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Swarf, also known as turnings, chips, or filings, are shavings and chippings of metal — the debris or waste resulting from metalworking operations including milling and grinding. It can usually be recycled, and this is the preferred method of disposal due to the environmental concerns regarding potential contamination with cutting fluid or tramp oil. The ideal way to remove these liquids is by the use of a centrifuge which will separate the fluids from the metal, allowing both to be reclaimed and prepared for further treatment.
The terms "swarf" and "chips" are also used to describe the waste shavings, sawdust, and cuttings from woodworking operations, as well as waste in constructed piping, such as welding metal or slag waste that is produced and trapped within the pipe during its assembly, and sometimes in masonry.
Definition: Swarf (in glass fabrication) (noun) Glass particles, a byproduct of cutting, breaking, drilling, or grinding glass in the course of glass fabrication. Synonyms: sludge, slag, fines, mud, crud.
General description: Swarf glass particles are a dusty byproduct from cutting, breaking, drilling, or grinding glass in the course of glass fabrication. They are often transported away from the Hot Zone (where tool and work-piece meet) by means of a pressurized water spray and through a pipeline with a water flow rate sufficient to carry the dense Swarf particles to a Solids Removal System, which is intended to separate solids from Production Water. “Clean” recycled Production Water is typically recycled back to the Hot Zone reiteratively.
These dense (~2.6g/cm₃), hard (~5.5HM) particles have a high propensity to bond to other Swarf (cohesively) and to other things (adhesively) such as fabrication tools, pipes and even fabricated glass surfaces. While quite small (most typically ranging from ~ 106 - 53 microns), Swarf particles are an expensive nuisance that affect competitive performance as they are often the root cause for: • Diminished tool life caused by Unintended Friction • Equipment failure and energy waste from pipe and water port obstructions and clogging • Poor performance as equipment becomes compromised and out of original spec due to Swarf buildup • Quality defects: Water Spot Etching (affects clarity and aesthetics), shiners, etc. Optimal Particle Removal Rate of Swarf throughout the recycled Production Water system is the key to good Swarf management, which also often includes the following: • a quality solids removal system capable of supporting production capacity • treatment with a coolant additive that sufficiently disarms the propensity for Swarf particles to bond, and promotes optimal Particle Removal Rate to reduce water pipe obstructions, Water Spot Etching, Unintended Friction, etc. • unobstructed pipes, nozzles, and water ports to provide water flow sufficient to carry Swarf particles away from the Hot Zone and to the solids removal system effectively • a relevant flocculant to encourage particles to behave in a manner that supports the solids removal system Definitions - other terms used: Hot Zone: where the glass fabrication tool and the work-piece meet (in the context of cutting, breaking, drilling, grinding). Primarily two types of friction heat are produced as a byproduct of fabricating: Intended Friction and Unintended Friction. Intended Friction: friction as a result of the fabrication tool meeting the work-piece. This friction type is closely calibrated by fabricator to achieve performance and quality. Unintended Friction: friction caused by Swarf particles or inadequate water flow rate. This type of nuisance friction creates quality problems (“shiners”, etc.) and diminishes tool performance and life. Production Water: being water used in the course of glass fabrication for the sake of cooling tool and work-piece and helping to mechanically remove swarf particles from the Hot Zone as quickly as possible. Quality Production Water: recycled Production Water “cleaned” by the Solids Removal System, now substantially free of Swarf. Solids Removal System: methods of removing solids, primarily glass swarf particles in this context, from Production Water. Various types exist: decanter system, centrifuge, henry, filter-press, etc. Each type may possess examples that range from crude to very sophisticated, and may employ both mechanical and/or chemical methods. Coolant Additive (for Production Water): a soluble or semi-soluble liquid or powder additive diluted in Production Water whose function is to encourage Particle Removal Rate superior to Production Water itself. Generally, coolant additives do not provide boil protection above water itself, but are designed to cool by supporting better Particle Removal Rate. Particle Removal Rate: the rate at which glass Swarf particles are removed from the Hot Zone (in this context), which is the key function of Coolant Additive, as it helps eliminate Unintended Friction caused by Swarf particles. Flocculant/Coagulant Additives: soluble or semi-soluble liquid or powder additive diluted in Production Water to promote Swarf solids removal, typically by helping particles to fall out of suspension (most commonly used by Solids Removal Systems) or become highly suspended (for Solids Removal Systems using a form of solids skimming technique). Water Spot Etching: often a serious quality defect caused by mineral or Swarf precipitate, from Production Water, bound to the surface of a fabricated work-piece.
Chips can be extremely sharp, and this creates a safety problem, as they can cause serious injuries if not handled correctly. Depending on the composition of the material, it can persist in the environment for a long time before degrading. This, combined with the small size of some chips (e.g. those of brass or bronze), allows them to disperse widely by piggy-backing on soft materials and also to penetrate the skin as deep splinters.
It is standard training for machinists, and usually a standing workplace rule, to avoid handling swarf with bare hands. Machinists generally adhere to this guideline to the extent practical. Although it isn't uncommon for machinists to touch swarf, it's always a risk-prone behaviour. There are some machining applications in which total avoidance of touching swarf is considered burdensome or impractical by the machinist, but employers should not expect or require that workers do it. Any machining textbook or manufacturing business insurance policy will insist that this not be done.
Similarly, it is also standard training for machinists, and usually a standing workplace rule, to minimize or entirely avoid blowing chips away with compressed air, but as with the avoid-handling rule, this rule is often broken, and there are some machining applications in which total avoidance of chip-clearing via air hose is considered burdensome or impractical by the machinist. Some machine tool manuals proscribe this practice both for safety and for the preservation of way wipers and bearing seals. Alternatives to blowing chips away include vacuuming them away with an industrial vacuum (shop vacuum); gently washing them away with a coolant hose discharging at typical garden-hose pressure values; or preventing their generation in the first place (for example, forming threads instead of cutting them).
It is not uncommon for chips flying off the cutter to be ejected with great force and to fly several meters. These flying chips present a hazard that is deflected with safety glasses, face shields, and other personal protective equipment, as well as the sheet-metal enclosures (and polycarbonate windows) that surround most commercial CNC machine tools.
Optimum cutting efficiencies often generate long spring-like swarf. This is hard to deal with as it is bulky and can clog the nozzle of a shop vacuum. Clean-up and disposal of this continuous-cutting swarf is made simpler by using a cutting tool with a chip-breaker. This results in denser, more manageable waste.
Disposing of swarf is a tedious but necessary task. For ease of transport and handling, swarf may be compressed into bricks, which greatly reduces associated problems with storing and cost; it also improves material handling for all concerned with its reclamation and recycling.
Machine shops are typically required by the scrap collector to: