Electric heating – Heating devices – Tool or instrument
Patent
1988-07-05
1991-06-04
Bartis, Anthony
Electric heating
Heating devices
Tool or instrument
219499, 219501, 219505, 228 51, H05B 102, B23K 302
Patent
active
050216341
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a temperature-controlled soldering iron especially adapted for soft soldering, silver soldering and the like, the power of which is varying. as a function of the thermal energy absorbed by the soldering tip, the sensing means for measuring the soldering temperature being formed of the same resistor supplying thermal energy to the soldering tip. Furthermore, the soldering iron of the invention has a very low thermic inertia so that the supplied power is immediately adapted to the required power.
Soldering irons available at the present time to carry out soft solderings are essentially of three different types: The so called quick or gun soldering irons with control switch adapted almost to soft soldering and having a soldering tip reaching very quickly the operating temperature corresponding to the melting temperature of the solder. Such soldering irons have a voltage transformer with the secondary winding connected to the soldering tip.
Soldering irons of the second type have a continuously energized resistance and soldering irons of the third type almost are the same as those of the second type with the provision of a thermostat controlling the power supply to the resistance and interrupting it when the soldering tip reaches an excessive temperature. All these soldering irons give troubles that do not allow satisfactory solderings to be carried out.
In fact soldering irons of the first type or quick soldering irons operate at varying soldering temperatures and with constant power so that soldering tip can also reach a very higher temperature than the melting temperature of the solder, which may cause the latter to "burn" and to "form alloy" with the soldering tip which may become inoperative.
Also soldering irons of the second type in which the temperature control occurs by heat dissipation in the room suffer of the same trouble of reaching very easily temperatures such as to burn the solder and to cause the latter to form alloy with the soldering tip.
Finally soldering irons of the third type have the essential drawback due to the high thermic inertia of the structure, even if they theoretically have the advantage that the soldering temperature is held by the thermostat substantially constant. The drawback resides in that sensing means and heating means are two different elements with the consequence of an unavoidable delay in the reciprocal adaptation to the sensed and caused temperature variations. This causes an overshoot i.e., an oscillation over and below the predetermined temperature which is very undesiderable especially in the soldering of delicate components so that the advantages of such soldering irons are more theoretical than practical.
Therefore the use of the soldering irons available at the present time gives rise to considerable troubles. As a consequence of above, in the use of such soldering irons in circuits comprising electronic components determinate precautions prolonging operating time and cost should be taken.
This invention seeks, therefore, to provide a soldering iron completely free from the drawbacks of the soldering irons available at the present time.
The soldering iron of the invention comprises a soldering tip temperature control circuit controlling automatically the supplied power according to the power absorbed by the soldering, with the consequence that the predetermined soldering decrease being in practice negligible.
The soldering iron of the invention is temperature controlled by means of a heating element having a resistance which varies as a function of temperature, mounted in close thermal contact with the soldering iron tip. A Wheatstone resistance bridge includes the resistive heating element as one leg thereof, and a DC power supply supplies power to the bridge and to the heating element therein. A switch means is connected to the bridge and includes a control lead for switching on and off current flow through the bridge. A comparator includes two inputs connected to opposite nodes of the bridge and an output connected to the control
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"Temperature Controlled Soldering Iron", by Planmen Pazov, ETI, May 1981, vol. 10, No. 8, pp. 24-27.
Francolini Emmanno
Santoro Giovanni
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