GB2342681A

GB2342681A - Step bolt with integral collar

Info

Publication number: GB2342681A
Application number: GB9922274A
Authority: GB
Inventors: Robert Harry Lench; Michael William Rowan
Original assignee: THOMAS WILLIAM LENCH HOLDINGS; BICC PLC
Current assignee: THOMAS WILLIAM LENCH HOLDINGS; Balfour Beatty PLC
Priority date: 1998-09-22
Filing date: 1999-09-22
Publication date: 2000-04-19
Also published as: GB9922274D0; GB9820494D0; WO2000017478A1; AU6104299A

Abstract

A step bolt 1 having a threaded end 4 and an opposite end 5 which is curled for receiving a safety rope. The threaded end 4 is provided with a collar 3, forming an integral shoulder 3a which engages the support so that a nut can be screwed on to secure the step bolt in place. The bolt may be made of fine grain steel where the grain flow in the collar is controlled with no end grain effects or defects.

Description

2342681 IMPROVEMENTS IN OR RELATING TO FASTENERS This invention relates to

improvements in or relating to fasteners and is more particularly concerned with bolts known as "step bolts".

Step bolts may be utilised as a means of climbing electricity transmission towers or the like. Such bolts normally comprise a threaded portion that may be passed through a hole in the steel section/s structure of the transmission tower and secured thereto by means of a nut introduced onto the free end of the threaded portion, which nut can be tightened up with the steel section/s being sandwiched in between said nut and a shoulder on the bolt, said shoulder itself being provided by a nut formation.

Traditionally, the end of the bolt opposite the threaded portion is fashioned with a hexagon head which can be utilised in attaching or detaching the bolt to/from the electricity transmission tower or the like. Once the step bolt has been firrnly secured to the transmission tower it forms a generally horizontally projecting rod like member that can be utilised as a step for a person climbing the transmission tower. Thus, once a number of these step bolts have been attached to the transmission tower at various heights they can be utilised as steps to climb the tower to a desired height. More recently, interest has focused on the health and safety aspects for persons engaged in I climbing the transmission towers, using the step bolts. One improvement has been to replace the hexagon head end of the step bolt with a curly Itpig tail", said pig tail being utilised for passing a safety rope therethrough, said safety rope being part of a known fall arrest system designed to prevent a person climbing the tower from falling off.

It is believed that such "pig tail" step bolts tend to have certain disadvantages or that the design has not been optimised. These disadvantages range from the strength or characteristics of the bolt e.g. at low temperatures and/or versatility of the bolt for attachment to supports of varying thickness in a safe, secure manner and/or ease of manufacture. In particular, the shoulder on the bolt may be provided by a separately formed nut formation engageable with the threaded portion in such manner that, disadvantageously, the cross-section of the thread is subject to the maximum bending movement when a person stands on the bolt.

An object of the present invention is to provide a step bolt which at least alleviates one of the aforementioned, or other, disadvantages of previous designs or proposals and/or to provide a step bolt which is improved in at least some respect.

2 According to the present invention there is provided a step bolt having a threaded end and an opposite end which is curled, said threaded end being provided with an integral shoulder for engaging a support such as an electricity transmission tower or the like, so that a nut can be screwed onto the threaded end and tightened up to attach the step bolt to said support.

The integral shoulder may be enhanced by a larger radius.

Usually, for strength, the integral shoulder will be forged into the step bolt and may be on a hexagonal or other nut-like formation. Preferably, the step bolt is made from a fine grade steel which may meet British Standard BS3111-type 9. Preferably, the portion of the bolt extending from the shoulder has a length greater than 50mm and preferably up to 65mm + I Omm. Preferably, said portion is threaded along the full extent of its length.

Further according to the present invention there is provided a step bolt assembly including a step bolt in accordance with the preceding statement of invention and a nut, at least one washer, and a locknut.

3 According to another aspect of the present invention there is provided a step bolt having a threaded end and an opposite end which is curled characterised by one or more of the following features:- a) the step bolt being made from a fine grain material, preferably steel, b) the step bolt having a threaded portion of length greater than 50mm and preferably up to 65 + 5 mm, C) the step bolt having an integral shoulder, preferably enhanced by a larger radius.

d) the step bolt as in c) in which the shoulder is cold formed on a collar have a controlled grain flow with no end grain effects or defects.

Further according to this aspect of the present invention there is provided a step bolt fastener assembly comprising a step bolt in accordance with the immediately preceding statement of invention and including a separate nut, at least one washer, and separate locknut.

Further according to the present invention there is provided a method of making step bolts having a threaded end and an opposite end which is curled, said method including one or more of the following:- a) forging an integral shoulder into the step bolt, 4 b) making the threaded end greater than 50mm long and up to 65mm or greater, C) forging the collar as in a) and controlling the grain flow in the collar without end grain effects or forming defects.

d) high temperature galvanising the bolt.

Many advantageous features of the present invention will be apparent from the following description and drawings.

An embodiment of a step bolt in accordance with the present invention, will now be described, by way of example only, with reference to the accompanying simplified, diagrammatic drawings in which:- FIGURE I shows a front view of the step bolt in accordance with the present invention positioned opposite a nut, a washer and a locknut.

FIGURE 2 shows a view of the step bolt looking in direction of arrow A of FIGURE 1; FIGURE 3 shows an underneath view of the step bolt shown in FIGURE I looking in the direct of arrow B; FIGURE 4 shows a view of a step bolt in accordance with the present invention prior to forming of a thread on one end of the bolt and prior to forming a curly "pig tail" on the opposite end, and 5 FIGURE 5 shows a macrosection of part of the step bolt exhibiting grain flow pattern after static and dynamic testing.

Referring to FIGURES 1-3 of the drawings, a step bolt I has a long shaft 2 with an integrally formed hexagonal collar 3 forming a shoulder 3a which, in practice, will seat against the steel section/s or structural member (not shown) of an electricity transmission tower or the like. The right hand end of the shaft 2 as shown in FIGURES I and 3 is provided with a screw thread 4 extending from the free end all the way up to the shoulder 3a. The left hand end of the shaft 2 is provided with a curly pig tail formation 5, the general shape of which should be evident from FIGURES 1-3 of the drawings.

The shape and characteristics of the step bolt I have been arrived at only after careful experimentation and testing in order to meeting rigorous health and safety standards. Most importantly, the hexagonal formation 3 is forged into the step bolt and the step bolt itself is made from a fine grade steel which will meet British standard BS31 11 -type 9.

The provision of the integral (hexagonal) formation 3 is an extremely important part of the present invention, more particularly because it obviates a weakness inherent in other designs of step bolts. Some step bolts are provided with a thread at one end without the integral hexagonal collar. Instead of the 6 hexagonal collar, a nut is screwed onto the free threaded end as far as possible on the shaft with the end of the nut nearest the free threaded end effectively forming the shoulder 3a. Thus, disadvantageously, the minimum cross-section of the thread is subject to the maximum bending movement when a person stands on the step bolt.

In tests performed on the step bolt I in accordance with the present invention, bending moments have been applied to the shaft 2 of the bolt about the integral hexagonal collar region on the shaft and the shaft can be very severely bent (approximately to an angle of 90o or more) without any weakness or cracking of the bolt occurring. The larger radius r enhances the integral formation 3.

In tests performed on similar prior art step bolts provided with a loose nut forming the shoulder, the shaft fractures under such tests and such bolts are, therefore, unable to meet British Health and Safety standards (BSEN795). Additionally, the step bolt I as shown in the FIGIMS is made of fine gain steel, hardened and tempered rather than mild steel as used in other step bolts.

Thus, the choice of material is also very important for the step bolt 3 since it enables the step bolt to retain high (good) ductility at high levels of 7 tensile strength unlike prior art counterpart bolts. The fine grain steel withstands low temperatures extremely well.

The dimensions of the step bolt I are also very important and of particular importance is the length 4a of the threaded portion of the shaft. The length 4a as shown in Figures I & 3 is 65mm which is long enough to allow the step bolt to be passed through two layers of steel section/s or two structural members (not shown) utilised in electrical transmission towers and for the bolt to be secured to the tower by the use of a nut 6, a washer 7 and a further locknut8.

Once again, for safety reasons, it is believed to be important that the step bolt can be utilised not only with a securing nut 6 but with a locknut 8 and at least one washer 7.

The hexagonal collar 3 is produced by a four stage die process.

FIGURE 4 shows a stage in the manufacturing process of the step bolt, after the hexagonal formation has been completely formed and prior to the curly pig tail being formed. The thread is rolled into the shaft portion prior to the shaft being bent into the curly pig tail shape. The length of shaft X extending to left of collar 3 prior to forming the pig-tail is 365mm + 5mm. 8 Advantageously, the free end of the shaft length X is bent by a cold bending process to form pig tail 5.

The nut 6 is a standard nut, grade 10 and the locknut 8 is grade 8, said washer 7 being a 4min thick, flat washer.

The bolt I and nuts 6,8 are made to conform to BS4190. The bolt I is heat treated to property class 8.8 after cold bending of the curly pig tail 5 and is high temperature spun galvanised in accordance with BS 7371 Past 6.

The precise dimensions and configuration of the pig tail 5 are important for allowing a safety rope (not shown) to be easily introduced into the eye 5a of the pig tail 5 whilst allowing the rope to extend vertically, in use, through the eye portion (i.e. in use the axis of eye 5a will be generally vertical). Since the shape of the pig tail is important for the safety rope to be easily introduced onto the tail and yet be captivated in the eye without easily becoming unintentionally dislodged from the pig tail, dimensions thereof are shown on the FIGURES of the drawings. It is to be noted that with the step bolt I in the orientation as shown in FIGURE I the pig tail 5 extends in a direction into, rather than out of, the paper, but other pig tail bolts in accordance with the present invention may have the pig tail extending in the opposite direction.

Thus a righthand or lefthand pig tail may be provided on the bolt. The pig-tail 9 spirals generally upwardly in use with a straight free end portion 5b extending generally horizontally. In this way the pig tail forms a stop to help prevent a foot from sliding off the step bolt. In use in the arrangement as shown in FIGURE 1, access for a safety rope will be from the left of the bolt from the aspect of the user looking along the bolt towards the threaded portion 4 although access could instead be provided for, from the right. It is to be noted that the spiral of the pig tail 5 is tighter than the spiral formations of previously proposed pig tail bolts and it is believed that the tighter spiral is better at retaining the safety rope within the eye.

The manufacture of the pig-tail may be on a modified spring coiling machine which enables a tighter twist to be obtained than can be obtained by other methods of manufacture. The advantageous tighter form of the pig tail reduces the possibility of the safety rope unintentionally coming out of the eye during use. This objective is also assisted by the straight free end portion 5b being longer than prior art designs and reduced gap g between the portion 5b and the coiled section 5c.

The step bolts I are able to meet the following British Health and Safety (BSEN795) static and dynamic tests, unlike any prior pig tail step bolts. FIGURE 5 illustrates the typical grain flow pattern in the step bolt I after static and dynamic testing.

Static Test A minimum of 6 samples shall be subjected to each of the static tests described below (the same sample may be used for both tests).

A static force of 4 kN shall be applied, in the direction of use in service, for a minimum of 3 minutes, the step bolt shall carry the load without failing, there shall be no more than very slight permanentbending of the step bolt and no deformation to the spiral end.

A static force of 6 kN shall be applied, in the direction of use in service, for a minimum of 3 minutes, the step bolt shall carry the load without failing, some bending of the bolt will be acceptable as long as there is no significant deformation to the spiral end of the bolt.

Dynamic Test A minimum of 8 samples shall be subjected to the dynamic tests described below (4 at ambient temperature & 4 at -I OOC).

This shall be carried out according to the principals set out in BS EN364 section 5.5.2.

A solid mass of 100kg shall be connected via connectors, to BS EN362, and a lanyard, to BS EN354, of length 2.00m +/- 50mm to the step bolt under test.

At a maximum of 300mm horizontally from the step bolt and by means of a quick release device, support the solid mass such that when released it will fall freely through 3.00m before the lanyard starts to arrest the fall. The solid mass shall be arrested, some bending of the step bolt will be acceptable as long as there is no significant deformation to the spiral end of the step bolt and there is no sign of cracking.

The Dynamic test shall be carried out at both ambient temperature and - I OOC.

Alternatively, the sample testing quantities could be: Static Test - I Dynamic Test - 4 Further details of the embodiment of the present invention are as follows:- Standard Nut Grade 10 (6) 12 The grade 10 nut 6 is specified to provide greater strength in the nut threadform. and reduce the possibility of failure during assembly by thread stripping. The nut 6 is overtapped 0.40mm to accommodate the thick galvanized coated on the bolt thread 4a.

Overtapping by 0.40mm reduces the loadable thread contact area by an average of -22%.

Lock Nut Grade 8(8) The lock nut 8 is fitted between the washer 7 and the ftill nut 6; although in general steel erectors will fit the lock nut 8 after the full nut 6. The lock nut 8 is intended to prevent loosening of the nut 6 and bolt threads, with the possibility of the movement of the "pig tail" and the bolt thread 4a being subject to the maximum bending movement.

Flat Washer (7) The washer 7 is fitted against the structural member (electricity transmission tower) and is used to provide a flat surface which reduces friction 13 between the nut 6 and the structural member during tightening. The washer 7 also acts to reduce the bearing stress under the nut face.

BS 4190: 1967 BS 4190 is a standard for "black" bolts and nuts that has recently been declared obsolescent for general use. Its use has been retained for Structural Bolting until the new standards have been prepared. "Black" is equivalent to product made to "Product Grade C" tolerances as defined by ISO 4759 pt 1.

PropeM Class 8.8 Property Class 8.8 is the lowest class of bolts known as High Tensile Bolts. The mechanical properties have to be generated by hardening and tempering to the properties specified in BS 3692:1967. Preferably the mechanical properties meet ISO 898/1 also.

The 8.8 designation means the following:

8- one tenth of the minimum tensile strength of 80 Kgf/mm'.

14 8- 80% of the minimum tensile strength of 80 Kgf/mm' is the minimum yield strength of 64 Kgf/mm'.

BS 7371 Past 6, 1998 BS 7371 Past 6 is the current standard for hot dip galvanizing and includes spun galvanizing with a minimum coating thickness requirement of 43 microns. The bolt I is fully heat treated after cold bending of the "pig tail" to remove any cold work that could result in embrittlement; it is prepared for galvanizing preferably by mechanical cleaning.

Production The initial blank for the step bolt 1 is cold formed on a four station progressive header which produces a controlled grain flow in the hexagonal collar 3, with no end grain effects or other forming defects. The routine quality procedures include a regular check of the material gain flow in the area of cold forming.

Cold rolled threads 4a are produced by a circular form generator resulting in threads with the minimum of defects, removing the possibility of failure by fatigue.

Desiian The cold formed hexagonal collar 3 and large radius r on the step side 2 of the bolt I and the structural member (i.e. electricity transmission tower - not shown) is designed to provide maximum strength at the point of maximum moment of force under a falling load. This compares with the reduction in cross-sectional area when a cut thread and nut are used or the introduction of defects and sites of failure for welded components.

The use of material heat treated to the fastener property class 8.8 means that the component can be tightened to a sufficiently high clamp force (or preload) that will prevent the hexagonal collar 3 from moving away from the structural member under load. Such a movement would subject the smallest cross-sectional area, through the thread form, to possible fatigue inducing loads over time.

Hardening and Tempering 16 Preferably a heat treatment process is carried out to harden and/or temper each bolt. The hardening process is preferably carried out at approximately 900'C for somewhere in the order of 40 minutes. The hardening process can be concluded by a quench and wash. Hardening in the order of 890-910T for times between 30 and 60 minutes are acceptable also.

Preferably the tempering process takes place at between 470 and 500T for around 2 hours. Again, the tempering process can be followed by a quench and wash. Alternatively air cooling can be allowed to take place.

High Temperature Galvanizing High temperature (560T) is used to reduce the effect of Silicon in the galvanizing process; Silicon being a necessary requirement of "killed" steels, which at certain concentrations 0.05-0.15% can result in unstable coating growth at the non-nal 480'C galvanizing temperature.

High temperature has certain other advantages, namely the higher fluidity of the coating which during spinning results in a smoother surface that has few imperfections, ensuring free running of the nut 6. The reaction of the zinc layer is more complete with an iron-zinc layer at the bolt surface instead of pure zinc. The iron-zinc layer is harder and less likely to weld to the nut 17 thread during tightening and cause failure by torsional shear. These benefits lead to a significant reduction in the risk of inutility of any given bolt by a worker in location upon a tower.

The high temperature galvanising is a very important part of the present invention, and while preferably this takes place in the order of 5600C, a temperature in the range of 5300C to 5700C is also appropriate.

Low Carbon, Manganese Boron Steel BS31 11 Type 9 The above boron steel is, advantageously, used for the step bolt I and is a fine grain steel with a closely controlled range of chemical analysis suitable for heat treatment to property class 8.8. The steel has high levels of ductility together with very good low temperature properties. Values are typically as follows for a fastener with a tensile strength of 800 - 1000 N/mm':

% Elongation 17 % Reduction in Area 65 Low Temperature Impact Properties FATT - 750C 150J at -40'C with a 2min V notch 18 The Expression FATT means Fracture Appearance Transition Temperature. As a material at progressively lower temperatures the appearance of the fracture surface changes from ductile (fibrous) to brittle (crystalline). The FATT is normally specified at 50% i.e. 50% ductile and 50% brittle failure.

It is to be understood that the scope of the present invention is not to be unduly limited by the particular choice of terminology and that a specific term may be replaced by any equivalent or generic term. For example, the term step bolt could be replaced by "fastener" or "climbing step". The terms "vertical" and "horizontal" as used throughout the specification should not be interpreted as limiting and are used merely to indicate the generally intended orientation in use. Further it is to be understood that individual features, method or functions related to the step bolt or step bolt assembly might be individually patentably inventive. In particular, any disclosure in this specification of a range for a variable or parameter shall be taken to include a disclosure of any selectable or derivable sub-range within that range and shall be taken to include a disclosure of any value for the variable or parameter lying within or at an end of the range. The singular may include the plural or vice versa. Further according to the present invention there is provided a step bolt or

19 climbing step (or method of making same) having any derivable feature or combination of features as herein described or illustrated.

1-

Claims

CLAIMS:-

1. A step bolt having a threaded end and an opposite end which is curled, said threaded end being provided with an integral shoulder for engaging a support such as an electricity transmission tower or the like, so that a nut can be screwed onto the threaded end and tightened up to attach the step bolt to said support.

2. A step bolt as claimed in claim I in which the integral shoulder is enhanced by a larger radius.

3. A step bolt as claimed in claim I or claim 2 in which the integral shoulder is forged into the step bolt.

4. A step bolt as claimed in claim 3 in which the shoulder is on a hexagonal or other nut-like formation.

5. A step bolt as claimed in any one of the preceding claims which is made from a fine grade steel.

21 6. A step bolt according to any preceding claim comprising a low carbon, manganese, boron steel.

7. A step bolt as claimed in claim 5 which meets British Standard BS_3) I I I -type 9.

8. A step bolt as claimed in any one of the preceding claims in which the portion of the bolt extending from the shoulder has a length greater than 50nun.

9. A step bolt as claimed in claim 8 in which said portion has a length up to 65mm + 10mm.

10. A step bolt as claimed in any one of the preceding claims in which the portion of the bolt extending from the shoulder is threaded along the full extent of its length.

11. A step bolt according to any preceding claim which has a high temperature galvanised finnish. 'I 12. A step bolt according to claim I I wherein high temperature galvanising took place in the region of 530'C to 570'C. 22 13. A step bolt according to claim 12 wherein the galvanising took place at approximately 560'C.

14. A step bolt according to any preceding claim having undergone a hardening process at a temperature in the order of 900'C.

15. A step bolt according to any preceding claim having undergone a tempering process in the order of 470-500'C.

16. A step bolt according to any preceding claim which meets standard ISO 898/1 and preferably Property Class 8.8.

17. A step bolt according to any preceding claim which meets standard BS4190.

18. A step bolt according to any preceding claim which meets standard ISO 4759 Part 1.

19. A step bolt assembly including a step bolt as claimed in any one of the preceding claims and a nut, at least one washer, and a locknut.

23 20. A step bolt having a threaded end and an opposite end which is curled characterised by one of more of the following features:- a) the step bolt being made from a fine gain material, preferably steel, b) the step bolt having a threaded portion of length greater than 50mm and preferably up to 65 + 5 mm, c) the step bolt having an integral shoulder, preferably enhanced by a larger radius, and/or d) the step bolt as in c) in which the shoulder is cold formed on a collar having a controlled grain flow with no end grain effects or defects.

2 1. A step bolt fastener assembly comprising a step bolt as claimed in claim 19 and including a separate nut, at least one washer, and separate locknut.

22. A method of making step bolts having a threaded end and a region which is curled, said method including forging an integral shoulder into the step bolt.

23. A method of making step bolts having a threaded end and a region which is curled, according to claim 22 or independent thereof comprising the step of making the threaded end greater than 50mm long and up to 65mm or greater.

24 24. A method of making step bolts having a threaded end and a region which is curled, according to claim 22 or 23 or independent thereof comprising the step of forging the collar and controlling the grain flow in the collar without end grain effects or forming defects.

25. A method of making step bolts having a threaded end and a region which is curled, according to any of claims 22 to 24 or independent thereof comprising the step of high temperature galvanising the bolt.

26. A method according to claim 25 wherin the galvanising takes place within the temperature range of 530'C to 570'C and preferably at 560'C.

27. A method according to any of claims 22 to 26 comprising the step of hardening the bolt using a temperature in the order of 900'C.

28. A method according to any of claims 22 to 27 comprising the step of tempering the bolt in a temperature range of between 470'C and 500'C.

29. A method according to any of preceding claims 22 to 28 comprising the step of making the bolt from a low carbon, manganese boron steel such as BS3111 type 9.

30. A step bolt substantially as herein described with reference to the FIGURES of the accompanying drawings.

3 1. A method as claimed in claim 2 and substantially as herein described.

26