GB2065262A

GB2065262A - Pipes Made of Reinforced Thermosetting Resins and Process for Making the Same

Info

Publication number: GB2065262A
Application number: GB8036821A
Authority: GB
Original assignee: SNIA Viscosa SpA
Current assignee: SNIA Viscosa SpA
Priority date: 1979-12-07
Filing date: 1980-11-17
Publication date: 1981-06-24
Also published as: DE3045036A1; IT1209155B; NO803694L; GB2065262B; SE8008445L; IT7927949A0

Abstract

Pipes made of reinforced thermosetting resins having a monolithic wall, is composed of two or more layers of different materials, comprising an inner layer of cellular material essentially consisting of unsaturated polyester resin and an outer layer of reinforced thermosetting resin.

Description

SPECIFICATION Pipes made of Reinforced Thermosetting Resins and Process for Making the Same The present invention refers to pipes having a wall constituting a single monolithic block but formed of two or more different layers.

More particularly, the present invention refers to pipes of reinforced thermosetting resins having an inner layer of cellular material essentially consisting of optionally reinforced unsaturated polyester resins.

The present invention also refers to a process for the production of said pipes.

Pipes made of thermosetting or of thermoplastic resins, optionally reinforced with the customary mineral charges and/or inorganic or organic, natural, synthetic or artificial fibres, are known.

The inner layer or "liner" of said pipes is constituted by a resin, optionally reinforced, which may be of the same type or of a different type than the resin which constitutes the outer layer. Pipes made of polymeric materials are already known. In daily practice polyethylene or polyvinyl chloride pipes are used. These, however, have the defect that because of their low softening temperature, they are subject to deformation when exposed to sunlight, e.g. before being placed in the ground to form conduits.

Further, said pipes have low resistance to chemical agents and high cost, whereby they are not adapted for many uses.

Tubes of reinforced polyester resins obtained by the centrifugation or filament winding technology, are also known. While they are adequate for many applications, they are not suitable for other applications because of their insufficient rigidity.

The applicant has now surprisingly found that it is possible to obtain pipes having a greater rigidity by coupling an inner layer of a cellular material essentially consisting of an unsaturated polyester, optionally reinforced, with an outer layer constituted by reinforced thermosetting resins.

An object of the present invention are therefore pipes made of reinforced thermosetting resins, having a monolithic wall, characterized by the fact that said wall comprises two layers of different materials, of which an inner layer is of a cellular material essentially consisting of an unsaturated polyester resin and an outer layer is of a reinforced thermosetting resin. More particularly, according to the present invention, the wall constituting a single monolithic block, is characterized by the fact that it is constituted by an outer layer essentially consisting of a commercial resin, in particular an unsaturated or epoxy or vinyl ester polyester resin reinforced with continuous or cut fibres of glass, carbon, polyamides or other, and from an inner layer or liner of a cellular material essentially consisting of a commercial polyester resin, optionally reinforced.

In the pipes according to the invention, the inner layer of cellular material has different functions: a) the function of a resistant chemical barrier; and b) a mechanical function consisting in increasing the rigidity of the pipe by the presence of a material having a low density and significantly high elastic moduli. As thermosetting resins constituting the liner, polyester resins obtained according to British Patent Applications No. 8014309 and No. 8014310 are preferably employed.The cellular materials essentially consisting of unsaturated polyester resins which form, according to the invention, the inner layer of the pipes, may be reinforced with mineral or organic charges in the form of powder, ground fibres or cut fibres, such as e.g. continuous or cut or ground glass fibres, or with other inorganic or organic, vegetable, artificial, or synthetic fibres, as well as with mineral loads such as calcium carbonates, alumina, silica.

The thickness of the liner may be varied in a suitable manner according to the functions which it is to carry out, and more precisely it will be minimal if it serves only as a chemical barrier and it will be suitably greater if it has a structural function.

Preferably the thickness of the liner varies, according to the invention, from 0.5 mm to 50 mm and more preferably from 1 mm to 20 mm.

The inner layer of the pipe, of cellular material, may be provided with an inner finish which will be in contact with the fluid flowing through the pipe, said finish being constituted by a gel-coat of polyester resin or by a glass mat reinforcement.

The outer layer, according to the invention, is destined to absorb the mechanical stresses deriving especially from the internal and external pressure. The pipes which are the object of the present invention may be made by different processes. Said processes may differ, depending on the desired diameter of the pipes, and by way of nonlimitative example two processes will be described, the one adapted for making pipes having a diameter up to 350 mm and the other adapted for making greater diameter pipes.

When pipes having a diameter up to 350 mm are to be made, a process may be used, comprising the steps of firstly making a reinforced unsaturated polyester foam liner and thereafter constructing, the reinforced thermosetting resin layer on the outside of the liner, by the filament winding method while using said liner as a mandrel. While any technique presently used for like manufactures may be employed, the process indicated in Example 1 is preferred.

When pipes having a diameter greater than 350 mm are to be made, a process may be used comprising the steps of constructing, e.g. by the filament winding technique, a reinforced polyester foam liner on a male mandrel (which represents the inner surface of the pipe), and thereafter, when the unsaturated polyester foam has completely gelled, constructing the reinforced resin layer (which represents the resistant mechanical layer of the pipe) on the outside of said liner. While any technique presently used for like manufactures may be employed, that indicated in Example 2 is preferred.

The following example are intended to illustrate but not to limit the present invention.

Example 1 Construction of a Pipe having an inner Diameter Smaller than 350 mm Characteristics of the Pipe inner diameter: 300 mm thickness of the liner: 6mm material of the liner; cellular material made of loaded, unsaturated polyester resin, having a density of 0.45 kg/dm3 resistant layer structure: commercial polyester resin structure reinforced with continuous glass fibre (roving), made by the filament winding technique thickness of the resistant layer: 2mm Construction of the Pipe A loaded, unsaturated polyester resin in the form of a liquid foam having a density of 0.45 kg/1, previously prepared according to Example 1 of British Patent Application No. 8014309 is poured and uniformly distributed, on a steel pipe having an outer diameter of 300 mm, maintained in rotary motion at a speed of 500 rpm, until a uniform thickness of 6 mm has been reached.The pipe is maintained in rotation until the liquid foam has hardened. This normally requires about two hours at a temperature of 200C. After hardening, the obtained cellular body is extracted from ths steel mandrel and is mounted on a winding machine in which the outer layer is applied by the filament winding technology, employing glass roving and a commercial unsaturated polyester resin having a gel time of 40 minutes. The thickness of each layer and the number of the layers is such that an overall thickness of 8 mm (comprising the cellular material layer) is obtained. The filament winding operation is continued until the outer resin has completely hardened (at least 1 hour) whereafter the finished pipe is removed.

Example 2 Construction of a Pipe having an inner Diameter Greater than 350 mm Characteristics of the Pipe inner diametr: 1200 mm thickness of the liner: 20 mm material of the liner: cellular material made of loaded, unsaturated polyester resin, having a density of 0.45 kg"dm3 resistant layer structure: commercial polyester resin structure reinforced with continuous glass fibre (roving) made by the filament winding technique thickness of the resistant layer: 5 mm Construction of the Pipe A film of polyethylenetherephthalate is laid on a collapsible mandrel having an outer diameter of 1200 mm, in such a way as to cover the entire surface of the mandrel.An unsaturated polyester resin, in the form of a liquid foam having a density of 0.45 kg/1, previously prepared according to Example 1 of British Patent Application 8014309 is poured and uniformly distributed while the mandrel is maintained in motion at a speed of 250 rpm, until a uniform thickness of 20.5 mm has been reached. The rotation is maintained until the resin has hardened, which requires about 2 hours at 2000. The thickness of the cellular material decreases to 20 mm because of the hardening. After hardening the outer winding is applied on the same apparatus by the filament winding technique, employing glass roving and a commercial unsaturated polyester resin having a gel time of 40 min. The thickness of each layer and the number of the layers is such as to produce a thickness of 5 mm (excluding the inner foam layer). The filament winding operation is continued until the outer layer has been completely hardened (at least 1 hour), whereafter the pipe is removed, after collapsing the mandrel.

Claims

1. Tubes of reinforced thermosetting resin having a monolithic wall, characterized by the fact that said wall is composed of two or more different layers of material, of which an inner layer in cellular material based on unsaturated polyester resin and an outer layer of reinforced thermosetting resin.

2. Pipes according to Claim 1, characterized by the fact that the outer layer of the monolithic wall is based on a commercial resin, particularly an unsaturated or epoxy or vinyl ester polyester resin reinforced with continuous or cut fibres of glass, carbon, polyamides and others, while the inner layer of said wall is constituted by cellular material based on a commercial polyester resin, optionally reinforced.

3. Pipes according to Claim 1 or 2, having the inner layer in cellular materials based on unsaturated polyester resin, optionally containing mineral or organic charges in the form of a powder, ground fibres or cut fibres.

4. Pipes according to Claim 1 and 2, having a surface reinforcement made of mat or a gel coat as a finish of the inner layer in contact with the conveyed fluid.

5. Process for making the pipes according to the preceding claims, characterized by the fact that firstly an expanded material is made in the form of a pipe and that subsequently one or more layers of unsaturated polyester resin reinforced with inorganic or organic, vegetable, artificial or synthetic fibres are applied on the outside of said pipe by conventional methods.

6. Pipes, according to Claims 1 to 4, characterized by the fact that they have been obtained by the described and exemplified technology.

7. Pipes substantially as herein described with reference to Example 1 or 2.

8. Process for making pipes substantially as herein described with reference to Example 1 or 2.

9. The features as herein disclosed, or their equivalents, in any novel selection.