Method and apparatus for the detection and measurement of particulates in molten metal

The invention provides a new method and apparatus for the detection of non-conductive particulates in molten metals, such as aluminum, gallium, zinc and lead, that can be liquified and drawn into a suitable refractory container. The passage into the container is of very small diameter (about 300 micrometers for aluminum) and it forms part of a current path between two electrodes carrying a current of about 1 to 500 amperes. The path is surrounded by liquid metal which forms an effective Faraday cage screening the path, enabling the passage of a particulate of about 15 micrometers or larger to produce a voltage pulse between the electrodes of greater than 5 microvolts, which is detectable above the inevitable background noise, which is of about that value. The size of the pulse gives an indication of the particle size and appropriate measurement and sampling electronically of the pulses gives a rapid evaluation (less than 3 minutes) of the particle size distribution, giving the operator an opportunity of deciding immediately whether or not further cleansing of the metal is required.