August 1, 1921 



THE INDIA RUBBER WORLD 



805 



The Lap Splice 



The scarfed surfaces are then given at least three coats of 

 good rubber cement, allowing each to stand about an hour before 



joining the belt 

 ends. The "step- 

 ped" ends are then 

 carefully fitted to- 

 g e t h e r, clamped 

 tightly, and al- 

 lowed to dry for 

 an hour or two. 

 When dry the 

 splice may be fin- 

 ished with fine leather lacing or machine stitching. Some use 

 copper rivets placed IH inches apart. 



Some recommend a jacket of rubber-covered duck for protect- 

 ing the lacing, the space inside the lacing being filled with pieces 

 of duck and the whole covered with a large piece, all secured 

 with rubber cement and dried under pressure. This protection is 

 especially urged when fine lacing in small holes is used. If the 

 jacket is provided, it need be placed only on the driving face 

 of the belt, unless a tightener is used, in which case both faces 

 should be similarly jacketed. The strips and cover should be 

 thoroughly rolled or pounded onto the belt. 



DIAMOND LAP SPLICE 



Another method of making a lap splice is known as the diamond 

 lap splice. It is made in a manner similar to the ordinary lap 

 splice, except that 

 the ends are cut 

 pointed, instead of 

 square, with right 

 angle and diagonal 

 lines, as shown in 

 the illustration. 

 The edges of the 

 plies should be 

 scarfed to insure a 

 close fit. 



The length of a 

 diamond splice 

 should be : for a 

 belt 6 to 9 inches, 

 inclusive, 24 

 inches; 10 to IS 

 inches, 30; 16 to 24 inches, 36; 26 to 32 inches, 42; and 34 to 48 

 inches, 48. This length is figured from the extreme points at 

 either side, and takes in the square in the center and the tri- 

 angular spaces at either end of the splice. Lap splices are ad- 

 vised for belts 16 inches or more in width. 



Diamond Splice 



AN EXPLOSION OF HARD RUBBER DUST' 



THE results of investigation of a recent explosion in the hard 

 rubber scrap grinding department of a large industrial plant 

 are given in a report by David J. Price" and Hylton R. Brown' 

 of the Bureau of Chemistry, United States Department of Agri- 

 culture. The salient points of this investigation are here ab- 

 stracted from the report. 



KEDUCTION OF HAKD RUBBER SCRAP 



The rubber scrap is first broken up into pieces about the size 

 of a pea. In some cases this material is heated in large tanks. 

 It is then ground between steam-heated rolls or in one of the 

 various types of pulverizers. Sifters are used to separate any 

 coarse particles from the rubber dust, and this coarse material is 

 returned to the grinders. During this process large quantities 



of very fine dust are produced which tests have shown will 

 explode violently under favorable conditions. Considerable sul- 

 phur dioxide gas is frequently produced during rubber grinding 

 and in many cases no provision is made to remove this gas from 

 the building. In such cases the atmosphere of the grinding 

 department becomes a bluish color while grinding is being done. 



EQUIPMENT ARRANGEMENT 



In the plant where this explosion occurred the grinding depart- 

 ment was located in the basement of a two-story brick building. 

 The space allotted to this work was about 60 by 120 feet. The 

 basement was about ten feet deep but only six feet was below the 

 ground level. Windows were provided above the ground line 



:Suciion pipe 



□^ 



i:-Foin 



Grinders- 



^ 



f^loofjine )■ 



I \fnoor line /■ ^\ / ' ' - ■ . 



Chemical & Metalljcrgical Engineering. 



Side and End Views of Grinders and Hoods 



for light and ventilation. Various types of grinding machines 

 were installed with the motors necessary to operate them. These 

 motors were of different makes, but were all of the squirrel-cage 

 induction type. All switches were of oil-immersion type and the 

 fuses were of the non-arcing type inclosed in covered steel boxes. 

 The electric lights were of the drop-cord type of installation and 

 were not provided with vapor-proof globes or guards. A suction 

 system was provided to remove the dust from the building. The 

 dust was drawn into hoods located over the grinding machines 

 and then into the fan, whence it was blown through a 24-inch 

 galvanized pipe into a dust-house located on the roof of the 

 building. This pipe ran up the outside of the building and had 

 two right-angle turns, one where the pipe came out of the base- 

 ment window, 



Muslin bags 

 5i-raH:had on 

 4"vjoodzn framcs- 



'Chemical and Metallurgical Engineering, April 27, 1921, page 737. 

 'Engineer in charge developmtnt work. Bureau of Chemistry. 

 ^Assistant in grain dust explosion preventitn. 



and the othter 

 where it turned 

 to enter the 

 dust-house on 

 the roof. The 

 d u s t-h o u s e, 

 which was of 

 frame construc- 

 tion with corru- 

 gated metal 

 sheathing, con- 

 sisted simply of 

 a n expans i o n 

 chamber with a 

 number of mus- 

 I i n bags 

 s t r e t c bed on 

 wooden frames 

 through which 



'yt ■. . . . *'^^ ^''' escaped, 



^^^^^^7^^^^^ While the dust 



fell to the floor 

 of the dust- 

 house. The dust 



produced during the grinding was so fine that a large quantity 

 was drawn into the collecting system, and this made it necessary 

 to clean tlic dust-house frequently. 



EXTENT OF EXPLOSION 



The explosion, which the evidence indicates originated in the 

 basement, occurred about 4 :35 a. m. The first explosion was 



Chemical ff Metalhirgical Engineering. 



DUST-CoLLECTING SYSTEM 



