Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to improvements in the joining
together of composites and in particular to the joining together
of fiber reinforced plastics pipes and pipe fittings.
Fiber reinforced plastics (FRP) pipes and fittings are
commonly bonded together by means of adhesives, the latter being
applied at the interfaces defined by bell and spigot type joints.
The bell and spigot type joints are, of course, formed at the
opposing ends of the pipe lengths and fittings, which pipe
10 lengths and fittings are placed in end-to-end relationship. In
order to provide for a strong bond between the surfaces, it is
important that they possess a certain degree of roughness and it
is also important that the surfaces be clean and free from
grease, moisture, and other forms of contamination.
The bell and spigot surfaces are formed during the pipe
and pipe fittings manufacturing procedure, which procedures are
generally well known in the art. The pipe lengths and fittings
are then ultimately transported to the region where they are to
be installed. During the course of transportation, storage,
20 and placement into the location where they are to be installed,
the pipe and fitting surfaces are exposed to numerous
contaminants. Accordingly, some means must be provided thereby
to allow the surfaces which
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are to be bonded together to be adequately cleaned thereby to
pro~ide a strong bond. The current practice is to machine and/or
abrade the surfaces which are to be fitted together and then
to clean the surfaces for adhesive bonding. The cleaning
operation is normally accomplished by cleaning the area with
an implement, such as a brush, wetted with a suitable solvent
such as acetone. This procedure is obviously relatively
inconvenient and time-consuming. The additional on-site joint
preparation time necessitated by these procedures adds
10 significantly to the overall installation cost.
A surface-preparation technique referred to as the
"peel-ply method" is briefly referred to in an article titled
"Design Guidelines For Joining ~dvanced Composites" by Donald
R. Dreger, Machine Design, May 8th, 1980. In this technique,
15 as outlined in that article, a portion of woven nylon cloth
is incorporated into the outer layer of the composite during
lay-up. When the component is prepared for bonding, the nylon
peel-ply is simply torn or peeled away, disposing a clean
roughened surface. The degree of roughness can be varied to
20 some extent by the choice of weave of the peel-ply.
SUMMARY OF THE INVENTION
It is a basic object of the present invention to provide
improved surface preparation techniques for use in the joining
together of composite pipes and pipe fittings and in
25 particular to provide a surface preparation technique
incorporating a peelable fabric ply in the joining together
of pipe lengths and fittings, thereby to provide a rapid and
convenient method of joint preparation capable of reducing
the amount of on-site joint preparation time appreciably.
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Accordingly, the invention provides a method of joining
together lengths of fiber reinforced plastics pipe and pipe
fittings wherein the pipe lengths and fittings are
each provided with an annular end portion
adapted to be bonded to an adjacent length of such pipe.
According to the invention such annular end portion is provided
with a surface layer of a textile fabric, such fabric being
embedded in plastics material and being
releasable therefrom upon application of sufficient force. In
lO preparation for joining said annular end portion to another
length of the pipe or fitting, a force is applied to such surface
layer which is sufficient to cause the same to be peeled off thereby
to expose a clean surface on the annular end portion. This
clean surface, having a roughness dependent upon the texture
15 of the fabric, serves to facilitate the making of a strong bond
between the surfaces which are to be joined.
The method recited above may be used in many
applications. For ~ple, the pipe and fittings to be joined may be
provided each with an externally tapered spigot end portion an~
20 an opposite internally tapered bell end portion, the spigot
end of one length being adapted to fit into the bell end of
another length in the manner well known in the art. In this
case, both the spigot and bell portions are provided with the
above-described peelable surface layer of textile fabric.
In another version of the joining procedure, tapered
butt joint arrangements may be utilized, i-e- wherein
externally tapered spigot-type ends are placed end-to-end and
are joined together by overlapping lengths of mat and woven
roving wound around the adjacent tapered surfaces, such mats
30 and roving being saturated with resin.
The preferred material for the peelable surface layer
referred to above is woven nylon cloth, the desirable
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characteristics of which will be described in more detail
hereinafter.
The present invention also provides improvements in
fiber reinforced plastic pipes and fittings having at least one annular end
portion adapted to be bonded to an adjacent length of such pipe.
The improvement is characterized in that such annular end portion
is provided with a surface layer of textile fabric, such fabri~
being embedded in plastics material and being
peelable therefrom upon the application of forces thereto
10 thereby to expose a clean bonding surface. As noted previously
the annular end portion may comprise an externally tapered
spigot end portion or an internally tapered bell end portion.
The invention further provides a method for providing
such surface layer of peelable fabric on end portions of pipes
15 and pipe fittings as recited in certain claims appended hereto.
Further features, advantages and characteristics of
the invention will be readily apparent to those skilled in the
art from a study of the following description of preferred
embodiments of the invention taken in conjunction with the
20 accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view, partially cut away,
of a tapered adhesive joint formed between bell and spigot end
portions of fiber reinforced plastics pipes;
Figs. 2A, 2B and 2C illustrate the major steps involved
in the preparation of the bell end surface of a pipe or pipe
fitting following the principles of the present invention;
Figs. 3A, 3B and 3C illustrate the major steps involved
in preparing a spigot end portion of a pipe following the
30 principles of the present invention; and
Fig. 4 illustrates a typical butt joint
configuration to which the principles of the present invention
are also applicable.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring firstly to Figure 1 there is illustrated
a tapered adhesive joint defined by mating bell and spigot
portions formed on the ends of pipes or fittings to be joined
together. As seen in Fig. 1 the spigot end comprises a tapered
male portion which fits into the correspondingly tapered
female or bell section of the pipe or fittings with the mating
tapered surfaces being bonded together with an adhesive.
The fiber reinforced pipes and fittings are manufactured
10 utilizing basically conventional techniques. For purposes of
the present description it will be assumed that glass fiber is
used as the reinforcing material with the matrix of plastic
material comprising a suitable polyester formulation,well
known as such in the art,although,of course other types of
15 plastic formulations such as vinyl ester or epoxy resins may
be utilized. The pipe or fitting structures may utilize a certain
proportion of hoop or spiral wound filaments and, if desired,
a certain proportion of longitudinally oriented filaments,
such longitudinally oriented filaments being in the form of
20 chopped filamentæ which may be applied in the manner described
in published British application No. 2 018 185 A
dated October 17,1979, and assigned to the assignee of the
present invention. A certain proportion of randomly oriented
chopped fiber may also be incorporated into the structure
25 depending upon end use requirements together with a certain
proportion of non-fibrous filler as desired.
The technique illustrated in Figs. 2A-2C and 3A-3C
involves the incorporationof a woven nylon cloth into the outer
layer of the bell and spigot joint areas of the glass fiber
30 composite structure. When the composite part is prepared for
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bonding, this nylon material is simply peeled off exposing a
clean rough surface ready for bonding. The use of this
technique eliminates the need for machining the surfaces of
pipe or pipe fittings and this represents a cost saving to the
manufacturer and eliminates an operation which otherwise
creates dust and airborne particles. As will be appreciated,
the degree of roughness of the joining surfaces afforded by
the practice of the present invention can be varied to some
extent by the choice of the weave of the nylon cloth. By way
10 of example, 4, 6, and 8 ounce/square yard 100% nylon material
has been utilized as well as 400 Denier and 400 Denier
fill/200 Denier warp 100~ nylon material. In general
the nylon cloths used herein are commercially available fabrics
which are readily available in the fabric industry. Generally
15 speaking any material which can release from the cured resin
laminate would be adequate provided it also gives the degree of
surface roughness and cleanliness one desires on the laminate. It is
contemplated that knit materials would also be useful depending
upon these considerations of release from the laminate and
20 adequate surface roughness. Furthermore, from experience, it
is believed that the finish variation on the various nylon
fabrics tested has an appreciable effect on the ability of the
fabric to release from the cured laminate.
The selection of the "peel away" fabric also involves
25 the considerations of whether the material can be cut easily
and in a manner so as not to create frayed lengths of loose
fibers which can become embedded into the laminate. Nylon
material is attractive in this regard since it can be cut by
conventional heat and sealing cutters known to the fabric trade.
30 Cutting with heat seals the severed nylon fabric threads so
that no frayed edges are present which would otherwise cause
stray fibers to become embedded into the polyester laminate
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making removal of the layer difficult.
The preparation of the bell surfaces will now be
described reference being had to Figures 2A-2C. In connection
with the bell surface, it is noted here that a urethane coated
fabric is sometimes preferred in this application since such a
coating on the exposed surface protects the bell surface from
contamination by dirt, oil or water. (It is noted here that
such urethane coated fabric cannot be used in the spigot
application as it is important to have the fabric porous in
10 order that air entrapment can be easily removed. This will be
readily appreciated later on in conjunction with the description
relating to the spigot surfaces.) It should be noted that,
although urethane coating is mentioned, other coating means
to produce an impervious surface could be used.
In a typical application, a woven nylon fabric was
used having yarn weight of 420 x 420 Denier (warp to fill)
15 having a weight of approximately 8 ounces per square yard. The
thread count per square inch (warp to fill)was 60 x 42 in the
finished material.
In preparing this 100% nylon fabric, known as a greige
fabric, typical yarn lubricants and warp sizing such as
20 starches and polyvinyl alcohol which are typically water
soluble are used in the weaving process and are allowed to
remain on the greige fabric. The greige fabric is then
washed and typically coloured with acid dyestuffs which are
common pigmented dye and binder products used in the textile
25 industry. The fabric is then coated on one side only with
1.25 to about 1.5 ounces of urethane per square yard utilizing
coating techniques well known in the art.
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The urethane coated nylon fabric is then fed through
a fluorocarbon water repellent material such as Dupont's
VYDAX* fluorocarbon telometer dispersion which coats
both sides of the fabric. The fabric is then fed
through an oven maintained at about 400F. with this oven
operation driving off the solvent used in the fluorocarbon
repellent as well as any solvent remaining from the urethane
coating.
Referring now to Fig.2A , a precut strip 10 of cloth
material prepared as described above is fitted to the tapered bell
portion of mould 12 with its urethane coated surface in contact
with the mould. The cloth material 10 is of a length such
that there is a slight overlap (approximately 1/8 inch)
at region 14. The cloth material 10 is held to the tapered
l~ mould section by one piece of double faced adhesive tape 16
located at overlap region 14.
With reference to Fig. 2B, the glass fibre composite
18 is then built up over the entire mould, including the tapered
bell portion,utilizing otherwise conventional composite fiber
reinforced plastics pipe manufacturing techniques. As a result
of this the above noted length of precut cloth material 10 is
thus incorporated into the tapered bell joint surface layer.
With reference to Fig. 2C,the mould 12 has been removed
from the glass fiber composite so that the layer of cloth
10 is exposed at the bell end of the pipe or pipe fitting. Since
the cloth material 10 was originally fitted to the bell portion
of the mould with its urethane coated surface in contact with
such mould, such urethane coated surface is exposed on the
final finished pipe or pipe fitting. This urethane coating
serves to protect the underlying bonding surface from oil, dirt
and moisture contamination. When the composite pipe or fitting
is being prepared for
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bonding, the cloth material 10 is simply peeled off by grasping
the cloth at the overlap 14 and peeling it off thus exposing
a clean rough surface 20 therebelow which is ready for adhesive
application.
Reference will now be had to Figures 3A-3C which
illustrate the preparation of the spigot surfaces. Insofar
as the fabric material is concerned, a white porous weave
material is preferably used so that air entrapment is easily
10 seen and removed. A greige or unfinished fabric 200 Denier
warp/400 Denier fill has been found to be highly satisfactory
since it has the required porosity and moreover has an adequate
finish to allow release from the laminate. This fabric is of
100% nylon having, as noted above, the weight of 200 x 400 Denier
15 with the thread count per square inch in the greige state being
60 x 40. Typical yarn lubricants and warp sizing (well known
to those skilled in the art) both of which are water soluble
are used in the weaving process and remain on the greige fabric.
Referring now to Fig. 3A, an end portion 24 of a
20 fiber reinforced pipe is brought into contact with a tapered
grinding wheel 26 and the pipe is rotated about its axis thereby
to provide an annular tapered spigot end portion 28. This
procedure is, per se, generally well known in the FRP pipe
industry.
Referring now to Fig. 3B, the annular tapered surface
28 is then coated with a suitable resin coating (e.g. polyester
resin and catalyst) and following this a precut strip of the
cloth material 30 as described above is wrapped around this
resin coated surface. The strip is preferably made long enough
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sv that there is a slight amount of overlap. Any entrapped
air beneath the cloth material is removed before the resin
cures by rolling the particular area in a manner consistent
with common fiberglass laminating practices. As noted above,
it has been found that air entrapment is easily seen and
removed when cloth 30 is of a white porous open weave material.
Referring to Fig. 3C, when the composite FRP pipe
is being prepared for bonding, the strip of cloth material 30
is grasped by the fingers as shown and peeled away or unwrapped
10 from the annular spigot end portion 28 thus exposing a clean
rough surface ready for adhesive application. It has been
found that during the course of the operation described above
in Fig.3B that sufficient resin seeps through the pores of the
cloth material 30 as to seal such pores against dirt, oil and
15 moisture penetration and contamination.
The purpose of Fig. 4 is to illustrate that the
teachings of the invention are applicable to pipe and fitting
joints other than tapered bell and spigot joints as described
above. Figure 4 illustrates a typical butt joint and it will be
20 seen here that the two pipe end portions which are brought into
abutting relationship both have externally tapered annular
end surface portions 34. These externally disposed tapered
surfaces are provided with a strip of the fabric material as
described above which is applied and then subsequently unpeeled
25 prior to bonding substantially as described with reference
to Figs. 3A-3C. Following this the abutting tapered surfaces
are then coated with resin-rich paste followed by layers of
resin saturated matting and overlapping lengths of such mat
and woven rovings thereby to build up a joint having the necessary
30 structural characteristics.
.
By virtue of the use of the peelable strip of material
as described above, the surface or surfaces to be bonded are
protected from oil, dirt and moisture contamination. Tests have
proven that surfaces employing the peel strips could be bonded
5 successfully after having been immersed in water for 18 hours.
In this case the adhesive bonding was done immediately after
removal from the water bath. The bond strengths obtained were
equivalent to those for laminates joined after they had been
conditioned in a drying oven. The contamination protection
lOafforded by the peelable layer taken together with its ease of
removal is highly important to the joiner of pipe and fittings.
No longer do the surfaces to be joined need to be sanded and
washed prior to joining. Besides the labour savings, the
creation of dust and airborne particles(which in a field
15installation situation can be quite bothersome due to the usual
lack of dust removal and ventilation provisions in these
temporary situations)is eliminated while following the practice
of the invention. A further significant advantage is that the
technique described also gives a very uniform surface pattern,
20considerably more consistent than what is usually produced by
the usual machining and grinding operations. Additionally,
the technique described has considerable importance in pipe and
fitting product developments involving laminates which are difftcult
to machine. Eliminating the need to machine gives substantial
25cost savings and allows more flexibility in laminate design.
For example, filler additions which could cause machining
problems can now be readily incorporated into pipe products due
to this novel technique.
