Testers

Last week the American Society for Testing Materials met in Atlantic City. The 4,400 members of this society are the insurance agents of U. S. industry. They decide exactly how thick and strong a piece of wire must be to make a good bridge cable. They decide how thick and strong a bolt must be to hold an automobile body securely on its chassis. Last week they were trying to establish criteria for the fastness of dyed or printed fabrics against washing. As tentatively established the test is as follows:

Fast Dye. Two specimens are cut from the piece of cloth. One specimen is used for the test; the other saved for comparison after the test. The test specimen is sewed to a piece of bleached cotton cloth and placed in a jar of hot (160 degrees F.) soapy water with ten 3/8-in. rubber balls. The jar is whirled in a rotating machine for 30 minutes. This procedure rubs the cloth samples as hard as any washing machine or washwoman can ever do. After thorough rinsing in warm (110 degrees F.) water, drying and ironing (at 275 degrees F.), the specimen is compared with the unwashed specimen. If no difference is discernible to the naked eye, and if the piece of white cotton cloth is not stained, the color is fast enough for the American Society for Testing Materials.

Footwear. After trying out fantastic "walking machines" to determine the durability of rubbers, tennis shoes and boots, and finding their results unreliable, manufacturers now test rubber footwear part by part. One machine, which Manager W. E. Glancy of Hood Rubber Co. Laboratories described last week at Atlantic City, has all the wheels and most of the gadgets of a lathe for turning out baseball bats. It is used to pull eyelets out of tennis shoes, a dial registering the force needed. A machine with a rocking arrangement stretches sheets of shoe rubber until they tear. To test the safety-toe caps of miners' boots, a cake of paraffin is put in the toe and an iron weight dropped from a height of 4 ft. on the boot tip. If the cake shows any signs of flattening, the manufacturer makes the toe cap stronger.

Such piecemeal laboratory tests however do not completely satisfy the conscientious manufacturer. He gives away footwear to people who are hardest on them--basketball players, garage and creamery workers, fishermen and miners, who will return the goods for examination when well worn. "At times," explained Tester Glancy, "men and young women are hired to walk daily, testing out new types of goods. Such walkers travel over a prescribed course and register at widely separated points to prove that they actually walked. Lastly, there is a group of boys and girls which often numbers 75 who wear test shoes. Once each week they report to have their shoews inspected."

Metallic Energy. To establish the strength of a metal engineers squeeze or pull (static tests) or hit (impact test) a sample piece until it breaks. Though one test is as good as another, none really explains why an automobile bolt occasionally cracks, an airplane strut snaps, a battleship's armor plate yields. By building a machine which hits a piece of metal with the whack of a bullet traveling 1,000 ft. per sec., H. C. Mann of Watertown (Mass.) Arsenal discovered that when a piece of metal is struck a very strong blow, its molecules release some of their potential energy, help shatter themselves. Mr. Mann's machine consists of a brace to hold the test metal and a flywheel with a bump on its rim. A motor works the fly wheel up to a rim speed of 680 m.p.h. at which point the bump hits the metal sample a single blow, breaks it clean as a whistle. For his inventiveness as a tester, the assembled testers last week presented Mr. Mann with a gold medal.

Fallible Wires. By no means are A. S. T. M. tests infallible. After satisfying A. S. T. M. specification for strength and flexibility, galvanized annealed steel wires were used for a suspension bridge over Mt. Hope Bay between Bristol and Ports mouth, R. I. Before the bridge was completed the cables inexplicably began to fray. The bridge was dismantled and rebuilt with galvanized cold-drawn steel wires. After yanking and bending in every which way the wires which failed, W.H. Swanger and G. F. Wohlgemuth of the U. S. Bureau of Standards learned that something had happened on the bridge which no tester had ever thought of reproducing in the laboratory. On the wires were tiny lumps of zinc put there by the galvanizing process. Where the cables rubbed against iron supports of the bridge, those tiny particles were driven into the steel wires, wedging apart the fine crystals of the annealed steel, causing the wire to snap. Coarse-grained, cold-drawn steel wire was found to resist this minute destructive process.

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