Metalworking covers a broad range of products from precise jewelry-making to large-scale industrial manufacturing. Creating metal goods involves processes like metal cutting, forming and mechanical surface cleaning.
Mechanical surface cleaning for metalworking includes grinding, buffing and polishing processes that clean metal surfaces in preparation for painting, welding, or other operations. Metal surfaces in need of cleaning may be covered with paint, rust or oxidation; plated with other metals; or covered with molding sand, organics, or biological materials. Donaldson Torit dust collection equipment and filters are ideal for collecting dust and fumes produced from these types of metalworking processes.
Mechanical cleaning for metals may also involve abrasive blasting, wire wheels, sandpaper/sanding belts, grinding wheels, or abrasive chips in tumbling mills. To capture and entrain the large heavy particles produced by cleaning, the required capture velocity is often very high with collection hoods positioned to direct materials towards the hood. Once captured, general practice recommends a minimum duct transport velocity of 1066 m/min / 3500 fpm, but 1219 to 1524 m/min / 4000 to 5000 fpm is often necessary. A hood that encloses as much of the operation as practical is generally desired. In situations where the material removed has toxicity concerns, complete enclosures may be necessary or workers may need to wear respirators in addition to using local exhaust ventilation.
Grinding operations employ abrasive grains in various forms for the removal of material and metal to produce of different types of surface finishes. Abrasive grains held together with a hard, durable bonding material make grinding wheels, abrasive stones, and sticks. Abrasives can also be applied on fibrous sheets, paper, or cloth with the principle materials being aluminum oxide and silicon carbide. Crushed diamonds called Bort are also used as abrasive grains.
Sanding, tumbling, belt grinders, core grinders, horizontal double spindle disc grinders, vertical spindle disc grinders, jack grinders, portable grinders, small radial grinders, surface grinders, swing grinders, grinding benches, and grinding tables.
Particulate from the object being finished including a variety of ferrous and non-ferrous metals such as aluminum, cast iron, steel, titanium as well as non-metals such as brake shoe, composites, and rubber.
Grinding Wheel Structure and Abrasives. The grinding wheel structure is the relative spacing of abrasive grains in a given volume of a grinding wheel and depends upon the abrasive grains, the bonding material, and the voids. A good structure will provide proper chip clearance so that as the abrasive grains cut chips out of the work the chips are thrown away from the face of the wheel. Wheels with a wide grain spacing are used generally when the contact area between work and wheel is large, material being ground is soft, or when rapid removal is required. Narrower grain structures are generally suitable when fine finishes are required or when contact area is small and the material being ground is hard.
Grinding Wheel Bonds are the materials that hold the abrasive grains together. It is the amount of bond used that determines the “hardness” or “softness” of the wheel. The heavier the coating of bond around the abrasive the harder the wheel is rated. Grinding wheel bonds are of six general types:
A combination of coating materials, metallic particulate, and grinding wheel abrasives and wheel bond agents are all generated during the grinding process. The dust will likely be abrasive, possibly agglomerative, and may often pose a potential fire and explosion risk.
Due to the variety of work and types of grinding machines employed, it is necessary to develop hoods adaptable to the machine in question, and such hoods should be located as close as possible to the operation. Do not mix ferrous and non-ferrous metals in the same exhaust system. Consult applicable NFPA codes.
Buffing — The objective of buffing is to make a rough surface smooth; however, every part does not have the same finish and will need to be worked differently. Buffing can be divided by three categories. They are defined as satin finishing, cut-down buffing for preliminary smoothness, and cut and color buffing for smoothness and luster.
Polishing — Polishing is not a precision operation. It is used to remove metal and produce fine-scale abrasion. Friction generates high temperatures that can soften the surface of the work piece. Polishing, which usually involves several stages, proceeds buffing.
Manual buffing and polishing, buffing lathe, backstand idler polishing machine, straight line automatic buffing, circular automatic buffing, and metal polishing belt.
Buffing Wheels or Buffs are created from cotton, canvas, chamois, sisal, or string. They may be loose, sewn ventilated, or pocketed. Buffing wheels have a variety of designs and run at speeds of 5000-6000 rpm. They have safe and unsafe areas of operation and care should always be taken when working around them. Several types of buffs are described here.
Buffing Compounds do the work. Compounds are applied to the buff prior to the work. The work is used to force the compound into the buff, speeding buffing time. Compounds are composed of fine, abrasive materials such as aluminum oxide, emery, silicon carbide, diamond, boron carbide, and zirconium. These are bonded together by grease, oil, or various types of waxes and are referred to as “Tripoli” compounds.
Contaminate from these operations can present itself in many forms, such as long fibrous stringers, agglomerated masses of cotton or fibers mixed with waxes or oil and abrasives. The abrasives can be generated from the wheels or the piece being worked. Particulate can or may be flammable or explosive and caution should be used when dealing with such.
Model | Product Family | Use | |
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Downflo Oval (DFO) 4-112 | Cartridge Dust Collector | Grinding |
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484RFW12 | Baghouse Dust Collector | Automatic Billet Grinding |
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Dalamatic Cased (DLMC) 6/6/15 | Baghouse Dust Collector | Buffing |
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64 Cabinet | Baghouse Dust Collector | Grinding |
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Downflo Workstation (DWS) 6-2 | Cartridge Dust Collector | Grinding |