Why Liquid Filter Bags Breaks

Bag Filter September 10, 2022 Filter Bag

As a common equipment for realizing solid-liquid separation, bag filter has the characteristics of simple operation and strong adaptability, and has been widely used in automobile coating process. In the assembly process, whether iron filings, iron powder, dirty oil and other pollutants can be effectively filtered out from the paint directly affects the quality of the paint, which in turn affects the appearance of the car body. The unfiltered liquid enters the filter from the inlet, and the liquid flows through the filter bag from the inside to the outside. After filtering, the liquid flows out from the outlet, and the impurities are intercepted in the filter bag. After the filter bag is replaced, it can be used continuously. The filter bag is the core part of bag filtration, and its performance determines whether the filtration goal can be successfully achieved. In the process of filter bag selection, matching, installation, use, replacement, etc., there may be the situation that filter bag is broken, impurities are not effectively intercepted, which in turn affects the operating load and product quality of the downstream process, causing economic losses, environmental pollution, and even safety accidents. Therefore, it is very important to quickly identify and analyze the causes of broken bags.

The reasons why filter bag breaks:

1. Design selection error:
The wrong type of filter bag causes the filter material to rupture due to corrosion, the material containing the filter bag is chemically corroded by the liquid to be filtered, and the working temperature of the application exceeds the tolerance temperature of the filter bag and thermal corrosion occurs. The concentration of mechanical impurities in the liquid is too high, and the apparent contamination of the filter bag is reached in a short time, it also shows that the number of filter bags selected is not enough. In addition, the liquid flow rate is large but the inlet and outlet dimensions of the filter are too small, which causes the flow rate of the liquid to pass through the filter bag to be too fast, exceeding the liquid flux and rated flow rate of the filter. It may also cause broken bags.

2. Improper installation of filter bags:
Pinholes appear in the filter bag due to the sharp objects encountered during the picking and installation of the filter bag. At the same time, when the filter bag is put into the bag filter, the support basket of the filter bag is not installed on the outside of the filter bag, so that the filter bag has no support. If the support basket is installed, the operator does not smooth the filter bag, the filter bag is in a discounted state in the support basket, and does not fit closely with the support basket. In particular, there are filter bags with special absolute precision, if the filter bag is not pre-wetted as required before feeding and filtration, or if the bags are turned over then they are easily broken.

3. The replacement pressure difference of the filter bag is too high:
As the filtration progresses, impurities will stick to the surface of the filter bag or be embedded in the inner void of the filter material, which will cause the flow resistance to rise, and the pressure drop inside and outside the filter bag to rise. When it reaches a certain level, the filter cannot continue to be filtered, and the filter bag needs to be replaced. According to Darcy's law, the pressure drop and volume flow rate of the filter bag are affected by the filter bag precision, material, thickness, cross-sectional area and application. The bag replacement pressure difference is not fixed, such as 0.10 MPa or 0.15 MPa and so on. If the filter bag is replaced, if the pressure difference is too high, it will prolong the life of the filter bag, but it will also increase the risk of the filter bag breaking. The filter function of the bag, this is because the high pressure difference will squeeze past the impurities that have been intercepted. Therefore, the replacement pressure difference of the filter bag, under the recommends manufacturers, needs to be determined after testing in combination with the actual situation of the filtration application.

4. Attachment does not match:
The filter float is a kind of hollow ball, which is a common accessory of the filter. It is installed inside the filter bag to replace the filtered liquid, reduce the loss and discharge of materials before replacing the filter bag, and shorten the purging time. Especially in applications where the filter is used for intermittent filtration or frequent switching of filtration products, there are many shut-offs of fluid and purging of material and liquid, and the liquid will impact the filter bag and the floating ball in the filter bag. At present, the float ball produced by many manufacturers is small in size, and there is no collar matching the filter bag and filter. The float ball is integrally inside the filter bag. Occurs at the inclined parking position of the contact between the float ball and the filter bag, and the inner filter material of the filter bag and the bottom of the filter bag are often broken. There are burrs on the surface of the floating ball or the supporting mesh basket, or the smooth transition at the bottom does not match the filter bag, and the bag will be broken by repeated friction on the bottom of the filter bag near the top of the arc.