur in the trough and chain conveyor, so as to ensure not only adjustment of the position of the reversal shaft but also to ensure the likewise important holding of that position and thus operational reliability and safety.

Moreover the examples described above give very great operational reliability more particularly in chain conveyors and also allow the conveyor per se to be utilised to a better extent by omitting a large "reserve" preload.

WHAT WE CLAIM IS: 1. A drag chain conveyor having a reversal shaft adjustable in position by a hydraulic adjustment piston and cylinder assembly, comprising a pump for delivery of hydraulic fluid under pressure to the adjustment cylinder by way of a pressure conduit, a non return valve intermediate the cylinder and the pump to check return flow of fluid, a first pressure limiting means upstream of the non return valve to limit to a selected first pressure value the pressure of the fluid presented by the conduit to the non return valve for onward transmission, a second pressure limiting means downstream of the non return valve to relieve the pressure of the fluid whenever it reaches a selected second pressure value higher than the first pressure value, the arrangement being such that as tension in the conveyor varies in course of normal operation the working pressure of the fluid can fluctuate between the said first and second pressure values and when it reaches the said second pressure value the conveyor can continue to operate with hydraulic pressure in the cylinder relieved to the said second pressure value.

2. Conveyor according to claim 1 wherein the first pressure limiting means is in the form of a first pressure relief valve that can limit to a given value the pressure from such pump and the second pressure limiting means is in the form of a second pressure relief valve set to a higher value than the first pressure relief valve.

3. Conveyor according to claim 1 wherein the pump and first pressure limiting means comprise a gear pumxp and a slip clutch adapted to be driven from such shaft and arranged to drive the pump, whereby the pressure delivered by the pump is limited to a given value.

4. Conveyor according to claim 1 wherein the pump is a piston pump whereof the piston is arranged to be moved in one direction by an eccentric adapted to be driven from such shaft and in the other direction by the action of a spring.

5. Conveyor according to claim 4 wherein the eccentric is a disc adapted to be mounted eccentrically with respect to such shaft.

6. Conveyor according to claim 4 or claim 5 wherein the spring is arranged to move the piston in the direction of hydraulic fluid delivery, whereby the spring constitutes the first pressure limiting means and limits the pressure that the pump can deliver.

7. Conveyor according to claim 6 wherein the spring is preloaded and the preload is adjustable, whereby the pressure that the pump can deliver is adjustable.

8. Conveyor according to any one of claims 4 to 7 wherein the piston and cylinder parts of the piston pump and the spring are mounted in a single unit to one side of the eccentric.

9. Conveyor according to claim 4 or claim 5 wherein the piston is arranged to be moved by the eccentric by way of a follower wheel and an interposed overload spring.

10. Conveyor according to any one of the preceding claims which includes a pressure accumulator connected to the adjustment cylinder downstream of the non return valve.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. also the pump is driven directly by the reversal shaft of the chain conveyor. However, this solution is particularly suitable also for independent drive for example by an electric motor. In this way the same pump can be used for two or more chain conveyors. It is also convenient to provide a pressure gauge 107 in the hydraulic system. Particularly in the case of independent drive, electrical interlock with the driving motor of the chain conveyor itself is very important in order to prevent it from being brought into operation without the necessary tension. In trough and chain conveyors or transporters it is often very difficult to calculate the frictional resistance between chain and floor, not least because in many cases pieces of the material being conveyed may wedge between the chain and the slide walls of the trough. In order to make it possible to prevent sagging of the chain, in trough and chain conveyors the adjusting device has to overcome these operational resistances in addition to the friction which occurs when the conveyor runs empty (or for that matter additional friction present in a newly installed conveyor which is not yet run in) since they occur in the return run of the chain likewise. The several constructions described above deal with these aspects very adequately. It will be appreciated that the constructions described above also take account of the fact that more particularly in trough and chain conveyors hydraulic adjustment must operate in an interplay between the pressure applied by the hydraulic pump and the forces which occur in the trough and chain conveyor, so as to ensure not only adjustment of the position of the reversal shaft but also to ensure the likewise important holding of that position and thus operational reliability and safety. Moreover the examples described above give very great operational reliability more particularly in chain conveyors and also allow the conveyor per se to be utilised to a better extent by omitting a large "reserve" preload. WHAT WE CLAIM IS:

1. A drag chain conveyor having a reversal shaft adjustable in position by a hydraulic adjustment piston and cylinder assembly, comprising a pump for delivery of hydraulic fluid under pressure to the adjustment cylinder by way of a pressure conduit, a non return valve intermediate the cylinder and the pump to check return flow of fluid, a first pressure limiting means upstream of the non return valve to limit to a selected first pressure value the pressure of the fluid presented by the conduit to the non return valve for onward transmission, a second pressure limiting means downstream of the non return valve to relieve the pressure of the fluid whenever it reaches a selected second pressure value higher than the first pressure value, the arrangement being such that as tension in the conveyor varies in course of normal operation the working pressure of the fluid can fluctuate between the said first and second pressure values and when it reaches the said second pressure value the conveyor can continue to operate with hydraulic pressure in the cylinder relieved to the said second pressure value.

11. Conveyor according to claim 10

wherein the accumulator or an additional accumulator are adapted for connection to or disconnection from the adjustment cylinder, such accumulator or additional accumulator having a shut off device for that purpose.

12. Conveyor according to any one of the preceding claims having pressure responsive safety means adapted to inhibit or help inhibit the drive to the chain of the conveyor when said pressure is below a predetermined minimum and when it is above a predetermined maximum.

13. A drag chain conveyor having an hydraulic adjusting device constructed and adapted for use and operation substantially as shown in and hereinbefore described with reference to any one of Figs. 2 to 5 of the accompanying drawings.

14. The method of operating a drag chain conveyor that has a reversal shaft adjustable in position by a hydraulic piston and cylinder assembly which method comprises delivering hydraulic fluid under pressure to the cylinder by way of a pressure conduit, checking return flow of fluid by a non return valve in the pressure con duit, limiting to a selected first pressure value the pressure of the fluid presented by the conduit to the non return valve from upstream of that valve for onward transmission, and limiting the pressure of the fluid downstream of the non return valve whenever it reaches a second selected pressure value higher than the first pressure value during normal operation namely so limiting the pressure by relieving the excess pressure whenever it reaches that second pressure value, whereby the working pressure of the fluid in the cylinder during normal operation of the conveyor is effectively held between the first and second pressure values.

15. The method of operating a drag chain conveyor that has a reversal shaft adjustable in position by a hydraulic piston and cylinder assembly which method is substantially as hereinbefore described with reference to Fig. 1 in combination with any one of Figs. 2 to 5 of the accompanying drawings.