Caterpillar-type Mold With Nozzle Having Self-lubricating Insert Means

Abstract

A nozzle for the delivery of the molten metal to a mold with continuously moving walls in a strip casting process for metals, especially non-ferrous metals such as aluminum and aluminum alloys, the nozzle including a mouthpiece having inserts provided on its outer edge portions over the entire extent thereof, the inserts protruding above a general surface of the mouthpiece to an extent preventing a direct contact of the nozzle surface with portions of the mold and entry of the molten metal between the nozzle and the mold, the inserts being made of a self-lubricating material.

Description

CROSS-REFERENCE TO OTHER PATENTS

Reference should be had to U.S. Pat. No. 2,640,235 relating to a machine provided with a mold substantially constituted by a pair of moving continuous metal bands and to U.S. Pat. No. 3,570,586 relating to a machine with caterpillar mold for casting strips from non-ferrous metals, especially aluminum and aluminum alloys.

FIELD OF THE INVENTION

The present invention relates to a nozzle for the delivery of the molten metal to a mold with continuously moving walls in a strip casting process in which the nozzle has to withstand the temperature conditions of the casting and to provide a high quality strip casting having a relatively wide width and a relatively thin thickness.

BACKGROUND OF THE INVENTION

For the continuous casting of strips from aluminum, copper, zinc and other metals there have been machines developed with molds constituted substantially by a pair of moving continuous metal bands or belts made usually of steel.

For the same purpose there have also been machines developed with caterpillar-type molds in which the casting mold is formed by a double row of mold halves which are connected into a pair of endless circularly running chains. At the inlet end the mold halves which are positioned opposite to each other will lie against each other and move in such position over a certain path over which they form the caterpillar-like mold itself. Then they become separated in order that after a short while to meet at the inlet end again.

In the "Handbuch des Stranggiessens" by E. Herrmann, published in 1958 by the Aluminium-Verlag GmbH, Dusseldorf, West Germany, on pages 47-49 a casting process employing a pair of continuous metal bands and on pages 51-63 a casting process employing caterpillar-type molds are described.

Especially in machines having caterpillar-type molds and employed for the casting of relatively thin strips such as those having a thickness of about 20 mm or less, the delivery nozzle for the metal is the most critical part. This is due mainly to the fact that there are very few materials available which are capable of withstanding the high temperatures of the metal flowing through them and, in cases where the casting material is aluminum or an alloy of aluminum, then the delivery nozzle must be capable of withstanding the erosion or the dissolution in the metal itslef. Among the very few materials which can meet these requirements, graphite is one. Graphite, however, has the disadvantage of possessing a very high heat conductivity and by it the heat becomes conducted so quickly away from the molten metal that the metal wil have the tendency to solidify in the nozzle itself.

Among the caterpillar-type casting machines which have become known during the last few years only one has been found as being accepted by the industry (see the abovementioned "Handbuch," pages 536/537 and 540/541), and that for the casting of strips of aluminum and aluminum alloys.

For the above mentioned machines a delivery nozzle has been constructed which is described in U.S. Pat. No. 2,752,649 and also in the above mentioned "Handbuch," pages 60 and 61. The portions of the nozzle which are in contact with the flowing liquid metal comprise a fire resistant material such as a mixture of about 30 percent diatomaceous earth (practically a pure silica in the form of microscopic cells), 30 percent long asbestos fibers, 20 percent sodium silicate (dry weight) and 20 percent lime (for the formation of calcium silicate). This material is commercially available under the trademark "Marinite." The nozzle according to U.S. Pat. No. 2,752,649 is intended to be used for the casting of relatively thick aluminum strips having a rectangular cross section. The mouthpiece has a middle front section which is perpendicular to the axis of the mold inner space as well as a pair of sides placed at an angle with respect to each other.

The main passage in this nozzle for the molten metal branches off in the mouthpiece in such a manner that in operation each metal stream becomes directed obliquely with respect to the smaller side of the mold inner space and one stream will go straightforwardly. The metal becomes solidified, as a result, beginning from the small sides and going toward the middle while the middle stream fills all shrink holes which are formed during the solidification of the metal.

This known nozzle cannot be used for the casting of relatively thin plates and wide strip widths, such as about 700 to 1,500 mm or more having a thickness of about 20 mm, also the shape of its mouthpiece does not meet the requiremenns. In general, the difficulties of the metal delivery increase with the width of the mold inner space and with the reduction of the width of the smaller sides thereof.

Past experiments of the present applicant have shown that if a clearance of about 0.1 to 0.2 mm around the entire nozzle circumference is not present, that is, when the front rim of the mouthpiece comes in direct contact with one or both halves of the mold, the front portion of the nozzle becomes too cold and the danger may be present that the metal becomes solidified in the nozzle. Such contact can take place easily when the realtively thin and very wide nozzle warps. Therefore, the nozzle must be constructed with high precision or at least in such a manner that a direct contact with the mold halves (or, in the case of molds substantially constituted by a pair of continuous metal bands, with the metal bands) will not take place, which fact in actual practice hardly can be established.

BRIEF SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a nozzle for the delivery of the molten metal to a mold with continuously moving walls in a strip casting process for non-ferrous metals, expecially for aluminum and aluminum alloys, wherein the nozzle is capable of withstanding the high temperatures and erosion affects of the metal and, at the same time, is capable of producing a high quality strip casted material havin a relatively wide width and a relatively thin thickness.

The portion of the nozzle which comes into contact with the liquid casting metal according to the present invention comprises a heat resistant material having a negligible heat conductivity and high chemical resistivity to the metal which flows therethrough, such as Marinite in case of aluminum and aluminum alloys. On a certain path beginning from the connection to the metal delivery trough the nozzle is preferably surrounded with a metal housing consisting of a cast material having a relatively low heat expansion coefficient and which housing provides the nozzle also with a certain support.

According to the present invention the nozzle is characterized in that its mouthpiece exit end, in the region of its outer edges, outwardly and all around has an insert or inserts from a self-lubricating material provided therein which project from the surface of the mouthpiece outwardly to an extent that a direct contact of the nozzle surface with the mold walls and the entry of the casting material into the clearance between the nozzle mouthpiece and the mold walls is prevented, thereby, this insert serves also as a spacer. If the casting material is aluminum or aluminum alloy, preferably the inserts are made from a non-metallic material such as graphite or boronitride. The inserts can protrude in a uniform fashion or with interruptions.

According to the present invention the exit of the mouthpiece of the nozzle in contrast to the construction according to U.S. Pat. No. 2,752,649 is made preferably slot-like so that during the casting a flat and uninterrupted stream of metal will stream out of the nozzle and into the casting mold.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventon will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of example, in the accompanying drawings, in which:

FIG. 1 is a schematic representation of a metal delivery device suitable for a caterpillar mold, the said device having a delivery trough, a nozzle support and a nozzle in partial section;

FIG. 2 is a plan view of the nozzle;

FIG. 3 is a longitudinal section across the mouthpiece of the nozzle; and

FIG. 4 is a perspective view of the nozzle protruding into a mold interior.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

With reference to FIG. 1, it is seen that the metal delivery device 10 comrises a delivery trough 11 (or delivery container) lined with a fire resistant material and made from welded steel plates, a nozzle support 12 (the nozzle supporting means) and a nozzle 13 which in the region of its mouthpiece 14 is shown in a partially cutout fashion for illustrative purposes. The metal delivery device 10 is intended to be used with a strip casting machine having caterpillar-type molds according to U.S. Pat. No. 3,570,586 and mounted slightly obliquely with respect to the horizontal, but may be also used for a machine provided with a mold constituted by a pair of continuous metal bands according for instance to U.S. Pat. No. 2,640,235. The delivery device 10 is pivotably mounted to the body of the strip casting machine (not shown) by means of the axle 15. The casting material is delivered by means of a launder (not shown in the drawing) which is placed into the recess 16 and which fills the trough 11 up to a certain height controlled by means of a float (not shown in the drawing) and thereafter flows into the nozzle 13. The aperture 17 in the bottom of the trough 11 can be closed and serves for the emptying of the trough 11 during an interruption of the casting process or at the end of a casting operation. To the trough 11 the nozzle 13 is secured by means of a support 12. For the metal entry into the nozzle 13 the trough 11 at the point of connection is provided with a slot 18 which corresponds to the cross sectional area of the inner space of the portion of the nozzle connected thereto. In the illustrated embodiment the support 12 is made from a machined cast material having a low coefficient of expansion and is formed from two parts, namely from an upper portion 19 and a lower portion 20 which are then secured together by means of bolts. Each support portion 19 and 20 has a flange portion 21 and an intermediate plate 22. The portions 19 and 20 of the supporting device 12 are offset at 23 and have a wedge like extension 24 tapering in the direction of the nozzle mouthpiece 14. After being secured to the trough 11, the support 12 forms a rigid structure which projects forwardly over the inner hollow space of the mold so that it surrounds the nozzle 13 for about half of the extent of its length thereof and supports it in an immovable fashion in its position. The support 12 is exclusively supported in its position by means of the flange 21, there are no other additional supporting means present.

The nozzle 13 is formed from a pair of symmetrically bolted together Marinite plates 25 from which raised edges 26 having a height of about 4.2 mm and a width of about 16 mm over their main longitudinal extent, as well as wedges 27 and 28 are formed through which bolts are passed at the places indicated by the cross lines for securing them together. The front edge (at the exit end) on both ends has a wedge-like projection 29 formed thereon which has the purpose to keep the molten metal on its edges hot for somewhat longer so that it becomes solidified later. The back portion of nozzle 13 is supported by means of the intermediate plate 22 of the supporting device 12. The longitudinal edges 26 of the nozzle 13 are reduced by about 5 mm as indicated at 30. On the back edge of the nozzle 13 on each plate 25 a ledge 31 projecting upwardly out of the upper surface of the plate 25 is formed having a width of about 40 mm and a height of about 5 mm and being formed from the Marinite plates 25 themselves. These ledges 31 serve to secure the nozzle 13 to the supporting device 12.

Without considering the raised edges 26, the wedges 27 and 28 as well as the ledges 31, the plates 25 have a thickness of about 5 mm. The width of the illustrated nozzle 13 at its mouthpiece 14 is 500 mm and its overall length without the projection 29 is 520 mm. The nozzle 13 illustrated is capable of delivering a metal stream having a depth of 8.4 mm and a width of about 460 mm. According to the present invention the mouthpiece 14 of the nozzle 13 is on its all sides, that is, about its entire circumference provided with a glide insert means 32 functioning also as spacer. The glide insert 32 comprises in the illustrated embodiment graphite having a high density (such as a quality EK 412 of the Ringsdorff Werke GmbH). The glide inserts 32 have a width of about 15 mm and a thickness of about 2 mm and project above the surface of the mouthpiece 14 at its widest section for about 0.25 mm out. The insert means 32 can have a continuous length or stand out intermittently for about 12 mm in length then after a distance of about 50 mm another insert follows. On the small sides of the nozzle mouthpiece 14 the insert 32 stands out over its entire length. The distance between the insert 32 and the exit and of the nozzle 13 is in the illustrated embodiment about 10 mm.

For the accommodation of the spacer glide insert 32 grooves are machined out with a corresponding cross sectional area from the surface of the plates 25. The grooves on the edges facing the exit end of the mouthpiece have a depth of 1.75 mm so that the insert 32 having a thickness of 2 mm at that place will project out of the surface of the mouthpiece for about 0.25 mm. Both edges of the insert 32 are suitably rounded off. In addition the back edge of the insert 32 as indicated at 33 is slightly slanted with respect to the horizontal for about 15.degree.. The slanting is continued up to the surface of the plate 25 so that a thickness reduction of about 1 mm is attained (FIG. 3).

The amount of 0.25 mm by which the graphite insert 32 projects out of the surface of the mouthpiece 14 is sufficient, when casting aluminum or an aluminum alloy with a precisely manufactured nozzle, to prevent a direct contact of the surface of the nozzle with the surface 34 of the mold halves 35, as illustrated in FIG. 4. A projection of the graphite insert 32 to the extent of 0.2 mm may be just satisfactory. A projection of 0.3 mm represents the upper limit of the effective projection regarding the prevention of the entry of the molten metal. Therefore, one may state that the amount of projection preferably lies between the limits of 0.2 - 0.3 mm.

The graphite inserts 32 are preferably glued into the grooves and for this purpose the commercially available 2-component-glue known under the trade name "Araldite" (an epoxy resin) is preferred.

For the casting of aluminum strips of about 1,500 mm width preferably three nozzles having a width of 500 mm are used adjacently secured to the support and in which arrangement the middle nozzle does not have any projection 29 while both outside nozzles are provided with such projection 29 only on their outer edges. In adition, only those side edges of the mouthpiece 14 are provided with glide insert 32 which come in contact with the side walls of the mold without pressure. Instead of using three nozzles having a width of 500 mm for the casting of strips having a width of 1,500 mm, one may use also six nozzles having a width of 250 mm and, for the casting of strips having a width of 1,000 mm one may use, for example, five nozzles having a width of 200 mm each, or four nozzles having a width of 250 mm each or two nozzles having a width of 500 mm each.

From the above, it is apparent that although the invention has been described hereinbefore with respect to a certain specific embodiment thereof, it is evident that many modifications and changes may be made without departing from the spirit of the invention. Accordingly, by the appended claims, we intend to cover all such modifications and changes as fall within the true spirit and scope of this invention.

Claims

I claim:

1. A device for the delivery of molten metal to a stationary mold with continuously moving opposite substantially parallel internal wall surfaces in a strip casting process, particularly for non-ferrous metals such as aluminum and aluminum alloys,

said device comprising in combination,

a flat nozzle protruding into the upstream portion of the mold interior,

at least the portion of said nozzle which comes into contact with the molten metal, being made of a heat resistant material having a negligible heat conductivity and a high chemical resistivity to the molten metal flowing therethrough,

spacer means including insert means of self-lubricating non-metallic material encircling the nozzle exterior near the discharging end of the nozzle and projecting beyond the external surface of the nozzle for a distance sufficient for preventing any direct contact of the nozzle with any part of the mold interior, but sufficiently small to restrain the entry of molten metal into the space defined by the mold interior and the nozzle exterior.

2. The device as claimed in claim 1, wherein said insert means protrude out of the general surface of said nozzle to about 0.2 to 0.3 mm.

3. The device as claimed in claim 2, wherein at least one groove is formed in said surface of the nozzle, said insert means being cemented into said groove.

4. In a caterpillar-type mold with continuously moving opposite mold halves for strip casting, a flat nozzle for the delivery of the molten metal, at least the portion of said nozzle which comes into contact with the molten metal, being made of a heat resistant material having a negligible heat conductivity and a high chemical resistance to the molten metal flowing therethrough, said nozzle comprising spacer means including a series of inserts provided on outer edge portion of the nozzle over the entire extent thereof and protruding above a general surface of said nozzle to an extent preventing a direct contact of the nozzle surface with portions of the halves forming said mold and entry of the molten metal between the nozzle and the mold, said inserts comprising a self-lubricating material.

5. The device as claimed in claim 1, said nozzle being supported for movement in a plane perpendicular to the plane of the cast strip.

6. The device as claimed in claim 5, wherein the inserts are made of graphite.