An Improved Thixotrometer R. W. KEWISH, The Lowe Brothers Company, Dayton, Ohio
T
traveled by the disk in 5 minutes for a torsion setting of 50'. D,!.. is the Corresponding value obtained from a line fitted
HIS thixotrometer is an improved design of one that wm .' . described in connection with a study of the leveling of paints (d). Apparatns of somewhat similar construction has been used by Schofield and Scott Blair (3) and by Freundlich and Rlider (1).
to the data by the method of least squares. (In fitting the line the number of the observation was chosen as the abscissa and the corresponding distance of travel as the ordinate for the plotted points.) I n the last column the per cent differences of the calcnlated from the observed values are given.
To obtain better insulation fmm building vibration, the thixotrometer is now mounted an B pair of slings (Figure 1). Rubber bands suspend it so that the base just touches four ruhher balls, placed under the corners of the base and flattened on one side to prevent their rolling. The balls furnish a damping effect and prevent swaying of the thixotrometer. The insulation from building vibration is very satisfactory. To reduce to a minimum the stirring which resulted from the insertion of the sphere (2) into the material being examined, several changes were made (Figure 2). The torsion wire assembly was mounted an 8. recision rack and pinion (Pillor rack and pinion unit, Spencer fens Company), the sphere was replaced by a steel disk of the same diameter, an electromagnetic clamp t o hold the disk prior t o release was constructed, and extension arms were made t o permit operation of the micrometer (2) and the rack and pinion without jarring the thixotrometer. (Two mechanical clamps which were tried before resorting to the electromagnetic clamp were unsatisf&ory. A wooden core i s used in the electromagnet, since an iron core becomes permanently magnetieed. Because alternating current causes a stirring - action. direct current must be used in thz electromagnet.) To overcome any irregularities which might result from variations in filling the container (I?), a funnel was constructed to permit filling while the container was in nosition in the water bath @), and ; Ivertical tube was mounted i t the end of the Container so that the courvc of filling woulJ always tic at the same p 4 n t . This nietirod oi tilling ?nu be used only 1~1111tl.iir riiaterials, and su i:v no advant:iue in i t s use I.:Istree!! demonstratcd. To use the thixotrometer, the torsion wire assembly is raised, the torsion setting is made, and the disk is clamped in Dosition bv turning un t h e Clcctromapnct. .\ stop mtch is i t u n e d ttrc rnome1.t that the pounrig oi tile matennl iiuo the wntainer is started. The didk L+ luacrcd into tlic material at the cnd of 1 minute and the disk is released at exactly 10 minutes. The dis~~
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TABLE I. MEASUREMENT OF PAINT NO.
DObh..
Dda.
1 2
0.1229 0.1070 0.1075 0.1173 0.1215 0.1242 0.1247 0.1276
0.1120 0.1140 0.1161 0.11s1 0.1202 0.1222 0.1243 0.1263
a
4 6 6 7
8
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gives the true EGODosition of the disk. In order 6 keeD the disk dear of the c l m p , t h e rlampd position is chosen 0.015 invh (0.04 em.) behind the [rue zero pos.tlon. If llie dn1uirr.e trnvelrd by the disk i> Irss than 0.015 inch, tlie dirtnnrr is determined by notinn the iiiitiul m i l hi~1 nosiliuus on tlir kvetiew micrometer scale
