GB2165200A

GB2165200A - Improvements relating to belt scrapers

Info

Publication number: GB2165200A
Application number: GB08512192A
Authority: GB
Inventors: Anthony Bush
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-05-15
Filing date: 1985-05-14
Publication date: 1986-04-09
Also published as: GB8512192D0; GB8412395D0; GB2165200B

Abstract

A belt scraper has a replaceable blade (11) mounted on a carriage (10) mounted between the couplers (9) of two parallel linkages (5,6). The parallel arms (7,8) of the linkages have cranks (12,13) between which act gas springs (14) in a manner to urge the linkages in a direction to press the blade against a belt. <IMAGE>

Description

SPECIFICATION Improvements relating to belt scrapers This invention relates to belt scrapers.

Most conveyor belts acquire a deposit from the material they are handling, and this is particularly so with coal and some other minerals. Such deposits do not always build up evenly, which can cause the belt to track sideways on its guide rollers. Also, of course, they represent a waste of material which should be taken off at the delivery end, and they add to the mass which has to be driven.

It is therefore normal to scrape a conveyor belt at an early point on its return run. A number of problems then arise. Scraper blades wear, and so there should be some means for adjusting the blade to compensate. Springs or counterweights are often used to do this, but they have a marked tendency to oscillate or 'bounce' the scraper on the belt, thus reducing its effectiveness. Also, what is scraped off should go with the material that is delivered normally by the belt. Very often, a conveyor belt discharges into a hopper or chute, and therefore it is advantageous to have the scraper mounted over the mouth so that the material scraped from the belt falls directly into it rather than requiring separate collection. Not all scrapers are suitable for this position.

It is the aim of this invention to provide a belt scraper of a design which can readily fit below the delivery end of a conveyor, within the mouth of a hopper or chute, and in which there is automatic adjustment without oscillation.

According to one aspect of the present invention there is provided a belt scraper wherein gas spring means urge a blade into contact with a conveyor belt.

Conveniently, the blade is mounted between pivotal arms, the gas spring means being applied to those arms.

According to another aspect of the present invention there is provided a belt scraper comprising a pair of parallel linkages, laterally spaced and with co-incident pivot axes, a scraper spanning the linkages and being fixed to the couplers, and spring means acting between the parallel links of urge them in a direction to press the scraper in a working direction.

This arrangement can ensure that the scraper blade will retain its set angle of incidence to the belt even as it wears away.

These aspects will generally be combined, so that there are gas springs associated with each linkage, acting as dampers as well as springs. Conveniently, each parallel link will have a crank at its pivoted end thus forming a bell-crank lever, and the spring means will act between the cranks.

The couplers may be spanned by a carriage, and the blade will be replaceably fixed to the carriage.

Generally, such an assembly will be for operating on the downstream end of a belt, within the mouth of a chute or hopper, and the linkages themselves will then be inside the chute or hopper, close against the side-walls and pivoted thereon.

The blade will act upwards, co-operating with the belt as it leaves the drum. The cranks and the spring means will conveniently be outside the chute or hopper.

The linkages will form an exact parallelogram if the blade is to act the belt slightly downstream of the drum, so that the angle of incidence is kept constant. However, if the blade is to act on the belt before it leave the drum, as it wears its line of incidence will track around the circumference of the drum and a true parallel linkage would cause its angle of incidence to change. To compensate for this, and to keep the angle substantially constant, the links would be of slightly different length.

For a better understanding of the invention one embodiment will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a side view of a belt scraper assembly, a hopper being shown in outline, and Figure 2 is a plan view of the assembly of Figure 1.

A conveyor belt 1 is entrained around a head drum or roller 2 which is driven through its shaft 3.

The return run of the belt commences below the drum 2, which is arranged at the mouth of a chute 4. A scraper assembly is mounted in association with this drum to remove deposits from the belt 1 as it leaves the drum.

Parallel linkages 5 and 6 are carried by side walls. Each linkage comprises, just inside the associated side wall, parallel arms 7 and 8 joined at their free ends by a coupler 9. The couplers 9 are spanned by a carriage 10 to which a replaceable blade 11 is fixed. The plane of the blade is generally radial to the drum 2 and will remain so even as it wears and the parallel linkages adjust accordingly, as described below.

Fixed to the arms 7 and 8 just outside the chute side walls there are cranks 12 and 13 extending in opposite directions. Each pair of cranks is coupled by a gas spring 14, which urges the cranks apart.

The effect of this is to bias the whole linkage in an anti-clockwise direction as seen in Figure 1, pressing the blade up against the belt 1. This pressure will be maintained as the blade wears.

It would be possible to have the cranks inside the chute, but generally it is more desirable to have them, and the springs, out of the way. Normally, they will be encased in box 15, indicated in broken lines, fixed to the outside of the chute and providing further journals for the linkages. The links 7 and 8 will not provide any impediment to material discharged from the belt.

In the drawing, the drum 2 is shown rather smaller than it would normally be in relation to the other elements.

The choice of gas springs is a departure from normal practice, and in this particular field, brings very considerable advantages.

One particular one is that, with a high initial charge the force that they exert at the end of a working stroke differs very little from that at the start. A typical blade might be allowed 50mm of wear, and, depending on the geometry of the lin kage, the working stroke of each spring might be slightly less than that. It has been found that a compact gas spring, of 20mm diameter, can still be pushing at 92% of its initial force at the end of such a stroke. A mechanical one of comparable size could easily lose 50%.

Another significant advantage of gas springs is their universality. Conveyor belts come in a range of widths, mostly from 600 to 1500mm with intermediate sizes at 150mm intervals. The effectiveness of a scraper is related to the force exerted per unit length of blade edge, and the optimum figure is virtually the same whatever the width of belt.

Thus the total force exerted by the springs on the blade must be greater the wider the belt. With mechanical springs, this would mean that different sizes would have to be manufactured and stocked for all the different belt widths. However, with gas springs it has been found that one basic 20mm diameter unit will serve the entire range quoted above, and it is simply a matter of charging and sealing it at a particular pressure. For example, for the narrowest width considered here (600mm) each gas spring unit might be charged to exert an initial 400N, while for the largest width (1500mm) it would be charged to exert 1000N, with the intermediate ones in proportion. This would provide a working linear blade pressure of the order of 1.25kg per cm, which would be maintained almost at this level throughout the life of the blade.

Claims

1. A belt scraper wherein gas spring means urge a blade into contact with a conveyor belt.

2. A belt scraper as claimed in Claim 1, wherein the blade is mounted between pivotal arms, the gas spring means being applied to those arms.

3. A belt scraper as claimed in Claim 2, wherein the arms are part of a pair of parallel linkages, laterally spaced and with coincident pivot axes, the blade being fixed to the couplers.

4. A belt scraper comprising a pair of parallel linkages, laterally spaced and with coincident pivot axes, a scraper spanning the linkages and being fixed to the couplers, and spring means acting between the parallel links to urge them in a direction to press the scraper in a working direction.

5. A belt scraper as claimed in Claim 3 or 4, wherein each parallel link has a crank at its pivoted end, thus forming a bell-crank lever, and the spring means act between said cranks.

6. A belt scraper as claimed in Claim 3, 4 or 5, wherein the couplers are spanned by a carriage and the blade is replaceably fixed to said carriage.

7. A belt and scraper assembly, wherein the scraper is as claimed in any preceding claim, and is arranged to operate on the downstream end of the belt, the working direction being upwards against the belt as it leaves a downstream drum or roller.

8. An assembly as claimed in Claim 7, in combination with a chute or hopper to which the belt delivers, the blade being mounted between arms pivoted to the side walls of the chute or hopper.

9. An assembly as claimed in Claim 7, as appendent to Claim 5, wherein the parallel links are within the chute or hopper and the cranks and spring means are external.

10. An assembly as claimed in Claim 7, 8 or 9, wherein the blade is arranged to act on the belt on its return run after leaving said downstream drum or roller.

11. An assembly as claimed in Claim 7,8 or 9, wherein the blade is arranged to act on the belt at a position where it is still in engagement with said downstream drum or roller, the linkage then not being truiy parallel linkages but having a four bar characteristic that maintains the blade at a substantially constant angle of incidence as the blade wears.

12. A belt scraper substantially as hereinbefore described with reference to the accompanying drawings.