The aspects of the disclosed embodiments are directed to a method to produce plastic tube with at least one stiffener, which plastic tube consists of at least an inner tube, stiffener and an outer tube.
The usages of the disclosed embodiments are light weight large diameter plastic tubes that have at least two walls and between them at least one spiral line shape stiffener. The mentioned tubes are used in sewer systems, bridge sewer ducts, containers, and in tube preforms to be machined later.
The before mentioned tubes are produced using the known technology so that first the inner tube is produced by for instance the spiral joint technique either upon a race or a rotating core of the starting tube by feeding plastic tape upon the mentioned race or the rotating support organ and by welding together in the spiral joint the meeting edges of the plastic tape and after this, a smooth surface or corrugated shape stiffener is installed following the shape of the spiral joint upon the inner tube and it is welded there fixed. In the next phase of the work, the outer tube is installed upon the stiffener with the same technique as the inner tube was installed upon the support organ and the outer tube is welded fixed to the stiffener, and at the same time the plastic tape edges that meet in the spiral joint of the outer tube are welded together. If the tube contains more cylinder layers and stiffener layers between them, it is continued in the same way until the desired construction has been achieved.
In the international patent publication WO 2012090185, a production method of the plastic tube with a stiffener strengthened tube using known technology has been presented. In this method, corrugated stiffener is fed upon a plastic tape composed inner tube and in the next phase the plastic tape forming the outer tube upon the mentioned stiffener. The stiffener that comes upon the inner tube has the same pitch as the plastic tape forming the inner tube and the stiffener has been adjusted to the joint of the inner tube. When the meeting edges of the tape forming the inner tube have been welded together with melted plastic material just before feeding the stiffener, the inner edge of the stiffener at the point of this joint sinks into this melted material and, additionally, the layer of the melted material upon the inner tube at the point of the stiffener welds the inner tube and the stiffener together. At the same time as the corrugated stiffener is fed upon the inner tube, the outside edge of this stiffener is stretched in order to make its peripheral length correspond the peripheral length of the inner surface of the outer tube. The welding of the outer edge of the stiffener to the outer tube and meeting edges of the plastic tape forming the outer tube are made at the same time.
One method of the known technology to produce large light weight construction plastic tubes is to make first U or L shaped tape from pre-fabricated tapes that then is fed upon a core and is then like a rotating screw, and then a spiral-weld tube is achieved with the pitch of the width of the tape that contains an essentially smooth surface buttress. The rounds beside the frame part are joined together and a new layer is formed upon the stiffener buttresses also by feeding tape in the shape of a spiral line.
This last described technology has been presented for instance in PCT applications no: PCT/IB2011/056029 and PCT/IB2011/056030.
One solution of the known technology is to fit the corrugated stiffeners upon the inner tube of the plastic tube essentially lengthwise of the mentioned tube. In this case, the stiffeners are produced during extruding the tube. This known technique is presented in the patent publication U.S. Pat. No. 7,550,102 B2 and the advantage of this construction is that it can be used in installations under water. The space between the inner and the outer tube can be filled for instance with concrete to balance the tube much easier that the corresponding state of the spiral stiffener tube.
The greatest draw-back of the firstly mentioned known technology is that keeping the stiffener that winds around the inner tube in the right position (upright) is very difficult, because when stretching the outer edge of the stiffener it gets thinner towards the outer edge. Therefore, it is necessary to arrange support for the stiffener and the tape to be welded to it forming the outer tube so that they would be in right position at the moment of welding. Without this kind of difficult to make support arrangement it is not possible to get suitable pressure to the welding point to achieve a sufficiently good quality weld. The pressure pressing the parts together must be within certain limits during welding and some time afterwards. This pressure is typically for polyolefin's about 100-200 kPa. Without the mentioned suitable pressure pressing together the parts to be welded it is difficult to get a weld that meets the quality criteria and when this pressure is set in using the known technique a danger of buckling sensitivity and malformations of the outer tube occur and this can lead to a collapse of the tube.
A drawback of this technique has also shown to be the limited flexibility of the corrugated stiffener, because it is always necessary to set a minimum value for the thickness of the stiffener material for the reasons of the durability and then the flexibility of the corner points of the corrugations is dependent on this thickness of the material.
Because of the structures (for instance overlapping when using U or L profiles) it is necessary to use more material than what the strength capabilities themselves demand.
The greatest drawback of the last presented known technique (U.S. Pat. No. 7,550,102 B2) is very high production costs. The tools that are used are very expensive, especially when producing large tubes and it is necessary to make own tools for every tube size.
The intention of the present disclosure is to achieve such a method to produce plastic tubes with at least one stiffener that avoids drawbacks of the known technology. It is characteristic for the solution of the invention what has been presented in the characterizing parts of the claims 1-3.
The greatest advantages of the disclosed embodiments come to that, that the installation and the welding of the stiffener or stiffeners and the outer layer get considerably easier and the high quality of the produced products can be assured without additional arrangements causing additional costs. Therefore, the production speed can safely be raised and then considerable economical advantage can be achieved.
The disclosed embodiments are described closer in the enclosed drawings, where
Now follows an explanation of the usage of the method of the disclosed embodiments as an example referring to the mentioned figures.
In
In order to be able to focus to the setting through the weight organ 33 or by tightening the plastic tape sufficient pressure to obtain faultless weld joints between the parts and at the same time to avoid the unfavourable malformations of the stiffeners 4 and the outer tube 8 and this way obtain the desired values set for the ring stiffness of the plastic tube 1; this present disclosure offers two different ways to realize it.
When instead of one stiffener 4 at least two parallel stiffeners are used following the pitch of the outer tube spiral joint, due to tighter stiffener construction the stiffeners and the outer tube maintain their favourable shapes and the welds of high quality can be made. In this case, the stiffeners can also be lower and the need to stretch their outer sides 4.2 is smaller and their tensile properties get better than in one stiffener known technology constructions.
Another way to achieve the mentioned good end result with the disclosed embodiments is to form such a one stiffener construction where the stiffener 4 is able to resist the buckling and other unfavourable twisting and thus to prevent unfavourable malformations to occur in the outer tube 8. It is known that it is necessary to stretch the stiffener outer side 4.2 when the welding is from the inner side 4.1 to the inner tube 2 to suite the inner race and thus the width of the outer side of the stiffener gets narrower than the inside width w of the stiffener preform 3 and the tensile properties of the stiffener get worse. It is also known that fitting the corrugated stiffener to correspond the outer tube 8 inner surface ring length with its outer circle length is often too challenging because it requires bending the corrugation construction from its corner parts and this causes problems for instance through unfavourable shape changes. In the method according to the invention, this problem is avoided by forming the corner parts 3.3 of the inside 3.1 and the outer side 3.2 of the stiffener preform thinner than the wall thickness s of its lamellas. In
Another way to produce the plastic tube 1 according to the disclosed embodiments has been presented in
When using more than one stiffener and being then able to reduce the height h of the stiffener and the need to expand the brush angle β between the stiffener lamellas 4.4 gets also smaller and then the lamellas 4.4 of the stiffener follow more precisely the round shape of the inner and the outer tube. The present disclosure gets realized when using any amount of the stiffener.
One solution according to the disclosed embodiments to produce a plastic tube with a stiffener is presented in
So it is possible to use the method according to the disclosed embodiments for instance by applying to the plastic tube to be produced one or more spiral stiffeners 4 (
In the different applications of the disclosed embodiments the sufficient tensile properties of the stiffener(s) 4 can be assured for instance by keeping the brush angle β between the lamellas 4.4 of the outside 4.2 of the stiffener 4 sufficiently small, so that too much stretching of the stiffener does not weaken the construction too much. It can be said that it is favourable to form the brush angle 13 smaller than 120°. The brush angle α between the lamellas 3.4 of the stiffener preform 3 depends, naturally, on the height h and the width w of the stiffener and also the outside diameter of the inner tube.
The stiffener can always be dimensioned by the size of the tube 1 and by the demanded properties, like the ring stiffness.
When installing the stiffener 4 or the stiffener layer 14 its sides to be welded can be preheated up to a suitable temperature that the situation requires and it is favourable that this temperature is such that a sufficiently thick melted material layer is formed on the surface of the part to be welded so that its temperature corresponds the temperature of the extruded tape. It is also possible to arrange support for the stiffener in the phase where it is fed upon the inner tube 2 or the plastic tape 6.
The production of the stiffener preform can be made beforehand using suitable as such known equipments either before producing the tube 1 or during this production process. The forming of the walls of the corner parts 3.3 of the stiffener preform thinner than the lamellas 3.4 can be made in the connection of making the mentioned corrugate structure by cutting away a part of the thickness of the walls of the corner parts. It can be said as an example that ½-¾ is cut off from the thickness of the corner parts. Also any other cutting depth or forming method realizes the present disclosure.
The preheating of the plastic tape 6 of the stiffener preform 3 of the inner tube 2 can be performed using any known technique method. It is essential for the disclosed embodiments that the welding temperatures are case by case in a favourable level. In
When using more than one stiffener 4 the plastic tapes 6 to be used can be wider than now to form the outer tube 8 and thus the production speed can be raised due to the greater pitch per round. It is known that with today's methods it is possible to reach 10 m/minute welding speeds and with the help of the disclosed embodiments this speed can be exceeded considerably.
The weight organ can be a reel or a dragging organ depending on the case. The weight organ can also consist of a number of reels or other organs in touch with the outer tube.
When using one wide corrugate it is always dimensioned so that no unfavourable malformations, like buckling, yielding, or blisters, occur in the parts of the tube 1.
As support organ 30, for instance a race or core or their combination can be used so that in the beginning end a rolling core is used and thereafter a race. In connection of the support organ, a gliding stopper can be used to guide the stiffener preform and the plastic tape.
The stiffener(s) can also be placed so, that none of them comes to the point of the spiral joint of the inner tube, or so that some of them come at least partly to the point of the spiral joint of the outer tube.
The inner tube 2 can be formed at the same time with the production of the tube 1 or in a separate process. So the inner tube is formed or is arranged upon the support equipment when producing the tube 1.
It is worth noticing that even though this description sticks to only one type of for the disclosed embodiments favourable realization example this does not want to limit the usage of the disclosed embodiments for only this type of example but many variations are possible in the scope of the inventive idea that is defined in the claims.
Number | Date | Country | Kind |
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20150128 | Apr 2015 | FI | national |
Filing Document | Filing Date | Country | Kind |
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PCT/FI2016/000009 | 4/15/2016 | WO | 00 |