US3883178A

US3883178A - Hydraulically actuated apparatus for the mechanical splitting of stones

Info

Publication number: US3883178A
Application number: US370470A
Authority: US
Inventors: Helmut Darda
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-06-20
Filing date: 1973-06-15
Publication date: 1975-05-13
Anticipated expiration: 1992-05-13
Also published as: DE2229940C2; ZA733993B; FR2189627A1; FR2189627B1; GB1411504A; CA985313A; CH568140A5; SE401706B; JPS5343121B2; ES416051A1; JPS4963602A; IT985681B; DE2229940B1

Abstract

An apparatus for the mechanical splitting of stone, comprising a cylinder block having a longitudinally movable hydraulicallyactuated piston located therein, adapted to be operatively engaged with, through a slide wedge connected with a piston rod fastened to the piston, sideways movable pressure wedges insertable into boreholes and preferably connected with the apparatus through an intermediate member, and being operative in correspondence with the slope of the facets of the slide wedge.

Description

United States Patent Darda [451 May 13, 1975 HYDRAULICALLY ACTUATED APPARATUS FOR THE MECHANICAL SPLITTING OF STONES Helmut Darda, lm Tal/Brd, 7712 Blumberg, Germany Filed: June 15, 1973 Appl. No.: 370,470

Inventor:

Foreign Application Priority Data June 20, 1972 Germany 2229940 US. Cl 299/22; 299/23 Int. Cl. E2lc 37/04 Field of Search 299/23, 22; 254/104; 144/193 A References Cited UNITED STATES PATENTS 12/1968 Darda 299/23 X 3,743,357 7/1973 Flechter 299/22 Primary Examiner-Ernest R. Purser Assistant Examiner-William F. Pate, Ill

[57] ABSTRACT An apparatus for the mechanical splitting of stone, comprising a cylinder block having a longitudinally movable hydraulically-actuated piston located therein, adapted to be operatively engaged with, through a slide wedge connected with a piston rod fastened to the piston, sideways movable pressure wedges insertable into boreholes and preferably connected with the apparatus through an intermediate member, and being operative in correspondence with the slope of the facets of the slide wedge.

26 Claims, 17 Drawing Figures HYDRAULICALLY ACTUATED APPARATUS FOR THE MECHANICAL SPLITTING OF STONES FIELD OF THE INVENTION The present invention relates to an apparatus for the mechanical splitting of stone, comprising a cylinder block having a longitudinally movable hydraulicallyactuated piston located therein, adapted to be operatively engaged with, through a slide wedge connected with a piston rod fastened to the piston, sideways movable pressure wedges insertable into boreholes and preferably connected with the apparatus through an intermediate member, and being operative in correspondence with the slope of the facets of the slide wedge.

The pressure wedges are connected either directly with the cylinder block, or indirectly connected with the apparatus through an intermediate member which is detachably mounted on the cylinder block.

With that type of shaped, relatively handy apparatus, there may be produced forces to the extent of 300 tons or more so that thereby stone blocks may be split or removed without the need for explosive materials. Since the portions insert into the bore holes, consisting of the pressure wedges and the slide wedge, notwithstanding the large surface pressure, have cross-sections to the overall extend of only 40 mm, only relatively small bore holes are needed.

DISCUSSION OF THE PRIOR ART Stone splitting apparatus of this type have shown themselves to be extremely useful in practice. For example, they may be utilized in sotne breaking, stone working operations, mountain works, as well as for stone breaking operations at high-level and subterranean construction. These apparatus are so constructed that their relatively narrow bore hole inserts, the suspension of the pressure wedges, and the piston rod which is connected with the slide wedge, may absorb bending loads within predetermined limits.

Certain difficulties may, however, occur when the loading on both pressure wedges is completely different so that the cylinder block, which is rigidly connected with the pressure wedges, deflects with respect to insert in the bore hole. For example, such kinds of asymmetrical loads occur when stone is removed in proximity to only one of the pressure wedges, while the stone adjacent the other pressure wedge has not yet been fractured. In that case, the cylinder block will deflect in view of the asymmetrical load or also through the stone blocks being raised in a direction towards the still unmoved stone. The above referred to stone splitting apparatus are so constructed to permit a deflection angle of up to between the cylinder block and the bore hole insert. However, at greater inclines the pressure medium supply to these apparatus must be interrupted, and a further stone splitting apparatus must be inserted proximate to the bore hole, although the first stone splitting apparatus still provides energy reserves.

By means of the present invention, the known stone splitting apparatus is so modified whereby, also during asymmetrical loading of the pressure wedges, dangerous deflection of the cylinder block in contrast with the insertion is effectively prevented.

SUMMARY OF THE INVENTION This task, in accordance with the invention, is solved in that the pressure wedges are mounted in an axially displaceable manner on the cylinder block or, respectively, on the intermediate connecting member.

Through this measure there is effectively prevented that one-sided loads occur within the cylinder block, or, in effect, in the region of the intermediate member of the apparatus, which in present apparatus are frequently the result of asymmetrical stone displacements which, for example, are caused by a one-sided fracture of the stone in the bore hole plane. It is known that with this type of an apparatus including a double-sidedly effective wedges, the insert members, such as the pressure wedges, may be held together by a longitudinally displaceable retaining ring. However, in this known apparatus, the insert members are not axially displaceable relative to each other. The foregoing also applies to other previously known stone splitting apparatus in which the pressure wedges are generally rigidly supported on the cylinder block or, in essence, the dashpot.

In apparatus according to that type, in contrast with the inventive apparatus, there is no way to prevent the exertion of dangerous bending forces on the cylinder block.

In a first embodiment according to the invention, the pressure wedges are radially and axially displaceably supported through pull and guide rods which are rigidly interconnected with the cylinder block, so as to be supported with their outer transverse surfaces against a member interconnecting the pull rods.

In order to provide for the secure support of the pressure wedges, return springs may be positioned between these and the intermediate member or, respectively, the cylinder block. It may also be advantageous to secure the pressure wedges in their normal postion, for example, by means of spring-loaded pins.

In a second and third exemplary embodiment, the basic inventive concept is carried out by having the pressure wedge connected with the cylinder block or, respectively, the intermediate member, through a rocker which is oscillatable in an axial direction. Thus, in this construction the unequal loading of the pressure wedges is balanced by the oscillations of the rocker. In this instance, the pressure wedges may rest with their shoulder-shaped head portions in a positive relation ship against concavely curved support surfaces of the rocker. When the rocker, as further proposed, comprises a rotary member rotatably mounted on the intermediate member and extending perpendicular to the axis of the slide wedge axis on the intermediate member and which, in order to form support surfaces in cluding thereagainst diametrically opposed cutout portions, it is recommended that also the surfaces of the cutout portions opposite to the support surfaces of the rocker be concavely curved in oppostion to the surfaces of the cutouts, so that the upper planar surfaces of the head portions may be similarly supported thereon. The radius of curvature of these support surfaces should increase from outwards inwardly, so that upon increasing tensile forces, for a reduction of the surface pressure there is an increase in the contact surfaces between the planar support surfaces of the head portion and the curved support surfaces of the rocker.

In the last-mentioned embodiment, the pressure wedges are suspended differently than in the abovementioned construction, by means of pins extending in parallel with the rocker axis parallel extending pins,

and which project through elongated eyelets of the pressure wedge head portions.

A particular advantage of the inventive stone splitting apparatus lies in that the axially displaceable pressure Wedges, for example, in the event of repairs may be exchanged without difficulty and replaced by new pressure wedges. Furthermore, these advantageous properties may also be of use when the strength of the utilized pressure wedge is insufficient so as to facilitate complete fracturing of the rock. In order to obtain the foregoing, subsequent to the previous splitting step, there may be employed a stronger dimensioned wedge.

While the inventively proposed measures prevent that the cylinder block with respect to the pressure wedges is excessively deflected by the influence of asymmetrical loads, the invention also provides an arrangement in which the axis of the cylinder block preknowingly subtends an angle with the axis of the slide wedge or, in essence with the insert. That type of arrangement is provided, for example, when the stone splitting apparatus is to raise stone blocks lying on the ground, in which the pressure wedges are slid below the stone blocks which lie on the ground, and the cylinder block rests with its outer shell surface on the ground surface. For this application, it is desirable to employ the most flexible, flat-shaped pressure wedges, which nevertheless permit for exertion of an appreciable cross lift.

In a further construction of the invention there are provided pressure wedges in the form of relatively thin, elastic steel bands, which may also be employed in connection with other types of stone splitting apparatus. In order to obtain the largest possible cross lifting effect, in accordance with a further proposal persuant to the invention, the pressure wedges in the forward direction of movement thereof may be extended by means of an inserted slide wedge, and be provided in the region of extension with shear-type interengaging grooves and springs, whose mutually facing lateral surfaces form slide surfaces for the wedge slide surfaces. If the pressure wedges, as proposed, are formed of elastic steel bands, in this arrangement one of the two pressure wedges in the region of the extension thereof is shaped in the form of a fork, whose both arms are interconnected at the lower end thereof by means of a transverse member, and in which the other pressure wedge includes a smaller arm extending between both fork arms.

For all stone splitting apparatuses it is recommended that the pressure wedges and/or the slide wedge in the region of their slide surfaces be reinforced by a frictionresistant layer, which is preferably constituted of a thereon welded hard metal.

BRIEF DESCRIPTION OF THE DRAWINGS The subject of the invention, upon consideration of the preferred illustrated embodiments is now more thoroughly described, having particular reference to the accompanying drawings, in which;

FIG. 1 is a longitudinal section of the slide wedge and pressure wedge arrangement of a first embodiment of a stone splitting apparatus in accordance with the present invention;

FIG. 2 is a tranverse section along line VIVI in FIG. 1;

FIG. 3 is a longitudinal section along line VIIVII in FIG. 1;

FIG. 4 is a longitudinal section of a second embodiment of the stone splitting apparatus in the region of the slip wedge and pressure wedge arrangement thereof;

FIGS. 5, 6 and 7 are each transverse sections taken along, respectively, lines IXIX, XX and XIXI in FIG. 4;

FIG. 8 is a longitudinal section of the arrangement of FIG. 4 illustrated with an asymmetrically loaded pressure wedges;

FIG. 9 is a longitudinal section of a third embodiment of a stone splitting apparatus in the region of the slip wedge and pressure wedge arrangement thereof; FIGS. 10 and 11 are transverse sections along, respectively, lines XIV-XIV and XVXV in FIG. 9;

FIG. 12 is a longitudinal section along line XVI- XVI in FIG. 9;

FIG. 13 is a longitudinal section of a fourth embodiment of a stone splitting apparatus in the region of the slip wedge and pressure wedge arrangement thereof;

FIGS. l4, l5 and 16 are transverse sections taken along, respectively, lines XVIII-XVIII, XIXXIX and XX-XX in FIG. 13; and

FIG. 17 is a longitudinal section along line XXI- XXI in FIG. 13.

DETAILED DESCRIPTION The slide wedge and pressure wedge arrangements shown in FIGS. 1 through 17 of the drawings are suitable, for example, for use with the stone splitting apparatus described in German Published Specification No. 1,249,194.

A slide wedge designated by reference numeral 11 is connected at its inner end with the piston rod (not shown) of a suitable hydraulically actuated piston (not shown). By means of this piston, the slide wedge 11 is adapted to be moved forwardly, and wherein the piston rod (not shown) is controlled by a guide conduit 12 within an intermediate or connector member 13, which is mounted on a cylinder block (not shown). The intermediate member 13 supports two

pressure wedges

14 and 15, supporting on the hardened metal reinforced slide surfaces thereof, the similarly hardened metal layerreinforced sliding surfaces of the slide wedge.

In the first embodiment according to FIGS. 1 through 3, both of the

pressure wedges

14 and 15, under the operative effect of the slide wedge 1 1, are axially movable with respect to the intermediate member 13 having the guide conduit 12 in oppostion to the force of a return spring. The pressure wedges include at their ends which are located within intermediate member 13, projecting or pivot-like or cup-shaped head portions 14b and 15b, and retained in their extending positions by pins 14c and 15, which are themselves subjected to the action of springs 14c and l5e which are pretensioned by set screws 1411 and 15h. Furthermore, the head portions 14b and 15b are supported against an elastic rubber disk 17b which is positioned along the lower surface of the dashpot collar. By means of this construction, the pulling forces of two pull rods 19 acting against the pressure forces of the slide wedges are absorbed so as to concurrently serve for guiding the pressure wedges l4 and 15, which are supported at their forward lateral surfaces on a connecting member 19a of both of the pull rods. The pull rods 19 lie at their upper ends by means of shoulder-shaped head portions 19b thereon, on the inner rim 13a of the intermediate member col- Iar, in view of which a ringe 18 located below the guide conduit is secured against axial displacement.

In this arrangement the two pressure wedges l4 and are positioned pursuant to the pulling forces acting thereon, without their movement being transmitted to the cylinder block.

The following described embodiments according to FIGS. 4 through 17 are somewhat differently formed, in which the pressure wedges are suspended in rockertype arranged rotary bodies.

In the embodiment according to FIG. 4 through 8, there is provided within the intermediate or connecting member 23 a rotary member 29 oscillable about an axis extending perpendicular to the plane of the drawing, and having radially extending cutout portions 29a in which the

pressure wedges

24 and 25 are suspended through their shoulder-shaped constructed

head portions

24b and 25b. As described with reference to the previous arrangement, these

pressure wedges

24 and 25 are also adapted to be moved apart by means of axially outwardly displaceable slide Wedge 21, in which in this drawing the partly ascertainable piston rods 20 are controlled by the guide conduit 22. In order to bring or maintain the pressure wedges 24 and in their extended positions, there are provided pressure pins 240 and 25, which under the influence of compression springs 24e and 25e located in bores 22a are forced into contact with the upper surface of

head portions

24b and 25b.

Whereas the

head portions

24b and 25b include planar support surfaces on their lower as well as their upper sides, the support surfaces 29b formed by cutout portions 290 are concavely curved. Corresponding curvature is imparted to the oppositely located surfaces 29c, against which the

head portions

24b and 25b are supported upon rotation of the rotary member 29, as may be ascertained in connection with FIG. 8 of the drawings. Suitably, the radius of curvature of these support surfaces 29b and 29c increases in a radial direction from outwardly inwardly, whereby the effective contact surfaces between the head portions and the rotary member increases with increasing tension forces, so as to lead to an equalization of the surface pressure in the region of support.

The arrangement according to FIG. 8 finally illustrates the operative effect of the spring-loaded pins 24c and 250 which at all times move the pressure wedges into their outermost extended position.

The

pressure wedges

24 and 25 may also be exchanged, or, in effect, replaced. For this purpose, at its lower end the intermediate member 23 is provided with slotted cutouts 23a dimensioned to correspond with the pressure wedges or, in essence, their head portions, and through which the upper ends of the wedges may be inserted after the covering cap 27 with the rubber disc 27a has been removed. In the presently described exemplary embodiment, the rubber disc also serves for the centering of

pressure wedges

24 and 25.

In order to obtain the largest possible cross lift, the

pressure wedges

24 and 25 may be provided at their lower ends with shear-like interengaging grooves and springs, as has been shown in the transverse sections pursuant to FIGS. 5, 6 and 7.

Through FIGS. 4 and 8 finally the process is clearly shown, which frequently occurs during the splitting of stone, and which in present stone splitting apparatuses leads to the deflection of the cylinder. block with respect to insertion into the bore hole. According to FIG. 4 this insert, consisting of the

pressure wedges

24 and 25 and the slide wedge 21, is inserted in the pre-bored hole B. Upon forward movement of wedge 21, the

pressure wedges

24 and 25 are separated to the extent so as to separate a portion G1 from the stone block G. Upon further forward movement of the wedge 21, the portion G1 is upwardly deflected and thereby takes the pressure wedge 25 along. Normally this generally leads to that the pressure cylinder in accordance with the arrangement of FIG. 8 is deflected toward the left. This deflection is, in accordance with the inventive proposal prevented, in that the axially displaceable pressure wedge 25 follows this movement without transmitting thereof to the cylinder block.

A modification of the apparatus according to FIGS. 4 through 8 is shown in FIGS. 9 through 12.

As in the embodiment of FIGS. 4 through 8, the rotary member consists of two mirror-image formed and supported discs 39, which are connected to each other through pins 39d. Corresponding to rotary member 29 in the embodiment of FIGS. 4 through 8, these discs 39 are also provided with cutout portions 39a, which form the support and opposite support surfaces 39b and 390 for the head portions 34b and 35b of the

pressure wedges

34 and 35. As soon as the lower support surfaces 39b, as well as the thereon supported surfaces of the head portions 34b and 35b, fall in the direction of the rotational axis from inwardly outwardly, as shown in FIG. 12. This will prevent, during exertion of a large tensile force on the

pressure wedges

34 and 35, that the discs 39 will deflect outwardly and an excessively large compressive force to be exerted on the dashpot 33.

Within the intermediary or connecting member 33, the discs 39 are provided with support rings 396*, which are rotatably positioned in the dashpot 33 under the intermediary of balls 39f located in annular grooves 33a in the rings.

The remaining portions of the construction of this rocker arrangement generally correspond to the arrangement of FIGS. 4 through 8. The forward movable slide wedge 31, actuated by means of piston rod 30 which is located within guide conduit 32, is positioned between both discs 39 and drives apart the

pressure wedges

34 and 35 introduced between stone portions G1 and G2.

In this apparatus also the

pressure wedges

34 and 35 are adapted to be removed from the intermediary member through side slits, not further detailed herein, when the protecting cap 37 together with the rubberformed cover disc 37a located on the lower surface thereof, have been removed.

In this embodiment there are utilized particularly

flexible pressure wedges

34 and 35 formed of relatively small steel bands, which are connected at their lower ends on the one side with each other by means of forked-shaped arms 34f interconnected through a member 34g, and in shear-like interengagement through a center arm 35f. This type of insert may be introduced into extremely small splits, or inserted below stone portions lying on the ground surface.

The last embodiment, according to FIGS. 13 through 17, is illustrative of a further modification of the rocker arrangement. In this apparatus the rotary member similarly consists of two mirror-image shaped and supported circular discs 49 which are rotatably supported in the intermediary member 43 through the intermediary of balls 49]". Both discs 49 again are connected to each other by means of pin 49d and 49g, the last of which extend through elongate eyelets 44g and 45g at the inner ends of the head portions 44b and 45b of the

pressure wedges

44 and 45. The pins 49g may be removed outwardly through side apertures 43b, whereby the

pressure wedges

44 and 45 may be pulled down and outwardly for replacement purposes. The rubber disc 47 located against the collar 43a of the intermediary member here again provides for the sealing of the interior of the intermediary member. The latter is connected with a housing portion 42 of the cylinder block (not shown) by means of screws 46, within which there is introduced the guide conduit 42a for the piston rod 40. The piston rod similarly is connected with the slide wedge 41, which is slid through between both rocker discs 49, and operatively engages the

pressure wedges

44 and 45 with its slide surfaces.

As in the apparatus of FIGS. 4 through 8, compression springs 44e and 45e located in the guide conduit 42a serve to operatively effect, through sleeve-like pushers 44c and 45c, the pins 49d, causing return motion of the rocker 49 and thereby the motion of the connected to the

latter pressure wedges

44 and 45 into their outermost extended position.

As may be ascertained from the sections of FIGS. 14 through 16, also in this embodiment the

pressure wedges

44 and 45 are provided with shear-type interengaging springs and

grooves

44f and 45 f, which facilitate an extensive separation of the wedges through the extensively forwardly displaced wedge 41.

While there has been shown what is considered to be the preferred embodiment of the invention, it will be obvious that modifications may be made which come within the scope of the disclosure of the specification.

What is claimed is:

1. In an apparatus for the mechanical splitting and fracturing of stone, comprising a cylinder block; a hydraulically actuatable piston longitudinally movable in said cylinder block; a piston rod connected to said piston; a slide wedge fastened to said piston rod; an intermediate member on said cylinder block; and pressure wedges adapted to be set into boreholes in said stone, said intermediate member forming a mechanical connection between said apparatus and said pressure wedges, said pressure wedges being sideways movable at a deflection conforming to the slope of said slide wedge, the improvement comprising; prestressed return spring means; said pressure wedges being connected to said intermediate member so as to be axially displaceable relative thereto in opposition to the force of said return spring means.

2. Apparatus as claimed in claim 1, comprising at least two pull and guide rods rigidly fastened to said intermediate member; a member interconnecting said rods, said pressure wedges being radially and axially movable between said rods, and said pressure wedges having external lateral surfaces supported on said rod interconnecting member.

3. Apparatus as claimed in claim 1, said return spring means being interposed between said pressure wedges and said intermediate member.

4. Apparatus as claimed in claim 1, comprising spring-loaded pin means adapted to bias said pressure wedges into their outermost extended positions.

5. Apparatus as claimed in claim 2, said slide wedge, pressure wedges and pull and guide rods forming a bore hole insert having a generally circular cross-section.

6. Apparatus as claimed in claim 1, comprising rocker means in said intermediate member adapted to be oscillated in an axial direction, said pressure wedges being operatively connected to said rocker means.

7. Apparatus as claimed in claim 6, said rocker means having two concavely curved support surfaces; said pressure wedges including head portions having lower planar surfaces in compressive contact with said curved surfaces.

8. Apparatus as claimed in claim 7, said rocker means comprising a rotary member positioned on said intermediate member and rotatable perpendicular to the axis of said slide wedge, said rotary member having two diametrically opposed cutout portions forming support surfaces, said head portions of the pressure wedges being suspended within said cutout portions.

9. Apparatus as claimed in claim 8, the support surfaces of said rocker means opposite said cutout surfaces being equally concavely curved, and the adjacent surfaces of said head portions being of planar form.

10. Apparatus as claimed in claim 9, said support surfaces and the opposed surfaces of the cutout portions in said rocker means having radii of curvature from outwards inwardly.

11. Apparatus as claimed in claim 6, comprising return spring means operatively connected to said rocker means.

12. Apparatus as claimed in claim 11, comprising spring-actuated return pin means acting on said head portions.

13. Apparatus as claimed in claim 6, said rocker means comprising on both sides thereof support discs and rings, said discs and rings being rotatably supported in complementary supports in said intermediate member.

14. Apparatus as claimed in claim 13, comprising bearing means being interposed between said support discs and rings of said rocker means and said supports in said intermediate member.

15. Apparatus as claimed in claim 8, said rotary member comprising a pair of circular discs having cutout portions; and pin means associated with said discs forming supports for said pressure wedge head portions.

16. Apparatus as claimed in claim 15, said supports and correspondingly the support surfaces of said head portions being in outwardly inclined depending relationship in the direction of the axis of said rocker means.

17. Apparatus as claimed in claim 6, said intermediate member comprising cutouts extending perpendicular to the axis of said rocker means, said pressure wedges and the head portions thereof being adapted to extend through said cutouts for replacement of said pressure wedges.

18. Apparatus as claimed in claim 17, comprising protective cap means covering said cutouts.

19. Apparatus as claimed in claim 6, said rocker means comprising a pair of circular discs; pin means interconnecting said discs extending parallel to the axis of said rocker means; said head portions of the pressure wedges having elongate apertured eyelets, said pin means extending through said eyelets for supporting said pressure wedges.

20. Apparatus as claimed in claim 19, said pin means supporting said pressure wedges being detachable, said intermediate member having apertures in the height of said pin means.

21. Apparatus as claimed in claim 1, said axially movable pressure wedges being replaceably mounted for exchange 'with differently dimensioned pressure wedges.

22. Apparatus as claimed in claim 2, comprising an elastic disc having central aperture being located on the under surface of said intermediate member, said pressure wedges, slide wedge and pull and guide rods extending through said aperture, said pressure wedges being sealingly positioned thereagainst.

23. Apparatus as claimed in claim 1, said pressure wedges being extended beyond said intermediately positioned slide wedge, and including shear-like interen- 10 gaging grooves and springs in the region of extension having surfaces forming slide surfaces for the slide surfaces of said slide wedge.

24. Apparatus as claimed in claim 23, said pressure wedges being'formed of relatively thin, elastic steel bands.

25. Apparatus as claimed in claim 23, one of said pressure wedges in the region of extension thereof being a two-armed fork; a transverse member connecting said arms; and said other pressure wedge having a smaller arm portion extending between said fork arms.

26. Apparatus as claimed in claim 1, said pressure wedges and said slide wedge being covered in at least the region of their contacting slide surfaces with a friction-resistant layer of hardened metal.

Claims

1. In an apparatus for the mechanical splitting and fracturing of stone, comprising a cylinder block; a hydraulically actuatable piston longitudinally movable in said cylinder block; a piston rod connected to said piston; a slide wedge fastened to said piston rod; an intermediate member on said cylinder block; and pressure wedges adapted to be set into bore holes in said stone, said intermediate member forming a mechanical connection between said apparatus and said pressure wedges, said pressure wedges being sideways movable at a deflection conforming to the slope of said slide wedge, the improvement comprising; prestressed return spring means; said pressure wedges being connected to said intermediate member so as to be axially displaceable Relative thereto in opposition to the force of said return spring means.

21. Apparatus as claimed in claim 1, said axially movable pressure wedges being replaceably mounted for exchange with differently dimensioned pressure wedges.

23. Apparatus as claimed in claim 1, said pressure wedges being extended beyond said intermediately positioned slide wedge, and including shear-like interengaging grooves and springs in the region of extension having surfaces forming slide surfaces for the slide surfaces of said slide wedge.

24. Apparatus as claimed in claim 23, said pressure wedges being formed of relatively thin, elastic steel bands.