US2176155A - Apparatus for elongating and decreasing the wall thickness of tubular blanks - Google Patents

Description

. 2,176,155 THE 4 Oct. 17, 1939. R. c. STIEFEL FOR ELONGATI ECREASING NG AND D 555 OF TU Sept. 3, 2 Sheets-Sheet 1 III'IIIE Patented Oct. 1 7, 1939 APPARATUS FOR. ELONGATING AND DE- OREASING THE WALL TBICKNESS OF TUBULAR BLANKS Ralph Q. Stieflil, Ellwood City, Pa, assignor to The Timken Roller Bearing Company, Canton. Ohio, a corporation of Ohio Application September s, 1936, Serial No. 99,228

9' Claims.

Therels a. well-known. type of rolling mill for producing seamless tubing wherein the work rolls are disposed equldistantly from the axis of the mill and with their own axes askew with, reference 6 to the axis of the mill and arranged to cooperate with a stationary mandrel located in the axis of the mill. The rolls of such mills may be either of the barrel-shaped type or of the mushroom or conical type; but in either case, the rolls function to simultaneously rotate and longitudinally to object'to devise a method whereby the tubular blank can be greatly elongated; and especially, to devise a method whereby the tubular blank can be greatly elongated with little or no enlargement of the diameter thereof. Another principal object is to devise means for efiecting such elongation of the tubular blank.

The invention consists principally in carrying out the rolling operation under such conditions that the tendency of the blank to bulge or enlarge in diameter is minimized or overcome and an effective tendency toelongate is brought about. It also consists in the mill and in the mandrel and in the combinations and arrangements of parts hereinafter described and claimed.

In the accompanying drawings wherein like reference numerals refer to they occur:

Fig. 1 is a side view of the pass forming elements of my invention showing a blank in process of manufacture, and as if the work rolls were diametrically opposed;

Fig. 2 is a cross-section through the pass, as indicated on the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary detail view showing the mandrel in elevation and the adjacent portion of.

a work roll and the intervening portion of the blank in longitudinal section Fig. 4 is a diagrammatic view illustrating the transverse flow angle; and

F g-'5 is a detail view of a modified form of mandrel head.

50 My mill'comprises two or more work rolls I and means for driving them. The rolls are disposed equidistantly about the axis of the mill and with I. their own axes 'askew so as to effect rotation and longitudinal movement of the tubular blank and it also comprises a stationary mandrel 2, which like parts wherever 7 is rotatable or is provided with a rotatable head 3, mounted in the axis of the mill for cooperation with the work rolls. The mill is provided with means for adjusting the rolls radially with respect to the axis of the mill and with means for adjusting the'skew of the feed angle of the rolls. Except as otherwise described herein, my mill conforms to a familiar type of cross-rolling mill'now in use for production of seamless tubing and no specific description or illustration thereof is needed herein. v

The particular work roll I shown in Fig. 1 is of barrel shape and has its outer surface divided into five zones. The endmost zone A (hereinafter called the centering zone) on the entering side is intended to facilitate the entering of the blank between the work rolls. It gradually increases in diameter from the end of the roll to the second or next-adjacent zone B, which also increases in throughout its width towards its delivery end and" is hereinafter called the rounding zone. Zone I) tapers to the fifth or rearmost zone E, hereinafter called the clearance zone, which tapers still more sharply and functions to allow the work to clear the rolls without being marked by them.

The mandrel 2 is mounted with its axis coincide ing with the axis of the mill. The mandrel is rotatable on its own axis or comprises a fixed mandrel bar 2 with a rotatable head 3', both of these types of mandrel construction being wellknown in the art. The endmost zone or face G of the mandrel head is convexed or tapered and merges at its large end into a cylindrical zone H which is located opposite the feeding zone B of the work rolls and extendssomewhat past the near margin of the main work zone C. Here the mandrel head widens out abruptly in the form of a steep conical shoulder I. From this shoulder to its rear end, the surface of the mandrel head is a substantially cylindrical zone K of the same diameter as the large diameter of the conical shoulder. The large cylindrical portion K of the mandrel head terminates opposite the middle portion of the rounding zones D of the rolls.

The operation of the construction hereinbfore described is as follows: The tubular blank W is fed endwise between the ends of the rolls and is guided and centered, by the centering zones thereof, with respect to the mandrel, the feeding zone B cooperating in the centering operation. The blank is thus brought within the range of action of the feeding zones of the rolls which bend the wall of the blank inwardly and grip it between them and the small cylindrical zone of the mandrel head. The blank is thus rotated and moved forwardly against the conical shoulder I of the mandrel head, which shoulder cooperates with the main work zones of the rolls to constitute the main pass and effect the plastic flow of the metal. The blank passes thence to the rounding zone, where it is rounded, and thence through the clearance zone at the delivery end of the mill. When the end of the blank has passed the feeding zone, the work of feeding is accomplished by the main working zone and the rounding zone.

In the operation above described, the plastic flow of the metal is mainly in the longitudinal direction, with a decrease in wall thickness, whereas heretofore, cross rolling of tubular blanks has usually produced little or no elongation. Applicant's new result is attributable to a new correlation of the factors that determine the direction of flow of the metal, that is, the factors are so related that the longitudinal flow angle is greater than the transverse flow angle. By

.longitudinal flow angle" is meant the angle ROP between the projected element P0 of the surface of the conical shoulder I and an element R0 of the surface of the main working zone D of the roll, that is, the angle between the portions of the inner and outer surfaces of the work blank W in the zone opposite said shoulder I. As the line R0 is substantially parallel with the axis T1" of the pass and of the mandrel, the angle of inclination of the shoulder I to such axis, namely, angle OPT, is substantially equal to the longitudinal feed angle ROP and is half the included apical angle OPP of the conical shoulder.

The term "transverse flow angle" means the angle XZY formed between a tangent YZ to the shoulder I of the mandrel head at the medial point Y of its contact with the blank W and a tangent XZ to the work roll at the medial point X .of its contact with the blank. By keeping this transverse flow angle smaller than the longitudinal flow angle, the main flow of the metal is in a longitudinal direction and the tendency of the metal to flow transversely and thereby enlarge the diameter of the tube is minimized or completely overcome.

What is contemplated by the expression flow angle" may be understood by consideration of the longitudinal rollingof hot sheet metal between cylindrical rolls. In such rolling the metal is not confined except by the rolls, and is therefore otherwise free to flow, and dOes flow, in the direction of least resistance while being subjected to rolling pressure. When so rolled, hot sheet metal does not spread laterally to increase its width because the lateral or transverse flow angle, namely. that formed between the parallel working faces of cylindrical rolls, is zero,- or substantially zero. It is the frictional resistance to flow of the metal laterally oilered by the parallel active working faces of the rolls that prevents its lateral flow. In such rolling '6? sheet metal of its metal in the direction opposite to that of the passage of the blank through the mill, or in other words, in a rearward direction, such direction being the path of least resistance to flow because of the larger flow angle.

The same general conditions prevail in the cross-rolling of a seamless tubular blank, which, in the case of a cross-rolling mill having two I cross-rolls, may be generally considered as being simultaneously passed through the two passes of a three-high mill formed by the mandrel and cross-rolls. The difference is that the axes of the outer or cross-rolls are inclined to the axis of the middle roll or mandrel. When being thus rolled, the metal of a tubular blank flows in the direction of least resistance, which, in the mill shown in the drawing, is longitudinally of the blank because the longitudinal flow angle ROP (see Fig. 3) is greater than the transverse flow angle XZY (see Fig. 4).

Preferably the transverse flow angle is less than the friction angle of the metal and the longitudinal flow angle is greater than the friction angle of the metal, bywhich is meant the angle of repose of the metal when heated to its working temperature. The coefllcient of friction for steel when heated to the temperature required for cross-rolling it in the form of a tubular blank may be taken as .4, which is substantially correct for some steels in tubular blanks. The tangent of .4 being 22, it is preferred in this example to use cross-rolls and mandrels of such diameters that the transverse flow angle XZY formed between them by tangents to their surfaces at their points of engagement with a blank is less than 22". For example, this flow angle may advantageously be about 12. The longitudinal flow angle ROP is greater than the friction angle of the metal, say about 30 without impeding the feeding and reduction of the blank. In all cases the longitudinal flow angle must be greater than the lateral flow angle of the metal in the practice of my invention. The steeper the conical shoulder I and, consequently, the wider the longitudinal flow angle, the narrower is the conical shoulder and the narrower the zone of the blank in which the work of reduction and elongation is effected.

The mandrel head of Fig. 3 comprises an endmost pilot zone G and a cylindrical zone H-that is adapted for cooperation with the feeding zones of the work rolls. These two zones may be dispensed with and the blank fed directly against a steep conical shoulder I of the mandrel head. Thus, in the design of mandrel head illustrated in Fig. 5, the peripheral portion of the end face of the mandrel head is made in the form of a steep annular shoulder or zone I and the portion of the face enclosed by said annular zone is shown as bluntly convexed. However, the portion enclosed by the annular zone is relatively unimportant, the most important feature of the mandrel head being the steep inclination of its peripheral portion, namely, the portion next to the outer periphery, which cooperates with the working zones of the rolls to constitute the gorge of the pass.

What I claim is:

1. A cross-rolling mill for elongating and reducing the wall thickness of a heated tubular blank comprising a plurality of skewed rolls and a mandrel arranged in the line of pass formed of pass and the working faces of the mandrel are abruptly diverging in the direction of feed and form steep and short contacts with the blank to effect reduction in wall thickness and minimize expansion of the blank, said principal pass-stage being preceded by a pass-stage in which the working faces of the cross-rolls converge slightly toward the line of pass in the direction of feed to grip the blank and helically feed it forward, said principal pass-stage being followed by a passstage in which the working faces of the rolls and mandrel are substantially parallel with the line of pass to smooth and feed the reduced blank forward.

2. A cross-rolling mill for elongating and reducing the wall thickness of a heated tubular blank, comprising a plurality of helically acting cross-rolls, and a mandrel arranged in the line of pass formed by the rolls, the work faces of the rolls and mandrel being shaped to form three successive pass-stages, in the first of which the active working faces of the cross-rolls converge slightly towards the line of pass in the direction of feed to grip the blank and helically feed it forwardly, in the second of which the coacting working faces of rolls and mandrel so converge towards each other in the direction of feed with the said working faces of the rolls converging also to the center line of pass in the direction of feed and the said working faces of the mandrel diverging also from the center line of pass in the direction of feed that. the longitudinal flow angle is greater than the transverse flow angle of the metal of the blank so as to effect reduction in wall thickness and minimize expansion of the blank, and in the third of which the active working faces of the mandrel and rolls are substantially parallel to the line of pass to smooth and feed the reduced blank forwardly.

3. A cross-rolling mill for elongating and reducing the wall thickness of a heated tubular blank, comprising a plurality of helically acting cross-rolls, and a mandrel arranged in the line of pass formed by the rolls, the work faces of the rolls and mandrel being shaped to form three successive pass-stages, in the first of which the cross-'- rolls converge slightly towards the line of pass to grip the blank and helically feed it forwardly,in the second of which the coacting working faces of rolls and mandrel so converge towards each other in the direction of feed with the said working faces of the rolls converging also to the center line of pass in the direction of feed and the said work'- ing faces of the mandrel diverging also from the center line of pass in the direction of feed that the longitudinal flow angle is greater than the transverse flow angle of the metal of the blank and than the friction angle thereof so as to effect reduction in wall thickness and minimize expansion of the blank, and in the third of which the active working faces of the mandrel and rolls are substantially parallel to the line of passto smooth and feed the reduced blank forwardly.

4. A cross-rolling mill for elongating andreducing the wall thickness of a heated tubular blank, comprising a plurality of helically acting cross-rolls, and a mandrel arranged in the line of pass formed by the rolls, the work faces of the rolls and mandrel being shaped to form three successive pass-stages, in the first of which the cross-rolls converge slightly towards the line of pass to grip the blank and helically feed it forwardly, in the second of which the coacting working faces of rolls and mandrel so converge towards each other in the direction of feed with the said working faces of the rolls converging also to the center line of pass in the direction of feed and the said working faces of the mandrel diverging also from the center line of pass in the direction of feed that the longitudinal flow angle is greater than the transverse flow angle of the metal of the blank and than the friction angle thereof and in which the transverse flow angle of the metal is smaller than the friction angle thereof, and in the third of which pass-stages the active working faces of the mandrel and rolls are substantially parallel to the line of pass to smooth and feed the reduced blank forwardly.

5. A cross-rolling mill for elongating and reducing the wall thickness of a heated tubular blank, comprising a plurality of helically acting cross-rolls, and a mandrel arranged in the line of pass formed by the rolls and fixed against longitudinal movement, the working faces of the rolls and the mandrel being shaped to form three successive pass-stages, in the first of which the crossrolls converge slightly towards the line of pass and the mandrel is substantially cylindrical for cooperation with the cross rolls in gripping the blank and helically feeding it forwardly, in the second of which the active working faces of the cross-rolls are substantially parallel to the line of pass and the mandrel is flared outwardly at an angle to the opposed active working faces of the rolls greater than the transverse flow angle formed between the rolls and the mandrel, and in the third of which the active working faces of the mandrel and rolls are substantially parallel to the line of pass to smooth and feed the reduced blank forwardly. Y

6. A cross-rolling mill for elongating and re-' ducing the wall thickness of a heated tubular cross-rolls converge slightly towards each other and the mandrel is substantially cylindrical for cooperation with the cross-rolls in gripping the blank and helically feeding it forwardly, in the second of which the active working faces of the cross-rolls are substantially parallel to the line of pass and the mandrel is fiaredoutwardly at an angle to the opposed active working faces of the rolls greater than the transverse flow angle formed between the rolls and mandrel and greater than the friction angle of the metal, and in the third of which the. active working faces of the mandrel and rolls are substantially parallel to the line of pass to smooth and feed the reduced blank forwardly.

7. A cross-rolling mill for elongating and reducing the wall thickness of a heated tubular blank, comprising a plurality of helicallyacting cross-rolls. and a mandrel arranged in the line of pass formed by the rolls and fixed against longitudinal movement, the working faces of the rolls and the mandrel being shaped to form three successive pass-stages, in the first of which the crossrolls converge slightly towards the line of pass and the mandrel is substantially cylindrical for cooperation with the cross-rolls in gripping the bank and helically feeding it forwardy, in the second of which the active working faces of the cross-rolls are substantially parallel to the line of pass and the mandrel is flared outwardly at the angle to the opposed active working faces of the rolls greater than the transverse metal flow angle formed between the rolls and mandrel and greater than the friction angle of the metal and in which the transverse flow angle of the metal is greater than the friction angle thereof, and in the third of which the active working faces of the mandrel and rolls are substantially parallel to the line of pass to smooth and feed the reduced blank forwardly.

8. A mill for cross-rolling tubular blanks to elongate themand decrease the wall thickness thereof, said mill comprising a series of work rolls arranged equidistantly from an axis and askew with relation thereto, and a stationary mandrel with a rotatable head which has a steeply inclined conical shoulder whose large end is immediately next to the outer periphery of said mandrel and in the gorge of the pass formed by said rolls, the angle between the surface of said conical zone and the surface of the roll on the entering side thereof being greater than the angle between transverse tangents to said conical zone and the surface of the work roll at their points of contact with the blank.

9. A mill for cross-rolling tubular blanks to elongate them and decrease the wall -thickness thereof, said mill comprising a series of work rolls arranged equidistantly from an axis and askew with relation thereto, and a stationary mandrel with a rotatable head, said head having a cylindrical zone rearward of the gorge of the pass and a steeply inclined conical zone contiguous with said cylindrical zone and located in the gorge of the pass formed by said rolls, the angle between the surface of said conical zone and the surface of the roll on the entering side thereof being greaterthan the angle between transverse tangents to said conical zone and the surface of the work roll at their points of contact with the blank. RALPH C. STIEFEL.

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