US2429239A - Explosive rivet - Google Patents

Description

G. D. ROGERS EXPLOSIVE RIVET Filed Sept. 20, 1941 2 Sheets-Sheet l gmm'm Eeurje' D-RCIQETE (M21, 1947. OGE S 2,429,239

Filed Sept 20, 1941 2 Sheets-Sheet 314) George ILRDQ Patented Oct. 21, 1947 UNITED STATES EXPLOSIVE RIVET George 1). Rogers, United States Army, Dover, N. J.

(Granted under the act of amended April 80, 1928;

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This application is a continuation-in-part of my copending application, Serial No. 388,769 filed April 16, 1941.

This invention relates to an explosive unit whlchis particularly adapted for use as arivet and to an improved method of forming the same.

In the employment of the explosive rivets known in theprior art, for example of a type similar to that shown in U. 3. Patent 2,080,220, it'has been noted that the powder gases and other products from the expanding charge have a deleterious eflect upon the metal of the plates that are to be united. It has also been noted that localized failure in the rivets may be attributed either to non-uniform deformation of the shank of the rivet in the expansion thereof or to an improper gradation of strength in the rivet structure.

Certain of the rivets of the prior art commonly fail at the head end during strength tests, a condition which may be attributed to the fact that the inherent strength oi the metal in the shank is more fully developed by the cold working undergone in expansion of the rivet. The head oi rivet which does not partake of this cold working is not so strengthened and failures are therefore more apt to occur at the head end.

It is therefore the'object of this invention to produce a, rivet which before application-to the work has a varying strength from the head to the tip ofthe-shank, the variation being such that it will be modified by the expansion of the rivet to a condition of substantially uniform strength from head to tip.

Broadly this object has been accomplished by the provision of a hollow rivet which is initially relatively strong at the head end, this strength diminishing gradually to acondition of relative weakness at thetip of the shank. Upon expansion, the tip of the shank, being deformed to a relatively high degree as compared to the deformation received by the rest of the rivet, will be correspondingly strengthened by work hardening with the result that substantially uniform strength will be developed in the full length of the rivet.

vA further object of this invention is to provide a novel and economical method of forming a rivet from a single piece of material to insure uniform centering of the chamber within the rivet shank PATENT OFFICE March 3, 1888, as 810 o. G. 757) and properly graduated thickness and strength from the head to the shank end of the rivet.

It is a further object to provide a rivet structure which will permit the utilization of expand ing media other than explosives.

, The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of several, embodiments as shown in the accompanying drawings in which:

Fig. 1 is a longitudinal sectional view of the rivet before being expanded.

. Fig. 2 is a similar view after expansion.

Fig. 3 is an enlarged longitudinal sectional view of a portion of the rivet and a cooperating fluid injector unit illustrating a method of application.

Figs. 4 to 7 are longitudinal sectional views illustrating certain of the steps in one method which may be employed in the forming of a rivet 20 according to my invention.

- Figs. 8 to 10 are similar views showing certain of the steps in the forming of a rivet adapted for flush riveting operations.

Figs. 11 to 14 are similar views showing certain 26 of the steps in the forming of an openshank rivet according to my invention.

Figs. 15 to 17 are similarviews relating to another method of forming an open shank rivet. Referring to Figs. 1 and 2 by characters of reference, the rivet comprises a head 5 and a shank 6 which is adapted to be inserted in the customary manner through apertures I and 8 formed respectively in plates 9 and I 0. The head is formed orprovided with a constricted axial passage I I 85 which is in communication with a chamber I 2 in the shank. The chamber I2 is preferably gradually enlarged toward the end of the shank remote from the head 5. The passage ll may be enlarged somewhat at its outer extremity. The strength of the rivet is graduated by varying degrees of cold working incident to forming, designed to provide the proper work hardening to insure that relatively high strength has been developed at the head end of the rivet which strength gradually diminishes toward the tip of the shank to a condition of relative softness and correspondingly lower strength. Upon expansion of the rivet sufllcient plastic flow of the-shank metal occurs to strengthen the shank by workhardening to a degree corresponding to the work hardness of the head. The chamber I 2 is intended to be filled with a material adapted to cause the expansion of the rivet shank, whereby the plates 9 and I0 may be secured to each other.

58 As shown in Fig. 1 the chamber I2 is filled with tralizing solution to the chamber.

an explosive material I such as nitrocellulose or other low explosive or one of the high explosives and the passage H may be filled with a more easily ignited priming charge, for example black .powdel' or a primer for a high explosive, which can be retained in place by the application of a nitrocellulose lacquer or similar binder 3 to the exposed end of the priming material.

The rivet is applied by placing it in position through the plates to be secured and exploded by the application of heat, friction, or a spark to the exposed priming material. The resulting explosion of the partially confined charge I causes the expansion of the rivet to a shape similar to that shown in Fig. 2 whereby the plates 9 and 10 will be firmly secured to each other.

In an alternative method of employing my rivet means are provided whereby a fluid material may be fed into the rivet chamber under pressure to cause the same to swell and secure the joint. In carrying out this method a hydraulic nozzle 18 shaped to cooperate with the passage in the rivet head is inserted therein as shown in Figure 3. Obturation is efiected by the expansion of the thin elastic wall at the tip of the nozzle. Other methods may be employed to efiect a releasably sealed connection. Preferably the chamber in the rivet will have been filled with a fluid or semi-fluid pressure transmitting medium in the course of its manufacture.

It is also contemplated that the chamber in my rivet might be filled with a solid or pulverous material capable of combining with a fluid plasticizing medium to form a plastic compound remaining in the rivet. It is contemplated that the expansion of the rivet could be brought about by the injection of the plasticizer under pressure as discussed above or by choice or a primary filling material of such a character that it will expand considerably upon saturation with the plasticizer, this expansion setting the rivet in place.

In ,a further method of utilizing my rivet it is contemplated that the cavity in the rivet will be filled with a material which on the establishment of a predetermined condition will swell and thus expand the rivet. As an example, a material which expands on freezing could be thus employed and frozen in place by the application of dry ice or the like.

Any method, such as those discussed above, which causes expansion of the shank of the rivet will cause sufllcient plastic flow or the metal of the rivet to produce work hardening of the metal with a corresponding increase in the strength thereof. I

It will be noted that in the use of a rivet such as that discussed above any of the by-prcducts of the expanding media which might tend to produce corrosion will be confined to the interior of the rivet itself or expelled to atmosphere through the passage in the head. In a rivet of this type the passage through the head makes it possible to remove or neutralize any corrosive products by the application of a suitable washing or neu- The inaccessibility of the inner end of the shank of an open ended rivet does not allow such treatment and requires the use in such rivets of explosives specially compounded for non-corrosive properties.

In order to insure that the rivet will not fail due to side blow-outs or other non-uniform shank deformations it is essential that the rivet be so that in planes normal to the axis of the rivet the structure of the rivet will have symmetrical strength characteristics with respect to the axis. Similarly in order to avoid failures due to an improper strength relation between shank and head it is essential that the relative strength and d1 mensions or these parts be carefully controlled. Several methods 01 forming the rivets allow both these ends to be achieved in practice. 01 these methods die forming is preferable in that the cold working involved compacts the material to uniform density and makes it possible to control the strength and hardness of the various portions of the rivet as well as the dimensions thereof. Die forming is also a desirable method in that it is readily adaptable to economical mass production of great numbers of units. In a. preferred method the blank material of which the rivet is to be formed is first drawn into the cup-like Iorm shown in Figure 4. In subsequent die operations the length of the cup is reduced and the wall thickened at the open end as the cup is shaped to tapered form similar to that shown in Figure 5. The head may next be roughly shaped as shown in Figure 6 and in final operations the shank is shaped to finished diameter and the head reformed about a passage shaping stud to a form similar to that shown in Fig. '7.

As is known in die forming practice suitable annealing may be required to prevent the development of work hardness sufilcient to cause rupture of the metal during forming. In one form of practicing the invention the material forming the cup shown in Figure 4 is annealed to relieve the relatively high strain in the edge of the cup, leaving a blank cup of substantially uniform hardness and strength. It will be obvious that in the transition from blank to rivet the section at the tip of the shankimdergoes almost no change in dimensions while a gradually increasing degree of plastic flow is experienced by increments of the shank approaching the head and by the head itself. Work hardening, unless relieved by annealing, is cumulative and it will be readily apparent that the material will be strengthened by work hardening in direct, proportion to the amount of plastic fiow involved in the shaping operations subsequent to any annealing which may have been required. When the rivet is expanded in use the tip sectionsof the rivet which have been left relatively soft during the forming process receive additional deformation and a corresponding increase in work hardness which gradually diminishes toward the head or the rivet and in those sections of the rivet shank supported by the work being secured.

Work hardening is necessarily cumulative and to the initial work hardness which grades'from a maximum at the head to a minimum at the tip will be added the work hardening due to the expansion of the shank which grades from a maximum at the tip to a minimum in the head. It follows that the rivet in the expanded condition will have a substantially uniform work hardness and correspondingly uniform unit strength from the head to the'tip of the shank. The results obtained approximate those which are obtained in a bucked-up" percussion riveted job of the type normally performed where both faces ofthework are accessible to tool operations.

Obviously a similar method of forming may be applied in the case of rivets having countersunk heads. Figures 8, 9 and 10 show certain of the steps in a desirable application of the invention formed that the chamber will be centered and to this type of rivet. As in forming this type of rivet a less severe working of the head end is experienced than in that previously discussed it may be desirable that the treatment of the rivet be modified accordingly. In the forming of the cup shown in Fig. 8 the metal of the wall will be.

worked to a relatively high degree at the open end and will have received less and less working down to a minimum at the closed end which is practically unstrained. The succeeding operations of upsetting the wall of the cup, forming the head and shaping the passage through the head indicated in Figures 9 and 10 also serve to increase hardness, and correspondingly strength, in a graded relation from a maximum at the head to a minimum at the tip of the shank in direct proportion to the amount of cold working -received in the forming operations. In the expansion of the rivet the shank will, as discussed before, receive a graduated degree of work hardening sufllcient to produce an expanded rivet of substantially uniform hardness and strength.

Depending upon the material with which the cavity is to be charged, the loading operation can be carried out either before or after the reshaping of the shank and shaping of the passage through the head. In the .case of certain explosive compounds which require consolidation to insure complete combustion or detonation and in the case offilling with a semi-fluid hydraulic pressure transmitting medium it is desirable that filling be carried out before final shaping. The expanding medium can be charged into the cavity in either semi-fluid or pulverous state and will be consolidated by the final press operation into a homogeneous material free from voids or air bubbles which might cause erratic action.

In case the cavity is to be charged with a finely relationship in accordance with the teachings of this invention.

In one method of forming an open shank rivet, certain steps of which are shown in Figures 11 to 14, a blank 20 is upset to form a flange 2! coaxial with the body of the blank 20 and of substantially uniform thickness similar to that shown in Fig. 12. This flange is then partially closed about the axis of the blank to form a chambered end having a larger exterior diameter than the blank proper and similar in shape to that shown in Figure 13. The blank is then preferably annealedto relieve the strains caused by the cold working of the chambered end. In

subsequent operations the chambered end is suitably supported to prevent deformation thereof while the shank is upset to the same external diameter as the chambered end and a head is formed in any convenient manner producing a rivet similar to that shown in Fig. 14. Obviously, there will be produced a rivet having a work hardened head and shank with a relatively soft chambered portion which will be work hardened by the expansion of the chambered end as previously discussed. The expanded rivet will therefore possess substantially uniform hardness and strength throughout its entire section.

thickening the wall In another method a rivet may be formed from a blank I: as shown in Figure 15 by piercing the end thereof toform a flange, indicated as It in Figure 16, coaxial with the shank, ll of the rivet and of substantially uniformthickness. In subsequent operations the flange may be partially closed about the axis of the shank to form a chamber indicated, as I! in Figure 17 while the shank It may be sized to finished diameter and the head l8 formed in any desired manner. It will be obvious that as the rivet was formed by cold working it will have been hardened thereby in proportion to the working received. In accordance with the principles of my invention it is desirable that the chambered end of therivet be selectively annealed to relieve the stresses therein. Upon expansion of the chambered end of the rivet this portion willbe work hardened to restore the desired relation of uniform hardness and strength through the length of the rivet. Obviously a similar'selective relief annealing can be applied to the chambered portion of a pre viously hardened rivet having the chamber formed by drilling or otherwise opening the end of a solid rivet.

I claim:

1. A method of forming a rivet which comprises drawing a. cup from a metallic blank,

of end thereof in a further drawing operation, forming a head about the open end of said cup, and simultaneously sizing the closed end of said cup to form the rivet shank and reforming the head to provide a restricted passage into the chamber thus formed in the shank.

2. A method of forming a rivet which comprises drawing a. cup from a metallic blank, thickening the wall of said clip toward the open end thereof in a further drawing operation, forming a head about the open end of said cup. partially filling the interior of the cup with a material adapted to cause expansion, and simulsaid cup toward the open taneously reducing the diameter of the closed end of said cup to form the rivet shank and reforming the head to provide a restricted passageinto the cup whereby the material confined within the rivet will be consolidated intoa homogeneous form free from air bubbles.

3. A rivet havingunit strength generally decreasing in the direction from the head to the tip of said rivet.

. d. A rivet comprising a head and a chambered shank adapted for expansion, the unit strength of increments of the unexpanded rivet generally decreasing in the direction from the head to the tip of said shank.

5. A rivet comprising a head, an expandible shank having a chamber therein, and means for applying an expanding force to said chamber, the unit strength of said rivet in unexpanded condition varying from a maximum at the head of said rivet. to a minimum at the tip of said shank whereby the strengthening produced by the work hardening given to the shank during expansion thereof 'will be added to the strength of the shank in unexpanded condition a to produce an expanded rivet of substantially uniform strength from head to tip.

6. A rivet comprising a head, a unitary shank integral with said head, means integral with said head defining a restricted passage through said head, means integral with said shank defining a chamber in said shank in communication with said passage, and means in said chamber for applying an expanding force to said shank, the

the interior of creasing in the direction from the head to the tip of the shank.

7. A method 01 forming an open ended rivet which comprises upsetting the end of a rod of metal to form a flangethereon, said flange being coaxial with said rod and of substantially uniform thickness, partially closing said flange upon the axis of said rod to form an open chambered end having a greater external diameter than said rod and having walls of substantially uniform thickness coaxial with said rod, annealing said chambered end, upsetting said rod to the same 8 duce a rivet whose walls are work hardened with the work hardness incrementally decreasing from the head end of the rivet to the opposite end.

10. An explosive rivet comprising a unitary head, an expandible unitary shank formed integrally therewith and having therein a chamber symmetrical about the axis of said shank, means integral with said head defining a restricted passage through said head and'in communication 10 with said chamber, explosive material confined in said chamber, and priming material loaded in said passage, the unit strength of increments of the rivet, prior to explosion of said explosive material, generally decreasing in the direction diameter as said chambered end and forming .a 1 from the head to the tip 01 the shank.

head on the end 01' said rod opposite said c'hambered end.

8. A rivet comprising a head and a shank, said head and shank being integral and formed wholly,

of a single piece of metal, the said shank having a cavity therein wholly enclosed by the material of the shank except for an opening into a passage through said head, said head having a passage into which said cavity opens and the hardness of said rivet generally decreasing from the head end to the free end of the shank.

9. A method 01' forming an open ended rivet GEORGE D, ROGERS.

20 file of this patent:

7 a UNITED STATES PATENTS Number Name Date 202,994 Clifford Apr. 30, 1878 25 415,298 Peck Nov. 19, 1889 2,170,556 Frost Aug. 22, 1939 1,406,693 Soderstrom Feb. 14, 1922 1,316,877 Clarkson Sept. 23,1919 1,483,947 Morse Feb. 19, 1924 30 1,400,401 Allan Dec. 13, 1921 2,080,220 Butter et a1 May 11, 1937 2,146,461 Bettington Feb. 7, 1939 1,013,046 Murphy Dec. 12, 1911 as FOREIGN PATENTS Number 4 Country Date 467,515 Great Britain June 17, 1937 648,842 Germany Aug. 12, 1937

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