Definition
Tusi Cup is a common instrument used to measure the viscosity of liquids, and its name comes from its standard outflow aperture of 4 mm. This instrument characterizes the relative viscosity of a certain volume of liquid by measuring the time it takes to flow out of the small hole at the bottom of the cup, which is a type of outflow cup viscometer. It is widely used in production and quality control in coatings, inks, adhesives, and other industries, providing critical data for process adjustment and product consistency assessment.
Principle
The measurement of Tu Si Cup is based on Poisuer's law and the principle of gravitational flow. When the cup is filled with liquid, the liquid flows out of the standard hole at the bottom by gravity. The outflow time is approximately linear with the kinematic viscosity of the liquid within a certain range. Its basic relationship can be expressed as:
η = k(t - c)
where η is the kinematic viscosity, t is the outflow time, k is the instrument constant, and c is the correction value. This formula shows that under the same conditions, the longer the outflow time, the higher the viscosity of the liquid.
Measurement method
Before measuring, four cups of coating and the liquid to be measured should be placed in a constant temperature environment, usually the standard temperature is 25 degrees Celsius. Use a level to adjust the cup to a level state. Use your fingers to block the small hole in the bottom of the cup and slowly inject the liquid into the cup until it overflows to avoid bubbles. Use a scraper to scrape the excess liquid along the cup mouth. Quickly remove your finger and start the timer at the same time to record the time when the first break point occurs during the liquid outflow, which is the measured value. After each measurement, the cup body should be thoroughly washed and dried.
Influencing factors
Temperature is a key factor in measurement, and liquid viscosity usually decreases with temperature, so the measurement ambient temperature must be tightly controlled. The cleanliness of the cup body directly affects the patency of small holes and measurement accuracy, and residues may change the effective pore size. Consistency in operating techniques, such as the judgment of the scraping action and the timing starting point, can also introduce human error. In addition, the thixotropy and volatility of liquids may require special operating procedures to guarantee reliable results.
Application:
Coating four cups are mainly used in the coating industry to control the construction viscosity of coatings during production and ensure the applicability of spraying, brushing and other processes. In ink manufacturing, it helps adjust printability. The adhesive industry uses it to monitor the flow characteristics of adhesives. The instrument is also commonly used in teaching and basic research as an introductory tool for viscosity measurement. The measurement results can be used to compare the uniformity of different batches of products or to verify that the product meets industry specifications.
Selection
The outflow cup with different pore diameters corresponds to different viscosity ranges, and the coating of four cups is suitable for medium viscosity fluids. In terms of material, the stainless steel cup body is durable and easy to clean. Products that meet national or international standards should be selected, such as GB/T 1723 standard. For scenarios where data logging is required, consider models with digital timers. Environmental requirements are also a selection factor, and a more robust design may be required for use in the field or on the workshop. Regular calibration services and support are also worth paying attention to.