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1. Working principle and performance characteristics of magnetic stirrer

The magnetic stirrer uses the principle of magnetic field and vortex to place the container of the liquid to be stirred into the stirrer on the base of the magnetic stirrer. When the magnetic stirrer is energized, a rotating magnetic field is generated near the base to drive the stirrer into a circular cycle. Movement, and then a vortex is formed in the container liquid, so as to achieve the purpose of stirring the liquid.

At present, there are two main types of agitators used in the laboratory: electric stirrers and magnetic stirrers. Among them, magnetic stirrers are suitable for liquids or solid-liquid mixtures with low viscosity.

Compared with electric stirrer, magnetic stirrer has the following advantages:

1) Using high-quality DC motor, low noise, stable speed regulation;

2) The stir bar is made of high-quality magnetic steel coated with PTFE, which is heat-resistant, wear-resistant and corrosion-resistant;

3) The mixing work is carried out in a sealed container, which is ideal and convenient to use;

4) The auxiliary heating device can be integrated into the system, which greatly facilitates the application that needs to be stirred and heated at the same time.

The general magnetic stirrer can have both stirring and heating functions at the same time.

The effect of stirring: 1) Mix the reactants uniformly, make the temperature distribution uniform, and accelerate the reaction rate or evaporation rate, thereby shortening the reaction time; 2) When heated in a closed container, magnetic stirring can prevent bumping. The function of heating: Of course, this function is aimed at specific applications. The temperature controlled by the heater integrated on the magnetic stirrer is generally between room temperature and 100°C. The simple magnetic stirrer only has the function of stirring.

 

2.The selection principle of magnetic stirrer

Due to the continuous efforts of many domestic enterprises, the magnetic stirrer has become a wide variety of low-cost laboratory routine instruments and equipment, which enables our laboratory to have the ability to choose the magnetic stirrer that we need. In the face of many types and different prices of magnetic stirrers on the market, how should we choose? Below, the author will talk about a few selection principles based on some of my own experience in use and some understanding of the market. refer to.

The principle of necessity

1) For applications that only need to be stirred at room temperature, choose a simple magnetic stirrer with only stirring function;

2) For applications that require stirring and heating at the same time, but the temperature requirements are not very strict, you need to choose a standard heating magnetic stirrer;

3) If you still need to display the temperature in real time during the working process, select the digital display temperature heating magnetic stirrer;

4) If you still need to set the working time, and stop working when the time is up, you can choose a timing magnetic stirrer;

5) If the heating temperature control requirements are relatively strict, you have to choose a water-bath heat-collecting magnetic stirrer. The water-bath heat-collecting magnetic stirrer is equivalent to a standard heating magnetic stirrer with a water bath integrated on the chassis. Everyone We all know that water bath heating has the characteristics of uniform heat transfer, precise temperature control, and safe heating. Therefore, the water bath collector magnetic stirrer is particularly suitable for applications where temperature control requirements are strict and the bottom of the container (such as a flask) is difficult to receive heat from the heating chassis. ;

6) If you need to accurately display the real-time speed during work, choose a digital display speed heating magnetic stirrer, but with this speed display function will greatly increase the price of the instrument, it is recommended to choose demanding research-level occasions use;

7) If the volume of liquid to be stirred is large, a large-capacity magnetic stirrer should be selected. The stirring capacity of a conventional magnetic stirrer is generally below 2000mL;

8) If conventional electric stirring is required at the same time as magnetic stirring, you can choose an electric magnetic compound stirrer;

9) If there are complex requirements for the mixing characteristics, such as turning for a while and stopping for a while, forward turning for a while, reversing for a while, heating for a certain period of time, keeping temperature for a certain period of time, cooling for a certain period of time, low speed for a certain period of time High speed and so on, you have to customize the intelligent program to control the magnetic stirrer, but the integration of so many complex functions will make the price of the instrument rise sharply, and it is only recommended for extremely demanding research-level occasions.

The principle of sufficiency

For your own application, choose the most suitable type, and avoid being idle and wasteful of certain functions due to greed for big plans.

Economic principles

We can also see many imported magnetic stirrers on the market. One of their most notable features is that they are more expensive. Is the more expensive the better the quality? The answer is generally self-evident, but the problem is that these are often thousands of times. Is the 10,000 (domestic-made magnetic stirrers generally hundreds of thousands) suitable for us? As you all know, with the continuous enhancement of China’s “world factory” role, the domestic magnetic stirrer market has developed rapidly in recent years. Through the tireless efforts of many companies, magnetic stirring technology has gradually become popular, and the varieties of magnetic stirrers are constantly diversifying, but the prices are becoming more commonplace. Although the price of a domestic magnetic stirrer is only a fraction or even a fraction of the imported one, it is functionally sufficient to satisfy most of our applications.

Therefore, the author also recommends that under the premise of meeting the needs and sufficiency, we should give priority to domestic magnetic stirrers with higher cost performance. This will not only save our investment, but also promote domestic enterprises to continuously improve R&D capabilities and competitiveness.

 

3. How to use magnetic stirrer

Since most of the magnetic stirrers on the market have similar functions, this section will briefly explain some general methods of use.

1). Plug in the power supply, place the vessel containing the solution in the middle of the base, and sink the stirrer into the bottom of the vessel;

2). Turn on the power, the indicator light is on, and then adjust the speed control knob clockwise, the speed is adjusted from slow to fast, to the required speed, the stirring bar rotates to drive the solution to stir;

3). When constant temperature heating is required, insert the temperature measurement probe into the solution, and insert the plug into the stirrer seat (corresponding to the water bath heat-collecting magnetic stirrer, because the temperature measurement probe is integrated inside the water bath pot, there is no such step ), adjust the temperature knob to the desired temperature;

4). If heating is not required, just adjust the temperature adjustment knob to below room temperature;

5). When timing operation is required, turn the timing switch clockwise to the required time position. At this time, the power light is on and the instrument is working. When the timing switch automatically turns to the starting position, the stirring stops automatically (this step is only for For models with this timing function);

6). After use, turn off the power switch, disassemble the reaction device, and unplug the power plug of the magnetic stirrer.

 

4.The matters needing attention of magnetic stirrer

Same as the previous part, only a brief description of some general precautions.

1). Choose the appropriate magnetic stirrer according to the application;

2). When using the instrument for the first time, check the instrument's manual to check whether the parts it carries, such as stir bar, power cord, etc.;

3). It is best to ground the instrument well when using it;

4). When placing the solution in the container, do not overfill it, and leave enough space to prevent the solution from spilling out during the mixing process and corroding the body of the disk;

5). When adjusting the speed, it should be gradually adjusted from low speed to high speed. It is best not to start directly from high speed, so as to avoid the agitator being out of synchronization and causing jitter;

6). Medium-speed operation can extend the service life of the agitator;

7). If the stir bar beats or does not stir during stirring, please check whether the beaker is stable, whether the position is flat, and whether the speed is appropriate;

8). When turning the timing switch, it should not be too fast or too strong to avoid damage (only for models with timing function);

9). The height of the temperature measuring probe placed in the solution should be appropriate so that the stir bar cannot collide with the probe to prevent damage to the probe. limit);

10). Ordinary heating magnetic stirrer can not be heated without stirring, and continuous heating above 70℃ shall not exceed 2 hours (the water bath heat-collecting magnetic stirrer does not have this limitation);

11). The instrument should be kept clean and dry, especially do not let the solution enter the machine. After use, the temperature measuring probe, stir bar, etc. should be cleaned, and the surface of the disk should be wiped clean with a clean cloth.