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A S A L Y TICAL EDI T I O S
T'ol. 2, KO. 4
Moisture-Proof Determination of Waxed Papers' Chas. Allen Thomas and Herman J. Reboulet THOMAS & HOCHWALT LABORATORIES, I \ c , D ~ Y T O SOHIO ,
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N D E T E R M I X I N G the moisture-proof qualities of waxed
papers, apparently no standard method has been eniployed. The usual method is to seal the paper in question over a vessel containing a desiccating agent such as calcium chloride or concentrated sulfuric acid, place the vessel in a constant-humidity cabinet, and observe the increase in weight of the desiccating agent. This method requires from 2 weeks to sereral months. The following accelerated method has given good results with paraffin waxed papers and requires only 2 hours for the test. This short time is valuable when testing a large number of samples or for maintaining a control upon the waxing machines in the plant. The apparatus is herein described.
30" C . is carefully maintained. A slight air pre*sure is put upon the apparatus which is regulated through the large 5gallon (18.9-liter) bottle, 0, by means of the stopcock, G, so that a small constant pressure of 0.2 inch ( 5 mm.) of mercury, as measured by the manometer, E , can be maintained. The entering air is saturated with water vapor by passing through the wash bottles F and F1 so that i t has a constant humidity at the temperature of the cabinet. By actual test the air was found to be 100 per cent saturated a t 30' C. at all rates used in the tests. The samples are run for 2 hours, after which time the U-tubes C and C1 are re-weighed, the increase in weight giving the moisture which passed through the samples.
Apparatus and Procedure
Results
9 and B (Figure 2) are two brass flanges made according to the diagram in Figure 1. The area of the paper exposed for the test is 6 square inches (38.7 sq. cm.) since the diameter of the raised portion of the flanges is 2.764 inches (7 cm.). The faces of the flanges are carefully ground and a thin film of petrolatum is placed on the ground surfaces, so that when
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In devising the test, the following points were considered: (1) The influence of the pressure in causing distortion of the paper, such as pulling the wax away from the fibers. (2) The effect of imperfections in the paper before waxing, such as small pieces of bark, pinholes, etc. (3) The effect of creasing the paper after waxing, as is generally done in practice.
The following data, taken from a large number of samples tested, show the influence of each of the above points: Samples in Tables I, 111, and IV tested a t 30" C., 0.2 in. ( 5 mm.), for 2 hours. Samples in Table 11, tested a t 30" C., for 2 hours a t the pressures indicated. Table I shows the results obtained from three typical grades of waxed paper. The figures give about the average that can be expected of papers of high, medium, and lorn moisture resistance. K i t h all of these tests, samples were chosen without defects, as far as could be determined.
A
Table I-Moisture
S?IIPI.&A Gram 0 0007 0,0006 0.0010 0,000.5 0.0013 0.0006 0.0008 0.0004 0.0006 0 0007
Passing through Three Typical Grades of Waxed Paper SAXPLE B SIMPLE c Grams Gram
0,0044 0 0009 u.0009 0 0009
0 0010
f / G /.
the samples of paper to be tested are clamped between the flanges b y means of the adjusting screws the apparatus will be absolutely air-tight. The samples are usually run in duplicate. From these flanges connections are run to the U-tubes, C and C1, which are filled with calcium chloride and which have previously been weighed to the fourth decimal place in grams. Figure 2 shows these U-tubes connected to the calcium chloride tubes, D and DI, which only serve to keep moist air from the tubes C and C1. The whole apparatus is placed in a constant-temperature cabinet where a temperature of 1
Received June 2, 1930.
1 1913 1,237: 1.0022 0.9516 0.9150
0,0896 0.0922 0.0602 0,0552 0.0700 0.0563 0.0851 0.0s4s 0,067: 0 . os54 0,0632 0 1073 0.07i7 0,0670
1.1482
0.8383 0,9372 1.1582 1 lL5Xi
In order to determine if a higher pressure would cause the n-ax to pull aIyay from the fiber, a high moisture-resisting paper was tested at various pressures. The results (Table 11) show that the pressures used are not high enough to cause a breaking down of the paper. Table 11-Effect of Pressure on Amount of Moisture Passing through Waxed Paper (Sample D) 2.OIK. 2.51s. 3 . 0 I N . 1,SIK. 021s. 0.51s. 1 . 0 I N . ( 5 MM.) (13 M M . ) (26 M M . ) (38 M M . ) (51 M Y ) (64 M Y . ) (76 MM.) Gram Gram Gram Gram Gram Gram Gram 0,0004
0,0012 0,0018
0,0009
0.0031 0,0000 0 0003 0.0006 0.0003 0.0001 0 0008 0.0009
0.0001 0,0004 0.0067
0,0015
0.0001 0,0002 0.0000
0.0004 0.0005 0.0009 0.0019
0.0004 0.0006 0.0006 0.0010
0.0003 0.0003
Table I11 gives the results on a sample which, on exainination with a magnifying glass, shows a large number of very
October 15, 1930
IiYD L-STRI.4L A S D EA-GISEERISG CHEAl1ISTRY
Table 111-Amount of Moisture Passing through Waxed Paper (Sample E) Containing Pinholes Gram Gram Gram 0 0434 0,0712 0 0065 0 0180 0.1352 0 0338 0 0762 0,0671 0 0479 0 0556 Table IV-Effect of Creasing Sample o n Amount of Moisture Passing through Waxed Paper SAMPLE A SAMPLE D Gram Gram 0 0001 0.0004 0 0002 0.0005 0 0043 0 0048 0 0002 0 00.56a 0 0126a 0
Very lieai-i!y creased.
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small pinholes. A marked variation due to the non-uiiiformity of the paper nil1 be noted. Using papers of high moisture resistance, Table I V gives the results of creasing the sample crosswse before testing. Unless the paper is T-ery heavily creased, the decrease in the moisture resistance is very small. From the results above it is erident that in papers of high moisture resistance the presence of pinholes in the original paper has a much greater effect on the moisture resistaiicc than the handling and creasing of the paper as done in practice. This method provides a short test by nhich the moistureproof qualities of m x e d papers may he determined with results comparable with the long-time t e d s usually employed.
Laboratory Evaluation of Flex-Cracking Resistance' L. V. Cooper FIRESTOXE TIRE& RUBBER COMPASY,XKROS,OHIO
A machine has been designed for laboratory evaluapressible as bronze ( 1 ) the ANY factors are intion of the flex-cracking resistance of any stock from movement is practically all volved in the proper compoundingofrubwhich a dumb-bell strip may be cut. The conditions elongation, and therefore flex eracaking may be considered ber stock. I n tread cornunder which the stock is tested may be varied at the pounding wear resistance is will of the operator. The results obtained on this as the result of elongation. tile major consideration, but machine on tread and sidewall stocks have always Therefore, a machine which subjects the rubber stock to other factors c l o s e l y apevaluated the flex-cracking resistance of stocks in the preach i t in importance, same order that actual road tests have. repeated elongation should produce flex cracks. Among these is the ability Since the rigidity of a tire 1s due chiefly to the carcass fabric, to withstand repeated flexing without cracking. Fles cracking produces an unsightly appearance which conveys the idea of the conditions under which the tread and sidewall operate inherent weakness in the tire, and also, if the flex cracking be- are almost independent of the stress-strain properties of these comes very pronounced, the tire may fail froin carcass break two stocks. A laboratory evaluating machine should therefore work to a definite elongation and not to a definite a t that point. A satisfactory tire must not flex-crack. load. Flex-cracking resistance is dependent on two things-the Ordinarily flex cracking does not become noticeable on stock itself and the stress under which it is working. The design of the tire-that is, size and shape of the buttons, the road test, even in poor tires, until 4000 or more miles have size and position of the side ribs, and the amount of lettering been run. If the machine duplicated road conditions, one on the s i d e r e g u l a t e s the working stress under which the sidewall and tread are operating. This accounts for the fact that two tires made b y different companies may be different in flex-cracking resistance although of very similar or even identical compounding. Various reasons have been advanced as to why one stock is better than another in regard t o flexing resistance. A few of these reasons are: (1) better dispersion of the pigments, (2) better surface continuity, (3) fewer stock folds during forming and curing, and (4) better stress-strain properties. Arguments for and against these reasons have been advanced without any definite conclusion as yet. Laboratory duplication of road-test conditions is the goal of all rubber technologists, as road testing is costly and timeconsuming. B short study of the stresses under which the stocks in a tire work should tell us some things concerning what the laboratory machine for evaluating flex-cracking resistance should be like. A normally inflated tire is under less than 5 per cent elongation. If the tire were of uniform thickness and construction from bead to bead, the elongation would be uniform. However, such is not the case and therefore the tire has points of greater and lesser stress. As a result some part of the tread or sidewall may be subjected t o an Figure 1-Apparatus for Evaluation of Flex-Cracking Resistance elongation of possibly 10 per cent as i t makes a revolution under load. Some parts of the tire are under compression test would last 100 or more hours, or the equivalent of about during road contact, but inasmuch as rubber is only as com- 12 working days. The ideal machine would be one that could be set to duplicate road conditions and also one that could be 1 Received June 2, 1830. Presented a t the meeting of t h e Akron so changed as to give accelerated teste. Rubber Group, M a y 1 2 , 1930
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