SLEEVE AND METHOD FOR MANUFACTURING THE SAME

Abstract

The invention relates to a sealing sleeve (112) for a prestressing cable anchor of a construction work, the sleeve comprising a first part (114) formed from a first polymer having a melting temperature of between 120 and 140°C; and a second part (113) formed from a second polymer having a tensile strength of between 25 and 40 MPa. The invention also relates to the method of manufacturing the sleeve comprising: placing, in a mold, an extruded high-density polyethylene insert; and hot-injecting a polymer resin into the mold. Abstract Figure: Figure 2A

Description

Title of the invention: SLEEVE AND METHOD FOR MANUFACTURING SAME Technical field

[0001] The present disclosure relates to the field of civil engineering works and in particular to sealing elements for an external prestressing cable. Prior art

[0002] Prestressing cables are generally made up of a plurality (or a bundle) of parallel reinforcements (strands) which are anchored at two points of a structure. In the vicinity of the anchoring, the reinforcements are arranged in a form of expansion, of an anchoring part, called "tromplaque", on which is supported a block allowing the individual anchoring of each reinforcement (strand).

[0003] The bundle of reinforcements of the prestressing cable is generally provided with a collective sheathing sleeve which allows the injection of a protective filler product for the reinforcements, cement grout or flexible material such as wax or grease. The sheathing sleeve equipping the external prestressing cables is most often made of high-density polyethylene (HDPE) tubes. The running part of the sheathing sleeve is connected to a flared tubular shape called a "trumpet", matching the inner surface of the trumpet and allowing a watertight connection between the sheathing sleeve and the inner chamber of the anchor. The trumpet is generally manufactured by injection molding of a polymer whose properties allow it to guarantee its mechanical strength at the trumpet. This polymer material is generally less flexible and more resistant than the HDPE constituting the running part of the sheathing sleeve.

[0004] It is essential to ensure a tight seal at the connection joint between the trumpet and the running part of the sheath. However, welding these elements of distinct materials is not easy. The good seal of the joint can then be established or completed by means of a heat-shrinkable joint cover. When injecting the filling product (cement grout or flexible product) into the sheath around the cable reinforcements, this connection joint can be caused to crack, thus posing the double problem of leaks during filling of the filling product and increased exposure to corrosion. Alternatives exist using special machines dedicated to the welding of distinct materials, but these machines are complex to implement on a construction site. Summary

[0005] The present disclosure improves the situation.

[0006] A one-piece sealing sleeve for a prestressing cable anchor of a construction work is provided, the sleeve comprising: a first part formed from a first polymer having a melting temperature of between 120 and 140°C; and a second part formed from a second polymer, different from the first polymer, and having a tensile strength of between 25 and 40 MPa. Optionally, the first polymer has a melting temperature of between 125°C and 135°C. Optionally, the second polymer has a tensile strength of between 28 and 32 MPa.

[0007] The sleeve thus produced therefore comprises a first part which is suitable for a junction (welding by thermofusion) with the current part of the sheath of the cable, and a part which guarantees the mechanical strength of the sleeve in the anchoring part. The sealing of the connection between the trumpet and the current part of the sheath is therefore guaranteed, allowing on the one hand an injection of the filling product without leakage, and on the other hand increased protection against corrosion, and therefore an increase in the service life of the reinforcements and the anchoring of the cable. The initial composition of the first and second polymers may be similar but their properties, once the sleeve is formed, are different.

[0008] According to another aspect, the first polymer is a high density polyethylene.

[0009] According to another aspect, the second polymer is a high density polyethylene. The second polymer may have a melt flow index high enough to make this material injectable. Conversely, the first polymer may not be injectable.

[0010] According to another aspect, the second part is flared.

[0011] According to another aspect, the second part has a first thickness at a end of the sleeve opposite the first part, and a second thickness in the vicinity of the first part, the second thickness being greater, preferably at least twice as great as the first thickness.

[0012] According to another aspect, at a connecting interface between the first part and the second part, the first and second parts have annular or helical grooves engaged in each other. The grooves of the first part are of complementary shape to the grooves of the second part. These grooves make it possible to improve the mechanical connection between the two parts of the sleeve.

[0013] The invention also relates to a method of manufacturing a sealing sleeve for a prestressing cable anchor of a construction work, the method comprising: placing, in a mold, an insert of a first polymer having a melting temperature of between 120 and 140°C; and hot injecting a polymer resin into the mold to form a second part of the sleeve formed of a second polymer having a tensile strength of between 25 and 40 MPa. Optionally, the first polymer has a melting temperature between 125°C and 135°C. Optionally, the second polymer has a tensile strength between 28 and 32 MPa.

[0014] This manufacturing process therefore incorporates an overmolding step which makes it possible to establish a connection between an injected part and the insert. The connection can be chemical and / or mechanical.

[0015] The insert also improves the mechanical strength and stiffness (in circumferential tension) of the sleeve when the cable reinforcements are tensioned and the filler is injected. The sleeve also has better resistance to hydraulic pressure.

[0016] According to another aspect, the polymer resin is a UV-stabilized high-density polyethylene resin with a density of between 0.950 g / cm3 and 1.000 g / cm3. Preferably, the density is greater than 0.960 g / cm3, such as for example 0.962, 0.963, or 0.964 g / cm3. A material of the KT 10000 type from the company Dow™ may be chosen.

[0017] This type of material is particularly mechanically robust and is therefore suitable for the cable anchoring area. In particular, it offers good resistance to punching in one end of the trumplate where the reinforcements converge into a compact bundle by exerting strong radial pressure. It is also suitable for establishing a connection during injection-molding with an HDPE insert.

[0018] According to another aspect, before injection, the mold and the insert arranged in the mold are heated to a temperature between 80°C and 110°C, preferably a temperature between 90°C and 100°C. This temperature allows good flow of the injected material, without damaging the structure of the insert.

[0019] According to another aspect, the polymer resin is injected into the mold while it is at a temperature between 140°C and 200°C. This temperature range allows good fluidity of the resin and allows superficial and local melting of the insert to create a fusion bond (physicochemical) between the two parts of the sleeve.

[0020] According to another aspect, before placing the insert in the mold, engravings are formed on an external surface of the insert. The patterns engraved in the insert may be annular or helical grooves. These engravings make it possible to create mechanical connections (such as those of a thread) at the interface between the injected part and the insert which improve the axial tensile strength of the assembly.

[0021] According to another aspect, the outer surface has annular or helical grooves. Thus, when the resin is injected, it will form a complementary shape with grooves inter-engaged in those of the insert.

[0022] According to another aspect, the outer surface is generally frustoconical of half- apex angle between 2% and 5%. This shape allows one thin end of the insert to melt on contact with the hot resin, while another, thicker end of the insert only melts superficially. This provides a good compromise between the mechanical strength of the insert and welding of the insert to the injected resin.

[0023] According to another aspect, the insert has a first thickness at an end opposite the second part, and a second thickness at an end arranged inside the mold and intended to be in contact with the polymer resin forming the second part, the first thickness being greater, preferably at least twice as great as the second thickness.

[0024] According to another aspect, the insert has a shape of revolution and in particular a cylindrical tube, preferably extruded. The insert can for example be obtained by cutting a segment of sheath. The insert advantageously has a variation in wall thickness, in particular a frustoconical shape, the thickness of its wall being minimal at its end placed inside the mold, maximal at its end placed outside or at the end of the mold. The insert has an excess length outside the mold, at its end intended for welding with the cable sheath. Alternatively, the insert is placed entirely in the mold and its end coincides with that of the injected part.

[0025] According to another aspect, during injection, the injected resin bonds by surface fusion on the external surface and on the end of minimum thickness of the insert. Thus, the external diameter of the mold in a part intended to receive the injected material is greater than or equal to the external diameter of the insert.

[0026] According to another aspect, during injection, the injected resin bonds to the insert over at least 60% of the length of the insert.

[0027] The invention also relates to a sealing sleeve as described previously and obtained by the method described above.

[0028] The invention also relates to a method of installing the sleeve, the method comprising thermofusion welding the first part of the sleeve to a running part of the sheath of a cable, the first part and the running part of the sheath being made of the same material. After securing the sleeve to the running part of the sheath, the installation can follow its usual course, in particular with the installation of a complete collective sheath for the reinforcements and the injection of a filling material into this sheath, around the reinforcements. Brief description of the drawings

[0029] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0030] [Fig.l] illustrates an anchoring zone with a classic trumpet.

[0031] [Fig.2A] shows an anchoring area with a trumpet according to the present disclosure.

[0032] [Fig.2B] shows an example of a sleeve.

[0033] [Fig.2C] shows an example of an insert.

[0034] [Fig.3] describes a manufacturing process. Description of the embodiments

[0035] [Fig.l] shows an anchoring zone 1 of a cable 2 at an anchoring point 4. The cable 2 may be composed of a plurality of reinforcements or strands (not shown), for example 19 strands of 7 wires. Each strand may be individually sheathed and each strand is individually anchored to the anchoring point 4 by known techniques (for example, jaws with conical keys).

[0036] The cable 2 has an envelope sheath 6 which may be made of high-density polyethylene (HDPE) and which contains the reinforcements as well as a possible filling product. A passage tube 8 (for example made of galvanized steel) is generally provided in the reinforced concrete formwork of each anchoring zone, as well as for the cable deviation zones.

[0037] In the vicinity of the anchoring point 4, the strands are spaced radially from each other (with spreading). Their protection is - in part - guaranteed by a flared sleeve made of polymer material, called a "trumpet" 12, matching the flared inner surface of the steel anchoring part, called a "tromplaque" 14, supporting the anchoring of the cable reinforcements.

[0038] The connection zone 16 between the sheath 6 of the cable 2 and the trumpet 12 may be the site of water / moisture infiltration or leaks of filling material during injection. The material of the trumpet 12 is not always compatible with the HDPE of the sheath 6 from the point of view of heat welding. The sealing of the connection joint can be completed by the addition of a heat-shrinkable joint cover sleeve. However, this design has limited reliability.

[0039] [Fig.2A] shows the same installation with a sleeve (a trumpet) 112 according to the present disclosure. This sleeve 112 may be of the same dimension, or axially longer, than the trumpet 12.

[0040] [Fig.2A] shows a junction 116 by heat welding between the sleeve 112 and the sheath 6.

[0041] As illustrated in [Fig.2B], the sleeve 112 is composed of a first portion 114 and a second portion 113. The second portion 113 may be made of injected polymer. A thin portion 113.1 may be flared and a thicker portion 113.2 may be substantially rectilinear / cylindrical. The thicker portion thick 113.2 (thickness E2) may be at least twice or at least three times thicker than the portion 113.1 (thickness e2). The second part 113 may comprise a flange (not shown) for its fixing in the trumpet 14 or in the anchor 4. The first part 114 may be made of HDPE material identical (or at least compatible from a heat-sealing point of view) to that of the envelope sheath 6. The first part 114 is formed by a molding insert (denoted 114' in [Fig.2C]). In the present disclosure, the expression "first part" referenced by 114 designates the part of the sleeve 112 which results from the use of the "insert", referenced by 114'. A bonding interface 115 covering substantially the entire length of the insert placed in the mold may be the location of the physicochemical and mechanical bond which is created during the overmolding of the part 113 on the external surface 114.1' of the insert 114'.

[0042] At the connection interface 115, the variable external diameter of the first part 114 is always less than that of the second part 113.

[0043] The insert 114' may be tubular and cylindrical. Advantageously, it has a frustoconical external surface, the thickness (denoted el in [Fig.2C]) of its wall being minimal at its end placed inside the mold, maximal (thickness denoted El in [Fig.2C]) at its end placed outside or at the end of the mold (see figures 2A, 2B, 2C). It may have an end 114.2' of minimum thickness el which is intended to promote the melting of the first polymer in contact with the resin during injection and another end 114.3' of thickness El, opposite the first end 114.2', and intended to be heat-sealed to the envelope sheath 6 in a zone 116. The outer surface 114.1' may be engraved with patterns, before the insert is placed in the mold, to promote a mechanical connection between the insert and the injected / molded part. For example, annular grooves 114.4' or helical grooves may be considered.These aspects of the insert 114' are found on the first part 114 of the sleeve 112: an outer surface 114.1, two ends 114.2, 114.3 and grooves 114.4.

[0044] The axial length L of the insert 114' which can be between 50 and 200 mm, preferably between 80 and 150 mm, can be 4 to 6 times less than the axial length of the injected part 113. The internal diameter of the insert 114' can be between 70 and 170 mm, preferably between 90 and 130 mm. The external diameter can be between 75 and 180 mm, preferably between 95 and 140 mm.

[0045] The length 1 of the interface 115 may be greater than 60%, preferably greater than 80% of L. The portion of the first part 114 which projects from the second part 113 may correspond to a portion of the insert 114' held outside the mold. In a variant not shown, 1=L: the end 114.3 is flush with the end of the second part 113.

[0046] [Fig.2C] also highlights the half-angle at the apex a which characterizes the slope of the truncated portion 115' (or the average slope in the case of the presence of grooves) intended to form the interface 115 with the second part. The angle a can be between 2% and 5%, and can preferably be approximately 3.5% (radians). The minimum thickness el can be 2 to 3 times smaller than the thickness EL

[0047] [Fig. 3] summarizes the steps of the manufacturing method 1000. During a first step 100, the insert 114' is prepared. This may consist of cutting a segment of HDPE sheath. This may also consist of giving a truncated shape and engraving the outer surface of the insert 114', by machining (turning).

[0048] The insert 114' is then arranged 200 in the injection mold. The mold can be arranged with a longitudinal axis arranged horizontally or vertically. In the latter case, the insert 114' is arranged at the lower end of the mold. The insert 114' can be completely received in the mold. In a variant, a portion of the insert (on the side of the end 114.3') can protrude from the mold. The internal surface of the insert can be pressed against a convex surface of the mold or a core. A space intended for the resin remains between the mold and the external surface 114.1' of the insert 114'.

[0049] The mold, closed, and the insert 114' are then raised in temperature during step 300. The preheating temperature can reach between 80°C and 110°C.

[0050] The next step 400 is the injection of resin into the mold, at a temperature between 140°C and 200°C.

[0051] The resin may be a UV-stabilized high-density polyethylene resin with a density greater than 0.960 g / cm3 (preferably a density of 0.964 g / cm3), in particular with a very narrow molecular weight distribution. A material of the KT 10000 type from Dow™ may be chosen.

[0052] The resin may have a melt flow rate (MFR) at 190°C of 8.0 g / 10 min for 2.16 kg and 22 g / 10 min for 5.0 kg. Once injected and cooled, the resin may have one or more of the following properties: tensile strength of 29 MPa; ultimate strength of 32 MPa; Shore D hardness 66.

[0053] The whole thing is then demolded, installed in the trumplate at the anchorage, then heat-welded to the cable sheath. Alternatively, it is possible to heat-weld a first segment of sheath before installation in the trumplate. The reinforcements are threaded individually or in groups into the sheath, then covering the entire length of the cable between anchors. The anchoring devices are then installed before tensioning the reinforcements by means of one or more hydraulic jacks. The injection of a filling product into the space between the sheath and the reinforcements takes place after or before tensioning, taking into account the technology used. List of reference numbers

[0054] 1: Anchoring zone 2: cable 4: anchor point or block 6: envelope sheath 8: reservation tube / formwork 10: filling material 12: sleeve (trumpet) 14: trumple 16: zone of weakness at the sheath-trumpet connection joint 112: sleeve (trumpet) 113: second part, in injected resin 113.1: first portion of the second part 113.2: second, thicker portion of the second part 114: first part of the sleeve 114.1: outer surface of the first part 114.2: end of the first part in abutment with the second part 114.3: end of the first part intended for connection with the envelope sheath 6 114.4: annular or helical grooves or engravings 114': extruded HDPE insert 114.1': outer surface of the insert intended for bonding with the hot resin 114.2', 114.3': ends of the insert 114.4': annular or helical grooves or engravings 115: connecting interface between the first and second part of the sleeve 115': area of ​​the insert 114' intended to be positioned in the mold 116: joint connection between sleeve / trumpet and the envelope sheath.

Claims

Claims

1. One-piece sealing sleeve (112) for a prestressing cable anchor of a construction work, the sleeve comprising: - a first part (114) formed from a first polymer having a melting temperature of between 120 and 140°C; and - a second part (113) formed from a second polymer, different from the first polymer, and having a tensile strength of between 25 and 40 MPa.

2. The sleeve of claim 1, wherein the first polymer is a high density polyethylene.

3. A sleeve according to claim 1 or 2, wherein the second polymer is a high density polyethylene.

4. Sleeve according to one of claims 1 to 3, in which the second part (113) is flared.

5. Sleeve according to one of claims 1 to 4, in which the second part (113) has a first thickness (e2) at one end (113.1) of the sleeve (112) opposite the first part (114), and a second thickness (E2) in the vicinity of the first part (114), the second thickness being greater, preferably at least twice as great as the first thickness (e2).

6. Sleeve according to one of claims 1 to 5, wherein at a connecting interface (115) between the first part (114) and the second part (113), the first and second parts (113, 114) have annular (114.4) or helical grooves engaged in each other.

7. Method (1000) for manufacturing a sealing sleeve (112) for an anchor (1) of a prestressing cable (2) of a construction work, the method comprising: a. placing (200), in a mold, an insert (114') of a first polymer having a melting temperature of between 120 and 140°C; and b. injecting (400) a polymer resin hot into the mold to form a second part of the sleeve formed of a second polymer having a tensile strength of between 25 and 40 MPa.

8. The method (1000) of claim 7, wherein the polymer resin is a UV stabilized high density polyethylene resin with a density of between 0.950 g / cm3 and 1.000 g / cm3.

9. Method (1000) according to one of claims 7 or 8, in which before injection, the mold and the insert arranged in the mold are heated (300) to a temperature between 80°C and 110°C, preferably a temperature between 90°C and 100°C.

10. A method according to any one of claims 7 to 9, wherein the polymer resin is injected into the mold while it is at a temperature of between 140°C and 200°C.

11. Method (1000) according to one of claims 7 to 10, in which, before placing (200) the insert (114') in the mold, the formation (100) of engravings (114.4') is carried out on an external surface (114.1') of the insert (114').

12. The method of claim 11, wherein the insert (114') has an outer surface (114.1') having annular (114.4') or helical grooves.

13. Method according to claim 11 or 12, in which the insert (114') has a substantially frustoconical outer surface (114.1') with a half-angle at the apex of between 2% and 5%.

14. Method according to claim 11 to 13, in which the insert (114') has a first thickness (El) at one end (114.3') opposite the second part (113), and a second thickness (el) at one end (114.2') arranged inside the mold and intended to be in contact with the polymer resin forming the second part (113), the first thickness (El) being greater, preferably at least twice as great as the second thickness (el).

15. Method (1000) according to one of claims 7 to 14, in which the insert (114') has a shape of revolution and in particular a cylindrical tube, preferably extruded.

16. Method (1000) according to one of claims 7 to 15, in which during injection, the injected resin bonds to the insert (114') over at least 60% of the length of the insert (114').

17. Sealing sleeve (112) according to one of claims 1 to 6 obtained by the method according to one of claims 7 to 16.

18. Method of installing the sleeve according to one of claims 1 to 6 or 17, the method comprising thermofusion welding the first part (114) of the sleeve to a running part of the sheath (6) of a cable (2), the first part (114) and the running part of the sheath (6) being made of the same material.

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