Brazing apparatus having a dual function heating and eddy current probe coil

A process of using a heater assembly having an electrical resistance heating coil to position the coil adjacent to a selected section of an elongated metallic structure which is adjacent to and parallel with a conduit, and to heat said section of said structure, wherein said conduit is elongated in a direction X, comprising the steps of:

• (a) moving the heater assembly through the conduit and through the vicinity of the structure with the axis of rotation of the coil oriented substantially parallel to the longitudinal axis of the conduit while conducting an alternating current having a frequency of between about 100 to 10,000 kHz through the electrical resistance heating coil in order to induce eddy currents in the elongated metallic structure;
• (b) monitoring the changes in impedance in the electrical resistance heating coil resulting from the eddy currents induced in the elongated metallic structure as a function of the position of the electrical resistance heating coil along the longitudinal axis X of said conduit;
• (c) locating the proximal and distal edges of the structure by noting the position of the electrical resistance heating coil along the longitudinal X of the conduit when the coil impedance achieves its first and last local maximum values;
• (d) positioning said coil adjacent to said selected section of said structure by referring to the positions of the proximal and distal edges of the structure, and
• (e) conducting a heat-producing current of electricity through said coil in order to apply radiant heat to said section of said structure.

A process for using a heater assembly having an electrical resistance heating coil to locate the edges of an elongated metallic sleeve circumscribed by at least one ring of brazing material within a tube having a longitudinal axis X in order that the coil may be positioned to accurately apply a brazing heat across selected longitudinal sections of the sleeve, comprising the steps of:

• (a) moving the heater assembly through the tube and through the proximal end of the sleeve with the axis of rotation of the coil oriented substantially parallel to the longitudinal axis X of the tube while conducting an alternating current having a frequency of between about 100 to 10,000 kHz through the electrical resistance heating coil in order to induce eddy current sin the metallic sleeve;
• (b) monitoring the changes in impedance in the electrical resistance heating coil resulting from the eddy currents induced in the proximal end of the sleeve as a function of the position of the electrical resistance heating coil along the longitudinal axis X of the tube;
• (c) locating the proximal edge of the sleeve by noting the position of the electrical resistance heating coil along the longitudinal axis X of the tube when the coil impedance achieves its first local maximum value;
• (d) moving the heater assembly along the longitudinal axis X of the tube a first selected distance from the proximal edge of the sleeve so that the electrical heating coil is adjacent to a first longitudinal section of the sleeve which is not circumscribed by a ring of brazing material;
• (e) connecting said electrical resistance coil to a heat-producing current of electricity so that said coil applies enough radiant heat to said first longitudinal section of the tube which surrounds the sleeve to thermally expand said first longitudinal section;
• (f) moving the heater assembly along the longitudinal axis X of the tube a second selected distane from the proximal edge of the sleeve so that the heating coil is adjacent to a second longitudinal section of the sleeve which is circumscribed by a ring of brazing material;
• (g) heating said second longitudinal section with enough radiant heat from the heating coil so that the brazing material melts and forms a braze joint between the tube and the proximal end of the sleeve.

A radiant heater assembly for selectively applying heat to one or more longitudinal sections of a conduit formed at least in part from an electrically conductive material, comprising:

• (a) a coil formed from an electrically conductive material for both generating radiant heat when an electric current of a selected magnitude is conducted therethrough, and for transmitting a time-varying electromagnetic field through the electrically conductive material when an alternating current within a selected frequency range is conducted therethrough;
• (b) means selectively connecting the coil to an electric current of said selected magnitude and an alternating current within said selected frequency range;
• (c) means moving the coil along the longitudinal axis X of the conduit when said coil is connected to an alternating current within said selected frequency range, and
• (d) means monitoring changes in the impedance of the coil to the alternating current flowing therethrough which result from electromagnetic coupling between the time-varying electromagnetic field generated by the coil from the alternating current and the electrically conductive material present in said conduit.

A radiant heater assembly for selectively applying heat to one or more sections of a metallic sleeve disposed within a tube that is elongated along an axis X in order to braze said sleeve to said tube, comprising:

• (a) a coil for both applying radiant heat to a selected longitudinal section of a sleeve when an electric current of a selected magnitude is conducted therethrough, and for serving as an eddy current probe when an alternating current within a selected frequency range is conducted therethrough wherein said coil is elongated and is wound so that adjacent coil windings do not come into contact with one another;
• (b) switching means for selectively connecting the coil to an electric current of said selected magnitude, and for connecting the coil to an alternating current within said frequency range, wherein said switching means disconnects the coil from the current of said selected magnitude whenever the coil is connected to the alternating current;
• (c) means moving the coil along the longitudinal axis X of the sleeve with the axis of rotation of the coil substantially parallel to the longitudinal axis X of the sleeve when the coil is connected to an alternating current within said selected frequency range, and
• (d) eddy current detection circuitry for monitoring changes in the coil impedance to the alternating current flowing therethrough which result from the generation of eddy currents in the metallic sleeve.