WO1992001544A2

WO1992001544A2 - Coated articles, method and apparatus for making same

Info

Publication number: WO1992001544A2
Application number: PCT/GB1991/001214
Authority: WO
Inventors: Douglas Badhams
Original assignee: Balmoral Group Ltd.
Priority date: 1990-07-19
Filing date: 1991-07-19
Publication date: 1992-02-06
Also published as: WO1992001544A3; GB9015852D0; AU8223791A

Abstract

A mold (1) which surrounds an article (5) to be coated with an elastomeric material (20) employs a number of actuators (4) which can be extended to cause plugs (8) mounted on end caps (3) to engage on the article (5) to hold this in position in the mold (1). After the coating (20) has hardened the actuators (4) can assist in separating the mold (1) from the coating (20). The cavities left in the coating (20) can be filled and/or a further coating built-up to provide a continuous outer skin to the first coating (20) by treating the coated article (5) in another similar mold.

Description

COATED ARTICLES, METHOD AND APPARATUS FOR MAKING SAME

TECHNICAL FIELD

This invention relates to coated articles and a method and apparatus for making same. More especially the invention relates to articles comprising an elastomeric material coating a core material especially a pipe. The invention has particular utility in coating pipes especially for pipelines and in coating buoys and fender but is not restricted merely to these objects.

Coating is performed for a number of reasons. Typically they include providing a corrosion inhibiting layer or providing an insulating layer. Other reasons can be the provision of impact resisting coating, and high visibility coatings.

BACKGROUND OF THE INVENTION

In the case of pipes, used for conveying gas or oil, it is often important that the pipe be centrally disposed in its coating. One common way of achieving this is to form separate discs of elastomer which are fitted around the pipe to be coated. The pipe with the fitted-on discs is then placed in a mold with the peripheries of the discs supported by the mold and the pipe is thus centralised. Elastomer is then introduced into the mold and allow to cure.

There are a number of problems associated with such a procedure. Faults such as gaps can occur between the discs and the subsequently introduced elastomer. In some severe environments, for example, salt water, the faults may be penetrated by corrosive material leading to damage. In some cases the introduced elastomer can adhere firmly to the mold and on removal the elastomer may be torn.

The invention seeks to at least mitigate either problem.

DISCLOSURE OF THE INVENTION

According to one aspect of the invention there is provided a method of coating an article comprising the steps of:

placing the article to be coated in a mold, the mold having displaceable location means for selectively engaging the article to be coated;

operating actuators to cause the location means to engage and position the article within the mold;

introducing coating material between the mold and the article.

allowing the coating material to harden, and

operating the actuators to withdraw the location means and release the coated article.

The cavities defined in the coating material by the location means may be plugged with elastomer or wood.

Alternatively or additionally some embodiments of the invention further comprise the steps of: placing the previously-coated article in another mold having displaceable location means for selectively engaging the coated article;

operating actuators to cause the location means to engage and position the coated article within the other mold;

introducing further coating material between the other mold and the coated article;

operating the actuators to cause the location means sequentially to retract from the coated article prior to exposure and contact with the further coating material; and

allowing the further coating material to harden.

The coated article may be released from the mold by operating some of the associated actuators causing them to bias the coated article away from the mold interior.

In another aspect the invention provides apparatus for coating an article, the apparatus comprising:

a mold

a nozzle for admitting coating material into the mold;

a vent for allowing escape of gas and coating material from the mold;

location means each movable between a first position wherein an article to be coated is supported in the mold by contact with the location means and a second position wherein the article to be coated is not supported in the mol d and

actuators for moving the location means between the positions. One form of actuator usable in the apparatus and method is a short-stroke hydraulic or pneumatic piston-and-cylinder unit. The location means may comprise a cap at one end of the piston rod of each actuator and a plastics plug attached to the cap. The caps may be shaped to engage in recesses in the interior of the mold so that when retracted the caps do not protrude beyond the mold interior.

BRIEF DESCRIPTION OF DRAWING

Embodiments of the invention will now be described, by way of examples, with reference to the accompanying drawings of which :

Fig. 1 is a schematic perspective view of a coating apparatus of the invention;

Fig. 2 is a scrap cross-section of a bush, cap and plug of use in the invention; and

Fig.3 is a schematic elevation of a mold positioned for a final skinning operator

BEST MODE OF CARRYING OUT THE INVENTION

The apparatus of the invention includes a mold 1. The mold 1 is conveniently made of ferrous material or glass fiber reinforced plastics material (GRP) and surrounds an article 5 to be coated with an elastomeric coating material. Metal especially polished aluminium is advantageous because it readily conducts that away from curing coating material. GRP is generally used because fabrication is inexpensive. Preferably as will be explained hereinafter the mold is resiliently deformable The article 5 can take various forms but in this example the article is a pipe with a wall 15. Other materials capable of withstanding the forces imposed on it by the process of the invention and not attacked by the elastomer may be employed for the mold 1.

The mold 1 preferably is in the form of two halfshells which can be fastened together and unfastened at will. More than two part-shells can be used if desired or if this is necessary to remove the article 5 from the mold.

Several strengthened locations are provided on the mold 1 for example, by means of steel bushes 2 encapsulated, cast or otherwise embedded therein. The single bush 2 shown in detail in Fig 2 slidably receives the rod 6 of a piston of an external hydraulic piston-and- cylinder unit actuator 4. The piston rod carries a frusto-conical cap 3 which can be snugly received in a frusto-conical recess 7 in the inner face of the bush 2 when the actuator 4 is retracted.

The cap 3 has can have at least its working face 4 made of nylon or polytetrafluoroethylene (PTFE) and serves to mount a tapered plug 8. Plug 8 is preferably screw mounted on the cap 3. The stroke of the actuator 4 is preferably fixed. Normally a number of bushes 2 with actuators 4 would be distributed around the pipe 5 in the mold 1 and preferably the actuators 4 and the associated plugs 8 are provided in opposed pairs or fours or in symmetrically disposed groups of three along the length of the mold 1. It is a matter of routine experiment to determine the optimum number of actuators. If too few are provided the article and mold may not conform closely enough between adjacent points of support. Beyond a point further actuators will be redundant giving little extra benefit. By way of example a 12m oil pipe may be coated in a mold having 6 sets of four actuators. The actuators are placed at 2m intervals with the end actuators 1 in from the pipe ends. Preferably the actuators 4 are all connected to a single pump 50 by an hydraulic ring main 19. Use of a ring main ensures that equal pressure is applied at all points improving the accuracy of alignment of the pipe 5 in the mold 1. As will be explained in more detail hereinafter in some embodiments means are provided to operate the actuators 4 at differing times. It will be appreciated that other forms of actuators 4 besides hydraulic units may be employed including actuators operated by pneumatic force or by electromagnetic force.

The tapered plugs 8 are each shaped such that the width is greater nearer the mold 1 than further out from the mold 1. Truncated cones are the preferred shape. The plugs 8 are made of material compatible with the elastomer used as the coating material and preferably the plugs 8 are made of nylon or PTFE. (polytetrafluroethylene). Other materials including resin-impregnated felt, DELRIN (Trade Mark) or synthetic foam may be used.

Generally the mold 1 is provided with one or more nozzles (1000, 2000, 3000, 4000) for introducing the elastomeric coating material between the mold 1 and the pipe 5 and one or more vents 60 which allow the escape of gas contained in the mold 1 or excess coating material.

In use, the caps 3 and the associated plugs 8 are all initially withdrawn away from the mold center. The pipe 5 serving as core material is then introduced into the mold 1. This step is relatively straightforward because there is a relatively large clearance. When the pipe 5 has been introduced the actuators 4 are caused to extend to move the caps 3 and plugs 8 away from the mold 1 until the plugs 8 abut the wall 15 of the pipe 5 and position it in the desired location. This location is generally in the mold center but for some applications may be elsewhere.

Pipes are relatively flexible along their length and if supported at each end the centre will ten to sag. A 12m length of 66cm diameter pipeline tends to sag about 75mm under such circumstances. While it would be possible to make a mould capable of bending the pipe into linear form a very strong press and powerful actuators would be required. It is more convenient to use a mold which has high hoop strength but is deformable in length. The actuators cause the mold to deform until the core is correctly positioned relative to the mold. To facilitate deformation weakening lines may be present in the mold. The coating will generally be sufficiently flexible as not to crack if the coated article is subsequently supported throughout its length.

It is not essential that the mold only moves to ensure accurate positioning. In some cases it will be the article to be coated which moves and in some cases both the article and the mold will move. The invention provides for positioning by relative movements of mold and article.

The mold 1 is then filled with the elastomeric coating material 20. When used for coating ferrous oil or gas conveying pipes polyurethane (PU) foam is a very suitable coating material. Typical thickness for insulating layers are 30-150mm, preferably 40-100mm especially about 75mm. Anticorrosion layers are preferably 1-30mm more preferably 3-15mm especially about 8mm. It will be within the capacity of the skilled worker to adopt or devise other suitable materials.

The coating material 20 is allowed to set, cure freeze or harden in some other way. The caps 3 and plugs 8 are then withdrawn and if necessary the mold opened. It may be found that thus the coated pipe 5 can be easily removed. If however the coated pipe 5 adheres to the mold 1 some of the actuators 4 can be extended. If the actuators are of fixed stroke spacers can be provided prior to this step. The coated pipe 5 is then 'sprung' from the mold 1 by resilient deformation of the coated article and/or the mold. The pipe 5 can be coated in stages by moving the pipe 5 longitudinally relative to the mold 1. The pipe 5 on removal from the mold 1 will be found to have to have uncoated cavities corresponding to the position of the piucs 8.

If the coated pipe 5 is for use in a benign environment these uncoated cavities may simply be filled by fillers, for example, of hard elastomer synthetic foam or foam or wood. Syntactic foams are composite materials in which light weight particles are bonded together in a matrix of high strength resin, usually either an epoxy or polyester resin. The light weight particles are generally microspheres that is to say small hollow glass bubbles. The fillers are glued or cured preferably using PU into place and fit flush with the outer surface of the coated pipe 5. Where use is envisaged in more severe environments an alternative or additional step may be employed. The coated pipe 5 either with or without the fillers can be centered in the manner substantially as hereinbefore described in a further but slightly larger mold 100.

In the case of a 66cm diameter insulated pipe the mold 100 can be about 8mm greater in diameter than mold 1. Mold 100 is preferably not horizontal and more preferably is at an angle of 15-75° still more preferably 20-60° yet more preferably at an angle of 30-45° to the horizontal. The plugs 8 are however not employed and the caps 3 directly abut on the exterior of the coating 20 or the outside of the pipe 15. Preferably the caps 3 bear on either the pipe 15 or more preferably on the fillers. The fillers can have greater load bearing capacity than the rest of the coating material.

A further layer of coating material compatible, but not necessarily identical, with the original coating material is introduced into the mold 100. It may be desired for example in the use of buoys to provide a brightly coloured and puncture resistant coating over a layer of foam. As the coating material advance the actuators 4 are restricted in sequence and progressively so that the caps 3 are selectively withdrawn into the associated recess 7 and the coating material completely fills any cavities or gaps. Preferably caps 3 are at least coated with nylon or PTFE. Initially the coated pipe will be supported by the unretracted caps but at a later stage the coating itself will provide support. On hardening a coated article with an intact outer skin will be obtained. It may be sprung from the mold 100 in the manner hereinbefore described.

The use of multiple nozzles is preferred and will be described by reference to Fig. 3. In this embodiment the pipe and mold 100 are inclined at an angle of around 30_o. A plurality of sets of actuators (200, 300, 400, 500) are provided as input nozzles (1000, 2000, 3000, 4000, 5000). Initially all the actuators abut the article. Coating material introduced through the lowest nozzle 1000 until the coating material reaches a level (A) just below the first actuator. Input nozzle is switched off and actuators 200 restricted. Coating material is then introduced through the lowest free nozzle 2000 until a level (B) just below the next unretracted actuator. The process is continued (at levels C & D) until the whole article is coated. This technique allows for support of the article by actuators and /or cured coating material without very high back pressures occurring.

Claims

1. A method of coating an article comprising the steps of:

a) placing the article (5) to be coated in a mold (1), the mold (1) having displaceable location means (3,8) for selectively engaging the article (5) to be coated;

b) operating actuators (4) to cause the location means (3,8) to engage and position the article within the mold

(1);

c) introducing coating material (20) between the mold and the article (5);

d) allowing the coating material (20) to harden, and e) operating the actuators (4) to withdraw the location means (3,8) and release the coated article.

2. A method as claimed in claim 1 comprising the further steps of:

f) placing the coated article (5) in another mold (1) having displaceable location means (3) for selectively engaging the selectively coated article (5);

g) operating actuators (4) to cause the location means (3) to engage and position the coated article (5) within the other mold (1);

h) introducing further coating material (20) between the other mold (1) and the coated article(5).

j) operating the actuators (4) to cause the location means (3) sequentially to retract from the coated article prior to exposure with the further coating material; and k) allowing the further coating material to harden.

3. A method as claimed in claim 1 or 2 and further comprising filling cavities defined in the coating material (20) by the location means (3,8) with plugs of elastomer or wood.

4. A method as claimed in any one of claims 1 to 3 and further comprising releasing the coated article (5) from the mould (1) by operating some of the actuators (4) to bias the coated article (5) away from the mold interior.

5. Apparatus for coating an article, the apparatus comprising:

i. a mold (1);

ii. at least one nozzle for admitting coating material into the mold;

iii. at least one vent for allowing escape of gas and coating material from the mold,

iv. location means (3,8) each movable between a first position wherein an article (5) to be coated is supported in the mold by contact with the location means and a second position wherein the article (5) to be coated is not supported in the mold and

iv actuators (4) for moving the location means (3,8) between said positions.

6. Apparatus as claimed in claim 5 wherein each location means (3,8) comprises a cap (3) of frusto- conical form receivable in a frusto-conical recess (7) a wall of the mold (1) when the associated actuator (4) is retracted.

7. Apparatus as claimed in claim 6 wherein each location means (3,8) further comprises a tapered plug (8) carried by the cap (3).

8. Apparatus according to claim 6 or 7, wherein the actuators (4) are piston-and-cylinder units and the caps (3) are mounted on piston rods of the units.

9. Apparatus as claimed in claim 8 wherein the pistonand-cylinder units are connected to a common pump via a hydraulic ring main.

10. Apparatus according to claim 8, wherein the piston rods of the units are slidably received in bushes (2) in the wall of the mold (1) and the bushes (2) have the frusto-conical recesses.