Apr.,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
TESTING THE STRENGTH OF GLUE JELLEIS By W.*lson H. Low THE CUDAHYPACKING Co., OMAHA,NBBRASKA Received September 8, 1919
Testing of t h e strength of glue jellies has been carried on in this laboratory for a great many years, and under t h e direct supervision of t h e writer for t h e last 2 1 years. I n t h a t time all kinds of devices have been used for this purpose, but until the Smith glue tester (Fig. I ) came out, there was none on t h e market sensitive enough t o show even fairly large differences or t o duplicate t h e “finger test” so valuable in the hands of an expert. This form of tester is far superior t o any other we have seen, b u t in its original form the testing, although sensitive enough, was subject t o some errors which affected t h e grading of t h e glues. Moreover, since i t was filled simply with water colcred with a dye t o make i t visible on the scale, glues were often met with which could not be measured on t h e scale. The tester t h a t we only modification of t h e Smith glue have seen illustrated is t h a t of E . C Hulbertl (Fig. 3).
3:s‘
The apparatus used in this laboratory (Fig. 2 ) consists of a Smith glue testing apparatus modified t o give more accurate results for grading glues correctly. Mercury is used in the U-tube, and above^ this colored water. The scale has slots a t each end t o allow of moving i t and setting it by the screws t h a t fit through t h e slots. All other parts of the instrument are as illustrated in Fig. I . I t was first determined by calculation and experiment t h a t t h e use of mercury covered by water in t h e scale tube gave correct results. It was found necessary t o correct for the force required t o deform the diaphragm itself, for this takes some force t h a t should not be credited t o t h e jelly, and this force is not a constant, for diaphragms vary much with different rubbers and vary from day t o day through permanent stretch of the rubber. Another point is t h a t it is necessary to find the force required t o deform t h e rubber when t h e instrument is set in t h e position for a test, that is, when the water stands at point A in the diagrams. Owing to changes in temperature of t h e water and
E
n
C
FIG.1
FIG. 2
The principal modifications are the use of mercury covered by water in t h e scale tube, and the use of air, instead of water, in the thistle tube, the mouth of which is covered with a thin, dental rubber diaphragm, as in the original Smith glue tester. The use of mercury is a distinct improvement and has been followed in this laboratory for years. We do not readily see the advantage of t h e substitution of air for water in t h e thistle tube, especially since leaks are not so easily noticed in the rubber diaphragm or where it is attached io t h e thistle tube. T H I S JOURNAL,
6 (1913), 235.
FIG.3
mercury in the instrument or of the whole instrument, t h e water will not always stand at the zero mark of the scale, as i t should in starting a test. To overcome this trouble we made our scale movable in a vertical direction. With these modifications and methods of application we found we could properlygrade our glues or glue jellies very closely and with comparative correctness. WETHOD O F U S E
Our instrument is kept permanently in a chill room connected with t h e laboratory and maintained close t o 40’ F., a t which temperature the glue jellies are.
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
tested; t h a t is, the jellies are a t the same temperature as t h e room and close t o 40' F. Standard glues of various grades are always run a t t h e same time, so temperature or other changes affecting the strength will act on the standards and jellies being tested in like manner. Eaough water is put into the thistle tube and capillary so t h a t when a flat glass plate is held firmly against the mouth of the thistle tube (covered with the rubber diaphragm) the water in the capillary will stand exactly a t the upper mark A, the three-way stopcock C being opened t o the air. Stopcock C is now closed t o the air and opened to the rubber bulb D and scale tube E, the water in which was set t o the zero mark. Pressure is now applied through the bulb (a screw clamp between the bulb and stopcock allowing only a steady, slow, and even pressure t o be applied t o the system) until the water in the capillary falls from the point A t o the point B. The height of the water in the scale tube is now read off, and this measures the force required t o deform the rubber diaphragm alone, and this force must be deducted from the tests on the jellies for the proper grading of the glues. If all joints of the instrument are tight, the stopcock C may be closed as soon as the water reaches the point B, and the height of the water i n the scale tube read off a t leisure, but this cannot be done unless everything is absolutely 'tight. To test a jelly in a tumbler, as illustrated, the stopcock is opened t o the air and i t is ascertained t h a t the water in the scale tube stands a t the zero mark. The tumbler is placed on the movable support shown (by coarse screw adjustment) and brought in contact with the rdbber diaphragm and forced against this diaphragm until the water in the capillary stands a t t h e point A. The stopcock C is then quickly closed and immediately the rubber bulb is squeezed steadily and the wafer in the capillary forced down t o the point B. The height of the water in the scale tube is now quickly read and measures the force required to deform the jelly by a definite volume, namely, the volume between points A ' a n d B on the capillary tube. It also includes the force required t o deform the rubber alone, so for the force required by the, jelly itself, the figure previously found for the rubber must be deducted. It is necessary t o operate with moderate speed in adjusting the jelly surface to the rubber diaphragm and in forcing down the water from A t o B. This should be done by a steady, even pressure, not by jerky or quick application of pressure on the bulb. Used correctly this instrument is very sensitive and gives concordant results. Used incoirectly i t is still sensitive, but will not give concordant results. The water in the capillary must stand a t the point A when a flat glass or metal plate is held firmly against the mouth of t h e thistle tube covered with the rubber, as only in this way can we start with the jelly and rubber forming an approximately flat surface. I t is assumed generally t h a t if the mouth of the thistle t u b e is forced against the jelly surface until the water i n the capillary stands a t point A we are starting under like pressures each time. But this is not SO, It
Vol.
12,
No. 4
makes a differenbe whether we press into the jelly so t h a t i t forms a convex surface upwards into the rubber and then force down t o a flat surface a t the end, or whether we start with a level surface on the jelly and force the rubber downward into the jelly. I n the first case the jelly itself tends t o return to its original position and acts with the rubber, in the other case it continually works against the rubber. An attempt was made t o use an artificial jelly surface by stretching a rubber diaphragm over the mouth of the tumbler through the side of which we made a hole and attached a long pressure measuring tube. The tumbler was then completely filled with water and pressures through the thistle tube applied t o the rubber surface. This did not work a t all, for the rubber of the tumbler not only was deformed through the thistle tube, b u t bulged up between the center and sides and the pressures recorded were not a t all proportional t o the pressures applied. This same thing undoubtedly occurs t o some extent in testing a glue jelly and occasions errors, but t o no such extent as with a liquid like water acting on an elastic diaphragm. Working against a mercury surface was also unsatisfactory for several reasons. I n short, nothing has been found t o replace running a set of standard grades with each set of tests. DETERMINATION OF THE TENSILE STRENGTH OF GLUE1 By George Hopp 828 ST. NICHOLAS AvE., NBw YORK,N. Y.
A t the present time the testing of glue consists for the most p a r t in the determination of the viskosity and jelly strength, as compared t o a standard glue. This standard glue is usually one which has been selected because of the satisfaction i t has given through years of practice. I n the purchasing of glue, manufacturers hesitate considerably in departing from a particular standard, because of their lack of knowledge of how another glue will act. As six t o ten months may elapse before the manufacturer knows the results, i t is quite obvious t h a t considerable risks may be run. The question also arises as to whether the standard adopted is what i t should be for a particular type of work, whether i t has the requisite strength or elasticity, is brittle or the reverse. Various methods of measuring t h e tensile strength have been tried, such as gluing together wood or biscuit ware, or soaking paper in glue and determining the strength of the glues. These have been unsuccessful, due t o the presence of so many variables, such as humidity, temperature, viscosity and temperature of glue, pressure a t which i t is applied a t the joints, and condition of the joints, such as the amount of moisture, smoothness of surface, etc. Recognizing the fact t h a t the most important test of a glue should be a knowledge of its actual strength and stretch or elasticity, and t h a t equipped with such knowledge, standards could then be scientifically established for every phase of work, a new method has been evolved. 1 Presented at the 58th Meeting of the American Chemical Society, Philadelphia: Pa., September 2 to 6, 1919.
