782
NEWS
EDITION
Vol. 19, No. 14
New Explosive Rivets Speed Production D . L. Lewis Jr.
E.
I.
du
Pont de Nemours & Co., Inc., Wilmington, Del.
XPLOSIVE rivets made by du Pont may prove an important factor in speeding American aircraft production and simplifying design. Nowbeing manufactured in commercial quantities, the rivet is of an entirely new type. A high explosive is secreted in a cavity at the end of t h e shank. Heat applied to the rivet head b y an electric gun detonates the charge. T h e explosion expands the charged end of the shank, forming a "blind" head and setting the rivet. T h e whole operation is performed from one side with greater ease and speed than is possible b y any mechanical means now in use in aircraft factories. Engineers estimate that 8 0 0 fastening points in an all-metal pursuit plane t o as many as 10,000 in the largest all-metal bomber are accessible from one side only. Under the best mechanical methods now employed, a skilled workman can set about two to four of these "blind" fasteners a minute after they have been placed in the holes. The equipment i s comparatively costly. T h e new rivets may be installed by one workman at a rate of 15 t o 20 rivets a minute, once they are i n place. T h e riveting gu. iron weighs less t h a n 5 pounds. T h rivets themselves weigh only about one fourth as much as generally used blind fasteners of mechanical design. S o finely has the explosive charge been controlled that the expansion it effects may be held within limits of 0.02 inch. T w o years of experimental work by the Explosives Department of the du Pont company, supplemented by extensive tests of the rivets on airplane production lines in recent months, stand behind t h e development. M u c h of aviation's phenomenal a d vance has been made possible b y development of the all-metal design, pre-eminently employing t h e lighter metals such a s aluminum and magnesium alloys. This style of construction requires 40,000 t o 500,000 rivets or more per plane. The job is one of t h e most exacting and tedious t h a t confronts plane builders, and grows more so as planes become larger, which i s the trend. T h e recently completed B-19 Douglas bomber, largest ship of its kind ever built, is said t o have 3,000,000 rivets. Gang riveting machines, automatic hole-punching and rivet-driving devices, and occasional replacement of rivets b y high amperage spot welding have tended t o simplify t h e tremendous fastening problem t o a n important degree. These methods, however, together with t h e
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driving of conventional rivets individually b y two-men crews—usually at a rate of two t o three rivets a minute—are applicable only in assemblies which permit access to both sides. Many structures or portions of airplane structures are totally or partially inaccessible from the rear. These require fasteners capable of being installed entirely from one side, usually termed "blind rivets". M a n y kinds of mechanical "blind" rivets have been developed, but in general they have compared unfavorably with "bucked" rivets in physical and structural properties and are difficult t o install economically. So serious has been this difficulty that it has influenced airplane designs through the efforts of designers to avoid it. In 1921, an American, Frank Allan, patented several t y p e s of explosive rivets and bolts, b u t these did not prove commercially feasible. I n 1937 a patent issued b y t h e United States Patent Office t o Karl and Otto Butter, t w o brothers employed b y Ernst Heinkel, builder of t h e famous German plane bearing his name, revived t h e idea of setting "blind" rivets b y expanding the shank with a minute explosive charge. Early in 1939, t h e du P o n t Explosives Department began seriously to explore possibilities of t h e idea. N o r t h American rights t o t h e Butter invention were purchased from the American Explosives R i v e t Co., which had previously acquired t h e m from Heinkel t o whom the Butters assigned their patent. A n intensive research and development program was launched b y d u Pont's Eastern Laboratory, Repauno, N . J. Apart from fundamental details which the patent disclosed, many problems remained t o be solved. Adjusting t h e design t o American standards of precision required m a n y hours of laboratory test work. A new method for manufacturing t h e rivet blanks was necessary, since the very small tolerances or allowances for microscopic variations in
D u Pont explosive rivet in original condition and in installed condition (right)
Application of iron to the rivet head size could not be m e t in existing equipment. T h e anodizing process or treatment of the surface t o prevent corrosion had t o be improved. Equipment for the extremely accurate loading of almost infinitésimal explosive charges had t o be designed and constructed. In t h e fall of 1940, after the improved rivets had been tested and evaluated by the United States A r m y and N a v y , they were sold in limited numbers t o a few aircraft manufacturers for further testing and actual shop installations. These rivets were made o n experimental tools but were loaded on production equipment. Working in close cooperation with American airplane builders, the company has perfected t h e multitudinous details of manufacture and use. T h e section photograph shows the rivet in both the original and installed condition. Prior t o installation the rivet is similar t o a solid rivet except for a cavity concentric with the shank and open at t h e shank end. T h e cavity holds the small explosive charge which, when heated to a certain temperature, detonates and expands t h e shank end uniformly without cracking. T h e rivet t o the right in the illustration shows t h e shape of the shank after expansion. Because of the nature of t h e explosive, n o wadding or no confinement is required. T h e heat necessary t o the installation is supplied b y a specially designed electric tool with a silver tip, the riveting iron. Time of installation is l 1 / 2 to 2 1 / 2 seconds from the time the iron is applied until expansion takes place. T h e rivets now being manufactured are of an aluminum alloy. Of varying diame-
NEWS
July 25, 1941 ters and sizes, they are of the modified brazier head and countersunk types, the latter permitting the flush riveting re quired by modern high-speed planes. The rivets are installed in the age hardened condition and do not require the re frigeration after heat treatment so neces sary with solid rivets in the same alloy. In shear and tension, these rivets develop values approximately the equivalent of driven rivets, the type now most widely used. The du Pont rivets are safe and may be used without fear of serious injury, al
though they should be handled with reasonable care. Numerous safety tests have indicated they will not detonate in mass and are quite insensitive to shock and friction. Fire or high heat of any kind will, of course, cause them to expand. Several million explosive rivets have already been sold and are being used in American aircraft actually in service. It is believed these rivets may find many applications in other industries. Manu facture in still larger sizes and in other metals, including steel, does not seem beyond the realm of possibility.
Rodent Repellent Tests η-Butyl Mer capta n against White and Wild Leonard A . Ford Donald F. Clausen
TΗΒ protection of commercial feedstuffs from depredations of rats and mice is both expensive and time consuming. In place of the common method of using poison and trapping, the authors have applied the principle of repellent odors for the protection of sacked commercial feedstuffs. This method, which involves the use of a re pulsive odor on the feedsack, was tried with a varying degree of success. Experi ments ( 0 have shown that the nose of man is extremely sensitive to certain odors. Should not certain scents like wise cause a reaction in rats and mice? To test the effectiveness of various scents it was decided to use mercaptans and thioesters which are present in the characteristic odors of weasels, skunks, ferrets, and minks. These animals are the natural enemies of rats and mice. According to Parten (2) the presence of ferrets and skunks on a farm will drive rats off until the former have left or are removed. The active ingredient of the odor of skunk, n-butyl mercaptan, was placed on the food of caged white rats. The food was untouched until the odor of the volatile mercaptan had disappeared. The hair was seen to rise on the backs of the rats and they became nervous and excited when the odor was present. The smell seemed to precipitate fights among them. Other volatile irritant compounds, such as carbon tetrachloride or denatured alcohol, had much the same effect but to a lesser de gree. The effect of the odors on the rats diminished during the months in which the experiments were conducted. To be effective as a rat repellent the 1 Present address. International Milling Co., Minneapolis, Minn.
feedstuffs treated with mercaptans may have been due to the fact that the treated substance wras not regarded as food. This leads t o the interesting question whether it would be possible to disguise feedstuffs with more agreeable odors than those of mercaptans so that rats would not regard them a s food. References Cited (1) Ford, Leonard Α., J. Chem. Educ, 17, 17 (19403. (2) Parten, Η . Ε., Minnesota State Exter minator, personal correspondence.
New Treatment Heals Lye Burns
Rats
State Teachers' College, Mankato, Minn. 1
783
ED I T I O N
Hubbard Milling Co. Mankato, Minn.
mercaptan must be absorbed in a sub stance which will retain the odor. In these experiments a substance which would hold the volatile mercaptan for four or five months was desired. It was found that honey held the odor for four months, dead mouse two weeks, and fat scraped from a rat skin six days. The following substances held the odor overnight: rat hide, stock concentrate, glycerol, soap, and castor oil. I t was hoped that print ers' ink would retain the odor since it is used on commercial feed sacks, but the odor disappeared from ink very quickly as it did from lard, mineral oil, petroleum, and many other substances. Commercial feedstuffs are ordinarily stored for periods up to four months. For the following investigation honey was selected since its ability to retain the odor of the mercaptan was still pronounced after this length of time. Honey con taining η-butyl mercaptan, when placed on feed on a farm was untouched by rats for four months. Rats here were accus tomed to eating from pans containing un treated feed. When this feed was treated with the honey-mercaptan mixture they refused it. When the same experiment was con ducted at a city dump it was found that the mercaptan had little repellent effect after three days. This would seem to indicate that these rats were used to the odor of mercaptans formed in decaying organic material. That the food supply was limited and the number of rats large also may have had a bearing on the results. These investigations have suggested the possibility of using mercaptans or similar substances to discourage the attacks of rats and mice on commercial feedstuffs. The failure of rats to eat commercial
ΠΡΗΒ daily press has recently described the use o f hydrosulfosol solution de veloped after "three years of research at the Institute of Pathology, Western Penn sylvania Hospital, Pittsburgh, Penna.r to alleviate pain and promote healing of burns caused by sodium or potassium hy droxide as well as b y ordinary causes. The report describes the use of this solution in t h e case of a man who had re ceived the contents of a quart jar of com mercial lye solution full in the face. His nose, mouth, eyes, tongue, and ears were burned, and t h e eyelids and eyeballs were severely burned. Physicians sprayed the burned areas thoroughly with hydrosulfosol solution every hour during the first 24. The patient i s reported as having regained the full eight of one eye, other parts of the face have healed, surprisingly free of scars, and treatment of the other eye is being continued. The solution laid down a thin coating over the burned areas, thus reducing pain because oxygen is excluded and speeds the healing process through stimulating growth of new cells.
Medicinal Imports into British Malaya Increase IN 1940, according t o the U. S. Department of Commerce, import trade into British Malaya of medicinal, biological, and pharmaceutical preparations was valued at S$5,548,207. The united King dom, China, and the United States, in the order named, are understood to have been the most important sources during the year, althongh trade with Australia, Hong Kong, and India also increased con siderably in compensation for the generally reduced trade with Europe. The United States is important as a sup plier of tonics and blood purifiers, tablets and pills, elixirs and tinctures, and various salves, ointments, mouth washes, laxa tives, cold and cough preparations, milk of magnesia, a n d similar products. During 1940 malaria, and fever preparations were an importarrt item, i t is understood.
