CA1174614A

CA1174614A - Composite pipe and pipe fitting joint surface preparation

Info

Publication number: CA1174614A
Application number: CA000389650A
Authority: CA
Inventors: Raymond C. Dahn
Original assignee: ABCO PLASTICS Ltd
Current assignee: ABCO PLASTICS Ltd
Priority date: 1981-11-06
Filing date: 1981-11-06
Publication date: 1984-09-18

Abstract

ABSTRACT OF THE DISCLOSURE
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 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 of the fabric, serves to facilitate the making of a strong bond between the surfaces which are to be joined.

Description

~L~7~

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 ~74614 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.

-~1'7'~6~

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 li7~6~

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.

1~17'~

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 ~17~
-- 6 ~

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 1~L7'~

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.

~1~4~1gL

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 ~*Trademark 1~7~6~9~
_ g 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 ~17'~61~

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.

Claims

1. The method of joining together lengths of fiber reinforced plastics pipes 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 or fitting, characterized in that said annular end portion is provided with a surface layer of a fabric; said fabric being embedded in cured plastics material and being peelable from said annular end portion upon the application of force thereto, and wherein, in preparation for joining said annular end portion to another length of said pipe or fitting, a force is applied to said fabric sufficient to cause the same to be peeled off thereby to expose a clean surface on said annular end portion having a texture related to that of the fabric.

2. The method according to claim 1 wherein said annular end portion comprises an externally tapered spigot end portion of the pipe or pipe fitting.

3. The method according to claim 1 wherein said annular end portion comprises an internally tapered bell end portion of the pipe or pipe fitting.

4. The method according to claim 1, 2 or 3 wherein said fabric comprises a woven synthetic plastic cloth.

5. The method according to claim 1, 2 or 3 wherein said fabric is a synthetic plastic cloth having a textile lubricant and/or sizing agent thereon to facilitate the peeling and release of same from the end portion of the pipe or pipe fitting.

6. The method according to claim 3 wherein said fabric is a synthetic plastic cloth having a coated substantially impervious surface thereon exposed to the interior of the bell to prevent penetration of moisture and contaminants into said fabric.

7. A rigid fiber reinforced plastics pipe length or pipe fitting having at least one annular end portion adapted to be bonded to an adjacent length of such pipe or fitting, characterized in that said annular end portion is provided with a surface layer of a textile fabric, said fabric being embedded in cured, rigid plastics material and being peelable from said annular end portion upon the application of force thereto to expose a clean bonding surface having a texture related to that of the fabric.

8. A pipe or pipe fitting according to claim 7 wherein said annular end portion comprises an externally tapered spigot end portion of the pipe or pipe fitting.

9. A pipe or pipe fitting according to claim 7 wherein said annular end portion comprises an internally tapered bell end portion of the pipe or pipe fitting.

10. A pipe or pipe fitting according to claim 7, 8 or 9 wherein said fabric comprises a woven synthetic plastic cloth.

11. A pipe or pipe fitting according to claim 7, 8 or 9 wherein said fabric has a coating thereon facilitating peel-ing and release of such fabric from the plastics material.

12. The pipe or pipe fitting according to claim 9 wherein said fabric is coated on that side which is exposed on the interior of the bell thereby to prevent ingress of moisture and other contaminants thereinto.

13. In the manufacture of rigid fiber reinforced thermo-setting plastics piping which includes forming an annular end portion on a pipe or pipe fitting which is adapted to be bonded to an adjacent length of such pipe or fitting;
the improvement which comprises embedding a surface layer of a textile fabric in thermosetting plastics material at said end portion, which fabric is peelable from said end portion upon the application of forces thereto to expose a clean bonding surface having a texture determined by the textile fabric.

14. The improvement according to claim 13 wherein said annular end portion is formed on the exterior of the pipe or pipe fitting to define a spigot end portion, with a liquid uncured plastics material being applied and the textile fabric being wrapped on the spigot end portion such that the liquid plastics material migrates into the textile fabric before it cures.

15. The improvement according to claim 13 wherein said annular end portion is formed on the interior of the pipe or pipe fitting to define a bell end portion, said textile fabric being first wrapped on a mould member shaped to define the bell end portion and the pipe wall being thereafter built up on said mould such that the textile fabric becomes adhered thereto, the textile fabric having a coated impervious surface thereon which is exposed on the interior of the bell end portion.

16. The improvement according to claim 13, 14 or 15 wherein said fabric comprises a woven synthetic plastic cloth.

17. The improvement according to claim 13, 14 or 15 wherein said fabric is a synthetic plastic cloth having a material thereon facilitating peeling and release of such cloth from the plastics material in which it is embedded.