Sunshine Instruments 22A Instruction Manual

Sunshine

Gel Time Meter 22A

Manual

APPLICATION:

The GEL TIME METER is a self-indicating device for measuring the gel time of a thermosetting fluid composition, i.e., the time at a
constant temperature for the material to reach the incipient gelled state. This point is usually characterized by a sudden, pro­nounced increase in the viscosity of the material. It is registered by the instrument through the closing of an electrical gap actuat­ed by the torsion exerted on a slowly rotating spindle suspended in the test sample. Materials exhibiting this thermosetting prop­erty, by which they may be evaluated, include monomers, resins, potting compounds, melamine formaldehydes, styrenes, waxes,
varnishes, unsaturated oils (i.e. tung oil) etc.

The gel time for a particular composition under well-controlled conditions may be reproduced by the instrument to within plus or
minus one percent. Since the gel time is temperature dependent, the temperature at which each gel time is determined should
always be controlled.

In a sense, the gel time value is a measure of the relative reactivity of material that undergo gelation; therefore, the instrument
offers a convenient means of assigning a number to each material characterizing its reactivity under the test condition. This num­ber is given in terms of minutes at a particular temperature. In the evaluation of reactivity, of course, a shorter gel time indicates a
greater reactivity, while a longer gel time signifies a lesser degree of reactivity.

The measurement of gel time is of considerable importance to quality control work. It also affords a means of studying the effect
of such variables as:

A. Composition
B. Reaction Temperature
C. Concentration and kind of catalyst, accelerator, inhibitor, retardant, diluent, etc.
D. Storage and shelf life

Furthermore, the shelf life of a composition at room temperature may also be estimated by determining the gel time at two or
more elevated temperatures and extrapolating to room temperature. This may be accomplished by plotting a log of gel time vs.
1/T, where T equals absolute temperature. The points should fall on a straight line.

In addition, the instrument can also be used to measure the "thickening times" of liquid materials which do not gel but undergo a
substantial increase in viscosity during heating. In this case, the thickening time is the time for the material to reach an arbitrarily
chosen viscosity sufficient to close a certain setting of the electrical gap.

DESCRIPTION:

The principal parts of the Gel Time Meter are: a constant temperature bath into which the test sample, contained in a test tube, is
immersed; a rotating spindle (glass rod) suspended in the sample from a torsion wire driven by a one rpm synchronous motor;
electrical contacts across the torsion wire connected to the control unit; a time counter, a buzzer and a signal light to provide both
an audible and a visible alarm when the gel point has been reached.

BATH:

In the determination of gel time, it is essential to maintain the boiling bath at a known constant temperature. Regulation of boiling
rate is obtained by means of a variable transformer (SSI V22 available as an extra) connected to the 650 watt immersion heater. A
convenient working temperature is 100 C, obtained by using water. When it is desirable to work at lower temperatures, another
non-flammable liquid such as methylene chloride (b.p. 40 C), chloroform (b.p. 61 C), carbon tetrachloride (b.p. 77 C), or a mixture
of this can be used. Temperatures above 100 C can be obtained with other liquids. When using temperatures other than boiling
points, the Davis Calibration Temperature Controller (cat. #2295A with 2296 T/C) can be used to keep the temperature constant.

1

CAUTION:

WHENEVER A BATH IS USED WHICH EMITS TOXIC VAPORS,THE OPERATION SHOULD BE CARRIED OUT UNDER A SUITABLE

HOOD. FOR REASONS OF SAFETY,THE USE OF FLAMMABLE LIQUIDS IN THE BOILING BATH IS NOT RECOMMENDED.

TORSIONAL SPRING:

The very heart of the Gel Time Meter is the torsional spring suspension. The fixed stiffness of this spring, referred to as the spring
constant, must be accurately maintained. It is realized by the use of a special torsion wire that is connected to an upper vise
assembly and a lower vise and magnet assembly.

ACTUATING SWITCH:

The switch referred to previously is an electrical gap, which, when closed, actuates the alarm and timing circuits. It consists of
two contacts that are fixed to the opposite ends of the torsional wire spring (Fig. 1). These contacts are adjusted to form a 3/32"
gap with no load. As variation in gap distance will somewhat affect the gel time, it is necessary to maintain this dimension.
Adjusting is necessary to maintain this dimension. Adjustment is made with the lower contact by simply rotating the contact sup­port clip until the distance between contacts is 3/32 inch.

ASSEMBLY:

Refer to Figure 1. The securing of the torsion wire to the two vise assemblies may be done on the bench. Slip the torsion wire
1/4" into the upper pin vise and tighten jaws. This may be done more easily if the jaws are open just enough to receive the wire.

Secure the other end of the torsion wire to the lower vise, simultaneously adjusting the exposed length of wire to 1.105" with the
feeler gauge. Be sure the vises grip the wire firmly and that the wire is centrally located in the jaws. Fasten the control power unit
to the stand and rod with the clamp on the back of the unit.

Place the heater condenser assembly into the empty jar. Place the test tube into the hole in the condenser using the rubber stop­per to hold the test tube in place. Place the spindle (glass rod assembly) into the empty test tube. Place this assembly on the
stand under the control unit. Secure the upper vise on the motor shaft by tightening the set screw. Use care so that the torsion
wire doesn’t kink out of shape. Raise the spindle and make the connection to the lower vise assembly by use of the magnets.
Adjust the height of the spindle rod by adjusting the clamp on the back of the control power unit until the spindle is 1/4" from the
bottom of the test tube.

Place the lower contact on the lower vise grip. The drive motor rotates counter clockwise, therefore, the upper contact should lag
behind the lower one. Arrange the contacts in this manner. Adjust the contact gap to 3/32" with the aid of the gauge furnished
with the equipment. This gauge is 3/32" thick thus greatly facilitating this adjustment. Rotate the lower contact to make this
adjustment. Remove the test tube, rubber stopper, and spindle rod. The heater and condenser connections should be located to
the rear of the Gel Time Meter to avoid unnecessary obstructions while operating the equipment.

CAUTION:

PREVENT POSSIBLE ELECTRIC SHOCK

WHICH COULD

RESUL

T IN SERIOUS INJURY OR DEATH BY:

Ensuring that the ground wire from the Cat. 22 control box is affixed to the terminal post on the heater assem­bly prior to turning on the Gel Time Meter or plugging in the heater.

The condenser tube is next connected to both a convenient cold water supply and a suitable drain using the
rubber hoses supplied. Turn on a slow water flow. Fill the glass jar with bath medium to within three inches
from the top. (Do not allow the bath level to become lower than the level of the test sample in place for test.)

2

OPERATION:
Model 22A Gel Time Meter

If temperatures lower than the boiling rate are to be used, refer to the instruction pamphlet for the temperature controller. If the
boiling temperature is to be used, plug in the heater. This heater is rated at 120 volts, 60-50 hertz, and at this voltage, will deliver
650 watts to the bath. This will be excessive power for the bath and may be reduced to the desired amount by the use of a vari­able voltage transformer such as the Davis Calibration- Cat.V-22*. Plug the heater into the V-22 and adjust the heater power just
high enough to maintain the bath medium at its boiling temperature. At this point, check the output of the cold water condenser
coil to assure that cold water is still coming out. If necessary increase flow of water to reduce the temperature of the exhaust
water. Plug in the control unit to a convenient outlet wired for 120 volts, 60-50 hertz. Place both the Power and the Test switch
on the "OFF" position and set the time meter to zero with the reset button.

* When the instrument is to be used on 240 volts, 50-60 hertz, a transformer, part #2250, has been provided to be used in the
heater circuit to step the voltage down to 120 volts.

Always bring the bath to a brisk boil or desired testing temperature prior to inserting the test sample. The bath temperature
should read to 1.0 degrees C and recorded with the gel time value. A rough temperature correction to a reference temperature can
be made on the assumption that the gel time generally changes by 10% for each 1.0 degrees C. Accurate corrections are found by
actual measurement of the temperature co-efficient of gel time. The instrument is used for this purpose by running tests at two or
more temperatures at least several degrees on each side of the reference temperature. The importance of temperature control and
corrections for day to day variations in boiling point caused by fluctuations in barometric pressure should not be overlooked.

The instrument should not be placed in a strong draft in order to maintain good heat transfer from the bath to the test sample.

Place a measured quantity of the sample in a clean test tube. The drag on the spindle is directly proportional to the depth of
immersion of the spindle in the sample. Insert a clean spindle.

Place test tube and contents into the bath using rubber stopper for alignment. At this instant, turn the power switch on the control
unit to the "ON" position. This action starts the drive motor and timer. (The timer should start as soon as the test solution is at
the elevated temperature so that an accurate measure of gel time at a specific temperature can be obtained.) Connect the spindle
to the driving assembly by means of the magnetic coupling and then re-align the tube so that the spindle rotates reasonably near
the center of the test sample. The bottom of the spindle should be 1/4" from the bottom of the tube.

The TEST circuit may now be energized by placing the test switch on the "ON" position. The red pilot lamp will glow indicating the
automatic alarm is energized and the instrument should require no further attention. Both the timer and stirring spindle driving
motor will stop automatically when the gel point is reached (red light goes out, timer stops, and buzzer signals the operator). Turn
off both power and test switches, promptly remove test tube from bath to avoid further solidification, record the gel time, and
clean the test tube and spindle. The timer reads elapse time to the nearest second. The reading on the display is totaled in sec­onds. To get the number of minutes, divide the total by 60. {Example: a reading of 10116 is divided by 60 to give you 168.6 min­utes, (multiply the .6 minutes by 60 to get 36 seconds) Total elapsed time is 168 minutes, 36 seconds. (Divide 168 minutes by 60
if hour reading is desired - reading till by 2 hours, 48 minutes, and 36 seconds.)

3