EXPANSION SCREW

Abstract: An expansion screw for fixing in a cavity is threaded at the outer end of its screw portion for co-action with a nut (2) and is provided with an expandable sleeve (10) about its opposite end. The sleeve has an inner profile coacting with an outer profile of the expansion screw for expanding the sleeve when the screw (1) is withdrawn from the sleeve. The outer profile of the screw portion (1) is formed by a plurality of coaxial cones (3-6) with intermediate cylindrical junction portion (7-19), all cones and junction portions being made integral with the rest of the screw portion. The inner profile of the sleeve (10) is formed by thickened places (12), projecting inwards from the inner surface of the sleeve and corresponding to the cylindrical junction portions, and by the attenuated places (13) of the sleeve corresponding to the coaxial cones. The thickness of the sleeve is adapted to allow portions of it to be expanded by the cones into bulges (37) going round the sleeves, said bulges being intended to penetrate into the wall of the cavity for fixing the expansion screw.

Description: EXPANS I ON TECHNICAL FIELD The present invention relates to an expansion screw of the kind disclosed in the preamble to the following independent claim. BACKGROUND ART Expansion screws for inserting in holes in concrete or rock walls for retaining machine parts are well known, and are available in many different forms. Most often, an expansion screw has one, or only a few means for expanding an associated sl.eeve, but expansion screws with a plurality of expander cones are known, e.g. from the German Published Patent Applications Numbers 2138246 and 1814485. Such expansion screws with a plurality of expander cones are fntended to distribute the pressure of the sleeve over a large portion of the hole wall so that the surface pressure there will be kept to a low value. Among known expansion screws, there are those having a sleeve with a crennelated profile. However, such a sleeve gets the profile flattened when the screw is Loaded and the walls of the hole consist of a very hard material, the screw can thereby be pulled out of the hole. DISCLOSURE OF THE INVENTION As is apparent from the characterizing portion of the following inde¬ pendent patent claim, the expansion screw in accordance with the in¬ vention is characterized, inter alia, by the inner profile of the sleeve having thickened places and attenuated places. The sleeve thick¬ ness is adapted such that when it is expanded into contact with the wall of the hole, continued thightening of the screw portion expands a part of the sleeve's thickened portions into bulges going round the sleeve, these bulges penetrating into the wall of the hole and pri- marily contributing to retaining the expansion screw. Developments of the invention are disclosed in the following dependent patent claims. With the expansion screw in accordance with the invention, there is achieved that expecially its sleeve with its thickened places can withstand even very heavy pressure coming on the sleeve when the ma¬ terial in the hole walls is hard. Other development forms of the ex- pansion screw are also suitable to use when the walls of the hole con¬ sist of soft material with low strength. BRIEF DESCRIPTION OF DRAWINGS In the following, examples of expansion screws in accordance with the invention are described with reference to the appended drawing, where Figure 1 illustrates a complete expansion screw Figure 2 illustrates the development of a sleeve Figure 3 illustrates an expansion screw with different spacings between the thickened places of the sleeve and the cones of the ex¬ pansion screw, Figure 4 illustrates the same expansion screw seen towards its innei — most end. Figure 5 illustrates buckling in the attenuated portions of the sleeve Figure 6 illustrates impressions in the thickened places of the sleeve Figure 7 is a section through the same sleeve and Figure 8 illustrates an expansion bolt with an expanded sleeve. BEST MODE FOR CARRYING OUT THE INVENTION. As is apparent from Figure 1, the outer end of an expansion screw screw portion 1 is threaded to co-act with a fixing element. In the example shown, the screw portion is threaded externally for co-action with a nut 2, although it can be alternatively made with an axial hole threaded for co-action with a screw. The screw portion is made with a plurality of cones, of which one cone 3, situated at the end opposite the one which is threaded, is directed with its minor end towards the threaded portion of the screw and is terminated at its outermost end by a short cylindrical portion. Remaining cones 4, 5, 6 , three cones in the example, are double cones with the bases towards each other. Both cones in a double cone have approximately the same vertex angle, but can also have different vertex angles. In principle, all the bases of the cones have the same diameter, which is somewhat greater than the diameter of the threaded portion of the screw. Between the cones there are cylindrical junction portions 7, 8, 9 with approximately the same diameter as the threaded portion of the screw. All cones and junction portions are integral with the screw portion 1. The screw portion 1 is surrounded by a cylindrical expansion sleeve 10, extending over all the expander cones and up to the nut 2, where a - flat washer 11 is suitably placed to distribute the pressure of the nut on the sleeve end. The expanding sleeve 10, illustrated in cross section in Figure 1, is swept round the whole circumference of the screw portion with the ex¬ ception of a narrow axial slit extending along the whole length of the sleeve. The sleeve 10 is substantially cylindrical on its outside and formed with thickened places 12 projecting in from the inner surface of the sleeve and corresponding to the cylindrical junction portions 7-9 of the screw portion, the sleeve also being formed with attenuated places 13, corresponding to the expander cones 3-6. The sleeve can, for example, be produced from a strip of great extension in the trans¬ verse direction of the shown sleeve, and with said thickened places and attenuated places running along the strip. A variant of the sleeve 10 can be made with two or more slits, which separate the sleeve into several co-acting segments. As illustrated in Figure 2, illustrating a development of the sleeve 10, the sleeve is further formed with a plurality of short slits 14 in the longitudinal direction of the sleeve over the thickened places corre¬ sponding to the cylindrical junction portion ' s 7-9. The sleeve can thus be more easily expanded by the action of the cones than if the circumference of the sleeve were unbroken. The expansion bolt with sleeve is intended for insertion in a hole in a wall or floor 15, see Figure 1, and to retain an object 16, e.g. the foundation for a machine. The form of the fixing means allows it to be inserted in the drilled hole in .the floor etc 15 while the object 16 is in place above it. Otherwise, the hole in the floor etc. can be bored through the hole in the object to be fixed, while the object is in ' its intended place. When the nut 2 is tightened, the the screwed portion 1 is pulled out somewhat from the sleeve 10, the expander cones 3-6 co-acting with the thickened places 12 of the sleeve to expand the sleeve. The thickness of the sleeve is adapted such that where the expander cones 3-6 press on the thickened places 12 of the sleeve, and expand the sleeve into contact with the hole wall, the edges of the thickened places, as is shown in Figure 8, are expanded into bulges 37 going round the sleeve 10. In continued tightening of the nut, the compres- sive force of the expander cones acting on the thickened.-piaces will be so high that the bulges are pressed into the hole wall, whereby the entire expansion bolt is kept in the hole with great force. An expanding sleeve 21 in Figure 3 can alternatively be made with longer spacing between the thickened places 22 than between the expan¬ der cones 3-6 of the screw portion 1. With this embodiment of the sleeve there is gained that with movement of the screwed portion 1 outwards in the direction of the arrow, the expansion of the sleeve 21 occurs first at the innermost cone 3, thereafter at the next innermost cone 4 etc. This results in increased certainty that the pressure of the sleeve on the hole walls primarily affects the interior of the hole so that risk of the hole edges being damaged is considerably re¬ duced. As is apparent from the end view of the sleeve 21 in Figure 4, com¬ pared with Figure 3, the sleeve is clipped up at a portion towards its end, and deformed into a support 23 for the innermost end of the expansion screw. This support 23 determines more accurately the in¬ sertion of the sleeve into the hole in the wall than what the nut by itself on the threaded portion of the expansion screw can effect. All the described expanding sleeves are intended to be made with one or more deformed supports 23. When the nut 2 is screwed onto the thread of the screwed portion 1, f OMPI see Figure 1, the screw will be pulled out of the expanding sleeve 10 with consequential expansion of the sleeve. Outward pulling of the screw portion presupposes a reaction force in the form of a pressure between the outer edge of the expanding sleeve and the nut 2 with its washer 11. The expansion of the sleeve 10 is determined only by the nut 2 tightening down on the threaded end of the screwed portion 1, and independent of whether the sleeve at the beginning of the nut being tightened down has already become clamped between the cones f the expansion bolt and the hole walls or not. The nut with its washer will now also press on the mounted object 16. This is possible since one of the attenuated portions 13 of the sleeve, often a portion which does not surround any expander cone, is deformed in a way apparent from Figure 4. After the innermost portions of the sleeve 10 have been clamped to the hole walls, both the screw portion 1 and sleeve are stationary. Continued tighening of the nut 2 results in that the atte¬ nuated portion 13 of the sleeve is deformed so that the outermost end of the sleeve 10 can be moved by the nut a further small distance in towards the hole. The nut and associated washer 11 can thereby be screwed so far that sufficient pressure for retaining the object 16 can be obtained. In a further development of the invention, which is apparent from Figures 6 and the cross section in Figure 7, the expansion screw sleeve 31 is formed with indentations 32 in its thickened portions. The screw portion 33 in this case has a plurality of double cones 34, the vertex angles of which are substantially equal. The cones in this screw portion have greater extension than in the previously described screw portions, which leads to the cylindrical junction portions 35 between the cones having less diameter than the junction portions in the previously described screw portions. The sleeve 31 illustrated in the figures is made with two indentations at each cylindrical junction portion, but the sleeve can be made with some other number of inden¬ tations than two at each place. The indentations 32 have the effect of the sleeve being expanded more due to them when withdrawing the screw portion 33 than with the sleeve in the previously described expansion screws. This expansion screw described last is therefore especially well suited for use in fixings for rather loose building material where sufficiently strong fixing can be first obtained with a large expansion of the sleeve. OMPI

Claims: CLAIMS : 1 An expansion screw for fixing in a cavity, having a screw portion (1) threaded at its outer end for co-action with a fastening element, e.g. in the form of a nut (2), and which is provided with an expandable, externally substantially cylindrical sleeve (10) about its opposing portion, an inner profile of the sleeve being adapted to co- act with an outer profile of the expansion screw for expanding the sleeve at withdrawal of the screw portion (1) from the sleeve, and the outer profile of the screw portion (1) being formed by a plurality of co-axial ' cones (3-6) with intermediate cylindrical junction por- tions (7-9), all cones and junction portions being made integral with the rest of the screw portion, characterized in that the inner profile of the sleeve (10) is formed by thickened places (12) corresponding to the cylindrical junction portions and thrusting inwards from the inner surface of the sleeve, said profile also being formed by attenuated places ( 13) in the sleeve corresponding to the coaxial cones, the thickness of the sleeve being adapted for allowing a portion of the thickened places to be expanded by the cones (3-6) more than the rest of the sleeve, into bulges (37) going round the sleeve and intended for penetrating into the wall of the cavity for fixing the expansion screw. 2 An expansion screw as claimed in claim 1, characterized in that the spacing between the thickened places (12) of the sleeve (10) is greater than the spacing between the cones (3-6) of the screw portion (1). 3 An expansion screw as claimed in claim 1, characterized by at least one groove (32) on the outside of the sleeve ( 31 ) in one of its thickened places and at right angles to the longitudinal direction of the sleeve and corresponding distention on the inside of the sleeve. 4 An expansion screw as claimed in claim 1, characterized in that the sleeve (10) extends forward to the co-acting fastening element (2 ) resulting in that when the fastening element (2) is tightened the sleeve is shortened by deformation in one of its attenuated places (13 ) , 5 An expansion screw as claimed in claim 4, characterized by a plurality of short slits (14) in the longitudinal direction of the sleeve (10) across its thickened places ( 12). OMPI

Inventors: TOOMINGAS I
Applicants: ERICSSON TELEFON AB L M, TOOMINGAS I
Application year: 1980
Main classification: F16B13
IPC codes: F16B13, F16B35