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Wet Machining

Mist collection helps maintain a better work environment and reduces maintenance in a manufacturing facility.

Why the Need for Mist Collection

Coolant mists, including water soluble or oil, when used in manufacturing processes often create droplets that can collect on surrounding surfaces. Mist collectors, when properly selected and applied, help reduce this situation, maintaining a cleaner work environment and reducing maintenance on process machinery as outlined in Donaldson’s Filtration Technology for Mist Industries. Workers do not have nuisance coolants, oils or lubricant mists in their work environment.

Many large facilities reclaim their coolant for re-use. Small machine mounted mist collectors can mount directly into equipment and drain the coolant back into the process minimizing consumption of metalworking fluids, achieving cost savings.

Mist Collection for Metalworking Brochure >>

Mist Generation

The industry’s need for more machined parts with extremely tight tolerances has led the metalworking industry to require faster production machines leading to increases in the amount of coolants, oils, and lubricants used and higher delivery pressures for those coolants plus increases in tool speeds. All these factors affect the size and amount of mist generated and the mist collector needed since they can contribute to the characteristics of the mist generated in the process. Typical metalworking operations vary in how the mist is formed, how much of a mist is generated, and size of the mist droplets needing to be captured. Some more typical metalworking operations with droplet sizes are as follows:

Mist Droplet Size

  Water-Soluble Oil Smoke Particulate / Fume
Milling 2-20 microns 0.5-10 microns .07-1 microns N/A
Turning 2-20 microns 0.5-10 microns .07-1 microns N/A
Grinding 2-20 microns      
Metal Forming:
- Die Casting*
- Heading / Stamping
2-50 microns

1-2 microns

0.7-1 microns

< 1 micron
Drawing* 1-20 microns 0.5-2 microns .07-1 microns  
Parts Washing** Up to 10 microns      
Heat Treating 0.8-5 microns 0.8-5 microns .07-1 microns 0.5-2 microns

*Caution: Waxes may be present
**Mist may contain water, water vapor and rust inhibitors

Beyond the typical operations noted above are operations such as EDM machines, lube oil reservoirs and plastic molding/extruding machines, which also produce mists. With over 40 years of experience, Donaldson Torit® can provide collectors and guidance in collector selection. Refer to Donaldson’s Technical Reference Guide on Mist Collection of Metalworking Fluids for in depth discussion on mist collection for these operations.

Donaldson offers a full line of mist collectors from a single source machine mounted unit, all the way to a central mist collector. Donaldson Torit’s WSO Mist Collector with its unique Synteq™ XP filter media is an extremely versatile collector for all operations. It can provide a solution for water-soluble coolants, straight oils, or operations that have oily smoke. If your machining operations change, the only modification is a filter change.

In addition to the WSO, you can apply the Dryflo® (MMA, MMB) Mist Collector and Centrifugal Mist Collector as single source machine mounted collectors. Single source collectors offers a production facility a compact solution. Donaldson’s Mini-Mist and Modular MediaFilter™ provide excellent solutions for operations where mist and particulate fume are generated in a process, and for general plant ventilation the horizontal Modular MediaFilter is an option.

Special Considerations

Some coolants can be corrosive to sealing materials and gasket material. Provide proper coolant data to your mist collector supplier to minimize any risk of coolant/oil not being compatible with the sealing and gasket materials used in the mist collector to avoid leaks.

The design and components of any duct system must take into account the amount of coolant or lubricant that may collect in the ducts prior to the mist collector. Sloping the ducts, and provide a means for coalesced coolants to exit the duct are just a couple of examples of actions to consider.

Mist collection hoods at the machine take-offs should be designed and located to limit mist collected to only airborne mist. Avoid directing excess coolant into a hood.

In order for a mist collector to properly function, always ensure a proper trap or storage device is used so collected coolant or lubricant can drain from the collector.

A monitoring HEPA or 95% DOP filter option is available. These after-filters commonly provide an indication of performance for the primary filter. These filters may also minimize the discharge of particulate smoke generated by metalworking operation.

Products for Wet Machining

Mist Collectors

We developed a broad range of smoke collectors, mist collectors, and mist filters that remove submicronic contaminants from the plant atmosphere.


The WSO mist collector filters three types of mist (water, smoke, oil) in one collector - simply by changing the mist filter.


The Dryflo® mist collector is a low profile, machine-mountable, high-efficiency mist filtration solution for wet machining with oil-based, synthetic, semi-synthetic, and water-soluble coolants.

Modular MediaFilter™ Vertical

Collects and filters mist, smoke, dust, fumes, vapors and odors from applications such as grinding, wet machining, rubber machining, die casting, wet grinding or soldering. 


A compact, direct machine-mountable mist collector designed to collect, filter, and reclaim mist generated from machines using oil-based, synthetic, semi-synthetic, or water-soluble coolants.

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