The present invention concerns a device and a method of providing a tensile-stress resistant as well as fluid- tight joint between two mutually insertable components, and particularly but not exclusively such components as tubes, bends, jointing sleeves, connecting boxes and similar components of synthetic resins used for electrical installations in buildings.

The inventive idea stems from the problems that are encountered in connection with joining together plastic tubes and boxes used in the installation of electrical wiring in buildings.

One such problem is the risk of disengagement or loosening of the joint before the installation of the electrical wiring, a problem which more often than not is caused by insufficient friction between the components forming the joint.

The disengagement problems are even more serious if they arise in wiring tubing that is already covered by wall slabs or similar covering elements. The problem is further aggravated in connection with tubing systems that are intended to be cast into or that already are cast into concrete and similar materials.

In an attempt to alleviate the problems outlined above the electrician usually applies tape around all joints.

According to one prior-art method of providing a joint possessing improved resistance to tensile stress a metal clip is inserted in the tube having the larger cross-sectional dimensions. The metal clip is designed to mechanically cut into the other tube having the lesser cross-sectional dimensions, to provide improved proper¬ ties of tensile strength.

A serious drawback connected with this method is

that it causes a slit to be formed inside the joint (the tube having the larger cross-sectional dimensions takes on an oval shape) with resulting problems when the details are to be cast into concrete. Because of the slit, water and concrete may leak into the tubing system proper, causing serious problems, such as obturation of the tube with the result that the electrical wires cannot be drawn inside the tube. In addition, in environments where moisture may occur water may seep into the tubing system and cause short- circuiting.

Another problem encountered in connection with this prior-art method is that during the drawing of the electrical wires they may catch in the slit found inside the joint between the components.

The metal clips are difficult to place in position and their installation is work-consuming/reguires a high degree of automatisation. It is not unusual for the clips to become loose before they are put to use, with the result that the intended quality of the joint cannot be obtained.

The purpose of the present invention is to elimi¬ nate the problems and disadvantages outlined in the aforegoing in a simple and efficient manner. in the device for providing a both tensile-stress resistant and fluid-tight joint between two mutually insertable components this purpose is achieved in accord¬ ance with the invention in that at least one of the components is provided on its end facing the other com- ponent with an elastic material adherent to said other component in such a manner that use is made both of the friction between the facing surfaces of the joint and of the sealing properties of the material.

According to the method of providing a joint of this kind the purpose is achieved in that on one of the components on the end thereof facing the second component is applied an elastic material which is adherent

to said second component, so that use is made both of the friction between the facing surfaces of the joint and of the sealing properties of the material.

The invention also concerns the use of the joint according to which at least one of the components is provided on its end facing the other component with an elastic material adherent to said other component and according to which the components involved are tubes, bends, jointing sleeves, connecting boxes and similar components of synthetic resin used to install electrical wiring in buildings.

The invention will be described in closer detail in the following with reference to the accompanying drawings illustrating some preferred embodiments of the joint and a preferred method of providing a joint of this kind. In the drawings,

Fig. 1 illustrates, in longitudinal sectional views, on the right-hand side a part of a socket of a tube, a bend, a connecting box or a similar component and on the left-hand side a part of a tube the end of which is intended for insertion into the socket,

Fig. 2 illustrates the components in accordance with Fig. 1 when fitted together to provide a tensile- stress resistant and fluid-tight joint between the com- ponents,

Fig. 3 and 4 illustrate, also in longitudinal sec¬ tional views, alternative embodiments of the socket in accordance with Figs. 1 and 2,

Fig. 5 illustrates schematically one of several possible methods of providing one of the components, in the shown example the socket, with an elastic mate¬ rial .

On drawing figures 1 and 2, illustrating a first embodiment of the invention, the right-hand part shows a socket 1 forming part of a component 2, such as a tube, a bend, a jointing sleeve, a connecting box or

other similar components of varying nature and dimen¬ sions, preferably made of plastics of the kind intended for use in electrical wiring installations in buildings. The left-hand side of Figs. 1 and 2 shows the end 3 of a component 4, such as a tube or similar element, the end 3 being of smaller cross-sectional dimension or diameter size and arranged for insertion into the socket 1 which has a larger cross-sectional size or diameter. In order to obtain a joint which at the same time possesses tensile-stress resistance and fluid-sealing characteristics an elastic material 6 is applied in accordance with the embodiment illustrated in Figs. 1 and 2 between the two mutually insertable components 2 and 4. In accordance with the embodiment illustrated in Figs. 1 and 2 the elastic material 6 is applied on the component 2 on the end or socket 1 thereof facing the second component 4 for adherence to the end 3 thereof. More precisely, the elastic material 6 is applied on the internal surface of the socket 1 but alternatively it may be applied on the external surface of the tube end 3.

In accordance with the embodiment illustrated in Figs. 1 and 2 the elastic material 6 is applied on the socket 1 by dipping the latter into a bath of liquid or powdery starting material, such as latex. In other words, the elastic material 6 possesses the elastic properties of rubber while at the same time being soft. After the dipping operation, the component is dried and/or vulcanized.

As an alternative, the elastic material may be applied by brushing or by spraying the starting material onto the components. In Fig. 5 is shown one spray-appli¬ cation method. In accordance with this method a nozzle 7 is inserted into the socket 1 and a jet of the elas¬ tic material is thereafter sprayed onto the internal faces of the socket.

Fig. 3 illustrates another embodiment according

to which two annular strands of the elastic material 6 is applied on the internal face of the socket 1 , for instance with the aid of the nozzle illustrated in Fig. 5. Fig. 4 shows yet another embodiment wherein the casting technique known as dual casting is used. Accord¬ ing to this method, a ring 8 of an elastic material 6 is cast directly onto the end of the socket 1 during the very manufacture of the component 2. Also in the case of the embodiments shown in Figs. 1-3 the application of the elastic material 6 could with advantage be performed during or in connection with the manufacture proper of the component to be pro¬ vided with the elastic material. At the time of installa- tion of the component by the electrician no extra work therefore is required but the electrician need only push (press) one component into the other to provide the interconnection.

One of the great advantages of the invention is that owing to the use of an elastic material on either one of the two- components the narrow tolerances normally required in jointing operations of components of the kind concerned no longer are necessary in order to achieve satisfactory friction between the surfaces to be joined together.

In addition, the finished joint' not only possesses a considerably improved tensile-stress resistance com¬ pared with joints using the clip method referred to in the aforegoing but also forms a considerably improved seal against liquids and concrete.

A further possible alternative is to apply the elastic material 6 on either one of the components by applying thereon a suitable powder material or similar product through electrostatic charging followed by heat- ing to melt the material, whereby an elastic surface layer is formed.

Independently of the application method used the

elastic material 6 could have a colour which entirely or partly differs from the colour of the components 2 and 4. The purpose of this colour differentiation is to allow the components provided with the elastic material to be easily distinguishable from those that are not and/or allow identification of the components on the basis of dimensions, usage and so on.

The invention has been described in the aforegoing with reference to components used in the installation of electrical wiring in buildings. However, the inven¬ tion is equally applicable to components of different design and serving other purposes, for instance compo¬ nents used in tubing generally, holding gases or liquids. Consequently, the invention should not be regarded as limited to-the embodiments described and shown herein but could be modified in a variety of ways within the scope of the appended claims.