JP2632824B2 - Method of casting metal sheet directly from melt - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a novel method for making a metal plate (strip or sheet) directly from a molten metal mass. From the prior art patents issued to King (US Pat. Nos. 3,522,836; 3,605,863) and others, it is known how to make boards in this manner. King discloses a method in which a liquid metal layer is deposited on the smooth outer cylindrical surface of a cooling roller by a so-called melt drag method. In the melt drag method, a moving support penetrates a liquid metal meniscus supplied by an orifice and draws metal from the orifice. The layer solidifies on the cold surface and is removed as a plate.

According to the melt drag method described above, or to the best of our knowledge, other methods that do not use a supply orifice,
The surface of the metal sheet formed by rapidly cooling the molten metal layer on a smooth surface may contain various casting defects. These defects are generally evidence that there is a poor (thermal) contact area between the liquid metal and the support. This bad contact results in slower metal solidification than in the adjacent good contact.

The Baxman et al. Patent (U.S. Pat. No. 4,250,950) discloses a metal mold with protrusions to control the rate of metal solidification, but obviously does not provide the improved surface finish presented here.

French Patent 1,364,717 teaches a method of continuous casting thick metal blanks in endless molds. Although somewhat obscure from that disclosure, at least one or perhaps both of the casting surfaces of the mold are rough, for example, grooved. From its disclosure and continuous casting technology,
Obviously, lubricants and release agents are used on the mold, and only thick plates can be formed in this manner. Thus, the disclosed continuous casting method differs from the method of the present invention in that a thin plate (less than 10 mm) is made and it must be temporarily bonded to a free casting surface for proper heat transfer. Substantially different.

Other methods exist for making plates replicating drum surfaces (see, for example, US Pat. Nos. 2,561,636 and 4,21
See 2,343). These methods are not relevant to the present invention, because the present invention produces a smooth metal plate, which plate preferably does not duplicate the drum surface. The plate is formed and used as cast (for example, for roof gutters) or is subsequently formed into a useful shape with only minimal cold rolling with a rather smooth Finish is desired.

SUMMARY OF THE INVENTION One object of the present invention is to improve surface quality (reduce surface defects) in metal sheets formed on cold surfaces directly from the melt.

The improved method involves casting a layer of molten metal on a cylindrical outer surface of a cold roll or drum having generally circumferential grooves separated by a ridge region, wherein the grooves are formed. Is at least about 8 grooves / cm. Typically, the melt does not completely fill the groove, nor does its lower or upper surface duplicate the shape of the groove. Periodic undulations are generally present in the lower surface of most plates, and there may also be periodic undulations in the upper surface of thin plates cast over widely spaced grooves. The metal is temporarily bonded to the outer surface of the cold roll for proper heat transfer, and then shrinks loosely. The board is preferably
The thickness is 10 mm or less, and more preferably 1 mm or less.

Preferably, an included angle between about 30 degrees and 60 degrees and about 0.025-0.2
Cut in at a depth of 5mm. The peak area between the grooves can vary in width from about 0.025 to 1.00 mm, and the ratio of peak width to groove width is preferably greater than 0.15, more preferably about 0.5
And between 1.5.

Brushing the cold roll between castings is desirable to clean the casting surface.

DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 show a model elevation and a plan view, respectively, of one tundish drum assembly for sheet metal casting.

FIG. 3 shows two cross-sectional views of ridge and groove geometries that can be used to cast an improved plate according to the present invention.

FIG. 4 is a representation of the behavior of the liquid metal on the surface in contact with the grooved drum.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show model views of one tundish and cold roll or cold drum assembly for practicing the present invention. The cylindrical drum 2 is mounted so as to rotate relative to the tundish 1, and it is convenient to perform water cooling (not shown). The tundish 1 has a profile fitted at one end to the roller surface and is spaced from the drum 2 so that the liquid metal 10 does not spill during rotation of the drum. Weir 4 dampens the flow of liquid metal formed by pouring into the tundish at the end opposite the wheel. The dam 3 forms an injection chamber together with the rear wall of the tundish. Weirs 3 and 4 also control melt levels 6 and 7, respectively. The weir 5 may be used to adjust the melt level 8 (static metal head) and also to adjust the length 9 of metal to drum contact. This contact length is important for adjusting the thickness of the plate 11. Weir 5 also
It can be placed at a short distance from the drum surface to supply a constant amount of liquid metal to the surface, ie, it acts as an orifice. The liquid metal 10 contacts the cooled drum and solidifies as a solid plate, which is then removed from the drum.

Typically, the bottom of the tundish is close to the drum at about 30 degrees from horizontal, but this close point varies substantially corresponding to the drum diameter, casting speed, and desired plate thickness. I do. The gap between the drum and the tundish may be on the order of 0.15-1.00 mm, and the melt contact length with the drum may be on the order of 4-120 mm. Preferably, these variables are adjusted to cast the plate to a thickness of less than 10 mm, more preferably less than 1 mm.

Apparatus, including that shown in FIG. 1, has been used in the past to cast metal on smooth, cylindrical drum surfaces (eg, a work surface polished with a 600 grain sandpaper). Unfortunately, surface defects occur when metals such as aluminum, copper or steel alloys are cast on smooth wheels. These flaws are either discolored dots, lines, or meshes, depending on the severity,
Macroscopically visible within the plate surface as surface texture, lift and / or cracks. These defects are related to poor contact areas between the liquid metal and the drum surface, and are due to the fact that such areas solidify relatively slowly with adjacent areas.
This differential consolidation seems to permanently define defective areas in the consolidation plate that are a remnant of poor contact.

The term "dimple" is used to mean a shallow defect area of 1-2 mm in diameter with a matte surface compared to the reflective appearance of the plate surface. This "cavity" is a common defect, which the present invention can reduce. The linear defects typically form an irregular mosaic-like indentation pattern that can be a crack site. As a result of the slow solidification, the depressions at the bottom provide craters on the top and the linear depressions on the bottom provide valleys at the top. Both cause variations in each formation and grain growth in those regions.

It has been discovered that casting on a drum with circumferential grooves in the mold surface can substantially reduce these defects and make both the top and bottom surfaces of the plate smoother. . Spiral (slit) or straight machined grooves are equally acceptable as long as they are substantially circumferential and closely spaced. If the wheel speed is high, it will cause turbulence in the liquid metal,
Surface grooves that are not substantially circumferential are not suitable. Grooving results in what is known as a peak-to-valley surface, which will have alternating grooves separated by raised mountain regions.

FIG. 3 shows two examples of groove cutting. FIG.
FIG. 3A is a reference example outside the scope of the present invention, and FIG. 3B is an example included in the scope of the present invention. In FIG. 3 (a), a simple V-shaped groove 32 is uniformly machined in the surface of the drum 31 (shown partially cut away). The upper end has no width,
Shown as a point or sharp protrusion 33a. on the other hand,
In FIG. 3B, the tip is removed and the peak area 33 is removed.
b has a width (w) separating the groove 32. In the present specification, the expression “mountain region” is not used in the sense that the peak width of the mouth is not essentially included where the peak is a sharp protrusion, that is, the scope of the present invention includes the embodiment of FIG. Is not included. Preferably, the ratio of average peak width to average groove width is about
Combinations between 0.5 and 1.5 but outside of this range are also useful. However, as the ratio of peak width to groove width increases, the drum surface approaches the conventional continuous (non-grooved) condition and is not particularly useful in providing significant improvements in plate quality. The grooving need not be uniform, but it is preferred. The peak area preferably has an average width of about 0.025-1.00 mm.

When subjected to machining, a pattern of sharp points and crests that are susceptible to deformation often forms, but is useful but not preferred. Prolonged use and cleaning of the drum may result in rounded peaks and flattened peaks.

The drum surface should be axially oriented along the
(B) It should have a groove frequency of greater than or equal to about 8 grooves / cm, preferably less than or equal to 35 grooves / cm, as measured from edge 34 to edge 35 in the middle. The groove does not need to be V-shaped, but is about 0.025-0.25m
Preferably it has an average depth of m. If they are V-shaped, the included angle formed by the walls is preferably about 30-60 degrees.

By supplying the molten metal to the frequent grooving surface at a reasonable pressure, a pattern is obtained in which the liquid metal does not completely fill the grooves. FIG. 4 shows the state of the liquid metal immediately after deposition. The lower surface of the metal is pushed down (at 46) into a groove 41 in the drum 40. The surface tension of the liquid causes the liquid metal to lift on the hill area 42 during the sag, but other pressures push the liquid down in the grooves. When solidifying,
The descender 46 rises above the drum surface due to shrinkage, depending on the thickness of the plate, resulting in a undulating lower surface. Except in the case of very thin metal plates and large groove spacing, the undulations in the lower surface caused by the grooves are not duplicated in the upper surface of the plate. The substantial shape of the grooving is not replicated on either the lower or upper surface. However, the upper surface is affected by the lower surface as the solidification propagates from the lower surface to the upper surface unlike the mold casting method where the solidification front begins at each mold surface.

After dispensing, the metal actually adheres to the outer mold surface. We believe that this is the atomic bond between the metal and the cold surface and is necessary to practice the present invention. This bonding is
It provides the rapid heat transfer necessary to solidify the plate with the desired microstructure, and the resulting shrinkage, freeing the plate from the cold surface and allowing collection. This is 100-1
It has to happen in a very short time at a wheel speed of 000cm / s. Brushing the drum surface is extremely desirable to keep the drum surface clean from oxides and other impurities that prevent the necessary bonding.

The continuous casting technique as disclosed in French Patent 1,364,177 does not. In continuous casting, the purpose is to cast into a mold rather than onto a free surface. This need limits the product to fairly thick blanks (eg, greater than 20 mm) and slow casting speeds. Lubricants and release agents must be used to avoid bonding the metal to the mold. Solidification also occurs from both sides of the mold, causing layered microstructures and possible internal shrinkage cavities. The heat transfer rate is at least as low as the rapid solidification method of the present invention.

The casting drum is preferably water-cooled. It may be made of any convenient metal that will withstand the conditions, especially the molten metal temperature. For example, copper, copper-chrome, steel or aluminum alloy drums
And optionally for casting steel. Grooves can be formed, for example, by machining or, if the metal is soft enough, by roll creasing or roll shaping.
May be introduced. Preferably, a cloth or wire wiper is used with the drum to keep the grooves clean during use.

If the groove is rough, sticking (not the necessary temporary connection) may be more frequent than with a smooth wheel. This is caused by too much straightening or wiping of the drum surface, which results in a score on the edge of the mountain. Too high a pressure on the liquid metal in the mold on such a rough surface pushes the metal too deep into the grooves, where the metal solidifies and sticks over its cut after solidification and shrinkage of the plate.

The drum speed during the casting operation is on the order of 100-1000 cm / sec. The slower speed can be used to make thicker plates, but, as with any casting method, this generally results in lower productivity. At the upper end of the above range and above, the cast plate tends to become thinner as the metal contact time is shorter. Depending on the size of the groove, this can result in a plurality of groove-induced undulations in the top surface of the plate. For some applications,
This is not harmful. The drum dimensions (width and diameter) do not appear to be critical as long as effective cooling is achieved and the metal is supplied from the tundish at the appropriate rate.

Preferred Embodiments As far as we know, plates cast directly on cooling drums by other devices and methods may benefit from drum grooving according to the present invention. However, our experimental trial mainly used the device as shown in FIGS.
Performed on a smooth drum and a grooved drum. Drums were made of either copper, copper-1% chromium alloy, steel or aluminum alloy. The metal to be cast is aluminum alloy 3105 (Nominally, Al-0.5% Mg-0.3
5% Mn), OFHC copper and low carbon steel (nominal Fe-0.35
% Mn-0.05% C). The cast plate is preferably crystalline and has a thickness of 0.25 mm or more.

The V-shaped groove is introduced by one-sided cutting or rolling. Acetate on the wheel surface collected after the test
Samples of the replica and the as-cast plate were examined and compared with a profilometer.

Example 1-Thickness variation Qualitatively, it is easy to see the difference in plate quality using a smooth wheel and a grooved wheel. Quantitatively, the definitive measure of plate quality is the thickness variation over a small area of the cast product, eg, 1 square inch, due to defects. Flat micrometer and point
-Micrometer measurements were performed on samples cast on smooth wheels and samples cast on grooved wheels according to the invention. The statistical difference between the thickness measurement obtained with a flat micrometer and the measurement obtained with a point micrometer, weighted by the nominal thickness of the substance (for example, the percentage difference) is the thickness over the proximity distance area. Give an indication of the fluctuation. A similar weighted difference between the flat micrometer reading and the thickness calculated from the weight, length, width and density of the material gives a similar indication, but the reading of the point micrometer Does not require subjective skills. The results in Table 1 for a 25.4 cm wide plate cast continuously on a clean 71 cm diameter drum show that the thickness was cast on a grooved wheel on a small area of the plate cast on a smooth wheel. It shows that the value fluctuates twice as much as that of the aluminum plate. Also, the scattering of data (eg, "S" values) is much less for products cast on grooved drums.

Numerous thicknesses (typically 10 to 2) with flat and point micrometers
Thickness measurements from the sample from 0) are gathered together, and the plates from each of 21 separate plate casting tests on a smooth wheel, representing various casting speeds, pools, thicknesses, etc. , The average percent difference was determined.

Two separate grooved wheel / plate casting experiments were evaluated in the manner described above and also by a similar (but easier) comparative method using flat micrometer readings and "calculated thickness" values.

 Table 1 shows the following.

a. for the smooth wheel and Yumizo wheel, and Δ _m
A direct comparison between S _m and b. Δ for the same material cast on a grooved wheel
between _m and delta _c, and between S _m and S _c, the relationship.

Experiments on an additional 6 grooved wheels are easier Δ
Evaluation was performed only by the _c method. "Group of 2" and "Group of 6"
The results during are statistically equivalent. Result of the inference, we, the "second group" and "6 group", if we delta _m values for "6 group" is measured, the statistical equivalent delta
We conclude that we would have shown the _m value. This is "a groove"
It leads to the conclusion that the relative variability of the thickness of the product cast on the wheel is only about half that of the material cast on a smooth wheel. The same conclusion exits from delta _m for the first and second rows in Table 1, however, additional delta _c value of the third row is assumed that certainly by either measure this conclusion.

Example 2 Several attempts were performed on a "smooth" wheel (ie, 600
1 with a grain size Al ₂ O ₃ sandpaper and a finished surface that has been polished to a matte surface by tapping with a rotating stainless steel brush. The drum surface was moving between about 4m / s and 6m / s.
The drum surface was kept clean using a rotating wiper. About 4
An inch of static metal head was required to manufacture the board in a somewhat continuous fashion. The plate quality fluctuated, but “hollow”
And other surface imperfections are clearly visible in virtually all plates.

Attempts on smooth drums with copper and steel have created similar defects in cast plates.

Example 3 Grooved Drum Casting An additional attempt was made using a grooved drum. The drum was cleaned to remove any impurities, including lubricants or other additives. Table 2 shows the conditions for each experiment. The brush was fixed and the wheel was cleaned at each rotation after peeling.

Experiment No. 102 is a special reference example in which the peak width is zero, and is not included in the scope of the present invention.

The grooves appear to provide a preferred site for initiating solidification (above the peaks) and to provide a passage for entrained gas escape. Cast plates using grooved drums exhibit substantially fewer defects on the upper and lower surfaces and substantially less thickness variability than plates cast on smooth drums.

 ──────────────────────────────────────────────────の Continuation of the front page (72) Inventor Maringer, Robert E. 815, Worthington, Greenridge Road, 43085, Ohio, United States of America 815 (72) Inventor Reimment, Judith Jay 43201, Ohio, United States, Columbus, West West Sixth Avenue 433 (56) Reference French Patent 1346717 (FR, A)

Claims (6)

(57) [Claims] 1. A method of casting a metal sheet of commercial quality having a thickness of less than about 10 mm directly from a melt, substantially substantially axially spaced on an outer cylindrical surface of a cold drum. Providing circumferentially extending grooves with a groove density of at least about 8 grooves / cm on the casting surface, a substantially cylindrical flat crest region between adjacent grooves, and a groove adjacent each crest region Forming a generally circumferential rim at the intersection with the, and rotating the cold drum to pass the fluted outer cylindrical surface through the melt pool and onto the fluted outer surface of the melt layer. Removal, wherein the lower surface of the melt layer is in direct contact with and substantially spans the grooves between the peak regions, and further, the upper surface of the melt layer is open and directly exposed to the atmosphere; and Removing heat from the melt layer through the grooved surface to form a groove; A method for casting a metal sheet, comprising: sequentially solidifying a melt layer from a set surface to an upper surface of the melt layer. 2. The melt pool is held in an open tundish having a cylindrical surface outside the cold drum as one wall, and the cold drum is moved upward with the outside surface facing the melt. 2. The method of claim 1, further comprising rotating in a direction to exit therethrough. 3. The method of claim 1 further comprising casting at a rate to form a crystalline metal plate having a thickness of about 0.25 mm or more and supplying molten metal at such a rate. 4. The ratio of the average peak width to the average groove width is 0.5 to 1.5.
4. The method of claim 3, further comprising introducing a metal melt onto the outer surface that is: 5. The method according to claim 4, wherein the groove has a depth of about 0.025 to 0.25 mm. 6. A metal melt is introduced onto the peripheral surface of a drum rotating at about 100 to 1000 cm / sec, with the grooves being generally cylindrical and having a diameter of about 0.025 to 0.25 mm in the peripheral surface. 4. The method of claim 3, further comprising the steps of: forming a groove having a depth of less than about 0.635 mm;