GB1582907A

GB1582907A - Apparatus for pre-stressing a screw-threaded stud during tightening of a nut screwed thereon and a method of tightening the nut

Info

Publication number: GB1582907A
Application number: GB934978A
Authority: GB
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1977-03-12
Filing date: 1978-03-09
Publication date: 1981-01-14
Also published as: FR2382982A1; DE2710964A1; FR2382982B1; JPS53113400A; DE2710964C2

Description

(54) APPARATUS FOR PRE-STRESSING A SCREW-THREADED STUD DURING TIGHTENING OF A NUT SCREWED THEREON AND A METHOD OF TIGHTENING THE NUT (71) We, KLÖCKNER-HUMBOLDT- DEUTZ AKTIENGESELLSCHAFT, a German Body Corporate, of K(iln-Deutz, German Federal Republic, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus for pre-stressing a screw-threaded stud during tightening of a nut screwed thereon for fastening one element of a machine to another one. The invention also relates to a method of tightening with the aid of a pre-stressing apparatus a nut screwed on a screw-threaded stud for fastening one element of a machine to another one.The term "stud" should be understood to include screw-threaded bolts of all kinds.

A known apparatus for pre-stressing a screw-threaded stud for tightening a nut screwed thereon with the aid of a hydraulically operable stud-tensioning device comprises a partly hollowed and internally threaded spindle screwable on to the stud's free end portion projecting beyond the nut and a sleeve surrounding both the spindle and the nut and abutting with its one end disposed in the vicinity of the nut on one of the elements to be fastened and with its other end on the hydraulic device. The sleeve has at least one aperture across which the nut can be tightened. In operation, the stud is stressed by means of the tensioning device to near its elastic limit, and as a result of the pressure transmitted by the sleeve the machine elements to be joined are appropriately stressed. Thereafter, the nut is manually screwed firmly against an abutment surface of the one machine element.

However, experience has shown that, if the nut is tightened manually, difficulties arise in as far as the tensional force acting on the bolted joint deviates from a predetermined one, the main causes of which are insufficient attention of the fitters and/or soiled abutment surfaces or even a defective tensioning device. The consequence is an inadequate or excessive tensioning of the stud and thus an unacceptable deviation from the predetermined deformation of the latter and of the machine elements. This means, expressed differently, that if the tension is inadequate the safety margin against a loosening of the bolted joint is insufficient whereas if the joint is excessively tensioned the stress to which the fastened elements are subjected will be increased to an unacceptable extent.Since apparatus of the type referred to is principally used for the purpose of hydraulically tensioning bolt joints in internal combustion engines such as the main bearings, connecting-rod bearings and cylinder heads, which are subjected to particularly high loads, any such deviation from the predetermined tensioning force could, possibly, lead to a total loss of the engine.

It is therefore an aim of the present invention to provide apparatus and a method by means of which the abovementioned difficulties can be avoided or at least minimised, and errors which may occur in the course of tightening a bolt joint can be substantially eliminated.

Accordingly, the invention is directed to apparatus for pre-stressing a screw-threaded stud during tightening of a nut screwed thereon for fastening one element of a machine to another one, the apparatus comprising: (a) a hydraulic tensioning device having a spindle displaceable in and projecting from one end face of the cylinder thereof for engaging the free end portion of the stud that projects beyond the nut; (b) a sleeve for supporting the device on an abutment surface of one of the elements to be fastened and being positionable so that its wall surrounds the projecting portion of the spindle and one of its ends abuts on the one cylinder end face, the wall of the sleeve having:: (1) at least one aperture for the passage therethrough of a nut-tightening implement; (2) a slit extending in length from the other sleeve end over a limited distance in the sleeve's longitudinal direction and in depth across the wall thereof; and (3) a recess also extending from the other sleeve end and being peripherally spaced in the nut-tightening direction from the slit by an angle corresponding to the difference between a first predetermined stud pre-stressing force and a second predetermined pre-stressing force; wherein the arrangement is such that, when the spindle has been brought into engagement with the free end of the stud and the sleeve positioned between the cylinder's one free end face and the abutment surface, operation of the device will cause the stud to be pre-stressed.

The invention is also directed to a method of tightening with the aid of a pre-stressing apparatus including a hydraulic tensioning device a nut screwed on a screw-threaded stud for fastening one element of a machine to another one, the method comprising the steps of: a) positioning the apparatus so that a spindle displaceable in and projecting from one end face of the cylinder of the device engages the free end portion of the stud which projects beyond the nut; (b) supporting the device on an abutment surface of one of the elements to be fastened by positioning a sleeve so that the wall thereof surrounds the respective projecting portions of the spindle and the stud and that the ends thereof abut on the one cylinder end face and said abutment surface respectively;; (c) subjecting the stud by means of the tensioning device to a predetermined pretensioning force and manually pretightening the nut by means of an implement arranged to extend through an aperture in the sleeve into one of a number of bores in the nut; (d) marking the nut through a slit in the sleeve and the abutment surface through a recess both extending from the sleeve end positioned remote from the cylinder and being peripherally spaced from each other by a predetermined angle; (e) subjecting the stud by means of the tensioning device to a predetermined final tensioning force and finally tightening the nut manually to a tight fit on the abutment surface; and (f) checking whether the marking on the nut is in line with that on the abutment surface.

The angle between the slit and the recess must be determined by suitable tests in respect of each type of bolt joint. These tests involve pre-tensioning the bolt joint to such an extent as to eliminate any play between - depending on the type of joint the nut and the respective abutment surface or the abutment surfaces of the two elements and to ensure - regardless of the type of joint - a tight, or full-area contact between all the surfaces of the joint. Thereafter, the stud, or bolt, will be subjected to the predetermined final tension and, when this has been reached, its elongation will be measured and converted into the appropriate rotational angle of the nut. In the course of tightening the bolt joint, the nut will be marked across the slit and the abutment surface across the recess when the joint has been pre-tensioned and the nut pretightened.When as a result of finally tightening the nut the final tension has been reached the markings on the nut must be in line with that on the abutment surface.

Thus, any incorrect final tensioning of the bolted joint - which may be caused by an inaccurate adjustment of the pressure of the hydraulic tensioning device for exerting the final tensioning and/or, in all instances of a manual tightening of the nut, by nonuniform torque - can be avoided. Any malpractice on the part of the fitters is therefore substantially excluded.

The angular spacing between the slit and recess may be subject to a certain tolerance.

In order to allow for the latter, it is advantageous if the extent of the permissible tolerance is determined by the width of the recess in the peripheral direction of the sleeve. The recess may over its full width extend radially across the sleeve towards the nut thus rendering it possible to observe directly the final tensioning angle while the nut is being tightened. The general shape of the recess may be such that it permits at least checking whether the two markings are in line after the removal of the sleeve or, preferably, while the nut is tightened.

In order to make the invention more readily understood one embodiment thereof will now be described with reference to the accompanying, simplified, drawings, in which: Figure I is a longitudinal cross-sectional view of apparatus according to the invention including a hydraulic tensioning device and a sleeve for supporting the device on an abutment surface of one of the elements to be fastened; Figure 2 a transverse cross-sectional view along the line 11 - II of the sleeve shown in Figure 1; Figure 3 a side view of the sleeve in the direction of the arrow III in Figure 1; Figure 4 a side view of the sleeve in the direction of the arrow IV in Figure 1; Figure 5 a bolt joint including a pretightened nut on a pre-stressed stud; and Figure 6 the nut finally tightened.

As far as illustrated, the reference numeral 1 in the Figures denotes a hydraulic tensioning device including a cylinder la and a spindle 2 displaceable in the cylinder and projecting from one end face thereof.

The projecting portion of the spindle 2 is externally screw-threaded over some of its length and engages the free end portion of an externally screw-threaded stud 3 by means of an internally screw-threaded bush 2a. The device 1 is supported through a sleeve 4 by an abutment surface 5 of a machine element 6 to be fastened to another element - not illustrated. One end of the sleeve 4 abuts on the surface 5 while its other end abuts on the end face of the cylinder la closest to the surface 5. The sleeve 4 surrounds the spindle 2, the whole length of the stud 3 that protrudes from the element 6 and a nut 7 serving to fasten the element 6 to the other element. The sleeve 4 also surrounds the bush 2a and thus the end portion of the stud 3 that projects beyond the nut 7.The cylindrical wall of the sleeve 4 is provided with an elongate aperture 8 extending in depth across the wall and in length along a part of its circumference, through which aperture an implement may pass for manually tightening the nut 7. For this purpose the nut is provided on its circumference with a number of bores 9 into which and through the aperture 8 the implement, for example a pin - not illustrated - may be inserted for the purpose of turning the nut 7. In addition, the sleeve 4 is provided at its end adjacent the element 6 with a slit 10 extending in length from said end over a limited distance in the sleeve's longitudinal direction and in depth across the wall thereof towards the nut 7.In addition, the sleeve has a recess 12 also extending from said end and being peripherally spaced in the nut-tightening direction from the slit 10 by an angle 11 correspond ing -to the difference between the stud pre-tensioning force and a pre-determined final tensioning force. A tolerance is allowed for the angular spacing, and the extent of this tolerance is determined by the width of the recess 12 in the peripheral direction of the sleeve. The recess is open towards the abutment surface 5 of the element 6. As may also be seen from the Figures, the nut 7 will be marked through the slit 10 and the abutment surface 5 through the recess 12 by a marker implement 13, for example a scriber.

The illustrations in Figures 3 and 4 show more clearly the elongate aperture 8, the recess 12 and the slit 10. Figure 5 illustrates the positions of the markings on the nut and on the abutment surface 5 when the stud 3 has been pre-tensioned and the nut 7 pretightened whereas Figure 6 illustrates the positions of the markings after the final tensioning of the stud and final tightening of the nut.

The appliance functions as follows: After the nut 7 has manually been screwed on to the length of the stud 3 that protrudes from the element 6 the spindle 2 of the tensioning device 1, and thus the device itself, will be secured to the stud 3 by means of the bush 2a and at the same time the sleeve 4 will be pushed over the nut 7.

Thereafter, the hydraulic system - not illustrated in detail - of the tensioning device 1 will be operated to produce pressure in the cylinder, which pressure acts on a flange of the spindle as a result of which the stud will be pre-tensioned and the element 6 be subjected, by means of the sleeve 4, to pressure. Once this has been effected the nut 7 will be manually firmly tightened by means of the aforementioned pin extending through the aperture 8 in the sleeve 4. This position of the nut 7 relative to the sleeve 4 will be marked through the slit 10 whereas the position of the sleeve 4 relative to the abutment surface 5,6 will be marked through the -recess 12. Subsequently, the tensioning device is operated to subject the stud to the predetermined final tensioning force, and the nut 7 is again screwed firmly with the aid of the pin against the abutment surface 5.Provided the hydraulic end pressure in the device 1 is accurately regulated and the stud subjected to the correct final tensioning force - and the nut 7 correctly tightened, the marking on the nut 7 must be in line with that on the abutment surface 5.

Depending on the shape of the recess 12 in the sleeve 4, the checking may be effected either while the nut 7 is being tightened or only after the sleeve 4 has been removed.

WHAT WE CLAIM IS: 1. Apparatus for pre-stressing a screwthreaded stud during tightening of a nut screwed thereon for fastening one element of a machine to another one, the apparatus comprising: (a) a hydraulic tensioning device having a spindle displaceable in and projecting from on end face of the cylinder thereof for engaging the free end portion of the stud that projects beyond the nut; (b) a sleeve for supporting the device on an abutment surface of one of the elements to be fastened and being positionable so that its wall surrounds the projecting portion of the spindle and one of its ends abuts on the one cylinder end face, the wall of the sleeve having: (1) at least one aperture for the passage there-through of a nut-tightening implement;

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. direction of the arrow IV in Figure 1; Figure 5 a bolt joint including a pretightened nut on a pre-stressed stud; and Figure 6 the nut finally tightened. As far as illustrated, the reference numeral 1 in the Figures denotes a hydraulic tensioning device including a cylinder la and a spindle 2 displaceable in the cylinder and projecting from one end face thereof. The projecting portion of the spindle 2 is externally screw-threaded over some of its length and engages the free end portion of an externally screw-threaded stud 3 by means of an internally screw-threaded bush 2a. The device 1 is supported through a sleeve 4 by an abutment surface 5 of a machine element 6 to be fastened to another element - not illustrated. One end of the sleeve 4 abuts on the surface 5 while its other end abuts on the end face of the cylinder la closest to the surface 5. The sleeve 4 surrounds the spindle 2, the whole length of the stud 3 that protrudes from the element 6 and a nut 7 serving to fasten the element 6 to the other element. The sleeve 4 also surrounds the bush 2a and thus the end portion of the stud 3 that projects beyond the nut 7.The cylindrical wall of the sleeve 4 is provided with an elongate aperture 8 extending in depth across the wall and in length along a part of its circumference, through which aperture an implement may pass for manually tightening the nut 7. For this purpose the nut is provided on its circumference with a number of bores 9 into which and through the aperture 8 the implement, for example a pin - not illustrated - may be inserted for the purpose of turning the nut 7. In addition, the sleeve 4 is provided at its end adjacent the element 6 with a slit 10 extending in length from said end over a limited distance in the sleeve's longitudinal direction and in depth across the wall thereof towards the nut 7.In addition, the sleeve has a recess 12 also extending from said end and being peripherally spaced in the nut-tightening direction from the slit 10 by an angle 11 correspond ing -to the difference between the stud pre-tensioning force and a pre-determined final tensioning force. A tolerance is allowed for the angular spacing, and the extent of this tolerance is determined by the width of the recess 12 in the peripheral direction of the sleeve. The recess is open towards the abutment surface 5 of the element 6. As may also be seen from the Figures, the nut 7 will be marked through the slit 10 and the abutment surface 5 through the recess 12 by a marker implement 13, for example a scriber. The illustrations in Figures 3 and 4 show more clearly the elongate aperture 8, the recess 12 and the slit 10. Figure 5 illustrates the positions of the markings on the nut and on the abutment surface 5 when the stud 3 has been pre-tensioned and the nut 7 pretightened whereas Figure 6 illustrates the positions of the markings after the final tensioning of the stud and final tightening of the nut. The appliance functions as follows: After the nut 7 has manually been screwed on to the length of the stud 3 that protrudes from the element 6 the spindle 2 of the tensioning device 1, and thus the device itself, will be secured to the stud 3 by means of the bush 2a and at the same time the sleeve 4 will be pushed over the nut 7. Thereafter, the hydraulic system - not illustrated in detail - of the tensioning device 1 will be operated to produce pressure in the cylinder, which pressure acts on a flange of the spindle as a result of which the stud will be pre-tensioned and the element 6 be subjected, by means of the sleeve 4, to pressure. Once this has been effected the nut 7 will be manually firmly tightened by means of the aforementioned pin extending through the aperture 8 in the sleeve 4. This position of the nut 7 relative to the sleeve 4 will be marked through the slit 10 whereas the position of the sleeve 4 relative to the abutment surface 5,6 will be marked through the -recess 12. Subsequently, the tensioning device is operated to subject the stud to the predetermined final tensioning force, and the nut 7 is again screwed firmly with the aid of the pin against the abutment surface 5.Provided the hydraulic end pressure in the device 1 is accurately regulated and the stud subjected to the correct final tensioning force - and the nut 7 correctly tightened, the marking on the nut 7 must be in line with that on the abutment surface 5. Depending on the shape of the recess 12 in the sleeve 4, the checking may be effected either while the nut 7 is being tightened or only after the sleeve 4 has been removed. WHAT WE CLAIM IS:

1. Apparatus for pre-stressing a screwthreaded stud during tightening of a nut screwed thereon for fastening one element of a machine to another one, the apparatus comprising: (a) a hydraulic tensioning device having a spindle displaceable in and projecting from on end face of the cylinder thereof for engaging the free end portion of the stud that projects beyond the nut; (b) a sleeve for supporting the device on an abutment surface of one of the elements to be fastened and being positionable so that its wall surrounds the projecting portion of the spindle and one of its ends abuts on the one cylinder end face, the wall of the sleeve having: (1) at least one aperture for the passage there-through of a nut-tightening implement;

(2) a slit extending in length from the other sleeve end over a limited distance in the sleeve's longitudinal direction and in depth across the wall thereof; and (3) a recess also extending from the other sleeve end and being peripherally spaced in the nut-tightening direction from the slit by an angle corresponding to the difference between a first predetermined stud pre-stressing force and a second predetermined pre-stressing force; wherein the arrangement is such that, when the spindle has been brought into engagement with the free end portion of the stud and the sleeve positioned between the cylinder's one end face and the abutment surface, operation of the device will cause the stud to be pre-stressed.

2. Apparatus according to claim 1, wherein a tolerance is allowed for the angular spacing between the slit and the recess, and wherein the extent of the tolerance is determined by the width of the recess in the peripheral direction of the sleeve.

3. Apparatus according to claim 1 or claim 2, wherein some length of the spindle's projecting portion is externally screwthreaded and provided with an internally threaded bush for threadingly engaging the free end portion of the stud.

4. A method of tightening. with the aid of a pre-stressing apparatus including a hydraulic tensioning device, a nut screwed on a screw-threaded stud for fastening one element of a machine to another one, the method comprising the steps of: (a) positioning the apparatus so that a spindle displaceable in and projecting from one end face of the cylinder of the device engages the free end portion of the stud which projects beyond the nut:: (b) supporting the device on an abutment surface of one of the elements to be fastened by positioning a sleeve so that the wall thereof surrounds the respective projecting portions of the spindle and the stud and that the ends thereof abut on the one cylinder end face and said abutment surface respectively; (c) subjecting the stud by means of the tensioning device to a predetermined pretensioning force and manually pretightening the nut by means of an implement arranged to extend through an aperture in the sleeve into one of a number of bores in the nut; (d) marking the nut through a slit in the sleeve and the abutment surface through a recess both extending from the sleeve end positioned remote from the cylinder and being peripherally spaced from each other by a predetermined angle; ; (e) subjecting the stud by means of the tensioning device to a predetermined final tensioning force and finally tightening the nut manually to a tight fit on the abutment surface; and (f) checking whether the marking on the nut is in line with that on the abutment surface.

5. A method of tightening, with the aid of a pre-stressing apparatus including a hydraulic tensioning device, a nut screwed on a screw-threaded stud for fastening one element of a machine to another one, substantially as herein described with reference to the accompanying illustrative drawings.

6. Apparatus for pre-stressing a screwthreaded stud during tightening of a nut screwed thereon for fastening one element of a machine to another one, constructed, arranged and adapted to operate substantially as herein described with reference to Figures 1 to 4 of the accompanying illustrative drawings.