Method of forming anchors

The inventive method of forming anchors comprises following steps. A rod-shaped workpiece is roll-formed by penetrating the rod-shaped workpiece with two wedge-shaped tools at two points. The two points are arranged on opposite sides and axially separated of a plane perpendicular to an axis of the rod-shaped workpiece. The two wedge-shaped tools are axially approaching to the plane while the rod-shaped workpiece is revolved around the axis. The roll-formed workpiece is separated along the plane for forming two bolts. A sleeve is applied around the anchor bolts.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

BACKGROUND OF THE INVENTION

The present invention relates to a method of forming anchors.

Expansion anchor systems are used in building construction in larger numbers. Thus, manufacturing methods of high efficiency are requested.

BRIEF SUMMARY OF THE INVENTION

The inventive method of forming anchors comprises following steps. A rod-shaped workpiece is roll-formed by penetrating the rod-shaped workpiece with two wedge-shaped tools at two points. The two points are arranged on opposite sides and axially separated of a plane perpendicular to an axis of the rod-shaped workpiece. The two wedge-shaped tools are axially approaching to the plane while the rod-shaped workpiece is revolved around the axis. Thus material of the workpiece is displaced by the wedge-shaped tools towards the plane. The roll-formed workpiece is separated along the plane for forming two bolts. A sleeve is applied around the anchor bolts.

The inventive method manages to roll-shape an increased diameter with sufficient surface quality. Surface defects by this method are shifted to about the middle of the workpiece. In the final anchor product the defects are located at the anchor's end and to which neither is under load nor limits for the setting process.

In an embodiment, a third wedge-shaped tool penetrates the rod-shaped workpiece in the plane while the two wedge-shaped tools are approaching the plane. The third wedge-shaped tool considerably helps to build a larger diameter for a conical area of a bolt.

In an embodiment, a flat-shaped tool penetrates the workpiece in an area between the two wedge-shaped tools and forms a void along the axis. The appearance of voids along the axis is usually due to bad settings of the roll-forming process. In this embodiment, the local generation of a void is, however, beneficial for an increase of the diameter. The material at the center of a conical portion of an anchor system does basically not affect the quality of an anchor.

In an embodiment, a flat-shaped tool penetrates the workpiece in an area between the two wedge-shaped tools, wherein the flat-shaped tool and the workpiece have a contact area of first dimension parallel to the axis which equals at least a half a diameter of the workpiece.

In an embodiment, a flat-shaped tool penetrates the workpiece in a contact area between the two wedge-shaped tools. The contact area of the flat-shaped tool and the workpiece has a first dimension parallel to the axis and a second dimension, which is tangential to the circumference of the workpiece. The first dimension is at least twice as large as the second dimension. The flat-shaped tool penetrates the workpiece over the whole contact area, and thus applies a force on the workpiece along the contact area. A significant part of material is going to flow in circumferential direction where the flat tool does not contact the workpiece. The workpiece will depart from its circular cross-section to a more elliptical or oval shape. The material of the non-circular shape is subdue to large stress and will relax by forming a void along the axis.

In an embodiment, a flat-shaped tool penetrates the workpiece by having a radial distance to the axis of 0.1% to 2% less than a diameter of the workpiece. The diameter of the workpiece is initial diameter or the diameter before the tool contacts the workpiece.

In an embodiment, a flat-shaped tool increases a radial distance of the flat-shaped tool to the axis increases after a void is generated.

In an embodiment, the wedge-shaped tools have inclined facets which have a first part of first inclination for tapering a portion of the workpiece to a cylindrical tapered portion and a second part of a second inclination for forming a conical portion. The second part succeeds the first part when the two wedge-shaped tools have approach closer than a predefined distance. The predefined distance defines the axial length of a cylindrical tapered portion of bolts and where the tapered portion merges into a conical portion.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, may be best understood from the following detailed description of the invention, when read with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates an expansion anchor assembly10made up of a bolt11and a sleeve-like expansion member12.

The expansion member12circumferentially encompasses or encloses a tapered portion of the bolt11. The tapered portion13is preferably of cylindrical shape. An outer diameter14of the tapered portion13is slightly smaller than an inner diameter15of the expansion member12so the expansion member12can axially slide along the tapered portion13with low friction. Axial dimensions of the tapered portion13and the expansion member12may be about equal.

The tapered portion13merges into a (frusto-) conical portion16of increasing diameter towards a leading end17of the bolt11. A cone angle16aof the conical portion16may be less than 60 degrees. A largest diameter18of the conical portion16is about equal to or slightly larger than an outer diameter19of the expansion member12. The conical portion16is designed to spread the expansion member12in radial direction while the conical portion16is pulled into the expansion member12. The expansion member12may have slits along an axial direction to reduce forces necessary to spread the expansion member12.

The bolt11has a collar20which is adjacent to the tapered portion13opposite the conical portion16. An outer diameter20′ of the collar20is significantly larger than the outer diameter14of the tapered portion13. The increase of the outer diameter is stepwise. A difference of the two outer diameters equals at least half of a wall thickness of the expansion member12.

A trailing portion21of the bolt11has means for connecting. These means may comprise at least one of an external thread22, an internal thread, a hook, an ear, etc. An intermediate portion23between the collar20and the means for connecting22may be cylindrical. A diameter23′ of the intermediate portion23is smaller than the largest diameter19of the conical portion16and may be equal to the outer diameter of the collar20.

The anchor10is installed by firstly drilling a hole of a diameter equal the largest diameter18of the conical portion16. The anchor10is punched into the hole with its leading end17pointing towards the bottom of the hole. The expansion member12contacts the wall of the hole due to their diameters. The collar20ensures that the expansion member12is forced into the hole along with the bolt11. When the bolt11is pulled out of the hole, the expansion member12stays in place due to its contact with the wall of the hole. The conical portion16is forced into the expansion member12leading to an expansion member12spread against the hole's wall.

The conical portion16needs a smooth surface such that friction of the expansion member12on the conical portion16is negligible compared to friction of the expansion member12with the hole's wall.

An exemplary method for manufacturing such an expansion anchor assembly is explained with reference to theFIGS. 2 to 5. The method makes use of at least three steps. At first a contour of the bolts11is roll-formed. Secondly, the bolts11are individualized. Afterwards, the expansion member12is applied to the bolts11.

The roll-forming process may make use of a die24which top view is illustrated inFIG. 2and cross-sections in the plane III-III inFIG. 3and in the plane IV-IV inFIG. 4. The die24has a profiled face25. The projecting structures on the face25are used as tools for shaping the contour of the bolts11. A rod-shaped workpiece26is pressed against the face25of the die24. The die's face25and the workpiece26are moved relatively to each other such that the rod-shaped workpiece26rolls along a movement direction27over the die's face25. An axis28of the workpiece26and the movement direction27are transverse. A circumference of the workpiece26repeatedly comes into contact with the die's face25and becomes structured. The die's face25may be flat and the movement direction27is linear. The die's face25may be formed on a cylindrical drum or related curved machine tools. The drum revolves around an axis perpendicular to the workpiece's axis28. The movement direction27is, hence, an angular direction. Preferably, the workpiece26is pressed against the first die24by means of a second die29which may have an equally profiled face25. The first die24and the second die29are moving in opposite directions such that the direction of relative movement of the workpiece26is equal to both dies.

The geometry of die's face25is described making reference to the intended relative orientation and relative movement direction27with respect to the workpiece26. The die's face25has a principal plane30which is parallel to a plane defined by the axis28, defining an axial direction40, and the movement direction27. In case a die's face25is formed on a drum, the principal plane30is bent to a cylindrical plane30.

The die's face25has a first side31and a second side32separated by a line parallel to the movement direction27. Both sides31,32are intended to form one bolt11each. Preferably, both sides31,32are shaped equally and are mirror symmetric with respect to the line. A center plane33is defined by the line and a direction perpendicular to the principal plane30.

A first wedge-shaped tool34is formed on the first side31and a second wedge-shaped tool35is formed on the second side32. The wedge-shaped tools34,35may have a triangular or a trapezoid-shaped cross-section perpendicular to the movement direction27. The side facets36,37of the wedge-shaped tools34,35are inclined by an angle36′ of significantly less than 90 degrees, typically in the range of 10 degrees to 60 degrees, with respect to the principal plane30. A top facet38of the wedges34,35is preferably parallel to the principal plane30and at preferably a constant height, i.e. at a constant distance to the principal plane.

The tools34,35are arranged, preferably symmetrically, on opposite sides of a center plane33. Each of the tools34,35has an inner, inclined side facet36,37which faces the other tool35,34. An axial distance39between the wedge-shaped tools34,35, i.e. their inner, inclined side facets36,37, continuously decreases along the movement direction27. The axial distance39is the distance measured in parallel to the axial direction40. The two wedge-shaped tools34,35are separated by smallest axial distance41, which is unequal to zero, at their trailing ends in movement direction27. A largest axial distance42appearing at the leading ends of the wedge-shaped tools34,35may be at least 1 cm larger than the smallest axial distance41.

The wedge-shaped tools34,35may be become wider in the axial direction40along the movement direction27. The active parts of the wedge-shaped tools34,35are the side facets36,37which displace material. The top facet38does not penetrate any further into the workpiece28or put load on the workpiece28. The wedge-shaped tools34,35may have a basically triangular shaped top facet38. In another embodiment, the top facet38has a constant width and basically the shape of a parallelogram. The wedge-shaped tools34,35may form a calibration structure at their end. The calibration structure has a constant cross-section perpendicular to the moving direction27for the length of the calibration structure.

There may be a thread forming structure43on the die's face25in each of the first and second sides31,32. The thread forming structures43are arranged on the outer rim of the die's face25, i.e. in a larger axial distance to the center plane33than the wedge-shaped tools34,35. The thread forming structures consist of a plurality of equal oblong wedge-shaped ridges44. Their longest extension is slightly inclined to the movement direction27. The ridges44are in parallel and a distance between two ridges44is less than 5 mm.

FIG. 3andFIG. 4illustrate different stages while roll-shaping the workpiece26. The initial workpiece26is a cylindrical or rod-shaped piece of steel. An endless wire of constant diameter45may be formed by drawing. The workpiece26is provided by cutting off a part of the wire at a predefined length. The length of the workpiece26is about twice the length of the bolts11to be formed. The roll-forming step elongates the workpiece26, this may be taken into consideration when selecting the initial length. The steel is preferably chosen to be ductile and suitable for cold metal forming. The steel has in preference a low content of carbon, e.g. less than one percent per weight.

The wedge-shaped tools34,35are penetrating at two points46,47into the workpiece26. The penetration depth may be at least 2% of the diameter of the workpiece and not more than 10% of the workpiece. The material formerly in the volume now occupied by the tools34,35becomes displaced. The material flows in axial direction towards the closest ends of the workpiece, thereby elongating the workpiece26while locally reducing the diameter for the tapered portion13. This is the preferred flow direction of the material as this reduces stresses due to the tools34,35most efficiently. As the workpiece26advances along the movement direction27the inner side facets36,37of the wedge-shaped tools34,35are approaching each other. Some of the displaced material is gathered between the tools34,35, thereby increasing the diameter above the initial diameter45. The die24may have a recess or opening between the two wedge-shaped tools34,35for allowing the material to pile up. The material is increased in form of two rings adjacent to the tools34,35. As the tools34,35further approach the rings meet and form a void48or fold between. Attempts to inhibit the void48or fold have failed so far. This led to the common opinion that an increase of a diameter causes a workpiece with cracks and inner deformations in the area of the increased diameter.

The wedge-shaped tools34,35may have end sections49where the inner, inclined side facets36,37are less inclined with respect to the principle plane30and the top facet38has a constant axial distance to the center plane33. This end section49forms the conical portion16. The inclination of the inner side facts36,37may be continuously reduced along the movement direction27.

The workpiece26is separated to two bolts11by a ridge51along the center plane33. The ridge51can be formed on the die24. The separation may be effected by other means, for instance, by a saw, a cutter, etc.

It turns out that the deformations of the surface appear in the area of center plane33. This area later forms the leading end of the bolt11which has a low structural importance. The surface of the conical area16, which is formed by the axially side facets36,37, however, is smooth as necessary for the installation principle of the anchor system10.

The expansion member12may be formed of a sheet of metal which is folded around the tapered part13. The expansion member12may well be made of two shells which are clamped around the tapered part13.

An alternative of the method uses a die52as illustrated inFIG. 5. Additional to the structures explained above, there is a third wedge-shaped tool53arranged along the center plane33. The third wedge-shaped tool53penetrates the workpiece26. The material displaced by the third wedge-shaped tool53contributes to an increase of the diameter18. The third wedge-shaped tool53has preferably a length of at least half the length of the two wedge-shaped tools34,35. The length is measured along the movement direction27.

An alternative of the method uses a die54as illustrated inFIG. 6. Additional to the structures explained above, there is an additional flat-shaped tool55. The flat-shaped tool55is designed to squeeze the workpiece26to an elliptical cross-section. This may be achieved by a huge width56, i.e. dimension in axial direction40, of a top facet57of the flat-shaped tool55, which is pressed against the workpiece26. The width56is selected several times larger than a length, dimension in movement direction27, of an area of contact between the top facet57and the workpiece26. The width56may be, for instance, larger than half the diameter of the workpiece26. The distance of the top facet57to the axis28is slightly smaller than a diameter23′ of the workpiece26, for instance, about a 0.1% to 2% of the diameter of the workpiece26or by about 0.01 mm to 0.5 mm. The forces applied on the flat-shaped tool55are maintained or even increased. This helps to increase the circumference due to the tangential deformation of the surface area leading to a slightly elliptical shape, even if this is counter intuitive and a reshaping to a cylindrical shape would be expected. When the elliptical shape reaches a critical relation of its longest axis to its shortest axis, the material cracks and a void48develops along the axis28. Once, the void48has a desired diameter, the forces of the flat-shaped tool55on the workpiece26are reduced, for instance, by increasing the distance of the flat-shaped tool55to the axis28. The workpiece26becomes reshaped to a cylindrical form, the void48along the axis28, however remains, thereby increasing the outer diameter.

The flat-shaped tool55may arranged between the two wedge-shaped34,35over their full length along the movement direction27. The flat-shaped tool55may finish at the end section49of the wedge-shape34,35.

The methods above were described with use of a die. Instead of a die, an individual roller for each of the wedge-shaped tools34,35, and other tools listed, may be used.