GB1604504A - Blind fastener - Google Patents

Description

PATENT SPECIFICATION ( 11) 1 604 504

t ( 21) Application No 2111/81 ( 22) Filed 16 May 1978 ( 19) ( 62) Divided Out of No 1604502 a ( 44) Complete Specification Published 9 Dec 1981 c ( 51) INT CL 3 F 16 B 19/08 @ ( 52) Index at Acceptance _ F 2 H 11 B 1 D ( 72) Inventors: WARREN FRANK DAHL RICHARD CLAUDE LANDT ( 54) BLIND FASTENER ( 71) We, SPS TECHNOLOGIES, INC, a Corporation duly organised and existing under the Laws of the Commonwealth of Pennsylvania, United States of America, of Jenkintown, Pennsylvania 19046, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it

is to be performed, to be particularly described in and by the following statement: 5

The invention relates to a blind fastener assembly similar to that described and claimed in our Patent Application No 19728/78 Serial no 1604502 from which this Application is divided and which is hereinafter called the "Parent Application".

The Parent Application provides a blind fastener assembly for installation in a workpiece having an opening therein, said assembly comprising a pin member having an enlarged head 10 at one end thereof, an elongate shank portion and means on said shank portion operative to advance said pin member in a direction along its longitudinal axis; expander means having an enlarged head at one end thereof formed to bear upon an accessible surface of the workpiece, a tapered surface of varying radial thickness in a longitudinal direction adjacent the other end thereof, said tapered surface varying from a minimum radial thickness at said 15 other end to a maximum radial thickness at a locus of points spaced from said other end, and a shank portion intermediate said enlarged head and said tapered surface, said shank portion having an outer surface formed to be placed in the workpiece opening, and an internal bore extending through said expander means carrying said pin member shank portion; and an expandable sleeve carried on said pin member shank portion adjacent said 20 enlarged head, said sleeve including a first portion of greater radial thickness adjacent one end thereof adjacent said pin member enlarged head and a second portion of reduced radial thickness extending from the end of said first portion remote from the enlarged head of said pin member and adjacent said minimum thickness end of said expander means tapered surface, said second portion having a reduced radial distance to the outside surface thereof 25 and an increased radial distance to the inside surface thereof each relative to the radial distance to the respective outside and inside surfaces of said first portion, whereby there is a discontinuity in the outside surface and in the inside surface of said sleeve at the junction of said first and said second portions thereof, said sleeve second portion being arranged to be advanced along said expander tapered surface and said expander outer surface and 30 expanded thereover upon advancement of said pin member toward a blind side surface of the workpiece, the second portion of said sleeve forming a radially outwardly extending bulb at said juncion of said first and second portions of the sleeve, said bulb ultimately bearing against the blind side workpiece surface.

According to the invention of this Application, the blind fastener assembly comprises a 35 pin member having an enlarged head at one end thereof, an elongate shank portion and means on said shank portion operative to advance said pin member in a direction along its longitudinal axis; expander means having an enlarged head at one end thereof formed to bear upon an accessible surface of the workpiece, a tapered surface of varying radial thickness in a longitudinal direction adjacent the other end thereof, said tapered surface 40 varying from a minimum radial thickness at said other end to a maximum radial thickness at a locus of points spaced from said other end, and a shank portion intermediate said enlarged head and said tapered surface, said shank portion having an outer surface formed to be placed in the workpiece opening, whereby a portion of said shank portion outer surface is confined and a portion extends beyond an inaccessible surface of the workpiece 45 1 604 504 and is unconfined, and an internal bore extending through said expander means carrying said pin member shank portion; and an expandable sleeve carried on said pin member shank portion adjacent said enlarged head, said sleeve including a first portion of greater radial thickness adjacent one end thereof adjacent said pin member enlarged head and a second portion of reduced radial thickness adjacent the other end thereof juxtaposed from 5 said minimum thickness end of said expander means tapered surface, said second portion having either, but not both, a reduced radial distance to the outside surface thereof or an increased radial distance to the inside surface thereof relative to the radial distance to the respective outside or inside surface of said first portion, whereby there is a discontinuity in the outside surface or the inside surface respectively of said sleeve at the junction of said 10 first and second portions thereof, said expander means having an axial length such that the unconfined portion of said expander means shank portion outer surface is less than approximately one half of the axial length of said sleeve second portion plus one half of a predetermined grip range and greater than approximately one half of the axial length of said sleeve second portion minus one half of a predetermined grip range, said sleeve second 15 portion being arranged to be advanced along said expander means tapered surface and said expander means outer surface and expanded thereover upon advancement of said pin member toward the inaccessible workpiece surface, said other end of said sleeve ultimately contacting the inaccessible workpiece surface and forming a radially outwardly extending bulb with its apex intermediate the ends of said second portion, said bulb bearing against 20 the inaccessible workpiece surface.

The invention also provides a joint assembly comprising in combination a workpiece having a first surface, a second surface and a hole therebetween and a blind fastener assembly as set out in the immediately preceding paragraph.

An embodiment of a blind fastener assembly in accordance with the Parent Application 25 and two modifications thereof in accordance with this Application are now described with reference to the accompanying drawings, in which:Figure 1 is a cross-sectional view illustrating the embodiment of a blind fastener assembly installed in a pair of workpieces prior to any forming operation; Figure 2 shows the embodiment of Figure 1 in an intermediate, partially formed 30 condition; Figure 3 shows the embodiment of Figure 1 in a finally formed condition; Figure 4 is a cross-sectional view of the sleeve and expander of the embodiment of Figure 1 showing certain dimensional relationships; Figure S is a cross-sectional view of the sleeve and expander of the embodiment of Figure 35 1 showing another possible dimensional relationship; Figure 6 shows the bulb formed according to the dimensional relationships in Figure 4; Figure 7 shows the bulb formed according to the dimensional relationship of Figure 5; Figure 8 illustrates a grip accommodation dimensional relationships of the sleeve and expander shown in Figure 1, and 40 Figures 9 and 10 are cross-sectional views of the two modifications according to this Application of the sleeve shown in Figure 8.

Referring to Figures 1 3, the first embodiment of a blind fastener assembly in accordance with the Parent Application is shown in varying stages of installation Fastener assembly 10 includes a pin member 12, an expander 14 and a sleeve 16 Pin member 12 has 45 an enlarged head 18 at one end thereof and may, in one configuration, include standard external threads 20 which are designed to engage mating threads 22 on expander 14 in order to draw sleeve 16, which is carried on the shank of pin member 12 adjacent head 18, axially toward expander 14 In the particular configuration shown, a wrenching configuration such as a pair of flats 23 are included on pin member 12 at a free end 24 for accepting a power 50 tool driving bit It should be understood that pin member 12 may include a plurality of circumferential grooves (not shown) adjacent end 24 instead of external threads 20 and mating threads 22 on expander 14 Such grooves are commonly employed on similar pulling pin devices and are formed to be gripped by any one of a number of conventional pull-type runs for exerting the necessary axial force on pin member 12 This arrangement is not 55 illustrated because it is quite conventional and fully known to those skilled in the art Pin member 12 also includes a breakneck groove 26 of reduced cross-sectional diameter, which is designed to fracture at a predetermined axial or torsional load Expander 14 includes an enlarged head 28, a shank portion 30 of constant outside diameter and a nose portion having a tapered surface 32 opposite from head end 28 Tapered surface 32 forms an angle 60 of the order of approximately 120 with the longitudinal axis of expander 14 Expander 14 extends through aligned openings in a pair of workpieces 34 and 36, with head 28 designed to bear upon a corresponding countersunk section in workpiece 34, and outer peripheral surface 31 of shank 30 designed to fit through the aligned openings with a relatively close fit, that is something less than an interference fit Head 28 may include a recess 29 for accepting 65 1 604 504 a portion of the power tool bit (not shown) to keep expander 14 from rotating during the assembly of the joint It is to be understood that head 28 may be of any configuration while still remaining within the scope of the present invention Sleeve 16 includes a portion 38 adjacent head 18 of pin member 12, and a portion 40 of reduced radial thickness adjacent tapered surface 32 of expander 14 Portion 40 includes an outer surface 42 and of a diameter 5 smaller than the diameter of the outer surface of the portion 38 of the sleeve a counterbored internal surface 44 A shoulder 46 joins surface 42 and the outside surface of portion 38, and a shoulder 48 joins inside surface 44 and the inside surface of portion 38 Shoulder 48, preferably, but not necessarily, forms an approximate 1200 included angle, while shoulder 46 preferably forms an approximate 200 angle with the longitudinal axis of sleeve 16 10 When an axial force is exerted on pin member 12, such as by applying torque to the pin or by pulling on the pin by means of a pull gunn (not shown), surface 44 on sleeve 16 contacts tapered surface 32 on expander 14, and portion 40 begins to advance over the tapered surface 32, where it is expanded from its original diameter Portion 40 continues to advance over intersection 33 of surfaces 31 and 32 along surface 31 of expander 14 until the free end 15 41 of portion 40 contacts the blind-side surface of workpiece 36 as shown in Figure 2 At this point, intersection 33 should be mid-way between the ends of reduced thickness portion 40 in an optimum configuration joint Optimum dimensional relationships between the length of portion 40 and the distance from the blind-side surface of workpiece 36 to intersection 33 of expander 14 will be discussed more fully hereinafter As pin member 12 continues to 20 advance in an axial direction, portion 40 begins to bulb radially outwardly at approximately the middle of its length, causing a maximum diameter bulb 49 to form in an optimum configuration adjacent the blind-side surface of workpiece 36 This maximum diameter bulb is typically 1 5 times the original unexpanded diameter of sleeve 16 During the formation of bulb 49, as shoulder 48 contacts the free end of tapered surface 32, a tip portion 47 of the 25 expander 14 deforms shoulder 48 producing an extruding effect on the thicker portion 38.

However, shoulder 46 is not affected during this extruding process, thus insuring that reduced thickness portion 40 always remains at a fixed position forward of shoulder 46 This assures optimum formation of the bulb within the reduced thickness portion Continued application of torque or pulling of pin member 12 causes the pin to fracture at breakneck 30 groove 26, resulting in the final assembled joint shown in Figure 3 It should be understood that some form of locking configuration (not shown) may be provided between pin member 12 and expander 14 to keep the pin member from moving in an axial direction after the joint is clamped, and to maintain preload in the joint It should be understood that the leading edge of the reduced thickness portion 40 of sleeve 16 could include a radius or combination 35 of curvatures which would help to prevent the sleeve from marring the blind-side surface of workpiece 36 as the bulb forms It is also pointed out that reduced thickness portion 40 could be selectively annealed along its length to provide a hardness gradient with the softest point being at approximately the mid-point of portion 40 to ensure that the bulb forms at the optimum point to produce a maximum diameter and optimum shaped bulb Lubricants 40 can be provided between the contacting surfaces of expander 14 and sleeve 16 to reduce the forces requires to expand and bulb the sleeve.

Referring now to Figures 4 and 5, the sleeve 16 and expander 14 of Figures 1 3 are shown Critical dimensional relationships will be discussed with reference to these Figures.

Dimension "L represents the axial length of reduced thickness portion 40 of sleeve 16, and 45 dimension "d" represents the distance from the surface of workpiece 36 to the intersection 33 of surfaces 31 and 32 on expander 14 A critical dimensional relationship exists between the position of expander 14 relative to the position of sleeve 16 at the time during installation when the leading edge 41 of the sleeve 16 contacts the blindside surface of workpiece 36 As mentioned previously with respect to the formation of the joint in Figures 50 1 3, reduced thickness portion 40 advances along surfaces 32 and 31 of expander 14, and is deformed at intersection point 33 when the leading edge 41 of sleeve 16 contacts the blind-side surface of workpiece 36 This is true, however, only if intersection 33 is located somewhere within dimension "L" of portion 40 on sleeve 16 when edge 41 contacts the blind-side surface of workpiece 36 The optimum location of intersection 33 is when d = 55 L/2, since with this dimensional configuration, the bulb will start to form in the centre of the column (reduced thickness portion 40), producing an optimum-shaped, maximum diameter bulb 86, as shown in Figure 6 If intersection 33 is not located within dimension "L", as shown in Figure 5, a bulb 88 of smaller diameter will form adjacent the blind-side surface of workpiece 36 As can be seen in Figure 7, bulb 88 is not optimally formed as is bulb 86 in 60 Figure 6 Since intersection 33 is not located within length "L" of reduced thickness portion on sleeve 16, the intersection 33 has no effect on where the bulb forms In this configuration, the column can be considered as having a free end 41 where it contacts the blind-side surface of workpiece 36, and a fixed restraint at shoulder 46 where it joins the normal thickness portion 38 of sleeve 16 The result of this configuration is non 65 4 1 604 504 4 symmetrically formed bulb 88, being smaller in diameter than bulb 86 in Figure 6 and having a gap 89 between normal thickness portion 38 and bulb 88.

In order to minimise the overall length of the blind fastener assembly, dimension "d" should be the minimum length at which an optimum-shaped, maximum diameter bulb will form 5 Referring now to Figure 8, if the blind fastener assembly is to accommodate a range of grip lengths, then the following optimum dimensional relationships should be used:

L G d MAX = 2 + 2 10 L -G d MIN 2 2 15 where G = a predetermined variation in workpiece thickness commonly referred to as a grip-accommodation A typical grip-accommodation value usable in accordance with the present invention is 1/16 inch ( 1 59 mm) Beyond "d Min" or less, the resultant bulb tends to form to a smaller final diameter due to the location of intersection 33, and, corresponding 20 ly, beyond "d M 8," or greater the resultant bulb also tends to form at a smaller diameter, as shown for example in Figure 7 Therefore, exceeding the optimum dimensional range results in a less than optimum bulb diameter and shape.

Figures 9 and 10 illustrate the modifications according to this Application of the sleeve shown in Figure 8 for which the above described optimum dimensional relationships shall 25 be used in order to accommodate a range of grip lengths In Figure 9, a sleeve 90 includes a reduced thickness portion 92 and a normal thickness portion 94 Reduced thickness portion 92 has a reduced radial distance to the outside surface 96 relative to the radial distance to the outside surface 98 of normal thickness portion 94 In Figure 10, a sleeve 100 includes a reduced thickness portion 102 and a normal thickness portion 104 Reduced thickness 30 portion 102 has an increased radial distance to the inside surface 106 relative to the radial distance to the inside surface 108 of normal thickness portion 104.

For a predetermined grip-accommodation value "G", optimum dimensional ranges have been determined for a nominal 3/16 inch ( 4 76 mm) diameter, and a nominal 1/4 inch ( 6 35 mm) diameter blind fastener assembly For a 3/16 inch ( 4 76 mm) diameter assembly, 35 d = 25 L to 75 L 40 and for a 1/4 inch ( 6 35 mm) diameter assembly, d = 33 L to 65 L 45 These dimensional ranges have generally yielded optimum-shaped, maximum diameter bulbs for the two sizes listed.

Claims (9)

WHAT WE CLAIM IS:

1 A blind fastener assembly for installation in a workpiece having an opening therein, 50 said assembly comprising a pin member having an enlarged head at one end thereof, an elongate shank portion and means on said shank portion operative to advance said pin member in a direction along its longitudinal axis; expander means having an enlarged head at one end thereof formed to bear upon an accessible surface of the workpiece, a tapered surface of varying radial thickness in a longitudinal direction adjacent the other end 55 thereof, said tapered surface varying from a minimum radial thickness at said other end to a maximum radial thickness at a locus of points spaced from said other end, and a shank portion intermediate said enlarged head and said tapered surface, said shank portion having an outer surface formed to be placed in the workpiece opening, whereby a portion of said shank portion outer surface is confined and a portion extends beyond an inaccessible 60 surface of the workpiece and is unconfined, and an internal bore extending through said expander means carrying said pin member shank portion and an expandable sleeve carried on said pin member shank portion adjacent said enlarged head, said sleeve including a first portion of greater radial thickness adjacent one end thereof adjacent said pin member enlarged head and a second portion of reduced radial thickness adjacent the other end 65 1 604 504 5 thereof juxtaposed from said minimum thickness end of said expander means tapered surface, said second portion having either, but not both, a reduced radial distance to the outside surface thereof or an increased radial distance to the inside thereof relative to the radial distance to the respective outside or inside surface of said first portion, whereby there is a discontinuity in the outside surface or the inside surface respectively of said sleeve at the 5 junction of said first and second portions thereof, said expander means having an axial length such that the unconfined portion of said expander means shank portion outer surface is less than approximately one half of the axial length of said sleeve second Portion plus one half of a predetermined grip range and greater than approximately one half of the axial length of said sleeve second portion minus one half of a predetermined grip range, said 10 sleeve second portion being arranged to be advanced along said expander means tapered surface and said expander means outer surface and expanded thereover upon advancement of said pin member toward the inaccessible workpiece surface, said other end of said sleeve ultimately contacting the inaccessible workpiece surface and forming a radially outwardly bulb with its apex intermediate the ends of said second portion, said bulb bearing against 15 the inaccessible workpiece surface.

2 A blind fastener assembly in accordance with Claim 1 wherein said first distance is equal to approximately one half of the axial length of said sleeve second portion.

3 A blind fastener assembly in accordance with Claim 1 wherein said first distance is within a range of approximately 0 25 to 0 75 times the axial length of said sleeve second 20 portion for a nominal 3/16 inch ( 4 76 mm) diameter blind fastener assembly.

4 A blind fastener assembly in accordance with Claim 1 wherein said first distance is within a range of approximately 0 33 to 0 65 times the axial length of said sleeve second portion for a nominal 1/4 inch ( 6 35 mm) diameter blind fastener assembly.

5 A blind fastener assembly in accordance with any preceding claim wherein said pin 25 member further includes a portion of reduced cross-section designed to break at a predetermined load greater than the load necessary to form said bulb.

6 A blind fastener assembly in accordance with any preceding claim wherein said means on said shank portion operative to advance said pin member is an external thread, and wherein said expander means further includes a mating internal thread on said internal 30 bore thereof.

7 A blind fastener assembly in accordance with any preceding claim wherein said expander means tapered surface forms an angle of the order of 120 with the longitudinal axis of said expander means.

8 A blind fastener assembly constructed and arranged substantially as described herein 35 with reference to the accompanying drawings when modified to have a sleeve as shown in Figure 9 or 10 of the drawings.

9 A joint assembly comprising in combination a workpiece having a first surface, a second surface and a hole therebetween and a blind fastener assembly according to any preceding claim 40 WALFORD & HARDMAN BROWN, Trinity House, Hales Street, Coventry, 45 CV 1 1 NP.

Agents for the Applicants.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey 1981.

Published by The Patent Office, 25 Southampton Buildings London WC 2 A l AY, from which copies may be obtained.