July 1, 1917. 



THE INDIA RUBBER WORLD 



581 



The conclusions were summarized as follows: (IS) It is not possible at present to suggest a method of ob- 



(1) Spontaneous coagulation of the latex usually yields rub- taining rubber with a uniform rate of cure, as samples made 

 ber of good quality, but the method is scarcely suitable for prac- under exactly similar conditions at different times vary con- 

 tical use. siderably in this respect. The bulking of the product obtained 



(2) Scrap rubber from the trees has invariably given a low over a considerable period would appear to be the only practicable 

 tensile strength after vulcanization. way of approximating to this result, until further research has 



(3) Acetic acid is quite satisfactory as a coagulant, and, so far thrown more light on the fundamental condition in rubber which 

 as the vulcanizing and mechanical properties of the rubber are influences rate ot cure. 



concerned, there would appear to be no advantage in using any 



°"?4''/pi'^'"^'^"?^i*-^ . KK • „ f „ . , COMMITTEE D-11 ON RUBBER PRODUCTS. 



(4) Flam unsmoked sheet rubber is usually of excellent qual- 

 ity, the unvulcanized product having, as a rule, a tensile strength At the meeting of the American Society for Testing Materials 

 of 2,300 to 2,400 pounds per square inch. The rubber also cures held at Atlantic City, New Jersey, June 26-29, 1917, the various 

 fairly rap.dly the average time under the conditions of tlie pres- sub-committees of Committee D-11 on rubber products reported 

 ent series of tests being about 70 minutes. , u ■ • ■ ■ , 



(5) Crepe rubber invariably takes a much longer time to cure Progress only on their assignments, except sub-committee 1 

 (105 to 130 minutes) than the corresponding plain sheet from on air hose, which offered a tentative specification on air line 

 the same latex, and this effect is brought about even if the freshly hose for pneumatic tools. The rubber qualities recommended in 

 coagulated rubber is only passed through the rough rollers four ^^is specification include IS-pound friction separation at a rate 

 times. I he mechanical properties of crepe rubber alter vulcaniza- ,. . , . 



tioh are very frequently inferior to those of the corresponding "°* exceeding one inch per minute. 



plain sheet. Test pieces shall be cut longitudinally from the hose. 



(6) The "over-working" of the freshly coagulated rubber in Tube and Cover. When stretched from two to nine inches the 

 the preparation of crepe (up to 70 times through the rough rol- ^t^ess upon the tube shall be at least 900 pounds per square inch, 

 lers) has very little effect on the mechanical properties of the , , r,r^ , . , 

 vulcanized rubber, and only slightly increases the time of cure, ^"^ t"^* "P°" *e cover 800 pounds per square inch, 

 compared with that of crepe made by passing through the rough The set, or permanent elongation, shall not exceed 25 per cent, 

 rollers only 5 or 7 times. The tensile strength shall not be less than 1,500 pounds per 



(7) Thick crepe rubber made by rolling together several pieces i„,h for the tube, and 1,300 pounds per square inch for 

 of thin crepe, does not differ from the latter m time of cure, /* > < i- f h ^ 



and the differences in tensile strength are not very marked or "^^ cover. 



constant. Thick crepe, made by rolling out the coagulum to the Both tube and cover shall have an elongation at the breaking 



required thickness, usually cures in a shorter time than the cor- point of at least 2 to lOV^ inches. 



responding thin crepe. 



(8) Different methods of drying (air-drying at the ordinary 



temperature, drying in hot air, and in vacuo) have very little rubber for new YORK fire department hose. 



effect on the time of cure or the tensile strength of the rubber. _,, ,. , r uu -it. 



(9) The smoking of sheet rubber increases the time of cure ^he quality and tests of rubber, required by the specifications 

 verv considerably, and in some cases appears to affect adversely °^ *« City of New York for fire and street-cleaning hose, are 

 the" mechanical properties of the vulcanized product. shown m the following tabulation: 



A B f D E 



Contents and Characteristics. ^ ^ s ^ ^'^ \ ^ ^' \ / ^ n ,. — ^ ^^ v 



Min. Ma.x. Min. Max. Min. Max. Min. Max. Min. Max. 



Vulcanized rubber gum by volume (per cent) 75 ... 75 ... /O ... 55 ... 55 ... 



Organic acetone extract (per cent by weight of vulcanized 



rubber gum present) ... 8 ... t ... 5 ... 15 ... IS 



Total sulphur in all forms (per cent by weight of vulcanized 



rubber gum present) ... 4 ... 4 ... 8 ... ... ... ... 



Free sulphur (per cent by weight of vulcanized rubber gura 



present) ... ... ... ... •-. 3 ... 5 ... 4 



Dry inorganic mineral fillers (not to contain carbon except as 



carbonates) Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance 



Tensile strength (pounds per square inch) 1,400 ... 1,400 ... I. .^00 ... 500 ... 1,000 



Reduction of tensile strength after being subjected to dry heat 



at 220 degrees F. for two hours (per cent) 20 ... 20 ... '20 ... 20 ... 20 



Tensile strength (pounds per linear inch in any seam) 90 (a) ... ... ... 75 (b) ... ... ... ... ... 



Elongation at breaking point (percent) 500 ... 500 ... 50O ... 300 ... 250 350 



Reduction in elongation at breaking point after being subjected 



to dry heat at 220 degrees F. for two hours (per cent) 20 ... (c) ... 15 (d) ... 25 ... 30 



Set (per cent of elongation at breaking point) 10 (e) . . . 6 ... 6 ... 10 ... 8 



(10) The addition of an alkaline solution of creosote to the 7777 . , ,, >, , , ^ • • 



1 . C c 1 *■ J i. cc i - *u.. 4.:„., Vulcanized lubber gum by volume equals specific gravity times per cent 



latex before coagulation does not affect in any way the properties by weight of rubber. ° ' 



of the dry sheet rubber. (a) Air hose tube only. 



/11 , ^1 -iir* 11 i_i » 1 ^L T-. t,t 1 J -.«J (b) Cotton rubber lined fire hose tube and rubber fire hose tube only. 



(11) The Wickham block and the Byrne blocked worm and (,,, K^ugh i,ore suction. 30 per cent; general water hose. 20 per cent, 

 thin crepe did not show to any advantage, so far as the mechanical rd) .Street cleaning hose, 20 per cent. 



properties of the vulcanized product are concerned. (^' Spray hose, six per cent. 



(12) Pressing the dry rubber into block, or rolling it up with The stocks indicated above are specified as follows: 



or without tension, has very little effect on the time of cure or A. Air hose tube and cover, and spray hose tube and cover, 



on the mechanical properties. B. General water hose (one and one-quarter inch and up) tube 



(13) There is no marked difference in time of cure or physical and cover, and rough bore suction cover. 



properties between the rubbers obtained by coagulating latex in C. Cotton rubber-lined fire hose tube; rubber fire hose tube 



two or three fractions. and cover, and street cleaning hose tube and cover. 



(14) Rubber which' is allowed to remain in a wet condition D- General water hose (one inch and under) tube and cover, 

 after coagulation (creosote having been added as a preservative) ^' Coupling washers for fire hose. 



appears to be invariably quick curing, and to give very good Specifications for gasoline and steam hose do not indicate per- 

 mechanical results after vulcanization. Such rubber loses some centages of rubber or chemical tests. The requirements of rub- 

 protein on washing. In these cases the rapidity of cure appears ber quality are limited to physical tests as follows : 

 to be related in some way to the moist condition of the rubber. Gasoline Hose. Tube and Cover. Tensile strength per square 

 and in some specimens the time of cure varies with the per- inch, 1,000 pounds, minimum. Elongation at breaking point 30G 

 centage of protein, the sample containing the lowest amount of per cent, minimum. Reduction in tensile strength per square 

 protein curing in the shortest time. It is, however, impossible inch after submersion in 60-degree Baume naphtha for a period 

 at present to connect these facts definitely, as a sample of rubber of 48 hours and dried in air 24 hours, 20 per cent maximum. Re- 

 prepared by evaporating the latex in vacuo, which contained a duction in elongation at breaking point after submersion, 30 per 

 very large amount of protein, also had a very short time of cure. cent maximum. Non-volatile matter extractabje in 60-degrees 

 Further work on this important point will be required, but if Baume naphtha, one and one-half per cent maximum. Set (per 

 in the meantime a quick curing rubber with good mechanical prop- cent of elongation at breaking point) six per cent maximum, 

 erties is desired by manufacturers, it would appear that it could Steam Hose. Tube and Cover. Tensile strength per square 

 be obtained by pressing wet creosoted sheet into blocks of suit- inch before heating, 800 pounds minimum. Tensile strength per 

 able size. square inch after being subjected in the hose to 60 pounds steam 



