April i, 1904.] 



THE INDIA RUBBER WORLD 



231 



A NEW LAW OF VULCANIZATION.* 



WHY one kind of rubber is strongerthan another which 

 has the same chemical constitution, why some kinds 

 vulcanize under conditions in which other kinds 

 will not vulcanize, why rubber vulcanizes at all — 

 we do not know. We know the facts, but we do not know the 

 reasons for them. We observe numerous chemical reactions, 

 and from our observations deduce the laws which govern them 

 — that is to say, the circumstances under which they take place. 

 But "the true nature of chemical force or affinity is still a se- 

 cret to us, as is the nature of the universal force of gravity." 

 Men of learning in all ages have sought by diligently observing 

 facts to discover the laws of nature. This field is so vast that 

 he must be bold indeed who would seek to penetrate the veil 

 that conceals from us her secrets, or to do more than from ob- 

 served facts deduce the ways in which nature acts. " The laws 

 of nature are only a summary of observed facts." " It is the 

 object of chemistry as a science to know the properties of sub- 

 stances and the relations which exist between them." Why 

 substances have their respective properties, and why those re- 

 lations exist, it is not the object of chemistry to discover. 



Any new theory or process of vulcanization should be tested 

 by a large number of experiments under varying conditions be- 

 fore it can be accepted as valuable. One or two experiments 

 can by no means be sufficient to establish the value of such 

 theory or process. The union of rubber and sulphur is a 

 chemical process and proceeds in accordance with well estab- 

 lished rules applicable to chemical processes in general. Such 

 rules are the result of deductions made from a very large num- 

 ber of observations by men of great experience, and have been 

 universally accepted as correct because as yet no exceptions 

 have been found that would impair their value. 



These observations seem necessary, as the theory concerning 

 vulcanization which will follow these remarks is believed to be 

 for the first time made public. The facts may possibly be 

 known to some observers, but a careful examination of author- 

 ities reveals no reference to them. The theory itself has been 

 tested by a large number of experiments during a great range of 

 vulcanizing temperatures without finding any variation what- 

 ever in the rule — which is as follows : The vulcanizing effect of 

 any particular vulcanizing temperature is the precise comple- 

 ment 0/ the vulcanizing effects of any other vulcanizing tempera, 

 ture, or combination of temperatures. That is to say, if a rubber 

 compound be submitted to any particular vulcanizing tempera- 

 ture for any proportion of the time required to vulcanize that 

 compound at that temperature, the vulcanization may be com- 

 pleted at any other vulcanizing temperature, if submitted to it 

 for the remaining proportion of the time that may be required 

 at the latter temperature. 



Thus if 30 minutes be required to vulcanize the compound at 

 one temperature and 90 minutes at another, the compound will 

 be equally vulcanized, whether it be vulcanized at either of 

 those temperatures in the required time, or whether it be sub- 

 mitted J3 of the time required at the one temperature and % 

 of the time required at the other temperature, or 73 (or any 

 other percentage) of the time required at the one temperature, 

 and ', (or the remaining percentage) of the time required at 

 the other. No difference can be perceived in the vulcanization 

 whether it be effected part at one temperature and part at 

 another, or whether it be effected entirely at one temperature. 



* Copyrighted 1904, by The India Rubber Publishing Co. 



From this rule it results, that it matters not to what vulcan- 

 izing temperature or combination of vulcanizing temperatures 

 the rubber compound may be submitted, the result will be vulcan- 

 ization, provided the compound be submitted for a proper length 

 of time. 



Though it is believed that this rule is now made public for 

 the first time, it has been known in effect to the practical rub- 

 ber manufacturer since the manufacture of vulcanized rubber 

 goods began, for the length of the process has always been 

 adapted to a combination of vulcanizing temperatures whether 

 the steam or the dry heat process was used. This adaptation 

 is necessary. For, as is well known, it is an impossibility to 

 vulcanize by either of these processes on a large scale at fixed 

 temperatures from the beginning to the end of the process. In 

 the laboratory, however, where only small samples are con- 

 cerned, there is no difficulty in doing so. There has therefore 

 been no difficulty in establishing the correctness of the rule by 

 a large number of laboratory experiments, each of which has 

 proved entirely successful and absolutely in accordance with it. 



Formulas are used in the manufacture of vulcanized rubber 

 goods in but two steps of the process— for the compounds, and 

 for the final or curing step. For the compounds, formulas are 

 necessary in order to secure uniformity in the goods, and in 

 order that the finished product may be adapted to the purpose 

 for which it is intended. These formulas are the result of ex- 

 periment, and when once established are not readily changed 

 by the manufacturer. If they were left to the judgment of the 

 workman who for the time being weighs them for the succeed- 

 ing steps, inextricable confusion would immediately result. 

 The formulas for compounds must not only be carefully ar- 

 ranged, but they must be exactly followed. This is the one 

 part of the manufacture in which under no circumstances, is 

 there any deviation allowed. Not that compounds cannot be 

 changed, for they are often changed. But this change is made 

 only by the manufacturer himself or by the superintendent as 

 the result of careful experiments. Many a factory has suffered 

 heavy losses by apparently slight changes in the compounds 

 which were thoughtlessly made. 



In the final or curing step of the vulcanizing process, for- 

 mulas are necessary in order to secure uniformity in the re- 

 sults. In the early stages of the manufacture this operation 

 was left somewhat to the judgment of the workman, who based 

 his judgment on an examination of samples withdrawn (in the 

 dry heat process) from the vulcanizing chambers. But in re- 

 cent years the formulas are not only strictly followed, but re- 

 cording gages are used for the purpose of enabling the manu- 

 facturer to know that the exact prescribed times and tempera- 

 tures have been followed. Such formulas are arranged with 

 the object of completing the vulcanizing of the goods in the 

 shortest time that will produce the proper results. They may, 

 however, be greatly varied, but such variations cannot be left 

 to the judgment of the operator except at the expense of uni- 

 formity in the result. 



The following are examples of formulas that are used in the 

 dry heat process. The first is as follows: 

 20 minutes from the closing of the vulcanizer until the tempera- 

 ture of the vulcanizing atmosphere reaches 200° F. 



30 minutes to 210° F. 



30 minutes to 220° F. 



30 minutes to 230 F. 



30 minutes to 2.40° F. 



30 minutes to 25°° F. 



