US2390937A - Method of manufacturing volute springs - Google Patents

Description

Dec. 11, 1945. V c. J. HOLLAND 2,390,937

METHOD OF MANUFACTURING VOLUTE SPRINGS Original Filed Dec. 10, 1940 2 Sheets-Sheet l INVENTOR.

HTHG

Dec. 11, 1945. c. J. HOLLAND 2,390,937

METHOD OF MANUFACTURING VOLUTE SPRINGS Original Filed Dec. 19, 1940 2 Sheets-Sheet 2 Patented Dec. 11, 1945 METHOD- OF MANUFACTURING VOLUTE' SPRINGS Cyrus J. Holland, Chicago, Ill., assi'gnor to Holland Company, a corporation of Illinois 7 Original application December 10, 1940, Serial No. 369,456. Divided and this application July 22, 1942, Serial No. 451,84?-

1 Claim.

This invention. relates. to springs, and more particularly to a new and improved method of manufacturing volute springs, irrespective of whether the cross-section of the bar be constant or'tapered.

An object, of the invention is the provision of a new and improved. method of coiling or manufacturing volute. springs, whether the coils be free-acting or fri'ctionally engage one another during compression Another, object, of the invention isv the provision of a new and improved method of manufacturing volute. springs that involves coiling the same on a mandrel that is tapered at a greater angle than the, conventional spring, so that the completed spring will develop augmented friction during compression sufiicient to prevent harmonic action of the. spring assembly on which it is used, and/or increase the resistance of a volute spring by adding the frictional resistance due to the wedging action to the elastic resistance of. the spring.

' Other and further objects and advantages of the" invention will appear from the following description, taken in connection with the accompanying drawings, in which Fig. l is a top plan view of a volute spring embodying the invention;

Fig. 2i's aside elevation thereof;

Fig.. 3 is a. vertical section of the spring showing a portion of the mandrel therein;

Fig. 4 is a vertical section of the spring showing the same in closed position;

Fig. 5 is a side elevation of a modified form of spring construction Fig. 6 isa plan view thereof;

Fig. '7 is a vertical section of the modified form of spring showing the mandrel in position therein, withparts broken away; and

Fig. 8 is a vertical section of the modified spring shown in closed position.

It is common practice, in the manufacture of volutesprings, to wind the same on a cylindrical mandrel; or, to facilitate removal from the mandrel after col-ling, on one that is tapered slightly. Any coiled spring must, of necessity, be removed from a tapered mandrel by sliding it toward the portion of the mandrel having the least diameter and in the direction away from the machine. Also; to prevent bending of the mandrel during coiling it is desirable that the thickest part of the mandrel be held by the coiling machine. Volute springs, designed to have internal friction orfriction between the turns and made according to'the conventional method, are wound tightly under great pressure if considerable friction is to be developed. But in 'order'that this method may be utilized, the machinery for coiling the springs must be very strong or massive, and is more or less complicated and expensive.

Another method, also employed in making volute springs having internal friction comprises heating the bar before coiling to a relatively high temperature; that is, to the'desirabiecoil-ing temperature, so, that the material of the metallic bar Will be more or less plastic during coiling. In this. condition it will retain buta small amount, if any, of its resiliency during, the coiling operation, and while thus heated the bar may be coiled into the desired volute with a smaller amount of pressure. If coiled when in a more or less plastic or semi-plastic state, it will not tend to uncoil after the coiling operation. If coiled at the most desirable temperature without enormous pressure, the resiliency of the bar may cause the turns to spring. back or to partially uncoil as soon as the bar is released from. the coiling operation. and there will be little or no friction between the coils when the-spring is compressed. But heating above the desirable coiling temperature, that is, heating the bar-t0 a more or less plastic condition of the material, ma produce excessive. grain growth and subsequent heat treating may not refine such grain growth to the most desirable grain size.

Springs made from metal that is heated above the desirable temperature, whether intentionally to facilitate forming or unintentionally due to lack of proper control, ma be unsatisfactory because of lack of toughness; that is, they may be, more likely to break due to their tendency to crystallize or develop metal atatigue in a short period ofuse. V V

The present invention seeks to avoid these defects and difficulties in tightly wound volute springs by coiling the bars on conventional spring coiling machinery at a temperature at which a suitable, grain structure may be obtained by correct heat treating. The bars are coiled on mandrels having a materially greater angle of taper than is required simply for the removal of the spring from the mandrel. and at, desirable coil.- ing temperatures, or at temperatures wherein. the grain growth has not, developed to such .an extent asto render the material unsuited for its peculiar use as a spring or resilient supporting member. where high fatigue strength and. great impact strength are. necessary For convenience. of. description, the end of the springs having turns of the largest diameter something like a wedging action tending to expand the outer turn and contract the inner turns. This will develop more or less friction, the amount of friction depending on the amount of divergence of the opposite walls of the turns of the spring. The greater this divergence the greater this friction will be.

Due to the inclination of, the spiral turns there is a radial expansion of the outer turn and con traction of the inner turns of the spring during compression which tends to augment this frictional resistance among the turns. The outermost turn ofthe spring, if it constitutes the base of the spring, will rest on a support and the friction between the base of this turn and the support will resist expansion of the turn to a certain extent when the spring iscompressed, and this in turn will cause an increase in the frictionalresistancebetween the remaining turns. ,The second largest turn will function inlike manner when it settles on the support during compression of the spring. It will thus be seen that friction is developed between the turns of the spring when it is compressed, due to the wedge form of the turns and also due to the radial expansion of these upper turns.

Referring now to the drawings, the reference character It! designates a volute spring, and H the mandrel on which the spring is wound. The mandrel has a winding section l2, which tapers from one end toward the other, as shown in Fig. 3. The spring I is fonned from a strip l3 of suitable spring material which is wound spirally, with lapping turns, on the mandrel II in the manufacture of the spring. The taper of the mandrel may be varied, and the angle of the taper will depend on the material of the bar and/or the amount of frictional resistance desired. Furthermore, the greater the angle the greater will be the friction developed between the turns as the Spring is compressed. For instance, where the spring is made from silico-manganese steel, with smooth, hard, friction surfaces, the angle will necessarily be greater than where it is made of softer material having a rougher surface. In other words, the higher the coefiicient of friction of the spring material the less acute the angle formed by the tapered walls of the mandrel may be. In any event, however, this angle must be such that the turns will release when the pressure is released.

In the manufacture of the spring the bar is heated to its most desirable coiling temperature and then is coiled on the mandrel in the usual manner. comparatively moderate pressure only is required in coiling the bar. After the spring has been formed on the mandrel it is removed therefrom and allowed to cool to a black heat and then reheated; or, it may be normalized to the desirable quenching temperature, quenched and tempered, as is usual in such constructions.

The spring, after it is coiled, may be heat treated in any approved manner. It has been found that the following heat treatment gives satisfactory results and is inexpensive and expeditious. After thecoiling operation the spring may be promptly removed from the mandrel, and, before it cools below its critical point, placed in an equalizing furnace for equalizing the tempera.- ture throughout the mass. After the spring has been brought up to quenching temperature in the equalizing furan ce, it is removed and promptly quenched in a suitable media. The spring is permitted to remain in the quenching media until a temperature of somewhere around 400 F. has been attained. It is then removed and placed in the drawing or tempering furnace and tempered in the usual manner.

' Since each turn has it walls converging toward the large end of the spring, it will be seen that when the spring is compressed the inner turns will function as wedges, and will frictionally engage the outerones with an increasing force as the spring is compressed. As a result of this construction all of the turns, with the Possible exception of the outermost, and, to a certain extent, the innermost, will be forced radially inwardly, thereby bending the turns of the spring as well as setting up torsional stresses therein. The com pression of the spring will also cause torsional stress on the turns of the spring due to the inclination of those turns. In other words, the spring will be subjected to both a bending and a torsional strain or force when it is compressed.

The frictional resistance of the turns will be such as to absorb energy and prevent harmonic action of the spring, but mustnotbe 'sufficie'nt to cause the turns to stick." ,The' frictional resistance may be varied by varying the taper of the mandrel on which the springs are wound.

Under certain considerations it is desirable that the turns of a volute spring be free-acting instead of developing friction among theturns. It is a common practice, in manufacturing volute springs having free-acting coils, to interpose 40 spacers, such as sand, wire, or the like, between the hot coils during the coiling operation, soithat these turns will be spaced apart durin the spring compression. Such a. method is objectionable because of lack of uniformity in manufacture on a productionbasis, especially if sand be employed as the spacer means. I

The present invention seeks to overcomejthis objection by the use of a tapered mandrel, whereby the springs produced will conform to a uniform standard of size, shape and quality.

In Figs. 5 to 8 isdisclosed a volute spring IS, in which the turns H5, or rather the lapping portions of the turns, separate from each other as the spring is compressed, so that the horizontaldistances l1 between the lapping portions of the turns are increased as thespring is compressed, thus providing a free-acting spring.

I am not aware that in making volute springs it has been proposed to wind the bar on a tapered mandrel so that the walls of each turn will taper toward the small end l8 of the spring-instead of toward the large end, as in the form of the spring previously described, because such a method of winding would require the removal of the mandrel from the coiling machine in order to remove the spring from the mandrel, during which time the sprin probably would cool somewhat and tend to shrink on the mandrel. The conventional method of coiling volute springs starts the coiling operation on the portion of {the mandrel close to the gripv of the machine on the mandrel, successive coils running away from the machine. In the form of volute spring now being described, the angleof the taper is materially greater than that conventionally employed for merely permitting the removal of the spring from the mandrel, and the coiling operation starts away from the machine and successive coils run toward the machine.

In order that the turns shall be free-acting, the mandrel on which the turn are wound tapers toward the small end of the spring, as shown in Fig. 7; that is, the mandrel tapers toward the small end of the spring, with a taper materially greater than is required for the mere removal of the spring from the mandrel. As a result of this arrangement the wall of the individual turns converge upwardly, as shown in Fig. '7, and it will be evident that upon compressing the spring the walls will move out of contact with each other as the spring is compressed, as indicated in Fig, 8.

This application is a division of my application Serial No. 369,456, filed December 10, 1940'.

It is thought from the foregoing, taken in connection with the accompanying drawings, that the construction and operation of my device will be apparent to those skilled in the art, and that changes in size, shape, proportion and detail may be made without departing from the spirit and scope of the appended claim.

I claim as my invention:

A method of manufacturing volute springs which comprises heating a substantially straight metallic bar of uniform thickness throughout its active length to a temperature high enough to provide ready coilin of the spring but low enough to avoid undesirable grain growth, winding the bar spirally about a tapered mandrel with the innermost turn in flat contact with said mandrel throughout its width to produce a tapered turn, and winding each succeeding turn in flat contact with the preceding turn and with the pitch of the turns of the volute increasing as the diameter of the turns increase, then heat treating the spring to give it desirable metallurgical properties, the taper of the turns being materially greater than stripping taper and large enough to compensate by wedging action of the turns for slight uncoiling of the spring during its fabrication and heat treatment, thereby to provide substantial frictional resistance between adjacent turns during some portion of the spring travel, said taper also being small enough so that the spring may bottom with heavy loads with all turns in lateral alignment and yet freely release when such load is reduced, said taper converging toward the turns of the largest diameter.

CYRUS J. HOLLAND.

Images