NZ198090A - Rolling thread on deformed bar - Google Patents

Description

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Complete Specification Filed; Class: Publication Date: P.O. JO'jjtic.', i\!o: ...... /r^T7.*? ;NEW ZEALAND ;PATENTS ACT, 1953 ;No.: Date: ;COMPLETE SPECIFICATION ;THREADING DEFORMED BARS ;P?We, THE TITAN MANUFACTURING CO. PTY. LTD., a company incorporated in the State of Victoria, of Woodstock Street, Mayfield, New South Wales 2304, Australia hereby declare the invention for whichjJ / we pray that a patent may be granted to »»3</us, and the method by which it is to be performed, to be particularly described in and by the following statement: - ;- 1 - ;I93090 ;/ ;20 ;30 ;This invention relates to deformed bars and to rolling threads thereon. It has been devised particularly to provide a deformed bar onto which a male thread may be formed without the need to remove the deformation on the surface of such bar, and to provide a method for forming such thread. ;Many applications exist where hot rolled or cold rolled bar section, having surface deformations and commonly given the generic name "deformed bar", require a threaded section to be formed thereon. ;The existing bar used for this purpose is of the type commonly having a herringbone or chevron pattern of ribs formed on the surface of the bar, frequently in conjunction with one or more longitudinal ribs, and is used in concrete reinforcing applications and in other applications, such as the manufacture of rock bolts for mining and civil engineering purposes. ;The existing methods of forming a rolled threaded section on deformed bar require that the deformations be removed prior to threadrolling. (Other threadforming processes, such as cutting, also remove the deformations to produce a standard thread). ;One known process normally employed to form this threaded bar when manufactured for use as resin or cement anchored rock bolts will now be described. ;Steel form bar (e.g. concrete reinforcing bar to Natf Zealand Standard NZS3402P: 1973^is sheared to length and turned down to the threadrolling diameter, (e.g. 21.7mm for a 24mm standard thread, 14.4mm for a 16mm standard thread, etc.) over a length of approximately 160mm at one end of the bar. A thread is then roll-formed onto the machined portion to enable tensioning in use with a nut. The remaining ;- 2 - ;deformations provide a mechanical lock in the anchor when the bolt is installed. ;An alternative process of producing resin or cement anchored rock bolts will now be described. Plain round steel bar is sheared to length and on one end approximately 150mm of thread is rolled to enable tensioning in use with a nut. At the other end, deformations, typically a thread form extending up to 900mm along the bolt, are formed to provide a mechanical lock in the resin or cement anchor. 10 With reference to bolts produced by the first process above, because of the sizes of presently commercially available deformed bar, it is necessary to reduce the shank diameter to that required for the rolling of a male thread thereon, if a standard thread size is required. This system has the disadvantage that it is an expensive operation to remove the deformations and to size the bar before thread-rolling, due to the labour and machinery involved. This method of production has a further cost disadvantage in that, because the strength of the bolt is limited to the strength 20 at its point of smallest cross-section (i.e. the root diameter of the threaded portion) and this diameter is significantly smaller than the effective diameter of the original bar, much of the material in the unmachined part of the deformed bar is thereby wasted. A further disadvantage of this method of production is that when existing deformed bar provided with a threaded end is used as a rock bolt in mining or civil engineering applications, the commercially available patterns of deformations do not provide optimal retention of the resin or cement in the anchor zone, as the 30 rotation of the herringbone or chevron pattern ribs may leave ;- 3 - ;198090 ;i ;Os ;*45 oo (jn air cavities which reduce the adhesion area and the anchorage strength.

With reference to bolts produced by the second process above (i.e., formed from plain round steel stock), the additional thread for positively keying into the resin or cement anchor on the second end of the bolt is formed at some cost penalty when compared with bolts made from deformed bar and which require only one treaded section. As the middle portion of the bar has no threading or 10 deformations, this limits the flexibility of application in that, if a shorter bolt is required during installation, this bolt cannot be shortened without reducing the bond length of anchorage. Similarly, if an increase in anchorage length is required for a given bolt, a limitation is apparent in that, beyond a certain point, increasing the amount of resin or cement anchor material will not significantly increase anchor strength, as this additional material is in contact with the unthreaded portion of the bar.

It is therefore an object of the present invention to provide a deformed bar and a method of producing threads thereon which will obviate or minimise the foregoing disadvantages in a simple yet effective manner or which will at least provide the public with a useful choice.

Accordingly, in one aspect, the invention may be said to consist in a steel bar incorporating a plurality of substantially regular surface deformations along at least ~ one end thereof, said deformations individually and collectively being shaped and sized so that the average 30 volume of material contained in the bar including said z Kj 3 m 2 —I O Tl Tl o m LH/57R 74446/81 1 9809 deformation(s) per unit length of said bar is substantially equal to the average volume of material required in the threaded section of the bar per unit length of bar when threaded, whereby a uniform standard thread of substantially constant pitch circle may be rolled on that portion of the bar incorporating said surface deformations by conventional thread rolling techniques without performance of an intermediate step between bar selection and thread production.

Preferably said deformations include one or more helical ribs.

Preferably the handedness of the ribs is opposite to that of the desired thread.

In another aspect, the invention may broadly be said to consist in a method of forming a uniform standard thread of substantially constant pitch circle onto a deformed bar comprising the steps of: selecting a said deformed bar incorporating a plurality of substantially regular surface deformations along at least one end thereof, 20 said deformations individually and collectively being shaped and sized so that the average volume of material contained in the bar including said deformation(s) per unit length of T said bar is substantially equal to the average volume of Vj ! ° material reauired in the threaded section of the bar oer jM ' - ~-j H I unit length of bar when threaded, whereby a uniform standard thread O T) Tl of substantially constant pitch circle may be rolled thereon o m | by conventional thread rolling techniques without performance of an intermediate step between bar selection and thread production; and thereafter using known thread 30 rolling techniques to thread said bar with a thread of LH/57R - 5 - ' 74446/81 -b- 198090 substantially constant pitch circle over so much of the length of said bar as is able to be threaded using the said deformations originally provided thereon without performing an intermediate step between bar selection and thread rolling.

Preferably, said step of selecting deformed bar of suitable cross-section includes selecting a pattern of deformation which will be suitable for use with a hardenable anchor, such as a resin or cement mortar anchor in, for example, a rock bolting or reinforcing situation.

Preferably, said step of selecting pattern of deformation comprises selecting a pattern of deformation having one or more helical rib deformations on said bar.

Preferably, said step of selecting said pattern of one or more helical rib deformations comprises selecting a helical form or forms of opposite handedness to that of said thread.

In a further aspect, the invention may broadly be said to consist in a threaded deformed bar made by the method described in one or more of the preceding six paragraphs.

Notwithstanding other forms that may fall within its scope, one preferred form of the invention will now be described with reference to the accompanying figures, in which; Fig. 1 is a view of a threaded end of a deformed bar according to one aspect of the invention; and Fig. 2 shows a similar deformed bar according to another aspect of the invention before threading and showing a typical cross-section and side elevation of the bar.

In the preferred form of one aspect of the invention, a deformed bar is as follows: The deformed bar (1) of Fig. 2 is formed with an overall 196090 average cross-sectional area substantially the same as the average cross-sectional area that is desired for the threaded section of the bar. Although the actual shape and pattern of the deformation is not overly restricted, as many shapes possess this geometrical relationship, a specially designed deformed bar section (1) is preferably used, which is particularly suitable for use as a rock bolt in mining or civil engineering operations, in that the configuration of the deformations is designed to be particularly advantageous for the mixing and retention of liquid polyester resin or cement mortar in the anchor zone and improved bonding with the anchor after hardening. In this form of the invention the deformations are formed as two left-handed helical ribs (2) and (4) .

The deformations could alternatively be a single helical rib or three or more ribs. One or more longitudinal ribs (5) may also be provided and the helical ribs (2) and (4) may possess a discontinuity where they abut ribs (5) at junction (6) as shown by the mismatching of portions (2A) and 20 (2B) of rib (2). As shown in Fig. (2), the helical ribs may be quite discontinuous at a longitudinal rib. The helical ribs (2) and (4), are chosen to be of opposite handedness to that of the required thread.

In a preferred form of one other aspect of the present invention, a deformed bar such as the bar (1), is selected and then inserted into a thread-rolling machine without any further treatment and the right-hand threaded section (3) is roll formed onto the bar. Neither the deformations (2) and (4), "Trjftgior the longitudinal rib (5) are"removed by turning, swaging or iplLing before the threaded section (3) is formed and the bar is not sized by turning, swaging or rolling to the size <3/ Quired before the threadrolling operation is performed.

The threadrolling operation displaces, by cold deformation, material from the original ribs (2), (4) and (5), and forms this material and other material from the body of the bar into the form of a thread, the thread thus produced being able to accept a female threaded coupling, e.g. a nut. In this manner a method of producing a threaded deformed bar is performed which enables the threaded portion to be formed quickly and cheaply with a minimum of manufacturing time and no wastage of raw material.

The preferred embodiment has left-handed helical ribs (2) and (4) with a right-handed thread (3) , but the ribs would desirably be right-handed if a left-handed thread was used. The reasons for this opposite handedness of ribs relative to threads are, firstly the thread is far easier to form and, secondly when resin anchored rock bolts are used it is often the practice to mix the contents of a resin anchor cartridge by rotating the bolt in the same direction as that for tightening the nut, whereupon if the thread and the helical ribs were of the same handedness, the resin or cement anchor material would tend to flow away from the tip of the hole due to the screw action. In the preferred embodiment, any screw action would tend to retain the resin or cement anchor material in the hole.

Known bolts from deformed bar, because of their substantially reduced diameter at the threaded region, have an overall strength that is considerably less than that of the original bar. As a method according to the present invention does not require the removal of material in the area to be threaded, it provides a bar or bolt of improved strength or, alternatively, allows less material to be used 198090 • • 1 C r ^ A I ✓ V- v.. , U ■ in the manufacture of bolts of a given strength, so giving considerable cost savings.

Standard concrete reinforcing bar may also be threaded in a manner according to the present invention.

Rods used in concrete reinforcing bars are generally obtained in standard sizes, e.g. to New Zealandstandard NZS3402P: 1973 Any thread thus formed, however, would not be to any standard known to us and special nuts would be required to be produced.

Threaded bolts produced by the above described method 10 possess characteristics which differ from those possessed by known bolts produced from deformed bar after removing deformations and sizing as follows: 1. For known bolts the average diameter of the threaded portion would be less than that in the deformed part of the bar. This can be simply determined by comparing the weight per unit length of each section. 2. Threadrolling dies are not normally completely "filled" with material during the threadforming process. Therefore when threads are being rolled directly onto a deformed bar a slightly fuller thread is formed at the point of coincidence between a hollow in the forming die and a deformation on the bar being threaded. Although this does not result in any variation in the strength of the thread so formed, the slight difference in height of individual threads is detectable. 3. For known bolts a portion of the machined section is normally visible between the threaded section 1 98091 and the unmachined deformed section as it is provided as clearance between the threadrolling dies and the deformed part of the bar.

Claims (8)

* " 198G90 WHAT t/WE CLAIM IS:

1. A method of forming a uniform standard thread of substantially constant pitch circle onto a deformed bar comprising the steps of: selecting a said deformed bar incorporating a plurality of substantially regular surface deformations along at least one end thereof, said deformations individually and collectively being shaped and sized so that the average volume of material contained in the bar including said deformation(s) per unit length of said bar is substantially equal to the average volume of material required in the threaded section of the bar per unit length of bar when threaded, whereby a uniform standard thread % o/jof substantially constant pitch circle may be rolled thereon ftt: i) /J •J" by conventional thread rolling techniques without performance of an intermediate step between bar selection and thread production; and thereafter using known thread rolling techniques to thread said bar with a thread of substantially constant pitch circle over so much of the length of said bar as is able to be threaded using the said deformations originally provided thereon without performing an intermediate step between bar selection and thread rolling.

2. A method as defined in claim 1 wherein said step of selecting deformed bar of suitable cross-section includes selecting a pattern of deformation which will be suitable for use with a hardenable anchor, such as a resin or cement mortar anchor, in a rock bolt or reinforcing situation.

3. A method as defined in claim 2 wherein said Step of selecting said pattern of deformation comprises 19809 selecting a pattern of deformation having one or more helical rib deformations on said bar.

4. A method as defined in claim 3 wherein said step of selecting said pattern having one or more helical rib deformations comprises selecting a helical form or forms of opposite handedness to that of said thread.

5. A threaded deformed bar made by a method defined in any one of the preceding claims.

6. A steel bar-incorporating a plurality of substantially regular surface deformations along at least one end thereof, said deformations individually and collectively being shaped and sized so that the average volume of material contained in the bar including said deformation (s) per unit length of said bar is substantially equal to the average volume of material required in the threaded section of the bar per unit length of bar when threaded, whereby a uniform standard thread of substantially constant pitch circle may be rolled on that portion- of the bar incorporating said surface deformations by conventional thread rolling techniques without performance of an intermediate step between bar selection and thread production. said deformations include one or more helical ribs, said ribs advancing along the longitudinal axis of said bar. said ribs are of the opposite handedness to that of the desired said thread. 9. A deformed bar substantially as described herein with reference to Fig. 2 of the drawings.

7. A deformed bar as defined in claim 6 wherein

8. A deformed bar as defined in claim 7 wherein N.Z. PATENT OFFICE 16 JAN 1985 DATED THIS I L DAY 0p A. J. PARK & SON ^ PEri agents FOH THE APPLICANTS -\a-