WO2012029079A2 - Reinforcing bar coupling and method - Google Patents

Reinforcing bar coupling and method Download PDF

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Publication number
WO2012029079A2
WO2012029079A2 PCT/IN2011/000604 IN2011000604W WO2012029079A2 WO 2012029079 A2 WO2012029079 A2 WO 2012029079A2 IN 2011000604 W IN2011000604 W IN 2011000604W WO 2012029079 A2 WO2012029079 A2 WO 2012029079A2
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WO
WIPO (PCT)
Prior art keywords
rebar
forming
threads
end portion
cold
Prior art date
Application number
PCT/IN2011/000604
Other languages
French (fr)
Other versions
WO2012029079A4 (en
WO2012029079A3 (en
WO2012029079A8 (en
Inventor
Gaurav Malhotra
Original Assignee
Gaurav Malhotra
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
Application filed by Gaurav Malhotra filed Critical Gaurav Malhotra
Publication of WO2012029079A2 publication Critical patent/WO2012029079A2/en
Publication of WO2012029079A3 publication Critical patent/WO2012029079A3/en
Publication of WO2012029079A8 publication Critical patent/WO2012029079A8/en
Publication of WO2012029079A4 publication Critical patent/WO2012029079A4/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/16—Auxiliary parts for reinforcements, e.g. connectors, spacers, stirrups
    • E04C5/162—Connectors or means for connecting parts for reinforcements
    • E04C5/163—Connectors or means for connecting parts for reinforcements the reinforcements running in one single direction
    • E04C5/165—Coaxial connection by means of sleeves

Definitions

  • the invention relates to a reinforcing bar coupling. More particularly, the invention relates to a method of forming a reinforcing bar splice.
  • Splicing techniques generally involve threading ends of the rebars to be coupled and using a coupler having complimentary threads to form the bar splice.
  • Another splicing technique involves cold forming the end of the rebar and cutting threads on the cold-formed section of the rebar. It is generally believed that cold forming the bar end compensates for the cutting of threads.
  • the cold formed section may include surface irregularities that may result in irregular threads.
  • rebar As construction rebar is generally manufactured from steel scrap instead of sponge iron, the micro structural properties of the rebar become difficult to predict. Therefore, an upset rate of 20 % of the rebar diameter while safe for one batch of steel rebar, may not be safe on another batch. Moreover, rebars are not always perfectly round and are often found to be a little oval. Even the ribs formed on the rebar may vary in thickness. Different rebar manufacturers also have different tolerances for the rebar further causing variations in the bar splice.
  • couplers are generally mass-produced in standard sizes for different size rebars, the variations in the rebar may often result in imperfect or weakened bar splices. As a result, the diameter of the rebar end is often further reduced to fit the coupler. Such on the spot modifications may further result in an imperfect or weakened bar splice, and cause delays on projects and financial losses.
  • a method of forming a rebar coupling comprises of cold forming an end portion of a rebar to flatten any projections thereon and obtain a diameter of the end portion larger than the inner diameter of a coupler to be mounted thereon.
  • the method further comprises of smoothening at least a part of the cold formed end portion of the rebar by a turning operation to a shape and diameter suitable for engagement with the coupler and forming threads on at least a part of the turned portion of the rebar by a rolling operation.
  • Figure 1A and IB are schematic illustrations of the cold forming to remove any irregularity in shape of the rebar in the formation of the bar splice.
  • Figure 2 is a schematic illustration of the turning of the cold formed rebars to further smoothen the rebar surface.
  • Figure 3 A is a schematic illustration of roll forming parallel threads on the turned rebar.
  • Figure 3B is a schematic illustration of roll forming taper threads on the turned rebar.
  • the first step in the formation of the rebar coupling involves cold forming the end of the rebar in a die to flatten the ribs and remove irregularities in the shape of the rebar.
  • the cold forming may be carried out by placing the rebar end in a pair of die faces, with one die face pressing the rebar against the second stationary die face, as shown in Figure 1 A.
  • both the die faces may be configured to press against each other as shown in Figure IB.
  • the die faces define recesses that are configured to receive the rebar end and are shaped generally semi-circular such that a round rebar end with compressed ribs is obtained.
  • a slightly oval rebar is compressed in the die to obtain a round rebar with compressed ribs.
  • Reduction in the diameter of the rebar by cold forming is such that the diameter of the cold formed end portion is larger than inner diameter of the coupler that is to be mounted thereon.
  • the cold formed rebar end is then further smoothened by a turning tool.
  • the turning operation prepares the rebar surface for threading and ensures that even threads are obtained that can be easily coupled with the coupler.
  • a turning tool carries out the turning operation.
  • the turning operation may be carried out along the entire length of the cold formed rebar end or a portion of it sufficient for threads. It is preferred that the turning operation is not carried out on the entire cold formed portion of the rebar.
  • the turning operation further reduces the diameter of the cold formed end portion of the rebar to obtain a consistent round shape and a diameter suitable for engagement with a coupler.
  • threads are formed on the turned rebar by rolling operation with rollers. Threads formed may be parallel as shown in Figure 3 A or tapered as shown in Figure 3B. Rollers for thread formation do not remove material from the rebar.
  • the cold forming increases the strength of the rebar which compensates for the relative loss in the strength on account of the turning operation.
  • the rolling operation ensures stronger threads that do not reduce the strength of the rebar.
  • a pair of rebar so formed is screwed onto a mechanical coupler to form the bar splice.
  • a rebar having diameter 32mm for coupling with a coupler having inner diameter of 31mm is first cold formed at its end portion to a diameter of approximately 31.5mm. The cold formed portion is then subjected to turning to further reduce its diameter to 31mm.
  • the turning operation is carried out to reduce the diameter of the cold formed portion of the rebar by not more than 0.5mm.
  • the method disclosed retains strength of the rebar and also provides for more even threads and a more perfect bar splice. Instead of cutting away the diameter of the rebar during thread formation, the diameter is reduced uniformly in the turning step. As the threads are formed on the rebar by rollers and not cutters no further reduction of diameter takes place. As a result, the strength of the rebar is not compromised but a more uniform bar splice is obtained.
  • a method of forming a rebar coupling comprising cold forming an end portion of a rebar to flatten any projections thereon and obtain a diameter of the end portion larger than the inner diameter of a coupler to be mounted thereon, followed by smoothening at least a part of the cold formed end portion of the rebar by a turning operation to a shape and diameter suitable for engagement with the coupler and forming threads on at least a part of the turned portion of the rebar by a rolling operation.
  • Such method(s) further comprising forming a bar splice by tightening an internally threaded coupler having matching threads onto two rebar couplings.
  • the method disclosed ensures a consistency in the size and the roundness of the rebar and thus provides for improved coupling with the couplers. Furthermore, the consistency in shape and size also avoids damage(s) to the couplers, reworking of the rebar and loss in time on account of these factors.
  • the method disclosed provides an improved tensile strength rebar splice for use in concrete constructions. The splice formed has superior tensile qualities. The method is inexpensive and may be accomplished at or near a construction site.

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  • Engineering & Computer Science (AREA)
  • Architecture (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Reinforcement Elements For Buildings (AREA)
  • Wire Processing (AREA)

Abstract

A method of forming a rebar coupling is disclosed. The method comprises of cold forming an end portion of a rebar to flatten any projections thereon and obtain a diameter of the end portion larger than the inner diameter of a coupler to be mounted thereon. The method further comprises of smoothening at least a part of the cold formed end portion of the rebar by a turning operation to a shape and diameter suitable for engagement with the coupler and forming threads on at least a part of the turned portion of the rebar by a rolling operation.

Description

REINFORCING BAR COUPLING AND METHOD
The invention relates to a reinforcing bar coupling. More particularly, the invention relates to a method of forming a reinforcing bar splice.
BACKGROUND
Reinforcement bar, or rebar, is a long generally cylindrical steel rod with ribs or ridges formed on it. The ribs are provided to anchor the rebar in the concrete and to restrict movement of the rod when embedded in concrete. Ribs are formed in different patters on the rod surface, with a typical rib formation including one or more longitudinal ribs that intersect a plurality of spaced apart annular ribs.
In use, it is often necessary to splice together two rebars end to end and there is a plurality of rebar splicing devices and couplers for this, with the taper thread system and the parallel thread upset forging system in wide use. Splicing techniques generally involve threading ends of the rebars to be coupled and using a coupler having complimentary threads to form the bar splice. Another splicing technique involves cold forming the end of the rebar and cutting threads on the cold-formed section of the rebar. It is generally believed that cold forming the bar end compensates for the cutting of threads. However, the cold formed section may include surface irregularities that may result in irregular threads.
As construction rebar is generally manufactured from steel scrap instead of sponge iron, the micro structural properties of the rebar become difficult to predict. Therefore, an upset rate of 20 % of the rebar diameter while safe for one batch of steel rebar, may not be safe on another batch. Moreover, rebars are not always perfectly round and are often found to be a little oval. Even the ribs formed on the rebar may vary in thickness. Different rebar manufacturers also have different tolerances for the rebar further causing variations in the bar splice.
While couplers are generally mass-produced in standard sizes for different size rebars, the variations in the rebar may often result in imperfect or weakened bar splices. As a result, the diameter of the rebar end is often further reduced to fit the coupler. Such on the spot modifications may further result in an imperfect or weakened bar splice, and cause delays on projects and financial losses.
SUMMARY
A method of forming a rebar coupling is disclosed. The method comprises of cold forming an end portion of a rebar to flatten any projections thereon and obtain a diameter of the end portion larger than the inner diameter of a coupler to be mounted thereon. The method further comprises of smoothening at least a part of the cold formed end portion of the rebar by a turning operation to a shape and diameter suitable for engagement with the coupler and forming threads on at least a part of the turned portion of the rebar by a rolling operation.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1A and IB are schematic illustrations of the cold forming to remove any irregularity in shape of the rebar in the formation of the bar splice.
Figure 2 is a schematic illustration of the turning of the cold formed rebars to further smoothen the rebar surface. Figure 3 A is a schematic illustration of roll forming parallel threads on the turned rebar.
Figure 3B is a schematic illustration of roll forming taper threads on the turned rebar.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof. Throughout the patent specification, a convention employed is that in the appended drawings, like numerals denote like components.
Reference throughout this specification to "one embodiment" "an embodiment" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase "in one embodiment", "in an embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
Referring to Figures 1A and IB, the first step in the formation of the rebar coupling involves cold forming the end of the rebar in a die to flatten the ribs and remove irregularities in the shape of the rebar. The cold forming may be carried out by placing the rebar end in a pair of die faces, with one die face pressing the rebar against the second stationary die face, as shown in Figure 1 A. Alternatively, both the die faces may be configured to press against each other as shown in Figure IB. The die faces define recesses that are configured to receive the rebar end and are shaped generally semi-circular such that a round rebar end with compressed ribs is obtained. As shown in the figures, a slightly oval rebar is compressed in the die to obtain a round rebar with compressed ribs. Reduction in the diameter of the rebar by cold forming is such that the diameter of the cold formed end portion is larger than inner diameter of the coupler that is to be mounted thereon.
Referring next to Figure 2, the cold formed rebar end is then further smoothened by a turning tool. The turning operation prepares the rebar surface for threading and ensures that even threads are obtained that can be easily coupled with the coupler. A turning tool carries out the turning operation. The turning operation may be carried out along the entire length of the cold formed rebar end or a portion of it sufficient for threads. It is preferred that the turning operation is not carried out on the entire cold formed portion of the rebar. The turning operation further reduces the diameter of the cold formed end portion of the rebar to obtain a consistent round shape and a diameter suitable for engagement with a coupler. Referring next to Figures 3A and 3B, threads are formed on the turned rebar by rolling operation with rollers. Threads formed may be parallel as shown in Figure 3 A or tapered as shown in Figure 3B. Rollers for thread formation do not remove material from the rebar.
The cold forming increases the strength of the rebar which compensates for the relative loss in the strength on account of the turning operation. The rolling operation ensures stronger threads that do not reduce the strength of the rebar.
A pair of rebar so formed is screwed onto a mechanical coupler to form the bar splice.
By way of specific example, a rebar having diameter 32mm for coupling with a coupler having inner diameter of 31mm is first cold formed at its end portion to a diameter of approximately 31.5mm. The cold formed portion is then subjected to turning to further reduce its diameter to 31mm.
In accordance with a preferred embodiment, the turning operation is carried out to reduce the diameter of the cold formed portion of the rebar by not more than 0.5mm.
The method disclosed retains strength of the rebar and also provides for more even threads and a more perfect bar splice. Instead of cutting away the diameter of the rebar during thread formation, the diameter is reduced uniformly in the turning step. As the threads are formed on the rebar by rollers and not cutters no further reduction of diameter takes place. As a result, the strength of the rebar is not compromised but a more uniform bar splice is obtained.
While example embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the invention as described in the claims.
SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW
A method of forming a rebar coupling comprising cold forming an end portion of a rebar to flatten any projections thereon and obtain a diameter of the end portion larger than the inner diameter of a coupler to be mounted thereon, followed by smoothening at least a part of the cold formed end portion of the rebar by a turning operation to a shape and diameter suitable for engagement with the coupler and forming threads on at least a part of the turned portion of the rebar by a rolling operation.
Such method(s) further comprising forming a bar splice by tightening an internally threaded coupler having matching threads onto two rebar couplings.
Such method(s), wherein cold forming is carried out by radially compressing the end portion of the rebar in a die.
Such method(s), wherein threads are formed on entire length of the turned portion of the rebar by a rolling operation.
Such method(s), wherein the cold forming forms a tapered cold formed end portion of the rebar.
Such method(s), wherein taper threads are formed on at least a portion of the turned rebar.
Such method(s), wherein taper threads are formed on at least a part of the turned portion of the rebar by a rolling operation. INDUSTRIAL APPLICABILITY
The method disclosed ensures a consistency in the size and the roundness of the rebar and thus provides for improved coupling with the couplers. Furthermore, the consistency in shape and size also avoids damage(s) to the couplers, reworking of the rebar and loss in time on account of these factors. The method disclosed provides an improved tensile strength rebar splice for use in concrete constructions. The splice formed has superior tensile qualities. The method is inexpensive and may be accomplished at or near a construction site.

Claims

I CLAIM:
1. A method of forming a rebar coupling comprising:
cold forming an end portion of a rebar to flatten any projections thereon and obtain a diameter of the end portion larger than the inner diameter of a coupler to be mounted thereon;
smoothening at least a part of the cold formed end portion of the rebar by a turning operation to a shape and diameter suitable for engagement with the coupler; and
forming threads on at least a part of the turned portion of the rebar by a rolling operation.
2. A method of forming a rebar coupling as claimed in claim 1, further comprising forming a bar splice by tightening an internally threaded coupler having matching threads onto two rebar couplings.
3. A method of forming a rebar coupling as claimed in claim 1, wherein cold forming is carried out by radially compressing the end portion of the rebar in a die.
4. A method of forming a rebar coupling as claimed in claim 1 , wherein threads are formed on entire length of the turned portion of the rebar by a rolling operation.
5. A method of forming a rebar coupling as claimed in claim 1, wherein the cold forming forms a tapered cold formed end portion of the rebar.
6. A method as claimed in claim 5, wherein taper threads are formed on at least a portion of the turned rebar.
7. A method as claimed in claim 1, wherein taper threads are formed on at least a part of the turned portion of the rebar by a rolling operation.
PCT/IN2011/000604 2010-09-03 2011-09-05 Reinforcing bar coupling and method WO2012029079A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IN2110DE2010 2010-09-03
IN2110/DEL/2010 2010-09-03

Publications (4)

Publication Number Publication Date
WO2012029079A2 true WO2012029079A2 (en) 2012-03-08
WO2012029079A3 WO2012029079A3 (en) 2012-04-19
WO2012029079A8 WO2012029079A8 (en) 2012-05-10
WO2012029079A4 WO2012029079A4 (en) 2012-06-28

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Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4584247A (en) * 1981-08-20 1986-04-22 The Titan Manufacturing Co. Pty. Ltd. Threading deformed bars
US5776001A (en) * 1994-02-16 1998-07-07 Ccl Systems Limited Thread formation
KR100248963B1 (en) * 1998-03-31 2000-03-15 정경옥 Thread formation on rods and the method of preparation of them
SG161135A1 (en) * 2008-11-03 2010-06-29 Dextra Asia Co Ltd Threading machine with coaxial peeling and threading means

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
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WO2012029079A4 (en) 2012-06-28
WO2012029079A3 (en) 2012-04-19
WO2012029079A8 (en) 2012-05-10

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