US2757268A

US2757268A - Electrical heating apparatus

Info

Publication number: US2757268A
Application number: US350131A
Authority: US
Inventors: John M Edwards
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1953-04-21
Filing date: 1953-04-21
Publication date: 1956-07-31
Anticipated expiration: 1973-07-31

Description

E John M. Ed

Y ffm ATTORNEY United States Patent ELECTRICAL HEATING APPARATUS John M. Edwards, Ruxton, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 21, 1953, Serial No. 350,131

3 Claims. c1. 219-10.75)

My invention relates to electrical heating apparatus and relates, in particular, to apparatus for heating by high frequency induction the valve seats of internal combus tion engines and similar surfaces of restricted area.

The repeated impacts which the valves of internal combustion engines impose on their associated valve seats makes it necessary that the surfaces of the latter be of hardened steel. It has been conventional practice in the automobile and other industries to make the valve seats as separate parts which can be heat treated and hardened before assembly with the engine body. It would, however, be possible to save material and expense if the valve seats could be made integral with the engine and hardened in place. Attempts have been made to do this by induction heating, using currents in the audio frequency range, i. e., not over 15,000 cycles per second; but it has been found impossible in these arrangements to avoid heating a large volume of the engine wall back of and around the valve seat, with a consequent high expenditure of heating energy and general expensiveness in the process.

One object of my invention is accordingly to provide an arrangement for heating valve seats and similar restricted surfaces of metallic bodies by induction heaters so designed as to confine the high temperature to a very restricted volume of metal in the immediate vicinity of the desired surface.

Another object is to provide an induction heating arrangement for metal surfaces which shall confine high temperature to a region of very small depth behind the surface.

Another object is to provide an arrangement for hardening or otherwise heat treating valve seats of internal combustion engines which shall confine the region of high temperature to the metal in the immediate vicinity of the valve seat surface.

Another object is to provide a new and more economical arrangement for heat treating valve seats of internal combustion engines.

Still another object is to provide an improved arrangement for heat treating valve seats or similar restricted surfaces of internal combustion engines.

Other objects of my invention will be apparent upon reading the following description taken in connection with the drawings, in which:

Figure 1 is a schematic showing in perspective of an apparatus embodying the principles of my invention for heat treating the valve seats in an internal combustion engine head;

Fig. 2 is an enlarged perspective view of the induction heating coil used in the Fig. 1 apparatus; and

Fig. 3 is an enlarged sectional view showing the heating coil in operating position for heat-treating the valve seat in the Fig. 1 apparatus.

In general, I attain the above-mentioned objects by employing radio frequency currents, i. e., currents of frequency above about 50 kilocycles, traversing inductors of conical or other form adapted to produce localized magnetic fields concentrated on the surface to be heated, and maintain these currents for such a short time that the heat inflow is cut off before the high-temperature zone produced in the surface layer has time to extend very far below the metal surface.

Referring to the drawings in detail, the engine block 1 to be heat treated is held by a table or other suitable support 2. The valve seats 3 which are to be heat treated are of circular section having the general contour indicated in Fig. 3 and their internal diameter is of the order of an inch at the narrowest section. To obtain close coupling between the heating coil 4 and the surface of valve seat 3, and to insure uniform distribution of heat around the circumference of the seat, considerable precision in relative positioning of the coil and valve seat is required. My experience indicates that this precision may be attained most readily by making the support 2 movable while the coil 4 is held stationary on a rigid support arm 5 which projects from the stationary transformer 6. Such a movable carriage or support 2 might, for example, comprise a base 7 on which the transformer 6 rests and having a frame 8 movable on one coordinate axis by threaded shafts like 9, a plate 11 moved along a second coordinate by threaded shafts like 12, and vertical screws 13 controlling the height above base 7 of engine support 2. Other arrangements for the desired adjustable positioning of support 2 could readily be devised by men skilled in the art.

The transformer 6 has a suitably low-voltage secondary winding 15 terminating in strap copper leads 16 which extend on opposite sides of the arm 5 which is of insulating material. The primary winding 17 of transformer 6 is connected to a suitable generator 18 of radio frequency oscillations which is controlled by a supply line switch 19 and a timer 21 which is, in turn, controlled by a foot-switch 22. The timer 21 may be set to cause generator 18 to impress radio frequency voltage on transformer 6 for any desired interval, usually of the order of 20 seconds.

On the ends of strap leads 16 are attached the vertical ends of the heating coil 4 which has the form shown in Figs. 2 and 3. This coil 4 comprises short vertical leads and two complete turns, in planes normal thereto, of copper tubing which may be of one-eighth inch outside diameter and about .020 wall-thickness for treating valve seats of the size mentioned above. The planes of the two turns may be about three-eighths of an inch apart and the vertical leads about nine thirty-seconds apart between the nearest portion of their surfaces. The outside diameter of the upper, and larger, turn may be about one and nine-sixteenths inches while the outside diameter of the lower turn may be about one and one-eighth inches. As is evident from Fig. 2, one vertical lead turns radially and continues as the upper turn; is then beat sharply inward parallel to said radial portion until near the center of the coil where it turns downward to the level of the lower turn. It then extends radially outward, turning sharply to form that turn, then extends radially inward nearly to the center where it turns upward to form the other vertical lead and attach to the end of strap 16. At their nearest points, the radial portions of the coil may be spaced about one thirty-second of an inch apart.

The ends of the copper tubing above their junction with the straps 16 are bent outward for connection to ducts 23 for cooling fluid, which flows continuously through the copper tubing of coil 4.

To harden a valve seat of the size mentioned above, the support plate 2 is adjusted so that it is positioned relative to heating coil 4 about as shown in Fig. 3, and foot switch 22 is then closed. Timer 21 then causes transformer 6 to produce a flow of about 450 amperes of five hundred kilocycle current in coil 4 for about 20 seconds. The eddy currents induced in the valve seat 3 generate a large amount of heat with extreme rapidity in a very thin surface layer of the valve seat to which these currents are confined by slrin-etfect. This thin layer is thus raised to a sufficient temperature to harden it, and this happens before the high temperature in the thin layer has time to cause much heat flow into underlying layers beneath the surface. The immediate interruption of current flow in heating coil 4 by action of timer cuts off further generation of heat in the surface layer and the high temperature there quickly disappears, thus pre venting substantial rise in temperature of any layers except the thin surface zone just mentioned. Thus almost all the electrical energy supplied is employed in raising temperature of the thin surface layer and very little wasted in the undesired heating of the remainder of the engine wall. A great saving in electric power and great reduction in size of the electrical equipment, compared with audio frequency heating, is thus attained.

Rise in temperature of underlying and interior layers of the metal is also minimized by quench spraying the metal body the instant current flow in heater 4 is cut off. For this purpose, a spray-head 25 is positioned to project water or other cooling media onto the valve seat and adjacent portions of the engine head. Cooling fluid is supplied through a duct 26 under control of an electrically operated valve 27. The latter is operated to project the quench stream by the timer 21 for any desired interval, preferably about 10 seconds, after it interrupts current flow in heater coil 4.

Although a specific embodiment of the present invention is shown and described, it is to be understood that still further modifications thereof may be made without departing from the spirit and scope of the invention.

1 claim as my invention:

1. A heat treating apparatus for a valve seat having a surface to be heat treated, said apparatus comprising a radio frequency transformer, a heating coil having an axis and being connected to said transformer and supplied thereby, said heating coil comprising two circular turns of conducting tubing respectively positioned eoaxially in parallel planes and having in-leads extending along said axis, and adjustable support means for supporting said valve seat with said surface being adjustably positioned between the respective parallel planes of said turns of said heating coil.

2. A heat treating apparatus for a valve seat having a circular surface to be heat treated, said surface hav- 5 ing an axis, said apparatus comprising a radio frequency transformer, a heating coil connected to said transformer and supplied thereby, said heating coil having an axis and comprising two circular turns of conducting tubing respectively positioned coaxially and in parallel planes and having axially extending in-leads, support means for supporting said valve seat with said surface coaxially positioned relative to said heating coil and between said parallel planes, current supply means for supplying said transformer with alternating current of a frequency in the order of five hundred kilocycles for a time period of the order of 20 seconds, and quench means for cooling said valve seats after the termination of said time period.

3. In heat treating apparatus for a valve seat having a circular surface to be heat treated, with said surface having an axis and internal diameter, the combination of a heating member having an axis and a first section positioned in a first plane and a second section positioned in a second plane, with said first plane being substantially parallel to said second plane, adjustable support means for supporting said valve seat with said surface coaxially positioned relative to the heating member and between said first and second planes, said first section of the heating member having an external diameter which is smaller than said internal diameter.

References (Iited in the file of this patent UNITED STATES PATENTS 2,378,890 Abe et al lune 26, 1945 2,397,629 Stevens Apr. 2, 1946 FOREIGN PATENTS 597,161 Great Britain Ian. 20, 1948 0 635,360 Great Britain Apr. 5, 1950 OTHER REFERENCES High-Frequency Induction Heating, by Frank W. Curtis, second edition, 1950, page 151, McGraw-Hill Book 5 Company.