About outside filtration and inside filtration of filter bags
Dust filter bags must match other parts to keep suitable shapes during filtration and dust cleaning and realize the dust filtration and removal, then keep dust collector and baghouse system in normal running state. Combination of filter bags and accessories are called filter units. Filter bags are divided into inside filtration and outside filtration filter bags.
The accessories used in inside and outside filter units are divided into two types:
1-Accessories stitched together with filter bags.The types of accessories shall be stitched onto the filter bag during filter bag stitching process. Such the snap band for outside filtration filter bags, support rings for inside filtration filter bags.
2- Accessories used to supporting or hanging a filter bag:these types of accessories are not stitched on the filter bags, but shall be installed on to the baghouse system together with filter bags. Such as the support filter cages for outside filtration filter bags, hanging accessories for inside filtration filter bags.
About accessories for outside filtration filter bags:
1-snap band at the top of outside filtration filter bags
Outside filtration filter bag top is fixed onto the cell plate holes, and need stable sealing. Because the air going through the cell plates are already purified, if there is leak at the installing position of plate and filter bags, the air with gas dust will go into the clean room, which will reduce dust removal efficiency of baghouse very much. There are two important points about sealing between filter bag top and cell plate holes: first, the diameter of plate hole shall be correct, the processing of each hole must meet the requirements. The size of all holes must be the same. The accuracy must be controlled within the range of 0 and 0.3 mm. Secondly, the material of the elastic snap band ring of the filter bag must be a stainless steel or spring steel with good elasticity, and the thickness of the 0.3~0.5 mm steel strip is different according to the diameter of the filter bag mouth. The finished snap band shall be attached with the strips which matched the thickness of cell plate. Strips materials are same with filter bags materials. Normally use the off-cuts of same filter materials. When stitching outside filtration filter bags, shall stitch snap band onto the bag top mouth. We shall use special measuring tool-plate with holes to measure the size of outside filtration filter bags.
2-accessories supporting outside filtration filter bags-filter cages
The dust filter bag cage is used to support the filter bag in the tension state during filtration and ash cleaning, and maintains the shape that is favorable for filtering and cleaning.
From this point of view, the supporting frame is the "rib" of the filter bag. It should be light and convenient for installation and maintenance. It should be smooth, straight and burr free, so that the filter bags are not damaged.
The shape of the filter cage matched with the filter bag is consistent with that of the filter bag, the circular filter bag is equipped with a circular filter cage, the flat bag is matched with the flat frame, and the envelope bag is matched with the envelope shape frame.
Matching of filter bag and cage：
matching of felt filter bag and cage is loose matching, diameter and length of filter bag is larger than that of filter cage. The distance between the vertical wires of filter cage shall be less than 40mm.
Matching of woven fiberglass filter bag and cage is close matching, the diameter and length of filter bag is almost same as that of filter cage, the distance between the vertical wires of filter cage shall be less than 20mm.
The vertical wires of filter cage shall use carbon steel wires with 3-3.5mm thickness according to the length of filter bag cage. The related anti-corrosions treatments are doing on the surface of filter cage. Use stainless steel material to make filter cage when it is necessary.
Apart from the filter bag cages, the accessories used for outside filtration filter bags also include filter bag base and venturies. There are some dust collector and baghouse manufacturers who are still using relative backward gas cutting process when make cell plate. Especially for some small pulse bag filters in the early days, the perforated plates are mostly gas cutting. The hole size is inaccurate and rough. When reforming the bag filter, an aluminum die-casting filter bag base is often used to make sure each hole of cell plate to match the beaded snap band filter bags. This is convenient for installation and maintenance and also favorable for reliable sealing between filter bags and perforated plates.
Venturi is installed on the filter cage to increase the guide air flow up to 5-7 times when air blowing. The advantage of installing venture is centralizing the natural diffusion airflow and sending the dust removal pressure to the bottom of the filter bag. But using venturi will increase the resistance of the dust collector.
About accessories of inner filtration filter bags
1-accessories stitched onto the inside filtration filter bags-supporting ring, snap band ring
The cleaning of inner filration filter bag is under the action of vibration or counter blow air flow. Force the filter bag to vibrate or bulge to clear the ash. To maintain the settlement of dust particles when filter bags deformed or shriveled, the anti deflated ring should be sewn on the filter bags at a certain distance. Supporting ring materials shall use 3-5mm carbon steel or stainless steel wires. The welding of supporting rings should be strong, and it can not be removed and polished without burrs. Carbon steel material should be treated as anticorrosion.
The inner diameter of supporting ring shall be same as outer diameter of filter bag. The supporting ring is covered by same material with filter bag when stitching. Normal is using off-cut of filter materials. Two stitching are sewn on both sides of supporting ring. Double needle long arm sewing machine is used often to stitch supporting ring. And it has strict requirement of sewing thread.
For inside filtration filter bags, normally stainless steel ring is stitched at the top of filter bags, therefore clamp is not used when installing the filter bag cap, more convenient for installation.
2-accessories for hanging filter bags
When installing the inner filtration filter units, filter bag bottom is fixing the bottom bag base, the gas dust air goes into the filter bag through filter bag bottom. Filter bag top is fixed into bag cap. Filter bag cap is made of carbon steel or stainless steel, used for sealing and hanging of inside filtration filter bag. Inner filtration filter bag is fixed on the crossbeam of the dust collector by hanging device.
When filtering and cleaning, the inner filter bag needs to maintain the set tension of the filter bag. A filter bag with a diameter of 100 millimeters requires the tension of 10kg. A filter bag with a diameter of 300 millimeters requires the tension of 30kg. The lack of tension will affect filter bag filter and ash cleaning. Too much tension exceeds the tensile strength of the filter bag, which will cause premature damage to the filter bag. The tension of the filter bag is set up through the hanger adjusting hole or chain of the hanging device, and the tension is maintained by spring or tension spring. It needs to be checked and adjusted many times in the future.
