Study on calibrating method of Coating viscometer

1 Overview

The paint viscometer is the most widely used viscometer . It is economical, practical and easy to operate. Its working principle is to use the sample to flow under the action of its own gravity, and describe the viscosity of the sample by the time for a certain amount of sample to flow out of the Viscosity Cup at a certain temperature . This paper describes the calibration method of Tu-4 viscometer and Tu-1 viscometer.

2 Metrological characteristics

(1) Appearance of the instrument

①The inner surface of the paint viscometer should be smooth, free from willow lines and scratches .

②The outflow pipe needs to be a straight pipe, the inner wall should be smooth without burrs, etc. The connection between the outflow pipe and the inner wall of the cup should be smooth, and there should be no gaps after replacing the outflow pipe.

③The paint viscometer needs to be marked with the name, serial number, inner diameter of the outflow pipe, manufacturer , etc.

(2) Time measurement error

The difference between the measured value and the calculated value of the flow time of the standard viscosity liquid with known kinematic viscosity from the paint viscometer should be within ±3% of the calculated value.

(3) Correction coefficient

0.95≤k≤1.05

3 Calibration conditions

3.1 Environmental conditions

The test temperature is any temperature between (20-30) °C, the laboratory temperature (within 2 hours) is controlled within the test temperature ±1 °C, and the relative humidity is ≤70%.

3.2 Measuring standards and other equipment

(1) Standard material for calibration

Standard viscosity fluids with certificates of reference substances, with kinematic viscosity values ​​at the instrument calibration temperature.

(2) Mercury thermometer

Mercury thermometers that have passed the inspection and have a division value not greater than 0.1°C (the indication value should be corrected when used ).

(3) Electronic stopwatch

After passing the test, the minimum division value is not more than 0.1s.

(4) Constant temperature device

A constant temperature bath or constant temperature box (with refrigeration .

(5) Other equipment

Bubble level, flat glass plate or straight edge scraper, gasoline and alcohol or petroleum etc., receiving cup (volume larger than paint viscosity meter).

4 Calibration items and calibration methods

4.1 Calibration items

The recommended calibration items are shown in Table 1. When the user has special requirements , the calibration items can be selected from Table 1 according to the user's requirements.

Table 1 Calibration item table

4.2 Calibration method

(1) appearance requirements

Visually inspect the appearance according to the requirements of 4.1.

Put the standard solution of the appropriate brand (within the outflow time of 30s to 100s ) into the constant temperature tank (if using a constant temperature box, put the standard solution and the paint viscometer together), and keep it within ±0.5°C of the verification temperature for 20 minutes ~ 30min.

●Clean the paint viscometer with gasoline, alcohol and petroleum ether, pull the outflow tube with a silk cloth soaked in solvent, and then dry it for later use.

(2) Time measurement error

●Put the paint viscometer on the special bracket, adjust the leveling screw to make the upper edge of the paint viscometer level (need to be tested by a level instrument), and place the receiving cup under the outflow tube.

●Use a thermometer to measure the temperature of the standard solution at constant temperature. When it reaches the calibration temperature ±0.1°C ( the standard solution is pre-adjusted 0.5°C lower when the room temperature is in the positive fluctuation range of the calibration temperature, and vice versa when it is lower than the room temperature), turn the thermometer Move it into the receiving beaker, block the outflow tube with your fingers, pour the standard solution along the inner wall of the paint viscometer until the liquid overflows, and scrape it with a straight-edged scraper until the liquid level is even with the upper edge of the paint viscometer (standard solution From pouring into the paint viscometer to the outflow tube to the receiving beaker, the temperature change shall not be greater than 0.1°C).

●Remove the finger and count the time at the same time. The liquid outflow pipe should be in a straight line. Stop the time when the flow breaks, and record the outflow time t 1 .

●Re-constant temperature standard solution, measure again according to the above method, record the outflow time t 2 , and then calculate the average of the two outflow times, the difference between the two measured values ​​shall not be greater than 3% of the average value. Take the average ​​as the calibration result.

●Choose another brand of standard solution and measure it according to the above steps,like,If the absolute value of the relative error between one of them and tn is greater than 3%, repeat the above operation.

(3) Calculation of correction coefficient k

For the calibrated paint viscometer, calculate the correction coefficient k value according to formula (1), namely:

In the formula: k —— correction coefficient of outFlow Cup viscometer;

t _n ——calculated value of outflow time of standard solution;

- Measured value of the outflow time of the standard solution.

5 Conclusion

This paper has certain guiding significance for chemical metrology institutions and legal metrology institutions to carry out the calibration of paint viscometers . It is recommended that the recalibration interval should not exceed one year.

About the Author

Zhang Weibin, senior engineer, is mainly engaged in the verification and calibration of measuring instruments and related scientific research work.