Abstract:
A device for permanent joining of plastic tubes intended for use as covering or lining tubes when drilling holes in the ground including a female portion on a first tube and a male portion interacting therewith on a second tube. The male portion being provided with annular projections and recesses round its outer circumference and the female portion being provided with annular projections and recesses round its inner circumference with the recesses and projections on one tube interengaging with the projections and recesses on the other tube in such a fashion that at least one of the tubes is radially deformed and the joint can withstand axial and torsional forces.

Description:
TECHNICAL FIELD 
     The present invention relates to a device for permanent joining of tubes made of a flexible material, such as polyethylene, and specially intended for use as covering or lining tubes when drilling holes in the ground, particularly soil or moraine, which device includes a female portion on a first tube and a male portion interacting therewith on a second tube, the male portion being provided with an annular projection round its outer circumference, which under radial deformation thereof and/or of an annular projection on the inner circumference of the female portion is arranged to pass this and to be inserted in an annular recess on the inner circumference of the female portion. 
     PRIOR ART 
     Devices of the above described kind are previously known but are used for joining of waste pipes. An example of such a device is shown in GB 2 166 826A. 
     The main disadvantage of said device is that the joined pipes may be turned relative to each other thereby causing leakage. Another disadvantage is that a relatively low force is required to unintentionally break the joint and a relatively high force is required to provide it. 
     Devices for joining tubes, together forming a cover or a lining, which are driven into the ground during or after making of a hole therein are previously known from, for example, SE 9200563-6. 
     The main disadvantage of the last-mentioned device is that special joining elements of metal have to be attached to each tube end, making the product more expensive, and that the joining elements are threaded, requiring turning of at least one of the tubes during the joining process. 
     DESCRIPTION OF THE INVENTION 
     It is an object of the present invention to eliminate, at least partly, the above stated disadvantages of previously known devices and to provide a device which is uncomplicated, reliable and strong. 
     This object is achieved in that the device according to the invention presents the features stated in the characterizing portions of the claims. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 is a longitudinal sectional view showing part tube provided with a female portion forming part of the device according to the invention, 
     FIG. 2 is a longitudinal sectional view showing part of a second tube provided with a male portion forming part of the device according to the invention, and 
     FIG. 3 is a longitudinal sectional view showing the male and female portions of FIGS. 1 and 2 joined together. 
    
    
     PREFERRED EMBODIMENT 
     In FIGS. 1 and 2 there is depicted part of a first tube 1 of circular cross section, and part of a second tube 2 of circular cross section, which in FIG. 3 are shown joined together. The tubes are made of plastic material, suitably PEH (high-density polyethylene) which is flexible, at least in the radial direction. 
     The tube 1 is provided with a female portion 3, which on the inside is provided with 12 radially inwardly directed, annular projections 4a-1, which are equally spaced in the axial direction and which delimit annular recesses 5a-1 therebetween. The projections 4 and the recesses 5 in cross section together form a saw-tooth pattern having essentially axially oriented surfaces forming an angle α of 5°-15°, preferably around 10° with the longitudinal axis of the tube 1, and having essentially radially oriented surfaces forming an angle β of 5°-15°, preferably around 10°, with an axis perpendicular to the longitudinal axis. The distance between two adjacent projections 4 is around 5 mm and the thickness of material in this area is about equal. The tube 1 has an outer diameter of around 100-300 mm, a thickness of material of around 8-10 mm, and a length of around 3 m. 
     The projection 41, which is nearest to the right-hand tube end, merges on the right into a conical, outwardly tapering portion 6 which is terminated by an end portion 7 of uniform thickness. The recess 5a farthest away from the right-hand tube end merges on the left into a conical, inwardly thickened portion 8, which merges into a groove 9, which merges into the tube 1 itself. 
     The tube 2 is provided with a male portion 10 provided on its exterior with 12 radially outwardly directed, annular projections 11a-1 which are equally spaced in the axial direction and which delimit annular recesses 12a-1 therebetween. The projections 11 and the recesses 12 in cross section form a saw-tooth pattern of the same dimensions as the saw-tooth pattern formed by the projections 4 and the recesses 5. The tube 2 is of the same dimensions as the tube 1, however, their female and male portions 3, 10 differ in the following respects. The outer diameter of the female portion 3 is equal to the outer diameter of the tubes 1, 2, and the inner diameter of the male portion 10 is equal to the inner diameter of the tubes 1, 2, but the maximum diameter of the projections 11 is larger than the maximum diameter of the recesses 5, and the minimum diameter of the recesses 12 is larger than the minimum diameter of the projections 4. The differences in diameter are around 4-5 mm. The outer diameters of the projections 11 of the male portion 10 is somewhat smaller than the inner diameter of the end portion 7. 
     The projection 11a, which is nearest to the left-hand tube end of FIG. 2, merges on the left into a conical tapered end portion 13. The recess 11l, which is located farthest away from the left-hand tube end, merges on the right into a conical, outwardly thickened portion 14, which merges into a groove 15, which merges into the tube 2 itself. 
     When making the joint, the male portion 10 is inserted in the female portion 3 or the female portion 3 is pushed onto the male portion 10, the portions 6 and 7 acting as guide means for the portion 13. When the projection 11a has contacted the portion 6 and is increased thereagainst, the diameter of the female portion 3 is increased and the diameter of the male portion 10 is reduced depending on the flexibility/elasticity of the material. On continued compression, the projection 11a will snap over the projection 41 and is inserted in the recess 51, the diameter of the female portion 3 being somewhat reduced and the diameter of the male portion 10 somewhat increased. However, the diameter of the female portion 3 will still be larger and the diameter of the male portion 10 smaller than is the case when the tubes 1 and 2 are separated. 
     On continued compression of the female and male portions 3 and 10, the projections 11 will snap over the projections 4 in the way described above in connection with the projections 11a and 41 until a shoulder 17 on the female portion prevents further movement of the portion 13 and a shoulder 17 on the male portion 10 prevents further movement of the portion 7. 
     Before the female and male portions 3 and 10 were brought together to form the joint, sealing rings, such as the O-rings 18 and 19 of FIG. 3, were inserted into the grooves 9 and 15. In the final stage of the compressive movement of the female and male portions 3 and 10, the O-rings were compressed to seal the joint at two points. 
     In FIG. 3 there is shown the tubes 1, 2 joined in the above described way. It is seem from the figure that the female and male portions 3 and 10 are thickened relative to the walls of the tubes 1, 2 connecting on to the portions 3 and 10. The total wall thickness of the female and male portions 3 and 10 is typically around 10-12 mm. The wall thickness is between 1.1 and 1.4, preferably around 1.25×the wall thickness of the tube 1 or 2. The reason for this thickening is that, as previously mentioned, the female and male portions 3 and 10 are continuously pressed towards each other in the radial direction so that an essentially torsion resistant joint is provided while the resistance of the joint against axial tension is increased. 
     The joint is permanent and cannot be loosened other than by destroying the female and/or male portions 3, 10. The essentially radially oriented surfaces of the projections 4, 11 abut against each other thereby preventing axial play between the female and male portions 3, 10. The relatively large number of projections effectively prevents the tubes 1 and 2 from being separated. To separate the tubes 1 and 2, when the projections will be deformed, a force is required which for a tube of an outer diameter of around 140 mm is about 55.000N, which should be compared to the fact that the force required to make the joint is only 1000N. The fairly large number of projections 4, 11 provides a large amount of friction between the female and male projections 3, 10, supplying a large amount of torsion resistance and stiffness. Owing to the fairly large number of projections, the difference between their outer and inner diameters may be made relatively small, implying that the thickness of material of the female and male portions may be made relatively large, which is essential to reduce the risk of wearing down of the walls of the female and male portions. Further, the forces that keep the tubes together at the joint are concentrated to the central portions of the joint, gradually diminishing towards the ends thereof, which reduces tendencies for the joint to open on inclining of the tubes 1 and 2. 
     While only one embodiment of the present invention has been described and shown in the drawings, it will be appreciated that the invention is not limited to said embodiment but only by what is stated in the claims.