[0002] A pipe fitting is used as a connection piece to connect, for example, a mounting piece, such as a tap, to a pipe or as a connection piece to connect a pipe to another pipe or to another similar object. Previously, mainly metallic pipe fittings were used. However, material and manufacturing costs of metallic pipe fittings are quite high. In addition, to make the connec- tions in the metallic pipe fittings tight requires remarkable expertise. Pipe fit- tings can also be made of plastic. Also when plastic pipe fittings are used, it is necessary to have a good knowledge of how to make the connections tight.

BRIEF DESCRIPTION OF THE INVENTION [0003] It is an object of the invention to provide a new and improved pipe fitting.

[0004] The pipe fitting of claim 1 is characterized in that on the bot- tom of a groove between ridges of the thread there are protrusions.

[0005] The pipe fitting is preferably made of plastic and at least its one end comprises a thread for connecting the pipe fitting to the mounting element. If the groove between the ridges of the thread is provided with protru- sions, a seal to be arranged onto the threads can be fixed very firmly to its place when the mounting element and the pipe fitting are connected to each other by means of a threaded connection. Also when the threaded connection is opened, the seal remains quite well in its place. The protrusions on the bot- tom of the groove also make the connection tighter so that no fluid can flow along the groove of the threads. Consequently, the connections are made considerably tighter. If the threaded end of the pipe fitting is provided with an unthreaded section in the starting end of the pipe fitting, this unthreaded sec- tion acts as a guide surface for the mounting element to be arranged in the pipe fitting, whereupon the mounting element provided with a thread suitably fits into the threads of the pipe fitting. Thus, the unthreaded part acts as a guide element which hinders the mounting element from being in an inclined

position with respect to the pipe fitting, which inclined position could damage the threads of the pipe fitting and/or mounting element. Thus, the tightness of the connection can also be improved by means of the unthreaded part, since the threads remain undamaged and the threaded connection can be imple- mented easily and properly.

BRIEF DESCRIPTION OF THE FIGURES [0006] The invention will be described in more detail in the attached drawing, in which Figure 1 schematically shows a side view of a pipe fitting, and Figure 2 shows a cross-section of the pipe fitting of Figure 1, taken along the line A-A of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION [0007] Figure 1 shows a pipe fitting 1, i. e. a connection piece. The pipe fitting 1 is used between two or more mounting elements to connect them.

The first mounting element can be, for example, a pipe or a mounting piece, such as a tap or the like, and the second mounting element can be a pipe, for instance. The pipe fitting 1 can be a bend, as shown in Figure 1, or the pipe fitting 1 can be a straight piece, for example. Furthermore, the pipe fitting 1 can be a T-piece, which means that the pipe fitting 1 is used to connect three dif- ferent mounting elements to each other. Thus, the appearance and purpose of use of the pipe fitting 1 can vary within very broad limits.

[0008] The pipe fitting 1 is made of plastic, such as polyethylene PE, polypropylene PP, cross-linked polyolefin plastic, such as cross-linked polyethylene PEX, polyamide PA, polysulphone PSU, polyphenylsulphone PPSU or polyvinyldene fluoride PVDF. If desired, additives, such as a rein- forcement, e. g. glass fibre, can be mixed into the plastic.

[0009] At the first end of the pipe fitting 1 there is an external thread 2. The thread 2 comprises a ridge 3. Between the ridges 3 there is a continu- ous helical groove 4.

[0010] On the bottom of the groove 4 there are protrusions 5. The pipe fitting 1 is connected by means of the thread 2 to the mounting element provided with an internal thread. In Figure 1, the mounting element is shown symbolically by means of a broken line. A seal is arranged in the threaded connection between the external thread 2 of the pipe fitting 1 and the internal thread of the mounting element in order to secure the tightness of the threaded

connection. Due to the protrusions 5, the seal 7 remains in its place at the thread 2 when the threaded connection is implemented. Furthermore, when the connection is opened, the protrusions 5 keep the seal 7 in its place. The protrusions 5 also prevent the leaking of the threaded connection by hindering the fluid from flowing along the bottom of the groove 4.

[0011] For example, a sealing strip, sealing tape, hemp or some other sealing can be used as a seal in a manner known per se. If the pipe fit- ting 1 is made of polyphenylsulphone PPSU, a sealing material with a trade name Loctite 5061 has proven to be a good seal. The seal 7 is preferably ar- ranged in connection with the pipe fitting 1 already during the manufacture of the pipe fitting 1 at the factory. Thus, it is ensured that a proper kind of sealing material is used and that the seal is properly arranged in connection with the thread 2.

[0012] The protrusions 5 do not necessarily extend to the starting end of the thread 2, and thus the starting end of the groove 4 can have an even bottom. This makes it easier to implement the threaded connection and the threads are set against each other easily. In Figure 1, the protrusions 5 are arranged in the same line with each other in the successive grooves, whereby the protrusions 5 form axial ribs. Thus, the manufacture of the pipe fitting 1 by means of injection moulding, for instance, is as simple as possible and it is easy to form an injection mould, for example. For the sealing effect, however, it is not necessary that the protrusions in the successive grooves are in the same line with each other but they may even be arranged randomly around the pipe fitting 1. On the other hand, the protrusions 5 can be arranged to form the ribs at an angle diverging from the axial direction.

[0013] There can be, for instance, 2 to 24 protrusions 5 that are ar- ranged at one point around the circumference, i. e. at a distance covered by one pitch. Typically, there are 4 to 8 protrusions at one point around the cir- cumference. In the case of Figures 1 and 2, there are eight protrusions 5 around the circumference.

[0014] The height of the protrusion 5 depends on the diameter of the pipe fitting 1 and the height of the ridge 3. The height of the protrusion 5 is typically 10 to 50% of the height of the ridge 3, for instance. The height of the protrusion 5 can vary between 0.2 and 2 mm, for example. The diameter D of the pipe fitting can vary between 10 and 30 mm, for example.

[0015] At the first end of the pipe fitting 1 provided with the thread 2 there can be an unthreaded section 6 in the starting end before the thread 2.

The unthreaded section 6 forms a guide surface, which guides the pipe fitting 1 and the mounting element to be connected thereto with respect to one another in such a manner they have parallel middle axes. Consequently, the threads are set precisely against each other and it is easy to implement a threaded connection and the threads will not get damaged. Furthermore, the unthreaded section 6 provides the advantage that at the point where the thread 2 starts, the wall of the pipe fitting 1 has a greater strength than at the very end of the pipe fitting. At the thread 2 the wall is not as elastic as at the end of the pipe fitting and due to the mould technique, the wall of the end part of the injection mould section must be made slightly thinner so that the section of the mould to be arranged inside the casting can be separated after the casting. Due to the unthreaded section 6, the thread 2 starts where the wall is a bit thicker than at the end of the pipe fitting 1. Consequently, it is easier to keep the thread 2 un- changed and the connection becomes very tight.

[0016] Typically, the length I of the unthreaded section equals to the pitch of ca. 1 to 2 threads. Preferably, the ratio of the length I of the unthreaded section 6 to the diameter D of the pipe fitting 1 is greater than 1: 6. Particularly preferably the ratio of the length I of the unthreaded section 6 to the diameter D of the pipe fitting 1 is greater than 1: 4.

[0017] The drawings and the related description are only intended to illustrate the idea of the invention. In its details, the invention can vary within the scope of the claims. The pipe fitting 1 can have any single feature de- scribed above either individually or in combination with other features. For example, the pipe fitting 1 can have the unthreaded part 6 before the thread 2, but it need not necessarily have protrusions 5 on the bottom of the groove 4 then. A very good tightness is provided in this case, too. If desired, the protru- sions 5 can be made of a softer material than the rest of the pipe fitting. Thus, when the threaded connection is implemented, the protrusions are shaped be- cause of the pressing of the threads of the mounting element. Furthermore, the protrusions can, if desired, also be arranged in a position diverging from the axial direction, i. e. obliquely in either direction. In this case, the protrusions wedge the sealing material towards the ridge, providing a better tightness. Fur- thermore, the protrusions 5 need not necessarily extend from one ridge to an- other but the seal remains in its place also when at least a part of the distance between the ridges is uneven. The upper surface of the protrusions 5 can be straight, as shown in Figure 1, or the upper surface of the protrusions 5 can be convex or concave, for example.