PIPE COUPLING, PARTICULARLY FOR PLASTIC HOSES

Abstract: A pipe coupling, particularly for plastic hoses, comprises a sleeve-shaped inner portion (11), which is intended to enter into the end of the pipe (10) to be coupled in order to support the pipe wall (12) on the inside of the pipe, and a sleeve-shaped outer portion (13), which is adapted to surround the pipe end on the outside of the pipe to force the pipe wall (12) towards the inner portion (11), so that the pipe end is clamped between the inner portion (11) and the outer portion (13) of the coupling. The external surface of the inner portion (11) and the internal surface of the outer portion (13) are provided with a plurality of ring-shaped ridges (21, 22), which run around the portions (11, 13) and have a substantially triangular cross section. The ridges (21) of the inner portion (11) are displaced axially in relation to the ridges (22) of the outer portion (13), and the ridges (21, 22) are provided to penetrate only partly into the pipe wall (12), so that a space (m) is formed between the pipe wall (12) and the inner portion (11) and the outer portion (13), respectively, between the ridges (21, 22). Thus, the thermal expansion of the pipe material can occur substantially radially, so that the risk of leakage due to the deformation of the material is eliminated.

Description: Pipe coupling-, particularly for plastic hoses Technical Field The present invention relates to a pipe coupling com¬ prising -a sleeve-shaped inner portion, which is intended to enter into the end of the pipe to be coupled in order to support the pipe wall on the inside of the pipe, and a sleeve-shaped outer portion, which is adapted to surround the pipe end on the outside of the pipe to force the pipe wall towards the inner portion, so that the pipe end is clamped between the inner portion and the outer portion of the coupling. Both the external surface of the sleeve- shaped inner portion and the internal surface of the sleeve-shaped outer portion are provided with a plurality of ring-shaped ridges running around the sleeve—shaped por¬ tions and having a substantially triangular cross section. The ridges of the inner portion are displaced axially in relation to the ridges of the outer portion, so that ' the ridges of the inner portion are positioned substantially half-way between the ridges of the outer portion. The pipe .coupling is particularly intended for connecting plastic hoses to metal tubes and for joining plastic hoses, but it can also be used for connecting tubes of other elastic materials than plastics. Background Art It is previously known to use pipe couplings compris- ing an inner portion and an outer portion between which the end of the pipe to be coupled is clamped, the one or the other portion being provided with ring-shaped ridges adap¬ ted to abut against and possibly penetrate into the pipe wall. It is also previously known, for example through DE Auslegeschrift 1 167 609 and US Patent Specification 3 017 203, to provide ring-shaped ridges on the inner por¬ tion as well as on the outer portion, the ridges of the inner portion being displaced axially in relation to the ridges of the outer portion, so that the ridges of the inner portion are positioned substantially half-way between the ridges of the outer portion. The ridges are in these cases adapted to penetrate completely into the pipe wall. However, when such couplings are used to connect plastic hoses, for example in a system for distribution of supply water in buildings, there is a substantial risk of leakage in the couplings, because the plastic materials normally used in the pipes have a comparatively large thermal expan¬ sion. When the couplings and pipes are exposed to heat cyc- les due to temperature changes in the medium stationary in or flowing through the pipes, permanent deformations of the material in the pipe walls adjacent the ridges will occur, and these deformations will sooner or later cause leakage. Disclosure of Invention The main object of the inventionm is to provide a pipe coupling that eliminates or at least substantially reduces the risk of leakage. This object is achieved by giving the pipe coupling the features set forth in the claims. Due to the fact that both the inner portion and the outer portion are provided with a plurality of ring-shaped ridges having a substantially triangular cross section, the ridges of the Inner portion being displaced axially in relation to the ridges of the outer portion, so that the ridges of the inner portion are positioned substantially half-way between the ridges of the outer portion, a reliab¬ le clamping of the pipe end is achieved at the same time as possible material movements in the pipe wall do not occur in an axial direction but substantially in a radial direc¬ tion without deforming the material in such a way that a risk of lekage occurs. Furthermore, by providing the ridges in such a way that they only partly penetrate into the pipe wall, thus providing a space between the pipe wall and the inner portion and the outer portion, respectively, between the ridges, the expansion of the pipe material during an increase of the temperature easily can be taken up in the coupling without causing any permanent deformation of the material, thus eliminating the risk of leakage. Brief Description of Drawings The invention will now be further described below with reference to the accompanying drawings. Fig. 1 is a side view, partly in section, of a pipe coupling according to one embodiment of the invention. Fig. 2 is an enlarged view of a portion of the pipe coupling according to Fig. 1. Best Mode for Carrying Out the Invention The pipe coupling shown in Fig. 1 is intended for con- necting a plastic hose 10, for example of cross-linked polyethylene, to a metal tube (not shown). The coupling comprises a sleeve-shaped inner portion 11, which is inten¬ ded to enter into the end of the hose 10 to support the hose wall 12 on the inside of the hose, and a sleeveshaped outer portion 13, which is adapted to surround the end of the hose on the outside of the hose to force the hose wall 12 towards the inner portion 11. The outer portion 13 con¬ sists of two halves 13A.13B which are connected for example by means of a double clamp ring 14,15 that is contracted by means of a bolt 16 and a nut 17, as shown in Fig. 1. The inner portion 11 is provided with a radially pro¬ jecting flange 18 adapted to penetrate into a groove 19 in the outer portion 13, sα that the outer portion is locked in relation to the inner portion 11. The flange 18 is pro- vided with an axially projecting sleeve 20 intended to be connected to the metal tube. The coupling portions 11 and 13 are preferably made of a metal enabling the metal tube to be solded or welded to the sleeve 20 of the inner por¬ tion. The outer surface of the inner portion 11 is provided with ring-shaped ridges 21, and the inner surface of the outer portion 13 is provided with ring-shaped ridges 22, as more clearly shown in Fig. 2. The ridges 21 run around the inner portion 11 in parallel planes which are perpendi- cular to the longitudinal direction of the inner portion. The ridges 22 run around the outer portion 13 in planes which are perpendicular to the longitudinal direction of the outer portion and also are parallel. The distance bet¬ ween the ridges 21 is the same as the distance between the ridges 22, but the ridges 21 and 22 are axially displaced in relation to each other, so that the ridges 21 are posi- tioned in the middle of the spaces between the ridges 22. The ridges 21 on the coupling portion 11 are provided at such a distance that the connection lines from two adjacent ridges 21 to the opposite ridge 22 on the other coupling portion 13 form an angle of 10-30°, preferably substantial- ly 20°. The ridges 21 and 22 have a cross section in the shape of a regular triangle, and the ridges consequently have an apex angle of 60°. The ridges are adapted to penet¬ rate only partly, for example half-way, into the hose wall 12, when the coupling is contracted by means of the clamp ring 15, so that a space always exists between the hose wall 12 and the inner portion 11 and the outer portion 13, respectively, between the ridges, as shown in Fig. 2. The disclosed coupling operates in the following way. When the coupling is applied, the ridges only partly penet- rate into the hose wall, so that a space exists between the hose wall and the coupling portions on the outside of the hose wall as well as on the inside of the hose wall. When the temperature increases, the material of the hose wall will expand. However, this expansion will occur into the existing spaces between the hose wall and the inner portion and the outer portion,- respectively. During this expansion the material slides on the side surfaces of the ridges which due to their shape do not cause any permanent defor¬ mation of the material. Due to the fact that the ridges on the inner portion and the outer portion are axially displa¬ ced in relation to each other, the material opposite to a ridge on one coupling portion always can expand towards the space between the hose wall and the other coupling portion. Due to the fact that the ridges on one coupling portion are situated opposite the spaces between the ridges on the other portion, the tensions in the hose material during temperature changes are reduced to a miniumum. This elimi- nates or at least to a very large extent reduces the risk of leakage. This provides an optimal design and positioning of the ridges, because each ring-shaped section is deformed individually due to the fact that the forces between the ring-shaped sections eliminate each other. An apex angle of 40-90°, for example 60°, of the ridges is particularly pre¬ ferable. The disclosed pipe coupling is based upon the main idea that the tightness during temperature changes shall be secured by confining the pipe material between the inner portion and the outer portion of the coupling in such a way that all axial expansion of the pipe material is prevented and that the radial expansion is controlled by the sector- shaped elements formed by the imagined connection lines between the ridges on the inner portion and the ridges on the outer portion, so that the expansion occurs alternately towards the outer portion and towards the inner portion. The sector-shaped elements act as wedges to provide the described result. Due to the cooperation of the wedge- action of the material inwards and the elastic and thermal properties of the material a certain pressure is always exerted on the inside ridges providing a permanent tight¬ ness during temperature changes without the use of any elastic sealing element, as for example of 0-ring type. While only one embodiment of the pipe coupling accord¬ ing to the invention has been described and shown, it is evident that many modifications and variations are possible within the scope of the invention. For example, the ridges on the inner portion do not have to be positioned exactly in the middle between the ridges on the outer portion, and the ridges can have an other apex angle than 60°. Further¬ more, the axially projecting sleeve on the inner portion can be replaced by an inner portion and an outer portion having the described shape, thus making the coupling usable for interconnecting two plastic hoses. Nor is the radially projecting flange on the inner portion absolutely necessa¬ ry, as the outer portion can be locked in relation to the inner portion in an other way. The mentioned angle of 20° can be varied between 10 and 30°. When the angle is increa¬ sed, the grip will be reduced, so that the coupling even¬ tually will become weaker than the pipe. When the angle is decreased, the distance between the ridges will become so small that the carrying capacity of the crests of the rid¬ ges will become too high, because the number of ridges will become so large. This will increase the necessary tighte¬ ning force ^

Claims: Claims 1. A pipe coupling, particularly for plastic hoses, com¬ prising a sleeve-shaped inner portion (11), which is inten¬ ded to enter into the end of the pipe (10) to be coupled in order to support the pipe wall (12) on the inside of the pipe, and a sleeve-shaped outer portion (13), which is adapted to surround the pipe end on the outside of the pipe to force the pipe wall (12) towards the inner portion (11), so that the pipe end is clamped between the inner portion (11) and the outer portion (13) of the coupling, both the external surface of the sleeve-shaped inner portion (11) and the internal surface of the sleeve-shaped outer portion (13) being provided with a plurality of ring-shaped ridges (21,22), which run around the sleeve-shaped portions and have a substantially triangular cross section, and the rid- ges (21) of the inner portion (11) being displaced axially in relation to the ridges (22) of the outer portion (13), so that the ridges (21) of the inner portion (11) are posi- • tioned substantially half-way between the ridges (22) of the outer portion, characterized in that the ridges (21,22) are provided to penetrate only partly into the pipe wall (12), so that a space (m) is formed between the pipe wall (12) and the inner portion (11) and the outer portion (13), respectively, between the ridges (21,22). 2. A pipe coupling according to claim 1, characterized in that the ridges (21) on one coupling portion (11) are pro¬ vided at such a distance that the connection lines from two adjacent ridges (21) to the opposite ridge (22) on the other coupling portion (13) form an angle of 10-30°. 3. A pipe coupling according to claim 2, characteized in that the angle is substantially 20°. 4. A pipe coupling according to any of the preceding claims, characterized in that the inner portion (11) at its outer end is provided with a radially projecting flange (18) intended to enter into a groove (19) on the inner side of the outer portion (13), so that the outer portion (13) is undisplaceably connected to the inner portion (11).

Inventors: SKAORUD BENGT OLOF ROLAND, SKAORUD, BENGT, OLOF, ROLAND
Applicants: WIRSBO BRUKS AB, WIRSBO BRUKS AKTIEBOLAG
Application year: 1985
Main classification: F16L33
IPC codes: F16L33