US2896936A

US2896936A - System for high-frequency heating of work pieces

Info

Publication number: US2896936A
Application number: US567576A
Authority: US
Inventors: Blok Lourens; Zwanenburg Gooitzen
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1955-03-03
Filing date: 1956-02-24
Publication date: 1959-07-28
Anticipated expiration: 1976-07-28
Also published as: NL87353C

Description

July 28, 1959 L. BLOK ETAL 2,895,936

SYSTEMYFOR HIGH-FREQUENCY HEATING OF WORK PIECES Filed Feb. 24, 1956 2 3 u. 2 EA c ED INVENTOR LQURENS m GOOTZEN ZWPNENUQG AG NT United States Patent SYSTEM. FOR HIGH-FREQUENCY HEATING OF WORK PIECES Laurens Blok and Gooitzen Zwanenburg, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application February 24, 1956, Serial No. 567,576

Claims priority, application Netherlands March 3, 1955 2 Claims. (Cl. 266-4) The invention relates to. a system for high-frequency heating of work pieces. More particularly;.the' invention relates to a high frequency heating system comprising a time switch to be operated by a startingwontact in order to heat the work piece for a limited period of time and, moreover, cooling means having a switchingdevice for the release of cooling fluid to cool the work piece with a certain time lag relative to the closureof the: starting contact. The cooling fluid may constitute, for example, a water jet applied subsequent to the thermal treatment.

The invention has for its object to materially simplify the control of the systems referred to above.

In accordance with the inventiomthe: system is provided with such a coupling between thestartingecontact circuit and the cooling switching device that the release or non-release of the cooling fluid depends upon the closure time of the starting contact being shorter or longer than the said time lag.

In order that the invention may be readily carried into effect, it will nowbe described more fully with reference to the following drawing, wherein: V

Fig. 1' is a schematic diagram of one embodiment of the system according to the invention in a perspective view;

Fig. 2 is a schematic diagram of an embodiment of a timing circuit which may be utilized in the system of Fig. 1; and

Fig. 3 is a schematic diagram ofan embodiment of a relay circuit which may be utilized in the system of Fig. 1.

The system shown in Fig. 1 is constituted by a highlfrequency furnace having a feed -back'electrontube oscillator, which is housed in a metal casing 1. The highfrequency furnace is preferably constructed as described in US. Patents 2,756,314, issued July 24, 1956 to Blok, and 2,773,192, issued December 4, 1956 to -Blok' et' al.

The front panel of the casing 1' is provided with. a plate 2 of insulating material, through which theoutput conductors 3, 4 of the high-frequency furnace are taken to the outside. To these output conductorsi'i, 4 is connected a working coil 5. The working coil 5 surrounds a work piece 6 to be heated, which bears on a working table 7, mounted on the front panel.

In order to control the power transferred to the work piece 6 the front panel is provided with a manualcontrol wheel 8, by which the coupling between the high-frequency oscillator and the load can be varied by mechanical means, as described for example in U.S. Patent 2,662,162, issued December 8, 1956' to Blok.

The side panels of the casing 1' are provided with air slots 9, and the right-hand side panel is provided with a switching arm 10 to switch on the supply devicefor the high-frequency generator.

Along the top side of the front panel provision is made of a measuring and control board 11, which is movable in order to render the control-apparatus mounted behind it readily accessible for supervision.

A starting contact S provided on the board 11,

"ice

which is also provided with awattmeter 13 to measurethe output power.

Behind the board 11 provision is made of a time switch 14, which is connected through a conductor 15 to the connecting terminals of the starting contact S. The time switch 14 serves to switch on the high-frequency heating for a limited period of time. In order to render this period adjustable, the time switch 14 is provided with a time-adjusting mechanism 16, the front side of which projects through a recess in the control-board 11, when it is closed, this front side being thus accessible to the operator.

The time switch 14 may, ofv course, comprise various types of apparatus, one of which types of apparatus may, for example, comprise a mechanical timeswitching clock. In the presentcase use is made of an electronic time switch, the details of which will be explained with reference to Fig. 2. p

The device comprises furthermore a cooling switching device 18, to be connected" tothe water mains through a pipe 17, in order to release a water jet through a pipe 19 providedover the work piece.

For the cooling operation the top surface 20 of' the work table 7 is depressed and provided with slots 21, which open into an 0utlet22;

If the. work piece 6 is only to beheated, the system is. controlled as follows.

First, bymeans of the time adjusting mechanism 16 of the time switch 14' the desired heating period is adjusted. Then, by transient closing of the starting contact S the time switch 14 is operated. The heating is then switched on and automatically switched out by the time switch after the predetermined periodihaselapsed; Then the high-frequency heated workpiece is cooled in the natural way..

If it. is desired to apply a forced cooling to the work piece, the starting'contact S. isnot. only closed'transiently, as in the aforesaid case, but it is kept closed, so that the cooling switching device 18,. after a period determined by a delay device 23, is excited automatically through a conductor 24. p

The delay device 23; as well as thetime switch'14, is connected through the conductor 15" to the connecting terminals of the starting contact S. The delay device 23 is preferably adjustableand may, for example, be constituted by a relay of known type, responding with time lag, for example a thermal relay or a switching clock work. As an alternative, use may bemade of an e'lec tronic delay device, for example", a" suitable trigger circuit (one-short multivibrator).

Since, in principle, in the system shownin Fig. 1 the] heating period and the delay 'before'switching on the cool ing fluid are independent of one another, it is possible to: cool forcedly the work piece duringthe last part of the heating period; This may be desired, forexample for tempering;

If a forced cooling is only' desired immediately after the heating operation, the control-

apparatus

14, 23, 18 may be simplified by'using thetime switch 14at the same time as a delay device. The timeswitch 1'4 is-connected, in this case, through the conductor 25- (shown in broken lines in Fig; 1') to the cooling switching device1 8 and the delay device 23 is dispensed with. p p p Figs. 2 and 3 are detailed embodiments of apparatus which are very suitable inpractice. p i i Fig. 2 is a timing circuit of known type, constructed as a multivibrator with a single stable: operational posivia a contact (not shown).

shown), via the energizing winding of a time-switch relay B and a working contact a of a switching relay A to be described hereinafter, this relay switching on, upon excitation, the high-frequency heating'for the work piece The time-switch relay B keeps a holding circuit of the'switching relay A closed by means of a working contact b for the duration of the energization.

r The control-grid of the triode 27 is connected, for direct-current feed-back, to a tapping point of a potentiometer with resistors 32, 33 and 34 connected between the anode of triode 28 and ground. The anode of triode 28 is connected via an anode resistor 35 to the anode voltage lead 31. Between the anode voltage lead 31 and ground provision is made of a

potentiometer having resistors

36 and 37. The control-grid of triode 28 is connected on the one hand via an adjustable resistor 39 to the junction 38 of the

potentiometer resistors

36, 37

and on the other hand via a capacitor 40 to a variable tapping point of the cathode resistor 29. The capacitor 40 is shunted by a rest contact [2 of the time-switching relay B in series with a resistor 41.

With a suitable choice of the control-grid voltage ap plied to the control-grids of

triodes

27 and 28 the triode 27 is cut off in the rest position of the multivibrator described above and the triode 28 draws current. upon the energization of the switching relay A, the working contact a is closed, the anode of triode 27 starts to take current, so that, as is known, a relaxation is produced and the multivibrator changes over into the socalled operational position, in which the triode 27 takes the full anode current and the triode 28 is cut ofi by negative grid bias voltage.

When the triode 27 is conductive, the time-switching relay B included in the anode circuit thereof is energized and the rest contact b is open. The capacitor 40 included in the control-grid circuit of triode 28 is then no longer shunted by the resistor 41, so that the triode 28 can become conductive only with a time lag determined by the charging time constant of the capacitor 40. The charging time constant of the capacitor 40 can be controlled coarsely to adjust the desired heating period by means of the variable resistor 39 and finally by the adjustment of the tapping point on-the cathode resistor 29. At the termination of the adjusted time, the triode 28 starts taking current, the multivibrator flops back into the rest position, the time-switching relay B is deenergized and the rest contact b is closed.

In order to render therest position of the triode 27 independent of temperature fluctuations, the resistor 32 of thepotentiometers 32, 33, 34 is shunted by a resistor 42 with negative temperature coetficient.

Fig. 3 is a relay circuit arrangement for use in conjunction with the time switch shown in Fig. 2, this arrangement being connected to

terminals

43 and 44 of an alternating-current source for energization of relays. This relay arrangement includes the starting contact S, described with reference to Fig. 1, a switching relay A (referred to above) with working contacts a and a;,, working contacts b b and rest contact b., of the timeswitching relay B of Fig. 2, an auxiliary relay C with a change-over contact and a working contact 0 and finally a cooling relay D, which forms part of the cooling switching device 1801:" Fig. 1 and which, upon energization, opens a valve (not shown in the figures) to release the cooling fluid.

In the rest position none of the relays A to D is enengized and the relay contacts shown in Figs. 2 and 3 occupy the positions shown.

The relay arrangement becomes operative by depressing and hence closing the starting contact S. The starting contact S completes the conventional energizing circuit of switching relay A via the change-over contact c When the switching relay A is energized, the working cona, and a are closed. and the high-frequency heating When,

current is switched on by means of a working contact (not shown).

The closure of the working contact a prepares a holding circuit for the switching relay A, this holding circuit including a working contact b of the time-switching relay B. p 7

By closing the working contact a included in the anode circuit of the triode 27 of the time-switch shown in Fig. 2, thetime-switching relay B is energized in the manner described above for a predetermined period. Thus the contacts b b 12 are changed over.

The working contact b completes the holding circuit of the switching relay A, already prepared by the working contact a so that upon release and thus opening of the starting contact S, or after the change-over contact c has been changed over into the working position, the switching relay A remains energized via an interruptor 45 (to be described hereinafter) and the working contacts a and 12 The working contacts b completes the energizing circuit of the auxiliary relay C via the push button 45 and the working contact a so that auxiliary relay C is energized, the change-over contact 0 is movedinto the working position and the working contact 0 is closed. The change-over of the contact 0 into the working position results in the completion of a holding circuit for the auxiliary relay C. This holding circuit extends from the terminal 43, via the starting contact S, the change-over contact in the operational position, and the energizing winding of the auxiliary relay C to the terminal 44. The working contact a; results in the preparation of the energization of the cooling relay D.

The closure of the starting contact S thus results, as is described, in the energization of the relays A, B and C in a rapid order of succession. The cooling relay D is not yet energized.

If the starting contact S is closed only transiently i.e. for a time shorter than the duration determined by the time switch, the time switch is operated by means of the switching relay A and the relays B and C are energized. When the time-switching relay B is deenergized, all relay contacts return into the positions shown, since the working contacts b and b open the holding circuit of the switching relay A and the normal energizing circuit of the auxiliary relay C respectively. Thus, upon a transient closure of the starting contact S the work piece to be treated is only heated, since the cooling relay D is not energized.

However, if, subsequent to its closure, the starting contact S is kept closed, the deenergization of the timeswitching relayB results it is true, again in the deenergization of the switching relay A, but the auxiliary relay C remains energized via its holding circuit including the starting contact S and the change-over contact 0 in the working position. The working contact c in the energizing circuit of the cooling relay D remains closed. When, upon deenergization of the time-switching relay B, the rest contact b returns into the rest position (termination of the heating of the work piece), the energizing circuit of the cooling relay D is closed. Relay D is thus energized, so that the water current flows until the starting contact is released.

Thus, when the starting contact S is kept closed, the work piece is heated and immediately thereupon a forced cooling of thework piece is automatically obtained.

The system described above may be constructed for manual operation in a simple manner. In such a case the time switch is not operated. To this end, the system is provided with an auxiliary switch, which, upon being changed over from the time-switch position T into the manual position H, interrupts the anode voltage le ad of the time switch via a contact 46 in Fig. 2 and shunts the working contact b in the holding circuit of switching relay A by means of a contact 46' in Fig. 3.

By a transient closure of starting contact S the switching relay A is energized and remains energized via its holding circuit. The high-frequency heating is then switched on by means of the working contact (not shown and referred to above) of switching relay A. In order to terminate the heating, the holding circuit of the switching relay A includes the interrupter 45.

While the invention has been described by means of a specific example and in a specific embodiment, we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. High frequency heating apparatus for heating a work piece, comprising switching means for applying heating energy to said work piece for a predetermined period of time, cooling means for applying a cooling medium to said work piece, means for starting the operation of said switching means and said cooling means, and means comprising said switching means for delaying the operation of said cooling means for a predetermined period of time after the actuation of said starting means upon continuous actuation of said starting means, and for preventing the operation of said cooling means upon actuation of said starting means for an interval less than said last-mentioned period of time.

2. High frequency heating apparatus for heating a Work piece, comprising switching means for applying heating energy to said work piece for a predetermined period of time, said switching means comprising a time switching relay having a working contact and a rest contact and means for energizing said time switching relay during the application of said heating energy, cooling means for applying a cooling medium to said work piece, means for starting the operation of said switching means and said cooling means, and means comprising said switching means for delaying the operation of said cooling means for a predetermined period of time after the actuation of said starting means upon continuous actuation of said starting means and for preventing the operation of said cooling means upon actuation of said starting means for an interval less than said last-mentioned period of time, said last-mentioned means comprising an auxiliary relay having a holding contact and a Working contact, means for energizing said auxiliary relay including the working contact of said time switching relay and means for holding said auxiliary relay energized including the holding contact of said auxiliary relay in series circuit arrangement with said starting means, said cooling means comprising a cooling relay and means for energizing said cooling relay including the rest contact of said time switching relay and the working contact of said auxiliary relay in series circuit arrangement with said starting means.

References Cited in the file of this patent UNITED STATES PATENTS