The first design, shown in Figure 1, is intended for mounting transistors and microcircuits on printed circuit boards. Soldering iron power is about 7 W. Supply voltage 6.3 V.
In Figure 1 the numbers indicate: 1 - washer 2 - bushing; 3 - base: 4 - cap; 5 - fiberglass; 6 - tube; 7 - sting; 8 stopper; 9 - asbestos thread; 10 - heating coil; 11 - handle.
The design of the soldering iron is traditional. A copper tube is attached to the handle, made of insulating material, into which the tip is pressed. 2-3 layers of fiberglass are wound on a copper tube, along which a heating coil is wound. From the outside, the spiral is insulated with asbestos thread. The entire heating element is covered with a metal cap from a multi-refill ballpoint pen. The soldering iron is assembled in the following sequence. The tube is heated with a powerful soldering iron and pressed onto the shank of a steel base.For greater reliability, drill a hole with a diameter of 0.8-1 mm in the place of attachment to the tube and rivet a piece of steel wire or nail into it. Two layers of fiberglass 40 mm wide and a nichrome spiral are wound onto the tube. The spiral is a nichrome wire with a diameter of 0.35 mm (the spiral of an electric iron) with a total resistance of 5-5.6 Ohms. The beginning and end of the winding are twisted with intermediate sections of 100 mm long copper wire with a diameter of 0.6 mm. The beginning of the winding is fixed on the tube as close as possible to the tip and nichrome wire is wound in increments of 0.3 mm. Then a thin asbestos cord is wound around the heater.
A washer is screwed to the handle and a power cord made of three insulated flexible conductors is passed through the hole in the handle and washer. They are passed through three holes in the base and screwed to the washer, installing three bushings. The insulation at the point of passage through the holes in the base should be additionally reinforced with two or three layers of fiberglass. One of the wires is connected to the shank of the base using a bandage of bare copper wire; this conductor serves to ground the soldering iron tip during operation. The remaining two are designed to connect the heater to a current source. A protective casing is put on the heater and secured with a stopper made of spring wire.
The transformer for powering the soldering iron must have good inter-winding insulation. The secondary winding current is about 1 A.
A special feature of the second design (Fig. 2) is the heater design; it is made of graphite and screwed directly onto the soldering iron tip. The design of the soldering iron is very simple. The tip is made from a copper rod with a diameter of 5 mm and an M5 thread is cut on it. Screw the nut onto the thread until it stops and put on a metal washer (Fig. 4).Then put on a mica gasket about 0.5 mm thick and carefully screw on the heater.
In Figure 2 the numbers indicate: 1 - handle; 2 - bracket; 3 - tip, 4 - mica spacer; 5 - heater assembly; 6 - petal; 7 - mica gasket; 8 - tube; 9 - graphite rod.
The heater is manufactured as follows. A graphite cylinder is tightly inserted into a piece of copper tube and ground flush with the edges. Graphite can be used from galvanic cells or commutator brushes of an electric motor. A hole with a diameter of 4 mm is drilled along the axis of the cylinder and an M5 thread is carefully cut. When screwed onto a tip, the threads undergo significant wear, so it is necessary that the threads on the tip are sufficiently clean and their length is minimal. The heater is screwed all the way into the mica spacer. Then a petal washer is put on the tip so that the copper tube of the heater fits into the recess of the petal, and a second mica gasket is put on, a second metal washer is put on, and the entire package is tightened with an M5 nut. The tip with the heater is attached to the bracket with the same nut. A 3.5 mm thick steel bracket is attached to the soldering iron handle with screws and serves as a heater conductor. The second conductor is screwed to the petal washer.
The operating voltage of the soldering iron is about 1 V, the current is approximately 15 A. The soldering iron is powered from the network through a step-down transformer. Due to the fact that the heater current is significant, the supply flexible conductors must have a cross-section of at least 3x3 mm. The heating time of the tip to operating temperature does not exceed 2 minutes. If you increase the heater current, you can reduce the heating time to a few seconds.The soldering iron is characterized by great durability, since its heater is heat-resistant and practically isolated from air oxygen.
