GB2408552A

GB2408552A - Threaded connection

Info

Publication number: GB2408552A
Application number: GB0426144A
Authority: GB
Inventors: Bugdayci Hasan Husevin
Original assignee: IHC Holland NV
Current assignee: IHC Holland NV
Priority date: 2003-11-26
Filing date: 2004-11-26
Publication date: 2005-06-01
Anticipated expiration: 2024-11-26
Also published as: DE202004018331U1; NL1024889C1; GB0426144D0; GB2408552B; BE1016259A6

Abstract

Threaded connection, in particular between a shaft (1) and a component (4) which is to be secured to it, in which the cross section of the screw thread formation (6, 9) is substantially trapezium-shaped. In this threaded connection, the vertex (5) of the screw thread (3) of the shaft (1) of at least the first turn (6), the one located furthest away from the end (2) of the shaft, is bevelled in such a manner that the height of this turn is lower than that of the adjacent turns (9), and the vertices are located on a conical surface (7). Furthermore, the base (8) of the screw thread (3) of the shaft (1) is rounded and/or rolled. The thread turns (9) of the screw thread (3) of the shaft (1) are higher, so that the base (10) of the screw thread (11) of the component (4) which is screwed onto the shaft (1) bears against the vertex (5) of the turns (9) of the screw thread (3) on the shaft.

Description

THREADED CONNECTION

Threaded connection, in particular between a shaft and a component which is to be secured to it.

The invention relates to a threaded connection, in particular between a shaft and a component which is to be secured to it, in which the cross section of the screw thread formation is substantially trapezium-shaped.

This may, for example, be a pump shaft of a centrifugal pump, as is used on a suction dredger vessel, onto which pump shaft an impeller is screwed.

It has been found that the shaft of these pumps may fracture. This fracture is caused in particular by fatigue resulting from a notch effect originating from the base of the screw thread.

Furthermore, it has been noted that in the case of the standard trapezium thread the first turn of the screw thread, i.e. the turn located furthest from the end of the shaft, is in relative terms subject to the greatest load, specifically approximately 30% of the total force exerted on the screw thread. Consequently, the structure is, in fatigue terms, weakest at this highly critical cross section.

The object of the invention, therefore, is to improve the shape of the screw thread in such a manner that the risk of the shaft fracturing is considerably reduced.

According to the invention, this is achieved by bevelling the vertex of the screw thread of the shaft of at least the first turn, i.e. the turn located furt:-iest from the end of the shaft, in such a manner that the height of this turn is lower than that of the adjacent turns. - 2 -

Bevelling at least the first turn lowers the force exerted on this turn or these turns. Although the force exerted on the other turns will then increase, a better distribution of the total force exerted on the turns will be obtained. The maximum force exerted on any one turn will therefore be lower, which is extremely beneficial from a strength aspect.

A further possible way of reducing the risk of fatigue fracture is for the base of the screw thread of the shaft to be rounded.

Rounding of this nature will reduce the occurrence of a notch effect. The use of these measures will further reduce the risk of fatigue fracture.

To reduce the risk of a notch effect and therefore a fatigue fracture still further, according to the invention it is possible for the base of the screw thread of the shaft to be rolled.

This produces a smoother surface of the rounded base of the screw thread, with the result that this surface will offer resistance to fatigue loading, which can cause fatigue fracture, for a longer period of time.

With a standard trapezium-shaped screw thread, the thread is not remachined after it has been cut.

According to the invention, therefore, the base of the screw thread, after thread-cutting, is machined by rolling in such a manner as to produce the desired final dimension and a smooth surface.

In the known trapezium-shaped screw thread, the vertex of the screw tI-read of the component which is screwed onto the shaft will bear against the base of the screw thread on the shaft. This will no longer be possible as - 3 - a result of the rounding applied to the base of the screw thread of the shaft.

In conjunction with this, according to the invention it is also possible for all the turns of the screw thread of the shaft except for the bevelled turns to be made higher, in such a manner that the base of the screw thread, which is of standard design, of the component screwed onto the shaft bears against the vertices of the turns of the screw thread on the shaft.

This also has the effect that components which are to be screwed onto the shaft can be provided with a standard screw thread.

The invention is explained in more detail on the basis of an exemplary embodiment shown in the drawing and illustrating a cross section through part of the end, provided with a screw thread, of a shaft together with a part of the component screwed onto the shaft.

The shaft 1 shown in the figure is provided at the end 2 with a screw thread 3 for the component 4, which is only partially illustrated, to be fitted to, this component 4 being, for example, an impeller if the shaft is a pump shaft.

The vertex 5 of the screw thread 3 is bevelled over the first turns 6, so that the vertices are lower than those of the adjacent turns 7.

As has been indicated above, the base 8 of the screw thread 3 has been rounded and rolled.

Compared to the normal trapezium-shaped screw thread, the vertex 5 of the turns 9 located next to the first turns 6 on the screw thread 3 are higher, so that the base 10 of the screw thread 11 of the component 4 rests on the vertex 5 of the screw thread 3. With the - 4 - standard design of trapezium-shaped screw thread, by contrast, the vertex 12 of the screw thread 11 of the component 4 will bear against the base 8 of the screw thread 3 of the shaft 1.

It will be clear that only one possible embodiment of an assembly according to the invention is illustrated in the drawing and described above, and that numerous modifications can be made without departing from the scope of the invention as defined in the claims. - 5

Claims

1. Threaded connection, in particular between a shaft (1) and a component (4) which is to be secured to it, in which the cross section of the screw thread formation (6, 9) is substantially trapezium- shaped, characterized in that the vertex (5) of the screw thread (3) of the shaft (1) of at least the first turn (6), the one located furthest away from the end (2) of the shaft, is bevelled in such a manner that the height of this turn is lower than that of the adjacent turns (9) .

2. Threaded connection according to Claim 1, characterized in that the base (8) of the screw thread (3) of the shaft (1) is rounded.

3. Threaded connection according to Claim 1 or 2, characterized in that the base (5) of the screw thread (3) of the shaft (1) is rolled.

j/. Threaded connection according to one of the preceding claims, characterized in that all the turns (9) of the screw thread (3) of the shaft (1) except for the bevelled turns (6) are designed to be higher and rounded, in such a manner that the base (10) of the screw thread (11), which is of standard design, of the component (4) which is screwed onto the shaft (1) bears against the vertex (5) of the turn (9) of the screw thread (3) on the shaft (1).