Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Patent
1996-05-09
1997-12-02
Williams, Hezron E.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
374 43, G01N 2500, G01K 736
Patent
active
056938756
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for measuring the temperature of metallic workpieces and their solid content in a partially solidified state and a device, suitable for performing the procedure comprising a driving coil, an exploring coil and an electronic device for comparing the signals received from the driving coil and the exploring coil.
A variety of production processes demand as precise an understanding as possible of the temperature or the inner structural condition of a metallic workpiece. Whilst temperatures and related phase changes are of central importance in processes during which solid metallic materials are processed or refined (such as heat treatment, deformation, inductive hardening or such like), shaping in a partially solidified state (such as thixo-pouring, thixo-forging) center not only on defining the temperature, but also more significantly on accurately maintaining the required ratios of solid and liquid phases.
The object of the invention is a process for measuring a signal which depends on the electrical conductivity of the metallic workpiece and for evaluating this signal in order to be able to draw conclusions on the temperature or on the ratios of solid and liquid phases during partial melting.
Below the solidus temperature, there is a direct correlation in metals between electrical conductivity and temperature. Between the solidus temperature and the liquidus temperature, the ratios of solid and liquid phases generally cannot be recorded by measuring the temperature because the temperature can remain constant during melting and solidification until such time as the fusion heat is added or drawn off. Moreover, the temperature of the phase transition point is also affected by the heating or cooling rates. However, electrical conductivity is dependent, among other things, on the ratios of solid and liquid phases and can, thus, be used for calculating these ratios.
It is an established fact (GieBerei 80 (1993) no. 4/22nd Feb., pp. 111, 112) that a non-contact measurement of the electrical conductivity can also provide information in the solidus liquidus interval on the phase transition points and on the ratios of the solid and liquid phases in the workpiece under examination.
A separate driving coil is used there for the heating process. If the workpiece is heated up inductively, the heating device must be switched off in order to perform the measurement; otherwise, the field induced by the heating power would invalidate the measurement. At the specified measurement frequency of 1 kHz, the measurement is limited to an area of the workpiece near the surface because of the skin effect.
SUMMARY OF THE INVENTION
The present invention now entails defining a process and creating a device which is suitable for performing the process in order, principally, to avoid the above disadvantages and to find a simple and reliable solution.
This task is solved in the present invention in the form of a process as mentioned at the start, characterised in that the workpieces are sent a driving signal (i.e. reference signal) which turns into a measurement signal in an exploring coil situated near the workpiece; the measurement signal is compared with the driving signal, the driving signal is induced by an induction coil which serves to heat up the workpiece and surrounds same, a phase shift is defined between these two signals and/or a quotient is defined from the amplitude-related values of the two signals, a calibration curve relating to the inter-dependence between the phase shift and/or the value of the quotient on the one hand and the temperature of and percentage of solid matter in this type of workpiece on the other hand is plotted applying conventional methods, and in other workpieces of this type, the temperature and the percentage of solid matter are calculated from the phase shift and/or the value of the quotient by referring to the calibration curve.
The process in accordance with the invention records the condition of the entire inductively heated materi
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patent: 3222917 (1965-12-01), Roth
patent: 3981175 (1976-09-01), Hammond, III et al.
patent: 4381154 (1983-04-01), Hammond, III
patent: 4385843 (1983-05-01), Hammond, III et al.
patent: 5052819 (1991-10-01), Baratta
Patzold et al., "Determining the Solid Portion in Aluminum Alloys During Thixocasting by Means of New Eddy Current Sensor", Giesserei, No. 4, 1993, pp. 110-112.
EFU Gesellschaft fur Ur-/Umformtechnik mbH
Larkin Daniel S.
Williams Hezron E.
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