EP0080833A1 - Stahlstab für Bewehrung und Verfahren zur Herstellung dieses Stabes - Google Patents

Stahlstab für Bewehrung und Verfahren zur Herstellung dieses Stabes Download PDF

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Publication number
EP0080833A1
EP0080833A1 EP82306142A EP82306142A EP0080833A1 EP 0080833 A1 EP0080833 A1 EP 0080833A1 EP 82306142 A EP82306142 A EP 82306142A EP 82306142 A EP82306142 A EP 82306142A EP 0080833 A1 EP0080833 A1 EP 0080833A1
Authority
EP
European Patent Office
Prior art keywords
rod
pulley
pulley system
steel
steel reinforcement
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP82306142A
Other languages
English (en)
French (fr)
Inventor
Peter Gough Davies
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Allied Steel and Wire Ltd
Original Assignee
Allied Steel and Wire Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB08134660A external-priority patent/GB2109281A/en
Priority claimed from GB08134665A external-priority patent/GB2109719A/en
Application filed by Allied Steel and Wire Ltd filed Critical Allied Steel and Wire Ltd
Publication of EP0080833A1 publication Critical patent/EP0080833A1/de
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D11/00—Bending not restricted to forms of material mentioned in only one of groups B21D5/00, B21D7/00, B21D9/00; Bending not provided for in groups B21D5/00 - B21D9/00; Twisting
    • B21D11/14—Twisting
    • B21D11/15—Reinforcing rods for concrete
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/10—Modifying the physical properties of iron or steel by deformation by cold working of the whole cross-section, e.g. of concrete reinforcing bars
    • C21D7/105—Modifying the physical properties of iron or steel by deformation by cold working of the whole cross-section, e.g. of concrete reinforcing bars of concrete reinforcing bars
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
    • E04C5/02—Reinforcing elements of metal, e.g. with non-structural coatings of low bending resistance

Definitions

  • the invention relates to a process for producing reinforcement rod by cold working and to a steel reinforcement rod produced by cold working.
  • the cold working of steel rod improves its mechanical properties, in particular its tensile strength, and such cold working is usually effected either by rolling or drawing.
  • the material may initially be hot rolled and then cold drawn or cold rolled in order to achieve the necessary standard specification relating to its tensile strength.
  • Such specifications usually require a minimum proof stress of 485 N/mm 2 and state that the ratio of the ultimate tensile stress to the proof stress shall be more than a specified value.
  • the ratio specified is 1.05:1 in most European specifications.
  • Such rods may have a smooth surface or may be provided with surface deformations such as ribs to improve their keying or bonding capability to the concrete.
  • An object of the present invention is to provide a process for economically and effectively cold working steel rod to produce reinforcement rod, that is by avoiding the expense of wire drawing, avoiding the difficulties of producing a ribbed surface by cold rolling and avoiding the difficulties of handling finite lengths associated with cold twisting. It is also an object of the invention to provide an improved cold worked reinforcing rod.
  • a process for producing reinforcement rod by cold working of an indefinite length of steel rod characterised in that the rod is passed through a cold working station at which it is twisted in one direction about its axis and is then untwisted.
  • the ends of the rod which are normally carried in a coil or connected to plant to or from which the rod is fed in a continuous length, do not have to be twisted so that they are compatible with these end conditions.
  • the degree of twist, prior to untwisting is at least one turn in a length equal to thirty rod diameters.
  • the measurement intended is the notional diameter of a circular rod having the same cross-sectional area as the rod under consideration.
  • the degree of twist will lie between one turn in five diameters and one turn in twenty diameters.
  • the degree of twist is selected in relation to the composition and properties of the untwisted rod so that it increases the proof stress to a desired level without reducing the ductility of the rod below specification requirements.
  • the invention is particularly applicable to steel rod having a carbon content of not more than 0.3% by weight because low carbon steel can be manufactured readily, can easily be welded into mesh but normally requires cold working to give it sufficient strength for concrete reinforcement purposes.
  • the degree of twist should be chosen in relation to carbon content of the steel to result in a proof stress after ageing of between 450 and 540N/mm 2 according to the appropriate specification requirements.
  • the rod may be passed round a pulley system having one or more rotatable pulleys around which the rod runs continuously from an input side to an output side thereof, the pulley system being orbited about an axis other than the axis of rotation of the or each pulley whereby the rod is twisted in one direction at the input side of the pulley system and is then untwisted at the output side thereof.
  • the rod may be fed over a restraint pulley before it enters the input side of the pulley system whereby the rod is twisted in one direction between the restraint pulley and the pulley system as the rod enters the input side thereof and is then untwisted as it leaves the output side of the pulley system.
  • Both the orbiting pulley system and the restraint pulley may be driven in synchronism with each other whereby the speed of orbiting of the pulley system is at a predetermined rate with respect to the speed of input of the rod to the pulley system from the restraint pulley.
  • steel reinforcement rod which has been cold worked by twisting characterised in that the reinforcement rod has been produced by passing an indefinite length of rod through a cold working station at which the rod is twisted in one direction about its axis and is then untwisted.
  • the degree of twisting, prior to untwisting should be at least one turn in a length equal to thirty diameters and should preferably be between one turn in five diameters and one turn in twenty diameters.
  • the steel employed contains less than 0.3% carbon.
  • the steel may be the product of an electric arc furnace.
  • the degree of twisting, in relation to the composition and properties of the initial rod may be such as to produce a proof stress after ageing of between 450 and 540 N/mm 2 according to the appropriate specification requirements.
  • the twisting and untwisting operation not only improves the mechanical strength of the rod but also effectively descales it and straightens it.
  • the following description is with reference to a steel rod, which may have either a smooth or ribbed surface, and which is suitable for use, when cut to length, in the production of welded reinforcing mesh for concrete.
  • the rod to be cold worked is produced by conventional steel making methods and subsequently hot rolled to a typical diameter of 6 mm and, after cooling, is formed into a normal hot rolled coil.
  • the rod is then fed continuously from the stock coil through a cold working apparatus as illustrated in figure 1 in such manner, in accordance with the invention, as to increase the proof and ultimate tensile stress to specification requirements and maintain the ratio of the ultimate tensile stress to the proof stress of the rod at or above 1.05 after ageing.
  • the apparatus includes a fixed frame 10 upon which are mounted two plummer block bearings 12 and 14 for a hollow rotatable shaft 32.
  • Each of the bearings 12 and 14 is centrally apertured with the apertures in alignment with each other.
  • a stirrup shaped yoke is mounted on the end of the shaft 32, the yoke including two opposed parallel side plates 16 between which are mounted two freely rotatable pulleys 18.
  • the pulleys 18 are carried in the yoke adjacent one edge thereof whilst at the other edge counter-balance weights 20 are mounted.
  • the axes of the pulleys 18 are skewed slightly relative to each other to either side of an axis normal to the axis of shaft 32.
  • a relatively large diameter driven restraint pulley 22 At the input side of the apparatus there is a relatively large diameter driven restraint pulley 22 the lower edge of which is in alignment with the axis of the bearings 12 and 14.
  • a V-groove in pulley 22 provides drive between the rod and pulley.
  • Rod curved round the pulley acts as a lever arm to hold it against rotation of the pulley.
  • a freely rotatable guide pulley 24 onto which is fed the rod W from a convenient source such as a reel thereof. The direction of input of the rod W is shown by the arrow in the drawing.
  • an air or electrically actuated controllable torque motor 26 which drives the restraint pulley 22 through a suitable gear box 28.
  • the motor 26 is also coupled to rotate the shaft 32 and the yoke so that the rotatable pulleys 18 carried thereon are orbital about the axis of the bearings 12 and 14.
  • the pulley system is thus driven in synchronism with the restraint pulley 22 to provide a predetermined speed of orbiting with respect to the speed of input of the rod over pulley 22.
  • the rod is pulled through-the apparatus, for example from a rotating spool. If the rod is arranged to grip the restraint pulley 22 it transmits energy via the gear box 28 to the shaft of the motor 26 and hence to the yoke shaft 32, to contribute to the energy required for twisting.
  • the rod W to be cold worked runs from a stock reel thereof around the two pulleys 24 - 22, through the hollow rotatable shaft 32, and around both pulleys 18 in the pulley system before exiting around a reaction pulley 34.
  • the rod meets up with the pulley 34 at a point on the axis of shaft 32.
  • the output of the rod at pulley 34 is co-axial with its input from pulley 22.
  • Rod leaving pulley 34 at an angle acts as a lever arm to hold the rod against rotation.
  • the rod passes continuously through the apparatus and is twisted in one direction between the restraint pulley 22 and the orbiting pulley system and is then twisted in the opposite direction as it passes between the output side of the pulley system and the reaction pulley thereby imparting a substantial degree of cold working to the rod.
  • Cold worked rod produced by the apparatus is particularly suitable for use in concrete reinforcing mesh where cut lengths of the cold worked rod have to be welded together.
  • the rod fed through the apparatus may be ribbed transversely, as is known practice in use of reinforcing rod for concrete, and the skewed axes of the orbiting pulleys 18 particularly ensure that such ribbed rod does not snag or chafe upon itself between the input and output sides of the pulley system.
  • the rod is effectively descaled and straightened whereby it may be immediately cut and welded for use in concrete reinforcing mesh.
  • the rod may be coiled immediately after cold working and then uncoiled and straightened in a conventional manner prior to use in mesh manufacture.
  • the re-straightening only slightly impairs the properties of rod which has been cold worked in accordance with the invention and then aged, provided-that during the straightening operation the rod is not cold worked more than is necessary to straighten it.
  • pulleys may be provided in the pulley system provided that they are orbitable in the manner hereinbefore described; in particular it may be convenient to provide three separate freely rotatable pulleys in the pulley system having their axes of rotation parallel to one another and normal to the orbital axis of the pulley system.
  • an orbital guide system other than pulleys provided it deflects the rod from its input and output axes so that the orbital motion imparts twist to the rod.
  • pulleys are preferred in the interests of low friction.
  • the invention is of particular application to low . carbon steel containing up to about 0.3% carbon.
  • the invention has the advantage of enabling a high proof stress and a suitable excess of ultimate tensile stress over proof stress to be achieved, particularly after ageing, even with low carbon steel from an electric arc furnace.
  • This type of steel is not normally suitable for work hardening by cold drawing which is the conventional procedure for work hardening continuous lengths of rod because the free nitrogen content results in excessive work hardening in that the proof stress becomes too high a proportion of the tensile stress after ageing.
  • the nature of the apparatus is such that the degree of twist in both directions is equal so that the second twisting operation could be thought of as an untwisting operation.
  • the degree of twist affects the properties of the final material. Greater twisting leads to a higher proof stress but a smaller margin between ultimate tensile and proof stresses.
  • the degree of twist should be just sufficient to achieve the required proof stress and depends on the composition of the hot rolled material. For a typical rod, a pitch of less than 30 rod diameters should be employed. The preferable range if 5 to 20 diameters.
  • the degree of twist is controlled by varying the relationship between the rate of orbiting of the pulley system and the rate of passage of rod through the apparatus. A standard specification for reinforcement rod requires a minimum of 0.2% proof stress of 485 N/mm 2 so it is desirable to select a degree of twist of this order, a little above the minimum needed to meet the specification.
  • the cold working associated with the twisting and untwisting of the rod moves dislocations from local concentrations of free nitrogen and other interstitially dissolved elements and thereby work hardens the material. Because the slip planes associated with the cold working do not correspond to slip planes associated with applied tension, the migration of dislocations along the slip planes associated with cold working during ageing has a limited effect on the increase in longitudinal proof stress with age. This in turn prevents the proof stress approaching too closely to the ultimate tensile stress during the ageing process.
  • the shear strain during twisting is at a maximum near the surface of the rod and reduces towards the centre of the rod. Despite this, a major part of the cross- section of the rod is work hardened to a substantial extent.
  • a hot rolled steel rod with a nominal diameter of 6 mm has the following composition: Carbon 0.08%, Silicon 0.15%, Manganese 0.52%, Copper 0.42%, Sulphur 0.04%, Phosphorus 0.03%, remainder iron and incidental impurities. In the as-rolled condition this rod had the properties set out in row 1 of the table (see below).
  • This rod was then passed through the machine described with reference to figure 1 and during the twisting a tension of 3560 N was applied to the rod in the twisting zone. The degree of twist, followed by untwisting, was 360° in a length of 73.11 mm, that is a pitch of 12 diameters.
  • the rod was then aged for two hours at 100°C at which stage it had the properties set out in row 2 of the table. The decrease in diameter indicates a corresponding increase in length which was brought about by the tension in conjunction with the twisting. Although the excess of ultimate tensile stress over proof stress was decreased by the twisting operation, it still remained at a very satisfactory level.
  • Figure 2 is a graph wherein the 0.2% proof stress, the ultimate tensile stress and the percentage excess are plotted against days of ageing of a 6 mm nominal diameter steel rod corresponding to the rod described above, initially produced by hot rolling and then fed through the apparatus of figure 1 and twisted and untwisted with a pitch of 12 diameters under a tension of 2670 N.
  • the graph shows that the ultimate tensile stress of the rod rises at a faster rate with ageing than does the proof stress thus leading to an increase, with ageing, of the percentage excess.
  • the rod diameter decreased from 6.09 to 5.89 mm.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Architecture (AREA)
  • Mechanical Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Heat Treatment Of Steel (AREA)
EP82306142A 1981-11-18 1982-11-18 Stahlstab für Bewehrung und Verfahren zur Herstellung dieses Stabes Withdrawn EP0080833A1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB08134660A GB2109281A (en) 1981-11-18 1981-11-18 Cold worked rod or wire
GB08134665A GB2109719A (en) 1981-11-18 1981-11-18 Cold working of metal rod or wire
GB8134660 1981-11-18
GB8134665 1981-11-18

Publications (1)

Publication Number Publication Date
EP0080833A1 true EP0080833A1 (de) 1983-06-08

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EP82306142A Withdrawn EP0080833A1 (de) 1981-11-18 1982-11-18 Stahlstab für Bewehrung und Verfahren zur Herstellung dieses Stabes

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EP (1) EP0080833A1 (de)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE909562C (de) * 1951-09-13 1954-04-22 Alfred Otto Kolling Verfahren zur Entzunderung von Walzdraht
FR1565871A (de) * 1967-05-16 1969-05-02
DE1452201A1 (de) * 1965-09-16 1969-10-30 Albert Friedrich Wilhelm Verfahren und Vorrichtung zur mechanischen Entzunderung und Entrostung von Eisen- und Stahldraehten
GB1442097A (en) * 1973-10-19 1976-07-07 Voest Ag Apparatus and method for the continuous cold work hardening of filamentary metal stock
GB1453233A (en) * 1974-04-03 1976-10-20 British Steel Corp Steel reinforcement bars
US4075880A (en) * 1975-11-14 1978-02-28 Reinforcing & Allied Industries (Proprietary) Limited Machine for continuously cold working steel bar

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE909562C (de) * 1951-09-13 1954-04-22 Alfred Otto Kolling Verfahren zur Entzunderung von Walzdraht
DE1452201A1 (de) * 1965-09-16 1969-10-30 Albert Friedrich Wilhelm Verfahren und Vorrichtung zur mechanischen Entzunderung und Entrostung von Eisen- und Stahldraehten
FR1565871A (de) * 1967-05-16 1969-05-02
GB1442097A (en) * 1973-10-19 1976-07-07 Voest Ag Apparatus and method for the continuous cold work hardening of filamentary metal stock
GB1453233A (en) * 1974-04-03 1976-10-20 British Steel Corp Steel reinforcement bars
US4075880A (en) * 1975-11-14 1978-02-28 Reinforcing & Allied Industries (Proprietary) Limited Machine for continuously cold working steel bar

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

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Inventor name: DAVIES, PETER GOUGH