GB2123430A - Marine slipway, apparatus and method for its manufacture and bearing material therefor - Google Patents

Abstract

A marine slipway bearing material comprising a polyamide together with a filler comprising polytetrafluoroethylene, graphite and bronze. This material is preferably, applied to a steel backing in powder form, heated until fusion occurs and then quenched. Preferred apparatus for applying the material comprises a number of generally vertically reference legs 12, 13, and a plurality of weir plates 15 mounted on the legs and extending between adjacent legs. The weir plates are pivotally connected to each other and the distance between the lower ends of the legs and the bottom of the plates is constant thereby defining the thickness of the powder layer to be deposited. <IMAGE>

Description

SPECIFICATION Marine slipway, apparatus and method for its manufacture and bearing material therefor The present invention reiates to marine launching slipways, for example for oil drilling platforms.

One known marine launching slipway system utilises sheets of polytetrafluoroethylene (ptfe) which are grease-lubricated and co-operate with a hardwood counterface. This suffers the drawback that ptfe has a low abrasion resistance with the result that the ptfe sheets quickly become torn and frequently allow only a single launch from each slipway assembly.

It is an object of the present invention to provide an improved slipway bearing material which exhibits a higher abrasion resistance while still showing sufficiently low friction.

It is a further object to provide an improved method and apparatus for applying a slipway bearing material to a metal backing sheet.

It is a further object to provide a marine slipway which can be used repeatedly.

According to one aspect of the invention a bearing material for a marine slipway comprises a polyamide, for example nylon, together with a filler comprising polytetrafluoroethylene, graphite and bronze.

The filler may represent from 2 to 20%, preferably 5 to 15% and most preferably up to 10% of the bearing material by volume.

The grade of nylon is preferably Nylon 11 or Nylon 12.

The filler preferably comprises, by volume, from 50 to 70% preferably 60% ptfe; from 1 5 to 25% preferably 20% bronze, and from 1 5 to 25%, preferably 20% graphite. The purpose of the filler is to act as a solid lubricant and to render the nylon suitable for its function as a bearing material.

The bearing material is preferably applied to a metal, e.g. steel, backing. The bearing material may be applied as a sheet which may have previously been formed by combining the ingredients and extruding them as a sheet. The sheet and steel backing may then be heated until fusion of the coating takes place and subsequently cooled, or the coating may be roll bonded to the steel backing.

More preferably, however, the coating is applied in powder form, and heated until fusion of the powder takes place. The bearing material is then cooled and is thus bonded to the steel.

It has been found that in its usual form ptfe powder has an open fluffy texture which has a detrimental effect on the wetting, adhesion and melt flow properties of nylon such that even at levels as low as 3% ptfe by volume, a continuous, level void-free coating is almost impossible to achieve. Thus it appears that if nylon is to be applied to steel with ptfe in levels sufficiently high for it to be effective as a solid lubricant, it cannot be applied by conventional means.

According to a second aspect of the invention, a method of bonding a marine slipway bearing material to a metal backing comprises compounding a filler comprising ptfe, graphite and bronze and comminuting this into a powder form; mixing the filler with nylon in powder form; applying a layer of the powder mixture to the backing; heating the backing and powder layer, and cooling the backing and the coating produced.

Preferably the particle size of the filler powder is between 40 and 350ym and the particle size of the nylon powder is preferably between 20 and 20cm. Preferably, the surface of the steel to be coated is degreased, abraded and primed.

The filler is preferably reduced to powder form by compacting the ingredients into sticks, under pressure, and subsequently comminuting this into a fine powder.

The backing and powder layer may be heated by passing through an induction heater. Cooling may be natural or may be by water quenching.

Sheets comprising a steel backing coated in accordance with the invention may be very suitable for use in a marine slipway system.

The nylon used exhibits good abrasion resistance while the filler reduces the frictional properties. This can enable the sheets to be used more than once, resulting in considerable savings.

One problem which may be encountered in applying the coating material as a powder is the difficulty in obtaining a layer of constant thickness when the backing is large in area and therefore frequently uneven or displays significant "out-of-flatness" According to a third aspect of the invention, apparatus for spreading a bearing material comprising, in powder form, nylon and a filler consisting of ptfe, graphite and bronze, onto a backing comprises a plurality of generally vertical reference legs and a plurality of weir plates, in which the weir plates are mounted on the legs and extend between adjacent legs and in which adjacent weir plates are pivotally connected to each other, the distance between the lower ends of the legs and the bottom of the plates being constant thereby defining the thickness of the powder layer to be deposited.

According to a preferred form, the apparatus comprises a generally horizontal beam, two generally vertical fixed reference legs connected to the beam, a plurality of movable reference legs movably mounted on and extending downwards from the beam, and a plurality of weir plates mounted on the movable legs and pivotally connected to each other, the distance between the lower ends of the movable legs and the bottom of the plates being constant and thereby defining the thickness of the layer of powder to be deposited.

Preferably, the movable legs are connected to the beam by means of compression springs which tend to force the legs away from the beam. Preferably the plates overlap and those adjacent the fixed legs are pivotally connected to the fixed legs. Preferably, each plate is rigidly fixed to a single movable leg. Preferably, the fixed legs are at each end of the beam.

In use, the apparatus is preferably located above the backing strip to which the powder is to be applied with the fixed reference legs at the edges of the strip and a supply of powder located behind the weir plates. The strip is then advanced relative to the apparatus taking with it an even layer of the powder.

Should the strip itself be uneven, this may be compensated for by vertical movement of the reference legs relative to the beam and the consequent vertical pivoting of the weir plates to leave a constant thickness of powder.

The invention may be carried into practice in various ways and one embodiment will now be described in the following example. In the accompanying drawings; Figure 1 is a front elevation of a spreader; Figure 2 is a plan view of the spreader of Fig. 1; Figure 3 is a section on the line Ill-Ill of Fig. 2; and Figure 4 is an isometric sketch of an alternative design of the spreader.

EXAMPLE 1 In this example, mild steel bars 2 m in length, 0.68m in width and 5 mm in thickness were used as the backing. They were coated with Nylon 11, incorporating a filler, to a depth of 4mm, leaving 40mm bar steel selvedges on each side.

The process was as follows: 1. The bars were degreased and one surface was abraded (speed sand or shot blast).

2. A thin (1 O,um) coat of a proprietary primer (Epoxy-phenol) was sprayed onto the abraded surface and allowed to dry in air for one hour.

3. The filler material comprising, by volume, 60% ptfe, 20% natural graphite and 20% 200 mesh tin-bronze powder, and designated "DQ1" (registered trade mark) was compacted by pressing the DQ1 powder into sticks under a pressure of 14 psi (10,000 kg/m2) and comminuted into a free flowing powder (40-350pm).

4. Nylon 11 powder (20-200ym) was mixed with 15% by volume of the "DQl" powder in a high speed mixer.

5. An even layer of the mixed powder, 4mm thick was spread onto the steel sheets using a spreader (as described below).

6. The sheets were pulled slowly through the work coil of a medium frequency (approx 8 kHz induction heating coil.

7. The sheets were allowed to cool or were quenched with water.

It was found that the coated sheets showed good peel strength and a shear strength in excess of 1000 psi (7 x 105 kg/m2).

Referring now to Figs. 1 to 3 of the drawings, one embodiment of the spreader for applying the powder coating is shown. The spreader comprises a horizontal bar 11 and two fixed vertical reference legs 12, one at either end of the bar 11. These fixed legs 1 2 are rigidly connected to bar 11 and extend backwards from it.

A series of movable reference legs 1 3 are located between the fixed legs 1 2 and are attached to the bar 11 through compression springs 1 4 which tend to force the movable legs 1 3 downwards. A weir plate 1 5 is rigidly attached to each movable leg 13, each weir plate 1 5 having a straight bottom edge 16.

The distance between the plate bottom edge 1 6 and the lower end of the corresponding movable leg 1 3 is the same in each case.

The weir plates 1 5 are generally rectangular but with curved ends 1 7. The curved ends 1 7 overlap and adjacent plates are pivotally connected to each other by means of pivot pins 18. The two outermost plates are pivotally connected to the fixed legs 1 2 by means of pivot pins 1 9.

In use, a coating is applied to a substrate 21 by arranging a supply 22 of the powder behind the spreader assembly. The substrate 21 is then moved forwards (direction of arrow A in Figs. 2 and 3) thus drawing with it a layer of powder 23. To avoid leaving bare lines in the powder layer 23, the movable reference legs 1 3 are set back from the line of the weir plates 1 5 as shown at 24.

As can be seen most clearly in Fig. 1, outof-flatness of the substrate 21 can be overcome using this form of spreader and an even layer applied despite deviation of the substrate 21 from the horizontal, indicated by 25.

Thus, deviation of the substrate 21 is accommodated by the appropriate springs 1 4 urging their weir plates 1 5 down to "follow" the contour of the substrate. The pivotal interconnection of the weir plates 1 5 results in a relatively smooth lower weir edge defined by the edges 16, at a constant distance from the substrate surface.

The positioning of the fixed legs 1 2 leaves a slevedge edge (not shown) at each edge of the substrate.

Fig. 4 shows a simplified spreader which comprises four reference legs; two outer legs 31 and two inner legs 32. Each adjacent pair of inner and outer legs 32, 31 are connected by a weir plate 33 which is adjustably attached by means of bolts 34 which pass through corresponding slots 35, 36 in the legs and in the side flanges 37 on the weir plates 33. The thickness of the powder layer to be deposited can thus be varied by adjusting the bolts 34.

The weir plates 33 are each pivotally connected to a central weir plate 38 by means of pivot pins 39, thus allowing the weir bottom edge to follow undulations in the surface of the substrate. Naturally, further central plates 38 can be included, having further reference legs similar to those designated 32, mounted at their points of pivotal interconnection.

Claims (11)

1. A bearing material for a marine slipway comprising a polyamide together with a filler comprising polytetrafluoroethylene, graphite and bronze.

2. A bearing material as claimed in Claim 1 in which the polyamide is nylon.

3. A bearing material as claimed in Claim 1 or Claim 2 in which the filler represents from 2 to 20% of the bearing material by volume.

4. A bearing material as claimed in any preceding claim in which the filler comprises, by volume, from 50 to 70% PTFE, from 1 5 to 25% bronze and from 1 5 to 25% graphite.

5. A method of bonding a marine slipway bearing material to a metal backing which comprises combining a polyamide with a filler comprising PTFE, graphite and bronze to form the bearing material, applying the bearing material to the backing, heating the backing and the bearing material until the bearing material fuses, and cooling the backing and coating so produced.

6. A method of bonding a marine slipway bearing material to a metal backing which comprises combining a polyamide with a filler comprising PTFE, graphite and bronze to form the bearing material, applying the bearing material to the backing, and roll bonding the material to the backing.

7. A method as claimed in Claim 5 or Claim 6 in which the bearing material is formed by combining the ingredients and extruding them as a sheet and the sheet is applied to the backing.

8. A method of bonding a marine slipway bearing material to a metal backing comprising compounding a filler consisting of PTFE, graphite and bronze, and communiting this to a powder form; mixing the filler with a polyamide in powder form; applying a layer of the powder mixture to the backing; heating the backing and the powder layer,and cooling the backing and the coating produced.

9. A method as claimed in Claim 8 in which the particle size of the filler powder is between 40 and 350m and the particle size of the polyamide powder is between 20 and 200m.

10. A method as claimed in Claim 8 or Claim 9 in which the filler is reduced to powder form by compacting the ingredients into sticks under pressure and subsequently communiting this into a file powder.

11. A method as claimed in any of Claims 8 to 10 in which the backing and powder layer are heated by passing them through an induction heater.

1 2. A method as claimed in any of Claims 8 to 11 in which cooling is achieved by water quenching.

1 3. Apparatus for spreading a bearing material comprising, in powder form, a polyamide and a filler consisting of PTFE, graphite and bronze, onto a backing, the apparatus comprising a plurality of generally vertical reference legs and a plurality of weir plates, in which the weir plates are mounted on the legs and extend between adjacent legs and in which adjacent weir plates are pivotally connected to each other, the distance between the lower ends of the legs and the bottom of the plates being constant, thereby defining the thickness of the powder layer to be deposited.

1 4. Apparatus as claimed in Claim 1 3 comprising a generally horizontal beam, two generally vertical fixed reference legs connected to the beam, a plurality of movable reference legs movably mounted on and extending downwards from the beam, and a plurality of weir plates mounted on the movable legs and pivotally connected to each other, the distance between the lower ends of the movable legs and the bottom of the plates being constant.

1 5. Apparatus as claimed in Claim 1 3 or Claim 1 4 in which the movable legs are connected to the beam by means of compression springs which tends to force the legs away from the beam.

1 6. Apparatus as claimed in any of Claims 1 3 to 1 5 in which the plates overlap and those adjacent the fixed legs are pivotally connected to the fixed legs.

1 7. Apparatus as claimed in any of Claims 1 3 to 1 6 in which each plates is rigidly fixed to a single movable leg.

1 8. Apparatus for spreading a bearing material on to a backing, constructed and arranged substantially as herein specifically described with reference to and as shown in Figs. 1 to 3 or Fig. 4 of the accompanying drawings.