A powder dusts because of its fines - the smallest particles, which lift into the air whenever the powder is poured, dumped, conveyed or blended. There are three ways to stop it: contain the dust, remove the fines, or hold the fines down by coating them or binding them into larger granules or pellets. The right choice depends on how much dust you have, whether you can add anything to the product, and what the material has to do next.
Why does a powder dust?
Powder dust is made of fine particles light enough to stay in the air once disturbed. Finer particles and rougher handling, like a long drop or a bag dump, mean more dust. Weak particles that break apart in handling make new fines, so dust can get worse between the plant and the customer.
Researchers describe respirable dustiness as "the tendency of a powder to generate respirable airborne dust during handling" (Ellickson, Kang and O'Shaughnessy, Journal of Occupational and Environmental Hygiene, 2012). It's a property of both the material and how it's handled. The same powder can be fine in a closed system and a problem at an open bag station. One patent on anti-dust coatings notes that fine particles "remain suspended in the air for extended periods of time" (US 8,163,059), which is why dust ends up on surfaces well away from the transfer point.
Why is dust worth fixing?
Dust costs product, housekeeping time and operator exposure, and it makes powders harder to dose accurately. For organic and plastic materials it can also be a combustible dust hazard. Fixing it at the source usually helps every downstream step, from packing to the customer's feeder.
A few specifics worth knowing:
- OSHA lists sugar, flour and plastic dust among the materials that can form combustible dust, and notes that "the ease of ignition and the severity of a combustible dust explosion are typically influenced by particle size" (OSHA, Combustible Dust: An Explosion Hazard). OSHA also calls for a routine housekeeping program so settled dust doesn't build up.
- In plastics additives, powder forms "can be difficult in terms of handling and feeding" and "can pose a potential health, fire, and explosion risk" (US 2010/0152341).
- Additive producers sell pelletized one-packs partly for "improving dosing accuracy, minimizing dust" (Songwon one-pack technical sheet).
What are the options for reducing powder dust?
The options for reducing powder dust fall into three groups: controls that capture dust without touching the material, treatments that remove or hold down the fines, and changes to the physical form so there are far fewer fines to begin with. Many plants use more than one.
| Option | How it works | Adds anything? | Changes the form? | Best when | Watch out for |
|---|---|---|---|---|---|
| Dust collection, enclosed transfer, lower drop heights | Captures or contains dust at the source | No | No | Dust is moderate and limited to a few transfer points | Dust is still made at every transfer, including at your customer's plant |
| Screening out fines | Removes the finest fraction on a screener | No | Slightly coarser powder | Fines are a small share of the material | Lost yield, unless the fines are reprocessed |
| Anti-dust oils and coatings | Liquid sprayed on to make fines stick to larger particles | Yes | No | Bulk products where an additive is acceptable | Foreign substance in the product, and the coating can wear off |
| Roll compaction (dry granulation) | Pressure bonds powder into a sheet, then it's milled and screened into granules | No | Granules in a target size range | The product can't carry a binder or additive, or needs to flow better too | Fines from milling must be screened off, and weak granules can break down |
| Pelletizing on a pellet mill | Powder is pressed through a die into dense pellets | No | Pellets, 2.5-5.0 mm at D&A | The user wants a uniform, dense form, such as feeding an extruder | Too coarse for some uses, and heat-sensitive materials need cooling |
| Melt forms (pastilles, flakes) | Molten material solidified on a cooled belt | No | Pastilles or flakes | The material melts cleanly without degrading | Only works for meltable materials |
One other route is wet granulation or agglomeration with a liquid binder, which we don't run at D&A. It works well for the right product, but it adds something to it.
When is screening out fines enough?
Screening out fines is enough when the dust comes from a small fine fraction and the rest of the powder handles well. The screener removes the particles that cause most of the dust, and nothing is added to the product. The catch is yield: whatever passes the bottom screen is no longer sellable as that grade.
Screening works best as a first test. If a quick screen at your target cut leaves a powder that handles cleanly and the fines are a small share, you may not need anything more. If the fines are a large share, or the product breaks down and makes new fines in transit, screening alone usually won't hold. The fines can often be granulated and returned as usable product, which is where screening and compaction work together. Our screening runs on Sweco and Kason screeners, with batches starting at around 500 lbs.
What about anti-dust oils and additives?
Anti-dust oils and coatings work by wetting the surface of the particles so fines stick to larger particles instead of lifting into the air. One patent describes coating granular fertilizer with natural or petroleum oils or waxes as "a historically established method for controlling dust and caking phenomena" (US 8,163,059).
The trade-offs are that you've added something to the product, and the coating has to survive handling. Another patent on conditioning agents found that when coated particles were blended with other solids, the hard particles were "damaging the coating layer, leading to an increased dust formation" (EP 3960724). For a bulk commodity an oil can be the cheapest answer. For a food ingredient, a nutritional ingredient or a polymer additive with a purity spec, adding an oil is often not acceptable.
How does granulating by roll compaction stop dust?
Roll compaction stops dust by binding fine particles into larger, denser granules using pressure alone. The powder is fed between two counter-rotating rolls, pressed into a dense sheet, then milled and screened to the target size. Nothing is added, so the granules are the same material as the powder, just in a form with far fewer fines.
That makes roll compaction a good fit for products that can't carry an additive: food and nutritional ingredients, plastics additives and specialty chemicals with tight purity specs. Flow and bulk density often improve at the same time, since the fines that dust are usually the same ones that bridge in hoppers and make a powder fluffy. A review in Pharmaceutical Technology notes that dry granulation methods are "especially suitable for moisture- and/or heat-sensitive compounds because no liquid or drying steps are required" (Jeon, PharmTech).
The main limitation is fines. The same review notes that "high amounts of fines remain" compared with wet granulation. In practice the fines are screened out after milling and fed back to the compactor, so the finished product can be cut clean. There's more detail in our comparison of roll compaction vs. wet granulation, and on our toll granulation page.
When are pellets the better choice?
Pellets are the better choice when the user wants a larger, dense form that pours and meters consistently, as with plastics additives fed to an extruder. A pellet mill presses powder through holes in a die, so pellets come out at a uniform diameter. At D&A that's a 100 HP California Pellet Mill making 2.5 to 5.0 mm pellets.
Pelletized one-packs are an established form in plastics. Songwon describes additives "integrated in a dust-free, pelletized form" with "improved feeding, handling and storage" (Songwon). Pellets that aren't hard enough will still wear down in transit, though. One patent application on additive pellets points out that pellets "with undesirable high attrition arrive at the user's facility with significant level of fine powder" (US 2010/0152341). A trial should check how pellets hold up in handling as well as how they look coming off the die.
Pelletizing also generates heat. For low-melting additives, we inject liquid nitrogen to keep temperatures down. See our pelletizing and plastics additives pages.
What about pastilles, flakes and other melt forms?
Pastilles and flakes are made by melting the material and solidifying it on a cooled belt, so they suit materials that melt cleanly, such as resins and waxes. One trade article describes pastilles as "dimensionally stable and practically dust-free" (Process Worldwide).
The limit is the material. Anything that decomposes, reacts or changes when melted isn't a candidate, and many mineral salts, food ingredients and high-melting chemicals fall in that group. For those, a dry route like compaction or pelletizing is usually the practical option. We don't make pastilles at D&A.
How do I choose the right option for my powder?
The right option depends on four questions: where the dust appears, whether anything can be added to the product, what the material does next, and whether it can be melted. Answer those and the field usually narrows to one or two options worth trialing.
- Where does the dust show up? If it's at one or two transfer points in your own plant, better collection may be enough. If customers complain, the material itself usually has to change.
- Can you add anything? If a label, purity spec or customer approval rules out an oil or binder, the choice is between screening and a dry form change.
- What happens next? A product that's blended with other granules, fed to an extruder, filled into capsules or dissolved in a tank each points to a different size range. Granules suit blending and filling. Pellets suit extruder feeding.
- Does it melt cleanly? If it does, melt forms are worth comparing. If it doesn't, compaction or pelletizing is the likely route.
Whatever you choose, define dust-free in numbers. A limit on the percentage passing a fine mesh is far easier to hit and check than "low dust".
What should I send for a trial?
For a trial, send the powder with its SDS, the size range you want, a limit on fines if you have one, and a short note on how the product is used next. Those four things decide whether roll compaction, pelletizing or screening fits, and how the run should be set up.
At D&A, granulation and pelletizing batches start at around 750 lbs, and trials usually run a day or two after the material arrives. We check particle size distribution against your spec and run dust collection during processing. Three of our seven processing rooms are dedicated to food and nutritional work, separate from the chemical rooms - see food ingredients.
If you have a powder that dusts, send us the details and we'll suggest where to start.
Frequently asked questions
Can a powder be made less dusty without changing its particle size?
Only up to a point. Dust collection and enclosed transfers reduce what reaches the air, and an anti-dust oil can hold fines down, but the fines are still there. Removing or binding the fines means changing the particle size distribution.
Does roll compaction add anything to the powder?
No. Roll compaction bonds particles with pressure only, with no water, solvent or binder. Compaction does generate some heat, so for low-melting materials we use liquid nitrogen injection to keep temperatures down.
Will granules dissolve or disperse differently from the powder?
They can. Larger, denser particles may wet, disperse or dissolve at a different rate than the original powder, so check the granules in your own process during the trial.
What happens to the fines screened out after granulating?
They are normally fed back to the compactor rather than thrown away. How many passes it takes depends on how well the material compacts.
Do you handle dusty food and nutritional ingredients?
Yes. Three of our seven processing rooms are dedicated to food and nutritional work, in an FDA registered, ISO 9001:2015 certified facility. Granulating by roll compaction or pelletizing is a dry process, so nothing is added to the ingredient to bind it.