Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-06-21
2003-08-12
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S169000, C156S187000
Reexamination Certificate
active
06605171
ABSTRACT:
The present invention relates to a hollow body of revolution based on a thermoplastic organic material, in which continuous glass filaments, helically wound around its axis, are embedded.
Although the invention is not limited to such an application, it will be more particularly described with reference to the manufacture of pipes of all types, especially those intended for conveying pressurized fluids.
Another advantageous application is the manufacture of tanks intended to contain fluids, especially pressurized fluids.
Plastics have already been widely used for this type of manufacture, but, in order to withstand the high pressures encountered, the wall of the pipes manufactured must necessarily have a very great thickness. This very great thickness gives the pipes a considerable weight.
In order to reduce the weight of such pipes, it has already been proposed for them to be reinforced by means of reinforcing fibres arranged at their surface. Such a solution has been envisaged, for instance, by Patent GB-A-2,077,880 which describes a composite pipe consisting of an extruded former made of PVC or of polypropylene immediately covered, in the axial direction, with continuous glass yarns impregnated with a thermoplastic resin, helically wound around which are continuous glass yarns impregnated with a thermosetting resin, the latter yarns themselves being covered with a layer of thermoplastic resin.
Apart from the fact that the continuous manufacture of these pipes is expensive and very complex, the life of these pipes is very short. This is because the various aforementioned materials of which they are composed rapidly delaminate from each other, thereby rapidly reducing their burst strength.
This is why Patent EP-A-0,697,553 has proposed another type of composite pipe consisting of an extruded plastic former within which short reinforcing fibres are dispersed, parallel to its axis, and around which continuous reinforcing fibres are helically wound.
It turns out that the short fibres very rapidly become detached from the extruded former, thereby creating in the latter fracture initiators which propagate rapidly. Consequently, the burst strength of the pipe rapidly decreases. To guarantee a minimum long-term burst strength, especially one that meets the standards in force, it is then necessary to compensate for rapid propagation of fractures by again increasing the thickness of the extruded former, which results in a non-negligible increase in the weight of the pipe.
Furthermore, even if a minimum long-term burst strength is guaranteed, short fibres, once loosened, appear at the inner surface of the former. When the fluid intended to be conveyed by the pipe is water, the food-related criteria that the pipe must meet are no longer satisfied since the visible short fibres run the risk of contaminating the said fluid.
The object of the present invention is therefore to alleviate the aforementioned drawbacks and especially to propose a pipe of the aforementioned type which is lightweight and has an excellent long-term burst strength.
To do this, the subject of the invention is a hollow body of revolution intended especially for containing a pressurized fluid, the wall of the body comprising in its thickness:
a first region, the internal periphery of which is intended to be in contact with the fluid and at least the external periphery of which is made of a single thermoplastic organic material A, and
a second region made of a thermoplastic material identical to the material A and of continuous glass yarns which are embedded in the said thermoplastic material and are wound helically around the longitudinal axis of the hollow body of revolution,
characterized in that
the second region comprises in its thickness a first part arranged so as to be continuous with the first region of the body and made of the thermoplastic material A and the glass yarns, and a second part forming the external periphery of the body and made only of the thermoplastic material A, and
the wall of the said body has a volume void content V
v
of less than 0.5%, preferably less than 0.2%.
It is specified that, within the context of the invention, the volume void content according to the invention may be measured in a known manner using a micrographic method of the image-analysis type. It is therefore appropriate to take several local measurements on the hollow body and to carry out a statistical analysis thereof.
It is also possible to calculate the volume void content differently, in a generalized way using the following formula:
V
v
=(
d
th
−d
r
)/
d
th
in which d
th
and d
r
represent the theoretical density and the actual density of the body of revolution, respectively. The theoretical density is calculated from the density of the glass and from the various densities of the thermoplastic organic material A weighted by their relative percentages. As regards the actual density, this is calculated by taking the ratio of the actually measured mass of the body of revolution to the actual volume of the body.
The solution completely solves the problem posed. To achieve this, the inventors have firstly been able to analyse the key functions that a composite pipe must fulfil and to demonstrate the shortcomings of the composite pipes according to the prior art, such as those mentioned in the preamble.
According to this analysis, the reinforcing fibres must in principle withstand all the hoop and axial stresses due to the pressure exerted by the fluid flowing inside the pipe and the internal region made of thermoplastic organic material must be impervious to and chemically compatible with this same fluid. A simple hooping of continuous reinforcing fibres over a former made of thermoplastic organic material should therefore fulfil these functions.
Now, the inventors have discovered that, in order to guarantee the durability of a composite pipe of this type over time, it is absolutely necessary for there to be both effective protection of the fibres and perfect adhesion between the various elements of which it is composed.
They have thus been able to devise a body, as claimed, with a sufficiently intimate union between the various elements of which it is composed that a lifetime much longer than those encountered hitherto can be guaranteed.
Furthermore, the invention makes it possible to obtain pipes which are much easier to transport and handle.
According to one advantageous characteristic of the invention, the thermoplastic organic material A may be a polyolefin, of the polyethylene PE or polypropylene PP type, or else polyvinyl chloride (PVC). These materials have the advantages, among others, of being chemically inert, of being able to withstand very low temperatures and of having a low manufacturing cost.
The density d of the thermoplastic organic material A may vary through the thickness of the wall and may, especially, be between 0.915 and 0.960 g/cm
3
.
According to an advantageous variant, the continuous glass yarns embedded in the thermoplastic organic material make an angle of between 50 and 55° with the axis of the said body. Such an arrangement allows the axial and hoop resistance of the body to the pressure exerted by a fluid flowing through or contained within it to be further increased, for the same amount of continuous glass yarns used.
According to another advantageous variant, the continuous glass yarns embedded in the thermoplastic organic material make an angle close to 90° with the axis of the body and other continuous glass yarns are embedded in the thermoplastic organic material, these being arranged longitudinally along the axis of the body.
The choice of one of these variants, of their combination or of another variant giving preference to a different angle of winding of the continuous glass yarns, as well as the choice of the respective amounts of the glass yarns in the direction in which they are placed, will be made according to the specific constraints associated with each application, such as the resistance to pressure, resistance to ovalization, flexural strength, tensile streng
Cividino Alexandre
Debalme Jean-Paul
Voiron Jacques
Aftergut Jeff H.
Saint-Gobain Vetrotex France S.A.
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