Toilet Roll Log Saw Dust Hood Design Guide 2026
Expected Publish URL: toilet-roll-log-saw-dust-hood-design-guide-2026
The Housekeeping Bill That Kept Coming Back
Ingrid Halvorsen, plant engineer at a toilet roll mill outside Gothenburg, watched the same cost line climb for three quarters. Her line was fine; her housekeeping was not. Two operators spent most of the second shift sweeping fine white fiber dust off the mezzanine around the log saw, and the mill was still failing its own internal housekeeping audit twice a month. Ingrid first tried a bigger general ventilation fan, then a portable vacuum station, then a shift rotation that simply moved the problem to a different pair of operators. The turn came when the maintenance lead traced the dust back upstream and found that the existing hood over the log saw discharge had been sized for chip removal, not for the airborne fines a rotary log saw actually throws. A re-designed hood with the right capture velocity pulled housekeeping labor down by roughly a third within six weeks. This guide covers how to design a log saw dust hood that does that.
A toilet roll log saw throws a mix of coarse trim chips and very fine airborne fiber, and a hood sized for chips will miss the fines entirely. Design the hood to capture the fine fraction at the generation point: hold capture velocity at the hood face at 1.0-1.5 m/s, keep the transport duct above 18 m/s so fines do not settle, use a tapering side-entry hood rather than a simple canopy, and pair a cartridge or baghouse collector with a rotary airlock. The blade condition matters as much as the hood: a dull log saw blade shears fiber instead of cutting it and can increase the fine dust load by 30-50%. Get hood geometry, duct velocity, and blade maintenance right together, and housekeeping labor typically drops by a quarter to a third.
Why Log Saw Dust Is Not Trim Dust
Trim dust from a separating or perforating station is relatively heavy and short-lived; log saw dust is finer, more airborne, and stays suspended far longer. That distinction is the reason a hood copied from a trim station under-performs on a log saw. The saw blade enters a compressed log at high surface speed, and the material removed at the kerf is a mix of chips, fiber bundles, and single fibers. The chips fall; the single fibers follow the local air currents around the spinning blade and the log rotation.
Airborne fiber generated at a log saw kerf can represent between 0.5% and 1.5% of the paper cut on that line, and unlike trim chips it stays suspended long enough to migrate 10-20 m from the saw before settling, which is why canopy hoods without strong local capture leave the surrounding mezzanine fouled.
The upstream reel and winder behavior that determines how much dust the log saw will see is covered in our [tissue paper machine guide](https://yoco-group.com/blog/tissue-paper-machine-guide-2026).
Hood Geometry and Capture Velocity
A log saw hood has two jobs: enclose the kerf so that fiber cannot escape laterally, and accelerate the captured air to a velocity that beats the blade-induced turbulence. A canopy over the top of the saw does neither. The hood that works is a tapered side-entry design, sometimes called a slot or plenum hood, that presents a narrow high-velocity slot close to the kerf and expands into a larger plenum behind it.
| Hood parameter | Poor value | Design target | Consequence if ignored |
|---|---|---|---|
| Capture velocity at hood face | 0.4 m/s | 1.0-1.5 m/s | Fines escape the hood |
| Slot standoff from kerf | 300 mm | 80-150 mm | Capture falls with distance squared |
| Hood entry taper | abrupt | 15-20 degrees | Turbulence, re-entrainment |
| Transport duct velocity | 14 m/s | 18-22 m/s | Fiber settles in the duct |
| Make-up air opening | blocked | matched to exhaust | Starved hood, weak capture |
| Duct length per branch | 20 m+ | under 12 m | Pressure loss, imbalance |
The standoff distance is the parameter that cables are usually run past. Capture velocity falls roughly with the square of the distance from the hood face, so doubling the standoff can cut capture efficiency to a quarter. Hold the slot within 150 mm of the kerf and make the opening as long as the log travel.
Duct, Collector, and Air Movement
Once the hood captures the fines, the duct has to keep them moving. Hold 18-22 m/s in horizontal runs, use 30-45 degree branch takeoffs rather than 90 degree tees, and put a manual blast gate plus a pressure tap on every branch so the system can be balanced in the field. For the collector, a cartridge unit with a 0.5-1 micron rated media is appropriate for most single log saw lines; a pulse-jet baghouse with antistatic bags is the safer choice where multiple saws feed one collector and the dust load is high.
National occupational safety agencies classify cellulose and paper dust as a combustible dust when dispersed, and the U.S. OSHA guidance on combustible dust treats accumulations above roughly 1/32 inch (0.8 mm) over 5% of a room's floor area as a housekeeping action trigger, which is why log saw dust control is a safety obligation and not only a housekeeping cost.
Guard the collector inlet with spark detection and extinguishing, and discharge collected dust through a rotary airlock, not a slide gate, so that the hopper never dumps a suspended cloud.
Blade Condition and Fine Dust Load
The cheapest way to reduce log saw dust is often the cheapest maintenance item on the line: the blade. A sharp blade cuts the fiber cleanly and produces chips; a dull blade shears and crushes, generating additional fines that no hood can fully compensate for. Track two indicators - the operator's report of cut quality (tearing, dust puffing at the kerf) and a fixed-number count of blade sharpening cycles - and replace or sharpen on cycle rather than on failure. This blade-to-hood interaction follows the same cost logic we apply in our [paper machinery maintenance guide](https://yoco-group.com/blog/paper-machinery-maintenance-guide-2026).
ISO 12100 requires that rotating saw blades and their drive zones be guarded so that operators cannot reach the cutting zone during normal production, and any hood re-design must preserve that guarding function rather than trading safety for dust capture.
Commissioning and Ongoing Verification
Test the hood before you trust it. Run a smoke test at the hood slot, take a pitot-tube traverse at each branch, and record the collector differential pressure in both a clean and a loaded state.
| Test | Acceptance criterion | Frequency |
|---|---|---|
| Slot capture smoke test | Full capture within 150 mm | At commissioning |
| Branch airflow | within 10% of design | At commissioning |
| Transport velocity | 18-22 m/s | At commissioning |
| Filter dP clean | below 250 Pa | At commissioning |
| Floor dust accumulation | below 0.8 mm | Daily visual |
The Bottom Line
A log saw hood fails quietly: the line keeps running, the counter keeps counting, and only the housekeeping crew and the audit score know. Fix it with geometry, not with a bigger fan. Put a tapered side-entry slot within 150 mm of the kerf, hold capture velocity at 1.0-1.5 m/s and transport at 18-22 m/s, choose media for the sub-micron cut, and keep the blade sharp so the mill is not fighting its own fines. The reward is measurable: less housekeeping labor, a lower fire risk, and a stable housekeeping audit.
FAQ
How close should a log saw dust hood sit to the blade kerf?
Keep the hood slot within about 80-150 mm of the kerf. Capture velocity falls with the square of distance, so doubling the standoff can cut capture efficiency to a quarter.
What duct velocity keeps log saw fiber from settling?
Hold 18-22 m/s in horizontal duct runs. Below 15 m/s the fine fiber settles and the system loses balance within weeks.
Can a bigger general ventilation fan replace a log saw hood?
No. General ventilation dilutes the air but does not capture fiber at the point of generation; a local hood with 1.0-1.5 m/s capture velocity is required.
Does blade condition change dust generation?
Yes. A dull blade shears rather than cuts the fiber and can raise the fine dust load by 30-50%. Sharpen or replace on a fixed cycle.
Why is log saw dust a fire concern?
Cellulose dust is combustible when dispersed. OSHA housekeeping guidance treats accumulations above about 0.8 mm over 5% of floor area as an action trigger, so capture and cleanliness are safety obligations.