Make Parts, Not Health Problems

Oil particles within the range of 0.3 to 3.5 microns need to be removed from shop air, preferably at the source. Photo courtesy of Filtermist Intl.

Coolants and lubricants are a necessary part of nearly every machining operation. However, as spindles, turrets, rotary tables, and tooling spin, these liquids become airborne and can leave the machining envelope. The high heat produced by the machining operation also affects water-based emulsions when they reach the boiling point and enter the air.

High-speed CNC machines that run for long hours can create large amounts of oil mist and vapor.

This situation results in hazardous substances entering the workplace. Depending on the type and amount of coolant or oil used, employees can be exposed to chemicals that are carcinogenic. Skin rashes, eye problems, and respiratory illnesses also are possible.

Reducing the volume of airborne pollutants is key to keeping a shop’s workforce healthy and reducing downtime.

During the machining process, cooling metalworking fluid can generate fume, steam, and aerosol, all of which are forms of oil mist. When the level of this mist in air is more than 5 mg/m3, the shop is no longer compliant with most jurisdictions’ allowable levels.

“A cleaner working environment is now mandatory under legislation in many countries to protect personnel from the health and safety risks associated with oil mist,” explained Filtermist Intl. Managing Director James Stansfield. “Primary concern is directed at respiratory problems caused by the retention of oil particles within the range of 0.3 to 3.5 microns. Above 3.5 micron, the particles are usually blocked by the body’s natural filters, for example nasal hairs, and below 0.3 micron the particles are usually exhaled.”

Oil Mist: The Source

“There are two types of fluids used in a machining operation that create mist,” explained John Dauber, Handte product manager – Americas for Camfil Air Pollution Control (APC). “Mist either comes from coolant, which is roughly 90 percent water and 10 percent oil, or from straight oil, which is used as more of a lubricant than a coolant.”

Both the coolant emulsion and the straight oil create mists that are hazardous.

“If you go into a manufacturing plant, it’s very easy to tell if they have too much mist in the air,” said Dauber. “You typically see a haze in the shop and can taste and smell the oil in the air. Floors can even be slick with it. If that’s the case, you are likely over the standard.”

Keeping this oil mist out of the air is a key concern to shop owners.

The Handte EM Profi emulsion mist collector from Camfil APC helps reduce downtime with long change-out cycles. Photo courtesy of Camfil APC.

“You want to leave the oil and the chips in the machine but also have enough airflow that a small vacuum is created,” said Dauber. “If your collection point is too close to the tool, you may also pull a lot of oil unnecessarily into the collector. Understanding airflow and how much you should have is as important as the collector itself.”

There are a few ways to filter oil mist:

1. Cartridge-based mist collector. Also called media filter mist collectors, these units use high-efficiency particulate air (HEPA-) type filters to screen oil mist by forcing contaminated air through the cartridge media, where the droplets, mist, and contaminant particles are trapped.

   Cartridge mist collectors do tend to become clogged over time, reducing airflow. The filters also need to be replaced frequently.

2. Centrifugal mist collector. These machines work by rotating the filter, which forms oil mist into large droplets that fly outward through centrifugal force to the walls of the unit before falling into a drain. Fresh air is returned to the shop, and the oil is collected for filtering and reuse or disposed of.

   These units sometimes have difficulty collecting small droplets and require frequent cleaning to remove accumulation from the impeller.

3. Electrostatic precipitator mist collector. These machines use electric charges to gather small mist particles and droplets. This method of filtration can eliminate even submicron contaminants. Electrostatic precipitator mist collectors are suitable for petroleum-based cutting oils, mist, and even smoke.

More Than Air Changing

Most modern manufacturing systems have enclosed work envelopes, which helps contain oil mist and prevents it from going directly out into the shop’s air. The key is to have enough airflow to pull out the oil mist and leave the oil and chips inside the machine.

“Oil mist often escapes the machine when the door is opened to remove parts or load raw materials,” said Dauber. “If a machine runs 24/7 with the use of automation, those doors can open and close a lot. Those are all opportunities for oil mist to enter the shop air.”

Typically, shops use a chevron-style filter/fiberglass V-bag filter for filtering both neat oils and emulsions.

“The downside of V-bags is that they must be taken offline, drained, and cleaned without any air running through them,” said Dauber.

Some companies produce separate technologies for emulsions and straight oil fluids.

“The particle size in straight oil is much smaller—even submicron— which is the hardest application for these systems,” said Dauber. “That’s why having two filters, one for emulsions and one for straight oils, is a good idea. Shops should look for systems that can be loaded with both types of filter at the same time.”

Dauber advises testing the air to show what the mist level is and, if it’s above the 5 mg/m3 threshold, add a system that can capture mist at the source. Even after installation, an air quality test should be routinely scheduled.

“Ambient capture works well during welding operations because the smoke will rise to the ceiling and a ceiling-mounted hood can be used to capture it,” said Dauber. “But oil does not act that way …. it gets in everywhere. I have even seen motors that have shorted out because oil has gotten inside them.”

Keeping oil in the machine by containing it before it gets out into the plant is always the best choice. However, difficulties can arise with older machines that have no enclosures or have only partial enclosures or missing seals.

“Apart from the direct hazards to humans, slippery walkways caused by oil deposits can cause accidents. Also, an oil coating on the fabric of a building and on the equipment within it creates a natural fire path,” said Stansfield.

Choosing a System

Three goals of an oil mist filtering system are:

1. Employee health.
2. Equipment efficiency.
3. Reduced downtime for maintenance.

“Extraction units are chosen by application— machining, welding, dust control— and then by size,” explained Stansfield. “For instance, if extracting from an enclosed machine tool, we would normally recommend a unit that can change the air volume at least six times per minute.”

Removing contaminants from the oil before returning it to the machine is also important.

“We recommend that any oil collected by the extraction units is returned to a collection vessel, which can then be treated accordingly. If the contaminants are returned to the machine, there is a risk they will recycle through the machining process,” said Stansfield.

No matter the type of manufacturing process being performed, Dauber’s advice is simple: Always examine total cost of ownership, including downtime. It’s also a good idea to look for a system that can run 24/7.

“When shops spend a lot of money on a machining center, for example, they don’t want the machine sitting there for 30 minutes while the filter drains down and can be cleaned. Downtime costs a lot of money. That’s what we want to avoid. We’ve found that shops don’t want to deal with maintaining their filters and collectors when they should be making parts,” said Dauber.

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