WO1995029344A1

WO1995029344A1 - Screw/bolt joint

Info

Publication number: WO1995029344A1
Application number: PCT/SE1995/000465
Authority: WO
Inventors: Sven-Erik Svensson
Original assignee: Svensson Sven Erik
Priority date: 1994-04-27
Filing date: 1995-04-27
Publication date: 1995-11-02
Also published as: SE9401432D0; AU2423195A

Abstract

The invention concerns a screw/bolt joint comprising a screw fastener element screwed into a blind hole or into a hole formed with an abutment shoulder, said screw fastener element having an externally threaded shank. The invention is characterized primarily in that the threaded shank (4) comprises a cavity (6) which opens towards the free shank end (7) and at least one longitudinal/axial through-slit (8) which extends towards the free shank end (7) into the cavity (6), and in that a spreader/expander member (Z) when supported against the bottom (5) of the hole (13) or against said abutment shoulder is arranged, upon screwing of said screw fastener element (E) into said hole (13), to be driven into the cavity (6) at the free end (7) of the threaded shank (4). The member (Z) then expands the threaded shank (4) in such a manner that the external threads (5) on the threaded shank (4) are pressed against the wall of the hole (13), essentially at right angles to the direction of introduction of said screw fastener element.

Description

SCREW/BOLT JOINT

The subject invention concerns a screw/bolt joint of the kind defined in the preamble of claim 1, and a threaded furniture knob, a holding or tightening screw or a stud bolt in accordance with the dependent claims 8, 9 and 12, respectively.

Threaded knobs in the form of fittings intended e.g. for cupboard doors or drawer fronts that conventionally are made from wood, are, when mounted, generally screwed all the way through the material of the door/drawer front and are secured by means of a nut on the reverse side or back of the material. However, it is likewise known to screw such threaded knobs formed with a threaded shank into a blind hole from the external face of the door/drawer front. When this is the case the knob is retained in position by means of the hold of the thread engagement and usually the knob cuts the threads in said blind hole formed in the material. Experience has shown that owing to the (natural) desiccation of the wood and/or the frequent use of the fitting the threaded knob tends to loosen in time from its securement, resulting in the knob finally falling off completely. Similarly, screw/bolt joints that lack special screw-securement arrangements may come loose during the frequently repeated intermittent loads. Also stud bolts, used for instance in engine cylinder blocks, have a tendency to become loose in time and come off their anchoring holes. The purpose of the subject invention is to considerably improve a screw/bolt joint of the kind defined in the introduction so as to ensure a secure and permanent attachment of the threaded element by means of a minimum amount of simple components. In addition, furniture fittings in the form of a threaded knob or a fastening or tightening screw combination or a stud bolt are provided wherein the risk that they become loose has been eliminated by the design of the component itself and/or said component may be additionally tightened later in a simple and efficient manner to ensure that the element is positively anchored in position. From the German Patent Specification DE-GM 70 38 975 is known a threaded furniture knob designed to be quickly fastened and comprising a sleeve-like slitted shank portion provided with external longitudinal grooves, said portion being pressed into the hole drilled in the furni- ture material to be retained in position therein by means of a pin which is inserted into the sleeve-like portion to widen the latter. This prior-art furniture knob comprises not only a plurality of components and consequently is expensive to manufacture but in addition it is also difficult to use this knob in many applications.

Furthermore, it does not guarantee permanent and positive anchorage. On the contrary, it is comparatively easy to pull it out from the furniture material after some time of use. Also from the German Patent Publication

DE-GM 74 13 632 is known a pin joint intended for furniture, according to which publication a retainer pin, which is secured in the furniture in the internal hole of a clamping bushing, attached to the furniture, is retained in position by means of barbs. The holding force of the clamping bushing is, however, also in this case unsatis¬ factory in the long run as it is based essentially only on the holding force of the engagement of the threads. In accordance with the teachings of the subject invention the screw/bolt joint is primarily characterized in that the threaded shank is formed with a cavity which opens towards the free shank end and with at least one longitudinal axial slit which extends towards the free shank end and through the shank into the cavity, and in that a spreader/expander member supported against the bottom of the hole or against an abutment shoulder is arranged, upon screwing of said screw fastener element into said hole, to be forced into the cavity at the free end of the shreaded shank, whereby the member expands the threaded shank in such a manner that the external threads on the threaded shank are pressed outwards against the wall of the hole, essentially at right angles to the direction of introduction of said screw fastener element. Owing to this solution an extremely favourable force transmission ratio is created in the respect that the comparatively small force imparted to the screw fastener element when the latter is being screwed into the furniture material is sufficient to realize and to retain the required degree of expansion of the threaded shank inside the blind hole in the furniture material. Not only will the screw fastener element be extremely well anchored against rotational movements owing to this solution but in addition its configuration ensures a positive frictional grip, preventing it form being axially pulled out of the material. The construction of the screw/bolt joint is simple and it is easy to manipulate and handle. The components from which it is formed may be manufactured at low costs. The dimensions of the threaded shank in relation to the blind hole cause no problems since the expansion of the threaded shank in a simple manner compensates for any existing manufacturing tolerances. The blind hole, alternatively, the through-hole or open-ended hole formed with an abutment shoulder in said furniture material, may be internally tapped, particularly when the furniture material is comparatively hard. When the furniture material is somewhat softer, such as wood, the threaded shank itself is able to cut the opposite threads in the blind hole wall.

The application of this principle in a threaded furniture knob having a knob handle and a threaded shank results in an extraordinarily, durable anchorage of the threaded knob in furniture or other material despite the absence of a counter-locking member on the rear face of the piece of furniture. Should some play or loosening effect nonetheless arise with respect to the threaded knob or the latter tend to become loose after some time of use it is quite simple, by a follow-up tightening, to make it secure again, also in case the hole should already show some signs of wear, since if this happens the expansion plug continues to be driven further inwards, into the cavity in the threaded shank and in doing so expanding the latter further.

Also when the screw/bolt joint in accordance with the invention is used in connection with holding or tightening screws formed With a domed nut, the locking effect of the joint by means of the expansion of the screw obviates the need for expansive and often interfering special screw or thread securement arrangements. The same advantages are gained when the solution in accordance with the invention is used in connection with stud bolts. In case the internal threads in the blind hole are damaged for one reason or other the remaining minor thread engagement is sufficient to drive the expansion pin further into the cavity so that the latter in its turn expands the threaded shank further, thus again ensuring safe anchorage despite the damaged threads.

In order to allow the threaded shank to expand uniformly in all directions in the cavity the latter preferably is formed with a plurality of longitudinal/ axial slits around its periphery.

In accordance with one simple embodiment the cavity is essentially cylindrical. The expander member is con¬ figured to expand the threaded shank progressivly more and more as its depth of penetration into the cavity increases. Alternatively, the cavity preferably is of conical configuration, widening towards the free end of the threaded shank. If, at the same time, the expander member has a conical shape, large mutual contacting surfaces are formed between the cavity wall and the expander member, generating comparatively large expansion forces requiring comparatively small torque to screw the fastener element in position.

In accordance with one embodiment according to which the expander member is shaped like a cone or has a frustro-conical shape the smaller diameter of which is smaller than the cavity diameter at the free threaded- shank end and the largest diameter of which exceeds the same cavity diameter, advantageously a large part (length) of the expander member consequently is made use of for the expansion of the threaded shank. Preferably, the cone angle is between 5° and 25°, preferably approximately 12°. The cone angle preferably is chosen in dependence of the frictional characteristics of the co-operating surfaces of the material. Some form of self-restricting effect could sometimes perhaps be desirable. On account of the abutment of the expander member against the bottom of the blind hole or alterna¬ tively against the abutment shoulder in the open-ended hole, no- self-restricting effect is however required most of the time. Rather, it could normally be an advantage if the expander member, upon unscrewing of the screw fastener element, automatically leaves the cavity, allowing the screw joint to dismantled in its entirety without any problems.

In accordance with a further embodiment grip means may be provided at the expander member base, said means exerting a gripping force on the bottom of the blind hole or on said abutment shoulder in the open-ended through- hole, respectively. This may contribute to a more convenient dismantling of the screw/bolt joint. In the case of a holding or tightening screw of the kind mentioned above the expander member could be formed integrally with the domed nut so as to form one single component. However, it is likewise possible to insert the expander member in the form of a plug loosely inside the domed nut or to glue such a plug to the bottom of the domed nut (in order to prevent it from being "lost"). In the case of a stud bolt of the kind mentioned above it may be preferable to arrange a key grip area or the like, preferably immediately above the threaded section thereof in order to allow the stud bolt to be tightened or unscrewed from its position by means of some suitable tool. In the absence of such a grip area it would also be possible to screw the stud bolt in position with the aid of domed nut.

In accordance with all embodiments the cavity as well as said axial slits could extend along the entire length of the threaded shank. In most embodiments it is, however, sufficient that the cavity and the axial slits are formed only along the end section of the threaded shank. Various embodiments of the invention will be described in closer detail in the following with reference to the accompanying drawings, wherein:

Fig. 1 in a partly cut explosive view shows a screw joint wherein the screw fastener element is in the form of a threaded knob intended for furniture, such as cupboard doors or drawer fronts;

Fig. la is a sectional view according from Fig. 1; Fig. 2 illustrates the screw joint in accordance with Fig. 1 in a mounted position;

Fig. 3 illustrates a holding or tightening screw in an unmounted position;

Fig. 4 illustrates a stud bolt in an unmounted position;

Figs. 5-8 are a series of figures with suggested applications of the screw/bolt joint in accordance with the invention in different applications, the various sequencies of the mounting steps partly being illustrated.

A screw joint S in accordance with Figs. 1 and la comprises a screw fastener element E in the form of a threaded knob 1 to be used in pieces of furniture. The knob, when mounted, is to act as a fitting in a piece of furniture W, such as e.g. a cupboard door or drawer front by means of which the door or front may be opened. An expander member Z forms part of the screw joint S.

The piece of furniture W is formed with a blind hole 13 into which internal threads 14 may (but do not have to) be made in advance. The blind hole 13 has a bottom 15. Instead of with a blind hole 13 the piece of furniture W may be provided with a through-hole or open-ended hole formed with an abutment shoulder, which is produced in a two-step drilling operation and which in this case is used to support the expander member Z. Adjacent its manipulat- ing head 1 the screw-fastener element E has an abutment flange 2 with a flat rear face 3. From the rear face 3 extends a threaded shank 4 formed with external threads 5. The threaded shank 4 encloses a cavity 6 which is open toward the free end 7 on the threaded shank 4 and which is provided with at least one longitudinal/axial slit 8. The embodiment in Fig. la as shown is formed with several, in this case four, axial slits 8 of this kind, which are distributed uniformly around the periphery of the threaded shank 4. The cavity 6 may have an essentially cylindrical con¬ figuration. However, in accordance with the embodiment illustrated it is conical in such a manner that it widens towards the free end 7 of the threaded shank 4. The expander member Z is of a frustro-conical configuration 9, one 10 of its end having a smaller diameter and one end 11 a larger diameter. The area of end 10 is smaller than the mouth area of the cavity at the free end 7 of the threaded shank 4. The area of end 11 is larger than or at least as large as the mouth area of the cavity 6 at the free end 7 of the threaded shank 4. Said frustro-conically con¬ figured member 9 is essentially preferably as long as the cavity 6. However, it is likewise possible to configure the expander plug with a longer or shorter length than shown in accordance with the embodiment under discussion, however naturally always within the frame of what is possible, considering that is has to maintain its expander function. The cone angle a of the expander plug 8 may correspond to the cone angle of the cavity 6. At the base 11 of the plug gripping or holding means 12 may be .provided, gripping into the bottom face 15 of the hole 13. The depth of the blind hole 13 preferably is adjusted to the length of the threaded shank 4 in such a manner that as seen in Fig. 2 the reverse side or back 3 will lie flush against the outer face 16 on the piece of furniture W when the screw fastener element E has achieved a sufficiently secure anchorage in the blind hole 13. When the threaded shank 4 is to be screwed in position the expander plug Z is previously positioned inside the cavity 6, in which initial position it cannot to any extent or not at all expand the threaded shank 4. As soon as the expander plug Z, upon further screwing-in of the threaded knob 1 into the blind hole 13, hurts against the bottom 15 in the hole 13 the expander plug Z will, during the continued advancement of the screw fastener element 1 down into the bottom hole 13, penetrate to a corresponding degree deeper and deeper into the cavity 6 and in doing so forcing/spreading-out or expanding the threaded shank 4 transversely (essentially at right angles to the direction of insertion of the threaded knob 1) so that the external threads 5 will be pressed outwards, against the wall of the hole 13. It is likewise possible to screw the threaded knob sufficiently far into the hole to allow a small space to remain between the back 3 of the knob 1 and the outer face 16 of the piece of furniture W. In this manner, should, following some time of usage of the screw joint S, the holding force thereof contrary to prediction have weakened, it is only necessary to tighten the knob 1 somewhat further, whereby the expander plug Z will continue its expansion or spreading-out of the threaded shank 4 to a corresponding extent so that once again a sturdy and secure anchorage of the threaded knob 1 to the piece of furniture W is obtained. The screw joint S is easily loosened by untightening, i.e. turning the threaded knob in the opposite direction. Owing to the conical shape of the expander plug Z the expanding or spreading force on the threaded shank 4 will cease rapidly and efficiently, whereby the latter will resume its orginal configuration and the knob 1 allowed to be easily and conviently removed from the hole 13.

Fig. 2 illustrates a screw joint in its complete, mounted position. The expansion of the threaded shank 4 could for instance extend all the way up to the mouth of the bottom hole 13 on the external face 16 on the piece of furniture W.

Fig. 3 illustrates a holding or tightening screw joint consisting on one hand of a screw or bolt E cora- prising a shank 17, a key grip head 18 and an externally threaded section 4, and on the other a domed nut H. An expander member Z is supported against the bottom 15 in a blind hole 13 of the domed nut H. Preferably, the expander member Z is formed intergrally with, i.e. formed in one piece with, the domed nut H. However, it is likewise possible, after manufacture of the domed nut and the expander plug separately, to secure in any suitable manner, for instance by means of glue, the plug in the area 20 of the bottom hole 13 of the domed nut H. Like in accordance with the embodiment described above the expander member Z could be a separate component which prior to the mounting of the holding or tightening screw joint is positioned freely inside the cavity 6 in the threaded shank 4 of the screw/bolt E whereby it will receive its support in abutment against the bottom 15 in the hole 13 only when being screwed in position therein and upon continued screwing of the screw E it will perform its function, i.e. by expanding the threaded shank 4 on the screw against the internal threads of the blind hole 13 in the domed nut H. In accordance with Fig. 4 the screw fastener element E is a stud bolt 21 comprising a threaded section 22 close to one of its ends 23 which end 23 preferably has a key grip portion 24 for engagement with a suitable torsional tool. At the opposite end 7 of the stud bolt 21 a threaded shank 4 in accordance with the invention is provided.

An intermediate cylindrical section of the stud bolt has been designated by reference 25. Together with or in¬ stead of the key grip portion 24 a key grip portion 24' could be arranged on the cylindrical section 25 of the stud bolt. In the furniture part W in which the stud bolt is intended to be mounted the blind hole 13 is formed with internal threads 14 and encloses the expander member Z which may be secured in the area 20 of the bottom 15 of the hole 13. It may also be possible to position the expander member Z, in this case in the shape of a separate plug, freely inside the cavity 6 in the threaded shank 4 when the stud bolt is to be mounted.

In Figs. 5a-5c are shown three sequences of suggested applications of the invention in a stud bolt E to be mounted in a reception hole 13 in e.g. an engine block W (see also fig. 4). The intended use of this bolt is e.g. when the internal threads of the hole 13 in the engine block has been damaged. The application of the invention to mount the bolt is in this case very simple as there is no need to produce new threads. The bolt is simply pushed down into the hole 13 together with the expander/cone plug Z, see fig. 5b. The bolt is thereafter tightened with aid of the key grip means 24' until it is anchored in a secured position, see Fig. 5c. As mentioned earlier in the description the stud bolt could be very easily dismounted whenever desired.

Figs. 6a-6c show three sequences of a suggested application of the invention in connection with a bolt E to be mounted for instance in concrete W (such as floors, walls). Several holes may for instance be drilled into a floor in order to secure an object 0, such as pallet stands, machinery, and the like in a machine shop. The object is placed above the holes, bolts are carried down into the holes together with their associated expander/- cone plugs Z in accordance with Fig. 6b. The bolts are then tightened with the aid of the key grip means 24 on each bolt until the bolts are secured, see Fig. 6c. The greatest advantage of this application is that when the bolts need to be dismantled, for instance if one wishes to move the object in the machine shop, no remaining parts of the bolt joint will be left in the flooring which other¬ wise it would have been necessary to grind away or chisel away to restore the flooring to smooth and even conditions.

Figs. 7a-7c show three sequences of suggested appli- cation of the invention in connection with a bolt E to mount an object 0 to a material W behind. Together with the expander/cone plug Z the bolt E is screwed into an aperture 13 in the material W, see Fig. 7b. The bolt is tightened until the plug grips, see Fig. 7c. The greatest advantage of this application is that a bolt joint free of vibrational disturbances is obtained without the need to use any thread securing locking arrangements, such as LOCKTITE (registered trademark) or the like that may be detrimental to the health. Figs. 8a-8c illustrate an application of the invention with the aid of a dismantable double expander E intended for mounting e.g. a wooden knob 1 on a kitchen cupboard door (Fig. 8a) and for mounting an object 0 on material W behind with the aid of domed nut H. In the first case a blind hole is drilled into the cupboard door and a blind hole 13' in the wooden knob 1. The double expander E is then mounted together with two conical plugs Zl och Z2. The knob 1 is then pressed against the door while at the same time it lies flush with the door front. The domed nut H is mounted in a similar manner, see Figs. 8b and 8c. In both cases in accordance to Fig. 8, like in all other similar applications of the invention, several important advantages are obtained in that a smooth aesthetically appealing inner face (rear face) is obtained on the material W (such as the kitchen cupboard door) because on the rear there is no need to use any kind of locking element (such as a nut) for the screw joint.

In the screw or bolt joint in accordance with the invention the cone angle of the expander member Z generally preferably lies in the area of 5°-25° and preferably amounts to approximately 12°. The expander member Z could be made from the same material as the screw fastener element E. The choice of material with respect to the discrete components in the screw joint in accordance with the subject invention offers a large number of alternative possibilities. As an example only may be mentioned that when the invention is applied in furniture the threaded knob and/or expander plug preferably are made from a wooden or plastic material.

When the screw fastener element is made from some suitable injection moulded plastics material the cavity 6 could with advantage, if not exclusively so, be given some non-cylindrical configuration, for instance a square cross-sectional shape. In this case the expander member Z preferably is not either rotationally symmetrical but is formed with a cross-sectional configuration corresponding to that of cavity 6.

The present invention is not limited to the embodi¬ ment described in the aforegoing and illustrated in the drawings but a number of modifications and alterations are possible within the framework of the inventive idea.

Claims

1. A screw/bolt joint comprising a screw fastener element screwed into a blind hole or into a hole formed with an abutment shoulder, said screw fastener element having an externally threaded shank, c h a r a c t e r ¬ i z e d in that the threaded shank (4) comprises a cavity (6) which opens towards the free shank end (7) and at least one longitudinal/axial through-slit (8) which extends towards the free shank end (7) into the cavity (6), and in that a spreader/expander member (Z) when supported against the bottom (5) of the hole (13) or against said abutment shoulder is arranged, upon screwing of said screw fastener element (E) into said hole (13), to be driven into the cavity (6) at the free end (7) of the threaded shank (4), whereby the member (Z) expands the threaded shank (4) in such a manner that the external threads (5) on the threaded shank (4) are pressed against the wall of the hole (13), essentially at right angles to the direction of introduction of said screw fastener element (E).

2. A screw/bolt joint as claimed in claim 1, c h a ¬ r a c t e r i z e d in that the threaded shank (4) is formed with a plurality of longitudinal/axial slits (8) that are distributed around the periphery of the shank (4).

3. A screw/bolt joint as claimed in claim 1, c h a ¬ r a c t e r i z e d in that the cavity (6) has a conical configuration, widening towards the free end (7) of the threaded shank (4).

4. A screw/bolt joint as claimed in claim 1, c h a ¬ r a c t e r i z e d in that the expander member (Z) has a frustro-conical shape (9), the smallest cross-sectional area of which is smaller than and the largest cross- sectional area of which exceeds the cross-sectional area of the cavity (6) at the free end (7) of the latter.

5. A screw/bolt joint as claimed in claim 1, c h a ¬ r a c t e r i z e d in that the cavity (6) and the longitudinal/axial slit(s) (8) extend over only a part of the threaded portion of the shank (4) lengthwise.

6. A screw/bolt joint as claimed at least in one of the claims 1-6, c h a r a c t e r i z e d in that the cone angle ( ) of the spreader/expander member (Z) is approximately between 5° and 25°, preferably about 12°.

7. A screw/bolt joint as claimed at least in one of claims 1-7, c h a r a c t e r i z e d in that gripping means (12) are formed on the base (11) of the spreader/- expander member (Z).

8. A screw/bolt joint as claimed in claim 1, in the form of a threaded furniture knob comprising a grip portion and a threaded shank arranged to be screwed into a blind hole or into a hole formed with an abutment shoulder, c h a r a c t e r i z e d in that the threaded shank (4) is formed with a cavity (6) which is open towards the free shank end and which is slit longitudinal- ly, and in that a spreader/expander member (Z) is arranged to be introduced into the cavity (6) and, when in its introduced position, to project beyond the free end (7) of the threaded shank (4), and said member (Z) arranged, during the screwing of said threaded knob into position, to be driven into the cavity (6) while being supported against the bottom (5) of the blind hole (13) or against said abutment shoulder (5) in the open-ended hole, during which movement the member (Z) expands the threaded shank (4) essentially at right angles to the direction of introduction of said knob (1).

9. A screw/bolt joint as claimed in claim 1, in the form of a holding or tightening screw comprising a screw bolt and a domed nut comprising a threaded shank, c h a ¬ r a c t e r i z e d in that the threaded shank (4) is formed with a cavity (6) which opens towards the free shank end (7) and which is slit longitudinally, and in that the spreader/expander member (Z) is arranged inside the domed nut (H) and engages with a cavity (6) at the free end (7) of the threaded shank (4), said member thus expanding the threaded shank (4) while being driven axially into the cavity.

10. A screw/bolt joint as claimed in claim 9, c h a r a c t e r i z e d in that the expander member (Z) is cone-shaped or has a frustro-conical shape and is formed integrally with a domed nut (H) so as to form one single component.

11. A screw/bolt joint as claimed in claim 9 or 10, c h a r a c t e r i z e d in that the expander member (Z) is fixedly mounted at the bottom (15) of the threaded hole (13) of the domed nut (H).

12. A screw/bolt joint as claimed in claim 1 in the form of a stud bolt formed at one of its ends with a threaded shank to be screwed into a blind hole or a open- ended hole formed with an abutment shoulder, and optionally, at its opposite end, with a threaded section, c h a r a c t e r i z e d in that the threaded shank (4) comprises a cavity (6) which opens towards the free shank end (7) and which is slit longitudinally, said expander member (Z) being inserted in or arranged to be inserted in said cavity so as to project beyond the free end (7) of the threaded shank (4) when assuming its inserted position, and in that, while said stud bolt is being screwed into position, said expander member (Z) abuts against the bottom (5) of the blind hole (13) or against said abutment shoulder, whereby the member (Z), while being driven axially into the cavity (6), forces the threaded shank (4) to expand essentially at right angles to the direction of introduction of said bolt.

13. A screw/bolt joint as claimed in claim 13, c h a r a c t e r i z e d in that the stud bolt is provided in the area of its threaded section (22) or in the area (25) between the section (22) and the threaded shank (4) with a key grip portion or the like (24' ) for engagement with preferably a torsional tool, such as a spanner.