Key Words

Materials: Metal swarf from tool cutting.

Technologies: Scrubbing and separation of swarf to recover metal alloy.

Applications: Feedstock source for smelters, tool manufacturers, and specialty steel producers.

Abstract: Develop a scrubbing and separation technology that would produce a recyclable metal alloy acceptable as a feedstock source for smelters, tool manufacturers or other consumers of steel.

This project evaluated the feasibility of the separation and subsequent recovery of usable steel alloy from grinding swarf generated as a waste stream from high-speed tool cutting. The primary objective was to develop a technology that would produce a recyclable metal alloy acceptable as a feedstock source for smelters, tool manufacturers, or other consumers of quality steel. Testing and process development occurred at bench-scale level only; the process was not pilot tested.

Background

Grinding swarf is a significant by-product of tool cutting and other metal cutting technologies. In many cases, swarf is landfilled, although the metal constituents, oil, and filter media, if separated, are valuable feedstock materials. Depending on the cutting and grinding process and type of steel being cut, residual swarf usually contains steel cuttings, filter media, coolant oil, burr grit, phosphorus, and other potential contaminants.

The contaminants found in tool grinding swarf cause technical problems in a remelt process. Nonmetallics create undesired slag in the metal remelt process. Oil, if present above about 3%, can burn in the melt. If the oil concentration is too high, the oil can burn explosively. Phosphorus, which is present in the cutting oil, typically remains on the metal alloy particles as well, in levels greater than 0.03%. This level is unacceptable for recycling of the metal in a smelter or other recovery alternative.

A meeting in August 1996, facilitated by the Center for Waste Minimization (South Carolina), included three major cutting tool manufacturers (CTM) and three high speed steel (HSS) producers. This group agreed on the makeup of the recovered metals, including allowable contaminant levels, that would render the material useable in their processes. Those initial contaminant limitations (by weight percentage) were:

Oil Less than or equal to 5%

Nonmetallics Less than or equal to 14%

Phosphorus Less than or equal to 0.10%

Subsequently, the HSS producers stipulated a more stringent set of target contaminant limitations (by weight percentage) on the recovered metal:

Oil Less than or equal to 3%

Nonmetallics Less than or equal to 5%

Phosphorus Less than or equal to 0.03%

The 0.03% phosphorus limit is non-negotiable, and is the maximum allowed for the accepted standard for all HSS grades, as stipulated by the HSS producers and CTMs as buyers.

During the scope of the project, Timken-Latrobe, a steel manufacturer that uses electric arc furnances to produce their products, changed the nonmetallic limit to be less than or equal to 3%. This reduced level of allowable contaminants requires significantly more scrubbing and separation effort than the original limits of 5% oil, 14% nonmetallics and 0.1% phosphorus.

Project Description

A tool manufacturer provided swarf samples for use in the process development. The manufacurer uses two different filter media, diatomaceous earth (DE) and perlite. Samples of both were acquired and tested.

Under the scope of this project, bench-scale process development and testing was conducted to optimize a process design for removal of the higher-value steel cuttings from the swarf, for reuse, in a pilot-scale separation. The following parameters were optimized for scrubbing/washing, and separation of the metal from the remaining constituents by various means:

Percent solids (pulp density)

Surfactant type and add rate

Number of scrub cycles

Residence time in each rubbing/washing cycle

Residence time for oil settling and removal

Foaming reagent type and add rate

Findings and Recommendations

The perlite-bearing swarf cleaned better than the DE-bearing swarf using this scrubbing technology. The scrubbing and decanting sequence, through 11 cycles, provides adequate oil removal for use of the scrubbed solids in Timken-Latrobe’s processes. 76% of the contained oil was easily removed during scrubbing and decanting, and may be clean enough for alternative uses, such as cogeneration.

A magnetic separation technology, called wet high intensity magnetic separation (WHIMS) produced an acceptable

notmetal removal efficiency in one sample. This, or another technology that produces less than about 3% nonmetallics in the scrubbed solids is necessary to produce a feed acceptable for remelt.

The phosphorus content of the samples analyzed indicate that the level, at an average of 0.031%, is still too high for use by HSS producers and CTM buyers. Attempts to remove phosphorus below this level, such as pH alteration, were not successful.

Bench scale testing did not produce enough clean metal cuttings for evaluation by Timken-Latrobe. They would require 25 tons of metal cuttings to evaluate in a production furnaces. Because the production of such a huge quantity of material was not possible under this project scope, this usability evaluation could not take place.

Additional research is necessary to develop an efficient pilot scale process, achieve the required purity of the metal, and determine if the oil and filter media can be recovered for alternative uses.

Markets

The markets for recovered swarf are somewhat limited. Timken-Latrobe is one potential buyer, however, since the aforementioned meeting, two of the major HSS producers are no longer producing HSS in quantity for CTM consumption and therefore are not viable markets. There are a few specialty steel producers in the U.S. that may be interested in the scrubbed swarf, especially since the alloy contains Molybdenum. Typically, 5% to 8% of HSS swarf is molybdenum. Other HSS producers exist in the foreign arena. The metal in the swarf could likely be brokered to several manufacturers/producers overseas, especially in countries when there is a solid metal working industrial base (e.g., CTM customers) and specialty steel producer(s).

Report Date: August 2000