US1731923A - Helical spring - Google Patents

Description

Oct. 15, 1929. G. M. EAToN4 HELICAL SPRING Filed June 18, 1927 smmxm llml A Patented Oct. 415, M1929 UNITED STATES PATENT OFFICE GEORGE M EATON, F PIT'ISBULRG'ZH, PENNSYLVANIA HELICAL SPRING Application led ,Tune 18,

, quench the spring after vhot coiling, by im- Inersingit in a tank containing a 'quenching medium. To hold the temperature of the quenching medium within proper limits, the medium is either circulated through a cooling system, or else cooling coils are installed in the tank. It has been found that when a helical spring is immersed in a quiet body of quenching medium, the resulting physical characteristics of the steel located at the largest diameter of the coil are superior to the physical characteristics of the steel located at the smallest diameter of the coil. This superiority at the outside increases as some direct function of the ratio expressed by the diameter of the rod from which thev spring is made, divided by the diameter of the mandrel on which 'the spring is coiled. It also increases as some indirect y function of the space between adjacent convolutions ofthe coiled spring. These functionscombine in limiting conditions to produce avery pronounced difference between the physical characteristics of the outermost and innermost fibres of the coils. I have known of cases where by the Brinell test the hardness of the steel on the outside of the coil was about twice the hardness on the inside of the coil. This is an entirely unsatis- 'factory condition, because in such a spring,

the weakest material has inflicted uponit the highest service stresses.

.Others have attempted to improve this situation by setting up a carefully directed circulation of the quenching medium, in an immersion quench, so that in the finished spring the hardness ofthe surface of the 1927. Serial No. 199,835.

steel is practically uniform throughout the active coils. a

The purpose of my invention is to produce a method of heat treatment whereby a still further improvement is made in the ability of the spring to resist the stress concentrations to which I have referred in my above mentioned co-pending application.

In the accompanying drawings, in which like reference numbers indicate like elements, Fig'. 1 shows across section ofJa coil of a spring during the earily stages of a quench by immersion in still oil.

Fig. 2 shows a similar cross section except that the oil is circulated.

Fig. 8 shows across section of a? spring quenched in accordance with my invention.

Fig. 4'shows a vertical section through one form of quenching rig. l

Fig. 5 shows a plan view, partly in 'section on-the line A-A of Fig. 4. l

In my c o-pending application, I have called attention to the fact that 'heat treatment tends to damage the metal in and adjacent Ito streaks. Referring to the drawings, in Fig.

1, the black area indicates metal which has been cooled by the action of the quench, theshading off representing a temperature gradient, and the unshaded core indicates that the metal in that location is still at practically the quenching temperature.

As theI metal cools, it must shrink', setting up hoop tension, unless the character of the steel'and of the quenching medium is such that martensite is formed in suiicientquantity so that its characteristic dilatation compensates for the temperature shrinkage. But it is current practice in the overwhelming majority of springs to aim at securing a 'troostitic structure, when the shrinkage mentioned will occur. The core is practically incompressible, and the rod is, too longand the ends are too rigid due to rapid cooling to permit of relief of pressure by axial plastic flow. Therefore it is inevitable that the cooler outer shell must stretch by the amount that the existing temperature gradient forces it to shrink. It is also inevitable that this stretch must concentratehn the weakest porsol tions of the outer shell. These weakest portions are of two general classes.

First-The hottest portions of the shell,"

the smallest diameter of the coils, where the forced opening of the streak during the hoop tension stage of the quench, will inevitably lead to premature failure, in the case of a hard worked spring.

Fig. 2 shows the cross section of a coil of a spring. during the early stages of an i111- mersion quench in which the quenching medium is circulated relative to the coils in a way that produces an equal cooling rate over the entire surface of the coil. While a superior peripheral uniformity of grain structure is secured by this type of quench, it is at once obvious that little if any improvement is effected if a streak is unfortunately located near the critical smallest diameter of the coil. Rigid hoop tension is set up over the entire perimeter of the section, and actual opening of any streak is almost inevitable, again resulting in premature failure.

Fig. 3 shows the cross section of a spring quenched in accordance with my invention. Briefly my invention consists of introducing the quenching medium axially into the space inside of the spring coils, or in passing the spring over a quenching rig where the spring surrounds the quenching medium, and then directing the quenching medium'radially outward against the inner surface of the coils. Within the scope of my invention, the entire quenching may be carried out from the inside, or the early stages may be handled in this Way, the completion of the quench being effected by immersion or inany other desired manner.

It will be clear to anyone skilled in the art that by cooling the critical region of the spring while regions immune from failure remain hot, I have relieved the critical region of mostof the destructive hoop tension imposed upon it by quenching methods employed prior to my invention.

It is clear that quenching rigs may be devised in great variety for carrying out my invention. I have shown only one rig which is adaptable to either liquid or gaseous quenching media, in order to demonstrate that my invention is thoroughly practical. But I Wish it to be clearly understood that my invention covers in the broadest sense the new process of quenching helical springs from the initiation of the quenching action to any desired stage,'with a quench directed outwardly from the space inside the convolutions.

In Fig. l a stand pipe 1 is connected at its lower end with alsupplyof quenching-medium 2 under any desired pressure. This supply connection is equipped with a quick acting control valve, located as may be desired, and not shown since it is obvious. The outer cylindrical surface 4 of the stand pipe 1 is machined to receive a series of pulley shaped members 5, which are all alike. The hub 6 and the rim 7 are finished oil square with the b ore 8, to a common axial length. The bore 8 is finished to an easy sliding fit on the stand pipe 1. The spokes 9 of the members 5 are of relatively small cross section and are arranged in angular spaced rel-ation throughout the stack, to offer a minimum resistance to downward flow of the quenching medium. In stacking the members 5 on the stand pipe 1, a thin washer 10, of an inside diameter equal to the diameter of the bore 8 and of' an outside diameter no greater than the outside diameterof the hub 11, is alternated with the members 5. This assembly provides an easily adjustable circular slit 12, in the horizontal plane, for the emission of a thin sheet of outwardly directed quench of uniform thickness. At the upper end of the stand pipe 1 is a return bend distributor 18 of approximately torus form. This distributor reverses the motion of the quenching medium which travels upward through the stand pipe 1 and downward through the members 5. The emission slits 12 are adjusted to a suliciently narrow opening to permit the maintenance of pressure at all the emission slits, and also to secure the desired distribution among the various slits. Below the lowest member 5 is placed a closing flange 19 which is supported on a thimble 20.

The stand pipe 1 is supported by and emerges from a tank 14 in which is a body of quenching medium 15. From this tank a hot quench outlet pipe 16 connects to the suction of the pump which supplies the pressure to the quenching medium in the stand pipe. This pump and the necessary cooling facilities are not shown, as they are familiar to those skilled in the art.

Guides 17 serve to center the spring during the operation of internal quenching. A guard 18 surrounds the stand pipe, but the radial distance between the guard and the spring is suliciently great to prevent improper internal cooling of the spring by external spatter of the quenching medium during the internal quenching operation.

In practicing my invention I enter the spring into the guides 17 from above the top of the stand pipe 1. I then open the quenching medium control valve, and drop the spring past the quenching planes and into the Amomentum. Since there are many obvious ways of doing this, no cushioning facilities are shown.

When the desired reduction has been prol duced in the temperature of the spring, it is lifted out over the stand pipe. This may be done by means of hooks, or more elaborate facilities may be provided in a variety of obvious ways.

perating under my invention, the critical inner surfaces of the coils are carried through recalescence before the spring is immersed in the bath. It is therefore evident that I have invented an improved method of quenching helical springs, which gives material protection to the critical regions during the stage of quenching in which material damage is inflicted by methods now in common use. t

`While I have described a specific form of my invention in some detail, and while I have referred briefly to a few other possibilities, it is 'obvious that a wide variety of other devices may be made and used without departing from the spirit and scope of my invention as set forth in the appended claims.

I-claim as my invention:

1. The process of quenching helical springs which comprises introducing a quenching medium inside the coils in an axial direction and then directing it outwardly into contact with the coils.

2. rIhe process of quenching helical springs which comprises moving the successive coils of the spring past a plane of quenching medium which radiatesl from the axis of the spring.

3. The process of uenching helical springs which comprises su jecting lthe same to a quenching medium acting upon the coils of the spring in a radial direction and outward- 1y from the axis of the spring and simultaneously subjecting the spring to movement longitudinally of its axis and lin the direction of the quenching medium. t

4c. The process of quenching helical springs which comprises subjecting the same to a .quenching medium acting upon the coils of the spring in a radial direction and outwardly from the axis of the spring, subjecting the spring to movement longitudinally of its axis and in the direction of the quenching medium, and subsequently immersing the spring in a quenching bath.

In testimony whereof I have hereunto set m hand.

y GEORGE M., EATON.

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