Particles of dry ice (frozen carbon dioxide) entrained in gas flows would be used during machining to cool cutting tools and workpieces, according to a proposal. Solid carbon dioxide particles that impinge on a tool and workpiece would absorb heat generated in the cutting process. The absorbed heat would cause the particles to vaporize. The consequent outflow of cold carbon dioxide gas would remove cutting debris and would provide additional cooling.

A Slightly Modified Atomizer would generate a spray of particles of dry ice entrained in a flow of transport gas. The spray would be used to cool a cutting tool and workpiece.
The cooling capacities of the liquid coolants used customarily in machining are marginal. Most such liquids are at least mildly hazardous and at least mildly corrosive or otherwise harmful to cutting machines, and they contaminate workpieces, making it necessary to clean workpieces after machining. Moreover, it is expensive to separate coolant liquids from machining debris for environmentally sound disposal.

In contrast, carbon dioxide is already present in the atmosphere and would not introduce any contamination. In addition, the vaporization of carbon dioxide is expected to remove heat more effectively, thereby extending the useful lives of cutting tools, increasing the accuracy of cutting, reducing and/or preventing damage to heat-sensitive materials to be cut, and/or making it possible to cut at higher speeds without degrading the cutting tools and/or the materials to be cut. Yet another advantage is that out-flowing carbon dioxide could help to prevent burning of workpiece materials (e.g., magnesium and titanium) that are susceptible to combustion when cut in air.

An apparatus for cooling by the proposed method could be constructed by (1) modifying an atomizer to handle particles of dry ice instead of a liquid and (2) adding insulation to limit the sublimation of the dry ice during storage and transit to the point of application. Referring to the figure, a supply of transport gas (e.g., air, carbon dioxide, or nitrogen) would be introduced at the inlet at sufficient pressure to provide adequate flow through the pressure regulator. Downstream from the regulator, the gas would flow through the flow-control valve, then would be throttled by the restriction before entering the delivery tube.

The hopper above the delivery tube would contain the supply of dry ice. The delivery-control valve would adjustably throttle the flow of particles of dry ice into the delivery tube. The particles would become entrained in the flow of transport gas, and the resulting mixture of transport gas and dry-ice particles would flow to the discharge port, which would be positioned to deliver the flow to the cutting tool and the workpiece.

This work was done by Thomas A. Hall and Thomas O. Hall of Johnson Space Center. For further information, contact the Johnson Commercial Technology Office at 281- 483-3809; This email address is being protected from spambots. You need JavaScript enabled to view it.


NASA Tech Briefs Magazine

This article first appeared in the July, 2002 issue of NASA Tech Briefs Magazine.

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