October I. 1913. 



THE INDIA RUBBER WORLD 



11 



The Plastometer — A Rubber Testing Instrument. 



By B. Denver Coppage. 



THK inslrunient illustrated here, kuowu as "The Plastom- 

 eter," was exhibited by the inventor at the Rubber 

 Conference. It was designed primarily to meet the 

 needs of its manufacturers, The Pusey & Jones Co., manu- 

 facturers of paper making machinery. 



The rubber covered rolls used in the "press part" of paper 

 machines must be covered with "densities" that have been 

 selected suitable to the paper to be made ; and it is very im- 

 portant that the "density" be as ordered or the rolls will not be 

 acceptable to the purchaser. 



The Pl.astometer. 



Since the adoption of this instrument, there is no uncer- 

 tainty of knowledge as to the "density" of the covering of 

 the roll, conforming to the "density" of samples selected. 



The Plastometer, as its name implies, is an instrument by 

 which the quality plasticity may be indicated. Its method 

 is direct reading without injury to material tested; i. e., 

 unlike a "tensile-test" in which the material is tested to its 

 destruction. The Plastometer does not make a vicarious 

 test. It is, therefore, to be classed with the most advanced 

 ideas, as a means of determining rubber quality. Plasticity 

 is so intimately related to the group — elasticity, softness and 

 hardness, density, resiliency, etc. — as to indirectly indicate 

 them. 



The fundamentals of the Plastometer are the combination 

 of parts whereby a weight may be supported wholly upon a 

 sphere, said sphere being sufficiently hard to sustain such 

 load without appreciable deformation, and means whereby the 

 amount of penetration or indentation of said sphere into the 

 material upon which it rests, at the e.xpiration of one minute, 

 can be determined. It will be evident that the dimensions 

 of the sphere can be selected to suit the weight to be applied 

 and the materials to be tested, or the mass of the weight 

 varied, or both, and that the amount of penetration may be 

 measured by an instrument integrated to various units of dis- 

 tance. For example, most grades of commercial rubber may 

 be tested by the Plastometer in which the sphere is a hard- 

 ened steel ball, J4 inch diameter, upon which is placed a 

 weight of one kilogram, the penetration or indentation of 

 such ball being indicated by the micrometer dial gage, indi- 

 cated to one 1/100 millimeters. The softer materials would 

 require larger ball or less weight or both. The harder ma- 

 terials would require smaller ball or more weight or both. It 

 is possible that certain very hard materials would require a 

 longer application of the weight than one minute and it is 

 possible that very soft materials would require a shorter ap- 

 plication of the weight than one minute to obtain satisfac- 

 tory indications. In each case, the principle remains the 

 same, that of lowering without shock a weight upon a 

 sphere which is free to penetrate material being tested upon 

 which the sphere rests, and means whereby said penetration 

 may be observed. 



The Plastometer has been designed with a base particu- 

 larly adapted to the testing of rubber covered rolls of more 

 than 6 inches diameter. Our type "C" instrument has addi- 

 tional fixtures which adapt it to being mounted in a vice 

 for testing small samples or pieces of rubber or other ma- 

 terial. It is evident that the base could be altered to make 

 it suitable for testing material in any form. 



It seems possible that through the co-operation of some 

 of the societies for testing materials, or a Bureau of Stand- 

 ards, that the Plastometer may be utilized to establish a 

 standard scale of qualities for rubber. The inventor believes 

 it is possible to utilize the Plastometer to determine raw 

 rubber values, since it lends itself to the determination of 

 "eflfect" resulting from "cause"; i. e., an increase of quality, 

 due to treatment, or a decrease of quality, due to environ- 

 ment; such as deterioration of a rubber sample which is 

 subjected to or acted upon by such causes as time, light, 

 gases, acids or fatigue due to mechanical work, etc. These 

 observances may be made for the reason that the test pieces 

 are not affected by the Plastometer tests and can, therefore, 

 be re-tested again and again after a lapse of time during 

 which the sample has been subjected to some influence or 

 treatment, the test being repeated hourly, daily or weekly, 

 etc., as desired. To make tests of this sort, the inventor 

 recommends that test pieces be prepared in a definite way 

 and be contained in a metal ring of given dimensions, say 

 five centimeters diameter and two centimeters thick, such 

 samples being adopted for purposes of selection and stand- 

 ardization. It is obvious that samples of uniform dimensions 

 are desirable. 



The inventor believes that such samples should be kept 

 and transported in air-tight, light, containers, such as are used 

 for mailing bottles of liquids; i. e., the screwed-top, parafined 

 receptacle of suitable diameter and length for the number of 



