US3626733A - Truncated through feed thread rolling die for rolling flat rooted threads - Google Patents

Abstract

A THROUGH FEED THREAD ROLLING DIE WHICH ACTING IN COOPERATION WITH ONE OR MORE IDENTICAL DIES WILL PRODUCE SO CALLED ACME OR SIMILAR THREADS ON A WORK PIECE. THE THREADS ON THE RELIEVED STARTING SECTION IN WHICH THE ROOT DIAMETER IS CONSTANT HAVE A NOVEL CONSTANTLY CHANGING CROSS SECTION. THE CRESTS OF THE THREADS CONSIDERED IN LONGITUDINAL SECTION ARE FLAT AND LIE IN THE SURFACE OF A TRUNCATED CONE. THE FLANKS OF THE THREADS THAT FIRST CONTACT THE WORK ARE AT A RELATIVELY WIDE ANGLE SO THAT GOOD STARTING THREAD FORMATION IS PRODUCED IN THE WORK. AS THE THREAD ON THE DIE INCREASES IN DIAMETER, THE FLANKS ASSUME A DUAL ANGULARITY WITH THE WIDE ANGLED FLANKS MERGING WITH STEEP INNER FLANKS. WHEN THE TAPERED STARTING RELIEF SECTION REACHES THE FULL DIAMETER INTERMEDIATE DWELL SECTION, THE WIDE ANGLED FLANKS WILL HAVE GRADUALLY DISAPPEARED TO BE REPLACED BY THE STEEP FLANKS OF ACME CONFIGURATION.

Description

, E 3,626,733 TRUNOATEO THROUGH FEED THREAD ROLLING OIE FOR Dec. 14, 1971 E. s. 200K. ETAL ROLLING FLAT ROOTED THREADS 3 Sheets-Sheot 2 Filed March 26, 1969 l V. Izwezaow.-

E'Zw 4S. Zoo, Pani W Rom,

Dec. 14, 1971 E 5, 200K ETAL 3,626,733

TRUNOATED THROUGH FEED THREAD ROLLING DIE EOE A ROLLING FLAT ROOTED THREADS Filed March 26, 1969 3 Sheets-Sheet 5 mom x10;

.m-O lx/ ,I lll Ill Ilwlll f 4\\|ll\ \.\\\r WQWQQ@ 4\`\ m5 1 .r l l l ll4|\l 4 mmv .v up 4 U- nwfl'wA oww y ml'mx O mmm om 4 [all i i, x @hm v Mom." .I-N|-l\\ ,t y OQWO WOM Yom Om @mlm m` mQm x10? 'United States Patent O TRUNCATED THROUGH FEED THREAD ROLLING DIE FOR ROLLING FLAT ROOTED THREADS Elmer S. Zook, Princeton, and Paul W. Ronn, Gardner,

Mass., assignors to Reed Rolled Thread Die Co.,

Holden, Mass.

Filed Mar. 26, 1969, Ser. No. 810,485 Int. Cl. B21h 3/04; B23g 7/00 U.S. Cl. 72-104 21 Claims ABSTRACT OF THE DISCLOSURE A through feed thread rolling die which acting in cooperation with one or more identical dies will produce so called Acme or similar threads on a work piece. The threads -on the relieved starting section in which the root diameter is constant have a novel constantly changing cross section. The crests of the threads considered in longitudinal section are llat and lie in the surface of a truncated cone. The flanks of the threads that first contact the work are at a relatively wide angle so that good starting thread formation is produced in the work. As the thread on the die increases in diameter, the flanks assume a dual angularity with the wide angled Iflanks merging with steep inner flanks. When the tapered starting relief section reaches the full diameter intermediate dwell section, the wide angled flanks will have gradually disappeared to be replaced by the steep flanks of Acme configuration.

BACKGROUND OF THE INVENTION This invention relates to thread rolling dies for producing so called Acme or similar threads on work pieces which are passed through a cluster of such dies (two or more) while the dies are rotating in unison to produce a surface metal flow in the work piece, whereby a continuous Acme thread configuration is formed.

It is conventional practice to have a tapered entry section on thread rolling dies so that a converging opening is provided between the dies to permit the work piece to enter the cluster. The die threads on the starting section after initiall contact enter progressively deeper into the work piece. The displaced metal rises in the space between the diepthreads so that the finished thread on the work piece Will have a mean diameter equal to the initial work piece diameter.

The prior art devices for rolling wide, flat rooted threads of the Acme type provide a tapered starting section having flat rooted threads which taper at the root diameter. The tapered starting thread turns have pointed crests as distinguished from flat crests. These pointed crests in the tapered starting section change to flat crests of increasing width as the dwell section is approached. The bottom portion of each thread flank slopes approximately at the flank angle of the finished Acme thread and the top portion is at a greater flank angle. In the prior art construction just referred to, the height of the bottom flank portion increases and the height of the top flank portion decreases as the thread turns progress away from the starting end.

While it has been the generally accepted practice to start the threads in the work piece with a sharp crest on the die thread, it is also known that this results in frequent misalignment of the work relative to the axial path through the die cluster and causes what are commonly referred to as drunken threads.

Attempts to initiate metal flow with llat creasted, fully formed die threads of Acme or similar configuration with the crests and roots uniformly tapered in the starting section have been unsatisfactory because the surface Fice metal of the work piece is necessarily forced at once laterally and outwardly in a manner that prevents proper following of the steep thread flanks. This acute metal compression and improper extrusion weakens the finished thread and produces a foiling effect wherein the metal at the surface of the finished thread peels off in foil-like layers.

SUMMARY OF THE INVENTION In accordance with our invention, a thread rolling die for rolling 'flat rooted threads is adapted to be rotatably supported in a cluster of normally two or three rolls with the roll axes either parallel to or skewed from the axis of the work. The starting section of the die roll has a plurality of thread turns of constant root diameter. These thread turns have relatively Wide fiat crests uniformly tapered with respect to the roll axis to permit precise alignment of. the work axis with the pass line of the die cluster. This llat sloping crest configuration substantially eliminates the misalignment problems that heretofore have produced undesirable drunken threads. The initial thread turns in the starting section have single flanks for starting the work piece thread. Thereafter, the thread turns are provided with double sloped flanks. The single flanks of the thread turns initially contacting the work have a flank angle which is greater than the flank angle of the finished thread, preferably a 60 included angle. This enables the surface metal of the work piece to flow laterally and then outwardly along the wide angled flanks toward the die root without undue stress.

The starting section threads progressively remote from the starting end increase uniformly in height and develop a lower flank portion in which the flanks slope at the finished thread flank angle, which is normally an included angle of 29 for the Acme thread. The upper wide angled llanks are still present but of diminishing height. The height of. the lower steep llank increases as the height of the wide angled flanks decreases so that the metal of the work piece flows first over the wide angled upper flanks and then into the space between the developing lower steep flanks, whereby the finished thread is gradually built up by an extrusion action which eliminates the tendency to foil.

The principal object of our invention is, accordingly, to provide a through-feed thread rolling die for rolling Acme type and similar wide, flat rooted steep flanked threads. Such threads can be produced by using a cluster of two or more identical dies each having an axis of rotation either parallel to or uniformly skewed from the pass line of the work through the cluster. Our dies have an improved starting thread configuration which permits accurate initial alignment of the work and improved metal deformation of the work to produce mechanically sound threads that do not tend to peel or li-oil.

In the simplified construction, the die will carry a single continuous thread, but other thread forms may be used according to the thread requirements of the work piece without in any way changing the nature of the invention. For example, double continuous threads might be utilized. Or, the threads might be annular rather than helical, in which case the die axes would be skewed with respect to the work axis.

DESCRIPTION OF THE DRAWINGS FIG. l is a view partially in section `and broken longitudinally of a thread rolling die having a helical thread made in accordance with our invention and shown in relation to an incoming workpiece.

FIG. 2 is an enlarged detailed view of the die construction and work piece showing in better detail the nature of the die threads in the starting `section yand the development of the threads in the work piece.

FIG. 3 is a modification of the die thread construction in the starting section.

FIG. 4 is a view similar to FIG. 1 showing the invention when applied to annular threads.

DETAILED DESCRIPTION OF THE INVENTION yReferring now to FIG. l, a thread rolling die generally indicated at 2 is shown in the form of a roll with an external helical Acme thread formed thereon. The roll 2 may be any desired diameter and is adapted to be driven in a cluster of two or more rolls Kspaced to form a pass line between the rolls which is correct for the size of the work to be threaded. In this embodiment of the invention a single Acme thread is developed on the surface of the roll 2 consisting of a plurality of turns in the form of a continuous helix over the central or dwell portion of the die. Depending upon the diameter of the dies in relation to the work, multiple helical thread configurations may also be employed. For 'simplicity of illustration, however, the invention is illustrated with respect to a single continuous helical thread configuration, as well as to an annular thread configuration as illustrated in FIG. 4.

The roll or die 2 comprises a starting relief section 4, a dwell section 6 and a finish relief section 8. The points of transition between the sections 4, 6 and 8 are indicated approximately by dot and dash lines 10 and 12 in FIG. l. Also shown in IFIG. 1 is the leading end of a portion of a work piece 14 which is progressing through a set of rolls with rolling forces applied by the rolls to the work piece such that the desired thread formation is rolled into the metal surface of the work piece. It will be understood that the rolling operation takes place with each die 2 rotating about its axis, which, according to the nature of the threads, may or may not be parallel to the direction of motion of the work piece 14 indicated by the arrow in FIG. 1. The roll axis about which the die 2 rotates is also taken as the axis of reference for the angles of the various portions of the helical thread on the surface of the die 2 hereinafter described.

The dwell section 6 of the die 2 is provided with a full sized Acme thread 16 having fiat crests 18 and fiat roots 20 which correspond in size and pitch to the desired finished thread formation for the work piece 14. The thread walls or flanks 22 and 24 in accord with Acme thread design form an included angle therebetween of 29. The length of the dwell section 6 includes a plurality of complete thread turns and operates in a known manner to finish the thread rolled onto the work piece into the final desired size and tolerance dimension.

The envelope of the crests 18 is cylindrical and parallel to the axis of rotation of the roll 2 and the envelope of the roots 20 is also cylindrical and parallel to the axis of rotation of the roll 2. Thus the dwell section serves to finish form the threads on the work piece 14 with the desired thread configuration having roots and crests that are uniformly distant from the axis of the work piece 14. The thread formed on the work piece will correspond in cross section to the thread 16 of the die.

The finish relief section 8 has a plurality of full size thread turns 26 having crests 28 and roots 30 but differs from the dwell section 6 in that the envelope of the roots 30 is conical and tapers towards the axis of rotation of the roll 2. Similarly, the envelope of the crests 2'8 is also conical and tapers towards the axis of the roll 2. These two conica] envelopes are parallel and coaxial, Thus. with respect to the work which passes through the set of dies, the threads 26 of the tapered finish relief section 8 move gradually away from the corresponding roots, crests and flanks of the finished thread on the work piece. The gradual changes in pressure of the dies against the work piece as the latter moves from the dwell 'section 6 to the finish relief section 7 insures that the thread surfaces will leave the dies in commercially acceptable condition.

The starting relief section 4, in accordance with the present invention, provides generally a continuation of the threads from the dwell section 6 with fiat roots 32 for all thread turns from the dot and dash line 10 to the starting end of the die. The roots 32 in the starting relief section 4 are spaced equidistant from 'che axis of rotation of the roll 2. Thus the envelopes of the roots 32 of the starting section and the roots 20 of the dwell section are cylindrical and of the same diameter and their axes coincide with the axis of rotation of the roll 2. The pitch of the threads in the starting relief section 4 is the same as the pitch of the threads in the dwell section 6.

The crests 34 of the threads in the starting relief section 4 are flat in longitudinal section and taper at a small angle relative to the axis of rotation of the roll 2. The flat surfaces of the crests 34 coincide with the conical crest envelope and thus the general shape of the starting relief section is simply a uniformly tapered portion with threads of decreasing height from the dwell section 6 to the starting end of the die. The angle and extent of the crest taper is such that the entry end 36 of the die has a diameter which, when mounted in a cluster, provides an entrance of greater diameter than the diameter of the work 14 as it enters the dies. Thus the crests 34 contact the work piece at some intermediate point suggested at 38 on the tapered surface of the starting relief section 4 and, as contact is made, the internal metal ow in the work 14 is initiated.

Referring now to FIG. 2, there is shown in greatly enlarged detail the nature of the thread construction in the starting relief section 4 which constitutes the invention. For purposes of easy reference, the individual threads have been indicated as T-1, T-2, T-3, T-4, T-S, T-6, T-7 and T-8. Thread T-1 is the first thread in the dwell section and is a fully formed Acme thread having flanks 40 and 42 which converge at the conventional Acme angle of 29.

Thread T-2 may be described as comprised of two superimposed trapezoids. The lower trapezoid 44 culminates at the dot and dash line 46 and has its flanks 48 and 50 converging at 29. The upper trapezoid 52 has a bottom side which coincides with the upper side of trapezoid 44 along the line 46. The flanks 54 and 56 converge at an angle of 60. The crest 58 is at the same radius as the crest 60 of thread T-1. Crest 58 is shown as parallel to the die axis, but it is to be understood that the tapering of the crests can commence at any selected thread. For example, the tapering of crests could commence at T-1 before the commencement of the generation of the wide angled Hanks first appearing in T-2 at 54 and 56.

In thread T-3, the lower part of the thread is in the form of a trapezoid 62 with flanks 64 and 66 converging at the 29 angle. On the upper side 68 of trapezoid 62 is the trapezium 69 having the fianks '70 and 72 converging at 60, and having a crest 74 which slopes at a small angle toward the die axis. It will be appreciated that the crest 58 blends into crest 74 during one turn of the thread from T-2 to T-3.

Thread T-4 has its lower part in the form of the trapezoid 76 with flanks 78 and 80 covering at 29 and above is a trapezium 82 with anks 84 and 86 converging at 60. The upper crest 88 slopes toward the die axis and preferably is aligned with crest 74 of thread T-3.

In thread T-5 the lower portion of the thread is in the form of a trapezoid having flanks 92 and 94 which converge at 29 and above trapezoid 90 is a trapezium 96 having flanks 98 and 100 which converge `at 60. The top of trapezium 96 is the crest 102 which is aligned with crests 74 and 88.

dt should be noted at this point that the trapezoid thread portions 44, 62, 76 and 90 are all of the same pitch as the threads in the dwell section 6, but these portions are progressively of less height and correspondingly of less area. On the other hand, the trapeziums 52, 69, 82 and 96 are of progressively increasing area and the crests 74, 88 and 102 are of approximately the same width which width is determined by the taper of the conical envelope in which the `crests 74, 88 and 102 reside.

Coming now to threads T-6, T-7 and T48, it will be noticed that the lower trapezoidal portion present in threads T1 to T-S has now disappeared. Thread T-6 is comprised solely of a trapezium 104 having flanks 106 and 108 and a crest 110 which is aligned with crests 74, 88 and 102 and is of slightly greater width than crest 102.

Thread T-7 is in the form of a trapezium 112 having Hanks 114, 116 and a crest 118, which crest is still wider than crest 110.

The Hnal thread T-8 is in the form of a trapeziurn 120 having Hanks 122 and 124 and a crest 126, which crest likewise is aligned with all of the other crests, but wider than crest 118.

The Hanks of threads T-6, T47 and T-8 `all converge at an agle of 60. The cross-sectional areas of trapeziums 104, 112 and 120 are of decreasing order.

The line 128 represents the outside periphery of the cylindrical work piece 14 that is being fed into the dies. It will be noticed that in FIG. 2 the work is initially engaged by the corner 130 of thread T-7. Thereafter, as the Work moves forward to thread T-6, the die will progressively force its way into the imetal of the work piece 14 causing the metal to How along the 60 sides of the threads T-7, T-6 and T-S to produce approximate formations such as indicated at 132 and 134. By the time the work piece has reached thread T-4, the metal will have been extruded to approximately the position 136, at which point the Acme type Hanks sloping at a converging angle of 29 begin to come into play. The initial outward displacement of the metal of the work piece has been caused by the crests and 60 Hanks of the trapeziums 112, 104 and 96 which makes it much easier for the extruded metal to move outwardly between the more steeply sloping Hanks as illustrated by the thread formation 138 developing between Hanks 78 and 66 of threads T-4, T-3.

As the steep Hanks of the lower trapezoids 90, 76, 62 and 44 continue to increase in height as illustrated by Hanks 94, 92, 80, 78, 66, 64, 50 and 48, the metal of the work piece, having initially been displaced by the 60 Hanks of the upper trapeziums, Hows far more readily into the space between the steeply sloping Hanks as indicated at 140 and finally 142 at which point the Acme thread is substantially complete and is then finished by the threads T-1 and the succession of identical threads throughout the extent of the dwell section 6.

From the foregoing explanation, the following important features will be noted. All of the threads T-1 to T-8, inclusive, are of the same pitch but starting with thread T-3 of decreasing radius. The =Hat crests from T-3 to T-8 all slope preferably in alignment as illustrated toward the die axis. The deformation of the work piece throughout the starting relief section 4 is initiated by threads which have Hanks converging at 60 and Hat crests. The starting threads T-'7, T-6 and T-S facilitate align ment of the work axis with the dies and minimize the tendency to develop so-called drunken threads. Thereafter, the outer portions of the developing threads are more readily forced outwardly between the steeper sloping Hanks 92-80, 78-66, `6450, and 48-42 without darnage to the outer periphery of the work piece thread structure.

The development of the thread on the starting relief section of the die is readily accomplished. The full sized Acme thread is machined or ground throughout the length of the starting relief section and the dwell section. With this accomplished, the crests of threads T3, T-4, T-S, T-6, T-7 and T-8 may be finished to a selected taper (preferably betweenr 11/2 and 5 but not over 12) to produce the sloping crests 74, 88, 102, 110, 118 and 126. Thereafter, the 60 Hanks may be machined or ground to the pattern disclosed in FIG. 2.

The dot and dash lines 144 and 146 are included to illustrate one way in which the changing dimensions of the die threads may be developed. The angle of these lines to the die axis may be varied. If of less slope, there will be more threads in the starting relief section having the dual sloping Hanks which would make metal movement in the work piece more gradual. Conversely, if the slope of the lines 144 and 146 is at a greater angle to the axis, then the starting threads will increase in height at a greater rate with a corresponding increase in the rate of the work piece deformation.

In FIG. 3 is shown a thread construction which performs substantially in the same manner as that shown in FIG. 2. The cross-sectional conHguration of each of the threads T-12, T-13, T-14 and T-15 (corresponding generally to threads T-2 and 2-5 in FIG. 2) is modified slightly, but the construction of the threads T-16, T-17 and T-18 is identical with the construction of threads T-6, T-7 and T-8 in FIG. 2. In FIG. 3 the lower portions of threads 164, 166, 168 and 170 are in the form of trapeziums instead of trapezoids. Thus the Hanks 172 and 174 are not of equal length as in the case of flanks 48 and 50 of the thread T-2. The same comment applies with respect to Hanks 176 and 178, 180 and 182, and 184 and 186. The Hanks just mentioned slope toward each other at 29 if an Acme thread is to be formed on the work piece.

The upper portions of the threads T-12, T-13, T-14 and T-15 are in the form of trapeziums 188, 190, 192 and 194. These trapeziums have their Hanks sloping toward each other at an angle of 60, the same as in the case of the upper trapeziums in FIG. 2. Crest 96 of thread T-12 is parallel to the die axis. The crests 198, 200 and 202 slope toward the axis of the die along a line 204 running at an angle which intersects trapeziums 190, 192 and 194 to produce crests of equal length.

The threads T-16, T-17 and T-18 are single trapeziums indicated at 206, 208 and 210 with their Hanks intersecting at an angle of 60.

The line 212 represents the periphery of the cylindrical work piece and as it advances into the die of FIG. 3, it is first engaged by thread T-17 at 214 and then progressively by threads T-16, T-llS, T-14, T-13 and T-12. The 60 sloping Hanks which initially encounter the work piece, accurately start the extrusion of the metal in a manner causing no damage to the thread through all of its development.

The development of the thread in the work piece is shown by consideration of the lines 216, 21'8, 220, 222, 224 and 226 which illustrate how the metal of the work piece progresses from its initial displacement by the 60 Hanks to its final flowing into Acme form between the 29 Hanks of threads T-14, T-13, T-12 and T-11.

The behavior of the developing thread in the work piece in either of the constructions shown in FIG. 2 and FIG. 3 is Substantially the same. As previously mentioned, the major features of the invention are the sloping Hat crests, the 60 thread walls that initially act on the work piece to force the metal to a position where it is readily received by the steep Hanks having the included angle of 29.

When the thread is finished, the amount of metal displaced in the work piece by the upper part of die thread T-l in FIG. 2 or T-11 in FIG. 3 above the pitch line 228 in FIG. 2 or 230 in FIG. 3 Iwill be substantially equal to the amount of metal in the work piece below line 228 or 230. Thus, as the work piece progresses through the dwell section 6 in which the threads 16 are identical with the threads T-1 and T-11 in FIGS. 2 and 3, there will occur a burnishing and finishing effect on the fully formed work piece threads so that when the work piece is discharged from the Hnish relief section 8, the threads will be in commercially acceptable condition.

Turning now to FIG. 4, an Acme thread rolling die according to an alternate embodiment of the invention is there shown in the form of a roll with annular threads as distinguished from the helical thread of FIGS. l, 2 and 3. A die 232 comprises a starting relief section 234, a dwell section 236, and a iinish relief section 238, which sections are substantially identical to sections 4, 6 and 8 of the embodiment shown in FIGS. 1, except, as just noted, the thread is not continuous but annular. Thus the envelopes of dwell section crests 240 and roots 242 are cylindrical and parallel to the axis of the die 232; t-he envelopes of the finish relief section crests 244 and root 246 are conical and taper toward the axis of the roll 232; the envelope of the roots of the starting relief section 234 is an extension of the dwell section root envelope and is cylindrical and parallel to the roll axis. Starting relief section crests 240 are flat in longitudinal section and taper at a small angle with respect to the die axis. The starting relief thread turns 250 have the flanks 252 of the upper portions at a wide angle (for example 60) and finished thread flank lower portions 254 substantially identical to the individual thread constructions T-1 to T-8 in FIG. 2, and T-ll to T-18 in FIG. 3 discussed above.

In operation a cluster of the rolls 2 or 232 are suitably spaced and rotatably mounted and driven about the pass line of the work piece. The work piece is fed into the die cluster within the confines of the tapered starting threads. The -flat crested wide angled threads grip the work causing the thread to be gradually and fully formed by the time the dwell section is reached. Thereafter, finishing and relief takes place.

The die according to the embodiment of FIG. 4 may be manufactured by forming a uniform Acme thread in annular form having a constant root depth and constant root radius from the roll axis on the starting relief section 234 and the dwell section 236 by conventional techniques. The starting relief section 234 may then be uniformly tapered by machining or grinding the crests 248y at a selected small angle which is preferably between l1/2 and 5, and, in any event, is not over 12. The flanks of the starting relief section threads 250 may then be machined or ground to produce the wide angled upper portions 252. The lower portions 254 are unchanged from the Acme thread configuration. Wide, flat rooted thread forms other than the Acme thread illustrated can, of course, be produced with dies manufactured in accordance with our invention by forming worm, drive screw or similar threads on the die with the threads in the starting relief section having flat tapered crests and having at the outer portions wide angled flanks which intersect steeper inner flanks along an increasing radical distance as the dwell section is approached.

With respect to the tapered crests running from the dwell section to the starting end of the starting section, it is to be understood that the thread turn at which the tapering of the crests commences may or may not be the same thread turn where the wide angled flanks start to be generated. The movement of the metal of the work piece to completed thread form when the dwell section is reached, is not affected in any way by the limited angular variation in the starting positions of the sloping crests and wide angled flanks.

In the claims, the broad 'word trapezium is used. This includes trapezoids. The lower trapezium might be a trapezoid as in FIG. 2, or not as in FIG. 3. Likewise, the upper trapezium might or might not be a trapezoid according to the designers preference. The dotted lines 256 and 258 inserted in FIG. 3 at the top of thread T-13, and the dotted lines 260, 262 and 264 inserted at the top of thread T-14 show how the upper part could be in trapezoidal form Iwhile leaving the lower portion as a trapezium.

In the light of the above explanation of the invention, other modifications within the scope of the claims will readily suggest themselves to those skilled in the art.

We claim:

1. A through feed thread rolling die for creating wide, flat rooted steep flanked threads by surface metal flow in a cylindrical workpiece comprising a roll die formed with an external flat rooted thread having a starting 8 section, a dwell section and a finish relief section; said dwell section having a fully formed flat rooted thread of uniform dimensions throughout its length; the thread in said starting and d'well sections having a 'common cylindrical root envelope whose axis coincides with the axis of said roll; the thread in said starting section being relieved and comprising a plurality of thread turns with flat crests that form a constant predetermined angle with the roll axis, said relieved thread having at the starting end a crest height below the mean height of the threads in said d'well section; said starting section thread turns comprising an upper portion the flanks of which slope toward each other at a flank angle greater than the flank angle of the threads in said dwell section, and a lower portion the flanks of which slope at the flank angle of said dwell section; the lengths of the flanks of said upper portion gradually decreasing in thread turns progressively remote from said starting section end, the lengths of the flanks of said lower portion gradually increasing in thread turns progressively remote from said starting section end; and said finish section having threads tapering to a reduced diameter thereby to provide adequate relief for a completed thread on the work piece as it leaves said dwell section.

2. A through feed thread rolling die as set forth in claim 1 in which said starting section thread crests have progressively increasing diameters as they approach said dwell section, the envelope of said starting section thread crests defining a truncated cone in which the apex angle of said cone is not greater than 12.

3. A through feed thread rolling die as set forth in claim 1, in which the envelopes of the roots and crests of the threads of said finish relief section define two spaced truncated cones Iwhose walls are substantially parallel.

4. A through feed thread rolling die as set forth in claim 2 in which said angle of said starting section flat crests is the same as the angle of said envelope of said starting section thread crests thereby locating the full width of said flat crests on said envelope.

5. A through feed thread rolling die as set forth in claim 1 in which said upper starting thread turn portion flank angle is approximately 60 to said die axis.

6. A through feed thread rolling die as set forth in claim 1 in which the flank angle of the said lower portion is approximately 75l/2 to said die axis.

7. A through feed thread rolling die as set forth in claim 1 in which said external thread comprises at least one continuous helical thread.

8. A through feed thread rolling die as set forth in claim 1 in which said external thread comprises a plurality of annular thread turns.

9. A through feed thread rolling die for creating in a cylindrical =work piece by surface metal flow threads of the type having wide roots and steep flanks, said die comprised of a starting section, a dwell section and a `finish relief section, the thread in said dwell section being complementary to the finished thread in said work piece, the thread in said starting section being formed as follows: the pitch of the thread is the same as that in the dwell section; the width and radius of the root is the same as that in the dwell section; in the thread turns of the starting section adjacent the dwell section, there are first flank portions which lead outwardly away from the root, the said first flank portions being of the same angularity as the flanks in the dwell section but becoming progressively of less height as the thread moves from the d'well section toward the starting end of the die until the said first flank portions disappear when the upper edge of each said first flank portion reaches the root; second flank portions on each thread turn extending outwardly from said first flank portions and having a substantially less steep slope than the said first flank portions and terminating at a flat crest; a

majority, at least, of all adjacent said flat crests sloping uniformly toward the die axis, the height of said second flank portions becoming constantly greater as the thread moves from the dwell section toward the starting end until the inner edges of said second ank portions meet the said root at the thread position where the said first flank portions disappeared; the thread height at the starting end of said die being less than the mean height of the thread in said dwell section; misalignment of the work piece when the dies are arranged in a cluster, the metal in said work piece is initially engaged by one of said sloping flat crests and is progressively extruded between said second flank portions as the work advances along the thread of the said starting section and whereby the iiow of metal into the space between said rst flank portions does not occur until the thread `formation in the work piece is sufficiently developed by said second flank portions to preclude subsequent misalignment of the work piece.

10. A through feed thread rolling die for creating in a cylindrical work piece by surface metal flow, threads of the type having wide roots, steep flanks and wide crests, said die comprised of a starting section, a dwell section and a finish relief section, the threads in the starting section being of the same pitch and root diameter as the threads in the dwell section, each thread in the starting section in cross section for a predetermined number of consecutive threads away from the dwell section toward the starting end of said starting section being comprised of la lower trapezium and an upper trapezium set one on the other, the lower trapeziums having the same base width and having upwardly extending flanks converging at the same angle, said lower trapeziums decreasing in height and cross sectional area as the thread progresses toward the starting end, the bottom sides of the upper trapeziums fitting on the top sides of the lower trapeziums and having flanks converging at an angle which is greater than the converging angle of the flanks of the lower trapeziums, said upper trapeziums as the thread progresses in the direction of the starting end of said starting section increasing in width and in cross sectional area, the upper side of each of said upper tnapeziuins forming a flat crest, a consecutive plurality of said fiat crests sloping toward the axis of said die, and additional continuing threads at the starting end of said die each of which in cross section is in the form of a single trapezium having a at crest and flanks generally parallel t the flanks of said upper trapezium.

11. The die set forth in claim in which said crests in the starting section are in alignment and reside in the surface of la cone whose axis coincides with the axis o-f said die.

12. The die set forth in claim 10 in which said sloping crests which engage the work piece are of less width than the crests of the threads in said dwell section.

13. The die set forth in claim 10 the cross sectional area of each said additional thread decreasing as the starting end of the die is approached.

14. The die set forth in claim 10 in which the flanks of the lower trapeziums are at an included angle of 29 and the flanks of theupper trapeziums are at an included angle of 60.

15. The die set forth in claim 10 in which said crests of said additional threads are of increasing width.

16. The die set forth in claim 10 in which the lower trapeziums are in the form of trapezoids.

17. The die set forth in claim 10 in which a consecutive number of the upper trapeziums are in the form of triapezoids.

18. A through feed thread rolling die for creating in a cylindrical work piece by surface metal iiow, threads of the type having wide root-s, steep flanks and wide crests; said die comprising a relieved starting section; a

10 dwell section and a finish relief section; the threads in said starting section being of progressively increasing outer diameter and of constant root diameter from the starting end to said dwell section; the threads in said dwell section being of constant maximum finished thread dimensions and having the same root diameter as in the starting section; the first thread in said starting section being of less outer diameter than the mean diameter of the threads in said dwell section; the first threads in said starting section having fiat sloping crests from which extend wide angled anks which terminate at the said constant root diameter; subsequent threads between said first threads and the threads in said dwell section having flat sloping crests from which extend wide angled flanks' of constantly changing dimensions whichterminate at the upper ends of steeper flanks of constantly changing dimensions extending outward from said root.

19. The die structure set forth in claim 18 in which the said wide angled flanks are at an angle of approximately 60 to said root line and the said steeper flanks are at an angle of approximately 751/2 to said root line.

20. The die structure set forth in claim 18 in which said subsequent threads in cross section comprise upper and lower trapeziums positioned one on the other, with the top side of the lower trapezium constituting the bottom side of the upper trapezium.

21. A through feed thread rolling die for rolling in a cylindrical work piece by surface metal flow, threads of the type having wide roots, steep anks and wide crests, said die comprising a starting section and a dwell section, the root diameter and pitch of the threads in both sections being the same, the threads in the dwell section being of full size with steeply sloping iianks and flat crests paralleling the die axis and lying in a cylindrical envelope, the threads in the starting section having iiat crests which taper outwardly from a diameter at the starting end that is less than the mean diameter of the threads in the dwell section to a maximum diameter to meet and blend into the first full diameter crest of the dwell section, the first threads at the starting end being in cross section in the form of trapeziums, the subsequent threads as they develop between the said first threads and the threads in the dwell Asection being in cross section in the form of two trapeziums one above the other, the lower trapezium having steeply sloping flanks and increasing in cross sectional area and the upper trapezium having yrelatively wide angled flanks and decreasing in cross sectional area as the thread of the starting section approaches the dwell section.

References Cited UNITED STATES PATENTS 1,592,765 7/1926 Hanson 10-141 1,961,003 5/1934 Lamond 10-141 2,179,157 11/1939 MacDonald 10-141 2,720,801 10/1955 Erdelyi et al. 72-103 1,846,501 2/1932 Thomson 10141 1,849,894 3/1932 Walker 10-141 3,220,032 11/1965 Van Vleet 10-141 2,828,493 4/1958 Koehler 10.-*152 3,069,961 12/1962 Baubles 10-152 3,131,407 5/1964 Roberts 10-152 FOREIGN PATENTS 380,391 9/1932 Great Britain.

CHARLES W. LANHAM, Primary Examiner E. M. COMES, Assistant Examiner U.S. C1. X.R. 10-152 P04000 UNITEB STATES PATENT GFFICE CERTIFICATE 0F CGRRECTIN Patent NQ," 31'6261733 Dated Decemberv 14, l

Elmer vS. Zook and Paul W. Ronn Inventor(s) It is certified that error appears. in the abovee-identified patent and that said Letters Patent are hereby corrected as shown below:

'r" y u co1. 6, Line 12: "2-5" should be ;-T-5-.

Col. 7, Line ll: "240" should be `248.

Col. 9, Claim 9, Line 9: should be Col. 9, Claim 9, Line 9: "misalignment of the workpiece when f the dies are arranged, etc., etc. to theend of Claim 9" should bev deleted from the printed patent. See our Paper No. 5, dated 6/28/'71 requesting cancellation of this portion of Claim 9.

Signed and'sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD yMJELETCIfIER,.TR. l ROBERT GOTTSCHALK Attesting Officer Commissioner' of Patents P04050 'UNTTED STATES PATENT 'OFFICE (5/69) n CERTIFICATE OF CORRLCTON PatentNo, 3,626,733 ma Dcembmfl 14, 1971 Inventor') Elmer lS. Zook and Paul W. Ronn It is certified that error appears. in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

co1. 3, Line 72:- I should be 8.

co1. 6, Line 12: "2-5" Should be ;-T-'5. coil. 7, Line 11: "2'4o" should be 9248--,

Col. 9, Claim 9, Line 9: 7 should be Col. .9, Claim 9, Line 9: "misalignment of the work vpiece when y the dies are arranged, etc., etc.

to theend of Claim 9" should be deleted from the printed patente. See our Paper No. 5, dated 6/28/71 requesting cancellation of this portion of Claim 9.

`Signed and'sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD `M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

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