US1946735A - Screw rolling die and method - Google Patents

Description

Feb. 12.,L 1934.

l.. AQ PRAYER SCREW ROLLING DIE AND METHOD Filed Feb. 15. 19.32 s sheets-sh t 1 Feb. 13, 1934. 1 A. FRAYER SCREW ROLLING DIE4 AND METHOD Filed Feb. 15. 1932 I5 Sheets-Sheet 3 Patented Feb.V 13, 1934 l 1,946,735 SCREW ROLLING DIE AND METHOD Lee A. Frayer; Ravenna. Ohio, assigner to Roy 11.` Smith, Kent. Ohio Application Febrpary 15, 1932. Serial No. 593,010

-20 Claims.

This invention relates to the formation of screw threads by rolling a blank between suitably shaped dies, and its generalobject is to produce work of uniform size from blankmaterial which is not uniform in size or degree of heat plasticity or malleability.

In the cold-rolling of screws, the method commonly employed involves the use of blanks with threading portions of less than the ultimate screw-thread diameter, which must be accurately made of determinate diameter and hence require a preliminary turning or equivalent operation on the blank, and dies which work simultaneously from both sides over the entire length of the screw, the metal being depressed from the blank diameter to form the inner portions of the thread groove, and raised beyond thev blank diameter to form the outer portions of the thread. In this method there is no elongation of thesblank, and the depthpf thread obtainable by cold rolling limits the size of work which can be produced.

The hot-rolling of screws is commercially practiced to a small extent by forcing a heated blank endwise between a set of die rollers whose axes are tilted and set at an angle to the axis of the blank, thereby forming the thread progressively .from the tip toward the head end of the blank, and

elongating the blank during the process. This,

method is not adapted to the formation of wood screws with pointed tips nor can it be satisfactorily used with substantially undersized material.

My present invention involves forging or swaging of the thread by working toward or to the tip end of the blank, accompanied by elongation or extrusion of the blank in that direction, and is adapted both to the forming and pointing of.

wood screws orthe making of .screws having a standard or machine-screw thread. Methods resembling'this in some particulars have previously been proposed, for example as long ago as the Beecher Patent No. 77,710 of May 12, 1868, employing either two roller dies or two flat dies whose ribbed portions are duplicates of each other, but so far as I am aware such devices have heretofore been unsuccessful, notwithstanding the potential saving in production cost as compared with cold rolling yor cutting, and the wide field for stronger and cheaper screws having threads .of reasonable accuracy.

Having ascertained the causes of prior failures, which lie principally in attempting too rapid an elongation of the blank and gathering a surplus of metal for the-initial portion of the thread which cannot be properly worked into the substance thereof, with the result'of piping or splitting the stock` or withdrawing of necessary metal from the partly-formed thread, I have been able in the present invention to provide a successful solution of this problem. Y c

It is of vital importance in progressively rolling 00 a screw thread uponfthe blank in the direction of its tip end, and incidentally elongating the blank,

to avoid the accumulation of superfluous metal between the rst two die ribs in the initial formation of the thread, for such excess in the later 05 stages mustbe squeezed out longitudinally of the thread, which produces a barrel-shaped screw or piping .ofthe stock caused by working it in an oval shape and forcing the material onward as a shell without a solid integral core. 0n the other 'I0 hand, if the proper amount of material is gathered in the thread, but the attempt is made to form a thread groove of the ultimate width andproille at the outsetl by means of the die rib which first takes hold, it will be found that said rib draws out 7l the thread metal which has just been raised and leaves a scant thread or none at all.

My invention ayoids these xdiiculties by providing dies of different characteristics for working on opposite sides of the blank so that, for l0 example, the die on one side may progressively measure out substantially the correct volume or cross-sectional area of stock for the thread, but leave it in a dierent shape or diiferent position or pitch spacing than it will ultimately BI assume, while the die on the other side may have the ultimate ypitch spacing and a groove shape whichfwill re-form the thread left by the rst die eitler to its ultimate shape or to a shape which is then further re-formed by the ilrst die. 00 The thread is thus given its ultimate shape and pitch spacing by the rst two ribs or ridges on one of the dies and the first rib on the other die, and subsequently-acting ridges and grooves which may be providedon both ofthe dies have 9| no further effect in forming the screw but act merely to guide it in order to preserve -its properly aligned position between the dies.

Of the accompanying drawings, Fig. 1 is a face or plan view of one of the thread-rolling 10o dies embodying and adapted to carry out my. invention', in this case the lower dies shown in Fig. 5, developed into a ilat surface, a wood screw being represented in four successive stages of formation along,` the die, the' integral die. sur- 10i face being divided at the dot-and-dash line and shown in two' parts placed one above the other.

Fig. 2 is a similar developed view of the opposite or upper die without the screw thereon.

Fiss. 3 and 4 are cross sections, each taken ire` through both dies and the intervening work at the positions 3-3 and 4 4 on Fig. 1.

Fig. 5 is an end elevation showing part of a screw-rolling-machine equipped with the roller dies, with the work in section.

Fig. 6 is a side view of a portion of a screw as partly formed by modified dies with a standard or machine screw thread in accordance with this invention.

Fig. 7 is a detail section of a second modication showing the pinching-oir action of suitablyformed dies in finishing the end of .a sharppointed wood screw.

While the screw-rolling dies might be nat and relatively reciprocated to act on the work in accordance with familiar practice, this would make an excessivels7 long rolling machine for large work and it is preferred to make them parts of die rollers 10, 1l, mounted one below the other on suitable shafts as indicated in Fig. 5, and rotated in the same direction at the same angular speed by means of suitable gearingconnected with their shafts as shown in broken lines. The adjacent working faces of the dies move in opposite directions, and they turn the work between them on a stationary axis. I prefer to employ overhanging die rollers, with shaft bearings on one side only.

12 and 18 are respectively the lower and upper dies proper, detachably held upon the roll bodies by suitable clamping devices. The circumferential length or each die is such as to leave preferably a In of about 30 degrees of open space bet: Us ends in order to allow ample time for i reduction of the blanks between the rolls while preserving the desired surface speed of the latter for accomplishing the production in a given time.

r"he work is laterally introduced fromy the iront or lethand side of the machine, as viewed in Fig. 5, with the aid of a reciprocating pusher i4 suitably timed by the machinewith reference to the rotary positions of the dies. A nxed abutment or back-stop 14.n is provided on the far side of the roll pass to limit the inserting moveM ment, but when. the dies have taken hold, the work moves forward slightly from this abutment and is automatically held in the narrowest part of the roll pass by the action of the dies themselves.

The ribbed thread-forming surface or' one of the dies, the lower one l2 in this case, is angularly advanced'with respect to that of the other die 13 by an amount corresponding to a half rotation of the screw blank, so that the first rib on the lower die begins to operate on the work a half-turn of the latter ahead oi the first rib on the upper die, and the lower die preferably also finishes approximately one half-turn of the work before the upper die, so that the trailing end of vthe upper die 13 lags behind that of the lower one, as seen in Fig. 5.

Advantage is taken of this trailing overlap of the upper die, in the case of short work, in helping to eject the nished screw into a notch 15 which is formed in the body of the lower die roller 10 parallel with the axis of said roller and adja- Vcent the trailing end of the lower die, whereby the finished screw, after being dropped into the notch, may be carried around to the lower side of the lower die and discharged into water in a cooling receptacle. In the case of long rods which require threading at several points along their length and are supported by a suitable work holder, or single-threaded rods so long that they would whip beyond the rolls if not so supported,

the notch l5 is not utilized but the nnished work is withdrawn laterally from between the die rollers oppositely to the. direction of its insertion.

16 indicates a cylindrical work blank or short rod which, by the operation of the dies, becomes a finished screw, as seen at the lower right in Fig. l, illustrating a railroad-spike wood-screw adapted to be screwed into a hole drilled in the tie. The blank in such a case is previously provided with a head 17 which may be forged by an upsetting operation on a heated section of the original rod. The screw body of the spike tapers down from the original diameter near the head and tapers to a blunt point at the tip or lower end, while the thread 26 is shallow at both ends and of full depth in the intermediate portion of the screw.

Both dies are provided with a series of slanting ribs or ridges and intervening thread-forming grooves having an angle to the direction of die motion corresponding to that or" the screw thread to be formed. The .rst r ing into action on the lower die I 19a and begins at a point or eno'. of Said die, preferabl'" 20 of said die which cons ward edge on the roller l0. ribabove the adjacent fiat s' is relatively small at the be te a maxirnu. at about t of the thread groove, erf; of said rib at the begin ln or front edge of the rib as gradually becomes parallel surface 2i at about the thi that the thread groove correspond shallow and increases to its bottom forming the sc threads tapers from the in 'irniun blank d eter to the intermediate gione-bottom dair and becomes fully cylindrical at about the groove turn. The ribs on the 'upper die rates o r' iivelent to those on the lower but hei 'ons er" proper height are longitud reference to the corresponding *I allow for the fact that they come into the thread groove a half-turn or the work later than the lower-die rib portions. At its trailing end this rst lower-die rib 191 e still higher, and the first rib on the upper d.V correspondingly elevated, as seen at the right in Figs. 3 and 4., to form the tapered point on the screw body.

The second rib on the lower die is numbered 19h, the third 19c and so on, while the intervening thread-forming grooves between the successive ribs are numbered 22a, 22h, 22C, etc. Each succeeding rib after the first one begins at a point further along the outer edge 2O of the die, and all of the ribs originating in this edge have pointed ends to provide an easy entrance into the blank metal or into the formed th-read groove. Each succeeding one, like the rst rib, is likewise shallowest at the beginning and increases to a 1UP. maximum depth further along, and the top face of each at the beginning is lowest on the side toward the die edge 20 and becomes parallel with the plain die face 2l at about the fourth turn of the thread groove so that the successive ribs 145 after the rst one will properly thread into the groove. As the trailing ends of the rst, second and third ribs 19e, 153b and 19c are approached, their adjoining sides forming the intervening die grooves 22E, 22b and 22c spread toward each othlo@ er, and the bottoms o! said grooves rise toward the tops of the ribs, so that the grooves taper on to nothing. The sides rof the first groove 22, and of the second one 22b to some extent, by working of the thread metal, correspondingly reduce the height of the thread which tapers down to nothing near the screw tiD,1as seen at the lower right in Fig. 1. The tops of the second, third and fourth ribs 19, 19c and 19d also rise further toward their trailing ends so 'that the second rib will participate in the tapering of the point and the third and fourth will follow the threadgroove bottom as the finished screw point rolls along to the trailing end of the die. Obviously the dies could be modified in these respects, if desired, to carry the thread clear to the end, forming an ordinary sharp-pointed wood-screw tip and pinching of! the excess metal, as shown in Fig. 7.

The opposing or upper die 13, whose development is represented in Fig. 2, except for differences in its swaging portion, has the same general form as the lower die, with thread groove-forming or groove-entering ribs 23e, 23h, 23c etc. and intervening thread-forming or guiding grooves 24e, 24", 24 etc., the ribs beginning at a shallow height at successive points along the outer edge 20 of the die, the guiding ribs having a side contour, longitudinal rate of rise and angle of top surface conforming to the corresponding ribs on the lower die but placed to act in the thread groove a halfturn of the work later than the lower die ribs. At their trailing ends, the first two ribs are raised to participate in tapering the point of the screw and the third one is also raised slightly to follow in the tapered groove bottom, while the sides of the first two and the front side of the third are spread and the rst two groove bottoms are raised so that the first groove assists tapering ofi the thread and the second one meshes with the tapered thread end. All of the ribs in this upper die have the ultimate pitch spacing of the thread turns and the groove turns to be formed on the screw, and the sides of all of them, including the first one 23, may have the ultimate thread-side angles, except that I prefer to make the angle on the back or upper side of the first rib, as viewed in Fig. 2, somewhat steeper or nearer to the perpendicular than the ultimate angle, for a purpose to be described.

In accordance with -my present invention, the profile of the first rib 19a on the lower die 12 differs considerably from that of the first rib 23n on the upper die. It forms the beginning of the thread groove with less displacement of blank metal than is required for the ultimategroove, especially at the front or lower side of said groove as viewed in Fig. I, and consequently the blank will not receive its full increment of elongation toward the tipby means of said first lower-die rib. Furthermore, this first rib is so placed in relation to the second rib 19b that the intervening partly formed thread 'in the die groove 24 to accommodate variations in circularity of the'rod stock in the blank, or variations in the diameter of the stock. For a wood screw thread having widely-spaced turns and a relatively wide groove bottom, the cross section of this first-entering rib, like that of the other ribs in bothfdies, is preferably a three-sided figure with a fiat top as previously described, but for a machine screw thread it may be two-sided as later pointed out.

The included angle between the sides of the first lower dierib 19a is greater thanthat of the second rib 19h', its top face is narrower and its pitch spacing with reference to the second rib is less than the ultimate pitch spacing. This will be evident inobserving the effect of the first lower-die rib in forming the leading end or first part 25a of the thread groove 25 as illustrated on the left-hand side of the screw in the first three positions in Fig. 1. It will also be evident on comparing the profiles and pitch spacing ofthe rst two lower-die ribs 1,9l and 19b in Fig. 4. These views further illustrate a displacement of blank metal by the first lower-die'rib less than the volume required for the intimate contour of the thread groove, and in consequence, there is only a partial increment of elongation of the blank in forming the first half-turn of said groove.

The measuring action of the first `diegroove 22B, whereby it raises .or extrudes 'the proper volume of metal for the first part of the screw thread 26, with suiiicient excess to allow for subsequent densiiication, is also illustrated in these views. The leading portion 26a of the partlyformed thread is somewhat wider at the top and its included thread-side angle less than when the thread is fully formed, 'and said top may be fiattened or slightly rounded, and the first lower-die groove 22a may be deepened and come to an apex so that the thread metal does not quite fill the bottom of the groove, as seen in Fig. 4.

Both the screw-thread groove and the thread, which were partially formed in a first step by the first-acting rib and groove of the lower die during that half-turn of the blank in which the forward end portions of said groove and thread are made, will, by a dissimilar but complemental'op- `eration in a second step performed simultaneously on the opposite side of the blank, further along said groove and thread, be wholly or partially rectified, re-formed or finished by the dissimilar 'but complemental first-acting rib and groove of the upper die in the next-succeeding halfturn, and the remaining increment of elongation will thereby be imparted to the blank without drawing out the thread metal which has been raised by the first die so as to leave a scanty or obliterated thread. This forging and re-forming action `of the upper die is effected mainly or wholly by its first rib 23a, and is illustrated on the right-hand side ofthe blank 16 in the first three positions on Fig. 1, wherein it will be seen that the rectified thread-groove portion 25b made by this first upper-die rib has been widened at bothA top and Vbottom to substantially the ultimate pitch spacing, while the adjacent thread portion 26b has been narrowed at the base, sharpened at the top and densified, and its included threadside angle increased, by the forging action `of theupper die between its first and second ribs 23 and 235. The thread may thus reach its ultimate contour in the second half-turn of the forming operation on the work or, if desired, it may be left slightly unfinished at the end of this second half-turn, by having a top slightly wider than the ultimate thread, due to an angle on the back side of the first upper-die rib slightly greater to the screw axis than the ultimate angle. and

then, by a third step complemental to the second one, be further re-formed and completely finished during the third half-turn, between the second and third ribs 1S)b and 19c on the lower die.

Thus it will be seen that the screw groove and thread formation is entirely accomplished by the rst two ribs on the lower die and the first rib on the upper die, the succeeding ribs on both dies serving merely to mesh into the formed thread groove, and by their guiding action on the screw thread, to maintain the work in proper alignment between the die rollers l0 and li, with its axis parallel to the axes of said rollers. As the formation progresses toward the tip of the screw and is nearly completed, beginning at approximately the third screw position on Fig. l, the fric tional grip of the die ribs upon the formed screw body at the bottom of the thread groove will have become so strong, owing to the increasing area of contact, that the formed thread. turns 'will begin to travel faster than their contact surfaces on the dies, and the rotating work will begin to unscrew itself in the direction of its head end, as though working against a stationary nut, such unscrewing being accompanied by some twisting of the partly-formed plastic screw upon itself as long as the screw remains unnished as indicated in the third position on Fig. l. This causes the screw-head 17 to move away from the die edges 20, as will be seen by comparing the last two positions with the first two in Fig. l, and the rate of this axial progression increases as the screw is finished and nears the trailing ends of the dies. n forming screws by this invention, the diam= eter of the stock employed may vary rather widely ior the same screw. For example, in threading the railroad spike here illustrated, the dies shown will produce the same thread from stock varying from t2; to We inch in diameter, the finished screw in each case having a inch thread. Where the blank employed is of less than that diameter, the forging action of the first ribs produces a wave in the blank metal on the advancing sides of said ribs, which brings the blank out to the iull diameter. if the screw is to be made in a relatively soft and ductile metal such as brass or copper, especially for the smaller screw sizes,

it will be unnecessary to ypre-heat the blank to increase its plasticity.

The plain-suriaced die portions 21 are made as led es of not less than one-half pitch width, formed on the respective dies adjacent the forward sides of the rst ribs i9a and 2311, and spaced apart a distance equal to the outer diameter of the screw cylinder, to limit the swelling of the blank due to forcing ahead of the` metal by these rst ribs or to reduce the blank to that diameter if it is oversize.

Fig. 6 illustrates the results of employing modied dies for rolling a standard or machine-screw thread upon a blank 16 in accordance with this invention, the head end of the blank being at the left and its tip end atV the right. The forging of the groove and thread is illustrated at the right-handv or advancing end thereof, and the effect of the first lower-die rib, whose outline is a two-sided gure, is shown on the lower side of the blank in broken and full lines as it would occur during the rst half-turn of the workat this locality. Said rib has formed a groove portion 25u for approximately one half-turn of the work in a. preliminary shape having a sharpbottomed apex lying to the left of the ultimate center pitch line of the thread groove 25, and the adjacent die groove between the irst and second refieres lower-die ribs has measured out the proper volurne of metal in the partially-formed first halfturn 25a of the thread, with a slight excess for subsequent. densification. Said excess is accommodated pe tly by a deepening ci the die groove which cav this thread portion slightly out beyond the angle betw the si s ci f thread por on being less, the th-ec.d top wider than i ultimate thread. During the next-succes half-turn, as illustrf'ited for qusi'tc the upper side or" the view, 't

ond step or operation di to the irst one widens i groove to a flatubottomed greater than the ultimate wi time rectifics reforms tn half-turn portion 26 between that of the and the ultimate top wi( included angle betw 5.1.1 re-formed and dimensions t the sides o the second in this case each stantially uniform t except for a the very hegi if desired of o is of different :mst-forma portion .fer-die lower-die i? the others, groove is "Lf than the seing uni id groove the irstntwo die rib es in mate, and form through-out, completely f lower-die ribs and the rst-described )I claim:

l. The method of cci-few thread time f a blank which consists in applying groove d thread forming operation upon one side ci said l2@ blank and simultaneously thererf'th applying e. dissimilar but complement-al g Jove and thread forming operation upon the opposite side of said blank.

2. The method or threading a screw which 12E comprises partially rolling a thread groove and the adjacent thread on a blank at the leading portion only 0f said thread and to the full ultimate depth of said leading portion, during a portion of a turn of the latter, thereby elongating the blank, further forming said groove and thread during the remaining portion of said turn and thereby further elongating the blank.

3. The method of threading a screw which comprises rolling a thread on a blank by dissimilar but complemental forming operations on opposite sides of the blank, causing progressive longitudinal displacement of material, with elongation of the blank, and completing the formation and pitch spacing of the thread in the leading portion thereof during substantially one and onelhalf turns of the blank.

4. The method of threading a metal screw between dissimlar dies whose formingl surfaces are confined to a pair of unlike ribs on one of the dies and a single rib on the other die, which comprises simultaneously imparting opposite dissimilar but complemental increments of thread and groove shaping at successive points by the action of the respective dies in a. progressive rolling actior on 15o its length.

A 5. The method of threading a'screw which comprises measuring the proper cross-sectional area of blank material for the thread and partially forming the thread with a side contour different than its ultimate contour, by displacement of said material, with elongation of the blank, in

one part of a lrolling operation, and further forming the thread to its ultimate side contour during a subsequent portion of said rolling operation.

6. TheA method of threading a metal screw which comprises partially forming a thread groove and measuring the proper cross-sectional area of blank metal for the adjacent thread, while elongating the blank, by a rolling operation on one vside 'of the blank which leaves the thread with a smaller included side, angle than the ultimate angle, and further forming the groove and thread by a rolling operation on the opposite sid'e of the blank which increases the included side angle of the thread, while further elongating said blank.

f 7. The method of threading a metal screw which comprises rolling a thread groove and the proper measured volume of adjacent thread metal on one side of the blank, while partially elongating the blank'by displacing less than the rethat side, and displacing the remainder of the groove metal while further elongating the blank and further shaping the thread by a rolling oper-v ation on the' opposite side of the blank, during a single turn of the blank at the leading portion of the thread.

-8. The method of threading a screw which comprises rolling -a thread 'groove and the adjacent proper volume of thread metal, with the bottom of the leading portion of the groove spaced closer tc the next groove turn than the ultimate pitch spacing, while partially elongating the blank, by a rolling operation on one side of the blank, reforming the groove to the ultimate bottom pitch spacing and re-shaping the thread while further elongating the blank by a dissimilar but complemental rolling operation on the opposite side of said blank.

9. The method of threading a screw which comprises progressively rolling a thread on a blank with. the proper volume of material in the leading portion for the ultimate thread, including a suicient excess for subsequent d'ensication, said leading portion having not less than the ultimate thread depth and other than the ultimate side contour and pitch spacing, and re-shaping and densifying said portion to the ultimate side contour and pitch spacing by subsequent'rolling in the same continuous operation.

10. The method of threading a screw which comprises rolling on a metal blank a thread having substantially the ultimate proper volume of metal and not less than the ultimate thread depth in the leading portion thereof, with an included thread-side angle less than that of the ultimate thread, and subsequently, during a continuation of the rolling operation, rectifying the thread angle.

11. The method of threading a screw which comprises forming on a metal blank a thread groove of less than the ultimate area and pitchspacing of groove bottom in the leading portion thereof and an adjacent leading thread portion having the proper volume of metal including an excess for subsequent densification, an included thread-side angle less, and a thread top width greater than the ultimate, While partially elongating the blank, by a rolling operation on one sidf of the blank, during approximately one halflturn of the blank, and th'en, during approximately the succeeding half-turn, increasing the area of the groove, rectifying its bottom pitch-spacing rectifying the thread-side angle, reducing the thread-top width and densifying the thread metal, While further elongating the blank, by a rolling operation on the opposite side.

12. A method according to claim l1 in which the, groove and thread are further rectified to their ultimate shape and dimensions during approximately the -third half-turn of the blank.

13. The method of threading an article of wood-screw form which comprises rolling a thread-groove and adjacent thread on a metal blank in successive stages at the leading ends ofsaid groove and thread while elongating the blankin partial increments during successive approximate half-turns of the blank, by an initial forming operation on one side and a concurrently performed later operation different than but complemental to the iirst operation, on the opposite side of the blank, and, while so forming the blank metal adjacent the tip and during completion of the operation, tapering off the thread and tapering down the adjacent blank metal to form a reducedven'd on the article.

14. A method according to claim 13 in which the thread and screw body are carried to a sharp point at the screw tip and the excess blank metal is pinched oi by completion of the rolling operation.

, 1 15. The method of threading a screw which w ving and less than the ultimate groove-bottom pitch spacing at the leading ends of said thread and groove while partially elongating the blank during a portion of a turn thereof, and rectifying said groove and thread by a dissimilar but complemental operation during a subsequent portion of the same turn, while further elongating the blank.

16. A methodaccording to claim 15 in which the leading portion of the groove is formed with two sloping sides meeting at an apex and the thread diameter is extended beyond the ultimate diameter during approximately one half-turn of the blank, the groove is increased in area and flattened at the bottom and the thread-side angle is partially rectified, the thread height reduced and the thread-top width partially reduced during 4approximately the next half-turn of the blank, and the thread is'further rectiiied to its ilnal shape and dimensions during approximately the third half-turn of the blank.

17. A pair of screw-thread forming dies, one of said dies'havlng thread and groove forming grooves and ribs and the other having thread and groove forming grooves and rib unlike the former but complemental thereto.

18. A pair of screw-thread forming dies provided with screw formlng ribs and grooves, a rib gli:

20. A pair of screw-rolling dies having leading screw-forming ribs which are o! different side contour and different pitch spacing in the two dies for completely forming e, thread-groove and the adjacent thread in successive stages, and following non-forming ribs for meshing between the turns of the fnished thread and maintaining the alignment oi the work between the dies.

LEE A. mm.

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