Gardner Standard Bubble Viscometers

The viscosity of many materials depends on shear rate and is classified accordingly, Fig 2. 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.

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.

Score Marks - 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

• 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

Comes without tubes. Weights: 1/2 lbs net; 2 lbs shipping weight.

Pictured right is a bubble tube shown with and without protective cap.

Prevents small extraneous bubbles from interfering with timed bubble movement.

Boxes are supplied with separate, correspondingly-numbered index charts for recording pertinent sample information, and an exterior card in a polished brass card holder for easily identifying the general contents of the sample storage box.