US3771587A

US3771587A - Continuous centrifugal casting apparatus for hollow shapes

Info

Publication number: US3771587A
Application number: US00185691A
Authority: US
Inventors: M Poran
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 1971-03-02
Filing date: 1971-10-01
Publication date: 1973-11-13
Anticipated expiration: 1990-11-13
Also published as: GB1373404A

Abstract

An apparatus for the continuous centrifugal casting of a cylindrical article including a mold rotatable about a generally horizontal axis; means for feeding molten metal into the mold; means for rotating the mold to centrifugally form a cylindrical article therein; a mold housing surrounding the mold over substantially its entire length; means for supplying cooling liquid to the mold housing so that said molten metal is progressively solidified along the entire length of the mold; means to oscillate the mold and the mold housing along the axis of rotation of the mold; secondary cooling means located downstream of the mold and adapted to complete the solidification of the molten metal; means to withdraw the solidified metal from the mold in the form of a cylindrical article; and means positioned downstream of the secondary cooling means and in axial alignment with the mold for supporting the cylindrical article after it passes from the mold and for rotating the cylindrical article at the same speed as the mold is rotated.

Description

United States Patent 91 Poran CONTINUOUS CENTRIFUGAL CASTING APPARATUS FOR HOLLOW SHAPES [75] Inventor: Michael Poran, New York, N .Y.

[73] Assignee: Officine Meccaniche Danieli, Udine,

Italy [22] Filed: Oct. 1, 1971 [21] Appl. No.: 185,691

[30] Foreign Application Priority Data Nov. 13, 1973 Primary ExaminerJ. Spencer Overholser Assistant Examiner-John E. Roethel AttorneyFleit et a1.

[57] ABSTRACT An apparatus for the continuous centrifugal casting 7 of a cylindrical I article including a mold rotatable about a generally horizontal axis; means for feeding molten metal into the mold; means for rotating the mold to centrifugally form a cylindrical article therein; a mold housing surrounding the mold over substantially its entire length; means for supplying cooling liquid to the mold housing so that said molten metal. is progressively solidified along the entire length of the mold; means to oscillate the mold and the mold housing along the axis of rotation of the mold; secondary cooling means located downtrcam he 11914, ndfidamw t0 Pomplete th solidification of the molten metal; means to withdraw the solidified metal from the mold in the form of a cylindrical article; and means positioned downstream of the secondary cooling means and in axial alignment with the mold for supporting the cylindrical article after it passes from the mold and for rotating the cylindrical article at the same speed as the mold is rotated.

16 Claims, 4 Drawing Figures Patented Nov. 13, 1973 3,771,587

I? Shuots-Shovt 1 Patented Nov. 13, 1973 23 Sheets-Sheet CONTINUOUS CENTRIFUGAL CASTING APPARATUS FOR HOLLOW SHAPES The present invention relates to the art of centrifugal casting of hollow products and to continuous casting as employed in the basic ferrous industry.

Without intending in anyway to limit the invention and only for the purpose of description, the use of the invention in connection with the continuous casting of hollow products such as tubes or pipes will be discussed.

While there are various forms of centrifugal casting machines being presently utilized in the ferrous industry we shall refer to the type, where the mold rotates around its longitudinal axis and which delivers as a final product a hollow shape such as a pipe. Furthermore, we shall refer to continuous casting methods being presently utilized.

The centrifugal casting machines utilized presently for casting hollow shapes employ a rotating around its axis mold cooled or uncooled on the outside, the effective length of which determines the final size of the cast product.

Thus the length of the centrifugally cast hollow shapes is dependant on the length of the rotating mold, which poses certain limitations due to technical difficulties in the rotating mold design and proper distribution of the molten metal.

Furthermore, for large scale production, a large amount of molds has to be used one after another or simultaneously, since the mold can be reused only after the cast shape has been fully solidified and removed from the mold.

The wall thickness of the hollow product cast in a rotating mold is being presently controlled by the amount of liquid metal poured into the rotating mold of a certain inside diameter at the beginning of the cast.

It is known, that the metallurgical quality of centrifugally cast products is in certain ways superior to that of normal castings and also superior to the products cast on continuous casting machines.

Presently, continuous casting machines deliver round or polygonic products for further manufacturing of tubes and pipes.

Continuous casting methods which employ a water cooled oscillating vertical straight or curved mold which is shorter that the final product, and where only a part of the solidification process takes place, the rest being accomplished in the subsequent cooling device by means of water sprays directed toward the surface of the emerging from the mold strand is a well proven an economic method of casting full crossection shapes.

Certain inventions which try to employ this method of continuous casting for casting hollow products are as yet unsuccessful, and the metallurgical and technological quality of the product is expected to be far lower than that achieved in centrifugal casting.

One of the main drawbacks of the present continuous casting machines as employed widely in the ferrous industry is the eccessive height they require and considerable floor space and length, not to mention the fact that the product undergoing a transition from the vertical into horizontal withdrawal is being stressed in bend- The present invention is addressed to a novel casting method and machine for casting hollow shapes, which combines and incorporates the benefits of the centrifugal casting and continuous casting methods, and which overcomes each and every one of the aforesaid difficulties.

Among the features of the present invention is the providing of an arrangement whereby the cast product is continuously formed and withdrawn from a short water cooled, revolving around its axis and oscillating along the axis of rotation mold, before the complete solidification process has been completed and subsequent cooling takes place outside the mold in immediate vicinity as the product passes a secondary cooling device.

The necessary mold tube length in order to accomplish this objective is so chosen as to allow the formation of a certain solidified wall thickness of the cast product which for the given casting diameter and withdrawal speed would allow safe continuous withdrawal without damage of the product.

Passing the synchroneously with the mold rotating dual-motion withdrawal unit, the rotating and moving along its axis product is being cut to any desired length units and transported to a position or storage arrangement, where it cools off to room temperature.

Another feature of the above said arrangement is the provision for varying the wall thickness of the cast hollow product without interupting the casting process by means of changing the metal fiow at constant withdrawal rate or varying the withdrawal rate at constant metal flow or both.

In one arrangement the axis of rotation of the mold and the cast product as well as the direction of withdrawal are in horizontal plane, whereby parallel to each other, fed from a common tundish several complete casting units are located so, that simultaneous multistrand continuous centrifugal casting of the same or different product sizes can take place.

In another preferred arrangement, the axis of rotation and direction of withdrawal are at an angle up or downwards direct from the horizontal.

It is still a further object of the invention to provide a new rotating mold system, secondary cooling and support device, dual motion withdrawal device and dummy bar device.

These features, as well as others will be better understood, when the accompanying specification is read in light of the attached drawing of which:

FIG. 1 is an elevational section-view of a continuous centrifugal casting plant incorporating the features of the present invention;

FIG. 1a is a section through the rotating mold shown as one of the possible solutions mentioned in the longitudinal section-view dual-motion withdrawalunit as one of the possible solutions discussed in the description in detail.

In first referring to FIG. 1, which as indicated above is an elevational section-view of the casting plant, liquid metal flowing from a ladle 1 through a ladle valve 2 or otherwise through a ladle nozzle opened and closed by a conventional stopper-rod not shown on the drawing, fills a tundish 3 to a certain level which is maintained till the ladle is empty.

Depending on the number of required strands on the bottom of the tundish inclined toward the horizontal and protruding into the mold space, one or more parallel to-each other metal delivery nozzles 5 are provided.

The rate of metal flow through the nozzle is being regulated by the tundish valve 4 which is similar in design to the ladle valve 2, being one of the types used in the ferrous industry.

Further, not specified but shown on the drawing are normally present in continuous casting plants support structure of the tundish, tundish overflow spout and launder. The liquid metal flows from the nozzle 5 into the rotating mold tube 8 which is made of good heat conducting metal such as copper, and which in the front extremity is fastened to and supported by the gate flange 6 and in the posterior part housed with sliding freedom to allow for heat expansion of the mold tube in the driving flange 11.

Both the front gate flange 6 and driving flange 11 are fastened to and fitted into a rotating mold jacket 9, which in the illustrated case is a tubular, perforated in the water cooling region member, supported on the extremities by several

radial rollers

12 and 13 and in the frontal portion axially restricted by axial thrust rollers 14 and 15 all of which are adjustably fastened on the mold housing 10.

The rotating mold jacket 9 is designed with the inside diameter layed out for the largest mold tube diameter to be employed, so that different mold tube sizes can be fitted into it.

It is however pointed out at this stage, that the usage of the rotating mold jacket is not a necessity for the functionning of the mold system, but merely a technical convenient measure.

It is also envisioned a design where the mold tube 8 via the front gate flange 6 and driving flange 11 is directly supported by the

rollers

12, 13, 14 & 15, or in large diameter bearings not shown on the drawing.

The frontal part of the mold tube 8 and the front gate flange 6 are equipped with a mortarred in place tapered refractory nozzle 7, the function of which is to protect the uncooled part of the front gate flange 6 and front portion of the mold tube 8 from impinging metal stream provide a spill-out barrier for the liquid metal and helping in proper metal distribution as well as providing liquid metal reservoir for progressive, gradual solidification of metal along the wall of the rotating 7 mold tube 8.

The mold housing 10 is a water reservoir equipped on the bottom posterior portion with a cooling water inlet manifold 16 and on the top frontal with a water outlet manifold 17.

The mold housing 10 is resting by means of wheels 18 on a track 19, however a sliding guide support system is also envisioned for more accurate guidance.

The entire mold system is oscillated with a sinusoidal motion by an oscillating device along the axis of rotation, here shown by a gearmotor 22 with a shaft mounted excenter 21 via a connecting rod pivoting on the mold housing 10.

The rotation of the'mold jacket 9 and via front gate flange 6 the mold tube 8, is provided by the driving flange 11, which in this design is shown to be at the same time a chain sprocket driven by a chain 23 from a sprocket 24 fitted by means of hearings on the mold housing 10 and sliding on a spline shaft 25 of the fixedly positioned driving gear 26.

Not shown on the drawing but envisioned is a mold tube lubrication system consisting of either an organic oil lubrication supplied from a pump and distributed evenly around the inside frontal portion of the mold tube wall, or a so called slag lubrication system consisting of a powdery material continuously distributed in the frontal inside portion of the mold-tube 8.

The function of the mold tube lubrication system is to reduce the drag-friction between the inside wall of the mold tube 8 and the continuously withdrawn product, and proved to be in continuous casting practice a satisfactory measure to reduce the surface defect of the strand.

The mold tube 8 itself can be made with equal inside diameter throughout the entire length or slightly tapering-off from a larger diameter at the end, in order to make up for product contraction due to the cooling effect, and so preventing the air-gap formation between the mold wall and the product surface which causes reduced effectiveness of the heat transfer.

It will be noted that in FIG. la which represents a section through the middle of the mold assembly, the mold housing 10 is represented to be divided along the horizontal axis to facilitate manufacturing and assembly, and that along the division line two partitions imparing the water flow on both side of the rotating mold jacket 9 are present.

These partitions have an effect of forcing the delivered through the inlet manifold 16 water through the orifices in the mold jacket 9 into the space between the mold tube 8 and mold jacket 9, and further on into the upper space of the mold housing 10, and toward the water outlet manifold 17.

Not shown on the drawing but envisioned if necessary, the orifices in the mold jacket 9 can be formed and profiled in such a manner as to ensure pumping-in action in the posterior part of the mold thus drawing water into the space between the mold jacket 9 and mold tube 8, and pumping-out action in the frontal part of the mold, thus expelling the water from the space between said mold tube and jacket into the discharge space of the mold housing 10. In this case however the partition in the mold housing will be horizontal, but vertical thus dividing the mold housing 10 into posterior water inlet chamber and frontal water outlet chamber.

Other improvements of the water circulating system such as stirring fins or impeller blades mounted inside the rotating mold jacket 9 or outside the mold tube 8 or a screw-like forming of theinside wall of the mold jacket 9 or outside wall of the mold tube 8 are also envisioned but not shown on the drawing for clarity reasons.

The operators control stand not shown on the drawing, is in the vicinity of the tundish 3, thus allowing the operator to control the rate of metal flow, withdrawal speed and rotational speed either by direct observation of the mold cavity through the front aperture, or through optic devices such as a periscope, flexible optic-fiber viewing equipment or closed circuit television system, or through reading the monitored wall thickness data of the cast product as recorded by various X- ray, isotope or other measuring devices.

Of course a complete automatic control system can be easily employed based on the readings of the above mentioned measuring devices.

Behind the mold in the nearest vicinity of the later, the secondary cooling and support device is located.

Shown of FIG. 1 in elevated section and in FIG. lb in transversal section are in the upper portion three spray headers 41 which accomodate a required amount of water spray nozzles 42 which thanks to the rotation of the product, spray its entire surface, thus finishing the solidification process and cooling the product to a desired temperature.

However the number of spray headers can be varied starting with one only and if required provided all around the product with variable water flow rates along its extension.

The lower portion of the secondary cooling device consists of a support structure 39 which houses rotating freely support elements, here pictured as balls 40 in spherical bearing pads, distributed along the lower portion of the product circumference and allowing for bidirectional motion of the product.

However it is pointed out here, that simple rolls allowing for free rotation and axial sliding motion could be used instead, since the withdrawal velocity is much lower than the rotational and the product still can be withdrawn without surface defects.

It is also envisioned that it may prove completely unnecessary to employ a support system of any kind with proper design of the withdrawal unit and its close location from the mold.

The entire secondary cooling device is enclosed in a spray chamber not shown on the drawing and a Vajnox exhauster for steam evacuation as well as a water drawing system are provided.

Behind the secondary cooling device FIG. 1 shows the dual-motion withdrawal unit consisting of a housing 56in which supported by bearings 57 a tubular roll carrier 31 is rotating, driven synchronously with the mold rotational speed by a common mechanically connected drive system from motor 27, through sprocket 28, chain 29 and mounted on the roll carrier 31 sprocket The ratio of the gearbox 26 is so chosen as to achieve exactly the same rotational speed of the mold and withdrawal unit.

Fastened to the roll carrier 31 and rotating with it is a roll holder yoke 32 better depicted on FIG. 1c which shows a frontal view of the withdrawal unit.

Sliding radially in the roll holder yoke 32 are individual roll holders 38 in which four contoured rolls 33 are located. Each roll is driven by a shaft mounted gearmotor 36 and the pressure between the rolls 33 and the cast product or dummy bar is provided by here shown springs 35 with pressure adjusting device 37. Not shown on the drawing but envisioned is an electromagnetic or electromechanical spring pressure release systern.

The gearmotors 36 equipped with DC motors provide infinitely variable withdrawal speed of the rolls 33 and receive the current from slide ring collectors 34 mounted on the rotating roll carrier 31 and shown on FIG. 1.

On the backside of the withdrawal unit shown on FIG. 1 a ball cradle 43 is located similar in design to the one of the secondary cooling and support device, and the function of which is to support the cast product.

It is wished to emphasize at this point that. the shown design solution is in no way the only envisioned, and that a gear drive system connecting the rolls 33 and driven by a single gearmotor or motor, could also be employed. Also the pressure condition between the rolls 33 and the cast product can be achieved by means of a motorized screw down system or electromagnetic linear actuators.

The depicted solution was chosen merely as simple way of achieving the objective.

Behind the withdrawal unit, FIG. 1 shows an elevational view of a torch cutoff system consisting of a carriage 45 which by means of wheels 47 moves synchronously with the withdrawal speed of the cast product on a track 49 actuated by a mechanical actuator or here depicted hydraulic cylinder 48. The oxygen torch 46 effecting the cut-off of the rotating cast product is provided with vertical and horizontal transversely to the axis of rotation motion system. A support cradle 44 designed similarly to cradle 43 is mounted on the carriage 45 to support the cut-off portion of casting product.

For transport of the dummy bar 51 and the cut-off cast product pieces a pinch-roll system such as used in pipe straightening devices is employed and shown in elevational section-view on FIG. 1.

It consists of a stander 52 in which supported by a swivel mounted bearing support 58 hyperboloid shaped, slanted in horizontal plane rolls 53 are mounted, driven electromechanically through universal joint spindles not shown on the drawing.

Behind the pinch-roll unit a roller table 54 consisting of a number of driven and undriven slanted hyperboloid shaped rolls 55 is provided for the transport of the dummy bar and the cut-off pieces of the cast product to the storage area.

At this point it is wished to emphasize that a similar but modified pinch-roll unit can be used as. a withdrawal unit.

For the beginning of the casting process a straight, rigid tubular dummy bar 51 is used the head 50 of which has the diameter equal to that of the cast product, is removably connected with the body 51 by means of screw or connecting pin and the-front end of which has a coarse threading to facilitate the fusion with the cast material.

The length of the dummy bar is chosen so, that when The dummy-bar head 50 is then sealed tight by means of an asbestos cord toward the inside wall of the mold tube 8 and some scrap metal is packed in the space between the coarsethreaded front end of the dummy-bar head and the mold in a manner done in conventional continuous casting machines.

The ladle l is brought into position over the tundish 3 and the later is filled to the desired level. The mold,

and the dummy-bar through the withdrawal unit are brought to the required rotational speed, mold lubrication system started, and the tundish valve 4 isopened releasing molten metal into the mold cavity.

Due to centrifugal force action, the liquid metal is spread evenly along and around the inside walls of the mold tube 8, melts the scrap between the dummy bar head 50 and the mold tube 8, solidifying quickly on the large cold mass of the dummy bar head and fastening itself securely to the latter.

The water cooled walls of the mold tube 8 cause the adjoining metal to solidify starting from the outside diameter of the casting toward the inside of the latter.

The oscillating motion of the mold begins and the withdrawal rolls 33 while rotating around the axis of rotation of the mold, dummy-bar and the casting start turning slowly beginning the withdrawal process gradually being brought to the required withdrawal speed.

In its progression along the mold tube axis the cast metal gradually builds up the thickness of the solidifying skin in contact with the cooled mold tube walls, so that at the mold end the casting has acquired such a solidified wall thickness that a safe withdrawal without the tearing of the product is possible, while on the inside the material is still liquid or partly solified.

The molten metal flowing from the tundish nozzle replenishes continuously the withdrawn material with the rate matching the withdrawal rate.

The pattern of solidification process is shown on FIG. 1 depicting a steady increase of the solidified wall thickness portion of the casting progressing along the mold in the withdrawal direction and steady decreasing complementary portion of liquid in a manner of two inverted hollow cones the sum of which constitutes a tube.

Passing the secondary cooling device located behind the mold, the casting gradually solidifies completely and is cooled to a certain required temperature by impinging water sprays from nozzles 42.

When the dummy-bar head 50 passes the withdrawal unit and comes in the range of the torch cut-off equipment while the casting is in grip of the withdrawal rolls 33, with the tail of the dummy-bar 51 in pinch-rolls 53, the torch 46 effects the first cut moving synchronously with the withdrawal speed separating the dummy-bar from the casting.

The dummy-bar 51 with head 50 and adjoining part of the cut-off casting are transported away with increased speed to the storage area by pinch rolls 53 and roller table rolls 55.

The torch returns then to the starting position shown on FIG. 1 and in the same manner effects the next cut of the cast product to a desired length.

The cut-off pieces of the cast product are transported in the same manner as the dummy-bar toward the storage and cool-off area.

When the ladle 1 and then the tundish 3 are empty, the casting process is finished by stopping the withdrawal and then gradually withdrawing the rest of the product from the mold after it solidifies completely, to prevent thinning out of the cast product walls.

The next casting operation can begin as soon as the last portion of the cast product is transported away and the start up procedures described above are completed.

What we claim is:

1. An apparatus for the centrifugal casting of a cylindrical article comprising a mold rotatable about a generally horizontal axis, said mold having a feed end into which molten metal can be continuously fed and a withdrawal end for withdrawing solidified metal in the form of a cylindrical article, means for feeding molten metal into said mold, means to rotate said mold to centrifugally form a cylindrical article therein, a mold housing surrounding said mold over substantially its entire length, means for supplying cooling liquid to said mold housing so that said molten, metal is progressively solidified along the entire length of said mold, means'to oscillate said mold and said mold housing along the axis of rotation of said mold, secondary cooling means located downstream of said mold and adapted to complete the solidification of said molten metal, means to withdraw the solidified metal from said mold in the form of a cylindrical article, means positioned downstream of said secondary cooling means and in axial alignment with said mold for supporting the cylindrical article after it passes from said mold and for rotating said cylindrical article at the same speed as said mold is rotated.

2. The apparatus of claim 1 in which said mold housing includes a mold jacket inside said mold housing and surrounding said mold and rotatable therewith and having a plurality of cooling liquid transfer openings therein.

3. The apparatus of claim 2 in which said means for supplying cooling liquid to said mold housing comprises a cooling liquid inlet near the bottom of said mold housing and a cooling liquid outlet near the top of said mold housing.

4. The apparatus of claim 2 in which said mold housing further comprises partition means substantially dividing the upper and lower portions of said mold housing between the outer wall of said mold jacket and the inner wall of said mold housing such that cooling liquid is forced to pass between said mold jacket and said mold in flowing from said cooling liquid inlet to said cooling liquid outlet.

5. The apparatus of claim 1 in which said mold contains a refractory nozzle at the feed end thereof to protect the front portion of said mold from impinging molten metal.

6. The apparatus of claim 1 in which support means are provided adjacent said secondary cooling means to support the formed article as it is solidified.

7, The apparatus of claim 1 in which said means for withdrawing the solidified metal from said mold includes means for withdrawing said article at a variable speed.

8. The apparatus of claim 7 in which said means for withdrawing the solidified metal from said mold at a variable speed comprises rolls each driven at substantially the same speed.

9. The apparatus of claim 8 in which said rolls are spring biased against said cylindrical article.

10. The apparatus of claim 8 and further comprising means for rotating said withdrawal rolls in the same direction and at the same rotational speed as said mold is rotated.

11. The apparatus of claim 1 in which said means for supporting and rotating said cylindrical article comprises a cylindrical member.

12. The apparatus of claim 1 and further comprising means downstream of said solidified metal withdrawal means for cutting off said cylindrical article to any desired length.

13. The apparatus of claim 12 and further comprising means for moving said cutoff means at the same axial speed as said cylindrical article.

14. The apparatus of claim 12 and further comprising means downstream of said cutoff means for transporting said cutoff cylindrical article away from said mold.

15. The apparatus of claim 14 in which said trans porting means comprises a pinch roll system.

16. The apparatus of claim 14 in which said transporting means transports said cutoff cylindrical article away from said mold at a speed greater than the speed at which said cylindrical article is withdrawn from said

Claims

1. An apparatus for the centrifugal casting of a cylindrical article comprising a mold rotatable about a generally horizontal axis, said mold having a feed end into which molten metal can be continuously fed and a withdrawal end for withdrawing solidified metal in the form of a cylindrical article, means for feeding molten metal into said mold, means to rotate said mold to centrifugally form a cylindrical article therein, a mold housing surrounding said mold over substantially its entire length, means for supplying cooling liquid to said mold housing so that said molten metal is progressively solidified along the entire length of said mold, means to oscillate said mold and said mold housing along the axis of rotation of said mold, secondary cooling means located downstream of said mold and adapted to complete the solidification of said molten metal, means to withdraw the solidified metal from said mold in the form of a cylindrical article, means positioned downstream of said secondary cooling means and in axial alignment with said mold for supporting the cylindrical article after it passes from said mold and for rotating said cylindrical article at the same speed as said mold is rotated.

6. The apparatus of claim 1 in which support means are provided adjacent said secondary cooling means to support said molten metal as it is completely solidified.

7. The apparatus of claim 1 in which said means for withdrawing the solidified metal from said mold includes means for withdrawing said article at a variable speed.

15. The apparatus of claim 14 in which said transporting means comprises a pinch roll system.

16. The apparatus of claim 14 in which said transporting means transports said cutoff cylindrical article away from said mold at a Speed greater than the speed at which said cylindrical article is withdrawn from said mold.