Grinding Booth Dust Extraction
Grinding booth dust extraction exists because the part will not fit on a bench. Once the work is bigger than a downdraft grille, the extraction has to enclose the operator and take the dust at the working face — and that changes the airflow, the media and the dust handling.
4 mg/m³
respirable limit for ferrous foundry particulate that a booth has to hold
< 50% removed
of respirable particles taken out of recirculated air on a downdraft bench study
20,000 m³/h
top of the air volume range for walk-in booth duty
When the part is bigger than the bench
A downdraft table assumes you can hold the work over the grille. The moment the casting is two metres long and a tonne and a half, that assumption is gone — and so is most of the capture.
The failure is geometric, not mechanical. Dust is generated at the contact point and travels outward and down; a downdraft grille only captures what arrives above it. When the part is large, the operator grinds at the far end of it, two metres from the grille, and the dust from that end never gets there. This is documented rather than theoretical: in a study of casting cleaning, the existing downdraft benches failed precisely because the size of the casting kept the work too far from the grates for efficient capture.
The answer is to change what is enclosed. Instead of putting the work over the extraction, put the operator in a booth where the air moves across the working face from every position he can stand in. A walk-in booth with backdraft or downdraft extraction, sized for the largest part that will ever go in it, keeps capture independent of where the grinding happens to be happening.
Why downdraft stops working on large castings
< 50% removed
Measured recirculated air from downdraft grinding benches removed less than half of the respirable particles from the airstream — so a bench that looks like it is working can still be putting the fine fraction back into the shop.[1]
1 in 3 over
Around a third of personal samples exceeded the recommended exposure limit for crystalline silica in hand grinding of steel castings; the largest wheels were identified as the major dust source.[1]
45 mg/m³
Measured exposure in a foundry grinding area where extraction was already fitted — against a respirable limit of 4 mg/m³. Booth duty is the case where extraction alone is not always the whole answer.[2]
10 → 20 ×10³
Air volume across the two walk-in booth units in this range, 5,000–10,000 m³/h (FDDM-100X) and 10,000–20,000 m³/h (FDDM-120X), sized from the booth face area and the operation rather than from the part count.[3]
Full sources are listed under References at the end of this page.
Enclose the operator, not the part
A grinding booth is an airflow design before it is a filter choice. The extraction has to hold a velocity across the whole working face, from the floor to head height, so that dust generated anywhere inside the booth moves away from the operator rather than across him.
Backdraft for standing work, downdraft for the deck
Most large-part booths use backdraft — a plenum along the back wall or under a raised deck, pulling across the working face — because the part can stand, hang or sit on trestles. FDDM-100X at 5,000–10,000 m³/h with 80 m² of media and FDDM-120X at 10,000–20,000 m³/h with 100 m² are the walk-in booth units; FDDM-36H and FDDM-50P cover the smaller booth and two-position cases. Both booth units use rotary-wing reverse-pulse cleaning on 0.5–0.6 MPa compressed air, which is what keeps a booth working through a shift of heavy grinding without a filter change.
Plan the dust, not just the air
Large-part grinding produces kilos of material, not grams, and most of it is coarse enough to settle. The booth design therefore has to decide what happens to it: a drop-out or pre-separation section ahead of the cartridge, a bin that can be emptied with a forklift rather than by hand, and ducting sized so that heavy particles do not settle and block the run. Where the material is aluminium or magnesium, the collector has to be explosion-protected and the design changes again — see the aluminium dust page.
Booth and large-part grinding units
Four units cover booth and large-part finishing duty from a small booth to a walk-in cell with 20,000 m³/h of airflow. All of them filter to 0.3 µm.
What a grinding booth includes
- Booth extraction — backdraft plenum, downdraft deck or a combination — sized so the face velocity holds from floor to head height
- Pre-separation or drop-out section ahead of the cartridge for the coarse fraction, and a bin that can be emptied mechanically
- Rotary-wing reverse-pulse cleaning on 0.5–0.6 MPa compressed air, with the air preparation included
- Commissioning with face velocity measured across the booth opening at several heights and positions, recorded so the figures can be re-checked at the next examination
Send the largest part envelope, the door size you can live with, the operation and the material. Booths are usually constrained by the opening, not by the airflow, so the envelope comes first.
Large parts this suits
Aerospace component finishing, rail and rolling stock refurbishment, wind energy component manufacture, large fabrication and weld dressing, foundry casting cleaning, composites and GRP finishing, and repair shops working on parts that cannot be lifted onto a bench. Materials include steel, stainless, cast iron, aluminium and composites. Two material cases leave this page: aluminium and magnesium dust in explosive concentrations, and any work that generates crystalline silica from castings or stone — both need their own design.
In the booth
Questions from fettling and finishing shops
Send us the part envelope and the operation
Send us the largest part envelope, the door size, the operation, the material and the hours per shift. We will come back with the booth airflow, the extraction arrangement and the dust handling, and flag it if the material changes the collector specification.
References
- O’Brien D, Froehlich PA, Gressel MG, Hall RM, Clark NJ, Bost P, Fischbach T. Silica exposure in hand grinding steel castings. Am Ind Hyg Assoc J 1992;53(1):42–48. — downdraft bench performance on large castings, and measurement of recirculated air.
- Health and Safety Executive (UK). Respiratory protective equipment at work: a practical guide. HSG53 — worked example: foundry grinding area, respirable limit for ferrous foundry particulate and measured exposure. hse.gov.uk
- Health and Safety Executive (UK). Controlling airborne contaminants at work: a guide to local exhaust ventilation. HSG258, 3rd ed. — Table 9 capture velocities for welding fume, and the commissioning checks for a moveable extraction arm. hse.gov.uk
- Determination and prediction of respirable dust and crystalline-free silica in the Taiwanese foundry industry. Int J Environ Res Public Health 2018;15(10):2105. doi:10.3390/ijerph15102105