Abstract:
The production method according to the invention for creating a thread in an elongated semi-finished product comprises the following steps: shaping, especially lengthwise rolling, of at least two lengthwise grooves into a blank and lengthwise rolling of a thread into the areas circumferentially delimited by the grooves. The distance from the beds of the grooves to the axis of the blank is smaller than the distance from the root of the thread to the axis.

Description:
The present invention relates to a production method for a semi-finished product, especially an elongated semi-finished product having at least two differently profiled sections, for instance, an anchor bolt. 
     BACKGROUND 
     A thread on an anchor bolt can be created by means of cross-rolling. A cylindrical blank is inserted between two roller profiles and is then rolled along the roller profiles while being rotated around its axis. In this process, the roller profiles emboss ridges for the thread into the circumference of the blank. The high quality of the thread that can be achieved is due, among other things, to the rolling procedure and to the associated uniform radial dimensions. 
     SUMMARY OF THE INVENTION 
     A drawback is that the length of the thread is prescribed by the width of the roller profiles employed. 
     The present invention provides a method for creating a thread in an elongated semi-finished product comprises the following steps: shaping, especially lengthwise rolling, of at least two lengthwise grooves into a blank and lengthwise rolling of a thread into the areas circumferentially delimited by the grooves. The distance from the beds of the grooves to the axis of the blank is smaller than the distance from the root of the thread to the axis. The distance from the root of the thread to the axis equals half the core diameter of the thread. 
     Lengthwise rolling is actually unfavorable for creating a thread since, in contrast to cross-rolling, it does not take into account the rotating symmetry of the thread. The material that flows during the rolling procedure is not pushed uniformly along the circumference. The material can escape in an uncontrolled manner in the area of the lateral edges of the roller profiles. The grooves can collect the laterally escaping material in order to prevent the formation of burrs or other structures protruding radially into the thread. Here, weakening of the thread due to gaps formed in the thread by the grooves has to be accepted. 
     One embodiment provides that the blank is conveyed along a direction of movement. Rollers that serve to shape the thread rotate around a rotational axis perpendicular to the direction of movement. 
     One embodiment provides that, in the case of a number N of grooves, the rollers are rotated with respect to the grooves around the axis by a quotient of 180° relative to the number N. A lateral edge of a roller profile of one of the rollers can be moved in a plane with the axis and with one of the grooves. The grooves can likewise be rolled lengthwise. The rollers for the lengthwise rolling of the grooves are arranged so as to be rotated around the axis by the quotient with respect to the rollers for the thread rolling. The rollers for the thread rolling can surround the blank annularly. 
     A semi-finished product according to the invention, especially an anchor bolt, has a cylindrical section into whose circumference at least two grooves have been formed that run parallel to the axis of the cylindrical section. The areas between the grooves are shaped to form segments of a thread. One embodiment proves that flanks of the thread each adjoin two of the grooves. The percentage of the thread on the circumference of the semi-finished product can amount to at least 80%. One embodiment provides that each groove extends over the entire length of the thread. 
     One embodiment provides that another section is shaped to form a conical expansion element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description below explains the invention on the basis of embodiments and figures provided by way of an example. The figures show the following: 
         FIG. 1 : an anchor; 
         FIG. 2 : a cross section in the plane II-II through the anchor; 
         FIGS. 3 and 4 : a method step for the production of the anchor; 
         FIGS. 5 and 6 : another method step for the production of the anchor. 
     
    
    
     Unless otherwise indicated, identical elements or elements having the same function are designated with the same reference numerals in the figures. 
     DETAILED DESCRIPTION 
       FIG. 1  shows an anchor  10  that, by way of example, is configured as an expansion anchor with an anchor bolt  11  and an expansion sleeve  12 . Along the axis  13  of the anchor bolt  11 , there is an expansion element  14 , a neck  15 , a shank  16 , and a thread  17 . The expansion sleeve  12 , which can move along the anchor bolt  11 , is pre-mounted on the neck  15 . The outer diameter  18  of the expansion sleeve  12  is about the same size as the largest diameter  19  of the expansion element  14 . The anchor  10  is driven into a drilled hole having a diameter corresponding to the outer diameter  18  of the expansion sleeve  12 . A ring-shaped collar  20  between the neck  15  and the thread  17  can prevent the expansion sleeve  12  from sliding off of the anchor bolt  11 . When the anchor  10  is tightened against the substrate, for example, by means of a nut  21 , the expansion element  14  is pulled into the expansion sleeve  12  and the expansion sleeve  12  is firmly clamped onto a side wall of the drilled hole. 
     The thread  17  is interrupted by several grooves  30  that run parallel to the axis  13 . The grooves  30  are preferably uniformly distributed around the axis  13 , for instance, four grooves at intervals of 90°. The grooves  30  preferably extend along the entire length of the thread  17 . Therefore, the single-flight thread  17  is made up of several segments  31 . Each of the segments  31  has the characteristic properties of a thread  17  such as, for instance, a rated diameter  32 , a core diameter  33 , a pitch angle  34 , a flank angle  35  and a thread lead  36 . The segments  31  are preferably configured in the form of a V-thread and they form the flanks of the thread. Preferably, the characteristic properties of all segments  31  are identical. The flank angle amounts to, for instance, 60°. The pitch angle  34  is preferably between 2° and 5°. The segments  31  only surround a fraction of the circumference; in case of the, for example, four grooves  30 , between 75° and 85°. 
     The groove bed  37  of the groove  30  is preferably at a constant distance  38  from the axis  13 . Half of the core diameter  33  of the thread  17  is preferably greater than the distance  38 , that is to say, the thread root  39  is located further away from the axis  13  than the grooves  37  are. The grooves  30  are shaped into the anchor bolt  11  at a greater depth than the thread  17 . 
     The width of the grooves  30  in the circumferential direction  41  is considerably smaller than the width  40  of the segments  31 . Preferably, the segments  31  take up a portion of more than 80% (approximately 300°) of the total circumference. The boundaries of the segments  31  can be defined, for instance, as the points where the trailing flank  42  is only at a distance from the thread root  39  over half of its maximum distance (equal to one-fourth of the difference between the rated diameter  32  and the core diameter  33 ). 
     By way of an example,  FIGS. 4 to 6  illustrate a production method for the anchor bolt  11 .  FIGS. 4 and 6  depict the cross sections through the anchor bolt  11  and a production tool in the planes IV-IV and VI-VI, respectively. A blank  50  is, for instance, a cylindrical piece of wire. The unshaped cross section of the wire is preferably circular. The diameter  51  of the wire is constant and harmonized with the thread  17 , at least in a section  52  for the thread  17 . For example, the diameter  51  of the wire can be the same as the flank diameter of the thread  17 , that is to say, approximately the mean value of the outer and core diameter of the thread  17 . The blank  50  provided by way of an example has already been shaped to form the expansion element  14  and the neck  15  in a section  53  by means of the rolling procedure. As an alternative, the entire blank  50  can have one diameter, especially if the thread  17  is supposed to be created along the entire blank  50 . 
     The blank  50  is fed to a first roller stand  54  that rolls the grooves  30  into the section  52 . The first roller stand  54  has several rollers  55  between which the blank  50  passes. The rollers  55  are rotated around their axes  56 , which are oriented perpendicular to the direction of movement  57  of the blank  50 . Each one of the rollers  55  embosses a groove  30  into the blank  50  along the axis  13 . The roller stand  54  shown has four rollers  55  that grip the entire circumference of the blank  50 . An alternative embodiment has two or more pairs of opposite rollers and the orientation of adjacent pairs with respect to the axis  13  differs. 
     The blank  50  provided with the grooves  30  is conveyed to a second roller stand  58  that creates the thread  17 . The second roller stand  58  has several rollers  59  between which the blank  50  passes. The rollers  59  are rotated around their axes  60 , which are oriented perpendicular to the direction of movement  57  of the blank  50 . Each of the rollers  59  embosses segments  31  of the thread into the blank  50  along the axis  13 . The advantageously configured roller stand  58  surrounds the circumference of the blank  50 . The number of rollers  59  corresponds to the number of previously embossed grooves  30 . Each of the rollers  59  completely covers an angular section  61  located between two grooves  30 . Each lateral edge  62  of the roller profiles is in a plane with one of the grooves  30 . The roller profile preferably does not touch the groove bed  37 . The groove bed  37  can be partially filled by flowing material during the rolling procedure. 
     The rollers  59  of the second roller stand  58  are arranged so as to be rotated around the axis  13  by 45° with respect to the rollers  55  of the first roller stand  54 . The angle of rotation corresponds to the quotient of 180° and the number of grooves  30 . 
     The blank  50  can be fed through the rollers in one direction of movement. As an alternative, the blank  50  can be preferably pushed between the rollers and then removed from the rollers opposite to the direction of movement.