Hardening or gelation measurement

Use

Various materials such as epoxy or other composite resins, slow curing adhesives, gelatins or hydrocarbon gels.

Test equipment

Instrument: Viscometer or Rheometer

Pin: Choice of standard pins or, preferably, disposable pins and chambers for easy cleaning.

Accessories: Various choices: Small sample adapter, TC-550AP programmable bath, Thermosel ™ with programmable controller

Speed: Various possibilities: Test method 100 to 0.01 rpm

The Cure Mode algorithm was developed in response to customer concern that their gel timers were not providing viscosity or rheology data. They couldn't afford expensive rheometers that would monitor gelation or "hardening" of materials such as epoxies. This algorithm makes it possible to take data over very wide ranges of viscosity - several decades, in fact. Brookfield Rheocalc ™ software is used for instrument control and data acquisition. The "assistant" software in Rheocalc is used - the "Cure Mode" is selected and the assistant guides the user in setting up a test.

In the following example, Brookfield DV3TLV was used with SC4-27RD disposable pins and SC4-13RD disposable sample chambers. The initial speed was 100 rpm. The viscosity increased as the epoxy system reacted or hardened. Whenever the measured torque reached 90 % of the full scale or "FSR" range, the speed was reduced by a factor of 10. The program terminated execution when 90 % of FSR was achieved at the slowest speed - in this case, 0.01 rpm. Figure 1 shows the data.

Figure 1: Curing of the epoxy at 23 ° C

% of torque as a function of time

Each curve represents data for a different rotational speed (RPM)

Each curve in FIG. 2 represents the rotational speeds of the spindle. The leftmost curve is the torque data at 100 rpm; the rightmost curve is 0.01 rpm. The spindle speed decreases by an order of magnitude with each successive time interval.

Figure 2: Spindle speed data versus time for the spindle test

curing of the epoxy The reaction or "curing" proceeds more quickly as the temperature of the test increases. Figure 3 shows the change in viscosity as a function of time for three different control temperatures: 23 ° C, 50 ° C and 60 ° C.

Figure 3: Viscosity versus time data for the epoxy cure test at three different temperatures.

Epoxy curing controlled at 23 °, 40 ° and 60 ° C