Extrusion Qualities of Rubber - Industrial & Engineering Chemistry

Publication Date: August 1937. ACS Legacy Archive. Note: In lieu of an abstract, this is the article's first page. Click to increase image size Free f...
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Extrusion Qualities of Rubber EFFECT OF TEMPERATURE AND MILL ROLL OPENING ARTHUR H. NELLEN Lee Tire and Rubber Company, Conshohocksn, Pa


plied to the diaphragm, ulls the barrel back with s ioroe of 13% pounds (625.97 kg.). '&he motion of t,he barrel is indioated on 8, dial placed behind the machine, also in view of t,he operator.


milling practice shows that rubber becomes s o f t e r when milled on a cold m i l l t h a n w h e n milled for the same length of time on a hot mill, and a h that a tight mill will p r o d u c e softer r u b b e r than an open mill, using the same uumber of p a s s e s . Although this may seem obvious to one who is experienced in rubber milling, the publ i s h e d work on variations in the softness of rubber r e s u l t i n g from differences in roll temperatures and mill roll setting is meager; additioilal data on this subject would not be iinwelcome in rubber literature. Also, a series of testa to determine the effwts of these fwtors on the working qualities of rubber provides a &isfactory means for describing a method for operating a tubing machine plastometer which has proved to be of considerable value in this laboratory.

Plasticity Determinations In the operation of this tubing machine for determining the plasticity of a sample, the rubher is cut into pieces smsll enough to be easily fed into the hopper. The cold rubher is fed at 8 uniform rate with the air pressure off, so that the barrel is in the forward position with relation to t,he worm. Exactly 200 g r m s of rhe rubber are run through beforr any readings are taken, in order to bring the rubber in tho machine and the die to a mnstant t,emperature. Then the tubing is continued with additional rubber, and three one-minute samplss are cut off by means of the cutter fastened in front of t,he die. During the extrusion of these three samples, temperature of the extruding rubber ia recorded and average power readings me taken. Any variations in the circulating wat.er tempemtwo are also not.ed. The three samples axe weighed individually, and bhe average is taken and recorded as "grams extruded per minute," which for brevit,y is called 0.. Tho worm is then stopped with the mschine loaded and held for exactly 3 minutes. Then the air valve is opened, and the 20 pounds per square inch pressure is applied t.o tlre diaphragm which forces the die hack against the rubber in t,he space betnecn t,he die and screw with rz pressure of 1380 pounds. The movement of the hsrrel hsekward &s the rubber is forced out of tlre die is'indicated on the dial back of the machine, and tho divisions on the dial correspond to the volume of ruhher extruded. With a stop watch the number of minut,es to extrude 5.4 ec. BI% taken and recorded 8s M . This completes the test, and the machine is cleaned out; each test is started with sn empty machine. The factor G, is a direct measure of tubeability or tubing speed, and M is an inverse measure of plastic flow. G,/M, for want of a better word, is called "plasticity."

Tubing Machine In this method a small tubing machine was specially built for the purpose: The tempersture is regulated by means of water passing through both barrel and worm at 180" F. (82.2' C.) in a closed svstem with thermostatir control. and temnerature variations &t.hii; circulating water are indibated on dial thermometer plainly visible i o the opcrator. Speed is held constant at 35 I. p. m. of the worm, ahieti is 1.25 inches (3.2 em.) in diameber with progressively deereasing pitch; the poa'er consumed 1s indicated on B wattmeter. also in front of the onciator. A dicator, also in posit& over the machine. The birrel of the tubing machine is free to move back and forth a short distance (0.75 inch, or 19 mm.) and is rigidly attached to a diaphragm operated by air pressure. This air pressure, obtained from a small tank under the machine, is maintained const,ant st 20 pnunds per square inell (1.406 kg. per sq. rm.) and, when &p886

An apparatus and procedure are described for accurately determining the extrusion qualities and plastic flow of rubber. Between 90"and 210"F. on a laboratory mill when temperature is the only variable, the lower the temperature the softer the rubber. At any temperature between 90" and 210"F. on a laboratory mill when the rubber is passed through an equal number of times, the tighter the mill, the softer the rubber. Between 120" and 2M)" F. in a tube machine used as a rubber plasticizer, the lower the temperature, the softer the rubber. In rubber compounds tubeability and plastic flow are not necessarily related.


ACGUST, 1937

Figure 1 and the following table give results on four 400gram samples taken from the same slab of factory milled and blended smoked sheet which were ground for 4, 6, 8, and 118 minutes on a 12 X 6 inch (30.48 x 15.24 cm.) laboratory

mill, front roll speed 22 r. p. m., back roll speed 32 r. p. m., ratio 1.45 to 1, roll temperature maintained a t average of 91)" F. (32.2" C.), and opening between rolls 0.010 inch (2.54 man.) : Grinding Time




Mzn. 4 6 8 10

37 47 52 57

Ob 07 81


0 4 0 2 0 11 0 os

92 235 480 715

6 4 5


These figures serve to illustrate the magnitude of differences in plasticity readings, even when samples are taken with only 2-minute variations in grinding.

88 7



Mill Mill Time of Open- Temp. Ten ing a t E n d Passes GL. Mm. C. Min. Mill Temp. 45.970.25 46.1 6 35.90 40.6 3 0.51 28.21 37.2 2 1.02 1 24.34 2.03 33.3 3.05 0.9 23.89 32.2 Mill Temp. 7.7 44.71 0.25 81.1 3.8 32.22 0.51 79.4 1.02 76.7 2.1 25.77 24.07 2.03 73.9 1.2 3.05 73.9 1.0 23.39 Mill Temp. 0.26 98.9 11.5 35.67 98.9 5.7 24.93 0.51 2.3 23.76 1.02 98.9 1.3 22.44 2.03 98.9 1.1 23.93 3.05 98.9 5



a t Start, 32.2" C. 230 0.20 0.44 81.5 37.6 0.75 1.04 23.4 1.03 23.2 a t Start, 73.9' C . 165.5 0.27 57.5 0.56 0.86 29.9 22.1 1.09 1.13 20.7 a t Start, 98.9' C. 0.45 79.3 0.83 30.1 0.97 24.5 1.14 19.7 1.30 18.4

yo in-

Increase from originala

crease from origind

213.5 65.0 21.1 6.9 6.7

1293 393 128 42 41

149.0 41.0 13.4 5.6 4.2

903 248 81 33 26

62.8 13.6 8.0 3.2 1.9

381 a2 48 19 12

G z / M on original factory slab, 16.5.

shows the effect of temperature, in each case the average of the five mill openings. Another test was run to determine the effect of temperature by using the tubing machine as a plasticizer and running samples of the same smoked sheet through the machine once each with the circulating water temperature varying

Effect of Temperature and Roll Setting In order to determine the effect on the rubber tubing qualities and plastic flow of the variations in roll temperature and roll settings, fifteen 400-gram samples, taken from a slab of factory milled and blended smoked sheet, were treated on the same laboratory mill as follows: Each passed through the rolls exactly ten times. Five samples were subjected to a roll temperature of 90" F. (32.2" C.) and openings between the rolls of 0.010, 0.020, 0.040, 0.080, and 0.120 inch (0.25, 0.51, 1.02, 2.03, and 3.05 mm.), respectively; five to a roll kmperature of 165" F. (73.9" C.) and the same openings; and &re to a roll temperature of 210" F. (98.9" C.) and the same openings. Samples were tested approximately 24 hours after milling.


The time for making the ten passes decreased as the mill opening increased. Also, the time increased as the roll temperature increased, as the spring of the rolls brought them closer together when the rubber on the mill was hot and soft. Table I gives data on samples milled a t the three temperatures. Figure 2 shows the effect of variations in mill openings, in each case the average of the three temperatures; Figure 3



between 120" F. (48.9" C.) a n d 200" F. (93.3"C.). After passing 400 grams of the rubber through the machine, it was run through the laboratory m i 11 t w i c e w i t h the 3.06-mm. opening and a t e m p e r a FIGURE 4. EFFECTOF WATER TEMt u r e o f 210" F. PERATURE OK EXTRUSION QUALITIES (98.9" C.) to sheet it out; it was then held approximately 24 hours before testing for plasticity. The following table gives the data obtained in running the rubber through the machine a t the various temperatures: Sample NO.

Circulating Water Temp.

Temp. of Extruding Rubber

Temp. Rise

Av. Watts

48.9 60.0 71.1 82.2 93.3

73.9 83.9 88.3 94.4 103.9

25 23.9 17.2 12.2 10.6

450 350 250 170 140



2 3 4 5



As is to be expected, the lower the temperature of the barrel and worm, the greater the temperature rise between the



water temperature and that of the rubber extruding through the die, and the greater the power consumption. Figure 4 and the following table show the effect on the extrusion qualities of the variation in circulating water temperature: 7 -


NO. 1 2

3 4 6 a



30.42 29.02 27.05 25.50 22.41

0 65


0.84 0 91

1 07

Original 40.8 37.7 32 2 28 0 20.9


Increase from original5 30.3 21.2 15.9 11.5 4.4


% increase from original 183 128 96 70 27

G z / M o n original rubber, 16.5.

VOL. 29, NO. 8

Jf have a direct relation when the same type of rubber or compound is compared, but not always when different types of rubber or different compounds are compared. For example, if we draw a curve of the G, values of five different types of rubber compounds and then below this show the J4 values, it becomes evident that tubeability and plastic flow are not directly related. Although the G,/M figure may mean little mathematically, it is a good index of the actual softness of the stock; if stocks are graded arbitrarily by "feel" on the mill, they fall into line with the G,/M figure more closely than with either G, or M . These data are given in Figure 5 and the following table: Qz


zoo 34







Relation of Tubeability and Plastic Flow

All of the data presented thus far show a direct relation between tubeability a n d plastic flow, and conclusions m~ould be i d e n t i c a l if either G, or M w e r e u s e d and FIGURE 5. RELATION OF TUBEABILITY G,/M o m i t t e d . However, G, and AND PLASTIC FLOW

Tread compound Cushion Inner tube Loaded tubing Friction

* Corrected


29.7 35.2 38.2 41.5 46.9

,If 1.23 0.51 0.58 2.44



24.2 08.0 05.8 17.0 260.5

t o 0.92 specific grairity.

In this paper only one procedure for the successful operation of this tubed machine plastonieter has been described. A discussion of other procedures designed for factory control of stocks which permit of rapid testing of samples, for development of stocks of certain desired characteristics, for determination of tubing and plastic properties of pigments, for scorch tests of compounds would provide data enough for a number of papers. RECEIVED dpril 17, 1937. Presented before the Division of Rubber Chemistry at the 93rd Meeting of the American Chemical Society, Chapel Hill, N. C . , Bpril I2 t o 15, 1937.

Viscosity of Hydrocarbon Solutions METHANE-PROPANECRYSTAL OIL SYSTEM

liquids. Hersey and Shore (4) also d e t e r m i n e d the effect of p r e s s u r e upon s e a r c h u p o n the physical and thermodythe viscosity of lubricatnamic properties of hydroing oils a t several temperatures. B. H. SAGE, B. N. INMAN, AND W. N. LACEY carbon systems, a study of The authors (6, 8, 9, 10, the effect of pressure and California Institute of Technology, Pasadena, Calif. comnosition unon the vis11) reported measurements upon - t h e v i s c o s i t y of cosiiy of the liiuid phase of hydrocarbon liquids saturated with gases a t pressures as a part of the methane-propane-crystal oil system was made. high as 3000 pounds per square inch. This work deterThe work was primarily limited to a temperature of 100" F. and mined only the combined effect of changes in composition to liquid aompositions containing less than 5 per cent methane and pressure upon the viscosity of these liquids and offered and 20 per cent propane by weight. The viscosity of the no information concerning the individual effects of the variliquid phase of numerous mixtures in this composition range ables. was determined in both the two-phase and condensed-liquid regions a t pressures up to 3000 pounds per square inch abMaterials solute. The oil used in this investigation was a water-white Experimental investigation of the effect of pressure and paraffin-base oil refined from Pennsylvania crude stock. The composition upon the viscosity of hydrocarbon liquids has average molecular weight, as determined by the freezing not progressed sufficiently to perniit correlation of the vispoint lowering of benzene, was 342. Its specific gravity a t cosity as a function of state. Bridgeman ( 1 ) made measure100" F., relative to water a t its maximum density, was 0.8244, ments of the effect of pressure upon the viscosity of several and the viscosity-gravity constant (5) was found to be 0.7979. hydrocarbons. His pressure range (17 X lo4 pounds per The results of an aniline extraction analysis upon similar square inch) was many times that recorded in the present material indicated that it was primarily composed of constitupaper, but no attempt was made to study systematically the ents of a narrow range of high molecular weights, which effect of composition upon the changes in viscosity of such


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