|Title of Invention||
|Abstract||The invention relates to a plastic tube whose tube wall comprises an outer layer, an inner layer and at least one intermediate layer, adjacent layers being linked to each other.|
The invention concerns a plastic pipe whose pipe wall is structured from an outer layer, an inner layer and at least one intermediate layer whereby adjacent layers are joined together.
Such a multiple-layer pipe can have diameters of 10 or 30 cm, but can also have diameters of several meters.
The pipes can be manufactured, for example, according to the centrifugal centrifugal casting method as known from EP 0 360 758 B1. With these methods, pipe sections with lengths of 6 meters and longer can be manufactured. The basic materials such as, for example, hardenable resins (particularly polyester resins), filling substances and glass fibres, are centrifuged in various mass portions for the formation of individual layers by way of a so-called feeder into a rotating mould. The pipe finally obtains its stability because of hardening of the resin.
The EP 0 360 758 B1 shows examples for the structure of the various layers. The quantity and the composition of the individual layers can depend notably on the size of the pipe and its usage. The state of the art identifies in an exemplary manner the differences between a "pressure pipe", through which a fluid is transported under pressure, and a "pressureless pipe", a waste-water pipe for example.
In most applications, the pipes are laid underground and are subject to various mechanical strains and stresses. A certain degree of flexibility is necessary for the pipe which is itself stiff by nature, in order to avoid, for example, destruction resulting from impact stress.
For this purpose, pipes of the type as mentioned above are known having individual layers which are reinforced with textile glass fibres and/or which have additives or filling substances, respectively. By rotation of the mould during manufacturing, the individual layers may be compacted before the finalising hardening process.
By these means, the stability of the whole pipe is improved. The pipes also present a resistance against impact stress or deflection, being sufficient for various areas of application.
The following test is known in this respect:
A pipe is placed on a V-shaped table which provides lateral stabilisation for the pipe. Weights having different masses (0.5 kg, 1 kg, 2 kg, 3 kg etc) are dropped from various heights (normally 0.1 to 2.4 meters with intervals of 0.1 meter) onto the outer surface of a pipe.
With each test from each height level, 15 repeat tests are carried out.
A visible crack on the inner surface of the pipe piece is assessed as being a "fracture". In this case, linear cracks (usually in the circumferential direction of the pipe) are distincted from star-shaped cracks.
At the maximum height and/or with the maximum weight where no crack on the inner pipe surface can be detected in all 15 repetitions, a 100% impact resistance is defined.
A complete failure is then assumed when visible cracks are observed with all 15 repeat tests.
The principle structural arrangement of the test facility is shown in Figure 1.
The objective of the invention is to present a plastic pipe of the type as described above which has a greater impact strength than pipes known up to the present. Such pipes are required for certain applications, for example in aboveground pipe installations.
Extensive experiments and tests were performed for the purpose of solving this task. The structure of a pipe as well as the structure of individual layers were systematically examined and analysed. The influence of the basic materials on the resistance capability towards impact was also examined as well as the change of the thickness of individual layers or their sequence.
The following terminology is adopted hereinafter: the pipe has an outer layer (= outer covering layer), an inner covering layer (= inner layer) as well as at least one structural layer in between, hereinafter called intermediate layers.
The invention is based on the knowledge that, for example, the change of the sequence of individual intermediate layers or the change of individual parameters of the manufacturing process only have a relatively minor influence on the mechanical properties of the pipe. These properties of the pipe can be improved decisively towards higher impact strength where, with the exception of the inner layer, at least one of the further layers (outer layer, intermediate layers) is changed with regard to its physical properties.
The change of the physical properties of such a layer, hereinafter called functional layer, can be achieved in two ways with the same final effects:
1st alternative: The functional layer comprises a resin which differs from a resin of at least one layer arranged radially to and inside of the functional layer in at least one of the following physical features: the modulus of elasticity is smaller, the fracture elongation (as well called elongation at break , ultimate strain) is larger, the softening temperature is smaller.
2nd alternative: The functional layer comprises at least one additive (aggregate) which deforms irreversibly, particularly plastically, in the event of impact energy acting on the outer layer of the pipe.
With the 1st variant, the resin is changed. With the 2nd variant, the composition of the layer is changed. The consequences resulting in both cases have the same effects. The impact strength of the whole pipe is significantly improved. The ductility of the pipe under load is optimised. Basically, particularly the following effects result in case of mechanical stress, in particular impact stress of the pipe:
In the functional layer, cracks, particularly micro-cracks or separations are formed
between the additive and the surrounding resin,
In the functional layer, zones which are filled out by a porous or deformable additive,
The surface compound between the functional layer and an adjacent layer is at least
A crack formation, particularly a formation of micro-cracks, can be obtained particularly in such a way that the functional layer in question comprises a resin whose elasticity module, fracture elongation and/or softening temperature differs in the dimension as stated from the corresponding values of a resin of at least one, radial internal follow-up layer.
Micro-cracks are cracks with a length of up to 1 mm, particularly up to 500 ym.
In this case, the elasticity module according to one embodiment should be at least 25% smaller than that of the radially and internally adjacent layer. The mentioned reduction can, according to embodiments be as well > 33%, > 50%, > 66%, > 75% or even > 90%.
So for example, an intermediate layer formed as a functional layer, may comprise a resin with an elasticity modulus of only about 100 MPa while the adjacent intermediate layer in the direction of the inner layer comprises a resin (polyester resin) with an elasticity modulus of 2000-4000 MPa. The effect achieved here according to the invention is as follows, among other things: The deformation wave caused by impact is partially reflected during the transition from the functional layer with low E-modulus into the follow-up layer with high E-modulus, so that only a part of the deformation energy is continuing further.
The selection of the resin for a functional layer can be made alternatively or cumulatively by way of its fracture elongation which should be larger than that of the resin in the layer following towards the inner pipe layer. Here, the resin of the functional layer can have a fracture elongation that is at least 30% larger. The fracture elongation, however, may also be > 50% or > 100% than the fracture elongation of the resin of the "internally" adjacent further layer.
In actual values, for example, the fracture elongation of an inner intermediate layer of the pipe can be 2-2.5%, while the fracture elongation of the externally orientated adjacent intermediate layer (functional layer) is at least 5%, but can also be 10%, 20% or even 50%.
A further possible criterion to solve the object is the selection of a resin for the functional layer(s) which softening temperature is lower than the softening temperature of a radially and internally follow-up layer. Whereas a conventional polyester resin for known centrifuged pipes has a softening temperature (determined according to ISO 75) of 100-130°C, the softening temperature for the resin of the functional layer established according to the invention should be at least 20% lower, whereby a reduction by more than 30% or more than 50% my be favourable. Accordingly, the resin for this functional layer is less interlaced and has, for example, a fusing temperature of The micro-cracks occurring in a functional layer under mechanical strain lead to a considerable energy damping and thus to a significant reduction of the elastic impact energy being passed into the internal adjacent layer. These functional layers do not influence the further principal structural properties of the pipe. The micro-cracks or separations have no negative influence on the usage characteristics of the pipe because all other layers are designed in such a way that the required structural properties are also fulfilled even if there were no functional layer.
For the impact test as described above this means that, on the inner wall of the pipe and under the same test conditions, significantly less cracks are observed compared with known pipes.
The outer layer and the intermediate layer(s) may comprise at least one of the following further constituents in addition to the resin (bonding agent):
In the layer, a filling material may be distributed, for example of the basis of Si02 , MgO, CaO, Al203, MgC03, CaC03, AI(OH)3, talcum, kaolin, BaS04, CaS04 or mixtures thereof. This filling material should normally have a grain size of
The filling material portion (within the respective layer), according to one embodiment, is between 25 and 250 mass-%, with reference to the resin portion of the respective layer.
In like manner, the outer and intermediate layers may comprise glass fibres (alone or together with filling material), for example glass fibres of a length of As additives for the functional layer(s), the following materials are suitable: foam glass, hollow glass, expanded perlite, expanded vermiculite, pumice, caoutschouc, elastomers, thermoplastics or the like, particularly with a particle size of In various embodiments, the particle size of the additive can also be significantly below 10 mm, for example The following applies in principle: many small cracks and many small new hollow spaces or material structure deformations increase the energy damping more than a few large cracks or a few large hollow spaces/zones.
The portion of the already mentioned additives is between 5 and 50 weight -% or up to 90 volume percent, with reference to the respective (total) intermediate layer whereby 60-80vol.-% will often be sufficient. But lower volume portions (up to 10, 20 or 30%), even though reduced, also lead to the effect as described.
The mentioned additive which separates from the surrounding resin matrix or deforms and/or breaks under the influence of mechanical forces, can also be applied for the purposes as stated, independent of the resin, for the formation of an invention-related functional layer.
To that extent the invention also comprises a pipe the functional layer of which comprises, in accordance with prior art, a conventional resin with an elasticity modulus of 2,000-8,000 MPa, for example, in which, however, at least one of the mentioned additives is distributed. The type of the additive, its size and its quota in the mass of the entire functional layer can correspond to the aforementioned details.
As observed from the outside to the inside, it supports the invention-related idea if a first functional layer of the type as described is followed by either a second functional layer of the type as described and/or a further layer (intermediate layer or inner layer) which is particularly suitable for stopping a crack propagation from a radially outer layer. This applies particularly for layers which also contain glass fibres in addition to resin. It is furthermore an advantage in this case if a portion of the glass fibres of the further layers runs in the axial direction of the pipe. With this further inner layer, a conventional resin in accordance with the aforementioned description can be adopted as a resin.
A pure resin layer is typically used as an inner layer because for this inner layer a very smooth surface is requested, along which the fluid flows, water for example. For this inner layer, a conventional resin of the type described can be used, for example a polyester resin on the basis of orthophthalic acid, isophthalic acid, terephthalic acid or tetrahydrophthalic acid, as well as for example a bisphenol resin, vinylester resin, epoxy resin or a polyurethane resin.
Further features of the invention result from the features of the sub-claims as well as the other application documentation.
The invention is described as follows in greater detail on the basis of various embodiments :
The Figures show the following - each in distinctive schematic illustration and not to scale:
Figure 2: A cross-section through a pipe wall in a first embodiment of a plastic pipe;
Figure 3: A cross-section through a pipe wall in a second embodiment of a plastic pipe;
Figure 4: A cross-section through a pipe wall in a third embodiment of a plastic pipe;
Each of the Figures 2-4 shows a cross-section through a pipe wall of a plastic pipe. Each of these plastic pipes consists here - in an exemplary manner - of five layers, meaning, an outer layer 10, an inner layer 12 and layers 14, 16, 18 arranged in between.
In all examples the outer layer 10 consists of a mixture of 30 weight-% of a polyester resin A (elasticity module: 3,000 MPa, tensile strength: approx. 60 MPa, fracture elongation: approx. 2.5%) and 70% weight-% quartz sand of a grain fraction The inner layer 12 in all examples consists exclusively of a polyester resin B with an elasticity module of approx. 200 MPa, a tensile strength of approx. 20 MPa, and a fracture elongation of approx. 50%.
In the embodiment according to Figure 2, the structural arrangement of the intermediate layers is as follows:
The intermediate layer 14 adjacent to the outer layer 10 consists of approx. 35 weight-% of the polyester resin B and approx. 65 weight-% calcium carbonate in a grain fraction The adjoining intermediate layer 16 is formed from a mixture of 40 weight-% of a special resin C and 60 weight-% calcium carbonate in a grain fraction Between this intermediate layer 16 and the inner layer 12, a further intermediate layer 18 is formed which consists of approx. 50 weight-% polyester resin A, 10 weight-% fine scale dolomite ( The impact energy as marked with an arrow in Figure 2, is dampened by the intermediate layers 14, 16, 18, and here in particular by the selection of resins with different and higher elasticity modules in each case, from the "outside" to the "inside". The intermediate layers 14, 16 are therefore functional layers in the sense as described above. In the zone of the intermediate layer 16, for example, micro-cracks are formed which are stopped in the further process by the following intermediate layer 18, so that the inner layer 12 remains undamaged to the greatest possible extent even with higher impact stress applications.
In Figure 2 and in the zone of layer 16, the micro-cracks are schematically symbolised in an exaggerated large manner. The symbolic illustration of the glass fibres in the zone of layer 18 and their course is also exaggerated.
In the embodiment according to Figure 3, the intermediate layer 14 following the outer layer 10 is formed as an energy-damping functional layer and consists of the mentioned special
resin C, in which hollow glass spheres with a diameter of This intermediate layer 14 is followed by a functional layer 16 which is arranged analoguesly to the intermediate layer 16 according to Figure 2. This applies also for the arrangement of the further intermediate layer 18 in front of the inner layer 12.
In an even larger scope than in the embodiment according to Figure 2, a pipe with a wall structural arrangement according to Figure 3 can absorb impact energy. The functional layer 14 with hollow glass spheres plays an essential role here. With an outer, for example, radial impact stress application, there occurs the destruction of the hollow glass spheres that are shown in an exaggerated large manner, leading subsequently to a deformation or destruction of the hollow spaces restricted by the hollow glass spheres in the material structure of the layer 14, through which stresses caused by the impact can be degraded.
This stress degradation continues in the layer 16.
By means of the "preliminary damping" of the impact energy in the layer 14, less micro-cracks are formed in comparison with the embodiment according to Figure 2 (symbolically recognisable by means of merely four crack illustrations). As a result, such a pipe can withstand a considerable and also durable impact stress application where no crack formation is observed on the inner layer 12.
The pipe cross-section according to Figure 4 corresponds to the example according to Figure 2 with regard to the outer layer 10 and the functional layer 14.
The follow-up intermediate layer 16, by contrast, consists of a pure special resin C of the type as stated whereas the further intermediate layer 18 formed between the intermediate layer 16 and the inner layer 12 is formed from the special resin C (with a softening temperature of 50°C) in combination with glass fibres.
In the zone of the intermediate layer 16 micro-cracks are formed again, insofar as the pipe is subjected to a corresponding impact stress application where the crack propagation in the direction of the inner layer 12 is stopped by the follow-up further intermediate layer 18.
Moreover a partial separation between the intermediate layer 18 and the inner layer 12 occurs in the corresponding surface area, as illustrated schematically by reference numeral 19.
Every one of these surface separations lies in the range of some mm2 as a maximum. By means of several of such separations along the surface between the layers 18, 12, a crack propagation starting from the outside is stopped at the inner layer 12.
Instead of the three intermediate layers shown schematically in the Figures, only two or significantly more than three intermediate layers can be provided whereby at least one, better at least two intermediate layer(s) are formed as a functional layer.
By means of the measures as described, the pipes designed and constructed according to the invention are superior with respect to their resistance to impact stress to pipes according to the state of the art.
Insofar as an elasticity modulus has been stated herein, this is determined according to ISO 527.
The given tensile strength data are determined in accordance with ISD 178.
The details of the fracture elongation are selected in conformity with ISO 527, ISO 178.
The softening temperature is determined according to ISO 75A.
Plastic pipe which pipe wall has an outer layer (10), an inner layer (12) and at least one intermediate layer (14, 16, 18) whereby adjacent layers are joined together, whereby at least one layer, with the exception of the inner layer (12), is formed as a functional layer, which
a) compnses a resin which, compared with a resin of at least one radially and internally following layer, differs in at least one of the following physical features: the elasticity modulus is lower, the fracture elongation is larger, the softening temperature is lower and/or
b) comprises at least one additive which irreversibly deforms in the case of impact energy application onto the outer layer (10).
Plastic pipe according to Claim 1 the functional layer of which comprises an additive which deforms plastically in the event of impact energy application onto the outer layer of the pipe.
Plastic pipe according to Claim 1 wherein the elasticity modulus of the resin of the functional layer is at least 25% smaller.
Plastic pipe according to Claim 1 wherein the elasticity modulus of the resin of the functional layer is at least 50% smaller.
Plastic pipe according to Claim 1 wherein the fracture elongation of the resin of the functional layer is at least 30% larger.
Plastic pipe according to Claim 1 wherein the softening temperature of the resin of the functional layer is at least 50% smaller.
Plastic pipe according to Claim 1 the functional layer of which comprises a resin which has at least one of the following properties:
- an elasticity modulus between 100 and 500 MPa,
- a tensile strength between 5 and 40 MPa,
- a fracture elongation > 10%,
- a softening temperature Plastic pipe according to Claim 1 wherein, with the exception of the inner layer (12), at least one layer (10, 14, 16, 18), in addition to a resin, comprises at least one of the following constituents:
- filling material on the basis of Si02 , MgO, CaO, MgC03, CaC03, AI203 , BaS04, talcum, kaoline, AI(OH)3, CaS04 or mixtures thereof
- glass fibres
Plastic pipe according to Claim 8 the filling material of which has a grain size of Plastic pipe according to Claim 8 comprising 25 to 250 mass-% filling material with reference to the resin portion of the respective layer (10, 14, 16, 18).
Plastic pipe according to Claim 8 the glass fibres of which have a length of Plastic pipe according to Claim 8 the glass fibre portion of which is 5 to 70 mass-%, with reference to the respective layer (18).
Plastic pipe according to Claim 1 the additive of which derives, individually or in combination, from the following group:
foam glass, hollow glass, expanded perlite, expanded vermiculite, pumice, caoutschouc, elastomers, thermoplasts.
Plastic pipe according to Claim 1 the additive of which has a particle size Plastic pipe according to Claim 1 whose portion of the additive is 10 to 90 volume percent, with reference to the respective layer (14).
Plastic pipe according to Claim 1 the inner layer (12) of which is a pure resin layer.
|Indian Patent Application Number||1234/CHENP/2007|
|PG Journal Number||08/2011|
|Date of Filing||23-Mar-2007|
|Name of Patentee||KNOCH, KERN&CO|
|Applicant Address||FERDINAND-JERGITSCH-STRASSE 15, A-9020 KLAGENFURT,|
|PCT International Classification Number||B23B 1/08|
|PCT International Application Number||PCT/EP05/12310|
|PCT International Filing date||2005-11-17|