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Introduction to the working principle of vacuum drying and the vacuum pump used for vacuum drying

In mechanical engineering, cleaning mechanical components has become an indispensable step in the manufacturing process of components. Depending on the degree of dirt and the geometric shape of the parts, various cleaning methods can be used. The choice of cleaning method has no impact on the subsequent drying process. In addition to using convection drying or circulating hot air for air drying in the thermal heating and cleaning process of the components themselves, vacuum pump vacuum drying is an effective and fast method in the drying process. Let's learn about vacuum drying and vacuum pumps used for vacuum drying through this article.

Industrial components are usually cleaned after processing or polishing work, or after heat treatment. The cleaning methods can be basically divided into two categories: aqueous solution cleaning and solvent cleaning. Of course, there are also some special processes. The final choice of cleaning method depends on multiple factors. The most suitable cleaning method must be selected according to the material of the part, the type of dirt (different types of oil, grease, lotion, dust, etc.) or the geometric shape of the part (surface structure, hole, undercut, etc.). It is also necessary to consider the required purity level of the components.

Subsequent drying of cleaned components is essential. In aqueous media, even the smallest residual moisture can cause corrosion damage to the finished product, leading to high subsequent costs. Undrying solvents can cause the workpiece to decompose. Convection drying is the simplest drying method. The components are heated to between 70 and 80 ℃ during the cleaning process, causing the attached moisture to evaporate. Circulating air drying is the process of hot air flowing above the workpiece, causing water to evaporate. Both methods are applicable to parts with simple geometric shapes. And vacuum drying is very reliable and effective, it can even ensure rapid drying of geometrically complex parts, and can be used for cleaning methods involving aqueous solutions and solvents.

The working principle of vacuum pump drying

Vacuum pump vacuum drying is based on the boiling temperature of liquid droplets under vacuum conditions, which means that liquids will evaporate even at low temperatures. For example, at the pocket position, the liquid still exists after cleaning and is difficult to remove by other methods, while vacuum drying with a vacuum pump can make it evaporate quickly like residual liquid on the surface of the workpiece.

Function description of aqueous solution cleaning system

Once the working chamber is occupied and sealed by the parts that need to be cleaned, a vacuum pump needs to be used to evacuate at a pressure of about 100 mbar. The cleaning medium is pumped into the working chamber through a water pump. The vacuum chamber ensures that the cleaning solution penetrates into the smallest chamber, for example, due to the spacing of the air, the socket cannot be ignored. There can be various different steps in the subsequent cleaning process. Usually includes the process of soaking and spray cleaning. Sometimes ultrasonic cleaning is used, which is usually accompanied by one or more cleaning cycles. After the cleaning solution is removed, the actual vacuum drying process occurs. During this process, the pressure inside the working chamber is further reduced by pumping gas through the vacuum pump. At this point, the steam generated is sucked out by a vacuum pump and transferred to the exhaust pipe.

Functional description of solvent cleaning system

In principle, the solvent cleaning process is similar to the water solution cleaning process. However, vacuum pumps generally require additional work to be completed. Firstly, meeting explosion-proof requirements is crucial, and there are two different solutions here. Either a vacuum pump with explosion-proof standard design can be used, or a cleaning system operation that does not require explosion-proof can be carried out under a constant pressure driving system of less than 100 mbar. The pressure of the system can be generated by any type of vacuum pump, but the second type of smaller vacuum pump is usually used to complete this work. Secondly, the solvent evaporated during the drying process can be evaporated in a vacuum still (a device where the solvent can be distilled out of the contaminated medium). The solvent distillate is returned to the cleaning process through a water tank, while the oil/dirt is collected in a bucket.

The use of vacuum generators

Oil lubricated rotary vane vacuum pump

Oil lubricated rotary vane vacuum pumps are widely used in cleaning systems. Experience has shown that this type of vacuum pump is very suitable for such application needs, and it has therefore become the standard pump in the drying process of cleaning systems. The rotary vane vacuum pump is a powerful vacuum generator with a long service life and high vacuum level. However, when it comes to cleaning processes with a high probability of steam generation, rotary vane vacuum pumps may not always be able to prevent condensation of steam during the suction and removal process of the vacuum pump. At the same time, the condensate oil emulsifies the vacuum pump oil. This may lead to insufficient lubrication of the rolling bearings and rotating blades, causing wear on other components of the vacuum pump, and the suction performance and expected vacuum degree may also be affected. These impacts can lead to an increase in maintenance and overall operating costs by more frequent damage to vacuum pump oil and filters.

Dry screw vacuum pump

Vacuum pumps have successfully met various specific application requirements and have been successfully applied in the field of industrial cleaning and drying technology since 2005, widely spreading as a new standard for vacuum technology in this field.

The screw vacuum pump does not require oil as the working fluid. During the drying process, its advantage lies in the condensation during compression, which does not come into contact with oil, thus eliminating the possibility of problems related to oil lubricated rotary vane vacuum pumps.

In a screw vacuum pump, the twin screw rotors rotate in opposite directions inside the cylinder and do not come into contact with each other or with the inner wall of the cylinder. Similarly, sealing is achieved through a non-contact method, resulting in no wear or tear. If steam condenses in the COBRA screw vacuum pump during the compression process, it will still be pushed by the airflow to the exhaust side of the compression chamber for discharge. Therefore, a few liters of liquid volume per hour can pass through the pump body without any problems. Designing the drainage outlet in this way allows for easy discharge of condensed liquid even when the vacuum pump is in a stopped state.

Unlike rotary vane vacuum pumps, screw vacuum pumps are water-cooled. The carefully designed cooling principle ensures an absolutely uniform and stable temperature throughout the entire pump body. The amount of coolant can be adjusted by the average of the constant temperature values, allowing the vacuum pump to have an ideal temperature control during this process and avoiding unnecessary water resource waste. In addition, a vacuum pump (heat exchanger) with a sealed cooling system can also be installed on devices where there is no available cooling liquid on site.

Comparison of vacuum pumps

It is difficult to say which is the better choice for cleaning systems, oil lubricated rotary vane vacuum pump or dry screw vacuum pump. In terms of technology, the principles of both pumps are possible. For cleaning systems with relatively low condensation risks, rotary vane vacuum pumps are a wiser choice to reduce procurement costs. However, if the impact of condensation leads to an increase in service and maintenance costs, screw vacuum pumps can save overall operating costs faster and more effectively. It is important to consult a vacuum expert before making a purchase decision for a vacuum pump.


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