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THE INDIA RUBBER WORLD 



April 1. 1921 



SUMMARY 



The intensities of illumination required for various industrial 

 purposes have generally been far underestimated in published 

 works on the subject. The most recent and reliable investiga- 

 tions show that a minimum of 10 foot-candles should be sup- 

 plied for close work. One-half of this amount should be fur- 

 nished for coarse work, and from one to two foot-candles for 

 general safety in all spaces regularly used by workmen. 



Mercury-vapor light enables the muscles to respond more 

 quickly to vision and brings out details more sharply than either 

 daylight or ordinary electric light. 



There are only two types of light-units to choose from for 

 factory use: the gas-lilled tungsten lamp with white-enameled 

 steel rericctor, and the Cooper-Hewitt lamp. These distribute 

 their light in the same manner, so that the same rules apply to 

 both in figuring a lay-out. 



These units, when spaced at distances equal to their height, 

 give uniform illumination on the floor. At twice this distance 

 apart the illumination midway between the units is one-half what 

 is directly underneath ; and at three times the distance, one-th!rd. 



The foot-candle intensity directly underneath may be found by 

 squaring the height of the unit in feet, and dividing the vertical 

 candle-power intensity by this product. 



The intensity of illumination on the floor produced by a single 

 unit is found as above for the point directly below ; at a distance 

 from this point equal to the height it is one-fourth as much, and 

 at twice this distance, one-sixteenth as much. The above two 

 rules will give sufficient data for figuring any lay-out with the 

 units described. 



The best distribution of illumination is one in which there 

 are no shadows so dark as to prevent seeing details, and which 

 gives such degrees of light and shade, or contrast, that all de- 

 tails can be sharply discriminated 



RUBBER SHOE SOLING 

 By B. W. Elberson 



IN THE COMPOSITION of rubber shoe soling there is generally a pre- 

 dominating proportion of reclaim in the mi-\ing, enough crude 

 rubber being added to ensure a measure of wearing quality. 

 Formerly the only reclaim used for this purpose was that 

 derived from reworking waste rubber from worn-out shoes. 



Since the great influx of reclaim from automobile and solid 

 tires these grades have found a place in rubber sole composition 

 and have improved the wear resisting quality of the product. 

 Plantation Para in the inventories of rubber manufacturers at 

 27 cents per pound, suggests the possibility of again using the 

 better formulas of forty years ago. In these mixings crude 

 rubber predominated rather than reclaimed rubber. 



BOUNG STOCK IN THE FACTORY 



The usual method of preparing soling in a rubber shoe factory 

 is to allow an interval of 24 hours between mixing and calender- 

 ing. The latter operation is accomplished with a small four-roll 

 calender of special design, one roll bears the knurling for heel 

 and forepart of the sole, these are separated by a smooth shank 

 interval l:)earing the brand of the manufacturer. The knurled 

 roll is suitably turned to give the desired variations in gage of 

 the soles. 



TUBED soiuro 



In European factories soling has been run by means of the 

 tubing machine, the cylinder of stock extruded being cut and laid 

 open as it emerges from the die, and the knurling effected by 

 passage of the stock through a pair of rollers close to the die 

 of the tubing machine. 



Better quality stocks are handled somewhat differently from 

 reclaim grades. For best results with good grades, batches 

 should be cooled after mixing and be allowed to rest for two or 

 three days before calendering. Otherwise the stock will work up 



too soft, and blistering and undercuring arc liable to result. On 

 the other hand, if insufficiently ground, soling will not calender 

 smoothly and will shrink several gages on cooling. Judgment 

 and care are necessary to maintain the medium condition of 

 softness, bearing in mind that the harder the stock when delivered 

 to the heater the firmer will be the cure. 



HANDLING SOLING 



Calendered sheet soling is usually cut in short lengths, received 

 on convenient thin boards with end cleats for separation in piling, 

 and the piles set aside for 24 hours of cooling before cutting up. 



SOLE CUTTING 



In small factories or for small quantities of soles needed in 

 large factories, soles are usually cut tby hand, using sheet metal 

 patterns as a guide. For large output the sole-cutting machine 

 has become indispensable, owing to the advantage of speed 

 attained. 



DELIVERY OF SOLES TO SHOEMAKERS 



It is impractical to bunch cut soles on boards for delivery to 

 shoemakers ; instead it is customary to use cloth leaf books for 

 this purpose, which are transported on edge in trucks, to avoid 

 pressing and adhesion in the book. 



These books are on a board, and have eighteen or twenty 

 leaves of canvas and a black-ruibber top leaf for chalkniarking. 

 In the making room the operative is not allowed to use cement. 

 A cup of naphtha and a brush to do the "gassing" will produce 

 enough adhesion for quick rolling on. This touching up is done 

 while the soles are in the book, the leaves of which become so 

 sticky after a time that they occasionally have to be dried out 

 in the heater. 



ROLLED-EDGE SHOES 



A large percentage of goods are made rolled-edge, which 

 necessitates the stock being cut face down, and therefore the back 

 of the sheet must be marked to show the position of the brands 

 and heel line. A small wheel may be used for this purpose, rest- 

 ing on the engraved roll and held in position by a hinged arm 

 attached to the calender frame. The wheel has a couple of brands 

 on its face spaced exactly like those on the roll : these and the 

 heel line are slightly raised, which makes the impression. 



VULCANIZING 

 Of the several methods of vulcanizing, the pressure-cure is the 

 best for heavy work, as the heat penetrates the goods, and pres- 

 sure ensures a strong union between the shoe upper portion and 

 sole. Red, maroon and white stock should be pressure-cured, 

 although maroon can be compounded with some litharge a:id 

 will then cure fairly hard in open heat. 



SERVICE 



If goods are to give longer service the bottoms must be of more 

 durable stock. An examination of a pile of worn-out shoes 

 will show that a large number were discarded because of leaky 

 soles ; generally the heels wearing through first. This is a very 

 noticeable defect in women's shoes. If a ply of good quality 

 and thickness of rubber were added, in making up, it would 

 prevent leaking, even after the regular heel had worn through. 



"ENGLISH WEAREVER" RUBBER SPONGE OF NATURAL COLOR 



A rubber sponge that is a very good imitation of a natural 

 sponge both in color and porosity is the "Englisn Wearever," 

 recently developed by an American manufacturer of rubber 

 sundries and specialties. This sponge is much firmer to the 

 touch than the ordinary red rubber article. Its natural light 

 tan color is very attractive. It has not the unpleasant, slimy 

 feeling often objected to in rubber sponges when used with 

 soapy water. The porosity is irregular as in a natural sponge 

 and it has unusual absorbent qualities. — The Faultless Rubber 

 Co., Ashland, Ohio. 



