806 



THE INDIA RUBBER WORLD 



August 1, 1921 



quickly followed by a second and some families living near the 

 plant report hearing three distinct explosions. The explosion 

 evidently propagated to tlie first floor of the building, where the 

 windows, doors' and one corner of the brick wall were blown 

 out. It also propagated through the suction system to tlie dust- 

 house, which was completely demolished. 



ORIGIN OF EXPLOSION 



The fact that so much damage was done to the fan and 

 exhaust-pipe would indicate that the explosion had built up 

 considerable force by the time it reached this point in the system. 

 It is believed that the explosion originated in or near one of 

 the grinding machines and was caused by foreign material 

 entering the grinder, by a broken electric light, or by a lighted 

 matcli. The flames propagated throughout the basement, where 

 the employes were severely burned, and extended to the first 

 floor. The flames entering the suction hoods flashed through the 

 suction pipe to the fan, where they met their first obstruction 

 and built up the pressure which blew out the weakest side of 

 the casing, the one containing the inlet opening. The flames 

 also propagated through the fan into the exhaust pipe, built 

 up sufficient pressure at each bend to rupture the pipe and con- 

 tinued into the dust-house on the roof of the building, where 

 enough dust was present, estimated at about 125 pounds, to 

 cause an explosion which completely wrecked the house. It 

 must be remembered that this is only a theory of what happened 

 during the explosion, built on the knowledge obtained during the 

 investigations of previous explosions in industries where the 

 conditions and some of the installations were similar to those in 

 the hard-rubber grinding industry. 



RECOMMENDED PRECATTTIONS IN HARD RUBBER GRINDING 



1. The grinding department should be segregated from the 

 remainder of the plant and, if possible, operated independently 

 of other units. 



2. The building containing the grinding department should be 

 of heavy framework with light walls and roof so as readily to 

 permit the release of pressure from the building should an ex- 

 plosion occur. 



3. Good ventilation should be provided and where gases heav- 

 ier than air are produced during the process, the air should be 



drawn out of the room near the floor and fresh air admitted 

 near the ceiling. 



4. Where fine dust is produced an efficient dust-collecting sys- 

 tem should be installed. The old-style dust-room, where large 

 clouds of dust are in suspension, should be eliminated. The dust 

 should be collected as near as possible to the point of origin 

 and conveyed through pipes with fewest bends to the collector. 

 ^\hich should be located outside of the building or vented to the 

 outside air. If sharp turns are necessary in the pipe line inside 

 the building, place a vent at the bend, leading to the outside 

 air with a cap which will be blown off should any high pressure 

 occur at this point. Drawing explosive dusts through a fan 

 should be avoided where possible. A suction through the col- 

 lector or an induced air current is preferable. 



5. Special precautions must be taken to prevent metal enter- 

 ing the grinding machines. This is the only way to guard against 

 ignition of dust by sparks struck in the machines. A vent from 

 the machine to the outer air often assists in preventing a disas- 

 trous explosion by providing a direct means of escape for the 

 primary explosion within the machine. 



6. Where clouds of explosive dust are produced, electric 

 lights should be inclosed in vapor-proof globes and be properly 

 guarded to prevent accidental breakage. All switches and fuses 

 or electrical equipment in which sparks might be produced should 

 be located in a separate room or at least inclosed in fire-proof 

 and dust-proof boxes. 



7. Rules against smoking and carrying matches, where con- 

 ditions are favorable for a dust explosion, must be rigidly en- 

 forced and special attention be given to prevention of hot-boxes 

 on machinery operating in dusty atmospheres. 



8. Cleanliness is the best general precaution to adopt for the 

 prevention of dust explosions. A disastrous dust explosion can- 

 not occur in a clean plant, because the flames cannot propagate 

 unless dust is present to he mixed with the air in sufficient 

 quantity. From 0.02 to 0.04-ounce of dust per cubic foot of air 

 is usually sufficient to form an explosive mixture. The plant 

 should be kept scrupulously clean, especially overhead structures 

 where dust accumulations could be thrown into suspension in 

 the air by a sudden jar or shock. 



The Determining Factors for the Life of a Pneumatic Tire' 



By WiUiam G. Nelson^ 



THERE are five very important and very decisive factors for de- 

 termining the life of a pneumatic tire. Each has a direct 

 bearing upon the other, and a weakness in any one will prove 

 a death blow to the ultimate mileage which a tire is supposed to 

 give. These five factors are: rubber and compounding mate- 

 rials, fabric, construction, vulcanization and usage. 



RUBBER AND COMPOUNDING MATERIALS 



The rubber and compounding materials are comprised of rub- 

 ber, fillers, softeners, accelerators and vulcanizing agents. A mix- 

 ture of rubber, sulphur and other materials is called a compound. 

 There, are various kinds of compounds used in a tire, as tread, 

 carcass friction and skim coat, breaker friction and skim coat, and 

 side-wall. The tread must have good wearing qualities, good ap- 

 pearance, and coordination with the carcass. By this last phrase 

 is meant the ability to properly adhere to the remainder of the 

 tire. Good wearing qualities are obtained by properly compound- 

 ing suitalile materials and curing agents with high-grade wild or 

 plantation rubber. The most finely divided fillers, such as zinc 

 oxide, gas and lamp black and similar mineral fillers, are ex- 



*Paper re.td at the meeting of tlie .\merican Institute of Chemical 

 Engineers, Detroit, Michigan, June 20-23, 1921. 



'Chief chemist, ?Jorgan & Wright, Detroit, Michigan. 



tensively used, due to their microscopical fineness, which gives 

 high tensile strength, good stretch, and resistance to abrasion, 

 cutting and aging. Friction and skim-coat stocks are so com- 

 pounded as to give good adhesion to the fabric and a cushioning 

 effect between the plies of fabric. These stocks are composed 

 almost entirely of rubber, softeners, sulphur and accelerators. The 

 vulcanizing agent which is sulphur, and the accelerators, except- 

 ing the rubber, are the most important parts of a compound. An 

 accelerator is a material which accelerates the chemical combina- 

 tion of the sulphur with the rubber. Since the action of accelera- 

 tors is so erratic in mixing, calendering, and vulcanizing, only 

 e.xperienced men should undertake the handling of these agents. 

 The side-wall must have good appearance, as it holds one of the 

 most conspicuous places on the tire. It is used for the protection 

 of the fabric against chafing and moisture. Since it is continually 

 exposed to atmospheric conditions it must have good aging quali- 

 ties rather than high tensile strength or long stretch. 



All compounds that come in contact with each other must have 

 good adhesion after vulcanization. The factors that bear upon 

 this condition are : type of rubbers selected : kind and amount 

 of fillers, sulphur, and accelerators; mixing and calendering of 

 the compound ; building of the tire ; and finally the degree of 

 vulcanization. 



