GB2161938A

GB2161938A - Probe for detection of surface defects in metal bodies at high temperatures

Info

Publication number: GB2161938A
Application number: GB08517563A
Authority: GB
Inventors: Federico Monti; Francesco Rossetti
Original assignee: Centro Sperimentale Metallurgico SpA
Current assignee: Centro Sperimentale Metallurgico SpA
Priority date: 1984-07-13
Filing date: 1985-07-11
Publication date: 1986-01-22
Also published as: IT8448558A0; IT1199159B; FR2567640A1; BE902862A; ATA199085A; DE3524167C2; DE3524167A1; GB8517563D0; NL8501941A; DE8519599U1; FR2567640B1

Abstract

The probe, which is especially suitable for measurement of surface defects in continuous casting products, has a structure which permits the sensor, for example a coil 7 which works on the eddy current or magnetic resonance principle, to be positioned at a distance from the surface under examination within its sensitivity limits. The probe has a metal frame 1, a coolant supply tube 3 and a protective casing containing the sensor and having a face intended to face towards the surface to be examined and acting as a window through which magnetic flux may pass from and to the sensor. The window consists of at least one sheet 11 of heat-resistant dielectric material. <IMAGE>

Description

SPECIFICATION Probe for control of surface defects in metal bodies at high temperatures The present invention relates to a probe which permits measurement of surface defects in metal bodies at high temperatures in general and especially in the products of the continuous casting process (slabs, blooms and billets) which, at the present state of the art, is an important step for achieving direct rolling which consists in rolling continuous casting products without first having to cool them.

As experts in this field are aware, methods have been proposed to solve this problem based on the use of a sensor (a coil) which works on the Foucault current or eddy current principle or on the electromagnetic resonance principle.

When making the measurements the sensor must be kept at a temperature of 60"-70" and sufficiently close to the surface under examination to ensure that it is within its sensitivity limits, whilst it scans the length and breadth of slabs whose temperature may exceed 1 000 C. A device is needed, therefore, which protects the probe and permits it to work under these conditions.

According to the present invention there is provided a container for the sensor consisting of the following elements, duly assembled: a frame designed to hold the various parts together and to provide connections for manoeuvring of the probe; a protective casing for containing the sensor and providing a chamber in which cooling fluid may circulate, the casing having a face intended to face towards the surface to be examined and acting as a window through which magnetic flux may pass from and to the sensor , said face consisting of at least one sheet of heat-resistant dielectric material the thickness of which is such that the distance between the probe and the surface under examination is kept within the limits of sensitivity of the probe; and a system for the feed and return of cooling fluid whose purpose is to keep the probe at a temperature no higher than 60"-70"C.

Preferably said face consists of at least two sheets of heat-resistant dielectric material, these sheets being given a mirror finish on their outwardly facing surfaces and being held apart from one another so as to create an air gap therebetween.

In order that the invention may be more fully understood, a preferred embodiment of the invention will now be described, by way of example, in which the single figure shows the probe in vertical section. Due to the particular construction used, the illustrated embodiment gives surprisingly satisfactory results.

The illustrated probe consists of a stainless steel frame 1, a tubular chamber made of refractory material 2 which forms the external lateral heat-screen casing, an axial tube 3 of stainiess steel for the passage of cooling air and connecting wires, and an inner frame of heat-resistant dielectric material (Teflon-Registered Trade Mark) which is connected to the axial tube 3 and is constructed in two parts.

The inner frame comprises an upper part 4 having an inverted tapered hole in its centre to facilitate connection to the axial tube 3 through which the cooling air passes and tapered on its outside towards the bottom so that, when it is assembled by screwing it to a lower part 5, the two parts 4 and 5 define a seating for a sensor comprising a circuit 6, a coil 7 and a ferrite core 8. In the upper part 4 of the inner frame there are two holes, one for the connecting wires of a thermocouple 9 and the other for the connecting wires 10 of the circuit 6. Two sheets 11 of heat-resistant dielectric material (quartz) form a wall of the probe intended to face towards the surface to be examined and act as a window through which magnetic flux may pass from and to the coil 7, so that the maximum distance between the probe and the surface under examination is 22 mm.The sheets 11 are given a mirror finish on their outwardly facing surfaces and have a stepped recess on their mating surfaces so as to form an air gap 1 2 therebetween. The thickness of the two superimposed sheets 11 is 10 mm.

1. A probe for control of surface defects in metal bodies at high temperatures, permitting measurements to be made based on the Foucault current or eddy current principle or on the electromagnetic resonance principle, whilst keeping the sensor temperature at 60"-70"C, the probe comprising: a frame designed to hold the various parts together and to provide connections for manoeuvring of the probe; a protective casing for containing the sensor and providing a chamber in which cooling fluid may circulate, the casing having a face intended to face towards the surface to be examined and acting as a window through which magnetic flux may pass from and to the sensor, said face consisting of at least one sheet of heat-resistant dielectric material; and a cooling system for the feed and return of cooling fluid whose purpose is to keep the probe at a temperature no higher than 60"-70"C.

2. A probe according to claim 1, wherein said face consists of two sheets of heatresistant dielectric material separated by an air gap.

3. A probe according to claim 1 or 2, wherein the frame comprises an outer frame made of metal, the cooling system comprises

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Probe for control of surface defects in metal bodies at high temperatures The present invention relates to a probe which permits measurement of surface defects in metal bodies at high temperatures in general and especially in the products of the continuous casting process (slabs, blooms and billets) which, at the present state of the art, is an important step for achieving direct rolling which consists in rolling continuous casting products without first having to cool them. As experts in this field are aware, methods have been proposed to solve this problem based on the use of a sensor (a coil) which works on the Foucault current or eddy current principle or on the electromagnetic resonance principle. When making the measurements the sensor must be kept at a temperature of 60"-70" and sufficiently close to the surface under examination to ensure that it is within its sensitivity limits, whilst it scans the length and breadth of slabs whose temperature may exceed 1 000 C. A device is needed, therefore, which protects the probe and permits it to work under these conditions. According to the present invention there is provided a container for the sensor consisting of the following elements, duly assembled: a frame designed to hold the various parts together and to provide connections for manoeuvring of the probe; a protective casing for containing the sensor and providing a chamber in which cooling fluid may circulate, the casing having a face intended to face towards the surface to be examined and acting as a window through which magnetic flux may pass from and to the sensor , said face consisting of at least one sheet of heat-resistant dielectric material the thickness of which is such that the distance between the probe and the surface under examination is kept within the limits of sensitivity of the probe; and a system for the feed and return of cooling fluid whose purpose is to keep the probe at a temperature no higher than 60"-70"C. Preferably said face consists of at least two sheets of heat-resistant dielectric material, these sheets being given a mirror finish on their outwardly facing surfaces and being held apart from one another so as to create an air gap therebetween. In order that the invention may be more fully understood, a preferred embodiment of the invention will now be described, by way of example, in which the single figure shows the probe in vertical section. Due to the particular construction used, the illustrated embodiment gives surprisingly satisfactory results. The illustrated probe consists of a stainless steel frame 1, a tubular chamber made of refractory material 2 which forms the external lateral heat-screen casing, an axial tube 3 of stainiess steel for the passage of cooling air and connecting wires, and an inner frame of heat-resistant dielectric material (Teflon-Registered Trade Mark) which is connected to the axial tube 3 and is constructed in two parts. The inner frame comprises an upper part 4 having an inverted tapered hole in its centre to facilitate connection to the axial tube 3 through which the cooling air passes and tapered on its outside towards the bottom so that, when it is assembled by screwing it to a lower part 5, the two parts 4 and 5 define a seating for a sensor comprising a circuit 6, a coil 7 and a ferrite core 8. In the upper part 4 of the inner frame there are two holes, one for the connecting wires of a thermocouple 9 and the other for the connecting wires 10 of the circuit 6. Two sheets 11 of heat-resistant dielectric material (quartz) form a wall of the probe intended to face towards the surface to be examined and act as a window through which magnetic flux may pass from and to the coil 7, so that the maximum distance between the probe and the surface under examination is 22 mm.The sheets 11 are given a mirror finish on their outwardly facing surfaces and have a stepped recess on their mating surfaces so as to form an air gap 1 2 therebetween. The thickness of the two superimposed sheets 11 is 10 mm. CLAIMS

3. A probe according to claim 1 or 2, wherein the frame comprises an outer frame made of metal, the cooling system comprises an axial tube, and the protective casing comprises an external lateral protective casing made of refractory material and an inner frame made of heat-resistant dielectric material, connected to the axial tube and constructed in two parts, namely a lower part and an upper part having an inverted tapered hole in its centre to facilitate connection to the axial tube and tapered on its outside towards the bottom so that, when it is assembled by screwing it to the lower part, the two parts define a seating for the sensor, the upper part of the inner frame being provided with two holes for connecting wires, and the window through which magnetic flux may pass from and to the sensor being formed of a number of sheets of heat-resistant dielectric material which passes electromagnetic waves, the sheets being given a mirror finish on their outwardly facing surfaces and being held apart from one another.

4. A probe for control of surface defects in metal bodies at high temperatures, the probe being substantially as hereinbefore described with reference to the accompanying drawing.