US3021412A

US3021412A - Heat treating method and apparatus

Info

Publication number: US3021412A
Application number: US735252A
Authority: US
Inventors: Carl G Whitman; Alfred T Swain
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1958-05-14
Filing date: 1958-05-14
Publication date: 1962-02-13
Anticipated expiration: 1979-02-13

Description

Feb. 13, 1962 c. cs. WHITMAN ETAL 3,021,412

HEAT TREATING METHOD AND APPARATUS Filed May 14, 1958 Emmi-U: M 9. Mad 3? $WW Mrhwy a 021 412 HEAT TREATING METIIOD AND APPARATUS Carl G. Whitman, Mukwonago, and Alfred T. Swain,

Waterford, Wis., assignors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Filed May 14, 1958, Ser. No. 735,252 9 Claims. (Cl. 219-1041) This invention relates to a heat treating apparatus and more particularly to an induction heating'apparatus and method for successively heat treating a series of metallic substantially cylindrical parts, such as rods and pins.

In the heat treating of metallic cylindrical articles there I are generally four possible types of heat treatments. It may be desirable to produce a pin that is casehardened; or one might wish to produce a pin that is through-hardened. A third alternative is annealing. The fourth is to produce a pin that has acquired certain physical and/ or chemical characteristics 'due to heat treating, such as the solutioning of austenitic stainless steel.

In thecasehardening heat treating of metallic cylindrical pins, such as piston pins, the pins are usually successively passed through an induction heating coil and quenching medium in such a manneras to form a hard exterior surface only on the pins; the interior remaining in the original state. 'In such processesit is desirable to manufacture a pin having a hardened surface of certain and uniform depth both circumferentially and longitudinally. Although the induction heating 'coil of such apparatus is generally of circular configuration and the pins are passed through the geometric center of the coil there is not always a certain and uniform. depth of hardness circumferentially on the surface of the pins. I This is largely because of the two coil leads which outwardly ex-' tend from the induction coil and, consequently, distort the coils otherwise symmetrical magnetic field. Also,

due to the mechanical clearances required to permit longitudinal feeding of pins, and deflections imposed by feeding mechanisms, precise location of pin centers relative to the magnetic field center cannot be maintained. I

The problem of having a nonuniform magnetic field is well known in the induction heating art and has been through an induction heating coil is impractical and subject to the above erratic and unsatisfactory results. The aforementioned shortcomings of the processes to produce casehardened pins also apply to the processes to produce the other three types of heat treating of metallic cylindrical parts such as pins or rods.

In accordance with our invention, an induction heating apparatus is provided which rotates pins while passing same through an induction heatingcoil in such a manner that rotation and longitudinal feed are constant and uniform in their respective rates. This desirable function is achieved by establishing a rotating magnetic field about a pin, causing rotation of the pin. The rotating magnetic field causes the pin to rotate similar to the rotor of an electric motor. out the circumference of the pin, thereby causing pins stacked above it to rotate substantially freely in the induction'heating coil.- In this manner articles are produced which are heat treated certain and uniform in depth both circumferentially and longitudinally.

It is, therefore, one object of the present invention to provide a method articles. 7 Another object of the invention is to provide a method for rotating metallic articles in a heat treating apparatus.

Another object of the invention is to provide an apparatus for uniformly heat treating metallic pins and rods.

A further object of the invention is to provide a means for rotating a metallic article in the work coil of an induction heating apparatus.

Objects and advantages other than those set forth above will be apparent from the following description when read in connection with the accompanying drawing, in which:

' fied for long rods.

partially overcome by rotating the pins as they enter and induction heating coil contacts the pins and applies torque to the pins to maintain rotation before contact is lost between the preceding rollers and the pin.

However, the pinsmust also maintain a longitudinal movement relative to the rollers or wheels in order to pass through the induction heating coil. This sliding action of the pins across the driving faces of the rollers or wheels means a loss of friction between the same and, therefore, a loss of driving force to maintain rotation. The rotation of the pins is, consequently, not positive nor constant in rate, and the hardened exterior of the pins is not certain 1 and uniform in depth circumferentially. Any arrangement of skewed rollers or wheels to achieve a combination of rotation and longitudinal feed only serves to compound the error by producing variations in the rate of rotation and longitudinal feed and, therefore, the hardened exterior surface of the pins is still not certain and uniform in depth both circumferentially and longitudinally.

In the present state of the art the rotating of short pins FIG. 1 is a cross section of the heating apparatus for metallic pins.

means for obtaining a rotating magnetic field.

FIG. 3 is a cross section of the heating apparatus modi- A preferred embodiment of the invention is illustrated in FIG. 1 which discloses apparatus particularly suitable for casehardening metallic pins. Tube 11 is provided for maintaining pins 12 in a stacked relationship. Tube 11 has an inside diameter slightly greater than the outside diameter of pins 12 to permit the pins to freely pass through the tube. A heating means such as an induction 'coil 13 connected to a high frequency source, not shown,

encircles the tube. In close proximity to the induction coil is a' quenching manifold 14. Manifold 14 has an inner diameter substantially identical to the inner diameter of tube 11 and is secured to end 16 of tube 11 and to end 17 of a second tube 18. Adjacent toend 19 of tube 18 is a means 21 for generating a rotating magnetic field which is preferably in close proximity with the induction coil. 7

Means 21, which may be referred to as a stator and is illustrated in FIG. 2 in a preferable form, comprises a series of superposed disk laminations 23 of substantially circular configuration having six equiangularly spaced poles 24- extending toward the geometric center of the laminations. Each pole supports an electrical coil 27 and all of the coils are connected in conventional manner to a three phase alternating current source (not shown).

'Ends 28 of poles 24 converge toward each other but remain spaced at a distance slightly greater than the inside diameter of tube 18. A bushing 29 having an outside diameter substantially equal to the spacedddistance of the ends of the poles and an inside diameter of the same dimension as thatof tube 18 is inserted between the pole ends 28 to electrically insulate the poles from the articles being heat treated. If desired, bushing 29 may be removably mounted so that stator 21 can ac- Thus, a uniform force is applied throughv i for uniformly heat treating metallic a commodate other bushings of smaller inside diameters. In a like manner the tubes may also be removably mounted to allow substitution of smaller tubes. Consequently, the heating unit will be capable of heat treating pins which have smaller diameters. A casing 31 which is made of an insulating material such as an epoxy resin is then formed over the entire means 21 with the exception of coil leads 32 which emerge from the casing to connect withthe electrical source. An exit tube 33 also having an inner diameter slightly greater than the diameter of pins 12 is secured to stator 21 at its exit.

In order to control the rate of descent of pins 12 a control means 36 is provided at the exit of tube 33. As illustrated in FIG. 1, a preferable means for controlling cylindrical pins comprises a roller 3'7 which is driven by an external power source and a second roller 38. Both rollers have circumferences modified to increase frictiona1 contact with pins 12, such as a bonded facing of rubber 39. The two pinching rollers are spaced from each other at a predetermined distance in order to have a gripping effect on pins 12. It may be desirable to mount the rollers in such a manner as to be able to vary their spaced relationship in order to handle pins with smaller diameters.

In operation, for the purpose of casehardening articles, pins 12 are automatically fedinto vertical tube 11 and are moved by gravity in an end to end contiguous relationship through the induction heating coil 13. In the event that the heating apparatus i arranged in a position other than substantially vertical, an external power source may be used to propel the pins. However, it is essential that the pins are maintained in friction engagement sufficient to transmit rotary action. The amount of time that it takes to pass a pin completely through the heating coil is controlled by control means 36. Thus, if a greater depth penetration is desired in the hardened zone of a pin the rotational velocity of roller 37 may be decreased. In turn the rate of travel of the pin between

rollers

37 and 38 is reduced thereby causing the rate of travel of the succeeding pins to be reduced.

As a pin emerges from the heat induction coil, it passes through the quenching manifold 14 which quickly cools it, thereby completing the hardening treatment on the outer surface of the pin. The pin continues its journey through stator 21 which produces a rotating magnetic field upon the pin. This is not to imply that the stator or its magnetic field actually rotates. The rotations are from the resultant force of the magnetic fields of the coils of each phase. Although the stator 21 of FIG. 2 has six poles, any plural number of poles maybe suitable, depending upon the rotary speed desired for the pin. In addition, although stator coils 27 are shown connected to a three phase source, a two phase source may be used and even a single phase if an additional starting means is provided to commence rotation of the pin.

The resulting uniform torque obtained from the magnetic field of the stator windings causes a rotation of pin 12a which can be considered somewhat analogous to" the rotor of an electric motor. The rotating action of pin 12a is transmitted to the succeeding pin 12b which rotates'in the induction coil 13. The transmitting of the rotation of pin 12!: to pin- 12b and the other pins stacked above is dependent on the frictional force between the two surfaces of the pins which is determined by thecoefiicient of friction of the two surfaces and the force or the weight of pin 12b and the preceding pins exerting on the surface of pin 12a. The number of pins which can be stacked without overcoming the rotary action of pin 12a is also dependent on the strength of the rotating magnetic field in addition to the frictional force between the pins end surfaces. Preferably, a shield 41 made of copper and maintained at ground potential is spaced between the induction heating coil and the coils of the stator to prevent intermixing of the magnetic fields produced therebetween.

It is noted that nonmagnetic as Well as magnetic pins may be treated in our apparatus. Whereas in the hardening of a magnetic pin, such as a steel pin, the combination of the pin and stator is somewhat like an induction motor, the combination of a nonmagnetic pin such as an aluminum pin, and the stator is similar to a repulsion motor. Furthermore, the use of the term pin in this application and the appended claims is not restricted to cylindrical pins. A pin having a plurality of circular cross sections normal to its longitudinal axis taken at the pins widest sections whereby the pin is maintained in axial alignment with the tubes may be treated in the described apparatus. Thus, a pin having a cylindrical portion at its widest section is suitable. A pin with a concave lateral surface with circular ends is also suitable. in the treatment of such modified pins a substitute means, such as a cam arrangement may be used in place of control means 36 to control the gravitational rate of descent of the pins.

The modified apparatus of FIG. 3 illustrates how a lengthy rod, perhaps twenty feet long, can be heat treated. In order to assure rotation of rod 46 throughout its passage in the induction coil 13 a second stator 47, similar to stator 21 may be positioned at the entrance of the induction coil. Stator 47 causes rod 46 to rotate as it enters the coil and stator 21 maintains rotation of the rod while it exits the coil 13. A second shield 48, similar to shield 41, is placed between the induction coil and stator 47 to prevent intermixing of their magnetic fields.

In a manner similar to the treatment of pins, thin disks such as-washer rings or circular cutting knives may be heat treated in the apparatus of FIG. 1. The disks are passed in'frictional engagement through stator 21 which exerts a rotating magnetic field on the disks. Consequently, the disks rotate and transmit the rotary action to preceding disks which rotate in the induction coil 13.

It isapparent that with a few modifications the described apparatus may be used for the other types of heat treating previously mentioned. For instance, if an annealing treatment is desired the quenching means is removed. In such a treatment it is likely that the treated articles are still at a high temperature as they engage the

rollers

37 and 38. Therefore, instead of using a bonded facing of rubber, the rollers may be serrated to provide a heat resistant gripping surface.

In view of our invention and the several modifications described, it will be apparent to those skilled in the art that other variations and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

What isclaimed is:

1-. ha method of heat treating a series of solid metallic articles the steps comprising: passing said articles in frictional engagement for transmitting rotary action through a heating means and passing each of said articles through a magnetic field that rotates in a plane that is substantially normal to the path of said articles to rotate said series of articles preceding and throughout subjection to said heating means.

2. In a method of heat treating a series of metallic pins the steps comprising: successively passing said pins in frictional engagement for transmitting rotary action througha high frequency magnetic field by gravitational movement; andpassing each of said pins through a rotating magnetic field causing rotation of said articles and transmission of said rotation to said succeeding. articles.

3. In a method of heat treating a series of metallic disks the steps comprising? passing said disks in frictional engagement for transmitting rotary action through a high frequency magnetic field and passing each of said disks through a-magnetic field that rotates in a plane that is substantially normal to the path of said disks whereby a rotary action is exerted'on said disk and is transmitted to said succeeding disks passing through said high frequency magnetic field.

'4. In a method of heat treating a metallic rod the steps said article continuously rotates while passing through i said unit.

6. In an apparatus for successively heat treating a V series of solid metallic articles: an induction heating coil;

means for moving said articles in a contiguous relationship through said coil; an array of coils positioned around the path of said articles for producing a magnetic field I that rotates around the path of the heat treated articles 1 whereby said articles continuously rotate while subjected to said heating coil.

7. In an apparatus for successively heat treating a series of metallic pins: an induction heating coil; means formoving said articles in an end to end frictional engagement through said coil; a stator defining an opening positioned in the path of said articles subsequent to their moving through said coil; and an alternating current 1 power source for electrically energizing said stator whereby a rotating magnetic field is generated in said opening, said field causing rotation of each of said articles upon entering said opening and transmission of said r0.- tation to said succeeding articles. V

8. In an apparatus for heat treating a metallic rod:

an induction heating coil; means for moving said rod through said coil; a first stator defining an opening posi- I tioned in the path of said rod precedent to its moving through said coil; a second stator defining an opening positioned in the path of said rod subsequent to its 1noving through said coil; and an alternating current power source for electrically energizing said stators whereby a rotating magnetic field is generated in said openings, said fields causing rotation of said rodthroughout its movement through said coil.

9.111 an apparatus for successively heat treating a series of substantially cylindrical metallic articles stacked end to end: an induction heating coil; a control means for controllingthe gravitational movement of said stacked articles through said coil; and a generating means for generating a magnetic field that rotates in a plane that is substantiallynormal to the path of said articles subsequent to their passing through said coil. whereby said article in said generating means and articles in said coil rotate, said generating means comprising a stator having a plurality of poles, each said pole supporting a winding 7 energized by a three phase alternating current.

References Cited in the file of this patent UNITED STATES PATENTS 975,571 Potter Nov. 15, 1910 2,454,039 COX -2. NOV. 16, 1948 2,671,160 Segsworth Mar. 2, 1954- 2,676,234 Lackner et a1 -Q Apr. 20, 1954 2,714,647 Good Aug. 2, 1955 2,749,109 Maud June 5, 1956 2,819,370 Osborn Jan. 7, 1958 p McNulty Nov. 3.