The function and type of the filter

1 hydraulic system in the role of the filter

The role of the filter in the hydraulic system is:

1) filter out the dirt particles in the oil, to prevent the moving parts stuck, parts scratches, oil blockage and other failures, improve system reliability and stability.

2) filter out the fine particles of oil impurities, to prevent wear and tear parts, to extend the service life. To this end, the filter accuracy should meet the need to protect the sliding gap.

3) by analyzing the filter in the accumulation of pollutants, analysis of hidden dangers, find wear parts, monitoring equipment operation.

2 filter type

Hydraulic system using the filter, according to the filter material filter mechanism, divided into surface type, depth type and adsorption type three.

1) surface type filter

The filtering effect is achieved by a geometric surface.

The filter material has a uniform calibration hole, which can filter out particles larger than the size of the hole. The filtered particles are trapped on the surface of the filter on the upstream side of the oil.

As the particles gathered on the surface, the filter element is easily blocked and requires regular cleaning.

Woven filter and wire gap filter, belong to this category.

① mesh filter, the filter by the core frame wrapped copper wire mesh composition. Filtration accuracy is low, and the size of the mesh and the number of layers; 80,100,180μm. For the pressure pipe, commonly used 100,150,200 mesh copper wire mesh; for hydraulic pump suction pipe, commonly used 20 ~ 40 mesh copper wire mesh. Pressure loss does not exceed 0.004MPa. Simple structure, large capacity, easy to clean.

② wire gap filter, the filter core by winding the metal wire on the composition of the line, the use of small gaps between the lines through the block particles. High precision filter, 30,50,80μm and other three grades. For low pressure piping. Pressure loss does not exceed 0.03 ~ 0.06MPa. Simple structure, large capacity, the filter material strength is low, not easy to clean.

2) Deep type filter

The filter element is made of porous, permeable material with a tortuous passage inside. Particles larger than the surface pore size are trapped on the outer surface; smaller particles enter the interior of the material and are adsorbed by the channel walls. Paper, felt, sintered metal, ceramic, all kinds of fiber products such as filters are of such filters.

① paper core filter. The structure is the same as the wire gap filter, but the filter is made of plain and corrugated chemical fibers or wood pulp microporous filter paper. In order to increase the filtration area, the paper core is often made into a folded shape. To enhance the strength of the filter, the inside and outside the two sides are usually reinforced with metal mesh. Filtration high precision, up to 5 ~ 20μm. The pressure loss is about 0.01 ~ 0.4MPa.

② sintered filter. The filter element is made of metal powder sintered, and the particles in the oil are blocked by the micropores between the metal particles. Filtration high precision, up to 5 ~ 10 μm, by changing the size of metal powder particles to change the filtration accuracy. Suitable for fine filtration.

3) Adsorption filter

The filter material adsorbs the particles in the oil on the filter element. Magnetic filter belongs to the adsorption filter, made of permanent magnets, can adsorb the oil in the iron, iron or with a magnetic abrasive. Usually combined with other types of filters, made of double filter. Magnetic filters also monitor the wear of mechanical equipment.

Magnetic filter is divided into ordinary magnetic filter and high gradient magnetic filter. The ordinary magnetic filter utilizes the magnetic field of the magnet to directly capture the ferromagnetic contaminating particles in the oil. Among them, permanent magnet filter has the advantages of simple structure, convenient manufacturing, reliable operation and low running cost, so it is widely used, and its main drawback is that the particle effect is poor, and the particles adsorbed on the magnetic pole are difficult to be cleaned. High gradient magnetic filter can effectively overcome the above shortcomings, so that the performance of magnetic filters have greatly improved.

The attraction of ferromagnetic particles is proportional to the external magnetic field strength H, which is proportional to the gradation gradH of the magnetic field strength.

Ordinary magnetic filter is by increasing the external magnetic field strength H to improve the magnetic attraction, thereby enhancing the filtration capacity; high gradient magnetic filter is through the magnetic media to improve the gradient of the magnetic gradient gradH to increase the attractiveness to obtain efficient filtration of pollutants effect.

In the magnetic field, the magnetic field H and the magnetic field gradient gradH in the vicinity of the magnetic medium are much larger than those in the absence of the magnetic medium. In particular, the gradH is inversely proportional to the diameter d of the magnetic medium. When d is small, the value of gradH can be Very high Therefore, the high gradient magnetic filter based on this principle is also called high efficiency magnetic filter.

The high gradient magnetic filter utilizes the magnetic medium magnetized by the magnet to capture the contaminating particles. The magnetic media can greatly improve the magnetic field gradient around the medium, so the filter performance of the high gradient magnetic filter is significantly higher than that of the conventional magnetic filter.