In the world of industrial filtration, the quality of the filter media often takes center stage. However, a new industry focus emphasizes that stitching and thermal bonding processes, and the equipment used, are equally critical to filter bag performance and longevity. As filter bag designs and material types diversify, employing the correct manufacturing techniques becomes paramount for ensuring final product quality and reliability.
I. Filter Bag Material Preparation & Cutting:
Cutting length must account for the material's thermal shrinkage rate at operational temperatures. Length tolerances adhere strictly to GB/T 12625 standards (e.g., +15mm for 4000mm, +25mm for 8000mm, +30mm for 10000mm).
For internally filtering round bags operating under tension, the material's elongation rate under rated tension must be measured prior to cutting to determine final dimensions.
Cutting must include adequate allowances for seam widths, incorporating the multi-stitch width and the distance between stitches and the fabric edge.
For sewn bags, material is cut to precise width/length panels. For continuous seaming/thermal bonding, only width adjustment is typically needed, as length is automatically cut during tube formation.
II. Cylindrical Seaming (Tube Formation):
Cylindrical seaming "is the process of sewing or bonding a flat piece of filter material into a long roll, which is then fed through a fabric roller.
The material can ensure the overlapping size of the cylindrical diameter and the edge of the filter material. When using the sewing method for rolling, three needle chain thread should be used for sewing:
Sewn Seams: Require triple-stitch chain sewing.
Synthetic Filter Materials: Stitch width (1st to 3rd needle) = 9mm; Distance to edge = 2-3mm.
Fiberglass Filter Materials: Stitch width = 12mm; Distance to edge = 5-8mm.
III. Filter Bag Top & Bottom Sewing:
The already cylindrical bag body should be sewn with a bag opening, elastic ring, rope, reinforcement layer or bag bottom, using single needle double seam sewing. Elastic rings, ropes, reinforcement layers, bag bottoms, and other accessories should be prepared in advance. The reinforcement layer and bag bottom are made from scraps of the same filter material.
The sewing process of irregular shaped bags is basically the same as that of outer filter round bags. Although it is not circular, it can be cut according to its circumference and formed by cylindrical rolling. After sewing the bag opening ring and bag bottom, it forms a flat bag, rectangular bag or trapezoidal bag.
Non-round bags (flat, rectangular, trapezoidal) follow similar processes: cut to perimeter length, formed into a tube via seaming/bonding, then fitted with top and bottom components.
IV. Anti-Collapse Ring Installation (Internal Round Bags):
The inner filter round bag also needs to be sewn with an anti collapse ring. The anti collapse ring should be sewn with a cloth as needed and sewn with a double needle cylinder horizontal rotary shuttle long arm sewing machine. After the cylindrical rolling of the inner filter bag, the ring can be sewn first, or the bag opening and bottom can be sewn first, but the fiberglass filter material should be sewn first at the bag opening and bottom. For needle punched felt filter materials with stainless steel rings sewn on the bag opening and bottom, anti collapse rings should be sewn first.
V. Thread Selection & Stitch Hole Sealing:
Thread Material: For synthetics, must match or exceed the filter media quality, with a tensile strength > 27N. Glass fiber thread requires > 35N.
Anti-Collapse Ring Thread: Requires significantly higher strength (> 60N).
Ultra-Low Emission Bags (< 20 mg/m³ std): Stitch holes pose a leakage risk. These bags require specialized treatment-either sealing with a thin film patch or applying resin over the needle holes.
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