Common questions and answers for six types of standardized, calibrated Gardco Viscosity Cups designed and produced by The Paul N. Gardner Company.
All processors of liquid or semi-liquid materials are concerned with the ‘flow property’ of their products. This ‘flow property’, a sort of internal friction resisting flow, is measured as viscosity. Normally the amount of diluent in such products controls the viscosity of the product. Therefore, measuring viscosity is necessary not only to insure required and uniform product performance but also to control product cost.
The fundamental unit of viscosity is the Poise. It is the force required to move one surface of a known area at a given velocity with respect to another surface when the two surfaces are separated by a viscous material. The Centipoise is the Poise divided by 100. The Stoke is the Poise divided by product density (or weight per gallon in pounds multiplied by 0.1202) and is the unit of measure when gravity is the force causing product flow. When the Stoke value is known, the equivalent Poise value may be found by multiplying the Stoke value by product density (or weight per gallon in pounds multiplied by 0.1202). The Centistoke is the Stoke divided by 100.
Instrumentation commonly used for measuring viscosity can broadly be divided into two types:
There are many other specialty types of viscosity measuring instruments but they are beyond the scope of this writing. Most rotational instruments operate at more than one speed to permit a product to be evaluated at various rates of shear. They are, therefore, applicable to a higher level of product evaluation than viscosity cups. They are also applicable to the evaluation of materials containing a high ratio of solid materials and products that are above the range of instruments depending on gravity as a driving force. They are also expensive. Prices range depending on degree of sophistication, range, temperature control and data display.
Measuring viscosity by the use of viscosity cups has become the preferred method for production control due to their ease of use, their rugged nature, recent improvements in accuracy and relatively low cost.
Viscosity cups fall into two different types with those standardized and calibrated by the Paul N. Gardner Company shown for each type as follows:
Dip Viscosity Cups
EZ (Equivalent Zahn) Viscosity Cups - 5 Cup Ranges
Zahn Signature Cups - 5 Cup Ranges
Ford Dip Viscosity Cups - 6 Cup Ranges
Gardco/Fisher Dip Viscosity Cups - 4 Cup Ranges
Laboratory or “Ring Stand” Viscosity Cups
Ford Standard Viscosity Cups - 6 Cup Ranges
Gardco/ISO Viscosity Cups - 3 Cup Ranges
Much confusion has resulted in the selection of, as well as the use of ,viscosity cups due to the number of types available and inadequate standardization between the various manufacturers. It is the purpose of the balance of this writing to present the most common questions asked and the answers to these questions.
The questions are grouped into the following categories:
A. Cup Selection
B. Cup Accuracy
C. Cup Standardization and Certification
D. Cup Use
E. Temperature Control
Assuming that I proceed with the EZ Cup in my viscosity measuring program, I would like to proceed with questions relating to the cup accuracy, cup standardization, use and conditions under which viscosity measurements should be conducted.
The above listing of questions and answers covers the most important issues involved in the measurement of viscosity by the popular and widely used viscosity cups. They also cover the questions most frequently asked by our customers. Of course, there are many other questions that could be asked and it may be that some of the above answers need further clarification.
In any case, the Paul N. Gardner Company stands ready to assist you in your problems of viscosity measurement, not only with the finest possible products but also with information that has been garnered in the design and manufacturing of these products.