GB2246309A

GB2246309A - Composite sheet

Info

Publication number: GB2246309A
Application number: GB9114904A
Authority: GB
Inventors: John Robert Hoyes; Michael Eugene Grabowski; Frank Hampson; Anthony Paul Heslop
Original assignee: TBA Industrial Products Ltd
Current assignee: TBA Industrial Products Ltd
Priority date: 1990-07-26
Filing date: 1991-07-10
Publication date: 1992-01-29
Anticipated expiration: 2011-07-10
Also published as: DE4124403A1; GB9016383D0; GB2246309B; GB9114904D0

Abstract

In the manufacture of non-asbestos composite sheet suitable for use as piledriver pad material, comprising resilient facings which are of cured elastomeric material reinforced by non-asbestos fibres and which enclose and are bonded to a flexible core of metal, the non-asbestos fibres employed comprise metal fibres, preferably fibres of steel. The metal fibres are incorporated in a dough comprising uncured elastomer, inorganic filler, and elastomer-curing agent; the metal-fibre-containing dough is applied to each side of a flexible core of metal; and the coated metal core thus formed is subjected to conditions such as to cure the elastomer and form the coatings into resilient facings.

Description

-,il COMPOSITE SHEET This invention relates to composite sheet, and more

particularly to the manufacture of composite sheet suitable for use as piledriver pad material.

Piledriver pads, that is to say the cushions employed in pile driving in order to limit the very high impact stresses that occur during operation of the hammer, are most commonly based on asbestos fibre, and one form of pad in wide use is made by laminating composite sheet that comprises resilient facings which are of cured elastomeric material (eg styrenebutadiene rubber) reinforced by asbestos fibres. These facings enclose and are bonded to a flexible core of metal.

In recent years there have been proposals, as in our GB 2 208 625, to substitute certain non-asbestos fibres for asbestos fibres as reinforcement for the elastomeric material, and fibres of ceramic material, 2 mineral silicate, glass, aramid or polyacrylonitrile have been proposed. None of these, however, yields a pad that has a working life approaching that of pads made from asbestos-fibre-reinforced composite sheet.

According to the present invention, there is provided a method of making non-asbestos composite sheet suitable for use as piledriver pad material, in which metal fibres are incorporated in a dough comprising uncured elastomer, inorganic filler, and elastomer-curing agent; the metalfibrecontaining dough is applied to each side of a flexible core of metal; and the coated metal core thus formed is subjected to conditions such as to cure the elastomer and form the coatings into resilient facings which enclose and are bonded to said flexible core of metal.

The metal reinforcing fibres are preferably of steel, though fibres of aluminium, brass or bronze may be used if desired. The metal fibres preferably form at least 10% by dry weight of the dough, and a proportion in the range 20 - 45% of said dry weight is particularly preferred.

To improve the resilience of the facings, cellulose fibres may be incorporated with the metal fibres in the dough, and these preferably take the form of hammer-milled wood i i 1 1 1 i i 1 1 1 1 1 i i 1 1 1 i 1 3 1 PulP, whose use in the reinforcement of elastomeric sheet is disclosed in our GB 2 204 266 A.

The flexible metal core may be any of those conventional in this field, for example cold rolled steel. Most conveniently it is of aluminium, in for example the form of plain sheet.

The elastomeric material to form the resilient facings may for example be natural rubber, styrene but-adiene rubber, acrylonitrile butadiene rubber or polychloroprene, and can be employed in relatively low proportion (eg 15% or less) by weight of the facings. It may be admixed with any of the usual inorganic fillers, for example silica, a mineral silicate eg a kaolinitic clay such as china clay or ball clay, barytes, calcium carbonate or carbon black. The inorganic filler, which - as in the Example later in this specification - may be a mixture of materials, will ordinarily form at least 25% by dry weight of the dough, and preferably at least 40% by weight thereof.

4 The invention Examples.

is further illustrated by the following Exampl 1 Facing material was prepared from the following solid ingredients:

Nitrile butadiene rubber crumb Cellulose pulp (hammer-milled) Steel wool Barytes Whiting Anti-oxidant Cure system, processing aid and pigment TOTAL % by weight 5.12 1.14 33.37 33.69 24.70 0.22 1.76 100.00 Steel wool strand (strand mass, 49 g/m;filament hypotenuse 0.115mm) was cut into lengths of about 8 cm, and these were fed into a conventional spike mixer. Enough 1 c 1 i I 1 j j 1 1 I 1 i 1 j i 1 1 1 i i 1 1 1 time was allowed to elapse between successive feeds to ensure that the bulk volume of one feed was considerably reduced by the mixer spikes before the next was added. After addition was complete, operation of the spikes was continued for a further 30 minutes, by which time the bulked volume of the steel wool had been reduced by about 70% The other ingredients listed above, apart from pigment and anti-oxidant, were then added and blended with the spiked steel wool for 5 minutes. Toluene (volatile solvent for the elastomer; 14.7% by weight of the above total) was added to the mixer, followed by the pigment and anti-oxidant. After a further 40 minutes mixing, the processing aid (soda ash) dissolved in water was added. (Water is a nonsolvent for the elastomer, and prevents adhesion of the mix to the calender rolls used subsequently; water weight = 3% of the above total.) The dough formed by the above procedure was then applied to each side of plain aluminium sheet of thickness 0.25mm, following generally the procedure described in our British Patent 1 362 174 entitled "Production of sheet material for use as gaskets." First, the aluminium sheet was coated with a primer/heat-curable adhesive, and then fed, simultaneously with the dough, through a nip set to 6 give a facing coating of 0.85mm, between 2 calender rolls (diameter, 0.75 m) so as to spread the dough over one side of the sheet and form a coating on that side. The toluene and water ingredients of the sheeted dough were then evaporated off by passing the coated aluminium sheet through an oven drier at a temperature ( 850 C) such as not to cause curing of the elastomer ingredient of the dough.

Repetition of the above procedure, this time with a calender rolls nip set to give an overall thickness of 1.95mm, formed a dough coating on the other side of the aluminium sheet.

The sheet, coated on both sides with the facing material dough, was then passed through a further calender rolls nip to consolidate the coatings and bond them firmly to the sheet.The thickness after this operation was 1.58mm.

The resulting material was then passed to an oven, at a higher temperature (1500 C) than those used previously,to bring about curing of the coatings and to form resilient facings enclosing the aluminium core. The composite sheet produced had these properties:

i i i i 1 i i 1 1 i i j J i I 1 i 7 Thickness Density of facings Compression (ASTM F36) Recovery (ASTM F36) 1. 58 mm 2.40 g/CM3 13.7% 37% The composite sheet was cut into discs of diameter 585 mm, and seven such discs were, by bonding with contact adhesive, laminated to form a pad of thickness about 12 mm.

For evaluation, three pads one on top of another were tested in a service simulation pile driving rig with 7-ton drop hammer used at the maximum drop. After some 8,000 blows the top pad had yielded and flowed at the edge, but the condition of the bottom one was unchanged. The intermediate pad was serviceable.

These test results are at least as good as those obtained with currently used asbestos-fibre-reinforced elastomer pile driver pads.

8 Example 2

The procedure of Example 1 was followed with the difference that, instead of using steel wool as a raw material, pre-formed steel fibres of length up to were used.

3 mm The composite sheet product was in thickness, facings density, compression and recovery substantially identical to Example 1 material.

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Claims

1 A method of making non-asbestos composite sheet suitable for use as piledriver pad material, in which a dough is prepared which comprises uncured elastomer, metal reinforcing fibres, inorganic filler, and elastomer-curing agent; the metal-fibre-containing dough is applied to each side of a flexible core of metal; and the coated metal core thus formed is subjected to conditions such as to cure the elastomer and form the coatings into resilient facings which enclose and are bonded to said flexible core of metal.

2 A method according to claim 1, in which the metal fibres are of steel.

3 A method according to claim 1 or 2, in which cellulose fibres also are incorporated in the dough.

4 A method according to claim 3 in which the cellulose fibres are of hammer-milled wood pulp.

A method according to any of claims 1 to 4, in which the flexible metal core is of aluminium.

A method according to claim 5, in which the flexibl core is plain aluminium sheet.

A method according to any of claims 1 to 6, in which the elastomer content of the dough is not greater than 15% by dry weight thereof.

8 A method according to any preceding claim, in which the metal fibres form at least 10% by dry weight of the dough.

9 A method of making a non-asbestos piledriver pad in which discs or like elements of composite sheet made in accordance with any of claims 1 to 8 are superimposed one upon another and bonded into the form of a laminate.

Non-asbestos composite sheet, and piledriver pads made therefrom, substantially as described with reference to either of the Examples herein.

Flublisbed 1992 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 1 RH. Further copies mav be obtained from - - - R-. Newriort. NP1 7HZ. Printed by Multiplex techniques'ltd. Si Mary Crav. Kent- 1 Q J 1.

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