CA1076013A - Manufacture of fibre reinforced foam shells - Google Patents

Abstract

ABSTRACT
A boat hull is made by winding a layer of glass-fibre around a male mould, winding a layer of foam sandwich material on top of the glassfibre, and then winding a second layer of glassfibre on top of the foam.

Description

~ 10760~3 The present invention relates to a method of con-structing a boat hull or other hollow articles.
Foam Reinforced Plastic, commonly known as FRP,~is used for constructing boat hulls. FRP consists of a low density core between outer layers of highc'density material.
The core is shaped as required and the outer layers secured to it by a mechanical bond. The core material must be of sufficient stiffness and sufficiently shearproof to hold the outer skins apart. PVC Foam is an example of a core material of this type which possesses, in addition, *he capacity for recovery after compression loading and there -fore resistance to vibration. PVC Foam Glass Fibre and Polyester Resin are typical materials suitable for sand-wich construction.
A known method of sandwich construction used in boat building is familiarised as the "Male Plug" or "Male Mould"
Method. This method is to make a plug or mould constructed in the form of the required boat hull upside down and secured to a flat floor. It consists of athwartships frames or ribs fixed parallel to each other and to which battens are fixed longitudinally. The battens are spaced a few inches ~a~,a~t. PVC foam sheets are cut and "tailored"
to the form and strained, heated or preformed so as to wrap approximately around the mould. These PVC foam panels are then secured to the wood battens from within the mould by wood screws, or by headless nails or spikes driven from the outside through foam and batten so as to hold the foam securely to the battens. Each panel of foam is butted .~

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r j- against that which has been secured to the mould until - the whole surface of the hull is covered, after which the gaps and butt joints between panels of foam are filled with ~i grout and sanded fair, ready for the application of the out-er skin.
~' C ~ext~ an outer skin lay-up in ~ proceeds with the application of a quick cure polyester resin applied to ths ~ surface of the PVC foam followed by layers of glass fibre l' in the form of chopped mat, unidirectional and/or woven J ~ . . . .
¦ 10 rovings, wetted and fully impregnated with polyester resin.
he surface is usually finished at this stage b~ ~rinding . - . . : .
~ mooth.
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he hull, consisting of PVC foam with an outer skin - of GRP is moved from the wooden mould. Screws, nails or ¦ 15 fastenings are removed from the inside to rel~ase the in-ternal surface of the foam from the wood battens. The hull is then lifted clear of the mould, turned over and placed ¦ upright in chocks made ready to receive it.
-! ~ext an inner skin of GRP is provided in a similar manner as that of the outside of the hull, so as to form a "sandw~ch" of PVC foam between two skins of GRP mechanically - bonded to each surface.
~he construction of the deck, or "top section" of the hull proceeds either in the ~ame manner as that of the hull ' 25 or is built up with separate panels upon beams.
~he disadvantages of the"Male Plug Method" are that:
a. '~ailoring and cutting of foam in panels to fit com-pound curves is wasteful and requires a high degree of . .

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b. ~ertain portions of PVC foam must be fastened under ` varying degrees of tension to the wood battens of the mould.
; Since heat is generated by polyester resin in the course ,;
- j of curing, the surface of the PVC foam in contact with 5 _ G~P laminations appliéd to it, is warmed thereby reducing the rigidity of the foam. At the same time, shrinkage i - occurs in the curing of the skin lamination. ~he effect '- ~ o~ this action is to create distortions in the surface of the hull which appear as the skin cures and hardens. If .. . . .. ..
` l~ 10 a slow cure resin is used to minimise heat transference ' from lamination to foam, there is a danger of styrene being il released from the resin upon the foam and causing soft-.
ening and similar distortion, particularly in those areas !; whsre pressure has been applied to secure a tight fit between foam and mould.
c. Application of GRP laminations over a fixed mould ` from the horizontal at the centre of the hull to vertical ~1 at the gun~Jhale line cause inevitable variations in lay-up , and consequent waste.
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d. Standardised control of lay-up of both outside and j inside skins becomes problematical when scaffolding is - , required to enable operators to handle resin and glass , materials over the whole surface of the hull. Special ventilation must be provided for working upon the inside ; 25 GRP skin.
e. ~he common use of slow cure resin enables an operat-or - ` , 3 .

~ - . to complete one lamination of glass fibre and to allo~J this ; to cure partially before applying subsequent laminations.
However, in this case it is necessary to grind and remove rough edges from the partially cured surface between each - i 5 application of laminations.
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. Removal of the wood male-plug tend to cause damage j to the plug itself and to the inner surface of the fo~m.
g. ~ifting, turning and lowering the partially fabricated - - hull to enable the internal surface lay-up to take placemakes demands upon the time and expertise of the builder~
-: including the realignment of the hull in its upright posit-- ion so as to avoid distortions developing during subsequent ~ nternal skin lay-up.
`~' 3' ! h. As the result of a,b,c,d,e and f, abovej a considerable j 15 amount of filling and grinding is required to produce a tandard of finiSh comparable with hulls built bg other - methods.
he "Male Plug Method" is usually employed for the construction of "one off" hulls or small numbers of hulls.
~urthermore the structural advantages of the monocoq Sandwich Construction, in which compound curves are so effectively achieved, together with the ease with which local areas of the hull may be stressed by the use of ~oven ` and unidirectional fibres, must be balanced against the cost of effective lag-up control and finishing.
An object of this invention is to provide a method of -; constructing a boat hull by which the advantages of Sandwich I - Construction are preserved~ the disadvantages reduced or .

avoided and the best use made of the materials employed~
~he present invention consists-in a method of con-structing boat hulls or other hollow articles comprising providing a male mould~covering the mould with a first ~- 5 layer or layers of resin impregnated fibre~ then with a - winding of at least one layer of synthetic foam about the fibre, and winding at least a further layer of fibre impre-gnated with resin about the foam to form a sandwich of foam between the layers of fibre.
It is possible to remove the mould by cutting the sand-wich into two parts and then to produce two hulls from one mould by making o~e said part as one complete hull. Alter-natively a single, decked boat can be produced by using the method according to this invention. A further advantage of -15 the present invention is that the method may be used by semi-skilled labour and for long productio line operat;ion.
According to one convenient method of applying the invention, by way of example, a small-craft hull is made specifically in relation to the opportunities offered by method and material. In this example, a yacht hull and deck is considered as one unit, the "top" and "bottom"
sections of which are designed to absorb compression and tension loads exerted by fore and back stays.
An example of the method of construction is as follows:
A rotatable mould is provided and the materials ~076013 t . .
required for sandwich lay-up are mounted on a trolley alon~side.
~he ~ould is ~irtually a complete hull and deck unit smaller in diameter of section than the finished hull by the thiclDless of the finished sandwich lay-up. ~he mould is supported at either end, motorised and geared to revolve - - .
~ elowly so that the materials may be unwound and applied from their trolley mounting and wound in sequence and under - : tension onto the male mould. ~he mould is first coated - 10 with a release agent such as ~VA or wax. Polyester , resin is activated and applied in suitable width to the - ¦ - mould. Woven glass rovings of the same width and under ~ tension are applied to the wetted resin. This in turn is !i -followed up by a second application of resin and woven ; 15 rovings and so on to the desired number of laminations of the inner skin, PVC foam of appropriate width, being wound under tension onto the last quick-cure wet lamination.
~his may be followed by a light wide mesh glass roving ¦ - wound dry over the surface of the PVC foam to ensure that it is compressed firmly and accurately into the surface of the inner skin. ~hen follows the application of a coat of quick-cure resin. ~ay-up of the outer skin lamin-ations commences as soon as the quick-cure resin application to the PVC foam surface has sealed it sufficiently against styrene action. At this stage any faults in lay-up may be rectified by the application of fillers. ~aminations proceed as with the inner skin, to the desired specification, , , .

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i ~ 1076013 ; ~3ina1 finish can be achieved by the positioning Or a ¦ "float", blade or wiper, set so as to smooth out and ' dist-ribute excess resin as the mould revolves.
~t this stage in a modification of the described method it is advantageous to pro~ide a final finish by bandaging with a strip of material such as Melan/ex Q,oo (Registered Trade Mark), aluminium foil of 1.009 inch - thickness, or suitable polyester resistant film.
~; ~he final stage in the manufacture of the complete ~` 10 hull involves the removal of the male mould from within it l~ by cutting the hull in half, removing the mould intact and ,j - ~oinin`g the two halves together again. This may be - conveniently done, if for example, prior to the application of , the release agent, an insert is provided in the mould ' 15 horizontally and at the point of maximum beam running round ¦ the hull to define a groove in the sandwich lay-up. By inserting a knife or saw at this point through the sandwich ~ - lay-up into the groove, a clean and precise cut may be - ¦ guided round the hull to sever top from bottom. The top section is then removed and hoisted clear and the mould hoisted out of the bottom section. ~oam from the top edge of the ,, lower hull section may conveniently be gouged out to a suitable depth. Resin is then applied and a preformed tongue inserted into the groove. ~ similar groove is made in the j 25 lower edge of the top "deck" section of the hull. The ¦ tonvue insert having been coated with resin, the top deck section is lowered onto the tongue and excess resin .
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~ . wiped away.
- , At this sta~e, when the resin skins are still in the I ~`process of curing, apertures, such as cockpit, hatches and ;! - windows may be cut out without fear of distortion. ~ffective bonding may also be achieved in this state i.e. before `¦ final cure has taken place, of internal bulkheads, keel ¦ ~ stringers, floors and furniture, to the internal and external kins of the hull.
~ariations of lay-up procedure may be employed, for I 10 example for the application of unidirectional fibres long-: . . ..
- itudinally by hand lay-up to the mould surface prior to the lay-up procedure of the inner skin, and again to the outer ~¦ sur~ace of the cured foam prior to lay-up of the outer skin.j Heat may be applied locally to either surface of the P~C foam during lay-up.
`1 Widths of PVC foam may be increased by using foam in j which grooves have been cut on one or both surfaces so that only the centre area is compressed in bending.
C ~ of thickness of foam core 'o GRP skins in~ ~and-¦ 20 wich boat hull construction may be about 6:1 for a PVC foam core of density of 5 lbs per`cu.ft. Variations of skin ~ thickness and in the composition of glass fibres in the skinj laminations may be made to absorb local loading. Compression! Or "distance" pieces may be inserted in place of the PVC core where, for example, bolts are used through the core, having the effect of spreading the load between both skins. At , these points it may be desirable to appl~ additional lamin-! ations to spread the load over a larger area of the skin .
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surf~ce tha~ that of the compression insert. Compression plugs or plates a~ electrical circuits ma~ co~veniently be inserted into the PVC foam core prior to the application of the outer skin.
In the application of this example of the invention, a sandwich construction is used which æimplifies the building of boat hulls in ~RP. X~tation of the mould combined with the ability to control under tension, the application of materials laid up over compound curves is the basic advantage - 10 of the system. ~his applies in particular to PVC loam used as a core which is bonded effectivelg within the outer GEP
sk~s.
- By slight modifica~ions to both hull design and the make-up of materials used in FRP construction, without detriment to the performance of hull or the mechanical and structural qualities of the materials, material wastage is eliminated, standardised structural control is achieved and much labour saved in relation to the present customary method of sandwich construction. ~he invention may be used both as a hand lay-up and a mechanised lay-up technique for the purpose of building production ru~s from the male mould.
~urther advantages of the method according to the invention are as follows. Air bubbles within the resin are forcedfrom each lamination to the sur~ace by the tensioning of materials in narrow widths about the mould~
Shrinkage of resin while curing causes increased . . .
, , tensioning of glass fibre around the mould a~d ensures an - accurate mechanical bond between the foam and glass fibre.
~ A che~ical bond is established between the inner and ' '~ outer layers of glass fibre along but-t joints in the foam.
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i~ 5 ~his area of butt joint may be reinforced during lay upj, ' with strands of fibre so as to provide an "H" section of GRP.
~'i ' ' Quick-cure resin may be used not onl~ to increase the ' speed of lay~up but to reduce or eliminate styrene action.
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' In the case of polyester resin and semi-rigid unplasticised ' , PVC foam, the foam is locally softenéd and distorted b~
' , slow curing resin.
j' ' ' Application of local heat to brittle or rigid PVC
' foam strips makes possible the use of this type of foam'~' 15 - for bending around compound curves. Local heat at the , point of lay-up may also increase the resin cure and lay-' up speed. Resin pigmented in one or more colours may ¦ ,be used in both inner and outer skin laminations to provide internal and external colour finish.
~he finished hull may be cut in two or more sections for removal from the mould within about fifteen minutes of completing the lay-up and virtually no distortion ~ ' takes place. Because of the absence of distortion '! æections can be stored separately to cure without the need for chocks. A,fter curing the parts can be fitted together with no misalignment or mating troubles. ~his would not be possible using conventional GRP methods lO ' .. . . . . . .

~076013 P-re-stressing fibres durin~ lay-up combined with exact control of resin to fibre ratios provides an improved strer~th to weight characteristic over conv~tional ~EP methods.
~lthough the inve~tion has been described primarily with the obaect of constructi~g boat hulls, the method is suitable for pipes, oontainers, wheelbarrows or any other articles suitable for the application of glass fibre and foam i~ the method described.
In the case of hollow article construction, the article may be made with parallel or tapered sides, and the mould can then be directly withdrawn from one end after construc-tio~ has finished. A tube i9 an example of such an article.
It would also be possible for the mould to be collapsed inside the finished moulding, and for the mould partæ to be subsequently withdrawn from the interior of the article.
~he above methods of mould remo~al are disclosed as examples o~ly. Ar~ other appropriate method can be used.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of constructing hollow articles comprising providing a male mould, coating the mould with a release agent, covering the release agent on the mould with at least a first layer of resin impregnated fibre, then with a winding of at least one layer of synthetic foam about the fibre, winding at least a further layer of fibre impregnated with resin about the foam with sufficient resin and under sufficient tension so that resin is forced into the joints between adjacent winds of foam to form a sandwich of foam between the layers of fibre and to form resin bridges connecting the first and further layers of fibre at the joints between adjacent winds of foam, removing the mould by cutting the sandwich into at least two parts, and rejoining the two parts with forming a tongue-and-groove interconnection in the foam layer.

2. The method of claim 1 further comprising winding a polyester resistant film around said further layer of fibre.

3. The method of claim 1 further comprising applying the foam in widths butt joined together.

4. The method of claim 1 wherein the first impregnated fibre layer is formed by coating the release agent on the mould with resin and winding a layer of fibre under tension on to the resin.

5. The method of claim 1 wherein the mould is arranged to be rotated.

6. The method of claim 1 wherein the mould is held stationary and the synthetic foam and fibre and wound about the mould.

7. The method of claim 1 wherein resin is applied to the outer surface of the foam and at least an outer layer of fibre is wound on to the resin to form the further impregnated layer of fibre.

8. The method of claim 1 wherein pigment is applied to at least one of the layers of resin impregnated fibre.

9. The method of cliam 1 wherein heat is applied to the foam before winding the foam on to the mould.

10. A method of constructing a boat hull with an integral deck comprising providing a male mould, coating the mould with a release agent, covering the release agent on the mould with at least a first layer of resin impregnated fibre, then with a winding of at least one layer of synthetic foam about the fibre, winding at least a further layer of fibre impregnated with resin about the foam with sufficient resin and under sufficient tension so that resin is forced into the joints between adjacent winds of foam, to form a sandwich of foam between the layers of fibre and to form resin bridges connecting the first and further layers of fibre at the joints between adjacent winds of foam, removing the mould by cutting the sandwich into at least two parts and rejoining the parts with forming a tongue-and-groove interconnection in the foam layer to form a hollow hull.