IL41889A - Method of producing concrete reinforcing steel rods provided with fins by rolling - Google Patents

Description

Method of produc ing : concrete reinforcing steel rods provided with fins by rolling KOEF INDUSTRIE UND HANDEL GMBH & CO. , C:- 39964 This invention relates to a method of producing a cold-shaped concrete reinforcing bar in which a steel bar produced by hot rolling is firstly made into a triangle-like cross-sectional shape and the shaped bar is provided with inclined transverse fins by means of cold shaping rolls which engage the corners of the triangular bar over the entire length thereof, the beginning and the end of the transverse fins merging smoothly in the surface of the triangular bar so that the projection of the envelopes in the axial direction of the bar is approximately circular.

Methods of this kind are known from German Offenlegungsschrift No. 1 777 052. In these methods, a breakdown pass is performed to impart a triangular cross-sectional shape to a smooth round bar, uniform compacting of the material being strived for, and then rows of fins are rolled at the corners of the triangular cross-section, in a fin pass. When, in accordance vith the method described in the above-mentioned Offenlegungsschrift, a smooth round bar is shaped into a triangular cross-sectional configuration in the breakdown pass, this results on the one hand in relatively substantial consolidation of the material, so that only steels of low strength can be used as the stock material, and on the other hand the spacing of the rows of fins in the fin pass becomes relatively large. Due to the substantial consolidation in the breakdown pass, the possibility of variations in shape in further shaping operations is reduced, and thus the fin height which can be achieved is severely limited. In connection with the large spacing between the rows of fins, it is often difficult to achieve the necessary relative fin area.

It is known from German Auslegeschrift No. 1 609 605 for a calibrated round bar to be flattened at three sides over a width of from about 10 to 30$ of the bar diameter, before the fins are formed by rolling between those regions. This method does in fact permit a finned srreel ^ bar to be produced, the spacing between the rows of fins of which is sufficiently small, but here too the fin height which can be achieved in the fin pass by the admissible shaping, within the limitations of material, does not satisfy all requirements.

Another method of cold drawing of steel wire is known from British patent specification No. 854,492. According to that specification grooves are formed by rolls on a wire of round cross-section in the cold state. Only after this operation does the wire take on triangular shape. This leads to the disadvantage that material from the areas where the rolls are applied is being squeezed into the spaces between the rolls. The material cannot flow freely at the edges of the rolls but is accumulated, leading to brittle areas of the material which results in notch sensitivity of the wire.

The invention is based on the problem of making it possible to achieve, with the same reduction in cross-section in the fin pass as in the known methods, a greater fin height, or, ith a comparatively smaller the same fin height, reduction in cross-section,/so that steels of higher strength can also be used as the stock starting materials. ' It should also be possible for the spacing between the rows of fins to be kept small, so as to provide a high relative fin area.

Starting from a method of the kind first mentioned above, this problem is solved in accordance with the invention in that the cross-section of the bar in the first cold-shaping operation (breakdown pass) is shaped into a triangle with curved sides, that the ratio of the radius of curvature r^ of the curved sides of the triangle to the radius r^ of the inscribed circle of said triangle _ i = 1.6 to 2.4, preferably: 1.7 with reductions in cross- φ rvi " section of about 18 in the fin pass, and : 2.0 with reductions in cross- section of about 24 in the fin pass, and that the radius r^ of the inscribed circle of said triangle is at most equal to the spacing kR of the centre point of the cross -section from the edge of the fin pass between the roll openings of the fin rolls.

Usually rV2 will be in the range of 1.6 to 2.0, rvi preferably 1.7.

The invention is based on the recognition that, in contrast to the view expressed in German Auslegeschrif t No. 1 609 6θ5, the material does not flow into the recesses in the rolls -when rolling the fins, but that at the point at which the fin is produced, it remains, but in general - a - flows towards the centre axis of the bar. Taking this recognition, the inventors have sought a cross-sectional shape in the breakdown pass, which, with a given percentage shaping in the fin pass, gives the maximum theoretical fin height and, dependent thereon, also the maximum actual fin height. The shape arrived at makes it possible, by means of a smaller degree of shaping, to produce fins of the same height as in the known methods, and thereby makes it possible to use higher-strength steels as the raw material. It was also found that the special cross-sectional shape permits a greater tolerance range as regards the dimensions of the starting material, so that in general an equalising pass is unnecessary.

The invention is described in greater detail by means of an embodiment with reference to two figures, in which: Figure 1 shows the breakdown pass, and Figure 2 shows the fin pass of a concrete reinforcing finned steel bar.

In Figure 1, the hatched surface represents the breakdown pass of a steel bar. The starting material was of the cross-section indicated by means of a dotted line 1. The starting material was shaped into the cross-sectional form, as illustrated by the hatching, of a triangle with curved sides 5 to 7» by means of three rolling rolls 2 to 4 which are o displaced relative to each other through 120 . The ratio of the radius of curvature r^ of *ne curved sides of the triangle and thus of the rolling groove in the breakdown pass, to the radius r^ of the inscribed circle of the triangle is in the present case 1.66. Reference iy denotes the opening of the rolling rolls, while reference Sy denotes the chord of the groove for the breakdown pass. The opening i^ also determines the dimension of the chord s... f The fin pass shown in Figure 2 is performed in the method according to the invention, using the breakdown pass member shown in 8,9.10 Figure 1. For this purpose, three fin rollers' which are displaced relative to the breakdown pass through 60 engage on the corners of the triangular cross-section of the shaped bar produced in the breakdown pass, as shown in Figure 2 by dash-dotted lines. The spacing of the centre point M of the cross-section of the fin pass bar, from the edge of the fin pass bar between the opening of the rolls is denoted by k^, the radius of the grooving of the fin rolls, which determines the cross-section of the core portion of thefimed steel bar, is denoted by reference Γ„η, the radius of the inscribed circle of the fin pass bar is denoted x -by reference ij^, the projection of the radius of the recesses for the fins in the roll groove onto a plane perpendicular to the axis of the bar is denoted by reference r^, the spacing of the fin rolls is denoted by reference i^, and the length of the groove chord is denoted by s^.

Besides the fins which are shown by broken lines 11 to 13» hatching also shows in Figure 2 an area ^ which is included for facilitating the calculation explained hereinafter. Of the above-mentioned parameters, particular emphasis should be placed on the spacing k which is to be it taken into account when determining the dimensions of the breakdown pass. So that congestion is avoided in the fin pass, the radius r^ of the inscribed circle in the breakdown pass indicated in dash-dotted lines in Figure 2, should not be greater than the spacing k^.

It is known that hot-rolled round bars are only available in a limited number of different dimensions. It may therefore be necessary, for producing finned steel bars whose diameter differs widely from the available diameter of starting material, for the diameter of the starting material first to be reduced. This is preferably effected by means of an equalising or conditioning drawing step or pass, also in the form of a triangle with curved sides. After the equalising drawing or pass has been carried out, the breakdown pass is performed in the manner described, with the grooved rollers of the breakdown pass engaging the corners of the triangular cross-section formed by the equalising pass.

The manner in which the roll grooving for a concrete reinforcing finned bar of a given nominal diameter is to be calculated, will now be illustrated with reference to an actual example.' The example is based on a nominal diameter of 8 mm. The calculation is carried out starting from the desired end product, in the opposite direction to the steps of the method for producing the finished bar, that is to say, the grooving and the dimensions for the fin pass are determined first, followed by those for the breakdown pass. Prom this is calculated the required diameter of starting material, and if the jump to the next larger hot-rolled round steel bar available as a commercial product is excessively large, the data for a possible equalising pass can then be determined. l) Roll grooving for the core cross-sections for the fin passes In forming the core cross-sections in the fin pass, the fins were taken as having a proportion by weight of 7. This value is produced by filing away and by theoretical calculation of clearly defined fins on bars having a diameter of 8 mm. The cross-sectional area of the core therefore corresponds to the nominal cross-sectional area, reduced by 7$· The following geometric relationships were derived for the configuration of the core cross-sections: a) the core area, that is to say, the area of the nominal cross-section less 7$> is composed of the area F 1 of the inscribed circle with a radius r^, and the area of the three hatched areas -^. In this case, the 3 ratio ^ is 9· F .

R2 These data are used to calculate the radius r^ of the inscribed circle. b) the ratio of the radius r^ of the roll groove to the radius of the inscribed circle r^ is 1.44. From this can be determined the radius Tji2 of the roll groove. c) the ratio of the radius of the inscribed circle r^ to the roll opening ijj was selected at 4.08. From this was .obtained the value of i^. d) the length of the groove chord s^ can be determined from the above data. 2) Boll grooving for the fins The roll spacings must be so selected that they substantially correspond to the dimensions set out in the regulations and together with the configuration of the fin height give satisfactory relative fin areas.

A number of measurements on finned bars with a nominal diameter of 8 mm showed that, with a 24$ reduction in cross-sectional area in the fin pass, the mean fin spacing in the bar is approximately 1.09 times as great as the spacing of the fins cut in the rolls. The reason for this is considered to be a flow of the material in the longitudinal direction in the vicinity of the outlet end of the roll gap. The stretch factor of 1.09 was taken into account in selecting the spacing of the fin shapes formed in the rolls.

The angle of inclination a. of the fins to the axis of the bar should, according to regulations, be from 45 to 60 , the angle selected was « 50 .

The fin flank angle β should be = 45 to comply with regulations. As there are also regulations for the mean crest width b of the fins, the flank angle β cannot be made too flat (about 45°)» as otherwise either the height h of the fin shapes is too low, that is to say, during rolling the fins are subject to pressure on their crests and are thus prevented from forming their maximum height, or the fins become too wide, that is to say, the mean crest width b becomes substantially wider than the regulations provide and the fin weight becomes excessive.

As the fins are only partly load-carrying, excessive fin weight means wasted material.

In addition, increased fin height is to be expected with increased flank angles. However, excessively large flank angles increase the notch effect of the fins so that bending stress properties and endurance limit of stress are reduced. A good compromise solution was found to be a flank angle of 55 .

The dimensions set down in the official regulations for the fins and the arrangement thereof are not uniform. For example, the minimum fin height, depending on particular dimension, is from 5.6 to 7·5 of the nominal diameter. That is because the minimum fin spacings remain the same for groups of different diameters.

For that reason, in the present roll grooving, the depth of the fin shapes formed in the roll groove was so selected that with the maximum theoretical fin height a^, the fins are produced without pressure on their crests, that is to say, the depth of the fin shapes corresponds to the theoretical fin height increased by an additional safety margin of The crest width of the fin shapes in the rolls was selected as follows: i) Nominal d intension 4.0 to 6.5 0: 0. 15 mm II) Nominal dimension 7· 0 to 12 mm 0.20 mm Thus the fins for any dimensions can be cut with two tool shapes. 3) Roll grooving of the breakdown -pass (triangle with curved sides ) The cross-sectional areas of the breakdown pass result from the areas of the nominal dimensions of the .finned bars (including 7^ fin proportion) , increased by the required 18 to 24 % cross-sectional reduction in the fi pass , according to the particular nominal dimensions of the f inished bar .

The radius of the inscribed circle Ty^ must be so selected that it is approximately equal to or smaller than the di stance l ^ in the fin pass . If it becomes greater than l ^, congestion occurs in the fin pass. The following relationship was iBed for the present roll grooving: For the breakdown pass , the ratio of the roll groove radius to the radius of the inscribed circle should be as large as possible , so that even rolled wire with large . tolerance deviations can be shaped without congestion. For here again the condition must be met, that the greatest radius of the rolled wire is approximately equal to or smaller than the distance ky in the breakdown pass. The following relationship was selected for the breakdown pass : •≥S = 1.66 rVl From this r can be calculated. ■ , ' V2 The roll opening i^. can be established again depending on the radius of the inscribed circle ry^ : *Y = ¾ 4. 15 The chord Sy can be determined from the above. 4) Equalising and pass sequences The roll grooving is so designed that as far as possible equalising of the rolled wire can be omitted. The normal sequence of passes is as follows: i) Rolled wire Breakdown pass ^ fin pass.

Breakdown and fin pass must be performed in directly consecutive working operations.

The rolled wire dimensions were so selected that a total cross-sectional reduction of about JOfo is effected, with respect to the finned wire. With some dimensions however, as already mentioned, the diameters of the rolled wires and the cold-finned wires do not coincide in the requiredrelationship, so that an equalising operation is necessary or conditionally necessary. In most cases the equalising operation only serves to eliminate possible plus tolerances in the rolled wire.

A drawing die can be used for the equalising operation. In that case the radius of the die should correspond to the dimension k^ of the breakdown pass. The sequence of passes would be as follows: II a) Boiled wire ^ equalising drawing operation ^breakdown pass ^ fin pass.

Two drawing drums would be required, one after the equalising drawing step and one after the breakdown pass and the fin pass. One drawing drum is also sufficient, after the fin pass, in the case of dimensions in which an equalising operation is only conditionally necessary.

In principle however, it is desirable that, instead of the equalising drawing step, equalising passes should be effected, with three-roll stand¾ displaced through 60. relative to the breakdown pass. By virtue of the use of the curved-sided triangle as the breakdown pass, with the roll grooving according to the invention a single three-roll stand is sufficient as the grooving pass. Roll groovings which operate with a flattened round section as the breakdown pass require two passes for the equalising operation, as the round section to be flattened can only be produced by way of an intermediate triangular section, for example: Rolled wire —> triangular pass ^ round pass ^ flattening pass ^ fin pass.

With the roll grooving according to the invention, a triangle with curved sides was selected as the equalising pass. The radius of the inscribed circle in the grooving pass must again correspond to the dimension ky in the breakdown pass. The sequence of passes is then as follows: II b) Rolled wire ^ equalising pass —^ breakdown pass —^ fin pass.

An attempt was made to combine together groups of dimensions which can be processed with the same equalising rolls, by adjustment. Account was taken of the fact that the ratio of the radius r^ of the roll groove cut into the equalising rolls, to the radius r^ of the inscribed circle in the equalising pass lies approximately between 1.7 and 2.0. The chord Sj, corresponds to the radius r^. The roll opening was set up on the smallest dimension of the series. With increasing dimensions, the roll opening increases. The follwing five groups were combined together: Group 1: Concrete steel dimensions 4.0 to 4.60 Group 2: Concrete steel dimensions 5.0 to 6.00 Group 3! Concrete steel dimensions 6.5 to 7·50 Group 4: Concrete steel dimensions 8.0 to 9·50 Group 5ϊ Concrete steel dimensions 10.0 to 12.00 The important fact for the roll grooving is that the three passes are performed directly one after the other. A drawing drum is required after the fin pass, or driven rollers are required in the fin pass.

Claims (5)

41889/3 .- CLAIMS ·

1. A method, of producing a cold-shaped concrete r^n- ^ forcing bar, in which a steel bar produced by hot rolling is . ¾.·' · . firstly made into a triangle-like cross-sectional shape ^and • . ' · ΛΑ, ··; then the shaped bar is provided with inclined transverse fins v . ¾ -i\ > ' ' by means' of cold shaprng rolls which engage the corners of the triangular bar over the entire length thereof, the beginning and the end of the. fins merging smoothly in the surface of the triangular bar so that the projection of the envelopes in the axial direction of the bar is approximately circular, characterised in that the cross-section of the bar in the first cold shaping operation (breakdown pass) is shaped into a triangle with curved sides, that the ratio of the radius of curvature r^ of the curved sides of the triangle to the radius x ^ of the inscribed circle of said triangle —~ = 1.6 to 2.4, preferably: 1.7 with reductions in cross-rvi section of about 18$ in the fin pass, and : 2.0 with reductions in cross- section of about 24 in the fin pass, and that the radius r ^ of the inscribed circle of said triangl is at most equal to the spacing kD of the centre point of the cross-section from the edge_of the fin pass between the roll openings of the fin rolls.

2. A nethod of producing a cold-sbaped concrete reinforcing bar, in -which a steel bar produced b hot rolling is firstly made into a triangle-like cross-sectional shape and then the shaped bar is provide'd with inclined transverse fins by means of cold shaping rolls which engage the corners of the triangular bar over the entire length thereof, the beginning and the end of the fins merging smoothly in the surface of the 41889/2 pass) is shaped into a triangle with curved sides , that the ratio of -the radius of curvature r^ °f the curved sides of the triangle to the radius Ty^ of the inscribed circle of said triangle rV2 ■ . — — = 1.6 to 2.0 , preferably 1.7» VI and that the radius of the inscribed circle of said triangle is at most equal to the spacing of the centre point of the cross-section from the edge of the fin pass between the roll openings of the fin rolls.'

3 . A method according to claim 1, characterised in that with starting material' whose diameter is excessively large for producing the desired 2 f V 1973 concrete finned bar, an equalising drawing operation or equali sing pass is also performed to reduce said diameter before the breakdown pass , the equalising drawing operation or pass imparting to the bar the shape of a triangle with curved sides , and that in the breakdown pass which follows directly the grooved rolls engage the corners of the triangular cross- section produced by the equalising drawing operation or pass .

4 . A. method according to Claim 2 , characterised in that with starting material whose diameter is excessively large for producing the desired concrete f inned bar , an equalising drawing operation or equalising pass is also performed to reduce said diameter before the breakdown pass the equalising drawing operation or pass imparting to the bar the shape of a triangle with curved sides , and that in the breakdown pass which follows directly the grooved rolls engage the corners of the triangular cross-section produced by the equalising drawing operation or pass .

5. A method according to ' any one of Claims 1 to 4,, characterised in that, to produce a finned bar in which the projection of the envelopes in the axial direction of the bar is approximately circular , the ratio of the radius rR2 of the roll groove in the fin rolls t:o the radius rR^ the inscribed circle of the fin pass HE:mr