Garnder Tube A- MT – MAS 1836

Gardner Tube A- MT      – MAS 1836

For Measuring Viscosity By The Air Bubble Rise Method Meets ASTM D 1545

bubble tube standards designated A thru T with 2 empty tubes (Grade A, Class G) and directions for use

  • Knowing the approximate viscosity, pick four standard tubes closest in viscosity to your sample
  • Fill the sample tube with liquid, insert a cork, and then using the tube holder insert the four lettered tubes and the sample tube into the holder
  • Turn over the holder and visually compare what letter best matches the rise time of the bubble in the sample
  • The rise time in seconds of the sealed tubes and samples can also be determined using a basic timer
Please be aware of the following accuracies when performing the test:
  • Temperature control: 1°C =  10% error
  • Verticality control: 5° slant =  10% error
  • Tube I.D. control: 0.1mm =      2% error
 Gardner Empty Viscosity Tubes
 

Viscosity Tube Information

For Measuring Viscosity By The Air Bubble Rise Method Meets ASTM D 1545 – Rheology is a branch of science dealing with the deformation and flow of materials which includes the subject of viscosity. Viscosity is a measurement of internal friction, or resistance, to flow by external forces. Viscosity is the ratio of shear force to shear rate (the slope of the curves in Fig. 1) expressed by:

The viscosity of many materials depends on shear rate and is classified accordingly, Fig 1b. Viscosity is expressed as Absolute, n, and Kinematic, v. Absolute viscosity is determined by measuring the shear force required to produce a given shear rate and is independent of the density of the liquid.

Kinematic viscosity is measured by the time required for a given volume of liquid to flow through a capillary or restriction. It is related to flow caused by the hydrostatic head of the liquid and therefore strongly dependent on density.

The relationship between Absolute and Kinematic viscosity is given by the following, where p is density:
 v = n/p
One of the simplest methods for determining Kinematic viscosity is by the rising bubble technique employing matched viscosity tubes. The method is visual, convenient, rapid and easily learned by technical and non-technical personnel.
Figure 1 and 2
Fig. 1 Fig. 2
Rising Bubble Technique, Principle
The time required for an air bubble in a liquid to rise is directly proportional to its viscosity. Bubble rise rates vary with the inside diameters of viscosity tubes; therefore, the tubes must be precision matched to a tolerance that will keep bubble rise rate variations below the level of visual detection. Variations in viscosity readings or comparisons are visually imperceptible from viscosity tubes with inside diameter tolerances closer than ±0.025mm. Any variations in readings are attributed to differences in viscosities.

Viscosity is determined by either measuring the time an air bubble takes to pass between two specifically spaced marks on viscosity tubes, or by comparison to the bubble rate rise of calibrated viscosity standards. The accuracy of the method is therefore a function of precision matching of tube bores and identical score heights, which are measured from the center outside bottom.

Other factors, such as uniformity of temperature and verticality of tubes, influence timed bubble travel and controlled laboratory techniques are essential for precise results. For example, a variation in temperature of 0.1°C will cause a 1% variation in the timed bubble travel, and a one radius departure from tube verticality may introduce a 10% error in the timed bubble travel.

Procedure For Using Viscosity Tubes
A viscosity tube is filled to the 100mm level score with the material to be tested. A cork is inserted to the 108mm score which provides and fixes a uniform air bubble. The sample, and standard if used, is placed in a suitable rack and immersed in a water bath until a uniform temperature of 25°C (77°F) is attained. If viscosity determinations are performed by referral to comparison samples of known viscosities or precisely calibrated standards, then they, too, should be at the same temperature as the samples. Viscosity is determined by one of two methods:

Comparison Method – The bubble rate rise of the samples is compared to samples of known viscosities or calibrated standards contained in tubes of the same dimensions. The rack containing the samples and standards is removed from the water bath, held vertically to stabilize the air bubbles and quickly inverted maintaining verticality. A comparison of air bubble speed of the samples to the standards permits estimation of viscosity; the faster the rate of bubble rise, the lower the viscosity. The user may prepare viscosity standards or employ Gardner Viscosity Standards.

Time-Method (ASTM D 1545) – TimeTest Tubes are required to determine viscosity by the Timed-Method. The length of time, in seconds, required for an air bubble to pass from the 27mm to 100mm score mark, a distance of 73mm, is approximately equal to the viscosity of the liquid in “Stoke” units; alternatively, viscosity may be expressed in “Bubble Seconds.” It is important to note that the position of the air bubble in relation to the 27mm score should be similar at the end of the test on the 100mm score.

Viscosity Tube Selection Guide
Viscosity Tubes are divided into three Classes as determined by precision sorting in accordance with bore size, number of score marks and contemplated method of use for bubble rise testing, Fig. 2. The numbers assigned refer to the bore size, which is expressed in mm.

Time-Test Viscosity Tubes, 10.65mm
Time-Test Viscosity Tubes are frequently referred to as ASTM D-1545 Tubes, which originated from the adopted standard method of test for viscosity as described in ASTM D-1545 issued by the American Society for Testing and Materials. Time-Test Tubes are scored in three places: Fig. 3: 27mm, 100mm and 108mm. The score mark at 27mm is used for a 73mm timed travel. Time-Test Viscosity Tubes are also subjected to additional testing procedures to ascertain the 10.65mm bore which is very critical for precision measuring.

Class “G-10.65” and “V-10.75” Tubes
Class “G-10.65” and “V-10.75” Viscosity Tubes are used principally for direct comparisons to Gardner Viscosity Standards. Both Classes of tubes are inscribed at the 100mm and 108mm lengths, Fig. 4. For bubble rate rise comparisons to Gardner Viscosity Standards, the following equivalency chart is provided.
Technical Data
Class Score marks I.D. ±0.025mm Method Of Testing
Time-Test, 10.65mm (ASTM D 1545) 108mm, 100mm, 27mm 10.65
(equivalent to Gardner
N Grade Tubes)		 Bubble time rise or bubble comparisons
Class “G-10.65” 108mm, 100mm 10.65
(equivalent to Gardner
A Grade Tubes)		 Bubble comparisons to Gardner Standards; or to calibrated standards with identical tube dimensions
Class “V-10.75” 108mm, 100mm 10.75
(equivalent to Gardner
B Grade Tubes)
NOTE: All score marks are measured from the center of the outside bottom.
Score Marks Diagram 1
Fig. 3Diagram 2
Fig. 4
All Viscosity Tubes are permanently inscribed with two score marks, at 100mm and 108mm heights (Fig. 3) with the exception of Time-Test Viscosity Tubes, which have an additional score at 27mm (Fig. 4). In compliance with ASTM D 1545, all score marks are measured from the center outside bottom of the tubes.

The score mark at 100mm represents the filling level and the 108mm score is used to fix the size of the air bubble in the tube by inserting a cork to this mark. The 27mm and 100mm scores on Time-Test Viscosity Tubes are used to time the bubble rise.
Specification References:
American Oil Chemists Society (AOCS), Method Ka6-63, American Society For Testing and Materials D1131 53 (1975), D1545 89 D1725 62 (1970), Federal Test Method Standard (FTMS) Method 4271
Technical Data
Viscosity Tubes are manufactured to the closest possible tolerances and then precisely measured for final selection.

Note: Inside diameter tolerance closer than ±0.025mm is unnecessary since variations in viscosity readings or comparisons would be imperceptible.
Length: 114mm ±2mm
Wall Thickness: .0.65mm
Tolerance, I.D.: ±0.025mm
Composition: Soda-lime glass, flat bottom
Score Height Tolerance: ±0.5mm

 

Viscosity Tube Accessories

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Rough Sort Tubes
Tubes unsuitable for viscosity applications are separated, sorted, matched and grouped into two ranges according to tube bore size. Although these tubes are not precision matched or scored, they are adequately matched in bore size for diversified use in general industrial and laboratory procedures.
Rough Sort Tubes-Low…..Range 10.50-10.75mm
Rough Sort Tubes-High….Range 10.75-11.00m
Corks Corks
High quality, short length corks, properly fit viscosity tubes so that the small end is in firm contact with inside of tubes.Prevents small extraneous bubbles from interfering with timed bubble movement.