Viscometer is a physical property analysis instrument that measures the viscosity of a fluid. Viscosity is a physical property of a fluid substance. It reflects the internal frictional forces between molecules when the fluid is subjected to external forces. The viscosity of a substance is closely related to its chemical composition. In industrial production and scientific research, the composition or quality of a substance is often monitored by measuring the viscosity. For example, in the production process of polymer materials, the application of a viscometer can monitor the viscosity of the synthesis reaction product and automatically control the reaction end point. Others such as oil cracking, lubricant blending, certain food and pharmaceutical production process automatic control, crude oil pipeline transportation process monitoring, and quality inspection of various petroleum products and paints, etc., all require viscosity measurement.
Main classification
Divided by working methods: capillary type, rotary type and vibration type.
Divided by working mode: offline viscometer (sampling test), online viscometer (24-hour continuous measurement), portable viscometer
Capillary viscometer: The capillary viscometer is usually a Saybolt viscometer, which is a common viscometer. Its working principle is: the sample container (including the outflow capillary) is filled with the sample to be tested, in a constant temperature bath, and the height of the liquid column is h. Open the cock, the sample begins to flow to the receiver, and at the same time, the time is calculated until the sample liquid level reaches the scale line. The greater the sample viscosity, the longer this period. Therefore, this time directly reflects the viscosity of the sample.
Rotary viscometer: A common rotary viscometer is a cone-plate viscometer. It mainly includes a flat plate and a cone plate. The motor drives the plate to rotate at a constant speed through a variable speed gear. The capillary action is used to keep the sample being measured between the two plates, and the friction between the sample molecules drives the cone and plate to rotate. Under the action of the torsion spring in the torque detector, the cone plate no longer rotates after rotating a certain angle. At this time, the torque applied by the torsion spring is related to the internal friction (ie viscosity) of the molecules of the tested sample: the greater the viscosity of the sample, the greater the torque. There is a variable capacitor in the torque detector, and its moving piece rotates with the cone plate, thereby changing its own capacitance value. The torque of the torsion spring reflected by this change in capacitance is the viscosity of the measured sample, which is displayed by the meter.
The rotary viscometer has the advantages of convenient use, stable performance, and simple maintenance. It is suitable for measuring various greases, paints, inks, paints, plastics, slurries, rubber, latex, detergents, resins, condensed milk, creams, drugs, and cosmetics. The viscosity of various fluids is a necessary instrument for laboratories and analysis rooms in textile, chemical, petroleum, electromechanical, pharmaceutical, food, light industry, construction and other industries, as well as colleges, scientific research units, and military departments.
After turning on the rotary viscometer, it is necessary to detect the zero position first. This operation is generally performed without installing the rotor. Then, the inner cylinder of radius R2 is coaxially installed in the outer cylinder of radius R1, which is filled with viscous fluid, and the synchronous motor Rotate at a stable speed, connect the scale disc successively, and then drive the inner cylinder (ie the rotor) to rotate through the balance spring and the rotating shaft. The inner cylinder (ie the rotor) is subjected to the viscous torque based on the fluid. The greater the torque produced by the counterbalance, the larger the scale indicated by the pointer on the dial. Multiply the reading by a specific factor to get the dynamic viscosity of the liquid.
Vibration viscometer: The working principle of this kind of viscometer is that objects in the fluid will be hindered by the fluid when vibrating. The size of this effect is related to the viscosity of the fluid. Commonly used vibrating viscometers include ultrasonic viscometers, with a shrapnel in the detector. When excited by a pulsed current, the shrapnel generates mechanical vibration in the ultrasonic range. When the shrapnel is immersed in the tested sample, the amplitude of the shrapnel is related to the viscosity and density of the sample. When the density is known, the viscosity value can be obtained from the measured amplitude data.
According to the type of measurement product:
Solder paste viscometer: The solder paste viscometer uses a coaxial double cylindrical rotary viscometer with a screw pump sensor, which is mainly used to measure solder paste, film thickness adhesive paste, adhesive, solder paste solder resist, liquid resistance Solder paint, other inks, pastes, etc. According to the tightness of the measuring part, with temperature adjustment skills, it can be connected to a personal computer to automatically measure and read data for automatic calculation.
Portable viscometer: The portable viscometer uses a coaxial double-cylinder type, a screw-type linear slide pump sensor maintains a fixed flow, and can accurately measure the viscosity of the viscous body according to the change of the stirring viscosity.
Viscosity controller: The viscosity controller can well manage the viscosity of various fluids such as paints, inks, adhesives, foods, medicines, oils, etc .; adopts a coaxial double-cylinder type; the spiral-line sliding method pump sensor maintain With a fixed flow, a stable value can be obtained; the viscosity of the viscous body that changes successively according to the stirring viscosity can be measured correctly.
Stormer viscometer: Stormer viscometer is a test instrument used to determine the viscosity of paint and other paints with KU value. The design basis followed by this instrument is ASTM standard and GB9269-88 standard. Tianjin Jingke Material Testing Machine Factory is the largest enterprise specializing in the production of paint, coating and ink equipment material testing machines and special equipment for the paint industry laboratory. This viscometer uses a single-chip microcomputer, and the operator can directly read the KU value of the measured sample from the instrument without looking up the table.
Working principle: Immerse the paddle rotor in the tested sample, increase or decrease the weight to keep the paddle rotor speed at 200 rpm, input the weight of the tested sample at 200 rpm through a single-chip microcomputer Replaced by viscosity KU value.
Instructions
1. The machine must be kept level
2. When the rotor is placed in the sample, avoid generating bubbles, otherwise the measured viscosity value will be reduced. The method to avoid is to put the rotor into the sample at an angle, and then install the rotor, the rotor cannot touch the cup wall and the bottom of the cup. The sample to be measured must not exceed the specified scale.
3. When measuring different samples, the rotor must be kept clean and dry. If the rotor has other samples or water remaining after cleaning, it will affect the accuracy of the measurement.
4. The maximum acidity (PH) cannot exceed 2. If the acidity is too high, a special rotor should be selected. When using ULA, the sample size must be determined (only 16ml)
5. Select the viscosity standard liquid according to the measured viscosity range, and verify the instrument before each use of the viscometer or rheometer, or periodically verify it to ensure the accuracy of the measurement. We can provide Newtonian fluids for each viscosity range The nature of silicone oil or oil standard products, accuracy is ± 1%, the recommended service life of viscosity standard fluid is one year from opening.
6. When connecting the rotor, use your left hand to gently lift and hold the mandrel (on the main unit), and the right hand to rotate the rotor. This operation is to protect the mandrel and hairspring in the fuselage, which can extend the life of the instrument
7. When the value is relatively stable, otherwise the obtained value will have a large error
8. When selecting the rotor, it depends on the viscosity of the sample to be measured and the measurement range of the rotor of which number is closest, so choose the number.
Precautions
According to its measurement principle, in order to obtain accurate and reliable measurement data, the following points must be noted:
1. The performance index of the instrument must meet the requirements of the national metrological verification regulations. The instrument in use shall be subjected to periodic verification. If necessary (the instrument is used frequently or in a critical state of qualification), an intermediate self-check shall be carried out to determine its measurement performance. The coefficient error is within the allowable range, otherwise accurate data cannot be obtained.
2. Pay special attention to the temperature of the measured liquid. Many users ignore this and think that the temperature difference does not matter. Our experiments prove that when the temperature deviation is 0.5 ° C, some liquids have a viscosity value deviation of more than 5%. The temperature deviation has a great influence on the viscosity. The temperature increases and the viscosity decreases. Therefore, pay special attention to keep the temperature of the measured liquid constant near the specified temperature point, and it is better not to exceed 0.1 ℃ for accurate measurement.
3. Selection of measuring container (outer cylinder). For the double-cylinder rotary viscometer, carefully read the instrument manual, different rotors (inner cylinder) match the corresponding outer cylinder, otherwise the measurement results will be huge deviation. For a single-cylinder rotary viscometer, in principle, the radius of the outer cylinder is infinitely large. In actual measurement, the inner diameter of the outer cylinder, that is, the measuring container, is not less than a certain size. For example, the NDJ-1 rotary viscometer produced by Shanghai Tianping Instrument Factory requires that the diameter of the measuring beaker or straight cylindrical container is not less than 70mm. Experiments show that especially when using the No. 1 rotor, if the inner diameter of the container is too small, it will cause a large measurement error.
4. Correctly select the rotor or adjust the speed so that the indicated value is between 20 ~ 90 divisions. This type of instrument uses a dial and a pointer to read. Its stability and reading deviation are combined with 0.5 grids. If the reading is too small, such as near 5 grids, the relative error caused is more than 10%. If you choose a suitable rotor or speed If the reading is at 50 divisions, the relative error can be reduced to 1%. If the indicated value is more than 90 divisions, the torque generated by the balance spring is too large, and it is easy to produce creep and damage the balance spring, so the rotor and speed must be selected correctly.
5. Frequency correction. For domestic instruments, the nominal frequency is 50 Hz, and the power supply frequency in China is also 50 Hz. The variability of the test with a frequency meter is less than 0.5%, so general measurement does not require frequency correction. But for some instruments in Japan, Europe and America, the nominal frequency is 60Hz, frequency correction must be carried out, otherwise an error of 20% will be generated. The correction formula is: actual viscosity = indicated viscosity × nominal frequency ÷ actual frequency
6. The depth of the rotor immersed in the liquid and the influence of bubbles. The rotational viscometer has strict requirements on the depth of the rotor immersed in the liquid, and must be made in accordance with the instructions * (some double-cylinder instruments have strict requirements on the amount of liquid tested, which must be measured with a measuring cylinder). The rotor is often immersed in the liquid with bubbles, and most of them will float up and disappear after a period of rotation of the rotor. The bubbles attached to the lower part of the rotor sometimes cannot be eliminated. The presence of bubbles will cause a large deviation in the measurement data, so tilt Immersing the rotor slowly is an effective method.
7. Cleaning of the rotor. The rotor (including the outer cylinder) used for measurement should be clean and free of dirt. Generally, it should be cleaned in time after the measurement, especially after the measurement of paint and adhesive. Pay attention to the cleaning method, soak it with a suitable organic solvent, and never use hard scrapers such as metal knives, because there will be deviations in the measurement results when there are serious scratches on the rotor surface.
8. Other issues needing attention.
1. Most instruments need to adjust the level, pay attention to the level problem at any time after replacing the rotor and adjusting the rotor height, and during the measurement process, otherwise it will cause reading deviation or even unable to read.
2. Some instruments need to be equipped with a protective frame, read the instructions carefully and install according to the regulations, otherwise it will cause the reading deviation.
3. Determine whether it is an approximate Newtonian fluid. For non-Newtonian fluids, the rotor, speed and rotation time should be specified after selection to avoid misunderstanding that the instrument is not allowed. In summary, although the structure of the rotary viscometer is simple and easy to use, if it is not used correctly, a certified instrument cannot obtain accurate measurement results, which affects the quality of the product.
main application
In actual engineering and industrial production, it is often necessary to check the viscosity of the fluid online to ensure the best process operating environment and product quality, thereby improving production efficiency. Through online measurement of liquid viscosity, liquid rheological behavior data can be obtained, which has important guiding value for predicting process control, conveyability and operability of products during use. The characteristics of the liquid are often related to the other characteristics of the product such as color, density, stability, solid content and molecular weight changes, and the most convenient and sensitive method to detect these characteristics is to online check the viscosity of the liquid. On-line viscosity testing within the range of process technology requirements can minimize the scrap rate of the product and the downtime of the production line.
Installation attention
1. Care should be taken when loading and unloading the rotor, and the connecting screw should be lifted slightly for loading and unloading. Do not apply excessive force or force the rotor laterally to avoid bending the rotor.
2. Please do not put the viscometer with the rotor on the side or upside down.
3. Keep the connecting end face and thread of the connecting screw and rotor clean, otherwise it will affect the sway of the rotor.
4. When the viscometer is lifted, it should be held by hand to prevent the viscometer from falling due to its own weight.
5. After changing the rotor, please input the new rotor number in time. After each use, the replaced rotor should be cleaned (wiped) in time and put back into the rotor frame. Please do not leave the rotor on the instrument for cleaning.
6. When changing the measured liquid, please clean (wipe) the rotor and the rotor protection frame in time to avoid measurement errors caused by confusion of the measured liquid.
7. The instrument and the rotor are matched one to one, please do not confuse several instruments and rotor.
8. Please do not disassemble and adjust the instrument parts at will.
9. When moving and transporting the instrument, install the yellow cap on the connecting screw, tighten the screw and put it in the packing box.
10. After installing the rotor, please do not rotate for a long time without liquid to avoid damage to the shaft tip.
11. Many of suspensions, emulsions, polymers and other high-viscosity liquids are "non-Newtonian liquids", and their viscosity values ​​change with changes in shear speed and time. Inconsistent with the measurement results under time is normal and is not an instrument error. The determination of non-Newtonian liquids should generally specify the rotor, speed and time.
12. Do the following points will help to measure more accurate values:
Precisely control the temperature of the measured liquid.
Immerse the rotor in the liquid to be measured for a long enough time to make the two temperatures consistent.
Maintain the uniformity of the liquid.
The rotor is placed in the center of the container during the measurement, and the rotor protection frame must be installed.
Ensure the cleanliness and sway of the rotor.
When the high speed measurement changes to the low speed immediately, you should shut down the machine, or take a little longer at the low speed measurement time to overcome the error caused by the rotating inertia of the liquid.
When measuring low viscosity, choose No. 1 rotor, and when measuring high viscosity, choose No. 4 rotor.
When measuring viscosity at a low speed, the measurement time is relatively longer.
Due to the need to change the rotor and the liquid to be measured during the measurement process, after changing the position of the viscometer by rotating the lifting chuck, the horizontal position of the viscometer should be checked and adjusted in time.
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