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Dust Collection Equipment
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Dust Collection Equipment |
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C.C.Steven & Associates, 1363 Donlon Street Ventura, CA 93003 since 1978 |
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Lasers' Capabilities Present Many Different Air Pollution Challenges If you're like most companies who use lasers, you probably bought yours with one or two key applications in mind. The filtration system on the laser seems to adequately cover the needs for that job (usually a metal operation) and it works just fine. However, the laser performs so well, you decide to use it for other materials also. Now you start getting new airborne contaminants and the need for filtration systems becomes more complex and urgent. The combination of particulate and fumes can be harmful to operators, violate local safety codes, lead to combustion hazards, and jeopardize your considerable investment in equipment - things the laser sales people and the operating manuals usually don't mention. Laser cutting operations generate extremely fine particulate and dusts that can accumulate quickly and cause extensive damage-even optical distortion that misaligns the laser's focus. Fumes from Metal Applications Most metal operations using lasers generate primarily fume particles, and if oil is present, a secondary contaminant of smoke. Molten metals combine with oxygen and condense into a small, dry particulate typically 0.5 microns or smaller in size. For example, cutting or welding common steel produces iron oxide, a particulate similar to baby powder. Plastics and Composites Applications When cut with a laser, plastics and composites give off oily fumes and smoke from the plasticizers used in manufacturing the materials. While these fumes are relatively easy to collect, the accompanying gases and vapors are much more difficult to collect because of their small size. With the enormous number of different plastic compounds available in industry, it is impossible to select a gas/vapor media that is applicable to all plastics and composites used in manufacturing today. Filter Requirements and Options No single air extraction system or filter medium will collect all gases, vapors, smoke, dust, fumes, and particulate from all laser operations. Here is an overview of the main types of systems available: Electrostatic Systems. Electrostatic precipitators are highly efficient for collecting the small submicron fume and smoke particles from many laser operations. Particles are first charged and then collected on oppositely charged collection plates. Filters are cleanable, eliminating repetitive replacement costs of disposable filters. If contaminants are oily or sticky-such as from certain composites and plastics or oil-coated metals-collection components can be washed. The main disadvantage to EPs is that they require routine service to maintain high collection efficiencies. Cleanable Mechanical Filter Systems. In both the two main types-fabric systems and rigid cartridge filters-air is drawn through mechanical filters, where suspended particles are removed from the airstream. Fabric filters are cleaned by shakers, vibrators or reverse air pulse, while cartridge filters are typically cleaned by a reverse pulse of compressed air. The main advantage of these systems is their ability to handle heavy concentrations of contaminants; the principle disadvantage is the high horsepower motors required to pull air through the filters. Disposable Mechanical Filter Systems. Generally these systems consist of one or more modular housings containing a variety of progressively higher efficiency disposable filters. In laser applications, a HEPA final filter stage is usually needed to capture the submicron particulates. These extremely flexible systems can collect both large and small contaminants efficiently, and are suitable for combustible contaminant applications. They're even adaptable to process changes by using alternate replacement filter media. The main disadvantage is higher costs for filter replacement in heavy or severe applications. Hybrid Systems. Because of the immense variety of contaminants generated by laser operations, specialized hybrid systems may be required. For example, a cartridge filter may be used for collecting particulates and a carbon module added for gas/vapor control. Or a fabric filter may be used for dry dusts and fumes, along with an electrostatic precipitator for oily contaminants. If you have a laser system installed or are contemplating purchasing one, make sure the filtration system can handle all the various contaminants generated by your operations. A good filtration system will protect your investment in the equipment and safeguard the operators from the harmful contaminants. Dangers of Lead Dust and Fumes from Soldering Operations Smoke and fumes from soldering operations may contain dangerous levels of lead, a basic chemical element which is a heavy metal at room temperature and pressure. Lead in this discussion refers to elemental lead, all inorganic lead compounds and a class of organic lead compounds called lead soaps. OSHA has established the allowable level of lead in the workplace, defined as follows: PEL (Permissible Exposure Limit) is 50 micrograms of lead per cubic meter of air (50µg/m3), averaged over an 8-hour workday. This is pro-rated downward for workers whose daily exposure extends beyond a typical 8-hour workday. For example, a worker exposed to lead for a 10-hour workday has a maximum average exposure limit of 40µg/m3. This level of exposure must be achieved through a combination of engineering, work practice and other administrative controls. Health Hazard Information When lead is absorbed into the body in certain doses, it is a toxic substance. OSHA standards are intended to protect workers from both the immediate toxic effects of lead, and also the serious effects of lead that may not become apparent until years of exposure have passed. Lead can be absorbed into the body by inhalation and ingestion, but (except for certain organic lead compounds, such as tetraethyl lead) is not absorbed through the skin. When lead is scattered in the air as dust, fume or mist, it can be inhaled and absorbed through the lungs and upper respiratory tract. According to OSHA, inhalation of airborne lead is generally the most important source of occupational lead absorption. A significant portion of the lead that is inhaled or ingested gets into the blood stream. In large enough doses, lead can kill in a matter of days, through a condition known as acute encephalopathy, which develops into seizures, coma, and cardiorespiratory arrest. Chronic overexposure to lead may result in severe damage to the blood forming, nervous, urinary and reproductive systems. Hygiene Facilities and Practices Employers must post a warning sign like the one shown here in work areas where exposure to lead exceeds the PEL. Additionally, OSHA says that employers must assure that the following hygienic practices are enforced: In areas where employees are exposed to lead above the PEL, food and beverage is not present or consumed, tobacco products are not present or used, and cosmetics are not applied, except in designated areas. Change rooms. Employers are required to provide clean change rooms equipped with separate storage facilities for protective clothing and for street clothes. Monitoring of Employees and Record Keeping Records must be kept of exposure monitoring for airborne lead, including names and job classifications of employees measured, details of sampling and analytical techniques, results of this sampling, and the type of respiratory protection worn by the person being measured. Records are to be kept for 40 years, or 20 years after employment termination, whichever is longer. Ventilation and Respirator Requirements When mechanical ventilation is used to control exposure to lead, the filtration system used must have a HEPA filter capable of trapping and retaining at least 99.97% of 0.3 micrometer (micron) diameter mono-disperse particles. Measurements such as capture velocity, duct velocity, or static pressure must be made at least every three months to demonstrate the effectiveness of the system. If air is recirculated into the workplace, the employer must assure that the system has a high efficiency filter with reliable back-up, and must also have controls installed that monitor lead concentration in the returned air, and bypass the recirculation system automatically in case of failure. Where engineering and work practice controls do not reduce employee exposure to or below the 50µg/m3 PEL, OSHA requires that employers must provide and assure use of respirators to workers exposed to lead. Understanding Weld Fume Threshold Limit Values Occupational safety is concerned with determining which controls to use and deciding when to use them, and OELs (Occupational Exposure Limits) serve as important measurement tools. The most widely used and influential OELs are the TLVs (Threshold Limit Values) published by the American Conference of Governmental Hygienists (ACGIH). Despite its name, ACGIH is only an advisory organization - it is not a governmental agency. Although not intended as mandatory standards when they were begun by ACGIH in 1946, TLVs have nonetheless become widely adopted and written into laws. The most prominent example is OSHA's Table Z, a part of the Code of Federal Regulations, 29CFR 1910.1000, listing the agency's PELs (Permissible Exposure Limits). The exposure limits specified by this table, which incorporates nearly the entire 1966 ACGIH TLV list, have been in effect since May 29, 1971. Measurement of contaminants is usually quantified for particulates in milligrams per cubic meter (mg/m3) of air in a worker's breathing zone. A subset of OSHA's Table Z is shown here for chemicals typically seen in the welding environment. Three definitions are important to us: 1.TLV-TWA, or time-weighted average, is the maximum level to which workers could be repeatedly exposed without adverse effects in a normal 40-hour workweek. 2.TLV-STEL, or short-term exposure limits, consider 15-minute time weighted average exposures. 3.TLV-C, or ceiling, indicates the maximum concentrations that should not be exceeded at any time. Items 2 and 3 set limits on transient excursions to significantly higher exposure levels. For example, a worker who only occasionally is exposed to high concentrations of toxic substances could be safely below the TLV-TWA, but dangerously above the TLV-STEL and/or TLV-C limits.
The process of setting TLVs involves determining exposure levels below which certain adverse effects are not expected to occur. These effects may be immediate and localized (such as eye irritation) or delayed and systematic (such as reproductive toxicity of glycol ethers). About 40% of TLVs were established to protect workers from acute irritation of eyes and mucus membranes of the nasopharynx, while about half of all TLVs were to prevent specific organ defects. Irritative effects are usually related to peak exposure levels, rather than cumulative levels, so TLVs for irritant chemicals consider peak levels measurable in the workplace. This "external exposure" of workers can be determined by measuring air concentrations of contaminants in a worker's breathing space. By contrast, systemic organ effects are related typically to cumulative doses that actually reach critical organs. Although this "internal exposure" is very difficult to measure, that does not diminish its importance. Despite the wide acceptance of ACGIH's TLVs, scarce human data has called their scientific adequacy into question. That doesn't mean these TLVs are wrong or incorrectly determined, or that they do not help protect workers, but it does indicate that future exposure limits must be carefully determined. What About Political Aspects of TLVs?
Others have questioned OSHA's decision to rely on ACGIH TLVs instead of NIOSH Recommended Exposure Levels (REL) when the air contaminants standard was developed. By relying on ACGIH values, so the argument goes, OSHA favored corporations rather than individual workers in its standards. Whether any of these arguments are correct, they have nevertheless changed the process for establishing TLVs . ACGIH now maintains extensive records of all documents reviewed and the minutes of discussions involving TLVs. Air Extraction Systems Help Compliance with PEL Standards One of the primary goals of occupational health and safety programs is to limit the exposure of workers to toxic chemicals and physical agents. A variety of methods may be useful: * respirators and air supply devices can reduce inhalation exposure OSHA requires that companies achieve compliance with the established PEL levels through administrative or engineering controls, and, failing that, to provide protective equipment to workers. Particularly as it concerns the smoke, dust, and fumes from welding operations, the use of proper air filtration equipment can help keep contaminants below specified levels. Dangers of Smoke and Fumes from Plasma Cutting Plasma-arc cutting (PAC) uses a high velocity jet of hot (50,000 F) ionized gas to sever almost any conductive material--carbon, alloy, and stainless steel, and most nonferrous metals and alloys. The nozzle of a PAC torch constricts the plasma gas--air, oxygen, or nitrogen--to heat and ionize it. The process blasts out molten material along the cutting path at high speed, up to 100 inches/minute through steel plate one inch thick or greater. In addition to high energy radiation (both UV and visible) generated by PAC cutting, the intense heat of the arc creates substantial quantities of fumes and smoke from vaporizing metal in the kerf. Because most of these submicroscopic particles and gases are harmful, air filtration systems must be designed to handle both large and small particulate. OSHA considers natural ventilation to be adequate if work space per welder is at least 10,000 ft3 and if ceilings are at least 16 feet high with no barriers or partitions to impede airflow. Welding in smaller areas, or in any area where exposures cannot be kept below specified PELs, requires forced ventilation. Beyond the minimum requirements, it is important to provide extra ventilation when welding materials contain large amounts of copper, lead, zinc, or beryllium. Welding Stainless Steel Calls for Extra Precautions Increasing popular concern for the environment, clean air acts of the federal government, various state and local regulations--everything points towards the importance of dealing with welding fumes. Stainless steels are a particular problem because concentrated chromate fume and dust irritates the respiratory system and skin. Worse yet, certain hexavalent chromium compounds are potentially carcinogenic. Protecting Workers' Health Fumes from stainless steel welding and cutting operations must be properly dealt with to prevent harm to the welders. OSHA limits maximum chromium compound contaminants exposure to less than 1 mg/m3 in a time-weighted 8-hour average workday. In addition to concern for workers' health, air quality managers must also address the cost for health insurance and potential liability for future lawsuits. Maintaining Productivity But there's another reason for using fume extraction equipment in stainless operations--if the air is dirty, productivity suffers. Also, sensitive electronic controls for manufacturing equipment can be damaged, and dust is attracted to fluorescent lamps, reducing visibility. The right weld fume extraction equipment can clean up the air, making the workplace brighter and more productive. Whether welding fabricators work with portables, mechanical arms or free-hanging systems, they have to discharge, recapture and clean up the smoke. HEPA-like filters, capable of filtering up to 99.9 % of all particulate, are an important component of any filtration system designed to manage fumes and smoke in the stainless steel welding environment. After OSHA's failed attempt in 1989 to establish more stringent oil mist exposure limits, the PEL remains at the pre-1979 level of 5 milligrams per cubic meter (5 mg/m3) of air in a worker's breathing zone, based on an 8-hour time-weighted average. However, prompted by OSHA and the UAW, mist collection in the industrial metal working environment is becoming increasingly important. The automotive industry has begun to tighten requirements. For example, Ford's current standard for mist control is 1 mg/m3, and plans are to lower it even further because of potential future health claims. Joint hazard review efforts by OSHA, NIOSH & EPA could likely drop the level to 0.5 mg/m3 or even to 0.25 mg/m3. How will this be achieved? Findings of Coolant Mist Collector Study The most definitive study of mist filtration efficiency to date was done in 1994 at the University of North Carolina. With help from Ford engineers, the Department of Environmental Sciences and Engineering developed laboratory methods to measure coolant mist collection. UNC tested collector types from several manufacturers, including media filtration and deep-bed filtration, reflecting plant conditions as much as possible, but maintaining lab control. Summary of Findings UNC concluded that the state of the art in mist collector technology is a three-stage collector incorporating a metal mesh first stage and a bag filter second stage. The final stage can be a 95% DOP filter; alternatively, a third stage HEPA or deep-bed fibrous filter could be used for extremely high filtration efficiency. UNC researchers suggested that more work needs to be done to establish how evaporation can be reduced or prevented. The key is in improving filter drainage. Recommendations for Current Practice * Collector specification - Three-stage collectors should be specified for control of coolant mist. * Collector efficiency - Measurements indicate that a new collector should be able to provide efficiency of >95% for droplets 0.4 micrometer in diameter and > 99% efficiency for droplets 1 micrometer in diameter with mineral oil. * Collector pressure drop - Pressure drop should not exceed four inches of water, because high pressure drop results in high operating costs. * Collector maintenance - Since filter efficiency degrades over time in mist collectors (but not dust collectors) , an effective monitoring program is essential to establish the condition of the saturated filters within mist collectors.
A showcase installation at Copeland Corporation, Lebanon, MO, is configured remarkably similar to what the UNC study recommends for optimum mist collection efficiency. Twenty-two systems combine three filter stages to dramatically improve air quality at this manufacturer's site. Air filtration units are mounted directly over coolant flumes, with a tight machine enclosure. The coolant trough discharges through a snug fitting opening in the coolant trough cover plate, with enough negative pressure to keep the mist contained in the machine tool and the coolant trough. Deep baffles in the coolant trough provide a hydraulic seal between zones to reduce air velocity created by coolant flow. Evaporative losses are kept to a minimum by one of Copeland's own manufactured condenser packages, which reclaims 2.5 gallons of water per hour from each unit. Reclaimed water goes back to the coolant system. Machine Enclosures are Key to Capturing Cast Iron Machining Dust If not properly contained and filtered, the wet dust generated by cutting, grinding, and polishing cast iron can play havoc with equipment (see side box) and threaten workers' health. Satisfactory resolution of the problem entails building good machine enclosures and installing the proper air filtration system. The B-11 subcommittee of the Association for Manufacturing Technology (AMT) has been writing new guidelines for a uniform approach to the control of airborne contaminants generated by stationary machine tools used to cut and form materials. AMT says a hood is a generic term for devices designed to capture contaminated air and conduct it to an exhaust system. For our purposes here, we are concerned with enclosures, which are the first choice for effective control. An enclosure is only part of a total mist control system that may include ductwork, mist collector and/or fan unit . Up front coordination between the machine designer and the ventilation designer/supplier can enhance control of airborne contaminants through proper design and installation of all the components of the system.
Airborne contaminants emitted from machining operations on cast iron take the form of coolant mist, vapor and smoke, and also dust from the material being cut and from the cutting tool. When enclosures are used contain contaminants, ventilation should be provided by a negative pressure exhaust system, with sufficient volume to prevent contaminants from escaping into the workplace. Close Capture Enclosure Design This preferred method of enclosure and capture mounts a device very near the source, before the breathing zone of the operator, such as a guard on a bench grinder. This technique has a high entrainment velocity and low air volume requirements. Design tips: get as close as possible to the source of contaminant generation; allow access for service and tool changes; at access points provide hinged or sliding doors; take care not to trap heat that may cause distortion. Total Enclosure Design Total enclosure is a complete box or housing mounted around the machine or process, and is the preferred method of enclosure when Close Capture is not practical. The housing is not intended to be tight(openings for parts, maintenance or utilities access also provide a path for entry of replacement air). In designing the enclosure, consider these factors: allow access to maintain machine and provide tool changes; design should limit free open area to minimize exhaust volume; select duct entry location to prevent chip and coolant entry; consider the environment for electrical, laser or other sophisticated equipment--preferably mount it outside the enclosure. Tunnel Enclosure Design A tunnel enclosure is a continuous enclosure over two or more connected workstations or machine processes. Principles for proper design are similar to the procedures used for Total Enclosure. General Design Considerations Capture velocities should be selected to adequately control any vapors, smokes and mists, while not removing chips and coolant. Suggested duct entry velocity: 2,000 feet/minute or less for cast iron. Ergonomics is also an important factor in design (see ANSI B11 recommendations) to make the equipment safe and efficient, and to facilitate service. Designers will also want to consider fire protection, lighting, and noise abatement control to arrive at a satisfactory enclosure for an application. (Note: Aercology feels that machine enclosure is the single most important consideration for optimum containment of mist or dust. Once airborne contaminants are properly entrained, Aercology has a wide selection of equipment specifically designed to handle most any kind of pollutant.) Controlling Wood Dust in the Workplace Seemingly innocuous, wood dust is largely ignored as a harmful air contaminant. But OSHA considers it to be a nuisance dust, and has established a PEL (Permissible Exposure Limit) of 15 milligrams per cubic meter (15 mg/m3) of air in a worker's breathing zone, based on an 8-hour time-weighted average.
Companies who saw, sand and turn wood must address the problems of wood dust in the workplace. Proper containment of air in the immediate vicinity of the woodworking machine is critical to capturing airborne pollutants (see also article on machine enclosures). Once captured, the air can be filtered in a variety of economical, effective ways. Bag Filtration Modular dust collectors using bag filters provide inexpensive control of wood dust. Bag filters can remove up to 99% of airborne particles from operations such as sawing, sanding, turning, buffing and polishing. A broad choice of filter materials is available, from woven bag filters for large particles and easy cleaning, to felt filters for highest filtration efficiency of minute particles. Manual or automated shaker systems extend maintenance cycles. Optional HEPA afterfilters provide maximum filtration capability. Ambient or Source Capture Media Filtration Modular media filter systems utilize a building block approach, combining a variety of specific filter modules in one unit, providing maximum flexibility to meet specific capture requirements. A typical system incorporates a series of disposable or cleanable pre-filters and a disposable vee-bag filter. HEPA or carbon final filter modules can also be added to remove fine particulate or gases and vapors that cause odors. Two-Stage Dust Collectors Wall or ceiling mounted two-stage filter systems are often ideal for filtering wood dust. Aercology's Smokebuster(tm) systems were developed for dust and smoke collection in tough commercial air pollution applications such as wood dust. A multi-vee pre-filter and a 95% efficient vee-bag main filter remove submicronic particles and heavy dust. Optional cleanable pre-filter and cleanable Unibag(tm) filter are recommended when dust generation is particularly heavy. Cyclone Collection Cyclone collectors utilize centrifugal force to extract large or heavy particles such as sawdust or sand. Polluted air enters the top side of a vertical cone, and a whirling circular air pattern throws larger particles against the outer wall of the cone where they drop out of the unit. A fan exhausts air up the middle of the cone. Cyclone collectors are effective only against particles 25 microns or larger; afterfilters are used to capture fine particulate. Facilities managers, usually focused on production issues, assume if the air doesn't look dirty, it's not a big problem. However, air inside most manufacturing and fabrication plants is filled with contaminants like smoke, dust, oil mist and fumes. Left unchecked, minute particles cause damage to servo motors, CNC drives and sensitive electronic controls of capital equipment. Reduce Equipment Maintenance Proper air filtration systems are increasingly important to keep plant equipment running properly. Dirty air can greatly reduce running time and needlessly add to maintenance costs. Increase Productivity Control of dust and smoke is also key to maintaining high worker productivity; studies show that a cleaner work place is a more productive one. Keeping the air clean helps improve employee morale and reduces absenteeism, positively impacting overall productivity. Decrease Health Risks Keeping a lid on employee insurance costs means the health hazards of air pollution must be minimized. Workers' concerns over in-plant air quality, the potential for lawsuits over health issues, plus regulatory agency requirements suggest paying close attention to airborne contaminants. Know Your Application Before Choosing Finding the right air filtering system requires balancing many factors, but no single type of filter system is best for all applications. Selection must be based on the type and quantity of contaminants in the air. Experience shows that cost differences between types of filter systems essentially comes down to a comparison of overall maintenance costs--pay for labor to clean filters, or pay for disposable filters. What is Clean Air? Why Worry About Clean Air? is a matter of degree. Air that is adequately clean for an office environment would be much too dirty for an industrial clean room area. Even air that is free of visible particulate (greater than 10 microns) may contain many smaller particles that result in high maintenance costs for a conventional air conditioning system.
Similarly, the specified dust removal efficiency of an air filter will vary widely depending on the method of measurement. Two measurement methods are Dust Holding Capacity and Arrestance. * Dust Holding Capacity is a measure of the weight of dirt a filter can hold before it reaches a predetermined final resistance. A filter with 100 grams dust holding capacity should last approximately twice as long as a 50 gram filter under the same conditions. * Arrestance is a measure of air cleaning based on weight of dirt collected. If 100 grams of particulate reach a filter and 80 grams are caught, the Arrestance level is 80%. Dirt getting through the filter is what damages equipment. A 90% efficiency filter allows 10% of the dirt to pass through; an 80% filter lets 20% through--only half as efficient. Even a 99% filter is less than 1/30th as effective as a filter with an efficiency of 99.97%
Double the Surface Area -- Triple the Filter's Life * Double the surface area -- triple the filter's life.
* The MAX line shows maximum expected increase in filter life due to an increase in filter area, under optimum operating conditions.
* The EXP line holds true most of the time in practice. It is most similar to the double the area, triple the life axiom. The Filtering Process -- Collection and Filtration What Happens When a Filter Gets Clogged? If a filter is clogged, it's simply doing the job it was designed to do--collect particulate. As dust builds up on a filter, increased resistance causes air flow to diminish so that the design CFM (cubic foot per minute) is no longer met. When system suction decreases or contaminants escape collection by the intake hood, it's time to clean, wash or change the filter. Most plant engineers and plant managers are keenly interested in extending filter life because of the cost of disposing of spent filters--often considered hazardous waste. Several things can be done to increase time between filter change-outs: * Determine if the system is drawing in contaminants that should ordinarily drop out of the airstream. * Add pre-filtration to collect particulate before it reaches the main filters. * Add higher quality filters that have more surface area, extending service life. * Change from a surface loading type filter to a higher loft filter media that provides in-depth loading. How to Know When It's Time to Change Filters Experience is often the best guide for determining filter change frequency. Observe a newly installed system frequently, filter change-out is required when airflow drops to minimum levels and contaminants are barely being captured. A magnehelic gauge shows pressure drop across the filters (indicating reduced airflow), when filters load up, note the gauge reading. From here on, observing the gauge tells you when to change filters.
CARTRIDGE FILTRATION Cartridge filters provide an economical, easy-to-maintain solution for filtration of dust, dirt and weld fumes. Paper type cartridges provide in-depth loading-- particulate is trapped within the media as well as the surface. Membrane type units, such as high tech 100% polyester cartridges, are surface loading--trapping particulate on the surface. Well-designed cartridges can provide efficiency higher than 99%, approaching HEPA-like capability. Most cartridge filter systems use a blow-down process to clean filters. A reverse pulse of compressed air may be either triggered by a timer (automatic systems) or actuated by an operator (manual units). There are many cartridge filters for a variety of applications. Standard paper type cartridges--used for dry contaminants--are made of cellulose. Higher quality, heavy duty cellulose/synthetic fiber (polyester) blend filters offer higher strength and efficiency. In many cases cartridges are treated to improve efficiency. A cartridge unit may be "seeded", i.e., impregnated with a powder before usage to improve both efficiency and release capability. For dry dust or fumes, high tech, heavy duty, 100% spun bonded polyester filter cartridges are suggested. Dirty cartridges can be washed and reused without loss of efficiency, and can be cleaned at lower air pressure (40psi) because of their enhanced release characteristics. Other special cartridges include: PTFE (Teflon;) coated, hydro/oleophobic units that resist water and oils, useful especially for sticky or moist contaminants.
BAG FILTRATION Dust collectors using bag filters are economical to operate and simple to maintain, removing up to 99% of airborne particles. A wide choice of filter materials is available, from woven bags for large particles and easy cleaning, to felt bags for highest filtration efficiency of minute particles. Better units have bag rack filter modules that are easily removed for quick replacement. Maintenance of bag filter systems is simple and inexpensive. A shaking mechanism removes collected dirt off the surface. A manual shaker is typically actuated by a lever. In automatic systems a timer control triggers the shaker to dislodge particulate. It's desirable to have the ability to add a HEPA afterfilter capability, providing 99.97% efficiency (99.999% also available). Because HEPA filters are located after the bag filters, the HEPA filter generally lasts a long time. ELECTROSTATIC PRECIPITATORS In many industrial situations an EP (electrostatic precipitator) is especially effective for removing submicronic particles such as oil smoke, welding fumes, and other sticky, wet contaminants. Particles are ionized as they pass by charged wires in the airstream, they are attracted to collector plates and removed. EPs are extremely efficient with very fine particles, but not very effective on large particles. Good EP units have prefilters to remove larger particles. For oil smoke containing oil mist, an impinger enhances efficiency and substantially reduces maintenance requirements. Extremely efficient performance must be weighed against the need for more labor intensive maintenance than other types of filter units. As contaminants accumulate, plates become insulated, leaving no place for the particles to collect, resulting in reduced efficiency. Cleaning components will return the system to its designed efficiency. Typically a visual indicator, such as a red light, tells the operator the unit is operating properly. If the light goes off, the unit should immediately be checked to determine if maintenance is needed. Maintenance is typically achieved either by wet washing (for wet smoke) or by impacting, rapping or vibrating (for dry fume). Optionally, the unit may have a timer driven system that shuts down the unit and automatically initiates the cleaning cycle. CENTRIFUGAL MIST COLLECTION Coolant mist from machining operations can be filtered by centrifugal mist collectors right at the source. As air passes through the filter media, submicronic mist particles are retained until they grow to droplet size, then thrown free of the perforated rotating drum to the inner wall of the casing. High velocity drives the liquefied oil along the walls and through a circumferential slot into a collection chamber. Clean air is returned to the plant environment by way of the exhaust grill, and the clean recycled oil drains from the unit for reuse or disposal. If the gap between the cover and the rotating drum is small enough, units can be up to 98% efficient at one micron, increasing to 99.97% at 0.3 micron by the addition of an optional HEPA afterfilter. Centrifugal mist collectors are equally effective with petroleum-based, synthetic, semi-synthetic or water-soluble coolants. In most cases it is desirable to have an inexpensive throw away filter liner. Where clean oil mist is being injected, the unit can easily run for a year without maintenance. If a heavy concentration of solids are present, monthly filter replacement may be necessary. Applications with heavy metal removal rates which cause build-up of swarf should have a pre-filter trap to extend the time between service intervals. When the unit is first installed, the throw-away liner should be checked periodically. Once the maintenance is determined, routine maintenance can be scheduled. Heavy contaminant build up can cause the high RPM rotating drum to become imbalanced, leading to vibration. Throw away liner replacement is recommended before this occurs. If pre-filter traps are used in high solids applications, maintenance is determined by loss of airflow. If the pre -filter plugs up, particulate can bypass the unit and enter the primary filter, which is usually much more costly and difficult to replace. When a HEPA afterfilter is used, here again loss of airflow dictates when to change filters. MODULAR MEDIA FILTRATION A modular media filter system utilizes a building block approach to provide maximum flexibility. By combining a variety of specific filter modules in one unit, these systems can provide solutions to many air contaminant problems. This customized approach helps achieve a proper balance between filtration effectiveness and acceptable maintenance cycles in a particular environment. A typical system incorporates pre-filters and a vee-bag filter or other disposable, or cleanable, filter media. HEPA afterfilter modules can achieve up to 99.999% filtration efficiency of submicron particles. Additionally, gas vapor final filter modules can be added to capture gas or vapors. Combinations of pre-filters in front of the main filters extend their useful life by preventing premature loading with larger particles. Disposable fiberglass may be used in light dust and fume environments, medium efficiency, pleated multi-vee filters may be used for dry or moderately wet environments. In oil mist applications, a chevron impinger prevents large droplets and swarf from entering the filters. A metal mesh filter further reduces the amount of mist entering the main filter elements, especially large droplets or heavy concentrations of mist. Both impingers and mesh filters can be removed and cleaned. A magnehelic gauge can greatly assist monitoring build-up of contaminants in the modular filter system. Since vee-bags cannot be cleaned, it is important to use efficient pre-filters to preserve the vee-bags. In applications involving fluids, vee-bags can be drained, removing solids with the fluids, extending the life of bags. Carbon modules (cells or trays) are used for removal of vapors and gases. Specialty carbons are treated in various ways to make them absorb a particular material. Other materials used for trapping vapors besides carbon include potassium permanganate/ activated alumina, zeolites, and CPZ (combinations of the three). One advantage of a carbon filter is that the module can be refurbished with fresh carbon, either by shipping contaminated trays to a refurbishing center, or by refilling on-site. A simple method for maintaining carbon modules is to replace the dirty unit with a clean one to minimize down time. How In-Plant Air Filtration Contributes to Manufacturing Productivity and Profitability The Hidden Cost of Make-Up Air In a typical manufacturing plant the single biggest energy expenditure is often the heating and/or cooling of the facility. Air heating usually constitutes 25% to 50% of the heating loads in commercial buildings while cooling loads are satisfied entirely by air1. One of the primary advantages of using air filtration systems in manufacturing facilities is the collection, filtration and recirculation of air rather than ducting contaminated air outdoors. This pollution control technique, while helping manufacturers comply with EPA clean air requirements, also avoids the considerable expense of replacing exhausted air with fresh outside air that must be heated or cooled to the temperature inside the plant. The added fuel to heat this make-up air during a full heating season can be substantial. Often overlooked in a maintenance analysis are the long-term, and sometimes hidden, costs resulting from venting oil mist and various plasticizers to the outdoors. Many oils are hydrocarbon-based or solvent-laden. When these oil mists settle on a roof, roofing materials quickly dissolve leading to an expensive, premature roof replacement. Oils settled on roofs will also eventually run off during rains contaminating area aquifers. This type of industrial contamination is under increasing scrutiny by government agencies such as the Department of Natural Resources and the Environmental Protection Agency. Calculating Costs For Plant Heating &Cooling Contaminated air ducted outdoors must be replaced with fresh outside air, and this air must be brought to the temperature maintained within the plant environment. While the added fuel utilization for heating make-up air is relatively small over short periods of time, during a full heating season substantial, unnecessary expenditures can be made.
Table 1 offers a formula to calculate the additional costs for heating outside air based on fuel consumption for each of the most common fuels-coal, oil, natural gas, and electricity-based on the "Degree Day" standard. A "Degree Day" is the mean outdoor temperature averaged over a 24 hour period and subtracted from 65° F. Since fuel prices vary greatly, use of the current price for your area in making the calculation is recommended for greater accuracy. Pick the city listed in Table 2 that is closest to your location. Applying this formula will give you a good estimate of what you might save each year in fuel costs alone by installing a proper in-plant air filtration system instead of exhausting polluted air to the outside. Similarly, cooling costs will vary widely from one location to the next, but a rule of thumb for typical moderate temperature areas is to estimate a cost of about $2 per cubic foot of air to exhaust it to the outside.
Using The Formulae In making the calculations, pick the city listed in Table 2 which is closet the location of interest. Select the Degree Days for that location and integrate into the formula for the fuel in use in Table 1. Each formula is based on a 40 hour work week and a 65 F inside temperature. For an 80 hour week, multiply by 2; for 120 hours, multiply by 3. For a 70° F inside temperature, multiply by 1.23 Reducing Equipment Repair and Maintenance Costs The air inside most manufacturing and fabrication plants is filled with airborne contaminants-principally weld fumes, smoke, dust, dirt, and oil mist from cutting fluids generated during machining operations. These contaminants coat work surfaces and equipment, playing havoc with electronic controls, servo motors, optics and DC &CNC drives of grinding machines, lasers, robotics, and other capital equipment. Every organization has a different method for determining the cost of lost production due to equipment failures. However, Table 3 presents a general formula for determining maintenance costs resulting from drive motor downtime, including both maintenance and labor costs. Calculating The Cost of Downtime C = (L x D x H) + (N x F x R)
Alert managers recognize that in an environment where airborne contaminants are present, in-plant air filtration systems can help minimize unexpected machine failures and extend the useful life of capital equipment. Improving Manufacturing Output &Productivity Productivity losses can result from any of several factors: actual time lost due to absenteeism; reduced efficiency resulting from poor working conditions; and reduced equipment effectiveness causing part rejection, re-working and lower overall part yield. Individually quantifying each of these productivity losses is difficult, but by identifying how in-plant air filtration can reduce or eliminate these factors, the productivity contribution of in-plant air filtration becomes clear. The environment in typical metalworking plants contains a variety of airborne pollutants that ultimately cause absenteeism and reduced effectiveness of workers. Experience has shown that installation of air filtration systems to remove particulate matter from the air and collect mists from cutting fluids generally can improve productivity by as much as 7-10%. Absenteeism and Productivity Today, hard data suggests that up to half of the upper respiratory diseases in the workplace may be associated with the work environment itself. A report published by the US National Center for Health Statistics in 1989 analyzed the reasons employees are absent from work on health grounds and found that just over 50% of the absenteeism from 1983 to 1985 was due to upper respiratory infections. In 1988 an American Medical Association news release reported on a Walter Reed Army Institute four-year study that concluded trainees housed in modern, energy efficient barracks were 50% more likely to contract upper respiratory infections than trainees housed in older, less airtight buildings. Employees are also concerned about other health effects. The fight over metalworking fluid standards began in 1993 when the United Auto Workers petitioned OSHA to reduce the PEL (Permissible Exposure Level) of coolant mist from 5.0 to 0.5 mg/m3. Their petition was based largely on results of epidemiological studies over the past 20 years that showed possible links between exposures to oil mists and occupational asthma, hyper sensitivity pneumonitis, larynx and rectum cancer, and dermatitis. Improving indoor air quality can also help prevent employees from resorting to litigation to have their complaints about unsafe working conditions addressed. Nominal individual awards (considered to be $5,000 to $15,000 per worker) resulting from typical lawsuits can add up quickly to enormous potential liability for the company found guilty of exposing workers to unsafe contaminants. Even the cost to defend successfully against these cases is substantial. Parts Production and Productivity Poor part quality also reduces productivity. If the air is dirty and the contaminants interfere with laser optics or parts finishing -e.g., spray booths-reject rates increase and parts yields decrease. In addition, if oil haze or fumes inhibit operator performance by preventing an operator from clearly seeing parts being machined, quality suffers, output goes down, and productivity is reduced. Minimizing Healthcare Costs Health insurance is an enormous expenditure for American companies today and is increasingly an issue with management and labor alike. In addition to annual costs for healthcare insurance premiums, long-term liability costs associated with contaminated air must also be considered. Worker compensation costs are also effected by the hazards of slippery surfaces due to oil mists. If oil covers the factory floor, it presents an extremely high fall rate potential that can negatively impact both healthcare and general liability insurance premiums- and create the potential for extensive litigation. The presence of in-plant air filtration systems can have a direct positive effect on the cost of healthcare insurance. Installation of adequate in-plant air pollution control equipment may influence an insurance carrier's view of financial liability for a company's healthcare costs, possibly resulting in lower insurance premiums. Again, generalizations are difficult, but manufacturing organizations can expect to save 10 to 15% on general liability and health insurance premiums if airborne contaminants are reduced to bring a sufficient improvement in air quality. Keeping Facilities Maintenance Costs In Check In emphasizing the large potential savings in maintenance, facilities maintenance costs should not be overlooked-in many cases these can be substantial. Without an in-plant air filtration system, maintenance becomes an entire plant problem. These costs can be minimized by confining contaminants to the filter elements, which can be easily handled. It's not hard to imagine what would happen if all the dust and dirt collected in an air filtration system were strewn randomly around the plant, or if even ten gallons of collected oil mist were scattered across the walls and ceilings of a modest size factory. Yet, without proper air filtration equipment, that's in effect what occurs. Additionally, airborne particulate can coat light fixtures with a film that reduces brightness. Increased electrical energy to provide the same level of lighting adds to utility costs. Bulbs are also likely to fail prematurely due to build-up of dust and oil film. Another factor frequently overlooked is the effect dirty air can have on the efficiency of a heating, ventilating and air conditioning system. Since many HVAC systems do not come with adequate filters for factory environments, dirt, dust and oil build-up prevents coils from transferring heat properly. Companies have learned that keeping air filters clean makes HVAC equipment work more efficiently, with up to 20% less energy use. Reducing Fire Hazards And Insurance Costs Machining operations occasionally result in flash fires or explosions caused by a spark in the presence of oil mist or dust and air. Eliminating the combustible material using an adequate air filtration system can avoid these problems. Mist collectors mounted directly on a machine are the best solution for oil mists. Because reducing contaminant build-up minimizes the potential for explosions and fires, in many cases installation of a collection system will reduce a company's insurance premiums for fire and general liability (conversely, rates can go up due to a dirty environment). Although generalizations are difficult, a metalworking organization can anticipate saving approximately 5 to 7% annually on fire insurance by installing proper air filtration equipment. Other Cost Considerations Other factors associated with uncontrolled airborne contaminants can have a definite impact on the cost of plant operations. If OSHA comes in because workers are being overexposed to some pollutant, what might compliance cost in lost work time, productivity, and litigation fees? If a potential client sees a dirty plant, how does that impact your chances of getting the contract? Although it's extremely difficult to quantify, that perspective certainly plays a role in how prospects and customers view your operations. Fortunately, achieving a significant improvement in air quality in most industrial plants can be easy and cost effective. Using the formulas and ideas presented here, you can begin to justify investing in air filtration equipment that will have a positive impact in many areas of your operations, especially the bottom line. Questions? E-mail or Contact C.C. Steven Customer Service at 805-658-0207. |
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Determining TLV Levels
Design Considerations For Machine Enclosures
Dust particles of widely varying sizes float
through the atmosphere. If the ratio of each particle size to the total is expressed as a percentage, the method of measurement must be known. The chart illustrated here shows three
types of measurements: by particle count, particle area, and particle weight. Particles smaller than 1 micron constitute less than 30% of the weight of the total dust load, but are 99.9% of the total number of particles.
Note in the table how a filter with an arrestance
of 99% for synthetic dust may have an efficiency of only 80-85% for atmospheric dust--even less for smoke particles.
Which are true? In practice, all these axioms have some
legitimacy, but often much more is involved. 
