Sorting carbide scrap before it goes in the pail

Steel, solder, coatings, oil and other cutting materials each push scrap toward a different recycling route.

The zinc process starts from hard scrap such as used tool inserts, and USGS says it is not a purification process, so careful sorting and the removal of oil, solder and coatings come first. Zeiler et al. (2021) say most soft scrap (grinding sludge, sweepings, powders, turnings) and most unsorted hard scrap goes the chemical route instead, which a 2005 USGS report (data year 2000) found tended to cost more and yield less than the direct methods.

The same 2021 paper says pre-sorting by material at the end user raises recycling efficiency. The end user is your shop, and nobody knows which machine a tool came off better than the people who ran it.

Sources: USGS Open-File Report 01-349; Zeiler et al. 2021, IJRMHM 98:105546 (ITIA-hosted copy); USGS Open-File Report 2005-1028.

Most mixing happens on a single tool. Take a tool apart only where it was built to come apart.

• Inserts on holders. ITIA marks an insert that is just screwed onto a steel holder as 100% hardmetal and easy to separate. Unscrew it; the holder goes with steel.
• Brazed tips. Leave the tip on. ITIA names carbide brazed onto or cast into steel as the main reason those products are recycled less, and the solder still has to come off later.
• Diamond tips. Same rule. Sandia describes an oilfield diamond cutter as a synthetic diamond layer on a tungsten carbide disc that is brazed to the bit body, so there is carbide under the tip.
• Saw blades. Look at the teeth first. ITIA notes that some bimetal blades have M42 high-speed steel teeth.

Zeiler et al. say alternative binders such as CoNiCr and FeNiCo, and parts made from two or more grades, pose a new problem in scrap identification. If you know the grade or binder, write it on the label.

Sources: ITIA newsletter on recycling (2018, file dated 2024); Sandia report SAND2024-13076; ITIA: tungsten in steel; Zeiler et al. 2021, IJRMHM 98:105546 (ITIA-hosted copy).

Oil matters most in fine scrap. A 2023 study says carbide grinding sludge often needs chemical recycling because of oil, refrigerants and other impurities, while chips from a dry grinding process run without oil could be recycled directly.

• Let solids drip on a screen or a tray with holes, and keep oily rags out of the pail.
• Pour off standing coolant from sludge, then close the lid against rain and wash water.
• Do not store anything wet. Cutting fluids can change with use and contamination, metal chips included, and grow microbes, especially when water is present. Water-based coolant also attacks the binder: a 1997 paper says cobalt leaching by water-based lubricants is usually considered the cause of sudden failures in WC-Co punching dies.
• Write down the fluid. OSHA sorts metalworking fluids into straight oils, not mixed with water, and soluble oils, semi-synthetics and synthetics, which are. Name the one that ran in the machine. Drained and dry is enough; there is no need for a solvent wash.

Sources: Pacini et al. 2023, Materials 16(4):1347; King Saud University slides: cutting fluids; Corrosion 53(10), 1997 (OSTI); OSHA: Metalworking fluids, health effects.

Picking through worn inserts is low risk: ITIA says normal use of finished tungsten carbide articles is expected to produce little or no exposure. Fine dust is the concern. OSHA says breathing cobalt dust may scar the lungs and sensitize the airways and skin, so sort at a bench, never with a grinder, and keep sludge and powder pails closed. This is not medical advice.

Sources: ITIA: health and environment; OSHA eTool: cobalt dust.