US2739372A - Method of making propeller-blade blanks - Google Patents

Description

March 27, 1956 A. F. KRlTscHl-:R 2,739,372

METHOD OF MAKING PROPELLER-BLADE BLANKS Filed March 30, 1951 4 Sheets-5heet l March 27, 1956 A. F. KRlTscHER 2,739,372

METHOD OF MAKING PROPELLER-BLADE BLANKS Filed Maren 5o, 1951 4 Sheets-Sheet 2 F EE;

March 27, 1956 A. F. KRlTscHl-:R

METHOD OF MAKING PROPELLER-BLADE BLANKS 4 Sheets-Sheet 5 /7/5 Mib/weg m @nm w` I I I Vm M i w Filed March 30, 1951 March 27, 1956 A. F. KRlTscHER 2,739,372

METHOD OF MAKING PROPELLER-BLADE BLANKS Filed March 50, 1951 4 Sheets-Sheet 4 I PROPELLER-BLADE BLANKS Andrew F. Kritscher, Pittsburgh, Pa., assigner to United States Steel Corporation, a corporation of New `lersey This invention relates to a novel tubular semi-finished blank forged from a single piece of metal, adapted to be formed into ya blade for an airplane propeller and to a method of making such blanks.

Metal airplane-propeller blades have heretofore been either cast or fabricated from several parts by numerous operations at the expense of many man-hours of labor. Cast blades are lacking in strength because of defects inherent in the method of manufacture. The fabricated product, furthermore, has not only been costly but is also inherently liable to failure because of its composite character. I have invented a novel one-piece forged blank which can be finished or converted into a propeller blade rapidly and at low cost by simple operations, and a method of making such blanks quickly and easily.

In a preferred practice, I heat a round billet of steel of suitable composition to forging temperature, place it in a die pot having an oval section and pierce the billet centrally to form a longitudinal cavity extending thereinto from one end. During piercing, the billet spreads, taking the oval shape of the pot and I utilize the spreading to form rudimentary longitudinal ribs extending through the ends of the major axis of the section of the billet made oval by displacement of the metal into conformity with the oval shape of the pot. I then hot roll the pierced billet on a mandrel in a roll push-bench to elongate it, reduce the thickness of the wall and the ribs and impart the proper shape thereto. As a result of the rolling, the ribs are reduced to tins adapted to provide solid leaning and trailing edges for the finished blade. The resulting hot-rolled shell is then stripped from the mandrel, cooled, placed on another mandrel and cold-rolled in a second roll pushbench to reduce the wall thickness to its final value. The semi-finished blank thus produced is stripped from the mandrel and is then ready for nishing operations, i. e., attening, twisting to helical shape, cropping, machining to nal shape and size and sealing the end opposite the hub. All portions of the blade thus produced are integral and the blade is inherently strong and free from liability to failure. The method outlined, furthermore, greatly reduces the labor required as well as the overall cost.

A complete understandingof the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the several steps of the method, the product at various stages of manufacture and the apparatus which I preferably employ in practicing the method. In the drawings,

Figure 1 is a plan view showing the oval die pot with a round billet therein ready for piercing and shaping;

Figure 2 is a section on line II-II of Figure 1 through the die pot showing the billet therein being pierced by a shaped punch;

Figure 3 is a similar action on the line III-III of Figure 1 taken at right angles to that of Figure 2;

Figure 4 is a series of cross sections, a, b, c, and d, taken on the planes of correspondingly designated lines in Figure 2;

2,739,372 Patented Mar. 27, 1956 ICC Figure 5 is a side elevation of the pierced billet;

Figure 6 is an end elevation thereof;

Figure 7 is a side elevation of the mandrel on which the billet is hot-rolled;

Figure 8 is a series of cross-sections, e, f, g, h, i, i, and k, taken along the planes of lines correspondingly indicated in Figure 7;

Figure 9 is a plan of the rolling push-bench;

Figure l0 is a side elevation thereof;

Figure l1 is a partial section through the rolls of the last stand of the push-bench;

Figure 12 is a side elevation of the finished shell after cold rolling;

Figure 13 is a series of cross-sections through the hotrolled shell corresponding to sections, g, h, z', j, and k of Figures 8 and l2; and

Figure 14 is a series of cross-sections through the coldrolled shell corresponding to sections g, h, i, j, and k of Figure 8.

Referring now in detail to the drawings and, for the present to Figures 1 through 4, I heat a cylindrical steel billet 10 of suitable size and composition to a temperature of about 2250 F. and place it in a die-pot or mold 11 having an oval cavity 11a therein with grooves 12 extending through the ends of the major axis of its section. Cavity 11a has a frusto-conical portion 11b adjacent the bottom of the pot. I then pierce the billet axially with a shaped punch 13, mounted on the movable head of a press of any suitable construction. Preferably, I form a centering hole lita for the punch in the upper end of the billet before piercing it. As a result of the piercing, the metal flows upwardly around the punch to some extent and also spreads laterally to conform with the interior of the die pot, thus converting the billet from round to oval section and shaping the lower end to a taper. The billet is not pierced clear through, however, the lower end thereof being left closed or solid. The punch is round in section at its extreme end, 'but has an oval or elliptical section in its upper portion as shown by the sections of Fgure 4. The elliptical section is rounded at both ends of the major axis in the intermediate portion of t-he punch. At the top thereof, one edge of the punch approaches a dihedral angle as indicated at 14.

The pierced billet 15 has a cavity 16 therein formed by the punch 13. If the cavity is eccentric relative to the pierced billet, the latter may be cooled and machined to make the cavity concentric. The piercing leaves a solid head 17 at the closed end of the billet for apurpose which will appear later, and rudimentary ribs 18 on both sides formed by the grooves 12 in the die pot. The piercedpbillet is reheated to about 2250 F. preparatory to elongation on a mandrel by passage through a roll pushbench.

Figures 7 and 8 show a mandrel 19 on which the heated billet 15 is symmetrically fitted for elongation into a tubular shell by rolling. The mandrel is adapted to be pushed through a roll push-bench comprising several stands of rolls, by a hydraulic cylinder and piston as will be explained later. The small end of the mandrel is similar in shape to the punch 1.3. This is shown by a comparison of sections e, f, g, and h of Figure 8 with the corresponding sections a, b, c and d of Figure 4. In the portions more remote from the small end, i. e., where sections i, j and k are taken, the elliptical section is accentuated and both sides are formed by dihedral edges 2li with a fillet 21 of small radius therebetween. As the billet is rolled on the mandrel as will be explained shortly, it is progressively elongated into a tubular shell the interior of which conforms in size and shape to the mandrel, the exterior size and shape being determined by the roll passes through which the mandrel and billet are pushed.

Successive roll 'passes gradually reduce the wall thickness of the billet iand the displacement 4of metal causes axial elongation and radial enlargement. For a given size of each roll pass, the exterior shape and size of the billet after passing ntherethrough are 'uniform throughout Yits length and the finished Ashell has the size "and shape of the ilast pass. Thus the wall thickness of 'the resulting shell tapers away from the head 17 since 'the mandrel increases in size in the direction away from its small end.

The apparatus for effecting the reduction and elongation of the billet 'as 'described above is 'shown diagrammatically in Figures 9, l and 1l. Athydraulic cylinder 22 disposed horizontally 'on posts 23 has a'piston rod'24 connected to a mandrel bar J2S by a hinge joint 26. Mandrel 19"is secured by 'any convenient means such as a threaded joint to the outer end of the bar in axial alinement therewith, and 'is adapted to be pushed thereby through the Ipasses of a plurality-of roll stands 27, mounted in close-order succession on a common base 28 and secured'togther by tiebolts 29. Thereaction of the push exerted by the 'cylinder is taken up by spaced parallel tie bars 30 secured to a yoke 31 abuttingr the housing of the first roll stand and to a yoke 32 throughwhich the cylinderexten'ds. Yoke 31 is secured to the housings of therollfstands by tie bolts 33. A steadying post 34 intermediatetthe cylinder and the rollstands'has bearings open onone side adapted to engage the bar 25 and 'bars '30. A cross "head 35 on the piston rod slides on bars 30.

The disposition of bars 30 in a 'vertical plane `andthe hinge e-joint`26 Aby'which bar 25 is 'connected to piston rod 24 permit the mandrel 19 to be swung laterally as indicated lindotted lines in Figure 9, when'the piston rod has been fully retracted, In this position, the mandrel is adapted to receive the heated billet from a A'suitable carrier (not shown), e. g., a pair of grippingtongs suspended vfrom a crane. While the billet is being placed on the mandrel, the latter is supported `on a beam 36 extending from a cross-head 37 lslidable on :bars`3tl to 'a wheeled carriage 38 traveling on a rail 39. In placing the billet on the mandrel, of course, 'care is taken to havethemajor and minor axes or" cavity 16 properly disposed Vrelative to the cross-section'of the mandrel. When the billet vhas Ibeen vcorrectly placed on 'the mandrel, the latter and bar lare swung back to a Iposition in ahnernent `withthepass line'of the roll stands and poweriiuid is admitted to the cylinder to'push the mandrel and billet through the Aseveral passes.

VFigure `ll'shows grooved rolls 4`forming an open `oval pass 1typical of those defined by 'the rolls -ofstands '27. It will lbe understood, of course, vthat the `rolls -of .the several stands `are adjusted to take successive drafts on ihe billet so Vas to elongate it progressively and reduce the wallthickness thereof to the same extent around'the entire periphery. The rolls of the last stand 'may V'be 'adjusted during the 'rolling of -a shellto `opeuup the-pass and thus reduce the draft taken on the portion of fthe shell 'adjacent the trailing end. This lpermits a nice control'of the Width of the iin and the taper of the wall. As shown in'Figure l1, the roll-pass contour conforms generallyto the shape of mandrel 19 in the portions remote from the small or yforward end. In any elongation of a metal ymass between a pair of grooved reducing'rolls, the metal has a tendency to flow laterally into the spaces between the rolls and yform iins of dash. Normally,'special precautions are taken to prevent flash 'so fas aspossible but I takeadvantage of this tendency and'even exaggerate it. By so doing, I provide solid iins on opposite edges of the semi-iinished blank which are ideally suited to be yformed into the finished leading and trailing fedges of a propeller blade by a simple'imachining operation. It is known thatthe amount ofspreadingfis determinedby the percentage reduction `in the thickness of fthezpiece and I utilize rthis phenomenon `to secure lthe wideningof the ribs into .tins of usubstantial width.

To this end, rolls 40 are shaped to form a pass favor- `ing -the lateral extrusion 'of vmetal from the -billet Yinto ash which converts the ribs 18 into tins of considerable width. The edges or shoulders 40a of the rolls are accordingly shaped smooth to reduce and widen fins 18 as the inner portions of the roll faces work on the body of the billet. The iins must be elongated at the same rate as the body of the shell. The reductionand widening of the tins on'the blank, 'of course, are dependent 'upon the contour of the rolls. I design the rolls to distribute the reduction effected by each roll pass so .as to vmake the tins wider than necessary for giving Sthe desirable =arioil shape to the blade blank. This kexcess iin width may be used to good advantage in the -finishing of the blade by stretch-forming between dies, since .it `aiitords a hold for gripping jaws. Moreover, since this lin is of solid metal, any excess width can easily be removed after forming the blade, because this does not involve -any machining over the Vhollow portion thereof.

Figures l2 and 13 show the tubular shell 41,produced by'the procedure described above, with its tins 42. 'The length of the shell is several times that of .the pierced billet 15 and the wall thickness is correspondingly .reduced. The exterior shape and dimensions are uniform along the length o'f the shell but the interior shape and dimensions correspond to those of the mandrel. As a result, the wall thickness tapers toward the open end of the shell. Therefore, bythe combination of a non-cir cular tapering mandrel whose major axis increases at a rate greater )than that at which the minoraxis increases, and positioning the mandrel 4in billet so .that its major axis 'lies in the plane of the ribs formed on the outside thereof, it ispossible to roll with any one setting of the roll passes a tube shell and the circular equivalent of which has not only a progressively increasing insidediarnet'e'ribut also a progressively increasing outside diameter. This could be shown lgraphically by blowing up crosslsections of the 'hot-rolled shell to a nearly circular shape but the `same periphery. That is to say, circular sections of the sameperiphery as those shown'in Figure '1'3 'have an increasing diameter toward the open end .of the 'rolled shell. This apparently occurs because of the dihedral angles in the interiors of the shell .adjacent ythe lins, in the portion of the s'hell nearer the open end. Seemingly, `these angles would open up and Aincrease the periphery if vthe shell were converted to circular shape.

After'the shell 41has passedthroughihe last roll stand, a gripper 43 '(see Figure l0) engages the solidhead 17 andthe pressure in the cylinder 22 is reversed. AA circumferential groove maybe machined in .the shell just back of l`head 17 to facilitate the engagement'by .the gripper. Engagement of the gripper with the end o'f alength 'of pipe 44 extending 'forwardly from the last stand of rolls arrests the shell andcontinued retraction of the mandrelwvithdraws it therefrom. The s'hell'isthen advanced alonga roller table 45 and is permitted-to cool to atmospheric'temperature.

Whenthe vhot-'rolled shell has cooled, it is ,placed'on another mandrel generally similar to that shown at 19 andcoldrolledto'nal shape and dimensions'bypassing it Vthrough one ormore stands of rolls similar to rolls 40, `arranged' in a push-bench like that of Figures '9 and 4l0. -After the cold -reduction lordrawing, the shell is stripped from ithe mandrel as before.

It should be noted atthis pointthatthe .inside shape and size of lthe blank are finally determined Vby themandrel tused'in hotrolling. In fact, the-dihedralang'les on the iinteriorlofltheshell adjacent'the'fopen end canlonty be rformed by hot-rolling. The 'cold rolling and lfinal forming of the blank to thin the Wall slightly, therefore, while it improves ltheesurface and the physi'caL'qualities of the steel, fit does not materially.alterthe :interior periphery .of .the ablank. :The y'mandrels-usedfor coldsrolling, therefore, accurately lits .the ycavity Iiofithe hubiportion f of the hot-rolled blank and the major axis of thermandrel increases along the length thereof at a rate greater than that at which the minor axis increases. In the cold-rolling, the interior periphery of the shell is increased but the elongation progressively advances each point on the shell to a point on the mandrel at which the section is larger, thereby maintaining a snug t.

Figure 14 shows sections of the cold-rolled shell corresponding to the several sections of Figure 13. On completion of the cold-rolling, the shell 41 is a semi-finished lank from which a propeller blade may be easily manufactured by known processing steps. These include stretch-attening, hot-twisting, cropping, machining and sealing the open end of the shell. The finished contour is shown by dotted lines in Figure 14.

It will be evident to those familiar with the prior practice in the manufacture of propeller blades that my invention makes possible the production of a stronger blade than has been available heretofore and at a much lower cost. The overall advantage of a blade made from a onepiece blank over a blade fabricated from several parts is readily apparent. The use of a tapered mandrel and a roll push-bench with close control of the last pass thereof permits the heated pierced billet to be forged progressively into proper shape with integral ins for cold-rolling to linal dimensions with great accuracy and at high speed. The accurate shaping of the blank by rolling reduces the amount of machining necessary in converting the blank to a iinished blade and effects a further economy in production cost. The apparatus and method for producing the blanks are simple and easy to utilize.

Although I have disclosed herein the preferred embodiment of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention as dened in the claims.

I claim:

l. In a method of making a propeller-blade blank, the steps including forming a metal billet of oval section having a tapering cavity extending thereinto from one end and rudimentary ribs extending therealong through the ends of the major axis of the cross section, heating the billet to forging temperature and placing it on a mandrel having a section which is round at its head end but merges to a section which is elliptical at the other end and has dihedral edges tapering to a rounded contour, and pushing the mandrel and billet through a plurality of plain elliptical roll passes in close-order succession thereby elongating the billet over the mandrel andre` ducing the wall thickness to form a shell of uniform outside circumference and simultaneously reducing the thickness of the ribs causing them to spread laterally and form ns of substantial Width.

2. The method defined by claim 1 characterized by forming said cavity elliptical in section for the most part, rounded on one side and with a dihedral edge on the other feathering to a rounded contour.

3. In a method of making a propeller-blade blank, the steps including forming an oval billet having a cavity extending into one end thereof and a rib along each side in the plane of the major axes of transverse sections therethrough, placing the billet on a mandrel having the shape of the interior desired in said blank, then pushing the mandrel with the billet thereon through a plurality of groups of rolls forming plain elliptical passes in closeorder succession thereby reducing and elongating said billet into a semi-finished blank and widening said ribs simultaneously with the elongation of said billet to form integral iins on opposite edges of the blank.

4. In a method of making propeller-blade blanks, the steps including piercing a heated billet throughout the greater portion of its length, forming therein a longitudiual cavity substantially circular in cross section at the bottom and of oval cross section at points spaced from the bottom, and simultaneously extruding the billet in a mold having an oval cavity and grooves extending through the ends of the major axis of its cross section, thereby shaping the billet to oval cross section and forming a rudimentary rib extending along each side thereof, placing the billet symmetrically on amandrel having a cross section which is substantially circular at its leading end but merges to an oval cross section at the other end having dihedral edges tapering to a rounded contour, and hot-rolling the billet on the mandrel in a plurality of open oval roll passes thereby elongating the billet over the mandrel, shaping the interior of the billet to conform to the mandrel and reducing its Wall thickness to form a shell of uniform ouside circumference, and simultaneously reducing the thickness of said ribs and widening them to form longitudinal tins of substantial Width to provide the leading and trailing edges of a finished blade.

5. In a method of making propeller-blade blanks, the steps including forming in a cylindrical billet a longitudinal cavity extending thereinto from one end, of substantially circular shape in cross section at the inner end and merging into increasing cross sections of oval shape spaced progressively from the said inner end, and simultaneously shaping the exterior of the billet to an oval cross section with longitudinal ribs extending through the ends of the major axes of successive sections, then fitting the billet symmetrically on a mandrel having a cross section which is substantially circular at its leading end but merges to an oval cross section at the other end having dihedral edges tapering to a rounded contour, and rolling the billet on the mandrel in a plurality of open oval roll passes thereby elongating the billet over the mandrel, shaping the interior of the billet to conform to the mandrel and reducing its wall thickness, and converting said ribs to iins adapted to constitute the leading and trailing edges of a nished blade.

References Cited in the le of this patent UNITED STATES PATENTS 331,574 Tasker Dec. l, 1885 721,211 Mannesmann Feb, 24, 1903 721,214 Mannesmann Feb. 24, 1903 722,398 Bock Mar. 10, 1903 1,325,301 Levy Dec. 16, 1919 1,448,747 James Mar. 20, 1923 1,503,170 Smith July 29, 1924 1,720,345 Peters July 9, 1929 1,774,563 Parsons Sept. 2, 1930 1,776,855 Holmes Sept. 30, 1930 1,839,919 Hall Jan. 5, 1932 1,869,478 Heath Aug. 2, 1932 1,900,630 Zagorski Mar. 7, 1933 1,916,027 Weinberg June 27, 1933 2,041,937 Korbuly May 26, 1936 2,104,222 Decker Jan. 4, 1938 2,138,127 Squires Nov. 29, 1938 2,151,243 Squires Mar. 21, 1939 2,193,351 Smith Mar. 12, 1940 2,278,325 Layton Mar. 31, 1942 2,308,344 vAndrake Jan. 12, 1943 2,312,094 Harmon Feb. 23, 1943 2,394,445 Handler Feb. 5, 1946 2,431,411 McKee Nov. 25, 1947 2,471,485 Gruetjen May 31, 1949 FOREIGN PATENTS 524,152 Great Britain July 31, 1940

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