Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
2000-08-02
2001-07-03
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
C073S856000
Reexamination Certificate
active
06253622
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for indicating when a set value of a clamping force of a tightenable clamp has been reached, wherein the tightenable clamp is comprised of a substantially C-shaped clamp strip having radially inwardly pointing end face walls at its axial ends and having clamping jaws provided on the end portions extending in the circumferential direction.
2. Description of the Related Art
In known clamps of this kind (DE 198 02 676 C1), which are used, for example, as pipe couplings for axially connecting two pipes, the clamping jaws are connected by at least one clamping screw which is tightened by a torque wrench in order to apply a predetermined force. The torque adjusted on the torque wrench, however, is not in all situations a precise measure for the set value of the clamping force. For example, when the screws are greased or provided with a washer or have different types of coatings, different radial clamping forces result for the clamp, and this leads to different mounting and operating results.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an indicator device of the aforementioned kind whose indication corresponds with high reliability and precision to the set value of the clamping force of the clamp.
In accordance with the present invention, this is achieved in that the indicator device has at least one breakable indicator element for each end face wall of the clamp strip which can be seated on the radially inner edge of the end face wall and, in the mounted position of the indicator element, will break upon reaching the set value of the clamping force of the clamp and a predetermined spacing of the inner edge of the end face wall from a cylindrical object clamped in the clamp.
According to this solution, the indicator elements will break upon reaching the set value of the clamping force of the clamp independently of possible diameter tolerances of the clamped objects, for example, pipes, or the surface condition of the employed clamping screw or screws. The breakage of the indicator elements then will provide a clearly noticeable sign during mounting of the clamp that the desired clamping force has been reached and, moreover, that the permissible or desired compression of the sealing sleeve or soundproofing sleeve, optionally provided in the clamp, has been reached.
In more detail, it can be provided that each indicator element has a substantially U-shaped part and a support leg oriented oppositely to one of the two legs of the U-shaped part and aligned with this one leg for supporting the U-shaped part on the cylindrical object clamped in the clamp, wherein the end face wall engages between the two legs of the U-shaped part, the length of the support leg is selected to be identical to the predetermined spacing, and the transverse portion connecting the legs of the U-shaped part has a breaking strength which is exceeded in the mounted position of the indicator element upon reaching the set value of the clamping force of the clamp. In this context, the end face wall provided with the indicator element presses against the transverse portion when the clamp is tightened while the indicator element with the support leg is supported on the clamped object until the transverse portion breaks at the predetermined set value of the clamping force determined by the selection of the breaking strength of the transverse portion.
As an alternative, it can be provided that the U-shaped part has a second support leg oriented oppositely to the other leg of the U-shaped part and aligned with this other leg and having a length corresponding to the spacing for supporting the U-shaped part on the cylindrical object, wherein the end face wall engages with play between the two legs of the U-shaped part.
Preferably, the support legs of the indicator element taper toward their free ends and axially outwardly. A bending moment or transverse moment is then exerted onto these tapered ends of the support legs of the indicator element during tightening of the cylindrical object, which moment causes a spreading of these support legs and this spreading assists in the breaking of the transverse portion so that breakage will occur for a very precisely defined value of the clamping force.
The leg of the U-shaped part of the indicator element, which is positioned at the axially outer side of the end face wall in the mounted position of the U-shaped part, preferably forms a portion of a C-shaped ring which rests against the end face wall. By means of this ring it is possible for the manufacturer of the clamp to pre-mount the indicator element on the clamp so that mounting of the indicator element at the assembly site is eliminated. Upon reaching the set value of the clamping force, not only at least one broken-off piece of the indicator element will fall off the clamp but also the C-shaped ring. This provides an even more noticeable indication that the clamping force has been reached.
Moreover, the C-shaped ring can be provided with projections distributed over the circumference of the C-shaped ring which, in the mounted position of the C-shaped ring, project axially inwardly and rest against the radially inwardly positioned edge of the end face wall. These projections prevent, in addition to the securing action of the indicator element, a radial movement of the ring in its plane when it is loaded in this plane by forces which do not act in a direction in which the indicator element prevents a displacement, for example, forces occurring during the transport of the clamp together with the ring. In addition, the ring can have a further projection which in the mounted position of the ring projects axially inwardly and engages a hole in the end face wall. This, moreover, prevents a rotation of the ring so that it maintains a predetermined rotational position relative to the clamp, preferably in such a way that the gap between its ends is congruent with the gap between the clamping jaws and that in the case of a radial mounting of the clamp on a pipe this pipe can be guided through both gaps.
Moreover, the leg of the U-shaped part of the indicator element, resting in the mounted position of the U-shaped part on the inner side of the end face wall, may be provided with a slanted surface on its side facing away from the end face wall, wherein the slanted surface extends to the free end of the leg. This facilitates mounting of the C-shaped rings provided with the indicator elements.
Preferably, two indicator elements are provided for each end face wall. This makes it possible to cover a greater range of set values of the clamping force in connection with greater diameters of the cylindrical objects, in particular, pipes, to be clamped or connected.
Moreover, when the two indicator elements are positioned in the mounted position diametrically opposite one another relative to the clamp axis, a more uniform distribution of the clamping force onto the indicator elements will result.
REFERENCES:
patent: 4629217 (1986-12-01), Straub
patent: 5528942 (1996-06-01), Baratta
patent: 5602341 (1997-02-01), Lee et al.
patent: 5945607 (1999-08-01), Peppel et al.
patent: 8521410 (1985-10-01), None
patent: 198 02 676 C1 (1999-05-01), None
Zuverlaessiges Verbindungssystem fuer Metall- und Kunststoffrohre, Bd. 37, No. 9/03, Sep. 1, 1998, p. 636.
Barbett Wolfgang
Scheit Peter
Kueffner Friedrich
Noori Max
Rasmussen GmbH
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