GB2109303A - Rubber element - Google Patents

Abstract

Wear-resistant rubber 1 has a perforate metal sheet 3 embedded therein (typically with an aperture ratio of 15-75% and circular perforations arranged in a hexagonal pattern) parallel to and adjacent one face 2 thereof so that rubber intercommunicates at perforations 4 with the thicker and thinner layers to either side. <IMAGE>

Description

SPECIFICATION Rubber element This invention relates to reinforced rubber cladding or structural elements.

It has been known for many years that there are advantages in constructing or lining materialshandling equipment with abrasion-resistant rubber.

Because the rubber, in addition to being wearresistant, resiliently resists sliding or crushing impact, it lasts longer than unprotected steel plates. It is also less noisy in use, lighter, and easy to fabricate.

Heavy-duty abrasion-resistant rubber layers have accordingly been proposed for a wide range of such equipment and used to line truck container bodies, mine car floors barges, hoppers for concrete or mineral working in mines and quarries, chutes, whether direct or cascade, excavator and bulldozer buckets, vibratory feeders, flotation launders, and other types of wet-or dry-handling equipment for granular, lump, boulder or mixed abrasive material.

Rubber materials used alone, even of heavy grade, i.e. of considerable thickness and high Shore hardness, are not always mechanically strong enough to be structural members per Se. Thus, they must usually be fixed to a steel frame.

One way of fixing such rubber layers is by securing them mechanically at a number of fixing points, e.g. holes extending partway or completely through the rubber to contain the heads of fixing bolts. If there are too any of such fixing points they weaken the layer. If there are too few, the layer takes up all the stresses at these relatively few points, and can start to tear. In practice, such fixing of unsupported rubber layers is not always successful.

Another way of fixing such layers is by adhesion, but this cannot be done in all constructions and typically needs an existing body panel or like extended area for attachment. Also, specialised operatives are necessary for such adhesion techniques.

It has become usual, therefore, to provide each rubber layer, prior to use, with its own steel backing sheet, typically of say 5 mm in thickness. This is glued to the rubber layer of e.g. 20.50 or 100 mm in thickness after careful cleaning and preparation of the contacting surfaces. This adhesion is carried out by the manufacturer as an additional manufacturing step. Typically the manufacturer then sells standard size composite steel/rubber sheets. These fequently need to be cut and bent to shape on site, in neither case behaving as conveniently as an unbacked rubber sheet. They are also heavier, and nosier in use. Moreover, although the adhesion layer itself is not often a source of problem ,the steel backing layer can corrode over long-term use, which is especially troublesome if it is in an inaccessible position.Therefore, although these steel/rubber composite layers present the great advantages of dimensional stability and secure fixing, they are not always suitable for every application.

The present invention sets out to provide a different form of composite metal/rubber having improved characteristics over these prior art layers.

In one aspect the invention provides a composite wear-resistant member comprising a layer of wearresistant rubber with a perforate metal sheet embedded therein parallel to and adjacent one face thereof with rubber on either face of the metal sheet and intercommunicating through the perforations.

Preferably, the perforate metal sheet is a steel or aluminium sheet having formed therein a multiplicity of regularly spaced perforations to a total aperture ratio of 15 to 75%. The perforations are each preferably circular and preferably arranged so that each circle is surrounded by six like circles equispaced at the vertices of a regular hexagon.

Other preferred features of the structure are described in more detail below.

In another aspect the invention provides a method of manufacturing a composite wear-resistant member as described above in which the perforate metal sheet is sandwiched between a thicker and thinner layer of unvulcanized rubber and subjected to vulcanization under temperature and pressure conditions such that the rubber layers flow into and join within the perforations.

In yet another aspect the invention provides self-sufforting materials-handling equipment having walls formed of wear-resistant composite members as described above with the perforate metal sheets nearer the outer surfaces.

While the invention extends generally to those various types of equipment listed above, particularly valuable examples of this type of equipment are constituted by lined hoppers and chutes for use in mines, or by rotary drum materials handling and treatment machinery. This latter category includes various types of milling equipment, and especially includes washer drums for the sand and gravel industry.

A particular advantage we have found in such equipment is that the rubber can abrade down to the perforate plate itself without becoming detached from the wall of the drum. Hitherto, especially with concave surfaces under abrasive impact, there has been a tendency for the layer to become detached well before total abrasion, with consequent inefficiency of utilisation.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a composite rubber-metal sheet according to one form of the invention, Figure 2 is a perspective view of one corner of the metal element of the composite sheet of Figure 1, Figure 3 shows how the sheet of Figure 1 can be secured to a support member, and Figure 4 shows a detail of fixing of the sheet inside a washer drum used in the sand and gravel industry.

In Figure 1 a rubber layer 1 has embedded therein, towards a back surface 2, a perforated steel sheet 3.

The rubber extends integrally to either side of the steel sheet and inter-communicates through the perforations 4. The surface 5 is operative wearresistant face of the rubber layer 1.

The distance between the steel sheet 3 and surface 2 is relatively small, being typically only sufficient to give a good grip on the steel sheet (by extending through its perforations) and to provide a smooth protective backing surface. The distance between the steel sheet 3 and the front surface 5 can be whatever is desired for the expected lifetime and environment in a given end use, as discussed below.

The thickness of the metallic sheet 3 is relatively low compared to that of the external unperforated sheet in the prior art, since its protected position guards against corrosion and consequent loss of material.

Figure 2 shows typical perforations in the sheet.

While these can adopt any individual shape or packing commensurate with the desired strength and flexibility of the layer they are circular in the embodiment shown and arranged so that their centres lie on the vertices of a multiplicity of equilateral triangles. Alternatively stated, each circular perforation is at the centre of a regularly hexagonal arrangnement of six identical circular perforations.

Specific dimensions in the example shown, and preferred ranges of dimension and relative proportion are as follows: (i) Length and width of composite layer This can be sheet-like e.g. of modular or standard widths from 400 to 2000 mm, and of standard lengths e.g. 2, 3, 5, 10 metres. It can also be presented as smaller bar-like elements or blocks provided these have a cross-section of the type shown above.

(ii) Thickness ofabrasion-resistantlayer This is for example the distance from metal sheet 3 to surface Sin Figure 1. It can vary widely, but is usually from 5 to 150 mm; more usually from 20 to 50 mm; and by way of specific example 25 mm.

(iii) Thickness of metal sheet This sheet which can be for example of steel or aluminium has a thickness suitable for the structural strength and flexibility desired. Usually this is between 0.5 to 3 mm and more usually from 0.5 to 1.5 mm, whereby it is appreciably easier to cut than the prior art (unperforated) steel backing sheets. By way of specific example it can be of 1 mm thickness.

(iv) Size ofperforations The size of perforations should be adequate to give good interconnection between the rubber on either side. A maximum dimension is usually about 10 mm, but more usually from 1.5 minimum to 6 mm maximum is used, e.g. as 1.5 to 6 mm diameter circular perforations. Specifically, 2 mm diameter circular perforations have been used.

(v) Spacing ofperforations The spacing of the perforations, in relation to their size, again affects strength and flexibility. Typically, it is such that the total aperture is from 15% to 75% of sheet area e.g. 25%. If "hexagonally-arranged" circles are used the spacing of centres can be from 1.2 to 2 times circle diameter; a specific example is circles of 2 mm diameter 3.6 mm apart for the 1 mm sheet described above, and used with the 25 mm backing layer.

(vi) Depth ofembedment This is the distance from the metal sheet 3 to surface 2 and is typically from 1 to 10 mm, more usually 1 to 3 mm e.g. 2 mm for the specific embodiment discussed above.

The rubber material is of a type known perse, being a vulcanized rubber product of hardness chosen for its particular environment (i.e. sliding, impacting or gouging particles or lumps) but typically 40, 50 or 60 Shore hardness.

Although the surface 5 is shown as a flat surface it is within the ambit of the invention to provide ribbed, grooves or otherwide configured surfaces, e.g. of a type to resist low-angle impact of material.

The composite sheet shown is manufactured without additional adhesive steps. A sheet of uncured rubber, corresponding to the eventual abrasion-resistant layer is covered with the perforated metal sheet and this is covered with a thin unvulcanized layer of the same rubber formulation. These three layers are pressed together and vulcanized so that the rubber intercommunicates through the perforations.

Figure 3 wherein like reference numerals are used as in Figures 1 and 2 shows how such a composite sheet can be secured to a frame member 6 by bolts 7 and washers 8. The head of the bolt lies within recess 9 in the layer 1. The floor 10 of this recess is spaced from the perforated steel sheet 3, although the extent or existence of this spacing is optional. It will be apparent that the essential dimensional stability and resistance to tearing imparted by the perforated steel sheet is still retained.

As shown, recess 9 is wide enough to receive a tightening or holding tool, but if desired the walls of this recess should contact the bolt head and thus prevent turning. Since the rubber is flexible, even an undersized recess, minimising the interruption in the abrasion-resistant surface 5, could be used. By constructional techniques of these types a dimensionally stable self-supporting structure e.g. a chute or hopper can be made, having not only the abrasion resistant interior but the low-noise corrosionresistant exterior of surface 2, as distinct from the metal backing, or existing constructional surfaces, normally encountered.

There are of course other ways in which the composite material can be fixed. Indeed, we have found that for some constructions, simple selftapping screws extending through the perforate plate and a support plate in either direction, can be used. Also, nails fixed from a nail gun are possible fixing means.

Cutting of the composite material is of course considerably easier than cutting of the rubberlsteel laminate of the prior art since the included sheet is both thinner and perforated. In case of cutting it resembles unreinforced sheet, and readily available hand or electric saws will suffice.

Thus, the novel composite as described in relation to Figure 1 is easier to manufacture, easier to cut and bend to shape, and lighter to assemble than the conventional steel-backed rubber material. It is also less prone to corrosion, and quieter in use, while preserving the strength and shape-retaining advantages of steel-clad rubber as compared to unclad rubber.

In Figure 4 there is shown the key constructional features of a horizontally mounted washing drum for sand and gravel. This is essentially composed of a concave steel shell 11 to which are fastened by normal screw fastenings 12 layers of the composite sheet material 13, 14. Each such layer is recessed at 15. Two such opposed recesses jointly accommodate a spacer or lifter bar 16, also made of wearresistant rubber and which may or may not possess internal reinforcement according to the invention.

The spacer bar 16 is bolted to the shell 11 at 17, thus further assisting in retention of the sheets 13, 14 especially at their longitudinal recessed edges.

In the construction shown, the lifter bar becomes worn by the abrasive material being washed. Wear arises disproportionately on the "upstream" corner 18 (with rotation as shown by arrow A) but the construction illustrated readily permits the bar to be removed and reversed for a further period of wear.

We have found that the sheets 13 and 14 in such a construction can in patches wear right down to their reinforcement 19 without becoming detached from the drum. Thus, a surprising improvement in operating life, over that of unreinforced rubber cladding, is achieved.

Claims (14)

1. A composite wear-resistant member comprising a layer of wear-resistant rubber which possesses a perforate metal sheet embedded therein parallel to and adjacent one face thereof with rubber on either face of the metal sheet and inter-communicating through the perforations.

2. A composite wear-resistant member as claimed in claim 1 in which the metal sheet is composed of steel or aluminium.

3. A composite wear-resistant member as claimed in claim 1 or 2 in which the aperture ratio, of total area of perforations to total metal sheet area, is from 15 to 75%.

4. A composite wear-resistant member as claimed in any one of the preceding claims in which the perforations are circular.

5. A composite wear-resistant member as claimed in claim 4 in which the circular perforations are arranged so that each circle is surrounded by six like circles equispaced at the vertices of a regular hexagon.

6. A composite wear-resistant member as claimed in any one of claims 1 to 5 in which the maximum dimension of the perforations is 10 mm.

7. A composite wear-resistant member as claimed in any one of claims 1 to 6 in which the thicker, abrasion resistant, layer of rubber is from 5 to 150 mm thick.

8. A composite wear-resistant member as claimed in any one of claims 1 to 7 in which the metal sheet is from 0.5 to 3 mm thick.

9. A composite wear-resistant member as claimed in any one of claims 1 to 8 which the thinner layer of rubber, embedding the metal sheet, is from 1 to 10 mm in thickness.

10. A method of manufacturing a composite wear-resistant member as claimed in any one preceding claim in which the perforate metal sheet is sandwiched between a thicker and a thinner layer of unvulcanized rubber and subjected to vulcanization under temperature and pressure conditions such that the rubber layers flow into and join within the perforations.

11. Materials-handling equipment having walls which comprise wear-resistant composite members as claimed in any of claims 1 to 8 with the perforate metal sheets nearerthe outer surfaces thereof.

12. Materials-handling equipment as claimed in claim 11 in which a self-supporting hopper or chute for abrasive materials is formed in the composite material.

13. Materials-handling equipment as claimed in claim 11 in which sheets of composite material are secured inside a rotary drum in a concave shape.

14. Materials-handling equipment as claimed in claim 13 formed as a washer for the sand and gravel industry, in which concave sheets of the composite material are secured inside the rotary drum with adjacent longitudinal edges each having a longitudinal recess therein over its whole length, each pair of recesses jointly accommodating a spacing bar extending above the sheet thickness along the drum.