Dust Collector Filter Bag

Function

As warm, dust-laden gas passes through the woven or needle-felt fabric, particles above the media's pore rating are arrested on the surface to form a secondary filtration layer — the dust cake — which progressively tightens the effective filtration cutpoint toward sub-micron levels. The fabric's air-to-cloth ratio, typically 1.0–1.5 m/min in asphalt baghouses, determines both steady-state pressure drop and required pulse-cleaning frequency. A well-maintained bag set delivers outlet particulate concentrations well within common regulatory thresholds. Because recovered filler is returned to the mixer via the filler elevator and weighed into each batch, bag efficiency also has a direct economic impact on raw-material consumption and recipe accuracy: a compromised bag set simultaneously raises stack emissions and reduces available filler, skewing the mix formula.

Construction & quality

Filter bags for asphalt batch-mix service are fabricated from 550 g/m² needle-punched polyester felt for standard-temperature duty (continuous ≤ 130 °C / 266 °F), or from 500 g/m² woven meta-aramid felt where exhaust temperatures may reach 160–180 °C. Bags destined for plants with elevated bitumen-vapour content are laminated on the clean-gas side with an expanded PTFE membrane — pore size typically 0.3–1.0 µm — which concentrates filtration at the membrane surface rather than within the felt depth, enabling more complete pulse cleaning and lower residual pressure drop over service life. All seams are sewn with high-temperature PTFE thread to the same thermal rating as the base fabric. The top snap-ring collar is formed from galvanised mild-steel wire swaged into a reinforced fabric sleeve for a positive cage-to-tube-sheet seal. The bottom cap is closed with a welded, folded seam. Felt fibres are heat-set and calendered after needling to stabilise pore geometry and reduce initial filtration bleed-through during the bag conditioning period.

When to replace

• Visible stack opacity or online opacity monitor readings above the site permit threshold, indicating fabric hole formation or collar seal failure
• Sustained rise in baghouse differential pressure that does not recover after pulse-cleaning cycles, indicating glazed or tar-blinded fabric
• Fine grey mineral dust accumulating on the clean-air side of the tube sheet, confirming a bag or collar seal breach
• Recovered filler hopper weight falling noticeably below historical norms on the same aggregate feed, suggesting internal bypass
• Physical inspection revealing brittle, discoloured, torn fabric, or deformed top-collar wire on bags removed during routine access