WO2001012405A1

WO2001012405A1 - Production of hollow articles

Info

Publication number: WO2001012405A1
Application number: PCT/ZA2000/000138
Authority: WO
Inventors: Donald Henry Hourahane
Original assignee: Donald Henry Hourahane
Priority date: 1999-08-19
Filing date: 2000-08-18
Publication date: 2001-02-22
Also published as: AU7391200A

Abstract

A method of making a hollow article is disclosed, the method comprising inflating a hollow former which has the shape of the article to be produced. The outer surface of the former comprises a fabric woven or knited from a yarn which includes a core and a multitude of staple fibres forming a layer which envelopes the core and provides an extended surface area and interstical spaces for infiltration by cement fines and hydrates, the staple fibres being spun around the core and attached to the core, the staple fibres having sufficient freedom of radial movement to provide said spaces and permit ingress of cement fines and the formation of its hydrates in said spaces. Cementitious mix then applied to the fabric to create an outer cementitious layer. Several such layers of fabric and mix can be applied to build a wall of the requisite thickness. The hollow former can be a bladder to the outer surface of which the fabric is applied. Alternatively the fabric can be laminated to an air impervious plastic film, and the former produced from said laminate.

Description

PRODUCTION OF HOLLOW ARTICLES

FIELD OF THE INVENTION

THIS INVENTION relates to the production of hollow articles.

BACKGROUND TO THE INVENTION

In the specification of my PCT application PCT/US97/00362 (published

as W097/26395) there is described a yarn which includes a core and a multitude of

staple fibres forming a layer which envelopes the core and provides an extended

surface area and interstical spaces for infiltration by cement fined and hydrates, the

staple fibres being spun around the core and having sufficient freedom of radial

movement to provide said spaces and permit ingress of cement fines and the

formation of its hydrates in said spaces. Such a yarn is known as a friction spun

yarn.

A specific feature of the friction spun yarn of PCT/US97/00362 is that

the fibres are attached to the core at intervals along the length cf the core. This

inhibits delamination, that is, sliding of the core with respect to the fibres. The

specification of my PCT application is hereby incorporated into the present

specification.

As is explained in the PCT specification, a cement tious mix bonds to a fabric woven or knitted using yarn of the type described above. The resultant

product is becoming known in the art as textile concrete which is a cementitious

material with one or more textile layers incorporated in it.

Layers of fabric woven or knitted using friction spun yarn can be

laminated to one or both faces of a water impermeable synthetic plastics material

film, or alternatively a single layer of such fabric can be laminated to one face of the

film. The film is preferably of polypropylene as this is unaffected by the alkalinity of

any concrete with which it comes into contact. If the fibres are of polypropylene then

the film must be of the same material otherwise hot melt lamination is impractical. If

acrylic fibres are used in the yarn then hot melt adhesives can be employed to

secure the fibres to an acrylic film. Acrylic is inert to cement an offers a polar

surface to which cementitious mixes bond. The lamination procedure assists in

preventing the core and fibres from delaminating as discussed above.

A composite material comprising a layer of air impermeable synthetic

plastics film laminated to at least one layer of fabric woven or knitted using friction

spun yarn will be referred to hereinafter as a composite material of the kind defined.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention there is provided a

method of producing a hollow article which comprises fabricating a former using a

composite material of the kind defined, the former being hollow and closed except for an inflation iniet and the woven or knitted layer being on the outside of the

former, inflating the former, and applying a cementitious mix to the outside of the

former thereby to create an outer cementitious layer.

The method can include the additional steps of applying a further layer

of said fabric to said outer cementitious layer before it has set, and then applying

further cementitious material to produce a wall having said further layer of said fabric

embedded in it between said outer cementitious layer and said further cementitious

material. These additional steps can be repeated a plurality of times to produce a

wall having layers of fabric embedded in cementitious mix.

Said cementitious mix is preferably sprayed on and can have chopped

reinforcing fibres in it.

For certain products the method can include cutting an opening in said

wall to provide access to the interior of the article. In this form said film can have a

woven or knitted fabric layer on both sides thereof, and the method can include the

further step of applying cementitious mix to the layer of fabric on the inside of the

former after cutting an access opening in the former.

The method can include the further step of providing an outer mould,

and expanding the former against a patterned surface of the mo.jld by increasing the

pressure in the former before the outermost cementitious layer applied to the former has set thereby to emboss onto said outermost cementitious layer the surface

pattern of the mould.

The air pressure in the former is preferably increased to expand the

former by heating the air in the former.

According to a further aspect of the present invention there is provided

a method of making a hollow article which comprises inflating a bladder, laying up on

the outside surface of the bladder fabric which has been knitted or woven from a

friction spun yarn thereby to form a fabric covering over the bladder, and applying a

cementitious mix to the fabric covering.

This method can include the step of applying further fabric layers and

further cementitious mix to build up a wall comprising layers of fabric embedded in

cementitious mix.

An outer mould can be provided and the bladder can be expanded by

increasing the pressure in the bladder before the outermost cementitious layer

applied to the bladder has set thereby to emboss onto said oute^rmost layer a

surface pattern of the mould. An increase in the air pressure in ihe bladder can be

achieved by heating the air in the bladder.

DETAILED DESCRIPTION OF THE INVENTION For a better understanding of the present invention the manufacture of

a pair of boat hulls, a water pipe and a building structure will be described by way of

example. The manufacture of a water tank will be described with reference to the

single Figure of the drawing. However, it will be understood that hollow articles of

any shape and for a variety of purposes can be manufactured by the techniques

described hereinafter.

WATER TANK FABRICATION

A composite fabric comprising a single layer of woven or knitted fabric

laminated to a layer of synthetic plastics material is cut into panels. There are a

number of panels 10 (see the drawing) each having the form of a truncated triangle,

plus a smaller disc 12 and a larger disc 14. The narrower ends of the panels 10 are

sewn or preferably ultrasonically welded to the periphery of the smaller disc 12. The

larger ends of the panels 10 are sewn or otherwise secured to the periphery of the

larger disc 14. The panels 10 have their edges sewn or ultrasonically welded

together. A hole 16 is left, preferably in the larger disc 14, through which an inflation

pipe 18 can be inserted and sealed in place. Once inflated the former has the shape

of a truncated cone with a flat bottom surface of larger diameter and a flat top

surface of smaller diameter. The woven or knitted fabric is outermost, but there can

be fabric layers on the inside and the outside of the tank.

The entire outer surface of the former is then coated with a

cementitious mix. The mix can have chopped reinforcing fibres in it and can be applied by hand or sprayed on. The interaction between the cementitious mix and

the sheath of the yarn is described in the specification of my PCT application and

will not be repeated here. After one or more layers of cementitious mix, and one or

more further layers of fabric, have been applied to achieve a desired wall thickness,

reinforcing hoops 20 of metal or plastics tape are dropped over the partly finished

tank and slide downwardly to their correct positions. Hoops 20 of different diameters

are used so that they engage the outer surface of the truncated cone at different

levels. They are temporarily fixed in place. Thereafter a final layer of fabric and a

final layer of cementitious mix is applied to conceal the hoops. The final layer of

fabric is, of course, applied before the previous cementitious layer has set. This final

layer thus integrates the hoops into the tank's wall.

If the hoops are of synthetic plastics, then they are preferably of

ultrasonically welded polypropylene strapping tape, or polyester or nylon webbing.

Instead of inflating the tank using air it is possible to use water, in

which event the hoops must be in place before filling takes place to prevent the

outwardly directed forces bursting the former.

An opening 22 can be cut in the smaller diameter disc using, for

example, an angle grinder and a pre-cast manhole dropped into the opening. Holes

24, 26 can be drilled in the tank to permit water pipes to enter th 3 tank. BOAT HULLS

The construction of a pair of boat hulls is similar to the procedure just

described. The shapes are, however, more complex and construction is facilitated

by the use of a computer program to enable composite material of the kind defined

to be cut into panels of the correct shape with an appropriate allowance for seam

width. The composite material used has woven or knitted fabric on both sides of the

synthetic plastics layer. In producing the boat hull, ultrasonic welding is preferred as

the method for joining the panels. If the panels are sewn together then sealing

tapes are required between adjacent panels. Two hull shapes are formed and

joined together at the gunnels. One hull is thus upside down with respect to the

other. A stiff diaphragm is provided at this level to prevent the hulls bulging when

they are inflated. The diaphragm can be sewn or pop rivetted to the fabric.

Inflation can be achieved by inserting a steel pipe from bow to stern

into the double hull structure. The pipe preferably lies horizontally and includes a

rotary joint at one end so that the two hulls can be rotated about the axis of the pipe

during the fabrication procedure. The other end of the pipe is closed and it has a

hole in the wailing thereof to permit air to be pumped into the two hulls. If the panels

forming the hulls are ultrasonically welded it should only be necessary to inflate the

hulls once as there should be no leakage.

The inflated hulls are preferably coated with a mixture of neat cement

and bonding liquid, mixed into a smooth paste. A thixotropic additive, for example, carboxy-methyl-cellulose, can be used to help keep the cement in suspension. The

paste may be applied by brush or spray as only small quantities are required. A

pressure pot sprayer with mixing agitator can also be used.

Once the hull surfaces are coated, one or more layers of material of

the kind described are laid up and bonded to the hulls by painting or spraying on a

cementitious mix. The fabric need not be pre-sewn or welded, merely over lapped at

the joint lines. The surface should be carefully smoothed and if a conventional

cement and a bonding liquid is used, should be allowed to air dry for 24 hours. If

time is available the hulls should be sprayed with water, wrapped in plastics film and

allowed to cure for four to six days.

The two hulls are separated at the diaphragm and the steel pipe

removed. The wall thickness of the textile concrete should be about 3mm, and at

this thickness it can be cut with a sharp knife, a garden scissors, metal shears, or by

using a cutting disk in an angle grinder.

The inside surface of the two hulls has a textile bondable surface. A

hollow keel and seats can be shaped and fitted into place, and bonded to the textile

surface by neat cement bonding liquid such as was used on the outside of the hulls.

Gunnel rails either of wood or fabricated from strips of textile concrete lapped over

the trimmed gunnel edges can be fitted. The insides of the hulls are desirably

painted with the cement bonding liquid mix. The finished hulls are water tight due to the laminated layers of

polypropylene in the fabric. The keel and seats can be hollow and injected with

polyurethane foam to provide buoyancy. The hulls can be decorated with outdoor

quality PVA/acrylic paint or a water based paint.

WATER PIPE

A concrete water pipe can be produced by overlapping the longer

edges of an elongate strip of material of the kind defined and securing the edges

together to form a seam. The strip thus takes on the form of a tube. If the

composite material includes a single layer of fabric then the fabric is outermost.

Caps are used to close the ends of the tube, one of the end caps including an air

inlet. The tube is then inflated and subsequently treated with layers of cementitious

mix and further layers of fabric until the desired wall thickness has been achieved.

Inflation of the pipe can continue to pre-stress the fabric layers.

BUILDING STRUCTURE A former of the requisite shape, preferably much like an igloo or a tent,

is formed by ultrasonically welding panels of the kind defined together. In this form

the synthetic plastics material is preferably sandwiched between two fabric layers so

that the building structure can be treated with cementitious mix and further layers of

material both on the inside and on the outside. The former is entirely closed except

for an air inflation pipe entrance. Once the former has been inflated cementitious

mix and further layers of fabric are applied externally until the desired wall thickness has been achieved.

Windows and doors can be cut using, for example, an angle grinder

and thereafter the inner surface of the former can be treated with cementitious mix

and layers of fabric to obtain the desired surface finish.

A floor can be cast on the laminated sheet constituting the base of the

former. A frame is erected inside the former to provide additional support for the

walls and roof.

Hot air under pressure can be applied to the inside of the former. This

causes the film to stretch and hence the former increases in size. If there is an outer

mould against which the former is inflated, fine detail can be embossed into the

outer surface of the former.

It is also possible to omit the film and use an inflatable bladder of the

requisite shape. Fabric made of the yarn described is then laid up on the outside of

the bladder and a cementitious mix applied. Further layers of fabric and mix can be

applied to achieve the desired wall thickness.

In this latter form it is also possible, whilst the wall s still flexible, to

further inflate the bladder thus pressing the wall outwardly against the inner surface

of a mould. This enables fine detail to be impressed into the outer surface of the wall. If the wall thickness has to be increased further, this can be done from the

inside when the bladder has been deflated and removed.

It is also possible to produce an article which has a hollow in one face

thereof. In one form of the method a sheet of composite material of the kind defined

is placed on a horizontal platen surface. The surface has an inlet in it through which

air can be supplied to the space between said surface and said composite material.

The face of the sheet which is uppermost has the fabric layer on it.

Cementitious mix is applied to this layer so that the layer is embedded. Further

layers and further mix can be applied to achieve the desired thickness.

A mould, which can be a rubber mould, is then placed over the sheet.

Edges of the mould contact said sheet and press it against said platen surface. The

mould is then clamped. When air is supplied through said inlet into said space, the

space expands and presses the mix against a patterned surface of the mould. This

is done before the mix sets so that the configuration of the patterned surface is

impressed into the mix. The mould has at least one recess into which the sheet is

pressed thereby to leave a hollow in the rear face.

If desired a deflated bladder can be used in place of the composite

material. The knitted or woven fabric is placed on the bladder a id the mix then

applied to embed the fabric. Several layers of fabric and mix can be applied before the mould is placed in position and clamped. Thereafter the bladder is inflated. This

has the effect, as previously described, of expanding the space behind the

composite material.

Claims

CLAIMS:

1. A method of producing a hollow article which comprises fabricating a

former using a composite material of the kind defined, the former being hollow and

closed except for an inflation inlet and the woven or knitted layer being on the

outside of the former, inflating the former, and applying a cementitious mix to the

outside of the former thereby to create an outer cementitious layer.

2. A method as claimed in claim 1 , and including the additional steps of

applying a further layer of said fabric to said outer cementitious layer before it has

set, and then applying further cementitious material to produce a wall having said

further layer of said fabric embedded in it between said outer cementitious layer and

said further cementitious material.

3. A method as claimed in claim 2, wherein said additional steps are

repeated a plurality of times to produce a wall having layers of fabric embedded in

cementitious mix.

4. A method as claimed in claim 2 or 3, wherein said former has the

shape of a truncated cone with its smaller end uppermost, the method including

providing strengthening hoops of various diameters around the tαincated cone after

forming said cementitious outer layer, the hoops being positioned at spaced

locations along the cone, and embedding the hoops in the wall by applying at least one further layer of said fabric and further cementitious material.

5. A method as claimed in claim 1 , 2, 3 or 4, wherein said cementitious

mix is sprayed on.

6. A method as claimed in any preceding claim, wherein said

cementitious mix has chopped reinforcing fibres in it.

7. A method as claimed in any preceding claim, and including cutting an

opening in said wall to provide access to the interior of the article.

8. A method as claimed in claim 7, wherein said film has a woven or

knitted fabric layer on both sides thereof, and the method includes the further step of

applying cementitious mix to the layer of fabric on the inside of the former after

cutting an access opening in the former.

9. A method as claimed in any preceding claim and including the step of

providing an outer mould, and expanding the former against a patterned surface of

the mould by increasing the pressure in the former before the outermost

cementitious layer applied to the former has set thereby to emboss onto said

outermost cementitious layer the surface pattern of the mould.

10. A method as claimed in claim 9, wherein the air pressure in the former is increased to expand the former by heating the air in the former.

11. A method of making a hollow article which comprises inflating a

bladder, laying up on the outside surface of the bladder fabric which has been

knitted or woven from a friction spun yarn thereby to form a fabric covering over the

bladder, and applying a cementitious mix to the fabric covering.

12. A method according to claim 11 , and including applying further fabric

layers and further cementitious mix to build up a wall comprising layers of fabric

embedded in cementitious mix.

13. A method as claimed in claim 11 or 12, and including the step of

providing an outer mould, and expanding the bladder by increasing the pressure in

the bladder before the outermost cementitious layer applied to the bladder has set

thereby to emboss onto said outermost layer a surface pattern of the mould.

14. A method as claimed in claim 13, wherein the air pressure in the

bladder is increased by heating the air in the bladder.

15. A method of producing an article, the method comprising providing a

sheet of composite material of the kind defined, applying cementitious mix to said

sheet so that the woven or knitted layer is embedded in the mix, clamping the edges

of said sheet by means of a mould so as to form a space on the side of the sheet remote from said mould, and supplying air under pressure to said space to displace

said sheet towards a patterned surface of the mould and cause said mix to be

pressed against said patterned surface so that the mix has the configuration of said

surface impressed into it.

16. A method of producing an article, the method comprising placing a

layer of fabric woven or knitted using friction spun yarn onto the surface of a bladder,

applying cementitious mix to said fabric layer so that the layer is embedded in the

mix, positioning a mould so that a patterned surface thereof is adjacent said mix,

and inflating said bladder to displace the mix and fabric layer towards said patterned

surface of the mould so that the mix has the configuration of said surface impressed

into it.