The Value of Open Pleats in Cartridge Filters for Dust Collection

Indoor air quality (IAQ) is an increasingly important issue in metalworking plants. From a workforce standpoint, keeping airborne particulates and pollutants at low levels is crucial for keeping employees healthy and productive. And from an operational standpoint, IAQ improvement efforts can help reduce energy, operating, and maintenance costs, plus help plants avoid fines by the Occupational Safety and Health Administration (OSHA).

Various metalworking operations generate dangerous pollutants that can pose serious health threats to workers. Most of these dangerous pollutants are found in weld smoke and fume or in particles generated during plasma and laser cutting.

In welding, 85 percent of fumes generated comes from the electrode. A good rule of thumb is, for every 1,000 pounds of weld wire used, 10-20 pounds of particles can be generated. During welding, about one to two percent of the weld-join metal in carbon steel converts to collectable particulate, which ranges in size from 0.1 to 5.0 microns. For welding aluminum, that figure is six to eight percent.

Laser and plasma cutting are the largest producers of pollution in many facilities, generating airborne carbon, metal oxide dust and other smokes, fumes and contaminants that are potentially hazardous to the health of the workforce. It is not uncommon for thermal cutting operations to generate 55 gallons of submicron-sized aluminum particles and other dangerous airborne contaminants in a single day.

Fortunately, with the proper air filtration systems, plants can significantly reduce or even eliminate dangerous airborne smoke, fumes and particles from the breathing air, helping to improve worker safety and reduce operating costs.

Effects of Airborne Pollutants

According to OSHA, acute exposure to metalworking fume can result in eye, nose and throat irritation, dizziness, and nausea. Prolonged exposure to metalworking fume may cause lung damage and various types of cancer, including lung, larynx and urinary tract. Health effects from certain fumes may include metal fume fever, stomach ulcers, kidney damage and nervous system damage. Gases such as helium, argon and carbon dioxide displace oxygen in the air and can lead to suffocation, particularly when welding in confined spaces. Carbon monoxide gas can also form, posing a serious asphyxiation hazard.

Several airborne hazards common to metalworking operations are of specific concern:

• Aluminum dust may create a problem when mixed with steel dust. The steel dust can act as an ignition for the aluminum dust and trigger an explosion.

• Hexavalent chromium, or Cr(VI), is formed during the welding process from the chromium component found in welding consumables. It is also found in stainless steel materials and can be generated from heat associated with cutting or welding operations. The fume is highly toxic and can damage the eyes, skin, nose throat, and lungs, as well as cause cancer.

• Manganese is a trace element found in virtually all types of welding. It can cause a condition called mangansim, which is similar to Parkinson's disease. In extreme cases, overexposure to manganese fumes can affect the central nervous system and change neuropsychological and neurobehavioral function.

Standard Air Filtration Options

Anyone who has walked into a metalworking facility and seen a blue haze around the lights knows that acceptable IAQ is not always a given. It requires special attention to the plant's ventilation and air filtration system.

For years, metalworking plants with reverse pulse dust collectors have used cartridge filters constructed with either a straight pleats or a dimpled pleat. These pleat designs allow the filter maker to squeeze more square footage of media in the cartridge. However, the cellulose-based media used is often on the lower end of the scale when it comes to price, strength and MERV rating, so durability, filtration effectiveness and long life may be compromised.

Another downside of traditional filter designs is that pleats are placed close together (typically about 8 pleats per inch of end cap) to provide support to the structure. One disadvantage to this tight pleat spacing is that dust can “bridge” across the pleats, leaving a large portion of the “valley” of the pleat unused. As seen in the photo, the clean area visible on the inside of these pleats indicates that the dirty air never reached this media, resulting in less effective loading and ineffective pulse cleaning. This bridging, plus the fact that the pleats are often pinched closed, does not allow for the total surface area of the pleat to be used for filtration. As a result, this type of filter has a shorter filter life.

A Better Air Filtration Option

Today, metalworking shops can take advantage of a new type of cartridge filter with reconfigured pleats and a media support structure, which when combined, provide for the highest filtration efficiency at the smallest particle size, superior particulate release during cleaning, and a significant reduction in static pressure.

Unlike with traditional cartridge filters, those with an open pleat spacing (as found in the Endurex RMO filters from RoboVent) ensure that all filter media is used, which results in an average 30 percent or more longer filter life than traditional filters. Longer filter life means fewer filter change outs, which saves money by reducing filter replacement costs and reduces environmental impact with less product ending up in landfills.

These open pleat filters are engineered with the following features that allow them to maximize efficiency while reducing static pressure for lower energy consumption and operating costs:

• Wide pleat spacing (five pleats per inch of end cap) maximizes surface area of media available to dust and fume particles.
• MERV 11-16 filtration efficiencies, with 99.99% particle capture down to 0.5 micron.
• Single piece gasket with no joints, made of pliable, non-forming polypropylene provides a perfect air-tight seal.
• Fast-curing urethane seal adheres to pan and media quickly and firmly.
• Internal metal spiral core prevents filter collapse.
• Cutting-edge pleating technology ensures proper calibration of the pleats and eliminates deformed or worn areas that compromise the integrity of the media.
• A fabric band provides structural support instead of an exterior metal cage, allowing for better pulse cleaning of the filter with no blowouts.

The open pleats in these high performance Endurex filters are strengthened with a proprietary media support structure called Reinforced Media Optimization (RMO). As shown in the photo, RMO support keeps filter pleats at optimum spacing, allowing for maximum loading on the media under pressure and more effective pulse cleaning without deforming or blowing out. The RMO support ribs (shown in blue) are continuous for the full length of the pleats, ensuring no pleat collapse. Multiple RMO structures ensure the media surface is maximized throughout the whole filter. With this design, it's no longer about media quantity, it's about media optimization.

However, keep in mind that the open pleat style filter does not work as well with oil mists as it does with dry particulate, unless a special-coated media fiber is used to allow sticky particulates to be removed during cleaning.

Other Considerations

In addition to the pleat style, a filter's orientation can impact its filtration efficiency and lifetime. Vertical filters allow collected dust and debris to shed off the filter and fall directly down into the containment or collection tray (in the direction of the ventilation system's airflow) when the filters are pulse-cleaned. With horizontal filters, dirt and debris tend to fall off only the bottom two-thirds of the filter, rendering the top of the filter ineffective as it becomes clogged with debris. This results in a 30-40 percent loss in filter area and a substantial reduction in filter life.

Be sure to consider the filter's lifecycle costs during the selection process. Filter life span, filtration efficiency, cleanability and operating costs are important factors to consider, and all of these impact the total cost of ownership. When metalworking plants evaluate lifetime costs, the advantages of open pleat filters with Reinforced Media Optimization become clear.