EP3497341A1 - Dispositif de fixation à anneau lubrifiant pour ajustement serré, et procédé d'assemblage utilisant un tel dispositif de fixation - Google Patents

Dispositif de fixation à anneau lubrifiant pour ajustement serré, et procédé d'assemblage utilisant un tel dispositif de fixation

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Publication number
EP3497341A1
EP3497341A1 EP17755132.2A EP17755132A EP3497341A1 EP 3497341 A1 EP3497341 A1 EP 3497341A1 EP 17755132 A EP17755132 A EP 17755132A EP 3497341 A1 EP3497341 A1 EP 3497341A1
Authority
EP
European Patent Office
Prior art keywords
fastener
ring
drilling
sacrificial
fitting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP17755132.2A
Other languages
German (de)
English (en)
Inventor
Alexandre Berthou
Florent Verdier
Charles Pham
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LISI Aerospace SAS
Original Assignee
LISI Aerospace SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by LISI Aerospace SAS filed Critical LISI Aerospace SAS
Publication of EP3497341A1 publication Critical patent/EP3497341A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B33/00—Features common to bolt and nut
    • F16B33/06—Surface treatment of parts furnished with screw-thread, e.g. for preventing seizure or fretting
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B19/00—Bolts without screw-thread; Pins, including deformable elements; Rivets
    • F16B19/04—Rivets; Spigots or the like fastened by riveting
    • F16B19/05—Bolts fastening by swaged-on collars

Definitions

  • the present invention relates to a fastener intended to be interference- fitted into a drilling of an aircraft structure and to a method for fitting such a fastener in an assembly of structures.
  • Certain aircraft structures are highly stressed in shear loading, and experience highly variable loading cycles, these typically being the structures of the wings or the joints between wing structures and fuselage.
  • interference-fitted fasteners which means to say fasteners fitted with a negative clearance between the shank of the fastener and the drilling in the structure intended to accept the fastener.
  • the outside diameter of the fastener is greater than the diameter of the drilling before the fastener is fitted.
  • Interference-fitted fasteners currently in use are of the pull type or of the push type.
  • a third type of fasteners referred to as sleeved or sleeve fasteners allows an interference to be created in the structure without having friction against the latter during the fitting phase.
  • Pull-type fasteners comprise an enlarged head intended to rest against one face of the structure, referred to as the "front" face, or in a countersink formed in this face, a shank, a blocking portion in the form of a screw thread or of crimping grooves, and a pulling stem comprising pulling grooves.
  • the fastener is dimensioned so that the pulling stem protrudes from the opposite face of the structure - referred to as the "rear" face. These grooves are gripped by a tool which pulls on the pulling stem and inserts the fastener until the head comes up against the front face of the structure. The stem is then broken or removed.
  • fasteners are typically the GPTM, LGPTM or XPLTM lockbolts by HUCK Manufacturing, or the PULL-INTM or PULL-STEMTM fasteners by LISI AEROSPACE. These fasteners are for example described in patents US RE30445, US 6,702,684, US 5,098,238 or US 6,665,922.
  • Push-fit fasteners are made up of the same elements as pull-fit fasteners except for the pulling stem. They are interference-fitted in the structure by pushing them in using a hammer, a hammer gun, or a ram if it is possible to position the structure in an assembly jig.
  • These fasteners are typically HI-LITETM fasteners described in patent US 4 326 825.
  • Sleeved fasteners are provided which a sleeve which accepts the shank of the fastener, and can be installed by pushing, by pulling or even by screwing.
  • the fastener is kept rotationally fixed and a nut is screwed on to the threaded end.
  • the turning of the nut forces the body of the screw, which is slightly tapered, into the sleeve which is held axial I y on the structure by its head, so that the sleeve expands radially in the structure.
  • Such a fastener is described for example in patent application WO 201 0/142901 .
  • the fasteners may also be covered with an organic coating containing aluminum pigment, typically from five to thirteen microns thick, of the HI-KOTETM type, which has been developed and marketed by the company HI-SHEAR Corporation, and which are described for example in patents US 3 979 351 and EP 2 406 336 B1 .
  • These coatings have a certain lubricating ability, limiting the efforts of installing the fastener during the fitting into the structure or into the sleeve in the case of a sleeved fastener.
  • Aeronautical fasteners are generally lubricated using cetyl alcohol applied to the entire exterior surface of the fastener.
  • Cetyl alcohol is a fatty alcohol with the semideveloped formula CH3(CH2)1 5-OH.
  • cetyl alcohol adopts the form of a waxy white solid or of flakes.
  • the flakes are diluted in a solvent and the fastener is dipped in the solution. Once the solvent has evaporated, the solid flakes of cetyl alcohol cover the fastener.
  • Figure 1 schematically depicts an insertable fastener of the prior art, during the course of being interference-fitted into a structure S featured in cross section, comprising a drilling 8 of diameter D s .
  • the fastener 1 comprises a protruding head, a cylindrical shank 2 of outside diameter Di greater than D s , and a threaded end 3 the maximum diameter of which is smaller than the diameter Di of the cylindrical shank and smaller than the diameter of the drilling Ds.
  • a transition zone 4 connects the shank 2 and the threaded end 3.
  • the transition zone may have various geometries, such as one or more radii, or even an angle.
  • the fastener here comprises a pulling stem 5 equipped with pulling grooves.
  • the fastener is entirely coated with an anticorrosion organic coating of the Hi-koteTM 1 type.
  • a chamfer or a radius is generally made on the entry to the drilling of the first layer S1 of the structure, so as to accommodate the radius under the head of the fastener.
  • This chamfer does not exist on the other layers S2 and S3 in the middle of the assembly when the drilling is made through all the layers.
  • a geometric staircase effect arises because the drilling of the first layer is expanded radially by the fastener shank already inserted, whereas the diameter of the drilling of the next layer is smaller.
  • the staircase effect accentuates the fitting force when the fastener 1 enters a layer comprising a material that is more rigid than the material of the layer previously passed through, for example when the fastener passes from a layer of composite material to a layer made of metal, for example titanium, aluminum or steel, or when the fastener passes through a first layer made of aluminum followed by a layer made of steel.
  • the staircase effect is weakly accentuated when the fastener enters a layer comprising a material that is not as rigid as the material of the layer previously passed through, for example when the fastener passes from a layer made of metal into a layer made of composite.
  • FIG 3 shows a schematic example of the effort required to insert a fastener 1 of the prior art interference- fitted into the structure S of figures 1 and 2, in the case of a total structure thickness of 60 mm, made up of three layers S1 , S2, S3 respectively made of aluminum, carbon fiber composite and titanium, each layer having a thickness of 20 mm.
  • the fastener in this example is able to withstand a maximum insertion force equal to 56 kN, represented by the dotted horizontal line. What that means to say is that, if a force greater than 56 kN is imparted to the fastener, the pulling stem of the fastener will break.
  • the fitting force increases substantially linearly with a first gradient.
  • the gradient of the fitting force decreases slightly because the composite material of the layer S2 deforms more readily under the imparted force needed to interference fit the fastener into the aluminum.
  • the gradient increases significantly because the layer S3 is made of titanium.
  • the insertion force here reaches the maximum threshold before the shank 2 of the fastener is completely inserted into the entire structure S.
  • the fastener is not fitted all the way in, which means to say that the head of the fastener is not in contact with the front face of the structure S and part of the shank 2 is outside the structure S. To fit the fastener all the way in a fitting force greater than the maximum strength of the fastener would have to be imposed on the fastener and that would cause the fastener to break inside the structure before it has been correctly installed.
  • the transition zone 4 is the first zone of the fastener to come into contact with the structure S. This zone is the most highly loaded in friction against the structure because during fitting it passes through the entire thickness of the structure.
  • the transition zone 4 will experience the geometric staircase effects as it passes through the layers which tend to localize the contact forces and lead to rapid deterioration of any coatings there might be or even of its geometry.
  • the rigidity of the titanium combined with the direct contact between the fastener and the structure lead to a sharp increase in the force needed to insert the fastener as an interference fit into the third layer.
  • the applicant company has also observed that the drillings made in different materials had different diameters, because of the different conditions in which the materials are cut during the drilling with the one same tool. The difference in diameter may therefore accentuate the geometric staircase effect phenomenon.
  • the staircase effect may also be created when the layers are predrilled and then aligned, and the drillings of the various layers have an alignment defect.
  • the more the thickness of the assembly increases the more the area for friction between the shank of the fastener and the drilling increases. At high levels of interference, there is therefore increased probability that the fastener will not be inserted all the way in for thick assemblies because of the greater probability of the anti-corrosion and/or lubricating coating being torn off.
  • one subject of the invention is a fastener for assembling at least two structural elements, the fastener comprising an enlarged head and a cylindrical or tapering smooth shank exhibiting, prior to fitting, an outside diameter greater than an inside diameter of a destination drilling, a blocking portion comprising a screw thread or annular grooves and exhibiting an outside diameter always smaller than the inside diameter of the destination drilling, and a transition portion between a distal end, with respect to the enlarged head, of said smooth shank and a proximal end, with respect to the enlarged head, of said blocking portion.
  • the fastener furthermore comprises at least one sacrificial ring containing a lubricant, of substantially toroidal shape, arranged on an exterior surface of the fastener, positioned on an exterior surface of the smooth shank and or of the blocking portion and or of the transition portion, said sacrificial ring exhibiting, prior to the fitting of the fastener into the structure, an outside diameter greater than a smallest diameter of the drilling with which the smooth shank will interfere after the fastener has been fitted.
  • a sacrificial ring containing a lubricant, of substantially toroidal shape, arranged on an exterior surface of the fastener, positioned on an exterior surface of the smooth shank and or of the blocking portion and or of the transition portion, said sacrificial ring exhibiting, prior to the fitting of the fastener into the structure, an outside diameter greater than a smallest diameter of the drilling with which the smooth shank will interfere after the fastener has been fitted.
  • the sacrificial ring is first to come into contact with the wall of the drilling when the fastener is being interference-fitted into the structure - or into the sleeve if the fastener is interference-fitted into a sleeve - and with each of the layers of the structure which are formed by the structural elements that are to be assembled.
  • the sacrificial ring corresponds to an additional deposit of material, separate from the structural part of the fastener formed by the head, the smooth shank, the blocking portion and, where appropriate, a pulling stem, the ring having a substantially toroidal shape with a generatrix cross section that is not necessarily circular in a generalized acceptance of the idea of a torus that is more or less regular and the central hole of which has the structural part of the fastener passing through it, and which ring has the ability to wear or erode easily when rubbed in contact with another material.
  • the sacrificial ring guarantees the reliability of the insertion of the fastener during the force-fitting into the structure: the ring will be gauged or eroded or worn by the structure or by the sleeve, thereby, gradually as the fastener is inserted, leaving the lubricating material of the sacrificial ring at the interface between the smooth shank and the structure or the sleeve, and the fastener will experience practically no wear.
  • lubricant is to be understood as meaning any material or substance which, interposed between two surfaces, reduces the friction or wear between these two surfaces in contact and in relative motion. Thus, the lubricating sacrificial ring wears away or becomes destroyed during insertion, and in so doing lubricates the interior surface of the drilling throughout the insertion.
  • the sacrificial ring exhibits, prior to the fitting of the fastener into the structure, an outside diameter greater than a largest diameter of the drilling with which the smooth shank will interfere after the fastener has been fitted.
  • the erosion or wearing of the sacrificial ring ensures that lubricating material is deposited over a length of the drilling that corresponds to the interference zone which is subjected to friction with the shank of the fastener during the fitting of the fastener.
  • the fastener according to the invention may also comprise at least one or more of the following features, considered in isolation or in combination where these combinations are technically feasible:
  • the sacrificial ring exhibits, after the fastener has been fitted into the structure, an outside diameter smaller than the outside diameter it had prior to fitting;
  • the sacrificial ring is sheared or cut into at least two portions after the fastener has been fitted into the structure
  • a sheared or cut portion of the sacrificial ring is positioned between an exterior surface of the structure and a surface of the head of the fastener after the fastener has been fitted into the structure
  • the sacrificial ring is arranged on the smooth shank
  • the sacrificial ring is arranged on the blocking portion
  • the sacrificial ring is arranged on the transition portion
  • a circular groove is formed so that it is recessed with respect to the exterior surface of the smooth shank, in the smooth shank or in the region of the transition portion, in which circular groove the sacrificial ring is positioned, the sacrificial ring having a shape that complements the circular groove so as to ensure retention of the sacrificial ring in the circular groove;
  • the sacrificial ring comprises polytetrafluoroethylene
  • the sacrificial ring comprises graphite and or bronze
  • the sacrificial ring comprises a lubricating polymer
  • the sacrificial ring comprises dry particles of graphite and or of cetyl alcohol
  • the sacrificial ring comprises a first ring comprising a pasty lubricant covered by a second ring forming a sacrificial solid casing;
  • the pasty lubricant comprises cetyl alcohol and an oil
  • the pasty lubricant comprises a grease with an NLGI grade of between 00 and 3, preferably between 00 and 2;
  • the grease comprises a mixture of wax and of oil, the wax representing between 20% and 50% by weight of the grease;
  • the second ring comprises an acrylic polymer, a silicone or a polysulfide polymer
  • the second ring is a fluidtight film resulting from an application of a liquid sealant and hardened by evaporation in the air;
  • the sacrificial ring is discontinuous and exhibits peripheral segments following on from one another to form a segmented ring.
  • Another subject of the invention is a method of assembly implementing a fastener of the invention.
  • the method For assembling at least two structural elements comprising a drilling exhibiting, before fitting, an inside diameter (D s ), the method comprises the steps of
  • a fastener comprising an enlarged head, a smooth shank exhibiting, prior to fitting, an outside diameter greater than the inside diameter (D s ) of the drilling or than an inside diameter of a sleeve that is to be inserted into said drilling, a blocking portion comprising a screw thread or annular grooves exhibiting an outside diameter always smaller than the inside diameter (D s ) of the destination drilling, and a transition portion between a distal end, with respect to the enlarged head, of said smooth shank and a proximal end, with respect to the enlarged head, of said blocking portion, and a lubricating sacrificial ring, of substantially toroidal shape, arranged on an exterior surface of the fastener, positioned on an exterior surface of the smooth shank and or of the blocking portion and or of the transition portion, said ring exhibiting, prior to the fitting of the fastener into the structure, a diameter greater than a smallest diameter of the drilling or of the sleeve with which the smooth sh
  • Lubricating substance stored in the sacrificial ring prior to the fitting of the fastener, is thus distributed gradually as the fastener is inserted, on to the contacting walls of the fastener and of the structure or of the sleeve.
  • the insertion forces are thereby reduced thereby guaranteeing that the fastener can be inserted with acceptable force and preventing the fastener or structure from being damaged.
  • the lubricating sacrificial ring is sheared or cut into at least two portions during the fitting step.
  • the method comprises a later step of eliminating at least one sacrificial-ring portion.
  • the method comprises a later step of cleaning a surplus of lubricating substance released during the force-fitting step.
  • FIG. 4 a fastener seen in side view according to one embodiment of the invention, before being fitted into a structure;
  • FIG. 4A, 4B, 4C details of figure 4, according to three embodiments of the invention, comprising a lubricating sacrificial ring in the transition zone, in cross section;
  • figure 4D detail of figure 4, according to one embodiment of the invention, comprising a lubricating sacrificial ring on the smooth shank;
  • figure 4E detail of figure 4, according to one embodiment of the invention, comprising a lubricating sacrificial ring on the blocking portion;
  • FIG. 7 detail of the structure of a sacrificial ring comprising a lubricating first ring and a solid second ring for protecting the first ring.
  • distal means “distant from the head of the fastener”
  • proximal means “close to the head of the fastener”.
  • FIG. 4 schematically depicts a side view of a fastener 10 according to one embodiment of the invention.
  • the fastener 10 substantially of revolution about an axis X of said fastener, comprises a countersunk head 12, a smooth cylindrical shank 14 exhibiting an outside diameter Di and a blocking portion 18, which in the fastener illustrated is threaded, exhibiting an outside diameter D 2 measured at the crests of the screw thread, D 2 being smaller than D-
  • a transition portion 16 connects the diameter Di of the cylindrical shank 14 to the diameter D 2 of the threaded blocking portion 18. This transition portion may be curved or tapering.
  • the fastener also comprises a pulling stem 19.
  • the fastener 10 is intended to be inserted into a drilling in a structure S, of diameter D s .
  • the diameter D s is, prior to the fitting of the fastener 10, smaller than the diameter Di of the smooth shank 14 and greater than the diameter D 2 of the threaded portion, so that neither the screw threads nor the structure are damaged as the fastener is introduced into the drilling.
  • the fastener 10 is made of titanium alloy and its exterior surface is fully coated with a layer of coating of the HI-KOTETM type 1 , intended to protect the structure against galvanic corrosion.
  • the fastener could, however, be bare, for example sand-blasted, comprise a thin layer of anodic oxide obtained, for example, by sulfuric anodizing, comprise a layer of aluminum or another coating.
  • the fastener could also comprise coating portions that are annular, in bands parallel to the axis of the fastener, or in the form of a helix, as depicted in the application company's patent FR3008754B1 .
  • the fastener 10 furthermore comprises a sacrificial ring 20, 30 (featured in cross section only in figures 4A, 4B, 4C, 4D and 4E) which extend at least over the transition zone 1 6, namely, at least in part, between a distal end of the shank and a proximal end of the threaded portion (figures 4A, 4B, 4C), over the smooth shank 14 (figure 4D) or else over the blocking portion 18 (figure 4E).
  • a sacrificial ring 20, 30 featured in cross section only in figures 4A, 4B, 4C, 4D and 4E) which extend at least over the transition zone 1 6, namely, at least in part, between a distal end of the shank and a proximal end of the threaded portion (figures 4A, 4B, 4C), over the smooth shank 14 (figure 4D) or else over the blocking portion 18 (figure 4E).
  • the sacrificial ring therefore has a toric shape surrounding the fastener, an axis of the torus being substantially coincident with the axis X of the fastener.
  • a broad definition of the idea of a torus will be considered here insofar as the cross section that generates the volume of the ring is not necessarily a circle and may adopt more or less flattened or deformed shapes, as in the examples illustrated, particularly as a result of the method used to deposit the materials that form the sacrificial ring and as a result of the characteristics they exhibit when being deposited.
  • the ring 20 covers a portion of the fastener over a length L in an axial direction of the fastener, comprising the first thread 24 of the threaded blocking portion 18 and the transition zone 1 6.
  • the ring may also, in this embodiment, extend over part of the smooth shank 14 adjacent to the transition zone (figure 4C) and or extend over a part of the blocking portion 18, advantageously a part of said smooth shank and or of the blocking portion.
  • the fastener comprises an annular groove 22 in the transition zone 16, characterized by a concave shape of said transition zone in the view in cross section of figure 4B.
  • the ring 20 in this example is an annular bead of which an interior surface, situated radially toward the side of the axis X of the fastener, conforms to the shape of the groove, and of which an exterior surface, situated radially on the opposite side to the axis X of the fastener, corresponds to a transition zone intended to be in contact with the wall of the drilling.
  • One advantage with this embodiment is that it uses the hollow geometry of this groove to mechanically hold the ring on the fastener, with no particular bonding or depositing means.
  • Other shapes of concave profile may be used to create the annular groove 22.
  • the sacrificial ring 20 covers part of the smooth shank 14, figure 4D. In another embodiment, an exemplary embodiment of which is illustrated in figure 7, the sacrificial ring 20 covers part of the smooth shank 14, the transition portion 1 6, and part of the blocking portion 1 8.
  • the sacrificial ring 20 covers part of the blocking portion 1 8, figure 4E.
  • the sacrificial ring which is formed with a plane of said ring substantially perpendicular to the axis of the fastener, may be continuous over the periphery of the fastener or may be discontinuous and exhibit peripheral segments following on from one another to form a segmented ring.
  • the portion of the perimeter covered by the segments is equal to or greater than 50 percent and the spaces separating the segments are small enough that the lubrication afforded by the segments as the fastener is being fitted is distributed substantially uniformly.
  • a lubricating sacrificial ring 20 may be produced from various materials.
  • the ring for example comprises a lubricating material.
  • a lubricating material may comprise a fluorinated polymer.
  • the material may comprise 1 00% polytetrafluoroethylene (referred to as "PTFE"), or a mixture of PTFE and another material having lubricating properties.
  • the ring 20 may comprise 85% PTFE and 1 5% graphite, or 40% PTFE and 60% bronze, or alternatively a mixture of PTFE and molybdenum disulfide.
  • particles of these materials are torn off and contained upstream of the site of the sacrificial ring on the fastener, the transition zone or another location as the case may be, namely in that part of the drilling into which the fastener has already been engaged, between the wall of the drilling and an exterior wall of the fastener.
  • Another lubricating material suitable for forming the ring 20 is a lubricating polymer, possibly containing lubricating solid particles, such as particles of graphite or particles of cetyl alcohol. During insertion, as with the fluorinated polymer material, lubricating particles are torn off and spread between the wall of the drilling and an exterior wall of the fastener.
  • the ring is for example obtained by mixing lubricating solid particles into a polymerizable liquid composition and then by applying the composition in the liquid or pasty state and comprising the lubricating particles, to the fastener to form the sacrificial ring.
  • the composition advantageously placed under conditions favorable to polymerization, for example at a recommended temperature for the polymer used, polymerizes, trapping the solid lubricating particles.
  • a sacrificial ring 30 comprises a lubricating first ring 26 comprising cetyl alcohol and a fatty body, covered by a solid second ring 28 creating a casing of said first ring, which casing is intended to be destroyed during insertion.
  • the ring 30 may be positioned on the fastener 10 in the embodiments illustrated in figures 4A, 4B, 4D or 4E.
  • the first ring 26 is obtained for example by dispersing raw crystals of cetyl alcohol in an oil, such as for example a commercially available oil sold under the trade name "biolub" in proportions making it possible to obtain a pasty compound, for example 3 ⁇ 4 w/w of cetyl alcohol and 1 ⁇ 4 w/w of oil.
  • the compound is applied in the hot state to the cold fastener. In practice, the compound cools in just a few seconds allowing the cetyl alcohol crystals to set.
  • a polymerizable liquid composition is applied to the pasty first ring 26 so as to entirely cover a free surface of said first ring 26 and form a second ring 28 superposed on said first ring.
  • the second ring 28 is then polymerized and/or dried, for example in the open air.
  • the second ring 28 makes it possible to provide containment for the pasty lubricating material of the first ring 26 and, because of its composition and the way in which it is applied to form a layer superposed on the first ring, is naturally destroyed as the fastener 10 is inserted into a drilling.
  • the second ring 28 is, for example, formed with a polymer marketed under the trade name Vibraseal® by the LOCTITE company, or based on a polysulfide polymer known as a sealant mastic in the aeronautical industry under the product name "PR", or even a silicone.
  • a thickness of the second ring 28, resulting from the quantity of the polymerizable liquid composition used to make it, is chosen so that said second ring deforms as the fastener is introduced into the drilling, then ruptures when the ring is compressed in the drilling once the fastener has been inserted into said drilling.
  • the first ring 26 may be produced from other pasty or even waxy lubricating compositions provided that they can be covered with a casing-forming second ring.
  • the lubricating product used to produce the sacrificial ring may be an oil containing cetylic acid, or a grease.
  • the oil which may be mineral or synthetic, will be chosen with due consideration to its kinematic viscosity and to its cetylic acid solubility limit.
  • the wettability is dependent on the rheological characteristics of the contacting materials and therefore on the material and surface treatment of the fastener and will advantageously be verified, if not determined, experimentally so as to form a lubricating ring with the desired mechanical and dimensional characteristics.
  • a grease with a low NLGI grade corresponding to a grease that is too fluid will not allow the creation of a stable lubricating ring.
  • a grease with a high NLGI grade corresponding to a grease that is too pasty will not be able to be deposited on the fastener satisfactorily.
  • the grease chosen will advantageously have an NLGI grade of between 00 and 2, or even a grade 3 for greases exhibiting numbers close to grade 3.
  • the grease used may be a simple product, where applicable containing additives.
  • the grease may be a mixture of wax with an oil, in which mixture the wax, representing between 20 wt% and 50 wt% of the grease, forms a porous matrix trapping the oil.
  • the grease will be selected from greases having a melting point higher than the temperature at which said grease is to be applied to the fastener, for example a melting point of between 25°C and 250°C.
  • the sacrificial ring 30 comprises a second ring 28
  • the latter forms a physical barrier which protects the lubricant of the first ring 26.
  • the second ring protects the first ring so that there is no loss of lubricating product during the various handlings of the fastener before said fastener is fitted.
  • the second ring also provides a fluidtight barrier which isolates the lubricating product from external agents (oxygen, moisture, contaminants) liable to degrade the quality of the grease.
  • the material of the second ring also needs to be able to be formed without damaging the first ring, and for that reason preference will be given to a material the hardening of which does not require a heating or does not produce excessive heat, for example a hardening by evaporation of a solvent or by photopolymerization. After hardening, the material of the second ring also needs to maintain sufficient flexibility so that it does not become broken by the handlings of the fastener up to the point at which it is fitted.
  • the second ring may be formed by means of a polysulfide-based mastic or a silicone mastic.
  • the second ring may also be formed using sealants often applied in the liquid state and hardening through evaporation of a solvent, such as the sealants used on the screw threads of nuts and bolts used for assembly.
  • the ring 20 or 30 may be formed on a tool and then slipped on to the fastener if this ring allows handling thereof without damage.
  • the ring 20 or 30 may also be formed by adding lubricating material directly to the fastener, for example by manual or automated depositing of a liquid or pasty composition which polymerizes or dries, by overmolding or by additive manufacture. This ring may be added at various stages in the manufacture of the fastener and possibly undergo grinding or machining operations required for the manufacture of the fastener.
  • composition and the shape of the ring, the thickness of the ring 20 or 30 and its position on the fastener are preferably chosen so that the surface of the fastener 10 that is covered by the ring 20, 30 is not the first surface to come into contact with the wall of the drilling during the fitting of the fastener.
  • the thickness of a ring 20 or 30 in the radial dimension is at least 0.2 mm, which is far higher than the thicknesses of the lubricating thin layers of the prior art which are designed not to become damaged when the fastener is being fitted.
  • the largest outside diameter of the ring 20, 30 is also chosen to be larger than the smallest diameter of the drilling into which the fastener is fitted, so as also to be an interference fit with all the elements of the structure that are to be assembled.
  • This largest outside diameter of the ring may be equal to or greater than the diameter of the smooth shank 14, provided that it remains greater than the diameter of the drilling which is to be understood here, for complex noncylindrical drillings, to mean greater at least than the smallest diameter of the drilling with which the fastener will be an interference fit.
  • this largest outside diameter of the ring is greater than the largest diameter of the drilling with which the smooth shank will be an interference fit after the fastener has been fitted.
  • Figure 5 shows the results of measuring insertion forces during tests conducted by the applicant company on four fasteners inserted into a structure 38.1 mm thick, comprising three adjacent layers each 1 2.7 mm thick.
  • the first layer S1 is made of aluminum
  • the second layer is made of steel
  • the third layer S3 is made of aluminum.
  • Each fastener has a diameter of 1 6/32" (1 2.70 mm), is able to withstand a maximum tensile force of 56 kN and is inserted into a drilling in the structure with a high level of interference of 1 54 ⁇ .
  • Fastener A is a bare, uncoated, titanium fastener representing a fastener of the prior art. This fastener barely enters the second layer S2 of the structure and cannot be inserted further, as the maximum insertion force is reached after 15 mm.
  • Fastener B is a titanium fastener fully coated with HI-KOTETM 1 NC anticorrosion coating, representing a fastener of the prior art, described in patent EP2406336B1 . This fastener goes in as far as the second layer S2 of the structure, but cannot be inserted into the third layer of the structure.
  • Fastener C is a titanium fastener coated with HI-KOTETM 1 NC and provided with a PTFE ring 20 on the transition zone. Fastener C is fully inserted into the structure with an insertion force of around 42 kN.
  • Fastener D is a titanium fastener coated with HI-KOTETM 1 NC and provided with a ring 30 comprising a ring 26 of cetyl alcohol and oil covered with a second ring 28 of Vibraseal® polymer on the transition zone and part of the smooth shank 14. Fastener D is fully inserted into the structure with an insertion force of around 19 kN.
  • a sacrificial ring could also perform a function of sealing the fastener in the structure.
  • fastener C or D is inserted into the structure, the ring 20 or the second layer 28 of the ring 30 is cut or sheared into two portions at its largest outside diameter.
  • fastener D the material of the ring 26 is crushed and retained between the two separate portions of the ring 28.
  • the proximal portion cannot enter the drilling, because of the interference, and remains situated between an exterior surface of the structure and the underside of the head of the fastener.
  • the distal portion is in the drilling and acts as a reserve of lubricant supplied by the ring 26, which is deposited on the walls of the drilling until the threaded portion reemerges from the structure.
  • the proximal ring portion is in contact with the underside of the head of the fastener and with the proximal exterior surface of the structure, and the distal ring portion is removed by the threaded portion of the fastener.
  • the sacrificial ring after insertion has an outside diameter smaller than the outside diameter prior to insertion.
  • the ring may be simply worn away or cut into at least two portions, pushed back on each side of the transition zone 1 6.
  • Figure 6 shows the results of measurements of forces of insertion during tests conducted by the applicant company, relating to three fasteners inserted into an assembly comprising four adjacent layers.
  • the first three layers S1 ', S2' and S3' are made of composite material, and the fourth layer S4' is made of aluminum.
  • Each fastener A', B' and C has a diameter of 1 6/32" (1 2.70 mm), is able to withstand a maximum tensile force of 56 kN and is inserted into a drilling in the structure with a medium interference of 89 ⁇ .
  • Fastener A' is a titanium fastener the exterior surface of which has undergone sulfuric anodic oxidation and is covered with a lubricating layer of a HI-SLIDETM coating comprising a mixture of polyolefin and of polytetrafluoroethylene, representing a fastener of the prior art, described in patent application FR3026446A1 .
  • This fastener is fully inserted into the structure with an insertion force of around 52 kN, which is therefore close to the maximum insertion force for fastener A.
  • Fastener B' is a bare titanium fastener comprising bands of HI-KOTETM 1 NC anticorrosion coating, representing a fastener of the prior art, described in patent FR3008754B1 . This fastener is fully inserted into the structure with an insertion force of around 46 kN.
  • Fastener C is a bare titanium fastener comprising bands of HI-KOTETM
  • the interference is smaller than it was in the previous test and the fasteners are inserted into materials that are "softer" than the materials in the previous test.
  • the fasteners of the prior art thus enter the full thickness of the structure, but with levels of force that are still high, or even very close to the maximum level of force permissible for these fasteners.
  • a screw or a collar can then be assembled on the blocking portion 1 8 of the fastener to finalize the fitting of the fastener and the assembling of the structure.
  • the sacrificial ring initially covers an anti-corrosion coating, this ring, sacrificed during fitting, prevents the coating from eroding so that it can then fully perform its anti- corrosion function in contact with the structure, with the nut, or with any other element in contact with the exterior surface of the fastener 1 0.
  • the reduction in the force of fitting means that installation is easier for the operators, more lightweight tooling can be used, and the risks of damage to the structure are limited. Maintaining continuous lubrication throughout insertion also prevents the fastener from breaking as it is being inserted into the structure and the complex operations of removing it and of fitting a new fastener.
  • the invention also makes it possible to fit fasteners as an interference fit in thicker structures, or structures with a higher level of interference, or into structures comprising multiple layers and "hard” materials such as titanium or stainless steel, which have the disadvantage of producing high friction forces.
  • a sacrificial ring 20 or 30 may be used on a fastener having, for example, a protruding head rather than a countersunk head, a tapering smooth shank rather than a cylindrical smooth shank, blocking grooves instead of a screw thread. It is also possible for the fastener not to comprise a pulling stem, and/or to comprise a sleeve the inside diameter of which is smaller than the outside diameter of the shank of the fastener - whether the fastener be cylindrical or tapering - and the outside diameter of which is smaller than the inside diameter of the drilling prior to the fitting of the fastener in the sleeve.
  • Such a fastener is, for example, described in the applicant's patent FR 2 946 707.
  • the invention also makes it possible in certain cases to omit the lubricating or anti-corrosion coating on the shank of the screw and/or on the inside of the sleeve, in the case of a sleeved fastener. Omitting the coating makes it possible to improve the electrical conductivity between the shank of the screw and the wall of the sleeve or of the structure, notably to pass lightning current when lightning strikes a fastener or a structure of an aircraft.
  • the ring may comprise a porous matrix, the pores of which are filled with dry or fatty lubricating substance. At the time of insertion, the matrix is worn away and the lubricating substance is released.
  • the sacrificial ring may comprise fatty or pasty lubricating particles microencapsulated and deposited in one or more layers, and a binder allowing the microcapsules to be held in position on the fastener to constitute the sacrificial ring. During insertion, the microcapsules are burst and the lubricant is released.
  • the sacrificial ring may comprise a lubricating coating designed to undergo abrasion, comprising a matrix and lubricating particles trapped in the matrix.
  • This type of coating is used for example in the field of turbomachines, to create seals subjected to abrasion in use.
  • One and the same fastener may also comprise a plurality of sacrificial rings.

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Insertion Pins And Rivets (AREA)
  • Connection Of Plates (AREA)
  • Bolts, Nuts, And Washers (AREA)

Abstract

L'invention concerne un dispositif (10) de fixation destiné à l'assemblage d'au moins deux éléments de structure, comprenant un alésage, le dispositif de fixation comprenant une tête élargie (12) et une tige (14) présentant, avant l'ajustement, un diamètre extérieur (Di) supérieur à un diamètre intérieur (Ds) de l'alésage, et une partie blocage comprenant un filetage ou des rainures annulaires. Le dispositif de fixation comprend en outre un anneau lubrifiant sacrificiel (20 ; 30) sur la surface extérieure du dispositif de fixation, s'étendant au moins entre une extrémité distale de la tige et une extrémité proximale de la partie blocage, ledit anneau ayant, avant que le dispositif de fixation ne soit ajusté dans la structure, un diamètre extérieur supérieur au diamètre de l'alésage. L'invention s'applique à l'assemblage de structures d'aéronefs.
EP17755132.2A 2016-08-12 2017-08-14 Dispositif de fixation à anneau lubrifiant pour ajustement serré, et procédé d'assemblage utilisant un tel dispositif de fixation Withdrawn EP3497341A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR1657749A FR3055034B1 (fr) 2016-08-12 2016-08-12 Fixation a anneau lubrifiant pour pose en interference et procede d'assemblage au moyen d'une telle fixation
PCT/EP2017/070591 WO2018029381A1 (fr) 2016-08-12 2017-08-14 Dispositif de fixation à anneau lubrifiant pour ajustement serré, et procédé d'assemblage utilisant un tel dispositif de fixation

Publications (1)

Publication Number Publication Date
EP3497341A1 true EP3497341A1 (fr) 2019-06-19

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP17755132.2A Withdrawn EP3497341A1 (fr) 2016-08-12 2017-08-14 Dispositif de fixation à anneau lubrifiant pour ajustement serré, et procédé d'assemblage utilisant un tel dispositif de fixation

Country Status (8)

Country Link
EP (1) EP3497341A1 (fr)
JP (1) JP2019528410A (fr)
CN (1) CN109863318B (fr)
BR (1) BR112019002759A2 (fr)
CA (1) CA3033100A1 (fr)
FR (1) FR3055034B1 (fr)
RU (1) RU2019106698A (fr)
WO (1) WO2018029381A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11365757B2 (en) 2016-08-12 2022-06-21 Lisi Aerospace Fastener with lubricating ring for interference fitting, and assembly method using such a fastener
EP3749867B1 (fr) * 2018-02-07 2023-05-17 Lisi Aerospace Dispositif de fixation à anneau lubrifiant pour ajustement serré, et procédé d'assemblage utilisant un tel dispositif de fixation
CN110425209A (zh) * 2019-08-30 2019-11-08 航天精工股份有限公司 一种具有凹槽结构的螺纹紧固件

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US3682508A (en) * 1969-11-19 1972-08-08 Franklin S Briles Re-usable, spin-stopping fastener
US3779127A (en) * 1971-09-02 1973-12-18 Mc Donnell Douglas Corp Stress coining bolt
US3979351A (en) 1973-01-26 1976-09-07 Hi-Shear Corporation Protective coating material
USRE30445E (en) 1974-08-26 1980-12-16 Huck Manufacturing Company Fastener with proportioned strength lock grooves
US3962775A (en) * 1975-01-17 1976-06-15 King John O Jun Method of forming a joint using a guide fastener
US4081012A (en) * 1976-02-18 1978-03-28 The Oakland Corporation Thread lock
US4326825A (en) 1979-12-31 1982-04-27 Hi Shear Corporation Balanced pin for shear flow joint, and joint including the pin
US5098238A (en) 1990-12-20 1992-03-24 Hi-Shear Corporation Fastener with internal threaded installation means
US6702684B2 (en) 2002-04-05 2004-03-09 Huck International, Inc. Method of designing and manufacturing a swage type fastener
US6665922B2 (en) 2002-05-13 2003-12-23 Hi-Shear Corporation Pull stem hi-lite pin with pull groove for swaging collars
US10259973B2 (en) 2009-03-13 2019-04-16 Hi-Shear Corporation Anti-corrosion and low friction metal pigmented coating
FR2946707B1 (fr) 2009-06-13 2011-05-20 Lisi Aerospace Famille de dispositifs de fixation a conicite variable.
JP5438837B2 (ja) * 2009-10-22 2014-03-12 アルコア インコーポレイテッド 電気伝導性を向上させたスリーブ付ファスナ及びその作製方法
DE102012100228A1 (de) * 2012-01-12 2013-07-18 Kamax Holding Gmbh & Co. Kg Schraube mit einer Kopfauflagefläche mit Schmiermitteltaschen
FR3008754B1 (fr) 2013-07-19 2015-09-04 Lisi Aerospace Fixation metallique
FR3013781A1 (fr) * 2013-11-25 2015-05-29 Airbus Operations Sas Element de fixation de pieces d'un assemblage
FR3026446B1 (fr) * 2014-09-30 2017-12-01 Lisi Aerospace Fixation en interference lubrifiee
CN204572681U (zh) * 2015-04-09 2015-08-19 浙江滨海汽车零部件有限公司 一种支轴承销

Also Published As

Publication number Publication date
JP2019528410A (ja) 2019-10-10
CN109863318B (zh) 2021-05-11
CN109863318A (zh) 2019-06-07
WO2018029381A1 (fr) 2018-02-15
BR112019002759A2 (pt) 2019-05-14
FR3055034B1 (fr) 2019-05-17
CA3033100A1 (fr) 2018-02-15
RU2019106698A (ru) 2020-09-14
FR3055034A1 (fr) 2018-02-16

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