Method Of Starting A Casting Machine Having Caterpillar-type Molds For Casting Nonferrous Metal Strips

Abstract

Disclosed is a method of pouring molten metal on caterpillar-type molds of a still-standing and a low angle inclined machine, until a leading end of the strip is formed. Thereupon, the mold tracks are set into motion and simultaneously the inclination of the entire machine is increased for an optimum continuous casting operation. The casting machine is mounted on a tiltable frame controlled by a hydraulic jack.

Description

BACKGROUND OF THE INVENTION:

This invention relates generally to machines having caterpillar or crawler-type mold tracks for casting and forming strips of nonferrous metal, especially of aluminum or aluminum alloys. More particularly, this invention relates to a pair of endless caterpillar-type half-mold tracks which, from a site of casting, run in parallel one opposite the other for a certain interval, and the facing half-molds produce actual molds. At the end of the track interval, the half-molds depart one from the other and, after a short period of time, they meet again at the site of pouring.

Similar type of such machine has already been described, for example in the copending U.S. Pat. application Ser. No. 758,367 filed Sept. 9, 1968, now U.S. Pat. No. 3,570,586, dated Mar. 16, 1971; according to this patent, the circulating half-molds are coupled to guiding and driving parts through supporting and fastening elements having reduced total thermal conductivity. The resulting machine enables casting of considerably wide metal strips such as, for instance, of 20 mm thick aluminum strips being 1,500 mm and more in width.

For vertical, downward casting in machines of this kind, a special metal feeding device is employed in practice. This feeding device has been described in the prior art, for example in the U.S. Pat. No. 3,552,476, dated Jan. 5, 1971.

It is also possible to cast obliquely downwards or entirely horizontally. For this purpose, the machine is inclined downwards in the direction of casting at an angle between 45.degree. and 0.degree., preferably between 10.degree. and 1.degree. with respect to the horizontal. Such an oblique or horizontal position offers considerable advantages in comparison with the vertical casting position. The metal feeding is facilitated and no underpressure is required. The cast strips are discharged from the machine in a more convenient position and need not be bent excessively when still in a hot, brittle condition. The strip can be easily watched by the operator, and the operator has much better access thereto. Difficulties, however, may occur too, especially in the case of an only slightly inclined or a horizontal position of the machine.

In the horizontal position, either gas bubbles are formed in the metal pouring nozzle, which have no possibility to escape, or existing gas bubbles are entrapped. For the same metallostatic pressure, the stream of melt is not so strong in the casting nozzle as if the machine is considerably inclined downwards in the casting direction.

On starting, that is at the beginning of the casting process, an inclination that is as small as possible is advantageous since the metallostatic pressure at the site of inflow of the melt into the molds is less and thus there is smaller danger that the metal melt will flow around the orifice of the nozzle into the clearance between the nozzle and the half-molds, as soon as the leading end of the casting has been completely formed against the dummy bar.

After the machine has been set in motion (when the half-molds initiate their circulating movement), the danger mentioned almost ceases to exist and, therefore, it would be advantageous to incline the machine into a more effective position.

SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to provide a method of starting a machine of the above-mentioned kind without any penetration of metal between the casting nozzle and adjacent half-molds.

Another object of this invention is to provide a casting machine of the caterpillar-mold type which makes it possible to change a horizontal or an almost horizontal position to an effective inclined position without the interruption of the pouring or casting operation.

The above objects are attained by starting the casting process under a small angle of inclination of the machine, preferably between 0.degree. - 5.degree. from a horizontal line, until a leading head is built up on the dummy bar; setting the caterpillar mold tracks in motion and inclining the entire machine to an effective position from 4.degree. - 45.degree. for the optimum casting operation.

The machine for carrying out the above method is characterized in that it is mounted together with the casting nozzle, melt feed trough, driving machines, cooling units and strip advancing mechanism, on a tiltable supporting frame.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in conjunction with the accompanying drawing, wherein:

FIG. 1 is a schematic elevation view, partly in section, of an aluminum strip casting machine having caterpillar mold tracks arranged almost in a horizontal position;

FIG. 2 is a similar view as in FIG. 1, but the caterpillar mold tracks are inclined at an angle of 6.degree. with respect to a horizontal line; and

FIG. 3 is a schematic elevation view of an embodiment of the machine of this invention.

DETAILED DESCRIPTION

In FIG. 1, the caterpillar mold tracks are inclined about 1.degree. from a horizontal line. For casting by descent, the metal inflow site is situated at the elevated end of the mold. The half-molds 10 circulating from opposite sides appear simultaneously at the orifice of the nozzle 11, the width of which corresponds approximately to the width of the strip to be cast. The nozzle 11 is connected to a melt feed trough 12 by a coupling flange 13. A flexible channel 14 communicates with the trough 12 to supply the aluminum melt. Before the start of the casting process, the outlet opening 16 of the trough 12 is closed by a plug 17 and the surface of the melt rises up to the level 15. A dummy bar 18 disposed in the composed half-molds 10 carries the poured-in melt during the standstill of the machine and the upper half-molds provide the forming space 19 wherein the metal strips are shaped. The distance between the outlet opening 16 and the orifice of the nozzle 11 amounts, for example, to 680 mm.

The difference h1 between the level 15 in the trough 12 and the lower edge of the orifice of the nozzle 11 determines the metallostatic pressure at the beginning of casting. This is practically the lowest metallostatic pressure which can be achieved; the metal level 15 must be provided a little distance, about 10 mm for example, above the highest point of the outlet opening 16. Taking into consideration the thickness (20 mm) of the outlet end of the nozzle 11 and the distance of the orifice from the opening 16, the dimension h1 will be equal to 42 mm provided that the mold tracks form an inclination of 1.degree..

The metal level 15 in the trough 12 is kept preferably constant.

Upon the removal of the plug 17, the metal melt flows through the nozzle 11 into the forming space 19 as far as to the dummy bar 18. At first, a leading end 22 with a molten core 23 is formed. As soon as the forming space 19 is filled up, the metal melt has a tendency to penetrate into the clearance 20 between the nozzle 11 and the opposite half-molds 10 inasmuch as the latter are not yet in circulation. This clearance 20 may amount to 0, 25 mm, for instance. Due to the almost horizontal position of the facing molds, the metallostatic pressure of the melt can be kept so small that the surface constraint of aluminum and the oxide-film on the melt prevent the melt from penetrating around the nozzle even if the machine is at a standstill. As soon as the caterpillar molds are set into motion, the possibility of the penetration of the molten metal into the narrow clearance around the projecting nozzle no longer makes any difficulties.

On the contrary, the penetration might happen at a stillstanding machine if the metallostatic pressure be considerably increased, for example if the inclination of the caterpillar mold be 6.degree. instead of 1.degree.. In other words, it is very difficult to start the casting operation with caterpillar molds inclined about 6.degree. without the penetration of the molten metal into the clearance 20 between the nozzle 11 and the facing half-molds. Due to the fact that prior to the movement of the dummy bar at a velocity that is a function of the inclination of caterpillar mold tracks, the kinetic energy of the metal stream is added to the static pressure of the latter so that a danger of penetration of the melt between the nozzle and the half-molds becomes at a relatively large inclination still increased. The resulting high metallostatic pressure does not make any damage, however, if the half-mold tracks are set into motion.

FIG. 2 illustrates the casting machine at an inclination of 6.degree.. The cast metal strip 21 is discharged at the right-hand side of the moving half-mold tracks and no disturbing deceleration can occur in the forming space 19 between the opposite half-molds. By contrast to the angular position of the molds as shown in FIG. 1, the vertical difference between the metal level 15 in the casting trough 12 and the bottom edge of the discharging portion of the nozzle 11 has become considerably increased and amounts to h1 = 101 mm (instead of former 42 mm).

As it has been found, an increased inclination of the mold with respect to the horizontal offers an advantage in that enclosed gas bubbles may move up through the casting nozzle, in spite of the narrowness of the latter, into the feed trough 12 and, therefrom, the bubbles escape through the molten metal into the atmosphere. An additional advantage is in that due to the increased flow velocity within the nozzle 11, the cast is less susceptible to disturbance, for example by reason of significantly reduced danger of clogging of the nozzle.

Still another advantage of the increased inclination is to be seen in that the molten core within the leading end contributes itself to the increase of the metallostatic pressure. By contrast to the conditions resulting from the 1.degree. inclination, the so-called apex of the core (the deepest point of the molten core within the leading end) lies at a lower level than the lower edge of the nozzle. In addition to the vertical difference h1 between the metal level 15 and the lower edge of the nozzle orifice, which upon the transition from the 1.degree. inclination to the 6.degree. inclination is increased anyway, a vertical difference h2 between the lower edge of the nozzle orifice and the molten core in the leading end will result.

The increased metallostatic pressure due to h2 still improves the further requisites for a sound casting, more particularly by diminishing the danger of development of pores and shrink holes in the structure of the cast metal. The follow-up supply becomes also improved and depressed areas in the upper surface of the strip are avoided. Since the velocity of the melt flow is increased, the streaming conditions in the nozzle are more favorable.

In starting a machine which is inclined about 6.degree., however, the formation of a leading end and the initiation of the circulation of the caterpillar mold tracks must be synchronized with an utmost accuracy, which can scarcely be achieved in practice. Considering the fact that each penetration of the melt between the nozzle and the half-molds necessitates an instant interruption of the casting operation, the primary object of this invention is to find a method which would avoid the above drawback.

According to the invention, the caterpillar mold casting machine is, prior to the circulation of the caterpillar mold tracks, inclined downwardly to the horizontal at a small angle, between 0.degree. and 5.degree., the metal is poured into the mold until a leading end is formed therein and, whereupon the machine is set in motion and further casting is carried out with the mold at a downward inclination which is greater than on starting and which is 4.degree. or more.

The angle of inclination at the start may be, for instance, between 0.degree. and 2.degree. from the horizontal, and on further casting it may be between 4.degree. and 6.degree.. It is also possible to start at an inclination of 3.degree. and 4.degree. and continue the casting at approximately 6.degree. to 10.degree.. In selection of the inclination, the metallostatic (hydrostatic) pressure and the clearance between the nozzle surface and the mold surface are to be taken into consideration above all.

Upon the starting of the machine, there are set into motion not only the caterpillar tracks and thus the half-molds, but also the dummy bar is pulled out from the forming space according to the casting speed. A casting machine which enables the performing of the above-described method is characterized in that the caterpillar mold tracks together with the casting nozzle, feed trough, driving mechanism, cooling system and advancing apparatus, are mounted on a supporting frame which is tiltable in the direction of casting.

An exemplary embodiment of the machine of this invention is illustrated in FIG. 3. The two opposed caterpillar mold tracks with half-molds 10, the casting nozzle 11, the flange 13, the trough 12, the melt feeding channel 14, the cooling system 24 (such as described, for example, in the copending U.S. Pat. application Ser. No. 758,492 filed Sept. 9, 1968, now U.S. Pat. No. 3,570,583, dated Mar. 16, 1971), as well as driving mechanism 25, are mounted on a common tiltable frame 26. The frame 26 is supported at the feeding end of the machine -- where the feed trough 12 is located -- on a horizontal thrust bearing 27.

The opposite end of the frame 26 is supported through a hinge 28 on a hoisting device 29, preferably a hydraulic jack, by means of which the vertical position of the latter end can be adjusted. As indicated by arrow, the machine can be thus tilted about an angle of 11.degree.. The tiltable frame 26 can be angularly displaced about 11.degree. from a horizontal position downwardly in the direction of casting. At the start, the casting process can be initiated at an inclination of 1.degree., for example, and upon the actuation of the caterpillar tracks, the frame 26 is inclined to 10.degree. to continue the casting process.

The feature that the machine can be tilted about an axis which takes place beneath the storing trough 12, greatly facilitates the casting operation. For example, should the hydraulic jack 29 be placed near to the feed trough 12 and the bearing 27 near to the advancing mechanism 25, the feeding of the molten metal would be considerably more difficult because of the increased height difference.

It is also very important that the advancing mechanism 25 be also arranged on the common tiltable frame 26, since the discharged aluminum or aluminum alloy strips are still in the temperature range of hot brittleness.

The tiltable frame 26 enables the transition from a horizontal or an almost horizontal position to a considerably inclined position without the interruption of the casting process. The design possibilities are not, of course, limited to the shown maximum angle of inclination (10.degree. or 11.degree.) but it is possible to design frames which can be tilted up to 45.degree..

It is to be understood that this invention includes all modifications and equivalents which fall within the scope of the claims, as set forth below.

Claims

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows:

1. A method of starting a casting machine having an endless series of caterpillar-type molds, especially for casting strips of nonferrous metal such as aluminum or aluminum alloy, comprising steps of pouring said metal into stillstanding molds at a relatively low angle of inclination of the machine, ranging between 0.degree. to 5.degree. with respect to the horizontal, until a leading end of the strip is formed, setting said caterpillar molds into motion and simultaneously increasing the inclination of the machine for further casting.

2. A method, as claimed in claim 1, said relatively low angle of inclination being between 0.degree. and 4.degree., and the angle of increased inclination being above 4.degree., from the horizontal.

3. A method, as claimed in claim 1, said relatively low angle of inclination ranging between 0.degree. and 2.degree., and the increased angle of inclination being between 4.degree. and 6.degree..

4. A method, as claimed in claim 1, said relatively low angle of inclination ranging between 3.degree. and 4.degree., and the increased angle of inclination being between 6.degree. and 10.degree..