SE439718B - INDUCTION HEATER FOR HEATING OF CIRCULATED PRODUCTS, SEPARATELY ROLLING STOCK - Google Patents

Description

8305807-5 at the known induction heaters, this reduction takes place by a controllable electric semiconductor valve connected in the circuit, e.g. a triac, gradually "strangled". This is done by the valve being phase-angled, whereby in each voltage period the valve is gradually switched on later and later, so that the initially sinusoidal waveform of the current is changed into current pulses, which become shorter and shorter. Such a valve, which during the heating period is to conduct the entire current through the primary coil but then, during the demagnetization period, is to conduct for successively shorter periods of time, must be provided with devices for dissipating heat. Another disadvantage is that phase-angled, electric semiconductor valves (triacs, thyristors) generally emit radio interference, which can often be extremely troublesome.

It is an object of the invention to eliminate these disadvantages. Another object is to achieve a simple and inexpensive construction for the circuits which are to provide the current reduction for the demagnetization function.

These and other objects and advantages are achieved according to the invention in that the switching means and the means for gradually reducing the current comprise two alternatively with each switch the said switch switchable PTC resistors, arranged to bypass the current coil after the switch of the switch, and which has a low resistance at room temperature of less than about 20 ohms and a resistance, heated after loading, which is at least 100 times higher.

PTC resistor is a type of resistor, the resistance of which increases with temperature. They are commercially available and are usually specified by the resistance value at room temperature and the so-called the switch temperature, at which the temperature resistance increases very sharply with relatively small relative temperature changes. In the invention, the function is as follows. Initially, the primary coil is connected directly, via the switch, which is closed, to the mains (50 or 60 Hz, eg 220 or 110 V), whereby the transformer in the annular product induces a current, which through the product's own resistance gives cause of heating. The desired degree of heating is obtained by appropriately determining the time of the heating moment. After the heating moment, the demagnetizing moment takes place, where the present invention becomes effective. When the switch is broken, the current is conducted through the PTC resistor, which then gradually becomes hot, whereby the current through it and thereby the current through the primary coil is gradually reduced, e.g. with a primary current of 10-15 A down to about 10 mA.

The magnetization of the heated product will take place in alternating directions during successive half periods of the mains frequency, with gradually decreasing amplitudes, leading to demagnetization in the same way as when the current heaters are reduced.

With regard to the switch, it is suitable to provide a timer which, after starting, carries out a switch after a predetermined time, which is determined with regard to the size, shape and other properties of the heated product and the desired final temperature. Preferably, the switch is a contact pair in a relay.

From what has been said, it appears that the PTC resistor is heated. Before it can work again, it must therefore cool down. In order to reduce the cycle time, two or more PTC resistors should therefore be inserted in parallel, of which only one is connected at a time, e.g. with separate switches, which can be triacs. In view of the fact that these are not to be phase-angled but are either switched on or off, only negligible electromagnetic interference is obtained.

It is suitable to connect e.g. a signal lamp, which lights up when the process is completed. In many cases, the heating process takes several minutes, during which time the operator usually does not have all his attention focused on the heater.

The invention will now be described in exemplary embodiment.

Pig. 1 shows a schematic embodiment. Figs. 2 and 3 show a more detailed, largely self-explanatory wiring diagram. Fig. 1 schematically shows a transformer construction with a U-shaped transformer core 1 and a magnetok or anchor 3, which is removable for threading an annular metal product, e.g. a ball bearing (not shown), to be heated. A primary coil 2 is wound with 260 revolutions and dimensioned for 10 ~ 15 A. The transformer itself contains about 12 kg of transformer plate. (For 110 V you can have half as many revolutions and twice as much current.) From a main switch not shown, the mains current is led through the coil 2 via a switch 4, which is a relay, the coil current of which is controlled by a timer T . You can have a mechanical timer or an electronic clock, e.g. driven with the mains frequency, which is preferred.

In parallel with the switch 4, PTC resistors 5 and 5 'are located in separate branches, in series with separate switches 7 and 8, intended for alternative connection and in this case in the form of triacs.

In use, the switch 4 is first closed for a predetermined time of 0.5-10 minutes, and then switched off. One of the triacs 7, 8 is leading. During the break, the current will then take the path via one of the PTC resistors, which soon becomes so hot that the current gradually becomes negligibly small. resistor (not shown) with in the cold state the resistance 10 ohms each, and thus together 5 ohms.

A small voltage drop occurs immediately, and the resistors become hot and the resistance increases rapidly to several kilograms ~ ohm.

According to data sheets, the PTC resistors had a switching temperature of 11s ° c. fi. 1 also shows a lamb a 9, which will be lit when I g P r the course ends.

The more detailed circuit diagram in Figs. 2 and 3 is largely self-explanatory and contains common components. It is seen that a voltage divider is inserted over the primary coil, and its output C is connected to a circuit, which via ignition outputs D and B selects either of the triacs 7 and 8 to conduct next time, and extinguishes the conductor of these when the voltage over the primary coil 2, and which further arranges the ignition of an LED 9 at the end of the demagnetization process. An electronic clock circuit receives 50 periods of alternating voltage at B and will at a time determined by the setting on the potentiometer 20 open the switch contact of the relay 4 via a signal A. As such circuit diagrams constitute the actual language of the electronics engineer, the above information is quite sufficient to make the wiring diagram understandable without difficulty. 5

Claims (3)

10 15 20 25 asossøv-3 * r * ~~ - ~ Patent claim An induction heater for heating annular products, in particular rolling bearings, comprising a U-shaped transformer core (1), provided with a primary coil (2), and a magnetic yoke (3) adapted to close a magnetic circuit by trans - the formatter, and to enter thereon an annular product, which acts as a single-speed secondary coil for heating with an induced current, a switch (4) for connecting an AC mains to the primary coil (2), and means for gradually reducing the current after heating through the primary coil to demagnetize the heated annular product before its removal, characterized in that the means for the current reduction comprise two or with each switch (7,8) the said switch bypassable PTC resistors (5.5) '), arranged to bypass the current to the primary coil after the switch of the switch, and which at room temperature have a low resistance of less than about 20 ohms and are heated after loading a resistance value at least 100 times higher. Induction heater according to claim 1, characterized in that said switch is a relay (4) and that an adjustable timer (6) is connected to the coil of the relay. Induction heater according to claim 1, characterized in that said switch (7.3) is triacs.