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Viscometer, Model 35

Sections

Section 1: Description

Section 2: Safety Considerations

Section 3: Viscosity Test

Section 4: Changing Rotors, Bobs, and Torsion Spring

Section 5: Instrument Calibration

Section 6: Data Reduction

Section 7: Measuring Range

Section 8: Trouble Shooting and Maintenance

Section 9: Specifications

Section 10: Accessories

Section 11: Parts List

Tables

Table 1: Six-Speed Testing Combinations

Table 2: Twelve-Speed Testing Combinations

Table 3: Dial Defection for Calibration Weights and Torsion Spring Assemblies

Table 4: Calculated C Values from Rotor-Bob Dimensions

Tabel 5: Speed Factor S Base 300 rpm = 1

Table 6: Measuring Range for FANN Direct Indicating Viscometer

Table 7: Rotor-Bob Dimensions

Figures

Figure 1: Model 35 Viscometer

Figure 2: Model SR-12 Gear Box

Figure 3: Rotor Removal/Installation

Figure 4: Torsion Spring Removal and Replacement

Figure 5: Dead Weight Calibration Check

Figure 6: Model 35 Parts Identification

Viscometer, Model 35

Sections

Section 1: Description

The FANN® Model 35 viscometer are direct reading instruments which are available in six speed and 12 speed designs for use on either 50 Hz or 60 Hz electrical power. The standard power source is 115 volts but all of the models may be fitted with a transformer which makes operation with 220/230 volts possible.

These are Couette coaxial cylinder rotational viscometer since the test fluid is contained in the annular space (shear gap) between an outer cylinder and the bob. Viscosity measurements are made when the outer cylinder, rotating at a known velocity, causes a viscous drag to be exerted by the fluid. This drag creates a torque on the bob, which is transmitted to a precision spring where its deflection is measured.

Viscosity as measured by a Couette type viscometer such as the Model 35 is a measure of the shear stress caused by a given shear rate. This relationship is a linear function for Newtonian Fluids, i.e. a plot of shear stress vs. shear rate is a straight line.

These instruments have been designed so that viscosity in centipoise (or milli-Pascal seconds) of a Newtonian fluid is indicated on the dial with the standard rotor, bob, and torsion spring operating at 300 rpm. Viscosities at other test speeds may be measured by using multipliers of the dial reading. A simple method of close approximation of viscosity in a plastic fluid, such as a drilling fluid is described in Section 6B.

The range of shear rates may be changed by selecting rotor speed and using various rotor-bob combinations. A variety of torsion springs are available and designed to be easily interchanged in order to broaden shear stress ranges and allow the measuring of viscosity in a wide variety of fluids.

Figure 1
Model 35 Viscometer

Section 2: Safety Considerations

SAFE OPERATIONs

The safe operation of the FANN Model 35 Series Viscometer requires that the laboratory technician be familiar with the proper operating procedures and potential hazards associated with the instrument. This instrument is driven by 115 volt or 230 volt electrical power. Keep hands, clothes and other objects away from the rotating parts of the machine.

The optional heated sample cups and recirculating sample cups are electrically heated. Make sure the power cord and other wiring associated with these cups is no good condition and properly grounded.

Make sure the viscometer is turned off and unplugged from the source before cleaning or other repair or maintenance. Do not allow the Viscometer Base to get wet. If samples have been spilled or splattered, wipe clean with a damp cloth. Do not allow water to run into the base, as exces-sive water could cause damage to the electrical components.

STANDARD B1 BOB

The standard B1 Bob normally furnished with the Model 35 Series Viscometer is a hollow Bob and must not be to test samples hotter than 200°F (93°C). Solid Bobs are available for this type testing.

SAFE OPERATION OF THE OPTIONAL HEATED SAMPLE CUP

Precautions should be taken when testing heated samples using the optional heated sample cups to avoid possible burns from spilled hot sample, or from touching the hot sample cup.

When heated sample cups are being used, do not exceed 200°F

Section 3: Viscosity Test

Viscosity Test Overview

The stainless steel sample cup provided has a line at the proper 350 ml test fluid level. Fill the cup to that line with recently stirred test fluid. A scribed line on the rotor indicates proper immersion depth. Refer to Fig. 1. Damage to the bob shaft bearings may occur if this immersion depth is exceeded. If other sample holders are used, the space between the bottom of the rotor and the bottom of the sample holder should be one-half inch (1.27cm) or greater.

WARNING
THE STANDARD B1 BOB IS HOLLOW AND SHOULD NEVER BE USED TO TEST SAMPLES HOTTER THAN 200°F. (93°C).

Model 35A and Model 35SA

The Model 35A and 35SA viscometer are instruments with the ability to test at six different speeds. Their range is from 3 rpm up to 600 rpm with the speed being determined by a combination of speed switch setting and viscometer gear knob placement. To select the desired speed, set the speed switch located on the right side of the base to the high or low speed position as desired. Then turn the motor on and move the viscometer gear shift knob located in the center of the top of the instrument to its desired position.

Table 1 lists the proper positions for the viscometer switch and the gear knob combinations to obtain the desired speed. The viscometer gear shift knob may be engaged while the motor is running. Read the dial for shear stress values.

TABLE 1

Speed RPM

Viscometer Switch

Gear Knob

600

High

Down

300

Low

Down

200

High

Up

100

Low

Up

6

High

Center

3

Low

Center

SR-12 Model 35A/SR12 and 35SA/SR12

The Model 35A/SR12 and 35SA/SR-12 have twelve speed testing capabilities. To achieve this broader testing range (from 0.9 rpm up to 600 rpm) an additional gear box shift lever is used and it is located on the right side of the gear box. Refer to Fig. 2. Position this lever to the Left or Right as determined from Table 2.


CAUTION

NEVER CHANGE THIS GEAR BOX SHIFT LEVER WHILE THE MOTOR IS RUNNING. GEAR DAMAGE WILL RESULT.

Only the viscometer gear shift knob on the top of the instrument can be changed while the motor is running.

After preparing the instrument for 12-speed testing by setting the gear box shift lever, select the proper speed range with the speed shift switch on the right side of the base, then turn on the motor and set the viscometer gear knob on the top of the instrument. Refer to Table 2 for the correct combination of gear box shift lever setting; speed switch selection; and viscometer gear knob placement. The stress values will appear on the dial.

Figure 2
Gear Box Lever

TABLE 2
TWELVE-SPEED TESTING COMBINATIONS
MODEL 35A/SR12 AND MODEL 35SA/SR12

RPM

Gear Box Lever

Speed Switch

Viscometer Gear Knob

600

Left

High

Down

300

Left

Low

Down

200

Left

High

Up

180

Right

High

Down

100

Left

Low

Up

90

Right

Low

Down

60

Right

High

Up

30

Right

Low

Up

6

Left

High

Center

3

Left

Low

Center

1.8

Right

High

Center

0.9

Right

Low

Center

Gel Strength

Gel strengths are measured by first stirring the sample thoroughly at 600 rpm. Set gears to the neutral position and turn motor off. After desired wait period, turn gel knob, located below gear shift knob, refer to Fig. 1, slowly counterclockwise and read the dial at instant of the gel break (Peak Dial Reading). Gel reading is in lbs/100 ft2.

Section 4: Changing Rotors, Bobs, and Torsion Spring

Overview

The R1-B1-F1 rotor-bob-torsion spring combination is standard for all FANN viscometer. Other rotor-bob combinations may be used, provided shear rates are calculated for the fluid being tested. Use of rotor-bob combinations which result in large gap sizes can lead to shear stress dial readings not consistent with readings from a smaller gap.

Rotor removal and Replacement

The rotor can be removed from its socket by twisting counterclockwise, when viewed from above, while gently pulling straight down.

The rotor may be replaced by aligning the rotor slot and groove with the lock pin in the main shaft socket. Push the rotor upward and lock it into position by turning it clockwise.

Bob removal and Replacement

The bob shaft end that fits into the Bob is tapered and fits into a matching tapered hole in the bob. To remove the bob twist the bob clockwise while pulling downward. To install the bob, twist it clockwise while pushing upward.

Torsion Spring Removal and Replacement

Refer to Fig. 4 for identification of parts.
  1. Remove the dust cap [A] and plug screw [B].
  2. Loosen set screws [C] and [D] about 1/2 turn. The spring can now be lifted out. Be careful not to stretch the spring.
  3. Insert the new spring, making sure the bottom mandrel is properly oriented and seated. Set screw [D] should line up with the point at which the spring leaves the bottom mandrel. A notch cut into the upper end of the bottom mandrel will help locate this point. Tighten set screw [D], so that it presses against the split ring to hold the bottom mandrel of the spring.

    NOTE: Before tightening set screw [C] be positive that the top of the adjustable mandrel is flush with the top of clamp [E]. It may be necessary to slightly compress or stretch the spring to accomplish this.

  4. Tighten set screw [C]. The slot in the top of the adjustable mandrel should line up with clamping set screw [C].
  5. Loosen set screw [F] to zero dial under index, then rotate knob [G] as required for alignment, then adjust knob [G] vertically to allow the spring to be clamped in a "free" position, neither stretched or compressed.
  6. Tighten set screw [F] and replace the dust cap [A].

Figure No. 4
Torsion Spring Removal and Replacement

Section 5: Instrument Calibration

Overview

Periodically the Model 35 Series Viscometer should be checked for proper calibration and if found in error the viscometer should be calibrated or repaired. Continued accuracy of measurements requires the instrument be properly calibrated. The calibration is checked by applying know torques to the bob shaft. For any applied torque, within the torque range of the spring, there should be a specific dial reading plus or minus a small tolerance. Two methods of calibration are described.

The Dead Weight Calibration is easier to perform and if the spring requires adjustment, the proper setting can easily be verified. The Standard Fluid Calibration check verifies the complete instrument is operating properly. It will determine problems of bent bob shaft, rotor eccentricity, and/or runout of the rotor or bob more effectively than the Dead Weight method. Refer to Section 5-B.

Dead Weight Calibration Check Using Model DW3 Calibration Kit.

Note: Refer to Fig. 5.
  1. Remove rotor and bob. Refer to Section 3-A and 3-B. Be sure that the tapered end of the bob shaft is clean, then install the calibrating spool.
  2. Install the DW-3 calibrating fixture by clamping it onto the upper portion of the viscometer support legs.
  3. Select a weight according to Table 3. Insert the bead at the end of the thread into the recess in the top of the calibrating spool. Wrap the thread a little more than once around the spool and then drape the thread over the pulley.
  4. Hang the selected weight on the thread and adjust the calibrating fixture up or down until the thread from the spool to the pulley is horizontal. Compare the dial reading with the reading on Table 3.
  5. If necessary, adjust the torsion spring. Refer to Section 5-C, "Adjusting Torsion Spring".
Factory tolerances for F1 spring only are 127 ± 1/2° for 50 g and 254 ± 1/2° for 100 g. A movement of ± 1/2° is permissible when the main shaft is turning. This movement will generally be dampened out when a fluid is being tested. Check the linearity of the dial reading with at least three weights. If the spring appears to be non-linear it is usually a sign that the bob shaft is bent. An instrument with these characteristics needs additional service and/or repair.

Figure No. 5
Dead Weight Calibration
DW-3 Calibration Fixture

TABLE 3
Dial Deflection for Calibration Weights And Torsion Spring Assemblies

Torsion Spring Assembly (with R1-B1 combination)

Torsion Spring Constant, K1 Dynes/cm/° def

Weight in Grams
   

10

20

50

100

200
   

Dial Reading

F-0.2

77.2

127.0

254.0

-

-

-

F-0.5

193.0

50.8

101.6

254.0

-

-

F-1

386.0

25.4

50.8

127.0

254.0

-

F-2

772.0

-

25.4

63.5

127.0

254.0

F-3

1158.0

-

-

43.0

84.7

169.4

F-4

1544.0

-

-

-

63.5

127.0

F-5

1930.0

-

-

-

50.8

101.6

F-10

3860.0

-

-

-

-

50.8

Fluid Calibration Check

This procedure is to be used for calibration using only Newtonian certified calibration fluids. Fann Calibration Fluids are available in nominal 20, 50, 100, 200, and 500 cP. All are traceable to ASTM standards and each bottle of fluid is furnished with a viscosity temperature chart certifying that batch of fluid.
  1. The instrument being checked must be clean before immersing the rotor and bob into the calibration fluid. If necessary, remove the rotor and thoroughly clean the bob, bobshaft, and rotor. Make sure the bob shaft and rotor are straight and have not been damaged.

    CAUTION:

    The batch number on the label of the calibration fluid must match the number on the viscosity/temperature chart.

  2. Fill the sample cup to the scribed line with calibration fluid and place it on the instrument stage. Elevate the stage so that the rotor is immersed to the proper immersion depth. Refer to Fig. 1.
  3. Place a thermometer into the sample until the bulb touches the bottom and then secure it to the side of the viscometer to prevent breakage.
  4. Operate the instrument at 300 rpm for three (3) minutes. This will equalize the temperature of the bob, rotor and the fluid.
  5. Read the dial at 300 rpm and 600 rpm. Record these numbers, and the temperature from the thermometer to the nearest 0.1° C,(0.15° F).
The viscosity from the temperature chart at the recorded temperature should be within ±2 cP of the 300 rpm reading. Twice the cP viscosity from the chart should be within ± 3 of the 600 rpm reading. Plot the 300 rpm reading and the 600 rpm reading then draw a straight line from zero through these two points. If zero, 300 and 600 points do not fall in a straight line, probably either the rotor, bob or bobshaft is bent or other eccentricity exists. Points at 100 rpm and 200 rpm can be plotted if verification is needed. Readings outside the specified limits are indications that the instrument should be either calibrated or repaired. Refer to Section 5-C for procedure to calibrate the spring. After completion of the calibration check, carefully wipe clean the rotor inner and outer surfaces, the bob, the thermometer, the sample cup, and work area.

Torsion Spring Calibration

Refer to Fig. 4 for identification of parts.

NOTE: Make sure the bob shaft is not bent before attempting to adjust the torsion spring.
  1. Remove dust cap [A], then loosen set screw [C] about 1/2 turn.
  2. Insert the calibration tool into the spring and rotate the adjustable mandrel (inside the spring) slightly. Turn the mandrel counterclockwise if the dial reading is too low or turn the mandrel clockwise if the dial reading is too high.

    NOTE: Before tightening set screw [C] check the top of the upper threaded mandrel and be positive that it is flush with the top of the clamp [E]. To accomplish this, it may be necessary to adjust the spring by slightly compressing or stretching the spring.
  3. Tighten set screw [C]. The slot in the top of the adjustable mandrel should line up with clamping set screw [C].
  4. Loosen set screw [F] to zero dial under index, then rotate knob [G] as required for alignment, then adjust knob [G] vertically to allow the spring to be clamped in a "free" position, neither stretched or compressed.
  5. Tighten set screw [F] and replace the dust cap [A].

Figure 5: Dead Weight Calibration DW-3 Calibration Fixture

Figure No. 4
Dead Weight Calibration
DW-3 Calibration Fixture

Section 6: Data Reduction

Newtonian Viscosity Calculations

Newtonian Viscosity in centipoise may be read directly from the dial when viscometer is run at 300 rpm with R1-B1-F1 combination. Other springs may be used providing the dial reading is multiplied by the "f" factor (spring constant).

To rapidly determine Newtonian viscosities in cP with FANN viscometer, use the following formula:

nN = S x  x f x C

where,

S = Speed factor (Refer to Table 5)

0 = Dial reading

f = Spring factor (Refer to Table 3)

C = Rotor-bob factor (Refer to Table 4)

nN = Newtonian viscosity - cP

Example: Using an R2-B1 combination at a speed of 600 rpm with an F5.0 spring, and a dial deflects to 189.

nN = 0.5 x 189 x 5 x .315 = 149 cP.
NOTE:
Combinations with the larger gaps are likely to give results that differ from these figures. For best accuracy, calibrate with a standard fluid having a viscosity near the range of interest and using the R-B-F combination to be used in the test.
TABLE 4
Calculated C values from rotor-bob dimensions

Rotor-Bob

Combination

R-B Factor

C

R1-B1

1.000

R1-B2

8.915

R1-B3

25.392

R1-B4

50.787

R2-B1

.315

R2-B2

8.229

R2-B3

24.707

R2-B4

49.412

R3-B1

4.517

R3-B2

12.431

R3-B3

28.909

R3-B4

57.815

TABLE 5
Speed Factor S base 300 rpm = 1

Rotor

rpm

Speed Factor

S

.9

333.3

1.8

166.6

3

100

6

50

30

10

60

5

90

3.33

100

3

180

1.667

200

1.5

300

1.0

600

.5

Approximation of Plastic Viscosity and Yield Point

Using R1-B1-F1 components, test a sample running the viscometer at 600 rpm and note the dial reading. Change the speed to 300 rpm and note the dial reading. Determine the PV and YP using the following equations. PV represents the slope of a straight line between the two dial readings. YP represents the theoretical point at which the straight line, when projected, will intercept the vertical axis.

PV (plastic viscosity, (lbs/100 ft2)/300 rpm) = 600 - 300

YP (yield point in lbs/100 ft2) = 300 - PV

CAUTION

A spring other than F1 may be used if the dial readings are multiplied by the proper "f" factor, but the other rotor-bob combinations can not be used for this rapid, two point method.

Calculation of the Spring Constant (Dead Weight Method

K1 = Grg /
Where K1 = spring constant - dynes/cm/degree deflection
G = Load in grams
g = 981 = gravitational constant (cm/sec2)
r = Radius arm = 1 cm
 = Dial reading in degrees

Example: The required setting for the F1 spring is 386 dynes/cm/degree deflection with the R1-B1 combination. Using the 50 gm weight supplied with the fixture, the formula is:

K1 =

Section 7: Measuring Range

Measuring Range for FANN Model 35 Viscometers

ROTOR-BOB

R1 B1

R2 B1

R3 B1

R1 B2

R1 B3

R1 B4

BASIC DATA

Rotor Radius, Ro, cm

1.8415

1.7588

2.5866

1.8415

1.8415

1.8415

Bob Radius, Rj, cm

1.7245

1.7245

1.7245

1.2276

0.8622

0.8622

Bob Height, L, cm

3.800

3.800

3.800

3.800

3.800

1.900

Shear Gap, in Annulus, cm

0.1170

0.0343

0.8261

0.6139

0.9793

0.9793

Radii Ratio, Rj / Ro

0.9365

0.9805

0.667

0.666

0.468

0.468

Maximum Use Temperature, oC

93

93

93

93

93

93

Minimum Use Temperature, oC

0

0

0

0

0

0

Overall Instrument Constant, K

300.0

94.18

1355

2672

7620

15,200

Standard F1 Torsion Spring   h= Kfq/N

SHEAR STRESS RANGE

Shear Stress Constant for Effective

Bob Surface k2, cm-3

0.01323

0.01323

0.01323

0.0261

0.0529

0.106

Shear Stress Range, dynes/cm2g = k1k2q

F 0.2 q = 1o

1.02

1.02

1.02

2.01

4.1

8.2

F 0.2 q = 300o

307

307

307

605

1225

2450

F 0.5 q = 1o

2.56

2.56

2.56

5.04

10.2

20.4

F 0.5q = 300o

766

766

766

1510

3060

6140

F1 q = 1o

5.11

5.11

5.11

10.1

20.4

40.9

F1 q = 300o

1533

1533

1533

3022

6125

12,300

F2 q = 1o

10.22

10.22

10.22

20.1

40.8

81.8

F2 q = 300o

3066

3066

3066

6044

12,250

24,500

F3 q = 1o

15.3

15.3

15.3

30.2

61.3

123

F3 q = 300o

4600

4600

4600

9067

18,400

36,800

F4 q = 1o

20.4

20.4

20.4

40.3

81.7

164

F4 q = 300o

6132

6132

6132

12,090

24,500

49,100

F5 q = 1o

25.6

25.6

25.6

50.4

102

205

F5 q = 300o

7665

7665

7665

15,100

30,600

61,400

F10 q = 1o

51.1

51.1

51.1

100.7

204

409

F10 q = 300o

15330

15330

15330

30,200

61,200

123,000

SHEAR STRESS RANGE

Shear Rate Constant k3, sec-1 per rpm

1.7023

5.4225

0.377

0.377

0.268

0.268

Shear Rate range, sec-1 ¡ = k3N

N = 0.9 rpm

1.5

4.9

0.4

0.4

0.24

0.24

N = 1.8 rpm

3.1

9.8

0.7

0.7

0.48

0.48

N = 3 rpm

5.1

16.3

1.1

1.1

0.80

0.80

N = 6 rpm

10.2

32.5

2.3

2.3

1.61

1.61

N = 30 rpm

51.1

163

11.3

11.3

8.0

8.0

N = 60 rpm

102

325

22.6

22.6

16.1

16.1

N = 90 rpm

153

488

33.9

33.9

24.1

24.1

N = 100 rpm

170

542

37.7

37.7

26.8

26.8

N = 180 rpm

306

976

67.9

67.9

48.2

48.2

N = 200 rpm

340

1084

75.4

75.4

53.6

53.6

N = 300 rpm

511

1627

113

113

80.4

80.4

N = 600 rpm

1021

3254

226

226

161

161

VISCOSITY RANGE IN CENTIPOISE

Minimum Viscosity(2)

All models, 600 rpm maximum

0.5(3)

0.5(3)

2.3

4.5

12.7

25

Maximum Viscosity(4)

For Model 34A & HC34A, 300 rpm min.

300

94

1,350

2,700

7,620

15,000

For Model 35A & 35SA, 3 rpm min.

30,000

9,400

135,000

270,000

762,000

1,500,000

For Model 35A/SR 12 & 35SA/SR 12, 0.9 rpm min.

10,000

31,400

400,000

890,000

2,550,000

5,000,000

Notes:
  1. Computed for standard Torsion Spring (f = 1) For other torsion springs multiply viscosity range by f factor
  2. Minimum viscosity is computed for minimum shear stress and maximum shear rate
  3. For practical purposes the minimum viscosity is limited to 0.5 cP because of Taylor Vortices
  4. Maximum viscosity is computed for maximum shear stress and minimum shear rate

Section 8: Trouble Shooting and Maintenance

Troubleshooting

Symptoms

Causes

Erratic dial motion

 1. Contaminated bob shaft bearings
2. Bent bob shaft
3. Rotor out of alignment
4. Incorrectly adjusted main shaft

Out of calibration

 1. Contaminated bob shaft
2. Bent bob shaft
3. Bent rotor
4. Friction in bob shaft bearings
5. Damaged or incorrectly installed torsion spring
6. Motor needs replacement

Excessive noise

 1. Lubrication failure or contamination in gears
2. Worn center shaft bushing
3. Top cover can create a bind in gear train if set improperly

Excessive run-out of rotor

 1. Damaged rotor
2. Contamination in main shaft recess

Sticking support legs

 1. Corrosion/contamination within support legs
2. Broken spring
3. Legs out of adjustment

Loose gear housing

 1. Bolts attaching gear housing to support legs are loose

Maintenance

The bob and rotor should be cleaned after each test and examined periodically for dents, abrasion or other damage. Oiling or greasing of the viscometer is not required in normal service. Always remove the bob from the bob shaft when transporting instrument to avoid bending bob shaft.

Periodically test the bob shaft bearings. Operate the instrument at 3 or 6 rpm with no sample around the rotor and bob. Observe movement of the dial. It should not move more that +/- 1 division. Rough bob shaft bearings should be replaced.

Instrument should be serviced by qualified personnel only. If factory service is required, contact Fann for return authorization.

Troubleshooting

Content does not exist!

Section 9: Specifications

Part No.

Model No.

Speeds RPM

Power Req.

Size

Weight
         

H

W

D

LB

KG

30164

35A

3, 6, 100, 200

300 and 600

115 Volts, 60 Hz,

.075 Amps

In.

Cm.

15.2

39

6

15

10.5

27

15

6.8

30165

35SA

3, 6, 100, 200

300 and 600

115 Volts, 50 Hz,

0.75 Amps

In.

15.2

6

10.5

15

6.8

30166

35A/SR-12

.09, 1.8, 3, 6, 30,

60, 90, 100, 180,

200, 300 and 600

115 Volts, 60 Hz,

0.75 Amps

In.

Cm.

15.2

39

6

15

10.5

27

17

7.7

30167

34SA/SR-12

0.9, 1.8, 3, 6, 30,

60, 90, 100, 180,

200, 300 and 600

115 Volts, 50 Hz,

0.60 Amps

In.

Cm.

15.2

39

6

15

10.5

27

17

7.7



TABLE 7

Rotor-Bob Dimensions

Unit

r-cm

Length-cm

Cyl. Area-cm2 x Radius-cm

B1

1.7245

3.8

71.005

B2

1.2276