US3006400A

US3006400A - Method for making coil springs

Info

Publication number: US3006400A
Application number: US5684A
Authority: US
Inventors: Edwin E Foster
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-02-01
Filing date: 1960-02-01
Publication date: 1961-10-31
Anticipated expiration: 1978-10-31

Description

Oct. 31, 1961 E. E. FOSTER 3,006,400

METHOD FOR MAKING COIL SPRINGS Filed Feb. 1, 1960 2 Sheets-Sheet 1 L INVENTOR. Lg} iakz/mflfjier,

E. E. FOSTER METHOD FOR MAKING COIL SPRINGS Oct. 31, 1961 2 Sheets-Sheet 2 Filed Feb. 1, 1960 INVENTOR ffi/m United States Patent G 3,006,469 hiETHGD FQR MAKENG CGIL SPRINGS Edwin E. Foster, PA). Box 714, Austin, Tex. Filed Feb. 1, 196i), Ser. No. 5,684 9 Claims. (Cl. 153-66) This invention pertains to a method for manufacturing springs arid in particular to those springscomposed of a plurality of tightly wound convolutions. In my copending application for United States Letters Patent, Serial No. 775,490, filed November 21, 1958, now Patent No. 2,956,795, there is disclosed a ti htly wound spiral spring having certain unique properties. The method disclosed herein is especially suited for the construction of the springs shown in that application.

The spring disclosed in the aforementioned application consists of a ribbon of spring material which has been set in at least two directions. Specifically, the spring has been set in a longitudinal direction in such a manner that the ribbon when in reposed condition coils into a plurality of tightly wound convolutions. The ribbon has been further set in a transverse direction so as to tend to assume a concave-convex curvature.

By way of definition, the term set means that the ribbon has been deformed or stressed beyond its elastic limit in a manner so that any segment thereof will assume a curved configuration, with the direction of curvature depending upon the direction of the set. Accordingly the setting operation will in many instances be referred to as stressing the ribbon. The ribbon after setting will generaliy have certain residual stresses which will affect the characteristics of the spring, as discussed in my issued Patents Nos. 2,609,191 and 2,833,534 and the aforementioned patent application. These residual stresses are oriented so that they are tensile in nature on the longitudinal concave side and compressive in nature on the convex side thereof.

The relationship of the transverse set and the longitudinal set provides certain features that were heretofore impossible. Specifically, the cross curvature may be used to enhance the strength of the longitudinal set, or it may in turn be used to diminish or ofiset part of the force generated by the longitudinal set. A further feature is that the stability of the spring ribbon may be enhanced to the point that it will remain in an extended position without tending to become entangled and at the same time may readily be returned to its coiled condition.

One of the problems encountered in constructing such a spring is a suitable method for forming the transverse curvature. Heretofore it has been the practice to bend or otherwise mechanically deform the ribbon by means of dies or rollers having a curved profile. It has been found that while ribbons, transversely curved according to conventional methods, may be used in many applications of the aforementioned invention, these methods do have some limitations which prevent their use in many applications of the invention. In particular, it is not possible to impart sufficient curvature in the transverse direction to the ribbon in order to achieve a complete range of the possible reiationship between the transverse and longitudinal sets. It has been found that when the ribbon is transversely curved by conventional methods, the longitudinal setting cancels out part of the curvature and acts as a limit to the magnitude thereof.

For the above reasons I have invented a method for manufacturing spiral springs which has the foremost feature and object of overcoming the aforementioned problem. Briefly this method consists of setting or stressing the spring ribbon at an angle to the longitudinal axis thereof so that the vector components of the sets provide the transverse and longitudinal sets, as will be more fully explained hereinafter. This method makes it possible to impart a much greater range in magnitude of transverse set regardless of the amount of longitudinal set in the spring ribbon.

Another object of the invention resides in the provision of a method for making spiral springs which consists of one continuous process that is readily adapted to a high speed production.

Another object of the invention resides in the provision of a method for manufacturing spiral springs in which substantially any desired relationship between the transverse and longitudinal sets may be readily achieved. These and other objects of the invention will be apparent upon reading of the specification with reference to the following drawings:

in the drawings:

FIGURE 1 is a side View in elevation of the spring that is the subject of my co-pending application, and which may be constructed by following the method embodying the invention.

FIGURE 2 is a sectional view taken along the lines 2-2 in FIGURE 1.

FIGURE 3 is a symbolic illustration of a preferred method embodying the invention.

FIGURE 4 is a sectional view taken along lines 4-4 in FIGURE 3.

FIGURE 4:: is a diagrammatic illustration of the set after the first step of the method.

FEGURE 5 is a sectional view taken along the lines 55 in FIGURE 3.

FIGURE 5a is a diagrammatic illustration of the set which will normally result from the second step of the method.

FIGURE 6 is a diagrammatic illustration of a second preferred method embodying the invention.

FIGURE 7 is a side view in elevation of the ribbon after the first step of the method embodying the invention.

Referring now to FIGURES 1 and 2, there is shown a spring constructed according to my co-pending application, generally denoted by the numeral 10. This spring is characterized as a spiral coil formed from a spring ribbon 12 set or permanently stressed to form a plurality of tightly wound convolutions when in a reposed condition. The spring ribbon 12 before forming will generally be flat both transversely and longitudinally and may be constructed of any one of several suitable spring materials such as spring steel, brass, or the like.

Hereinafter the process of forming the coiled portion from a flat ribbon will be called either setting or stressing so that the length of the ribbon which has been subjected to the process will be called a set or stressed ribbon. In this instance the set ribbon is shown as having an extended portion 14 and a coiled portion 16. The ribbon when extended assumes a concave convex cross-section indicated at 18 with the convex side toward the center of the coil 16. When the extended portion 14 of the set ribbon is wound into the coil 16, the crossse'ction generally loses its curvature and assumes a substantially fiat configuration, as shown in FIGURE 2.

As was pointed out in my co-pending application for patent, it is believed that the force necessary to flatten the cross-section when the ribbon moves from the extended to the coiled condition counteracts or resists the longitudinal forces that tend to cause the extended portion to move to the coiled condition. Thus it is possible to partially or fully offset or even to exceed the longitudinal set by using a preselected magnitude of cross-sectional sets or curvatures. For example, if the force required to flatten the cross-sectional curvature is less than the longitudinal set, then an extended portion will tend to rewind, so that the spring is self-winding. On the other hand, if the force required to flatten a crossthen the ribbon will tend to unwind from the coil and thus will form a self-extending spring. Of course, the sets may be in balance so that the spring is neither self-winding nor self-extending. The type of spring, of course, will be dictated by the specific application in which it is to be used.

It is to be noted that there is one desirable feature common to any relationship between the cross-sectional and longitudinal sets. This feature results from the fact that the cross-sectional curvature will tend to stabilize an extended portion so as to minimize the necessity of providing means for holding or guiding the same. Heretofore, tightly wound springs have been constructed so that if the extended portion were released, due to its instability, it would become completely entangled, thus preventing rewinding into the coiled condition. Thus it was necessary to restrain the extended portion by some suitable means. By constructing the spring with the transverse curvature, it is possible to eliminate such restraining means. The feature of stability permits the subject invention to be utilized in numerous applications not possible with prior art springs.

Referring now to FIGURE 3, there is shown a diagrammatic illustration of one preferred method by which the spring may be constructed. For purposes of illus tration the method will be described in terms of a first die member and a second die member, generally denoted by the

numerals

20 and 22, respectively. The die member 20, in its simplest form, consists of a first forming edge 24 and a second forming edge 26 which is at an angle to the first edge 24. As will be apparent, the apparatus used for the practice of the method may take on many forms and for that reason, the apparatus described herein is substantially in symbolic form and for that reason should not be construed as a limitation.

The first step of the process consists of bringing the ribbon .12 into association with a die or forming edge at an angle to its longitudinal axis. Generally the angle will be within the range of to 90 deviation from the axis in either the clockwise or counterclockwise direction and will be designated by the symbol 5. The forming surface 24 as can best be seen in FIGURE 4 is of a relatively small radius so that the ribbon when brought into association therewith so as to pass around or at least partially around is deformed beyond its elastic limit and is caused to take a set at the angle of 3 to its longitudinal axis. The ribbon may be held at the proper angle by any suitable member such as the guide member 25 and may be restrained so as to be subjected to the proper tension by a conventional brake member 27. After the ribbon has passed over the forming surface 24, the set imparted thereto will cause it to assume when unrestrained the form of a helix having a pitch length greater than zero as shown in FIGURE 7. The pitch length will of course depend upon the angle at which the ribbon 12 is presented to the forming edge 24, with the pitch angle of the helix generally being substantially equal to the angle of presentation.

From the diagrammatic illustration shown in FIGURE 40, it can be seen that the residual set in the ribbon after passing over the forming edge 24, acts at approximately to the axis of the ribbon 12. The residual set R may be broken into the components R; which is normal to the axis, and R which is parallel therewith. The component R represents the cross-sectional curvature and is dependent in magnitude in any specific operation upon the angle of presentation, i.e., the greater the angle of presentation, the greater the magnitude. The component R represents the longitudinal curvature or set which if uninhibited by the former would cause the ribbon to assume a plurality of tightly wound convolutions such as that shown in my Patent 2,609,191. The resultant of these two components causes the helix shown in FIGURE 7 having a pitch length greater than zero and substantially constant helical diameter.

Referring back to FIGURE 3, it can be seen that the second step consists of drawing the ribbon 12 over the second forming edge 26. From the drawing, it can be seen that the ribbon 12 is presented at an angle on to the forming edge 26 which is of sufliciently small radius to impart a set thereto as can be seen in FIGURE 5. The angle a is opposite in direction of angular displacement form the axis as the angle and may or may not be equal thereto, as will be explained more fully hereinafter. If for example, a is equal in angular displacement to 45, then a would be equal to 360 minus 5 when the longitudinal axis of the ribbon is taken as zero. In any event on will be counterclockwise if qb extends in a clockwise direction and vice versa.

In FIGURE So there is shown a diagrammatic illustration of the set imparted by the second step. The resultant R is at the angle a with the axis and consists of the transverse and longitudinal vector components R and R respectively. The R component in the preferred method is substantially equal to R so that they offset each other.

As was mentioned previously, on may or may not be equal to 95. The essential factor in the determination of the angle a is that the R components resulting from the two forming edges are substantially equal. Thus if m'is less in angular displacement than 4;), then it would be necessary to deform the ribbon to a greater extent as it is passed over the fonning edge 24. The increased deformation may be accomplished by constructing the forming edge 26 so as to have a smaller radius than forming edge 24 or by increasing the tension imposed upon the ribbon while in association with the forming edge 26 or both. On the other hand, if the angle or is greater than t, then the amount of deformation necessary by the forming edge 26 may be less than that resulting from the forming edge 24. The lesser amount of deformation may be brought about by having the forming edge 26 be of increased radius or by decreasing the amount of tension imposed upon the ribbon while in association with the forming edge 26 or both.

After the ribbon. has been brought into association with the forming edge 26 so that R offsets R it will then assume a concave-convex cross-section. In some instances the cross curvature may be sufiicient that the lateral edgesare in a touching relationship so that a tubular construction is formed depending at least in part on the angle of approach to the forming members during the preceding steps. It should also be noted in some instances that the ribbon will coil with the concave side toward the center of the coil; however, this is not always the case.

In order to achieve the configuration shown in FIG- URE l and the advantages resulting therefrom, it is necessary to subject the ribbon to a still further step. The third step consists of bringing the ribbon into association with a second forming member which in this instance is generally denoted by the numeral 22. The ribbon 12 in this step is back bent over the die member 22 with the longitudinal axis thereof presented at substantially right angles to the forming surface of the die member. The die member 22 is of sufliciently small radius that it will overcome the longitudinal component of the sets imparted by the forming

edges

24 and 26, so that the ribbon after it has left the forming member 22 will assume a coiled form consisting of a plurality of tightly wound convolutions in a direction reverse to that of the helices which the ribbon will assume after the first two steps. Thus the spring ribbon 12 will assume the form shown in FIGURE 1 consisting of a plurality of tightly wound convolutions when in the coiled form or of a concave-convex cross-section when extended with the concave side facing away from the center of the coil.

It can now be seen that the method described specifically lends itself to a high speed production and consists substantially of a single continuous operation. It can also be seen that it is possible 'to obtain many different relationships between the two components by simple variations in procedure. For example, variations in the relationships between the transverse and longitudinal sets may be accomplished by several ways, i.e., (1) changing the angle of presentation; (2) changing the tension used during forming of the ribbon; (3) changing the radius of the forming members; (4) any combination of the first three.

Referring now to FIGURE 6, there is shown another modification of the method embodying the invention. In this modification the spring ribbon 12 is first passed over a die or forming member 50 which for purposes of illustration is represented as being constructed of a circular rod member. The ribbon 12 is brought into association with the rod member 54) at an angle as to its longitudinal axis as was described with reference to the forming edge 24 of the diagrammatic illustration shown in FIGURE 3. At this point the processes are substantially the same so that as the ribbon 12 leaves the die member 50, it will assume when unrestrained, a helical configuration having a pitch length greater than zero, depending upon the angle of approach of the ribbon. The ribbon 12 is then passed over a second die member 52 which in symbolic form is represented as being constructed of a circular rod member. In this instance, the ribbon 12 is actually back bent over the rod member 52 with respect to the association with the rod member 50. The ribbon 12 is also brought into association with the rod member 52 at an angle B to its longitudinal axis. The magnitude of the angle B is determined by that necessary to offset the transverse component of the set imparted by the rod member 50. It has been found that when the ribbon is back bent over a die member such as the rod 52, a portion of the transverse component will be cancelled. As the result of this cancelling, it may be that B should be less than However, the angle of approach will also be determined by the relationship of the radii of the forming members 5% and 52 as Well as the tensile loads imposed upon the ribbon during the forming operation. In any event, the relationship of the angles of approach will be determined in accordance with these factors. After the ribbon has been set by the die member 52, then it will form when unrestrained a coil composed of a plurality of tightly wound convolutions or when extended a concave-convex cross-section with the concave side facing away from the coil.

Although two preferred embodiments of the invention have been described herein, it is to be understood that these are merely by Way of example and are not to be construed as limitations. It is contemplated that certain modifications may be made within the scope of the claims without departing from the spirit of the invention.

What I claim is:

1. In a method for making a spiral spring composed of a spring ribbon having a set tending to cause said ribbon to assume a concave-convex cross-section and a convoluted longitudinal section, the steps comprising inducing a set in a spring ribbon so that when unrestrained, it forms a helix having a pitch length greater than zero and then inducing a set in said ribbon so that when unrestrained, it forms a helix having a pitch length of substantially Zero.

2. In a method for making a spiral spring composed of a spring ribbon having a set tending to cause said ribbon to assume a concave-convex cross-section and a convoluted longitudinal section, the steps comprising stressing a spring ribbon so that when unrestrained, it forms a helix having a pitch length greater than zero and then stressing said ribbon that when unrestrained it forms a helix having a pitch length of substantially zero.

3. In a method for making a spiral spring composed of a spring ribbon which tends to assume a concave-convex cross-section and a convoluted longitudinal section comprising inducing a set in a spring ribbon with said set being directed at an angle to the longitudinal axis of said ribbon so that said ribbon when unrestrained forms a first helix having a pitch length greater than zero and then inducin a set in said ribbon at an angle opposite in direction to said first angle so as to form a helix having a substantially zero pitch length and a direction of curvature the same as said first helix.

4. A method for making a spiral spring composed of a spring ribbon which tends to assume a concave-convex cross-section and a convoluted longitudinal section comprising stressing a spring ribbon beyond its elastic limit at an angle to its longitudinal axis so that it normally forms a helix in which the pitch length is greater than zero and in which said ribbon has a first residual stress compressive in nature on its concave side and tensile in nature on its convex side, and further stressing said ribbon so as to offset the vector component of said first residual stresses causing said helix to have a pitch length greater than zero so that said ribbon when in repose forms a tightly wound spiral having a substantially zero pitch length in which the repose radius of curvature of any segment thereof is opposite in direction to the radius of curvature of any segment of said helix.

5. In a method for making a spiral spring composed of a spring ribbon which tends to assume a concave-convex cross-section and a convoluted longitudinal section comprising stressing a spring ribbon at an angle to its longitudinal axis so that said ribbon normally forms a helix having a pitch length greater than zero, and stressing said ribbon at an angle opposite in direction of rotation from the axis to said first angle so that said spring ribbon when in repose forms a tightly wound helix having substantially zero pitch length.

6. A method for making a spiral spring composed of a spring ribbon which tends to assume a concave-convex cross-section and a convoluted longitudinal section comprising stressing a spring ribbon at an angle to its longitudinal axis so that it normally forms a helix in which the pitch length is greater than zero and in which said ribbon has a first residual stress compressive in nature on its concave side and tensile in nature on its convex side, further stressing said ribbon at an angle opposite in direction to said first angle so as to form a tightly wound helix having a substantially zero pitch length and a direction of curvature the same as said helix, and further stressing said ribbon so that it forms, when in repose, a tightly wound spiral in which any segment thereof has a radius of curvature opposite in direction to that of a corresponding segment from either of said helices.

7. A method for making a spiral spring composed of a spring ribbon having a set tending to cause said ribbon to assume a concave-convex cross-section and a plurality of tightly wound convolutions comprising drawing a spring ribbon at an angle intermediate 0 and to its longitudinal axis over a die member having a radius of curvature sufficiently small to cause said ribbon to normally assume a helix having a pitch length of greater than zero, and further drawing said spring ribbon at an angle opposite in the direction of angular displacement of said first angle from said longitudinal axis over a radius of curvature sufiiciently small to cause said spring ribbon to normally assume a tightly wound spiral having a radius of curvature opposite in direction to that of said helix and a pitch length of substantially zero.

8. A method for making a spiral spring composed of a spring ribbon having a set tending to cause said ribbon to assume a concave-convex cross-section and a plurality of tightly wound convolutions comprising drawing a spring ribbon at an angle intermediate 0 and 90 to its longitudinal axis over a die member having a radius of curvature snlficiently small to cause said ribbon to normally assume a helix having a pitch length of greater than zero, further drawing said spring ribbon at an angle opposite in the direction of angular displacement of said first angle from said longitudinal axis over a die member having a radius of curvature sufficiently small to cause said spring ribbon to normally assume a helix having a pitch length of substantially Zero, and further drawing said spring ribbon over a die member having a radius of curvature sufliciently small to cause said spring ribbon to normally assume a tightly wound spiral in which any segment thereof has a radius of curvature opposite in direction to those of corresponding segments from said helices and a pitch length of substantially zero.

9. A method for making a spiral spring composed of a spring ribbon having a set tending to cause said ribbon to assume a concave-convex cross-section and a plurality of tightly wound convolutions comprising drawing a spring ribbon at an angle intermediate 0 and90 to its longitudinal axis over a die member having a radius of curvature sufiiciently small to cause said ribbon to normally assume a helix having a pitch length of greater than zero, further drawing said spring ribbon at an angle opposite in the direction of angular displacement of said first angle from said longitudinal axis over a die member having a radius of curvature sufiiciently .small to cause said spring ribbon to normally assume a helix having a pitch length of substantially Zero, and

further drawing said spring ribbon in a direction of curvature opposite to that of the preceding steps over a die References Cited in the file of this patent UNITED STATES PATENTS 2,301,960 Lermont et al. Nov. 17, 1942 2,326,470 Lermont et al Aug. 10, 1943 2,395,651 Anderson Feb. 26, 1946 2,480,826 tAnderson Sept. 6, 1949 2,851,080 Anderson Sept. 9, 1958