Test items of air dust filter bag

The appearance inspection of the filter bag is carried out from the following aspects

1. Adhesion of dust on the surface of the filter bag

If condensation, compaction, paste bag, etc. appear on the surface of the filter bag, it may be related to high-humidity flue gas and ammonia escape. After ammonia escapes, it will form ammonium bisulfate with sulfur oxides in the flue gas. Ammonium bisulfate is very viscous. Large, it is not easy to be removed by pulse blowing, the cleaning effect is reduced, and the resistance is likely to increase. The dust adhesion on the surface of the filter bag can preliminarily judge the operation resistance of the dust collector, thereby providing an early warning for on-site operation

2. Filter bag color

When the chemical properties of the filter bag change, the color will generally change, especially when the PPS filter material is oxidized or at a high temperature, the color will deepen, and the more severe the oxidation, the higher the temperature, the darker the color. The color change can be used as a basis for PPS filter bags subjected to oxidation or high temperature use.

3. The feel of the filter bag

When the PPS filter bag is severely oxidized, in addition to the darker color, the material will become brittle. Although both high temperature and oxidation will cause the color of the filter bag to become darker, the filter bag after high temperature use is generally harder and can rebound with memory.

4. Damaged filter bag

The filter bag damage may occur in the bag head, bag, bag end, and sometimes even the entire filter bag is damaged. The cause of the damage is generally different for different damaged locations. Through the appearance inspection, the cause of the filter bag damage can be preliminarily judged. The damage in a small area is generally mechanical abrasion, which is often related to the verticality of the filter bag and the fit of the filter bag and the bag cage. When a large area is damaged or the filter bag can be torn by hand, it is related to the severe oxidation and corrosion of the filter bag. The filter bag is prone to burn and damage when it encounters combustible burning and adhesion.

Test of breaking strength and breaking elongation of filter bag

The breaking elongation of the breaking strength machine is an important indicator of the use of filter bags. According to the requirements of GB/T 6719-2009, for ordinary filter media, transverse breaking strength ≥900N, transverse breaking elongation ≤35%, and longitudinal breaking strength ≥1200N are required. Longitudinal elongation at break ≤50%.

Determination of air permeability of filter bags

When there is a pressure difference between the two sides of the filter material, the air permeability is called the air permeability of the fabric. Air permeability refers to the air volume per unit area of the filter material per unit time when a pressure difference of 127 Pa is applied on both sides of the fabric. Of course, when the air permeability of the filter material has the same filtration efficiency, the greater the air permeability, the better, because this means that a lot of energy can be saved. The deviation of air permeability reflects the uniformity of the texture of the filter material. For this reason, the deviation of the air permeability of the filter material is specified in the standard. The air permeability of the filter bag is too small, and the resistance of the dust collector system may increase. Therefore, the test of the air permeability of the filter material can reflect the use of the filter bag, including whether it is hardened or not. Dust infiltration, etc.; on the other hand, it can infer the resistance of the dust collector system, which plays an important role in the operation and maintenance of the dust collector.

Test of mass per unit area

The national standard does not specify the value of mass per unit area, but there are regulations for its deviation. In the unit area test, a round cake with an area of 100 cm2 is taken as a sample, and samples are taken from different parts of the filter bag for testing. The value of mass per unit area is generally evaluated according to the requirements signed by both parties, which is an effective measure to prevent filter manufacturers from cutting corners. For the filter cloth of the same thickness, the change in unit weight will affect its air permeability and tensile strength.

Thermal shrinkage test

The heat shrinkage rate of the filter material is an important indicator. The longitudinal thermal shrinkage rate of the filter material is large, and for the pulse dust collector, the bag cage is often pushed out of the flower plate; while the horizontal shrinkage rate is large, the filter bag will tighten the bag cage, reduce the dust removal ability, and cause the resistance to increase. Even lead to broken bags.

Scanning electron microscope observation

Observe the filter material by scanning electron microscope, observe the fiber shape and dust adhesion from a microscopic angle, and judge the use condition of the filter material. When the fiber is broken in a large area, it can be seen that the filter material is severely oxidized and corroded; when there is a large amount of dust accumulation, it can be inferred that the air permeability of the filter material is affected, and the running resistance of the dust collector may be high.

Filtration performance test (VDI test)

The filtration performance test is to simulate the use of the filter material, to make a preliminary assessment of the filter efficiency and resistance of the filter material, and play an important role in the selection of the filter material. According to the test standards, the filtration performance test includes the resistance coefficient of the clean filter material, the static dust removal rate of the filter material, the dynamic dust removal rate, the dynamic resistance of the filter material, the regeneration resistance coefficient and the dust stripping rate.

Other testing content

In addition to the conventional performance testing, there are also some special performance testing, such as the corrosion resistance of the filter material, electrostatic characteristics, hydrophobicity, etc. These characteristics are specified in the standard.