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Direct Electric Resistive Heating of Parallel Combination of a Crucible and Metal Stock

IP.com Disclosure Number: IPCOM000173518D
Publication Date: 2008-Aug-11

Publishing Venue

The IP.com Prior Art Database

Abstract

A liquid metal jet (LMJ) can be used for metal cutting applications. A liquid metal jet has been shown to have the ability to deliver superior cut speed and cut quality when compared against competing thermal cutting processes. It is desirable to heat the cutting fluid (liquid metal) to as high a temperature as possible for the largest cutting performance capability. Using conventional heating techniques of heating the crucible and allowing the heat to flow from natural conduction or convection requires large driving temperature differences and sluggish thermal response times. Using direct electric resistive heating of the crucible and jetting material simultaneously reduces thermal lag and temperature gradients. A configuration is shown that allows for a single electric current source to supply the current for heating the crucible and the jetting fluid simultaneously.

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PUBLIC CONCEPT DISCLOSURE

Title: Direct Electric Resistive Heating of Parallel Combination of a Crucible and

Metal Stock

    A liquid metal jet (LMJ) can be used for metal cutting applications. A liquid metal jet has been shown to have the ability to deliver superior cut speed and cut quality when compared against competing thermal cutting processes. It is desirable to heat the cutting fluid (liquid metal) to as high a temperature as possible for the largest cutting performance capability. Using conventional heating techniques of heating the crucible and allowing the heat to flow from natural conduction or convection requires large driving temperature differences and sluggish thermal response times. Using direct electric resistive heating of the crucible and jetting material simultaneously reduces thermal lag and temperature gradients. A configuration is shown that allows for a single electric current source to supply the current for heating the crucible and the jetting fluid simultaneously.

    When using a liquid metal jet for metal cutting applications, various materials may be used for both the cutting fluid and the containment vessel. Of the materials available, there are specific advantages to using copper as the cutting fluid (high thermal conductivity) and graphite for the containment vessel (easy to make, good emissivity). Graphite also has the advantage of having high electric resistivity and therefore of being suitable for I2R resistive heating. However, the low electric resistivity of copper is a detriment if heating the jet in flight with applied current is desired as the required currents are very high and jet stability is difficult to obtain and maintain.

    An applied current can have an impact on the stability of a free flowing liquid metal jet. The applied current produces "pinch" forces from imperfections in the symmetry and geometry of the jet that tries to break-up the jet causing arcing. The arcing creates additional forces on the jet segments that further disrupts and destroys the jet resulting in a greatly reduced ability of the jet to serve as a cutting mechanism. A method of applying an I2R heating current to a liquid stream and preventing the resultant destructive electromagnetic "pinch forces" would be highly beneficial.

    Also of benefit to the heating process would be the reduction or elimination of the thermal gradients and thermal lags inherent in a conventional heating method.

    Conventional heating methods utilizing induction or radiation heating can be used for exemplification of the thermal gradients and lags. A typical induction heating arrangement is shown in Figure 1. In this simplified example, water cooled induction coils are placed around the graphite crucible. The high frequency electromagnetic fields couple from the coils to the graphite and induce currents on the graphite surface w...