Improvements in or Relating to Screwbolts

Abstract

The present invention relates to fasteners such as screwbolts in general and to anti-shake screwthreaded systems and anti-shake screwthreaded assemblies employing screwbolts in particular. As is universally known, in relation to screws and threaded fasteners, a thread comprise a continuous helical ridge formed on the inside (nut) or outside (screw) of a cylinder. An issue of concern for all types of screw fasteners is that if they rotate relative to a fastened item, they diminish the degree of fastening. Many methods of preventing a relative rotation between bolt and nut have been devised. The present invention seeks to provide an improved screwbolt system for use in engineering and construction. The present invention also seeks to provide a screwbolt for use as a fastener in harsh conditions of load and have a reduced tendency to unfasten. The present invention also seeks to provide a method of installing such screwbolts.

Claims

1. A screwthreaded fastening arrangement, the arrangement comprising a generally circularly cylindrical shank component having a first surface hardness and a nut component having a generally circularly cylindrical aperture with an inside surface with a second hardness, wherein an outside diameter of the shank corresponds with an inside diameter of the nut; wherein one of the components is provided with a screwthread helix angle in the range of 10-80, the screwthread having a surface hardness greater than the surface hardness of the other component, the screwthread extending outwardly with respect to the surface of the respective component; wherein the screwthread is operable to engage with the surface of the other component, and wherein, upon relative rotational movement and axial advancement therebetween, is operable to cut a corresponding thread therein; and, upon cessation of such rotational advancement to induce a state of fixation as between the screwthread and the corresponding cut thread, whereby to provide a vibration-proof fixing.

2. A screwthreaded fastening arrangement according to claim 1, wherein the inside diameter of the nut component is in the range of 110% -100% the diameter of the shank, with the diameter of the thread being greater than the inside diameter of the nut component.

3. A screwthreaded fastening arrangement according to claim 1 or 2, wherein the, the thread is raised from a working surface in the range of 0.5-10% of the diameter when arranged upon the shank or an inside surface of the nut component.

4. A screwthreaded fastening arrangement according to any one of claims 1-3, wherein the length of the nut comprises at least one turn of the helix thread.

5. A screwthreaded fastening arrangement according to any one of claims 1-3, wherein the length of the nut comprises at least two turns of the helix thread.

6. A screwthreaded fastening arrangement according to any one of claims 1-5, wherein the length of the nut is substantially plain yet comprises a threaded lead-in threaded portion comprising at least a one quarter turn of the helix thread.

7. A screwthreaded fastening arrangement according to any one of claims 1-5, wherein the length of the nut is substantially plain yet comprises a threaded lead-in portion comprising at least a one half turn of the helix thread.

8. A screwthreaded fastening arrangement according to any one of claims 1-7, wherein the inside wall of the nut is substantially parallel yet comprises a lead-in portion comprising at least a one quarter turn of the helix thread.

9. A screwthreaded fastening arrangement according to any one of claims 1-7, wherein the inside wall of the nut is substantially parallel yet comprises a lead-in portion comprising at least a one half turn of the helix thread.

10. A screwthreaded fastening arrangement according to any one of claims 1-9, wherein the hardness of the inside surface of the nut component is in the range of 10-200 HB and the hardness of the threaded helix being in the range 200-1000 HB, when the nut component is received in a substantially blank form.

11. A screwthreaded fastening arrangement according to any one of claims 1-9, wherein the hardness of the threaded helix when comprising part of an inside surface of the nut component is conveniently in the range of 200-1000 HB and the hardness of the shank in which it defines a fastening thread is conveniently in the range 10-200 HB, when the shank component is received in a substantially blank form.

12. A screwthreaded fastening arrangement according to any one of claims 1-11, wherein the component having the screwthread is the generally circularly cylindrical shank component and wherein the nut component comprises a simple tubular item with at least two flat surfaces (flats) upon an external surface defined parallel to an axis of the tubular item.

13. A screwthreaded fastening arrangement according to claim 12, wherein there are four or six flats arranged in, respectively, a generally square or a regular hexagonal arrangement.

14. A screwthreaded fastening arrangement according to any one of claims 1-11, wherein the nut comprises a two part member with a hardened outer radial tubular member, within which a relatively soft tubular section is placed.

15. A screwthreaded fastening arrangement according to claim 14, wherein the insert can be simply be removed by the use of a clip or other fastener.

16. A screwthreaded fastening arrangement according to any one of claims 1-15, wherein the screwthread comprise one of: a single helix thread, a pair of parallel spaced apart helical ridges or three parallel spaced apart helical ridges.

17. A method of providing a screwthreaded fastening between a generally circularly cylindrical shank component having a first surface hardness and a nut component having an inside face with a second hardness, wherein an outside diameter of the shank corresponds with an inside diameter of the nut; wherein the component having the greater surface hardness is provided with a screwthread having a helix angle in the range of 10-80, the screwthread extending outwardly with respect to the surface of the respective component, wherein the screwthread is operable to engage with the surface of the other component, wherein: upon relative rotational advancement thereof, to cut a corresponding thread therein; and, upon cessation of such rotational advancement to permit cooling and fixing of the joint, whereby to provide a vibration-proof fixing.

18. A method according to claim 17, wherein the component having the screwthread is the generally circularly cylindrical shank component.

19. A method according to claim 17, wherein the component having the screwthread is the nut component.

20. A method according to any one of claims 17-19, wherein the nut component can comprise a simple tubular item with at least two flat surfaces (flats) defined parallel to an axis of the tubular item.

21. A method according to claim 20, wherein the nut component comprises four or six flats arranged, respectively, in a generally square or a regular hexagonal arrangement.

22. A method according to claim 20, wherein the screwthread can comprise a single helix; pair of parallel spaced apart helical ridges, a triple arrangement of parallel spaced apart helical ridges.

23. A screwthreaded fastening arrangement according to any one of claims 1-7, wherein the inside wall of the nut is also provided with a helix thread.

24. A screwthreaded fastening arrangement according to claim 23, wherein the inside wall of the nut is substantially parallel.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0024] For a better understanding of the present invention, reference will now be made, by way of example only, to the Figures as shown in the accompanying drawing sheets, wherein:

[0025] FIG. 1 illustrates a portion of a screwthread from one side;

[0026] FIG. 1A illustrates a known screwbolt;

[0027] FIGS. 2A & 2B shows a drill tap;

[0028] FIG. 3 shows a fishplate join in a rail track;

[0029] FIG. 4 shows a set of points for a railway junction;

[0030] FIG. 5 shows a first view of the present invention in part side/part cross-section;

[0031] FIGS. 6A & 6B show side and perspective view form a distal of a fastener in accordance with the present invention;

[0032] FIGS. 7A & 7B show perspective view and plan views of a nut fastener in accordance with the present invention;

[0033] FIGS. 8A-8C show features of a first alternative nut section; and,

[0034] FIGS. 9A-9C show features of a second alternative nut section

[0035] FIGS. 10A-10C show features of a third alternative nut section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] There will now be described, by way of example only, the best mode contemplated by the inventor for carrying out the present invention. In the following description, numerous specific details are set out in order to provide a complete understanding to the present invention. It will be apparent to those skilled in the art, that the present invention may be put into practice with variations of the specific.

[0037] Referring now to FIG. 5, an example of a fastener shall be detailed in accordance with a first aspect of the invention, comprising a metallic screwbolt 50 comprising a shank 51 with a twin helix screwthread 52 defined thereon, a flanged head 53 and a metallic securement nut 54, which screwbolt in the form of the blank is of a right circular cylindrical form. The screwthread 52 comprises a ridge-groove-ridge twin helix configuration that extends helically along the shank 51 and comprises a pair of parallel opposed ridges 55 upstanding from an adjacent land 56, with a groove 57 defined therebetween. Two substrates 58 are fastened togetherwith washers 59 at either side thereof. In this instance the ridges of the screwthread 52 of the shank member are hardened and which ridges extend typically in the range of 0.5-3 mm, more typically in the range 0.8-1.6 mm above the diameter of the shank, which for this M10 bolt would be situated between the screwbolt head and the securement nut (ideally employing one or more washers to, inter alia, spread the load when securely abutting to opposite sides of the connected substrates). In this embodiment, the threaded shank member is an M10 bolt, meaning that the diameter of the shank is 9.7-9.9 mmi.e. has a nominal diameter not exceeding 10 mm, the screw pitch being of the order of twice the diameter, the major diameter of the helices being in the range of 10-15% of the diameter of the shank and the spacing between the helices is of the order of 4-6 mm, with a well-depth of 1-2 mm, being approximately 105 of the diameter of the shank. The internal diameter of the nut is 10.5 mm meaning that the hardened ridges will cut into the softer material of the inside surface of the nut. It will be appreciated that the lead-in thread at the distal end of the bolt must be sharp. It will also be appreciated that the outer surface of the nut can be heat treated whereby to enable purchase by wrenches and the like without significant rounding. Washers 59 are often used with threaded fastener. The use of a washer distributes stresses that arise around a bolted joint. Additionally, the washer reduces friction as the bolt turns. Generally, it is best to have at least one washer under the turning part of the fastener, either the nut or the head. These bolts are commonly available in shank diameter sizes of 6, 8, 10, 12, 16 & 20 mm, but other sizes can be made for particular applications.

[0038] It is believed that the components are substantially affixed to one another by means of friction welding where large turning forces applied with respect to one component relative to the other component cause significant pressures of the parts to act mutually against each other raising temperature. It is believed that by reason of such heat being generated at the weld interface a small heat-affected zone is created, which in turn leads to a fast joining time (of the order of a few seconds) noting that in the process of tightening one component with respect to another, the movement must be continuous and, it has been found that electrically powered/compressed air power tools (e.g. the so-called nut-runner) are conveniently employed whereby to provide constant/reactively increasing levels of torque, given that the use of hand operated spanners etcetera will generally provide discontinuous action as the hand wrench etcetera is operated in a to and fro operation, even if a ratchet mechanism is employed. Friction welding techniques benefit from the welds generally being melt-free, which mitigates grain growth in engineered materials, such as high-strength heat-treated steels, as is the case with the hardened thread helices. Another advantage is that the motion tends to clean the surface between the materials being welded, which means they can be joined with less preparation, with the debris being removed from contact surfaces. During such a welding process, depending on the method being used, small pieces of dirt will be forced out of the working mass (flash). It will also be appreciated that there are many variables that can be utilised in a custom product. For example, the relative hardness of the two metals can be adjusted; the softer that the soft material is, then the easier that it can be to screw the harder material into the softer surface; the length of the nut can be adjusted such that between one and two helical terms can be retained within the distance of the nut, with similar results being obtainable. A still further benefit of friction welding is that it is possible to weld two metals with wide differences in melting points of the two materialswhich may well have prevented such materials from being welded together with known welding techniques. Indeed, friction welding can provide a full strength bond with no additional weight. Common uses for these sorts of bi-metal joins has arisen with regard to cryogenic systems e.g. MRI imaging equipment, where copper-steel joints are common in the reactor cooling systems, and in the transport of cryogenic fluids, where friction welding has been used to join aluminium alloys to stainless steels and high-nickel-alloy materials for cryogenic-fluid piping and containment vessels. The gap between the shank and the aperture defined by the nut has been found to operate well in the range of 0.2-0.5 mm, with larger gaps being required for screwbolts with higher ridge members.

[0039] Referring now to FIGS. 6A and 6B, an example of a fastener shall be detailed, comprising a screwbolt 50 having a shank 51 with a screwthread 52 defined thereon, a flanged head 53 and a securement nut 54, which screwbolt in the form of the blank is of a right circular cylindrical form. In this embodiment, the threaded shank member is an M10 bolt, whilst the securement nut comprises a simple body having two flats defined thereon for engagement with a wrench. Following attachment, applying a suitable degree of torque, taking into account size of fastener and relative hardness of the components, the fastening nut 54 became fixed in position due, it is believed at least in part, to a friction welding action and, where the hardness of one material permits, to a degree of galling. The axial dimension of the land 56 is at least 50% of the blank diameter with the result that relatively large amounts of substrate material are disposed between the ridge-groove-ridge configuration when the fixing device is in place. The nuthaving two flats 59 has an internal diameter in of 9.7 mm. Prior to attachment, the nut has no particular thread design defined on an inside surface thereof; conveniently, it can be uniformly circularly cylindrical. The material surrounding the hole defined within the nut has a hardness in the range of 1-200 HB, compared to a hardness of the thread being typically 200-1000 HB.

[0040] Applicant has performed a number of tests using their Hexagon Screwbolt (HSB) bolts together with nuts fabricated from EN8M (080M40), an unalloyed medium carbon steel. The screwbolts are fabricated from boron 920 steel. Boron steels are medium carbon steels with added boron and are easily hardened and such boron steels can be hardened to a degree of hardness equal to higher carbon steels and more expensive low alloy steels, and distort to a minimal degree after heat treatment. An HSB 08/100 screwbolt was fastened to a nut with an 8 mm diameter (i.e. corresponding to the diameter of the shank), and had a length of 20 mm with no thread defined therein, although a 30 lead-in flange angle was provided. Light oil was employed as a lubricant to ease penetration of the upstanding twin-thread the initial cut and using a tool commonly referred to as a nut-spinner or similar. The twin thread helices upstand from the shank by typically by 0.5-1.2 mm, with a well between each pair of helices having similar dimensions. The nut was found to lock after a reduction of torque. Using limited testing equipment, a maximum torque of 128 Nm was applied to the bolt and failure of the fastening did not occur. For comparison purposes, the properties of an 8 mm ISO grade 10.9 (alloy steel, quenched and temperedISO, per Rockside Export limited) was provided with a torque limit of 32.8 Nm. Using an HSB 10/100 screwbolt, fastened to a nut with a 10 mm diameter (i.e. corresponding to the diameter of the shank), a maximum torque of 128 Nm was applied to the bolt and failure of the fastening did not occur. Again, for comparison purposes, the properties of a 10 mm ISO grade 10.9 material was provided with a torque limit of 65.5 Nm. Similar values achieved using basic equipment and an HSB 12/100 fastened to a similarly blank nut enabled a 305 Nm level of torque to be recorded. Once again, for comparison purposes, the properties of a 12 mm ISO grade 10.9 material was provided with a torque limit of 112.7 Nm. The steel employed for the bolt was Boron Steel BS3111/9/2.1.A, having a mechanical zinc finish, being case hardened and having a Brinell hardness of 200, not including the helices which are hardened within the range 600-1000. It will be apparent that the invention can be applied to a wide variety of metallic fastening materials.

[0041] FIGS. 7A and 7B show a second type of nut 70 to be employed with a screwbolt; the nut comprises a first hexagonal section 71, whereby standard wrenches, ratchet drivers and the like permit engagement with the nut 70. The second section comprises a circularly cylindrical element 72, which when rotated and supported by hand can be more easily handled, whereby to assist in control during a fastening process. The increased axial length provides a distance sufficient to enable a sufficient portion of thread to engage with a screwbolt, noting that a screwbolt pitch can be 2 cm or greater and the axial length of the nut must be at least equivalent to a pitch of the thread; preferably one and half times the pitch of the thread and more preferably twice the pitch.

[0042] FIG. 8A shows a first alternative style of nut 80 in perspective sectional view wherein the tubular inside bore 81 of the nut has a lead-in/chamfered section 82, the view being a section on A-A per FIG. 8C, which shows the nut from an off-axis perspective view, with a regular six-sided hexagonal head 84 having a flared section 83 operable to spread forces onto a part to be fastened when in use. FIG. 8B shows the profile of an inside wall section of the bolt 80, indicating the lead in 82 relative to an otherwise plain bore 81. The nuts are soft to allow the screwbolt with which the nut will cooperate with to cut its own thread. FIG. 9A shows a second alternative style of nut 90 in perspective view wherein the tubular inside 91 of the nut has no lead-in section, but instead has a lead-in thread section comprising two grooves 92, 93 the perspective view being a section on A-A per FIG. 9C, again in an off-axis perspective view, which shows the nut, with a regular six-sided hexagonal head having a flared section 83 operable to spread forces onto a part to be fastened when in use. FIG. 9B shows the profile of an inside wall section of the bolt 90, indicating the lead in screwthread 92, 93 relative to an otherwise plain bore 91. Again, the nut is soft to allow the screwbolt with which the nut will cooperate with to cut its own thread. FIG. 10A shows a second alternative style of nut 100 in perspective view wherein the tubular inside 101 of the nut has an alternative lead-in thread section comprising two female channels 103, 104 having a male helix 105 therebetween, the perspective view being a section on A-A per FIG. 10C, again in an off-axis perspective view, with the nut being a regular six-sided hexagonal head. FIG. 10B shows the profile of an inside wall section 101 of the bolt 100, indicating the lead in screwthread 103, 105, 104 as described above. This enhanced screwthread lead-in is believed to enable a torque load to be accepted without stripping and thereby facilitate use with screwbolts as shown in FIGS. 6A, 6B above.

[0043] Screwbolts as made by the Applicant Company are made of hardened steel; in particular, the helices are hardened beyond the standard Brinell hardness of approx. 200 up to 1000, preferably 600-1000, more preferably 700-900, to enable the screwbolts to have a self-cutting capability when used in, for example, a concrete bore, dimensioned to enable passage thereof upon driving by the use of a wrench or power tool driving the head or stud in the case of a stud-bolt which may have a drive head that has engagement features which do not extend beyond the diameter of the shank, two distinct types of thread may be applied upon the shank for engagement with distinct coupling nuts, as indicated in FIG. 1A.

[0044] Modern and traditional construction fastening bolts are made from a variety of steels which are manufactured to increase strength. Conveniently, extreme endurance fastening bolts are manufactured with boron steel, which are cold forged, thread rolled and then subjected to a heat treatment and yellow passivation. Tempering, following oil or water quenching after forming, toughens boron steels. The addition of only 0.001-0.003% soluble boron to a suitably protected base steel can produce an increased hardenability compared to that obtained by additions of about 0.5% manganese, chromium or molybdenum, but with little effect on the as-rolled, normalised or annealed strength.

[0045] An improved vibration-proof fastening in accordance with the invention can be provided by the use of a screwbolt in conjunction with a fastening means comprising a simply apertured memberi.e. without any internal threadwith a relatively low hardness, in common with that of a mild steel, for example. Equally, the nut may be provided with a hardened inside face for forming a die, which material, with a hardness of 800-1000 HB can then work around a untreated steel rod, such as re-bar, conveniently made of a general uniform cross section, having a hardness of 120 HB. Whilst specific values have been provided, it will be appreciated that a wide variation of values can be used in practice. Whilst the Brinell hardness (HB) of a heat-treated screwbolt is of the order of 800-1000 HB (or more), the Brinell hardness of mild steel is 120 HB, hardened AW-6060 Aluminium is 75 HB 18-8 (304) annealed stainless steel is 200 HB. Untreated/unalloyed (pure) metals such as Aluminium and Copper have hardness values of 15 HB and 35 HB.

[0046] Variations on the number of helices is possible; the Applicant Company has developed screwbolts with distinct arrangements of helices with respect to their number, relative spacing and relative height, which provide distinct benefits when used with particular material combinations. In the test examples, it is believed that the provision of the well between the helix threads enables any material displaced by the hardened helices to be retained, without preventing premature binding of the movement between the parts. Conveniently, a distal, entry end of the shank element is of a reduced diameter and is configured so as to provide a self-tapping capability, when the shank supports a threaded ridge element, the height of the ridges can be conveniently increased from zero to full height over the first full turn. In use, the fixing device is introduced into an apertured bore in a substrate such as a fishplate by turning so as to form a thread on the interior walls of the bore.

[0047] Generally speaking, the helix angle of the helical threads will be in a range from 20 to 80. Within this range of helix angles, one group of fixing devices conveniently has threads which have a helix angle of from 30 to 75 whilst the helix angle of the threads in another group is from 35 to 65, a third group having a helix angle of from 40to 55. The physical dimensions as between parts can also be permitted to vary; for example, the inside diameter of a nut component need not correspond generally to a shank diameter, but the helix diameter will matter more, with regard to an ease of fastening and to the ultimate loads that can be applied.

[0048] In addition to the material characteristics that are take into account to enable a screwbolt to be manufactured such that it has, inter alia, sufficient tensile strength, a lubricious coating to assist the two components to initially movegiven that the benefit of such coatings diminish under heat. Nonetheless, inventors have determined that a range of dry film lubricants can be selected; preferred dry film lubricants can have provide resistance to abrasion prior to cutting the thread in the desired fastened position. Friction results from two surfaces sliding across each other and friction is quantified as a dimensionless number that describes the reduction of drag (force) between the sliding parts, whereas release is the property of a surface which results in an inability of substances to adhere to it and is a function of surface energy.

[0049] In the event that the shank element is provided with a thread, the screwbolt can be formed by thread rolling with a helical bore wall engagement configuration by a thread rolling apparatus, as is known. A thread-rolling station comprises a fixed die and a displaceable die; the two dies are spaced apart by a gap therebetween being equal to the core diameter of the product being rolled. The displaceable die is displaceable in reciprocating fashion. In use, a blank is inserted between the fixed and moving dies by manual or mechanical means as is known in the thread-rolling art. The reciprocating action of the moving dye then carries the blank between them, during this time, the blank is plastically deformed to the face of the dyes as the blank rolls along the faces thereof. This gives rise to formation of the helical bore engagement configuration: die grooves give rise to ridges in the anchorbolt and die ridges give rise to grooves in the anchorbolt.

[0050] Whilst it is believed that for steel-steel metallic components, friction welds will result as a primary fastening force, galling will also occur to a degree. Galling is most commonly found in metal surfaces that are in sliding contact with each other. It is especially common where there is inadequate lubrication between the surfaces. However, certain metals will generally be more prone to galling, due to the atomic structure of their crystals. For example, aluminium is a metal that will gall very easily, whereas annealed (softened) steel is slightly more resistant to galling and fully hardened steel is very resistant to galling. Accordingly the issue of galling is unlikely to play a considerable part in the creation of a fastening with hardened steels, this further metal-metal surface reaction will play a part where appropriate material and surface conditions exist. Whilst such characteristics have hitherto been viewed as a problem, the present invention when dissimilar materials such as steel and aluminium are employed can benefit from the creation of a fixing member that seeks to benefit from this characteristic arising when two metal components bear against each other.

[0051] The skilled man will realise that the inventive concept of the present invention can have far reaching consequences; by friction welding similar and dissimilar metals together further benefits can be realised. By the creation of a weld about a screw fastening, the vibration proof aspect is substantial for many applications. For example, for example with electrical connections where materials of the same type of different types, the joints can be fully electrically conductive with respect to each other.