US 3779064 A
The invention provides a precision method and apparatus for surfacing and removing contaminants from the interior and/or exterior of a tube and for calibrating the interior or exterior of a tube.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Besson PROCESS AND APPARATUS FOR CALIBRATING AND SURFACING TUBES  Inventor: Louis Pierre Albert Besson,
Romainville, France  Assignee: Chabas & Besson S.A., Romainville,
France  Filed: Oct. 29, 1971  Appl. No.: 193,632
 Foreign Application Priority Data Nov. 6, 1970 France t. 7039913  US. Cl 72/283, 72/284, 72/348, 72/370  Int. Cl. 1321c 1/24  Field of Search 72/283, 284, 348,
72/370; 29/90, DIG. 11
7 Dec. 18, 1973 [5 6] References Cited UNITED STATES PATENTS 3,036,696 5/1962 Zimpel 72/348 FOREIGN PATENTS OR APPLICATIONS 1,914 8/1900 Austria 72/283 17,085 0/1898 Great Britain 72/370 Primary Examiner-Charles W. Lanham Assistant Examiner-Robert M. Rogers Att0rneyRichard L. Johnston [5 7 ABSTRACT The invention provides a precision method and apparatus for surfacing and removing; contaminants from the interior and/or exterior of a tube and for calibrating the interior or exterior of a tube.
19 Claims, 15 Drawing Figures PATENTEBUEE] 81975 SHEET 1 0f 8 v'lll I'll I PAIENTEDUECI 819 75 SHEEI 2 0f 8 .llllllllll SHEEI 7 GF 8 PATENTEI] DEC 1 81975 erally; isratherimperfectexternally as well astinternally, and theisurface condition, internally and externally, is rather mediocrex As a result, for numerous uses of such tubes inmechanics, it is necessary to machine said-tubes, externally, and/or internally, said operation usually being slowandexpensive. In the cases requiring a highlevel of precision, it may become necessary to refinish the tubes, and said refinishingmay require a considerable length of time, on the order of several hours;- when such'arefinishing is preformed by means of polishing or 'grinding stones, there always remainon the refi nished surface abrasive particles which, for certain'uses, may prove completely undesirable.
OBJECTS The present invention has as one of its objects the provisionof a process and apparatus making it possible l cold -conditions intheconventional manner, in which case calibrating of the tube can be done very rapidly and at low cost.
The present invention has as another object a new processand apparatus for the internal and/or external surfacing of tubes, havingas their transverse cross sections any closed ring, and for calibrating the inside and- /or outside of said tubes, aprocess and apparatus essentiallycharacterized bythe' use of a tool or mandrel of whichat least part of the external surface is harder than the metalof thetube onwhich the work is to bedone and is defined byjthedisplacementof a meridian curve fdrmedon a closed directrix approximately identical witltthe' edge corresponding to the surface of the transverse cross sectionof the tube, the profileof the tool alongya meridiancurve which generates its external surface being suchth at, passinggfrom a plane through the first end of the tool, which corresponds to the first point of contact of thetool with the tube, to a second plane through said tool, which corresponds to the point where contact of the tool with the tube ends, it varies in a continuous manner over the distance tothe axis of the tubeg increasingwhen workis done on the internal surface of the tube, and decreasingwhen work is done i onthe external surface, the maximum variation being greater than the maximum depth of the defects presenter! by the tube onthe surface on which workis done, andless than thevalue :which corresponds, to ensure the displacement of the tube along theaxis of the tube,
to a forceapplied onthe tubewhich exceedsthe mechanical resistance of said tube; hence, a relative transit lation displacement alongthe axis of the tube between the above defined tool and the tubeon to be done is assured.
BRIEFSUMMARY or THE" INVENTION A process and-apparatus for surfacing the interior and/or exterior of a tube and for calibrating the interior or exterior of said tube by the alternate steps of (a) forcing said tube axiallythrough adie having a curved surfaceadapted to contact theexterior surface of said tube to reduce its diameter; and (b) forcing. a tool through the interior of said tube-to increase its diameter.
DETAILED DESCRIPTION OF THE INVENTION When the process according to thepresent invention is used for tubes the section of which is circular, the
tool is limited for at least part of its external surface, by r a surfaceof revolution. It has been observed, and that surprisingly, that when there is defined, in an axial plane, the angle A formed with the axis by the straight line which joins the point of coming into contact of the tool with the tube, and the point whichcorresponds to the end of the contact of thetool with said tube, said angle must range approximatelybetween l2 and 20so that satisfactory results can be'obtained with steel.
Moreover, it has been observed that it is preferable for the angle formed with the axis by the plane which is tangent to the external surface of the tool, at the point where said tool comes into contact with the tube, to be greater than the angle formed with the axis by the plane tangent to the profile of the tool at the point where the contact between the tool and the tube ends in the courseof the work. For that purpose, it is preferred to give to the external edge of the tool the shape of a toric surface having as its section a half circle. When such a mode of execution is adopted, it will be seen that, inorderto obtain good results, especially in the case of a steel tube, the radius of the half circle constituting the section of the toric ring, should range between 3 and 6 millimeters. a
It has also been observed afterthe running of the tool, that a slight variation in the dimension of the tube took placeinthe direction of a return toward the initial dimension. As a result, the diameter of the tool at the end of the contact with the tube is very slightly different from the desired calibration diameter of the tube, said difference corresponding to the value of the return value of the tube. g
In accordance with the present invention it is possible to carryout the surfacing and the calibrating of the tubes in several successive operations usingfor successive runs tool diameters which are increasing whenexeouting an internal calibration, and which are decreasing when executing an external calibration.
For an internal calibration of a given tube by means of a tool shaped like a toric ringwitlt a half-round sec tion, it is assumed that the quality of the surfacing and calibrating result which is obtained is due to the fact that in the zone where the tool contacts the material of the tube, a plastic deformation occurs which fills the which work has on the tube is appreciably increased, a situation which decreases for a given variation in diameter, the local supporting pressure of the tool on the material of the tube, and, in that case, the desired result is not obtained. The fall in the local supporting pressure is further increased because the force necessary for the displacement of the tool is smaller when the radius of the right section of the toric tool is increased due to the descrease in the attacking angle of said tool on the material of the tube. Moreover, visual observation shows that defects in the tubes surface, as well as impurities and contaminants, such as rust or calamine, for example, are not completely removed from the surface but, on the contrary, may become encrusted in same, a situation which increases the imperfection of the internal surface. If, on the contrary, a radius for the right section of the toric tool is used which is less than 3 millimeters, the metal of the tube forms a swelling or ridge in front of the tool in the direction of displacement, and the low value of the radius of the right section of the tool causes an attacking angle of the tool on the tube strong enough for said swelling or ridge to be torn away which results in the production of shavings and the destruction of the surface.
Finally, by remaining within the limits previously defined, i.e., a radius for the right section of the tool which is greater than 3 millimeters and smaller than 6 millimeters after the passage of the tool inside the tube, the condition of the surface visually is perfect and calibration is obtained with a precision of a few hundredths of a millimeter. Moreover, the execution of the process according to the present invention makes it possible to obtain a cold reshaping of the metal in the zone of the layers which have been worked by the tool, said cold reshaping making it possible to obtain an increase in the hardness near the. surface which has come in contact with the tool. For the case of a steel tube drawn under cold conditions of the conventional type, the increase in local hardness rangesbetween percent and 30 percent, approximately.
It should be noted that it is also possible to use a tool the external surface of which is not limited by a toric surface the right section of which is not circular but elliptical or oval, it being understood that it is advantageous for the attacking angle of the tool on the tube, i.e., for the angle formed with the axis by the plane which is tangent to the profile of the tool, always to be greater than the angle of escape, i.e., the angle formed with the axis by the plane which is tangent to the profile of the tool at the point where the contact of the tool with the tube ends. However, in the case where the tube on which work has to be done internally has a suitable surface condition it is also possible to apply the process according to the present invention by means of a tool in the shape of a truncated cone in which the attacking angle is equal to the escape angle. In that case,
. sage in a drawplate the diameter of which at the neck is slightly less than the external diameter of the tube. It has been observed that such a preliminary operation very appreciably improved the results obtained. It is assumed that in the reshaping operation the contaminants which are on the internal surface of the tube are cracked and the internal defects of the tube are slightly shrunk. The subsequent passage of the tool according to the invention then makes possible not only the removal of the contaminants but also the disappearance of all of the surface defects. The process of the present invention, therefore, also includes the combination of a preliminary running of the tube through a drawplate with reshaping and of a running of the tool through the tube, as defined above. It has been observed that for the steel tubes, good results were obtained by adopting, for the neck of the drawplate, a profile formed by the arc of a circle the radiusof which ranges between 25 and 35 millimeters.
The present invention also has as its object a new industrial machine for the calibration and surfacing of tubes, essentially characterized by a fixed frame, a movable rod on which can be fixed a tool or mandrel such as defined in the process according to the invention, and finally means for holding the tube on which the work has to be done, with respect to the frame, and means insuring the displacement of the tool with respect to said tube.
In one preferred embodiment, the tool is fastened by screws at the end of a rod solidly connected to a movable piston of a hydraulic jack. The rod has an external diameter slightly less than the internal diameter of the raw tube on which the work is to be done. The frame carries, facing the movable piston of the jack, a drawplate. The drawplate is disposed by cone-shaped adjustment in a drawplate support with respect to which it is movable. The frame has jaws for the support of the tube against which the tube to be worked can be pushed when the tool enters the tube, said jaws being capable of being retracted. The drawplate and the lug jaws for the tube are placed in a manner such that the tube will cooperate successively in opposite directions with them when displaced by the movable jack piston.
The present invention also has as an object a new industrial product constituted by a bench for drawing under cold conditions a tube made of steel, for example, said bench having as one component, a drawplate disposed at right angles to a cylindrical bullet and, for the other component, traction means which insure the passage of the metal to be drawn through the drawplate around the aforementioned bullet, essentially characterized by the fact that the bullet has, in a forward cylindrical zone with respect to the direction of the drawing, a tool or mandrel which is connected with it, and which corresponds to the definition given above in the description of the process according to the present invention.
In order to assist in better understanding the object of the invention, there will now be described as examples which are illustrative only and not limitative, two 7 modes of execution illustrated in the attached drawing.
THE DRAWING FIG. 5 represents, in elevated section, the detail of the drawplate of the machine in FIG. 1, and the retractable. jaws of FIGS. 3 and 4;
FIGS. 6 to 12, 12 and 13 represent, in a schematic manner, the various phases of a calibrating and surfacingoperation of the inside of a tube, executed by means of the machine in FIG 1;
FIG. 11 represents, partly in section, the mandrel used forcalibrating the tube;
FIG. l4represents, in a schematic manner, a bench for the drawingof tubes under cold conditions, of the conventional type; and
FIG. 15 represents, schematically, a bench for drawingjtubes under cold conditions according to the presentinvention.
Referring to the drawings and more specifically to FIGS. 1 to 13, the embodiments illustrated comprise twomembers la and 1b connected by four rigid rods 2-which form a parallelelepipede the base of which is square. The combination of the ends 1a, lb and of rods Z'constitutes the frame of the machine. Said frame carries a double acting hydraulic jack 3, the movable piston of which is represented by 4, and the axis of which is disposed approximately in the direction of the axis of theparallelepipede with a square base defined by rods The hydraulic jack 3 is fed by a motor-pump means 5. The operation of the jack is effected by means of a distributor 7 which the user operates by means of a handle 8. Two ducts 9,9 connect the distributor 7 and the motor-pump means Sand two ducts l connect the distributor 8 and each one of the two ends of the hydraulic jack 3.
The movable piston 4 of jack 3 is fixed to a rod 11, the diameter of which is slightly less than the diameter of the tube, the inside of which it is desired to calibrate and to surface by means of the machine according to the present invention. Facing the end of rod 11, which is disposed according to the axis of jack 3, is an opening 12 in member 1a. Between, member la and rod 11, on supporting small plate 13 disposed transversely of the machine is a drawplate support 14 having a cylindrical element at the center in which is a cone-shaped cavity. In the cone-shaped cavity of support 14 is a drawplate 15, the external shape of which is a cone and the summit angle of which corresponds to the conicity of the central cone-shaped cavity of the drawplate support 14.
Drawplate 15 is a revolving part the internal surface of which has a neck 16 (see FIG. which separates a converging zone 17a and a diverging zone 17b. Neck 16 isdesigned so that in axial section it approximately corresponds to the arc of a circle the radius of which is 30 millimeters. Drawplate is removable with respect to said drawplate support 14, and the drawplate support 14 can roll over the small plate 13 which carries it. g
On the side of member 1a where there is no drawplate support 14 are placed two jaws 18,18, each one movable around a shaft 19. Shaft 19 is disposed below the axis of rod 11. Jaws 18,18 when in closed position define between them a cylindrical cavity. They each contain intermediately a groove 20 in which is a bronze segment'ZL-When the jaws 18,18 are in the closed position, the two bronze segments 21 are supported on rod 1 1', when the latter is forward enough to be at a right angle with jaws 18,18.
When it is desired to calibrate cold drawn tubes 22 having an internal diameter of 49.9 millimeters and an external diameter of 63.0 millimeters, rod 11 has a di ameter of 48.5 millimeters. In the example described, tube 22 on which work has to be done is made of semihard steel, having a resistance of 55 kilograms per square millimeter. The diameter of neck 16 of the drawplate 15 is 62.3 millimeters. In order to treat a tube 22 the length of which is 1 meter, there is used a jack having a run of 1.40 meter, with an advancing motion of l centimeter per second in the direction which makes it possible to go from member 1b to member 1a, and have a return motion, at a speed of 2 centimeters per second, approximately. The distance between the two members It: and 1b is 1.50 meter, approximately.
In order to carry out the calibration and surfacingof tube 22, said tube is placed on rod 11 and caused to slide on said rod through opening 12. At first, piston 4 of jack 3 is disposed in its most remote position from member In. Between piston 4 and tube 22 is disposed on rod 11, for one thing, a ring 23 the diameter and dimensions of which are ,aproximatelythose of tube 22 and also two half-shells 24, which approximately result from the sawing of a ring 23 along an axial plane. Said phase of the operation is represented in FIG. 6.
After drawplate support 14 and its associated drawplate 15 have been set in place on the transverse small plate 13, by moving handle 8 of distributor 7, a forward motion is imparted to piston 4 of jack 3. Rod 11, on which externally lubricated; tube 22 is disposed, runs through drawplate 15 and cavity 12. Jaws 18,18 are in their open position. This phase of the operation is represented in FIG. 7.
As the forward motion of piston 4 continues, the external surface of tube 22 comes into contact with drawplate 15 and is pushed by jack 3 through said drawplate with a force of 8,600 kilograms, so that its external diameter, which has 63 millimeters, becomes approximately equal to the diameter of the neck of the drawplate, i.e., 62.4 millimeters. During said reshaping, the particles of rust or of calamine, or the other contaminants which may be inside the tube, become separated from the internal surface, which has a diameter of 49.0 millimeters, approximately. Tube 22, under the pushing action of jack 3, a pushing action which is transmitted through ring 23 and through the half-shells 24, possibly shows a tendency to bend, but said tendency is limited by the presence of rod 11. This phase of the operation is represented in FIG. 8.
When piston 4 of jack 3 has moved a sufficient distance, tube 22 carried by rod 11 passes beyond drawplate 15 and continues its forward motion. At that moment, the jaws 18 are still open. The two half-shells 24 are then removed, leaving only ring .23 between tube 22 and piston 4, and pushing said ring toward piston 4. This phase of the operation is represented in FIG. 9.
When piston 4 has moved forward sufficiently with the rear part of tube 22 beyond jaws 18, the end of rod 11 nevertheless projects beyond the fore part of tube 22. At that moment, jaws 18 are closed so that the segments 21 come in contact with rod 11, to the rear of tube 22. The internal diameter of the jaws 18 is less than the external diameter of tube 22. The inside of tube 22 is generously lubricated and a tool 25 of hard steel is screwed on the end of rod 11. The right half section of the tool 25 isrepresented in detail in FIG. 11. Said tool is constituted by'a mandrel shaped like a toric ring, screwed at the end of rod 1 1 by means of a thread 25a. The toric ring has an edge the right section of which is a half-circle. The radius preferred for said halfcircle is 4 millimeters. The maximum external diameter of the toric ring is 49.81 millimeters'There is then executed by means of handle 8 a reversing of the run of jack 3, causing a return to the rear of piston 4. In the course of that motion, tool 25, which has been generously lubricated, comes to apply on the fore end of tube 22 (on the left side in the figure), and pushes that tube back until its rear end comes in contact with the fore face of jaws 18. At that moment, the tube is stopped and when piston 4 continues its return run, tool 25 enters inside the tube 22, deforming said tube and causing an increase in its diameter. Said penetration of the tool into the tube requires a force of 11,400 kilograms for the dimensions indicated. This phase of the operation is represented in FIG. 12.
Once tool 25 has run the whole length of tube 22, said tube 22 discharges from the machine and falls on a receiving tray. At that moment, jaws 18 are opened, tool 25 is unscrewed, separating it from rod 11, and the return motion of piston 4 is continued until it has come back to its initial position. There is thus obtained a very satisfactory surface condition for the inside of the tube, and it is observed that all the contaminants which were on the internal surface of the tube have been extracted from the tube and are mixed with the lubricant which covered tool 25 and rod 11. Moreover, all the surface defects which are characteristic of tubes drawn under cold conditions have disappeared. The tube which is obtained has an internal diameter of 49.7 millimeters, and an external diameter of 63.0 millimeters.
When it is desired to improve the calibration, which is thus obtained by a running of tool 25, it is possible to execute a second run of the mandrel, starting the operation from the phases represented in FIGS. 10, 12 and 13, and using a mandrel, the maximum external diameter of which is slightly greater than the maximum external diameter of the tool used in the course of the first phase. In the example which has been described, the second tool has a maximum external diameter of 50.] millimeters. The radius of the semi-circle which forms the edge of the toric ring which constitutes the mandrel is millimeters for, in the case of this second run, the radius under'consideration is not necessarily between 3 and 6 millimeters, and may be greater, since this is a finishing operation. The running of said mandrel requires a force of 6,300 kilograms. After the passage of the second tool or mandrel inside tube 22, it is observed that'the surface condition is perfect, and that the internal calibrating of the tube is obtained at the value of 50.00 millimeters plus or minus 0.02 millimeters. After each run of the tool or mandrel 25,
a slight reshaping of the tube occurs which explains why with this latter too], the external diameter of which is 50.] millimeters, a calibration at the diameter of 50.0 millimeters is obtained. The external diameter of the tube is 63.4 millimeters.
It is evident that when there are a series of tubes to be surfaced and calibrated, it is possible to effect the run through the drawplate and the first mandrel phase in a single operation for each tube, reserving the second phase or passage of the tool for an ulterior step after all of the tubes have been subjected to the first step. This mode of operation makes is possible to improve on the time required for the operation in the case of a series of tubes all of which are identical.
It has been observed that the preliminary operation of running through the drawplate to cause a'reshaping of the tube makes it possible to improve greatly the state of the surface which is finally obtained for the inside of the tube. It is assumed that such state results, on the one hand, from the cracking of the impurities due to reshaping and, on the other, from the shrinking of the surface defects which were on the internal surface of the tube. It is also assumed that the remarkable surface condition and calibration obtained, which it is possible to observe, results from the fact that tool 25, by bearing against the material of tube 22, causes a plastic deformation of said material, which makes it possible to fill the surface defects which existed initially. This I assumption is corroborated by the fact that there is obtained, near the internal surface of the tube, an increase of resistance of the tube, said resistance changing, probably by reshaping, from 55 kilograms per square millimeter to kilograms/mm? The machine which has just been described, and which makes use of the process according to the present invention, is used for surfacing and calibration of tubes obtained by cold drawing in the conventional manner. However, a second mode of application of the process according to the invention makes it possible to apply said process to the fabrication of cold drawn tubes, said mode of application being represented in FIG. 15, whereas a conventional drawing bench is represented in FIG. 14. Such a drawing bench has a drawplate 30 perpendicularly to which there is located a cylindrical bullet 31. The metal is drawn on a pincer 32 and the internal calibrating of the tube is done approximately to the external diameter of bullet 31.
To use the process according to the present invention in the drawing of tubes under cold conditions, it is sufficient to associate the cylindrical bullet with a mandrel 33 in the shape of a ring, the edge of which is constituted by the external surface of a torus having a circular section. Mandrel 33 connected to bullet 31 is placed behind said bullet, with respect to the drawing direction of pincers 32, and the direction of forward motion of the manufactured tube. When it is desired to manufacture tubes internally calibrated at 50 millimeters the radius of the edge circumference of mandrel 33 is 4 millimeters, and the maximum diameter of said mandrel is 50.] millimeters. In that case, the external diameter of the bullet is 49.8 millimeters. The condition of the surface of the tube thus obtained is truly remarkable, and the calibration is obtained with a precision of a few hundredths of millimeters.
It is well understood that the modes of operation described above are in no way limitative, and that they may be subjected to all desirable modifications without departing from the scope of the present invention.
The invention is hereby claimed as follows:
1. A process of surfacing the interior and/or exterior of a tube and of calibrating the interior or exterior of said tube comprising the alternate steps of: (a) forcing said tube axially through a die adapted to contact the exterior surface of said tube to reduce its diameter, and (b) forcing a tool through the interior of said tube to increase its diameter.
2. A process as claimed in claim 1 wherein said tube contains contaminants on the interior surface thereof which are loosened by step (a) and removed by step (b). i
3. Aprocess as claimed in claim 1 wherein the working surface of the die and tool are harder than the metal of the tube to be worked on and are defined by the displacement of a meridian curve resting on a closed directrix formed in a shape approximately identical with the border or rim corresponding to the surface to be worked on of the right section of thetube, the profile along a meridian curvegenerating said working surface being such that when passing from a first end plane, which corresponds to the coming-into-contact point of said working surface with the tube, to a second end plane, which corresponds to a plane marking the end of the contact of said working surface with the tube, it is made to vary in a continuous manner over the distance to the axis of the tube, increasing when the internal surface of the tube is worked on, and decreasing when the external surface is worked on, the maximum variation of said distancebeing greater than or equal to the maximum depth of the defects which the tube presents on the surface to be worked on, and smaller than the value required to insure the displacement of the tool along the axis of the tube by a force applied on the tube which exceeds the mechanical resistance of said tube.
4. A process as claimed in claim 3, used for tubes having a circular section, wherein said working surface is limited for part of its external surface at least by a surface of revolution such that the angle which is formed, with the axis of the tube by a straight line which joins the point of coming-in-contact of the working surface with the tubeito the corresponding point at the end of the contact of the working surface with the tube, approximately ranges between 12 and 20.
5. A process as claimed in claim 4 wherein the angle formed with said axis, by a plane tangent to said working surface at the initial point at which said working surface comes into contact with the tube, is greater than or equal to the angle formed with the axis by the plane which is tangent to the profile of said working surface at the point where said working surface contacts said tube in the course of work.
6. A process as claimed in claim 3 wherein said working surface is a toric surface having a circular section.
7. A process as claimed in claim 6 wherein the radius of the section of the toric surface which constitutes the edge of said working surface ranges between 3 and 6 millimeters.
8. A process as claimed in claim 4 used for tubes having a suitable state of internal surface wherein said working surface has the shape of a truncated cone.
9. A process as claimed in claim 5 wherein said working surface is a toric surface the right section of which is either an ellipse or an ovalv 10. A process as claimed in claim 1 wherein step (a) and step (b) are carried out in opposite directions.
11. A calibrating and surfacing machine for tubes comprising:
a. a fixed frame having opposing end members,
b. means forming an opening in one of said end members,
c. means forming a die disposed adjacent said opening of (b) and having a working surface adapted to engage the outer surface of a tube delivered axially in contact with said working surface and through said opening of (b),
c. means associated with said other end member of (a) including a rod adapted to be moved axially through said opening of (b) and meansformoving said rod in opposite directions, said rod having a diameter smaller than the internal diameter of the tube to be worked and said tube being adapted to slide on said rod,
e. means associated with said rod of (d) for pushing said tube through said die of (c), and
f. retractable jaws mounted on the outerside of the end member of (b) and adapted to provide a support against which said tube can be pushed during the internal working of said tube by a tool fastened to the end of said rod after said tube carried on said rod has been worked externally and passed through said opening of (b) and while said rod is being pulled in the opposite direction.
12. Apparatus as claimed in claim 11 wherein said die of (c) is a drawplate fitted by cone-shaped adjustment in a drawplate support with respect to which it is movable.
13. Apparatus as claimed in claim 11 wherein said means of (e) comprises two movable half shells of a ring which can slide on said rod and be locked thereon.
14. Apparatus as claimed in claim 11 wherein said die is a drawplate having a working surface profile formed by an arc of a circle the radius of which ranges between 25 and 35 millimeters.
15. In an apparatus for the cold drawing of tubes having a drawplate at a right angle to the tube and a cylindrical bullet within the tube together with means for moving said tube axially through said drawplate around said bullet, the improvement which comprises forming said bullet with a tool fixed thereon in the direction of drawing, said tool having a workingsurface which is limited for part of its external surface at least by a surface of revolution such that the angle which is formed, with the axis of the tube by a straight line which joins the point of coming-in-contact of the working surface with the tube to the corresponding point at the end of the contact of said working surface with the tube, approximately ranges between 12 and 20.
16. A process of surfacing the interior of a tube and of calibrating the interior of said tube which comprises contacting the interior surface of the tube with a tool having a working surface which is limited for part of its external surface at least by a surface of revolution such that the angle which is formed, with the axis of the tube by a straight line which joins the point of coming-incontact of the working surface with the tube to the corresponding point at the end of the contact of said working surface with the tube, approximately ranges between 12 and 20.
17. A process as claimed in claim 16 in which said tool has a toric surface with a circular section having a radius range between 3 and 6 mm.
18. In a calibrating and surfacing machine for tubes having a fixed frame, means for holding a tube on said frame, an internal mandrel for said tube mounted from said frame for movement internally with respect to said.
the tube to the corresponding point at the end of the claimed in claim 18 wherein said tool has a toric surcontact of said working surface with the tube, approxiface with a circular section having a radius range bemately ranges between 12 and 20. tween 3 and 6 mm.
19. A calibrating and surfacing machine for tubes as UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT N0. 3,779 ,064
DATED December 18, 1973 INVENTOR(S) Louis Pierre Albert Besson It is certified that error appears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:
Column 5, line 4, "12", first occurrence, should read --10--.
Column 10, line 1, "c." should read --d.--.
Signed and sealed this 6th day of May 1975.
C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks