CA2000116A1

CA2000116A1 - Rivet with integral heater

Info

Publication number: CA2000116A1
Application number: CA002000116A
Authority: CA
Inventors: Rodney L. Derbyshire
Original assignee: Metcal Inc
Priority date: 1988-12-02
Filing date: 1989-10-03
Publication date: 1990-06-02
Also published as: DE68905031D1; US5025128A; DE68905031T2; EP0372704B1; EP0372704A1; JPH02197346A

Abstract

ABSTRACT OF THE INVENTION

A blind rivet or bolt is rendered fluid tight by applying heat activated sealant to some or all of the surfaces of the rivet that contact surfaces of the structure into which the rivet is inserted. The sealant is activated by a temperature self regulating heater formed by applying ferromagnetic material to appropriate locations on the rivet and heating the ferromagnetic material by an energizing structure associated with the rivet actuation tool, the structure depending upon whether the heater is activated by flux coupling from a coil or by ohmic heating.

Description

RIVET WITH INTEGRAL HEATER
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The present invention relates to blind riveting systems and more particularly to blind rivets and associated equipment and method for heating the 5 rivets at the time of installation or subseguent thereto in order to heat a sealant to achieve fluid tight joining of materials.

BACKGROUND OF THE INVENTION
Blind rivets are widely used in industry, 10 commerce and by homeowners. The present invention is particularly applicable to industrial usage although it may be employed in the other areas mentioned above.
: In the modern aerospace industry, as an example, blind rivets or bolts as they are sometimes 15 called, are used extensively in assembling airframes ~:, ,, and particularly hollow wing sections ~mployed as fuel storage tanks. A problem often develops due to leakage around the rivets. As in other blind rivet installations for astening together two pieces of metal or other 20 materials such as composites, the rivet which may be of ; metal or a composite, is inserted in aligned holes of the plates or members to be joined, a center shaft of the rivet which is attached to the head of' the rivet on ~, the blind side, is clamped in jaws and pulled until the :s 25 head is upset and then the region of the rivet at the i................. access side is up~et with the plates clamped between the two upset regions~
In the above example, the rive~-hole ~ combination, although closely toleranced, often leaves '~' , 30 small spaces around the rivets causing drippage of fuel ~` usually at a very slow but s~ill undesirable rate.
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The above example is just one use for blind rivets where liquid or even fluid tight performance is desired if not required. Assembly of any structure requiring fluid tight construction with blind rivets is 5 a ready candidate for the improvements provided by ~he present invention.
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BRIEF DESCRIPTION OF THE INV'ENTION
In accordance with the present invention, a blind rivet has a region coated with a heat activated sealant and incorporates a temperature self reyulating ' heater which may~ be activated by the rivet insertion r- tool. Specifically, the rivet has a region adjacent to where the insertion tool is clamped to the rivet during '` insertion and/or activation, that is coated with a `.~ 15 ferromagnetic material, such as Alloy 42. The insertion tool may heat the ferromagnetic material by ~ resistive or inductive heating of the ferromagnetic ;~ material; the heat thus generated being transported ~ through the rivet to the region coated with the heat ;~ ~0 activated sealant. The sealant is thus heated and ; melted andJor cured to provide a fluid tight bond between the rivet and the adjacent surfaces of the member or members through which the rivet extends.
~` The temperature self regulating aspect of the 25 prPsent invention is based on the fact that all ferromagnetic materials have a Curie temperature that .
~:,, as it is approached the material loses its .' ~erromagnetic properties. If resistive heating is employed then the principles of operation are as set 30 forth in U.S. Patent No. 4,256,9~5 with or without the copper layer. If inductive heating is employed then as the ferromagnetic material becomes substantially non-~.~
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magnetic, the induction coupling to the material is reduced and the rivet cools, see U.S. Patent No.
4,745,264. Thus the temperature of such a system cycles in a narrow range about the effective Curie 5 temperature of the ferromagnetic material. The - effective Curie temperature refers to the temperature at which the material becomes substantially paramagnetic as opposed to totally non-magnetic. The difference between absolute Curie temperature and r 10 eff~ctive Curie temperature is a function of the material and may be a few degrees and as much as 100C.
By choosing a ferromagnetic material having a Curie temperature safely above the curing or activation temperature of the sealant, the seal is affected and 15 just as important the sealant is not subject to ; exsessive and very likely destructive heating. The subject matters of the aforesaid patents, to the extent ;~
; necessary to understand the operation of the heaters . employed in the present invention, are incorporated : 20 herein by reference~
The term "sealant" as used herein refers to any material that upon heating can form-a fluid tight ~ bond by simple melting or by curing or both; and '~ includes glues, mastics, resins, epoxies and the like.
25 Materials that may be employed are Dynamold, Inc.'s moldable shim material MS-26 or DMS-4-828.
In a specific embodiment of the present invention, the blind rivet comprises a tubular sleeve . integral with a shaped head that remains on the 30 accessible side of the structure with the sleeve ex~ending through aligned holes of members to be ' joined. The tubular sleeve has a sealant on its outer surface and if necessary, on its inner hollow surface.

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~6 The shaped head of the device has a ferromagnetic coating over at least that region that is either in contact with or closely adjacent khe jaws or anvil of the insertion tool. If magnetic coupling i5 employed, a coil is wound about a region of the anvil or jaws close to the ferromagnetic material. Thus upon . .
energization of the coil with pre~erably high frequency current, typically radio frequencies and preferably frequencies of 8 MHz to 20 MHz, eddy currents and 10 hysteresis heating of the ferromagnetic material results in heating the head and by conduction the . sleeve. It should be noted that a ferxomagnetic coating may also be applied to the pin which carries the head end employed to seal the blind side of the : 15 opening.
In operation the blind rivet modified in accordance with the present invention is inserted into ~_ a hole and the riveting or application tool actuated to complete the rivetiny effect. Thereafter either 20 immediately or at a subsequent time a coil associated with the appli~ation tool or a separate tool is energized and the heater is heated to activate the sealant and produce a fluid tight coupling.
As indicated above, the blind rivets of the ;, .
:.` 25 present invention may be employed preferably with modification, with structures fabricated from advanced r-- composite materials, for instance, KEVL~R and carbon fiber reinforced epoxy resin systems. See also :.i ~i, Advanced Composite Materials, Edited by D.J. DeRenzo, 30 Noyes Data Corporation, pp 573-577. Since such materials are not necessarily good heat conductors, the head of such a blind rivet is preferably quite large so as to soak the materials in heat, that is, develop .;, .
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large areas of heated composite material whereby the heat necessary to activate the sealant not only can be developed, but can be conveyed to the sealant in a reasonable length of time.

BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1-3 illustrate a prior art rivet in various stages of use, that is to be modified in accordance with the present invention;
Figure 4 illustrates the rivet before activation that has been modified in accordance with the present invention;
Figure 5 illustrates the rivet of Figure 4 after activation;
r Figure 6 illustrates an embodiment employing resistive heating, and Figure 7 illustrates a rivet modified specifically for use with structures made with composites.
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DETAILED DESCRIPl~ION OF THE INVENTION
Referring now specifically to Fiyure 1 of the accompanying drawings, there is illustrated one of !; several types of standard prior art blind rivets. The rivet has a head 2 and an integral deformable ~. cylindrical sleeve 4 in axial ali~nmen~ with the head.
', I 25 A pin 6 extends through the sleeve to a head member 8 at the end oE the pin 6 remote from the head 2. The ~'~ pin 6 terminates remote from head 8 in a series of threads or circumferential groove 10 adapted to be engaged by a set of jaws on the activation tool as is 30 illustrated subsequently.
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Figure 2 of the ~ccompanying drawings illustrates the prior art xivet located in aligned holes through two members to be joined. It is noted that the sleeve 4 of the rivet is spaced, space 15, from walls 12 o~ aligned holes through plates 14 and 16 to be joined. The pin 6 has an enlarged region or band 18 which when the pin 6 is pulled in the direction of arrow 20, enters a region 22 of sleeve 4 of reduced internal diameter so as to expand the sleeve 4 to fill the spaces 15 between the sleeve 4 and walls of plates 14 and 16 and any space that may exist between pin 6 and the sleeve 4, see Figure 3. The head 8 engages the blind end of sleeve 4 and buckles it, as at 24. An anvil or chuck 26, a part of the activation tool, presses a retaining sleeve or ring 28 into a gene:rally . conical space along the axis of head 2 to secure the position of the head 2 along the pin 6.
Referring to the expansion of the sleeve 6 to seal the space 15, quite often a fluid tight seal is ; 20 not obtained or if initially obtained, not maintained.
In order to overcome this problem the present ~' invention converts the blind rivet into a temperature self regulating heater to actuate a temperature activatable sealant also included in or on the modi~ied . 25 rivet.
,. Referring now specifically to Figures 4 and 5 of the accompanying drawings there is illustrated the blind rivet of Figures 2 and 3 modified in accordance with the present invention. The sleeve ~ in the region disposed within the aligned holes through plates 14 and 16 has a layer 30 of sealant on its external surface located so that upon the sleeve being expanded upon completion of the insertion procedure, see Figure 5 .~ .

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-- specifically, the sealant is in contact with the sides 12 of the aligned holes and the sleeve 4. A layer 32 of sealant covers the region of the pin 6 that upon completion of insertion of the blind rivet is disposed in a region 34 of reduced internal diameter of pin 6, such region being radially aligned with the region of the sealant 30.
The head 2 of the pin 6 has a coating 38 of ferromagnetic material. Breakneck 36 and the region of 10 the pin above and below the breakneck as viewed in the figures, regions 40 and 42, may also be so coated. To complete the neater structure, a coil 44 is wound around nose piece 46 of a conventional application ~
tool.
Little, if any, modification of the rivet is required. The coating thicknesses are measured in mils or tenths of mils and thus do not interfere with normal ~ operation of the rivet. Selection of xivet materials may be changed to increase, if desired, the ; 20 conductivity of the metals of the rivets to incraase the autoregulating ratios as explained in Patent No.
4,256,945. Alternatively, the heater may operate as one without the conductive layer.
.i- In practice, the blind rivet of Figure 4 is ~ 25 inserted in the aligned holes of the members to be ;, joined and by means of an application tool is caused to assume the configuration of Figure 5. When it is desired to activate the sealant 30 and sealant 32, if provided, the coil 44 is connected across a high ~ 5; 30 fre~uency constant current source to heat the .; ~erromagnetic layers 38, 40 and 42 to induce sufficient heat in the pin 6 and sleeve 4 to cure the sealant layer or layers. If a lock collar of a material having .;

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appropriate Curie temperature and strength is availa~le, the lock collar 28 may be of a ferromagnetic material. As to thQ high fxequency current, at present a frequency of 13.56 MHz is preferred.
The particular blind rivet illustrated in Figures 2 and 3 is that illustrated in Figures 8 and lO
of U.S. Patent No~ 4,432,679 and those illustrated in Figures 4 and 5 are modifications thereof. It should be noted that the present invention may be applied to . lO many other configurations of blind rivets and bolts.
An example OI another such rivet is found in Figure 1 - of Patent No. 4,432,679. Note Patents Nos. 4,473,914, 4,~63,311 and 3,726,553 as examples of other configurations to which the present invention is applicable. The important consideration is that ^ conventional blind rivets and bolts can readily be adapted to provide heaters in accordance with the ~ present invention as can be the actuating tool.
:~ Further the invention is not applicable to blind rivets . 20 only, since the same problems arise with rivets disclosed in U.S. Patents 3,425,259 and 3,726,553.
Thus~ although the uses to which blind rivets are usually applied are more susceptible to the problems ; discussed herein, the invention is o~ broader utility.
Referring now specifically to Figure 6 of the accompanying drawings there is illustrated in partial section a region of a rivet to be heated by resistive ,-' heating rather than inductive heating.
, A conductive sleeve 50 o~ the rivet has three . 30 coatings, an inne~nost coating 52 of a thermally and ;; electrically conductive sealant, an inte~nediate :.
coating 54 of ferromagnetic material and an outer coating 56 of non-conductive sealant.
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High frequency current is applied to the two ends of the sleeve from a constant current high frequency source 58; the remote end via the plates 14 and 16 to the ups~t 51 and the other end directly to the pin. In this case accessible head 53 is insulated from the plates. The ferromagnetic layer provides a pronounced skin effect at the frec~ency of operation confining the majority of current to the layer 54 Upon approach to Curie temperature of layer 54, heating - lO decreases but only at a temperature above the activation temperature of the sealant. It is to be noted that the thermally and electrically conductive sealant is a part of the heater since upon approach to Curie temperature of layer 54, the current spreads into 15 the layer 52 as well as the sleeve 50. It is realized that the layers 52 and 54 may be replaced with a sealant exhibiting ferromagnetic properties, if one is ; available at a proper temperature.
~eferring now specifically to Fig. 7 of the 20 accompanying drawings, there is illustrated a blind rivet 59 with a large head 60 on the accessible side of the structure in contat with upper composite layer 62.
The head 60 has a coating 64 of ferromagnetic material as does pin 66 at and above breaX 68, reference ; 25 numeral 70. Sleeve 72 depending downwardly from head r,'~ 60 has a coating of sealant 74 in the region of the holes through composite plates 62 and 76. Sealant 77 ~ is also applied over region 78 of the pin 66 which is ;~, seated, as seen in Fig. 5, in region 80 of sleeve 72 ~; 30 upon completion of the riveting function.
:i The main difference between the rivet of .; , Figs. 4 and 5 and the rivet of Fig. 7 is the size of , the head of the rivet and, in some instances, the ,....................................... ..
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sealant used. Composites such as KEVLAR and the aforesaid epoxy resins are poor heat conductors compared with metals and in order to activate the sealant, the composite layers are saturated with heat.
It should also be noted that the coil, coil 82, is made larger so that the flux coupling the ferromagnetic materials is greakly increased thus increasing the Joule heating of the head 60.
Two further ~oatings should be observed.
-~ 10 Coating 84 of ferromagnetic materiaL is applied to the underside of the head 60 and coating 86, designated by a dashed line is a coating on the upper surface, as viewed in Fig. 7~, of layer 62, of sealant to bond the head 60 to the layer 62.
It should be noted that some or all of the ~ rivet 59 may be fabricated from a composite material as desired~
-~ ~he term "constant current" as used herein is defined in col. 11 line 31, ~quation 2 of U.S. Pat. No.
4,752,673 and is incorporated herein by reference.
Many variations and modifications of the ' above-described embodiments are within the ordinary skill of the skilled artisan in this art, without ; departing from the scope of the invention.
,-,?,~,_ 25 Accordingly, those modifications and embodiments are intended to ~all within the scope of the invention as defined by the followin~ claims-. .' , .
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Claims

1. A heater system incorporated in a rivet and application tool comprising, a rivet having a pin that is to extend through a hole to be sealed, a rivet application tool having a member for gripping said pin, a ferromagnetic material applied to said rivet adjacent a region of said rivet to be contacted by said tool, and means associated with said tool to heat said ferromagnetic material to a temperature approaching its Curie temperature.

2. A heater system incorporated in a rivet according to claim 1 further comprising a heat activated sealant disposed on said pin in the region of the hole in which the pin is to be seated.

3. A heater system incorporated in a blind rivet comprising, a rivet having a pin and a sleeve in which the pin is axially movable, a region of said pin disposed in said sleeve having a circumferential coating of ferromagnetic material, and means for applying a current to said rivet at a frequency to cause the current to be largely confined to said ferromagnetic material when said ferromagnetic material is sufficiently below its Curie temperature to remain significantly ferromagnetic.

4. A blind rivet incorporating a heater comprising:
a pin of said rivet that is to extend through a hole in which the rivet is to be seated, ferromagnetic material, said rivet having said ferromagnetic material applied to and adjacent an end of the pin opposite the end of the pin that extends through the hole in which the pin is to be seated.

5. A blind rivet incorporating a heater according to claim 4 wherein said rivet further comprises a hollow sleeve disposed about a region of said pin, said sleeve having a sealant disposed on that region of its external surface located within the hole, said sealant having an activation temperature below the Curie temperature of said ferromagnetic material.

6. The method of sealing a hole closed by a rivet comprising coating a circumferential region of a rivet that is to be seated in the hole with a heat activated sealant, locating the rivet in the hole, and developing heat within the rivet to activate the sealant.

7. The method of sealing a hole with a blind rivet having a central pin and a sleeve disposed about a length of said pin said method comprising the steps of applying a coating of a heat activated sealant to a circumferential region of the sleeve to be located in the hole, applying a coating of ferromagnetic material to a region of the rivet which when subjected to a high frequency constant current will heat the sleeve of the rivet, the ferromagnetic material having a Curie temperature above the activation temperature of the sealant, inserting the rivet in a hole with the sleeve located adjacent to walls of the hole, expanding the sleeve to fill substantially the hole, and subjecting the ferromagnetic material to a constant current to cause the ferromagnetic material to approach its Curie temperature and suffer a decrease in permeability such that its temperature falls.