CA1290547C - Direct strip casting on grooved wheels - Google Patents
Direct strip casting on grooved wheelsInfo
- Publication number
- CA1290547C CA1290547C CA000520270A CA520270A CA1290547C CA 1290547 C CA1290547 C CA 1290547C CA 000520270 A CA000520270 A CA 000520270A CA 520270 A CA520270 A CA 520270A CA 1290547 C CA1290547 C CA 1290547C
- Authority
- CA
- Canada
- Prior art keywords
- melt
- metal
- grooves
- strip
- millimeters
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 238000005266 casting Methods 0.000 title claims abstract description 26
- 229910052751 metal Inorganic materials 0.000 claims abstract description 41
- 239000002184 metal Substances 0.000 claims abstract description 41
- 239000000155 melt Substances 0.000 claims abstract description 19
- 238000000034 method Methods 0.000 claims description 24
- 230000002093 peripheral effect Effects 0.000 claims 1
- 230000001105 regulatory effect Effects 0.000 claims 1
- 230000007547 defect Effects 0.000 description 14
- 229910001338 liquidmetal Inorganic materials 0.000 description 12
- 238000007711 solidification Methods 0.000 description 11
- 230000008023 solidification Effects 0.000 description 11
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 7
- 239000010949 copper Substances 0.000 description 7
- 229910052802 copper Inorganic materials 0.000 description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 5
- 229910000838 Al alloy Inorganic materials 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- 238000013459 approach Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000009749 continuous casting Methods 0.000 description 3
- 238000003754 machining Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 230000001680 brushing effect Effects 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000000314 lubricant Substances 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 1
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910000599 Cr alloy Inorganic materials 0.000 description 1
- 229910000881 Cu alloy Inorganic materials 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- GXDVEXJTVGRLNW-UHFFFAOYSA-N [Cr].[Cu] Chemical compound [Cr].[Cu] GXDVEXJTVGRLNW-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 239000000788 chromium alloy Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000012733 comparative method Methods 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000994 depressogenic effect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000002845 discoloration Methods 0.000 description 1
- 238000004049 embossing Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 230000005499 meniscus Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 238000007712 rapid solidification Methods 0.000 description 1
- 230000010076 replication Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 235000019587 texture Nutrition 0.000 description 1
- 239000011800 void material Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0637—Accessories therefor
- B22D11/0648—Casting surfaces
- B22D11/0651—Casting wheels
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Continuous Casting (AREA)
Abstract
DIRECT STRIP CASTING ON GROOVED WHEELS
Abstract Metal strip may be directly cast by deposit of a melt layer onto a chill surface. Quality of both the upper and lower surfaces of strip cast in this manner may be substantially improved according to the invention by casting on a chill roll having fine, circumferential, surface grooving of a particular geometry.
Abstract Metal strip may be directly cast by deposit of a melt layer onto a chill surface. Quality of both the upper and lower surfaces of strip cast in this manner may be substantially improved according to the invention by casting on a chill roll having fine, circumferential, surface grooving of a particular geometry.
Description
1~905~7 DIRECT STRIP CASTING ON GROOYED WHE~S
~ackqround of the Invention The ~nvention relate6 to a novel method for making metal str~p or sheet directly from a ~olten ~s8 of 05 the metal. From prior p~ten~s issued to Ring (U.S.
3,522,836, U.S. 3,605,863) and other , it i6 known how to make strip in this manner. Ring disclo~es a method whereby a layer of the l$quia metal i~ deposited onto the smooth, outer, cylindrical ~urface of a chilled roller by a 10 so-called melt drag proce6s. In the melt dras proce~s the moving substrate passes throuqh a meniscus of liguid metal delivered by an orifice and drags the metal from the orifice. The layer quickly Eolidifies on the chill ~ur-face and is removed as a strip.
By the above melt drag method or, so far as we know, by other methods not utilizing an orifice for de-livery, the surface of metal strip formed by rapidly chilling a molten metal layer on a smooth substrate may contain various casting defects. These defects are gen-20 erally a vestige of poor (thermal) contact regions of the liquid metal with the substrate. The poor contact results in slower solidification of metal than in adjacent regions of good contact.
A patent to Buxmann, et. al. (U.S. 4,250,950) 25 discloses a me~al mold with projections for controlling the rate of metal solidification, but apparently not for improving surface finish as proposed herein.
French Patent 1,364,717 teaches a method for continuous castinq of thick metal blanks in an endless 30 mold. It is somewhat unclear from the disclosure, but at least one and possibly both of the casting surfaces of the mold are r~ugh, for example, they are grooved. It is clear from the disclosure and the continuous casting art that lubrication and release agents are used on the mold and 35 that only thick strip can be formed in this manner. In this lX~05~7 way, the disclosed continuous castlng method is substantlally dlfferent than the present process whereln thin strip (less than 10 mm) is made and wherein it must be temporarily bonded to a free casting surface for proper heat transfer.
Other methods exist for producing strip which replicates the surface of the drum (see U.S. 2,561,636 and U.S. 4,212,343, for example). Such methods are not relevant to the present invention because the present method produces smooth metal strlp whlch preferably does not repllcate the drum. A rather smooth flnlsh ls deslred so that the strip may be formed and used as cast ~such as for roof gutters, for example) or may be further formed into useful shapes wlth only a mlnimum of cold rolling.
SUMMARY OF THE INVENTION
It ls an object of the present lnvention to improve the surface quallty (reduce surface defectæ) in metal strlp formed on a chill surface directly from the melt.
The method accordlng to the lnvention comprises:
rotatlng a chlll wheel comprlslng an outer cylindrical surface havlng (1) axially-spaced, substantlally circumferentially extendlng grooves with a groove density of at least about 8 grooves per centlmeter~(ii) substantially cylindrlcal fla~ land regions between adjust grooves and (iii) generally circumferential edges at the intersections of each land region with the adjacent grooves and passing the grooved outer cylindrical surface through a melt pool to extract a layer of the metal melt having upper and lower surfaces onto the grooved outer surface, wherein the lower surface of the metal layer directly contacts the land regions and substantially spans the grooves between the iand regions and A`
lX9OS47 2a 26494-109 wherein the upper surface of the metal layer is unconfirmed and directly exposed to atmosphere; and withdrawing heat from the melt layer through the grooved surface to progressively solidify the melt layer from the grooved surface to the upper surface of the melt layer.
The strip is preferably less than 10 mm thick and more preferably less than 1 mm.
.,, ~
~2905~7 Preferably the grooves are cut with an included angle of between about 30 and 60 degrees and a depth of about 0.025-0.25 mm. The land region between grooves may vary from about 0.025-1.00 ~m in width and the ratio of 05 land width to the groove width is preferably qreater than 0.15 and more preferably between about 0.5 and 1.5.
Brushing of the chill roll between castings is desirable to clean the casting surface.
Description of the Drawin~s Figs. 1 and 2 show a schematic elevation and plan view, respectively, of one tundish and drum assembly for casting metal strip.
Fig. 3 shows two cross-sectional views of land and groove geometries which may be used to cast improved strip according to the invention.
Fig. 4 is a representation of the liquid metal behavior at the surface in contact with the grooved drum.
Description of the Preferred Embodiments Figs. 1 and 2 show schematic views of one tun-dish and chilled roll or drum assembly for practicing theinvention. The cylindrical drum 2 is mounted for rotation relative to the tundish 1 and is conventionally water cooled (not shown). The tundish 1 has a contour matching the roller surface at one end and is spaced from the drum 2 such that the liquid metal 10 will not spill during rotation of the drum. Weir 4 smooths out the flow of liquid metal which is made-up by pouring into the tundish at the opposite end from the wheel. Dam 3 forms a pouring chamber with the tundish back wall. Dam 3 and weir 4 also control the melt level 6 and 7 respectively. Weir 5 may be used to control the melt level 8 (the metalostatic head height) and also to control the contact length 9 of the melt ~ith the drum. This contact length is impsrtant for con-trolling the thickness of the strip 11. The weir 5 may alternatively be closely spaced from the drum surface to 05 meter the liquid metal to the surface, i.e. serving as an orifice. Liquid metal 10 contacts the cooled drum and solidifies to the solid strip 11 before removal from the drum.
Typically, the bottom of the tundish approaches the drum at a point about 30 from horizontal, but this point of approach may vary substantially depending on the drum diameter, casting speed and desired strip thickness.
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 on the order of 4-120 mm. Parameters are preferably adjusted to cast strip less than 10 mm and more preferably less than 1 mm in thickness.
Apparatus including that shown in Fig. 1 have been used in the past for casting metal on a smooth, cylindrical drum surface (for example, a machined surface ground through 600-grit sanding paper). Unfortunately, when metal such as aluminum, copper or steel alloys are cast on smooth wheels, surface defects may arise. These defects are visually perceived in the strip surface as either points, lines or networks of discoloration, tex-ture, relief and/or cracking depending on the severity.
The defects appear to be related to areas of poor contact of the liquid metal with the drum surface causing slower solidification of such areas relative to adjacent areas.
This differential solidification appears to permanently define a defect region in the solidified strip which is a vestige of the poor contact.
1290~i47 The term ~dimple~ is used to mean a shallow ,defect area of 1-2 mm in diameter having a matte surface compared to the otherwise reflective appearance of the strip ~urface. The dimple is a common defect which the 05 present invention may reducer The linear defects typ-ically form an irregular mosaic pattern of depressions which may be the site of cracking. As a result of the slow solidification, bottom surface dimples may result in top surface craters and bottom surface linear depressions 10 result in top surface valleys. ~oth result in variations in nucleation and grain growth in the regions.
It has been found that these defects can be re-duced substantially and both the upper and lower surfaces of the strip can be made smoother by casting on a drum with 15 circumferential grooves in the casting surface. ~eli-cal (threaded) or straight-machined grooves are equally acceptable so long as the grooves are substantially cir-cumferential and closely spaced. The rapid wheel speeds preclude surface grooves which are not substantially cir-20 cumferential because of turbulence in the liquid metal.Grooving results in what is known as a land-and-groove surface having alternating grooves separated by raised land regions.
Fig. 3 shows common grooving which is useful in 25 the invention. In Fig. 3(a) a simple ~V" shaped groove 32 has been uniformly machined in the surface of a drum 31 (shown in cutaway). ~he land regions 33 approach zero width in this grooving and are described as tips or sharp projections. In Fig. 3(b) the tips have been removed such 30 that land regions 33 have a width ~ separating grooves 32.
Frequently, the machining process results in a variable pattern of tips and lands which may also be useful but is not preferred. Extended use and cleaning of the drum may round the tips and flatten the lands.
lXgOS4~
6 264~4-109 It has been found that the drum surface should have a groove frequency of about 8-35 groovestcentimeter measured axially along the surface of the drum from edge 34 to edge 35 ln Fig. 3(a). The grooves need not be "V" shaped but pre~erably have an average depth of about 0.025-0.25 millimeters. If they are "V"-shaped, the included angle formed by the walls is preferably about 30-60. The land regions preferably have an average width of about 0.025-1.00 millimeters, more preferably less than 0.635 millimeters. However, the term land is also used herein to include a land width of essentially zero where the land is a sharp projection. Preferably the ratio of average land width to average groove width is about 0.5~1.5, but patterns outside of this range are useful. Generally, only the high land to groove ratio is not particularly useful in producing significant improvement in strip quality as the drum surface approaches the prior art continuous (ungrooved) condition. The grooving need not be uniform but is preferably so.
~ elivery of the molten metal at reasonable pressure to the high frequency grooving results in a pattern in which the liquid metal does not completely fill the grooves. Fig. 4 shows a condition of the liquid metal 43 immediately after deposit. The lower surface of the metal is depressed (at 46) into grooves 41 in the drum 40. The surface tension of the liquid may cause the liquid metal to be raised over the land regions 42 between depressions but other pressures may depress the liquid in the groove. Upon solidification the depressions 46 may, depend$ng on the strip thickness, rise above the drum surface due to shrinkage resulting in an undulating lower surface. Except in very thin 1290S~7 6a 26494-lOg me~al strip and large spacing of grooves, ~he undulation in the lower surface caused by the grooves is not replicated in the upper surface of ~he , .~ ., , lZ9~)547 strip. The actual shape of the grooving is not replicated in either the lower or upper surface Bowever, the upper surface is affected by the lower surface because solidi-fication propagat~s from the bottom to the top, unlike 05 mold casting process where solidification fronts begin from each mold surface.
After delivery, metal actually adheres to the outer casting surface. We believe this is ~n atomic bond between the metal and the chill surface and that it is necessary for practicing the present process. The ad-hesion results in the rapid heat transfer necessary to solidify the strip with the desired microstructure and the consequent shrinkage which causes the strip to break free of the chill surface to be collected. This must all take place in a very short time at wheel speeds on the order of 100-1000 cm/sec. Brushing of the drum surface is ex-tremely desirable to keep the drum surface clear of oxides and other impurities which would prevent the necessary bonding.
Such is not the case with continuous casting arts such as disclosed in French Patent 1,364,177. In continuous casting, the object is to cast into a mold, not on a free surface. This necessary limits the product to rather thick blanks (for example, greater than 20 mm) and slow casting speeds. Lubricants and release agents must be used to avoid bonding of metal to the mold. Solidi-fication also takes place from both sides of the mold, causing a layered microstructure and the possibility of internal shrinkage void. Rates of heat transfer are at least an order of magnitude less than for the present rapid solidification process.
The casting drum is preferably water cooled. It may be made of any convenient metal which will withstand the conditions, in particular, the temperature of the 35 molten metal. For example, copper, copper-chromium, steel ~290547 or aluminum alloy drums may be used selectively for cast-ing aluminum, copper and ~teel. The groove~ may be introduced, for example, by machining or, when the metal is soft enough, by roll threading or embossing. Prefer-05 ably, a cloth or ~ire wiper is used with the drum forkeeping the grooves clean during use.
Sticking (not the necessary temporary bonding) may be more frequent than with a smooth wheel if the grooves are rough. This can be caused by over-aggres~ive 10 redressing or wiping of the drum surface causing burrs to form on the land edges. Too hiqh a pressure on the liquid metal during casting on such rough surfaces forces the metal too deeply into the grooves where the metal can solidify and stick on the burrs after the solidification 15 and shrinkage of the strip.
Drum speeds during the casting operation are on the order of 100-1000 cm/sec. Lower speeds can be used to produce thicker strip but, as with any casting process, this would generally result in lower productivity. At the 20 upper end of the stated range and above, the cast strip tends to become thinner as the metal contact time is decreased. Depending on the groove size, this can result in replication of the groove-induced undulation in the upper surface of the strip. For some uses this is not 25 detrimental. Drum size (width and diameter~ does not appear to be critical so long as effective cooling can be accomplished and metal can be delivered at the proper rate from the tundish.
ExamPles of the Preferred Embodiments So far as we know, strip directly cast on a csoled drum by other apparatus and methods may benefit from the grooving of the drum according to the invention.
However, our experimental trials have been made on smooth and grooved drums usin~, primarily, the apparatus as shown lX!~ 7 in Figs. 1 and 2. The drums were made with either copper, copper-1% chromium alloy, steel or aluminum alloy. Metals cast were aluminum alloy 3105 (nominally Al-0.53 Mq-0.54 Mn), OFHC Copper and low-carbon steel (nominally Fe-0.35%
05 Mn 0.05S C). The cast strip is preferably crystalline with a thickness of greater than 0~25 mm.
~ V-shaped grooves were introduced by sin-gle-point machining or rolling. Acetate replicas of the wheel surfaces taken after runs and samples of the as-cast strip were examined with a profilometer and compared.
ExamDle 1 - Thickness Variation Qualitatively, it is easy to see the difference in strip quality using smooth and grooved wheels. Quanti-tatively, a definitive measure of strip quality is the thickness variation over a small area, for example one square inch, of the cast product due to defects. Measure-ments with flat and point micrometers were taken on sam-ples cast on smooth wheels and those cast on grooved wheels according to the invention. The statistical difference between thickness measurements taken with flat micro-meters and those with point micrometers weighted by the nominal thickness of the material (e.g. the percent dif-ference) gives an indication of thickness variation over closely spaced regions. The similarly weighted dif-ference between flat micrometer measurements and thick-ness calculated from the weight, length, width and density ' of the material gives a similar indication but without the subjective skill required to read a point micrometer. The results in Table 1 for 25.4 cm wide strip continuously cast on a clean, 71 cm diameter drum show that the thick-ness varies by twice as much over a small region of smooth-wheel-cast aluminum strip versus grooved-wheel--cast aluminum strip. Also, the scatter in the data (e.g., the s" values) is much less for product cast on the ; 35 grooved drums.
lX905~7 . ~ .
Strip Cast on:N ~ Sm ~tc Sc Smooth Wheel 21 29.5 7.8 Grooved Wheel 2 14.0 1.4 11.5 0.2 05 6 -- -- 11.1 1.4 Where: N c number of casting experiments for which average thickness difference statisticC
were evaluated. For each experiment, sev-eral individual samples were measured.
tm = average measured thickness variation, per-cent (point micrometer vs. flat micrometer) among ~ experiments Sm = standard deviation, percent (among N exper-iments) tc = average calculated thickness variation, percent (flat micrometer vs. calculated from density~
Sc = standard deviation, percent (among N ex-periments) Numerous (typically 10 to 20) sample measure-ments of thickness with flat and point micrometers were ~ompiled to determine the average percent difference for strip from each of 21 separate strip casting trials on a smooth wheel representing different castin~ speeds, pool, 1~90~47 thickness, etc. These averages were then combined, re-sulting in an overall average, ~m~, ~ith a variability defined as ~Sm" for smooth-wheel casts.
Two separate-grooved wheel strip casting ex-05 periments were evaluated in the above manner, and also bythe similar (but easier) comparative method utilizing flat micrometer readings and ~calculated thickness" values.
Table 1 show~:
a. A direct comparison between ~tm and Sm for smooth and grooved wheels, and b. the relationship between ~tm and ~tc, and between Sm and Sc for the same materials cast on a grooved wheel.
An additional 6 experiments on a grooved wheel were evaluated by the easier ~tc method only. The results between the Wgroup of 2~ and the ~group of 6~ were statis-tically identical. By inference, we conclude that the "group of 2" and group of 6~ would have shown statis-tically identical ~tm values if these had been determined for the "group of 6n. This leads to the conclusion that the relative variability in thickness of product cast on ~grooved~ wheels is only about half of that for ma-terial cast on smooth wheels. The same conclusion results from ~tm for only rows 1 and 2 of Table 1, but the added ~tc values of row 3 make this conclusion much more certain.
Example 2 Several trials were made using apparatus such as shown in Fig. 1 with a ~smooth" wheel ~i.e. a machined surface ground through 600-grit A12O3 sanding paper then finished to a matte surface by peening with a rotating stainless steel brush~. Aluminum 3105 alloy was melted and introduced to the chilled copper drum in a thin layer by the tundish. The drum surface was moving at between 1~90S47 about 4 and 6 meters/second. A rotating wiper was used to keep the drum surface clean. A metallostatic head of about 4 inches was required to produce strip in a rather contin-uous mode. Strip quality varied, but dimples and other 05 surface defects were plainly visible in virtually all the strip.
Trials with copper and steel on smooth drums produced similar defects in cast strip.
Example 3 - Grooved Drum Castinq Additional trials were run using grooved drums.
The drums were cleaned to remove any impurities, including any lubricants or other additive. Table 2 gives the conditions of each run. A brush was fixed to clean the wheel on each rotation after release of the strip.
The grooves appear to afford a preferred site (on the lands~ for initiation of solidification and afford channels for escaping of entrained gases. Cast strip using the grooved drums showed substantially less defects on upper and lower surfaces than strip cast on smooth drums and substantially less thickness variability.
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~ackqround of the Invention The ~nvention relate6 to a novel method for making metal str~p or sheet directly from a ~olten ~s8 of 05 the metal. From prior p~ten~s issued to Ring (U.S.
3,522,836, U.S. 3,605,863) and other , it i6 known how to make strip in this manner. Ring disclo~es a method whereby a layer of the l$quia metal i~ deposited onto the smooth, outer, cylindrical ~urface of a chilled roller by a 10 so-called melt drag proce6s. In the melt dras proce~s the moving substrate passes throuqh a meniscus of liguid metal delivered by an orifice and drags the metal from the orifice. The layer quickly Eolidifies on the chill ~ur-face and is removed as a strip.
By the above melt drag method or, so far as we know, by other methods not utilizing an orifice for de-livery, the surface of metal strip formed by rapidly chilling a molten metal layer on a smooth substrate may contain various casting defects. These defects are gen-20 erally a vestige of poor (thermal) contact regions of the liquid metal with the substrate. The poor contact results in slower solidification of metal than in adjacent regions of good contact.
A patent to Buxmann, et. al. (U.S. 4,250,950) 25 discloses a me~al mold with projections for controlling the rate of metal solidification, but apparently not for improving surface finish as proposed herein.
French Patent 1,364,717 teaches a method for continuous castinq of thick metal blanks in an endless 30 mold. It is somewhat unclear from the disclosure, but at least one and possibly both of the casting surfaces of the mold are r~ugh, for example, they are grooved. It is clear from the disclosure and the continuous casting art that lubrication and release agents are used on the mold and 35 that only thick strip can be formed in this manner. In this lX~05~7 way, the disclosed continuous castlng method is substantlally dlfferent than the present process whereln thin strip (less than 10 mm) is made and wherein it must be temporarily bonded to a free casting surface for proper heat transfer.
Other methods exist for producing strip which replicates the surface of the drum (see U.S. 2,561,636 and U.S. 4,212,343, for example). Such methods are not relevant to the present invention because the present method produces smooth metal strlp whlch preferably does not repllcate the drum. A rather smooth flnlsh ls deslred so that the strip may be formed and used as cast ~such as for roof gutters, for example) or may be further formed into useful shapes wlth only a mlnimum of cold rolling.
SUMMARY OF THE INVENTION
It ls an object of the present lnvention to improve the surface quallty (reduce surface defectæ) in metal strlp formed on a chill surface directly from the melt.
The method accordlng to the lnvention comprises:
rotatlng a chlll wheel comprlslng an outer cylindrical surface havlng (1) axially-spaced, substantlally circumferentially extendlng grooves with a groove density of at least about 8 grooves per centlmeter~(ii) substantially cylindrlcal fla~ land regions between adjust grooves and (iii) generally circumferential edges at the intersections of each land region with the adjacent grooves and passing the grooved outer cylindrical surface through a melt pool to extract a layer of the metal melt having upper and lower surfaces onto the grooved outer surface, wherein the lower surface of the metal layer directly contacts the land regions and substantially spans the grooves between the iand regions and A`
lX9OS47 2a 26494-109 wherein the upper surface of the metal layer is unconfirmed and directly exposed to atmosphere; and withdrawing heat from the melt layer through the grooved surface to progressively solidify the melt layer from the grooved surface to the upper surface of the melt layer.
The strip is preferably less than 10 mm thick and more preferably less than 1 mm.
.,, ~
~2905~7 Preferably the grooves are cut with an included angle of between about 30 and 60 degrees and a depth of about 0.025-0.25 mm. The land region between grooves may vary from about 0.025-1.00 ~m in width and the ratio of 05 land width to the groove width is preferably qreater than 0.15 and more preferably between about 0.5 and 1.5.
Brushing of the chill roll between castings is desirable to clean the casting surface.
Description of the Drawin~s Figs. 1 and 2 show a schematic elevation and plan view, respectively, of one tundish and drum assembly for casting metal strip.
Fig. 3 shows two cross-sectional views of land and groove geometries which may be used to cast improved strip according to the invention.
Fig. 4 is a representation of the liquid metal behavior at the surface in contact with the grooved drum.
Description of the Preferred Embodiments Figs. 1 and 2 show schematic views of one tun-dish and chilled roll or drum assembly for practicing theinvention. The cylindrical drum 2 is mounted for rotation relative to the tundish 1 and is conventionally water cooled (not shown). The tundish 1 has a contour matching the roller surface at one end and is spaced from the drum 2 such that the liquid metal 10 will not spill during rotation of the drum. Weir 4 smooths out the flow of liquid metal which is made-up by pouring into the tundish at the opposite end from the wheel. Dam 3 forms a pouring chamber with the tundish back wall. Dam 3 and weir 4 also control the melt level 6 and 7 respectively. Weir 5 may be used to control the melt level 8 (the metalostatic head height) and also to control the contact length 9 of the melt ~ith the drum. This contact length is impsrtant for con-trolling the thickness of the strip 11. The weir 5 may alternatively be closely spaced from the drum surface to 05 meter the liquid metal to the surface, i.e. serving as an orifice. Liquid metal 10 contacts the cooled drum and solidifies to the solid strip 11 before removal from the drum.
Typically, the bottom of the tundish approaches the drum at a point about 30 from horizontal, but this point of approach may vary substantially depending on the drum diameter, casting speed and desired strip thickness.
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 on the order of 4-120 mm. Parameters are preferably adjusted to cast strip less than 10 mm and more preferably less than 1 mm in thickness.
Apparatus including that shown in Fig. 1 have been used in the past for casting metal on a smooth, cylindrical drum surface (for example, a machined surface ground through 600-grit sanding paper). Unfortunately, when metal such as aluminum, copper or steel alloys are cast on smooth wheels, surface defects may arise. These defects are visually perceived in the strip surface as either points, lines or networks of discoloration, tex-ture, relief and/or cracking depending on the severity.
The defects appear to be related to areas of poor contact of the liquid metal with the drum surface causing slower solidification of such areas relative to adjacent areas.
This differential solidification appears to permanently define a defect region in the solidified strip which is a vestige of the poor contact.
1290~i47 The term ~dimple~ is used to mean a shallow ,defect area of 1-2 mm in diameter having a matte surface compared to the otherwise reflective appearance of the strip ~urface. The dimple is a common defect which the 05 present invention may reducer The linear defects typ-ically form an irregular mosaic pattern of depressions which may be the site of cracking. As a result of the slow solidification, bottom surface dimples may result in top surface craters and bottom surface linear depressions 10 result in top surface valleys. ~oth result in variations in nucleation and grain growth in the regions.
It has been found that these defects can be re-duced substantially and both the upper and lower surfaces of the strip can be made smoother by casting on a drum with 15 circumferential grooves in the casting surface. ~eli-cal (threaded) or straight-machined grooves are equally acceptable so long as the grooves are substantially cir-cumferential and closely spaced. The rapid wheel speeds preclude surface grooves which are not substantially cir-20 cumferential because of turbulence in the liquid metal.Grooving results in what is known as a land-and-groove surface having alternating grooves separated by raised land regions.
Fig. 3 shows common grooving which is useful in 25 the invention. In Fig. 3(a) a simple ~V" shaped groove 32 has been uniformly machined in the surface of a drum 31 (shown in cutaway). ~he land regions 33 approach zero width in this grooving and are described as tips or sharp projections. In Fig. 3(b) the tips have been removed such 30 that land regions 33 have a width ~ separating grooves 32.
Frequently, the machining process results in a variable pattern of tips and lands which may also be useful but is not preferred. Extended use and cleaning of the drum may round the tips and flatten the lands.
lXgOS4~
6 264~4-109 It has been found that the drum surface should have a groove frequency of about 8-35 groovestcentimeter measured axially along the surface of the drum from edge 34 to edge 35 ln Fig. 3(a). The grooves need not be "V" shaped but pre~erably have an average depth of about 0.025-0.25 millimeters. If they are "V"-shaped, the included angle formed by the walls is preferably about 30-60. The land regions preferably have an average width of about 0.025-1.00 millimeters, more preferably less than 0.635 millimeters. However, the term land is also used herein to include a land width of essentially zero where the land is a sharp projection. Preferably the ratio of average land width to average groove width is about 0.5~1.5, but patterns outside of this range are useful. Generally, only the high land to groove ratio is not particularly useful in producing significant improvement in strip quality as the drum surface approaches the prior art continuous (ungrooved) condition. The grooving need not be uniform but is preferably so.
~ elivery of the molten metal at reasonable pressure to the high frequency grooving results in a pattern in which the liquid metal does not completely fill the grooves. Fig. 4 shows a condition of the liquid metal 43 immediately after deposit. The lower surface of the metal is depressed (at 46) into grooves 41 in the drum 40. The surface tension of the liquid may cause the liquid metal to be raised over the land regions 42 between depressions but other pressures may depress the liquid in the groove. Upon solidification the depressions 46 may, depend$ng on the strip thickness, rise above the drum surface due to shrinkage resulting in an undulating lower surface. Except in very thin 1290S~7 6a 26494-lOg me~al strip and large spacing of grooves, ~he undulation in the lower surface caused by the grooves is not replicated in the upper surface of ~he , .~ ., , lZ9~)547 strip. The actual shape of the grooving is not replicated in either the lower or upper surface Bowever, the upper surface is affected by the lower surface because solidi-fication propagat~s from the bottom to the top, unlike 05 mold casting process where solidification fronts begin from each mold surface.
After delivery, metal actually adheres to the outer casting surface. We believe this is ~n atomic bond between the metal and the chill surface and that it is necessary for practicing the present process. The ad-hesion results in the rapid heat transfer necessary to solidify the strip with the desired microstructure and the consequent shrinkage which causes the strip to break free of the chill surface to be collected. This must all take place in a very short time at wheel speeds on the order of 100-1000 cm/sec. Brushing of the drum surface is ex-tremely desirable to keep the drum surface clear of oxides and other impurities which would prevent the necessary bonding.
Such is not the case with continuous casting arts such as disclosed in French Patent 1,364,177. In continuous casting, the object is to cast into a mold, not on a free surface. This necessary limits the product to rather thick blanks (for example, greater than 20 mm) and slow casting speeds. Lubricants and release agents must be used to avoid bonding of metal to the mold. Solidi-fication also takes place from both sides of the mold, causing a layered microstructure and the possibility of internal shrinkage void. Rates of heat transfer are at least an order of magnitude less than for the present rapid solidification process.
The casting drum is preferably water cooled. It may be made of any convenient metal which will withstand the conditions, in particular, the temperature of the 35 molten metal. For example, copper, copper-chromium, steel ~290547 or aluminum alloy drums may be used selectively for cast-ing aluminum, copper and ~teel. The groove~ may be introduced, for example, by machining or, when the metal is soft enough, by roll threading or embossing. Prefer-05 ably, a cloth or ~ire wiper is used with the drum forkeeping the grooves clean during use.
Sticking (not the necessary temporary bonding) may be more frequent than with a smooth wheel if the grooves are rough. This can be caused by over-aggres~ive 10 redressing or wiping of the drum surface causing burrs to form on the land edges. Too hiqh a pressure on the liquid metal during casting on such rough surfaces forces the metal too deeply into the grooves where the metal can solidify and stick on the burrs after the solidification 15 and shrinkage of the strip.
Drum speeds during the casting operation are on the order of 100-1000 cm/sec. Lower speeds can be used to produce thicker strip but, as with any casting process, this would generally result in lower productivity. At the 20 upper end of the stated range and above, the cast strip tends to become thinner as the metal contact time is decreased. Depending on the groove size, this can result in replication of the groove-induced undulation in the upper surface of the strip. For some uses this is not 25 detrimental. Drum size (width and diameter~ does not appear to be critical so long as effective cooling can be accomplished and metal can be delivered at the proper rate from the tundish.
ExamPles of the Preferred Embodiments So far as we know, strip directly cast on a csoled drum by other apparatus and methods may benefit from the grooving of the drum according to the invention.
However, our experimental trials have been made on smooth and grooved drums usin~, primarily, the apparatus as shown lX!~ 7 in Figs. 1 and 2. The drums were made with either copper, copper-1% chromium alloy, steel or aluminum alloy. Metals cast were aluminum alloy 3105 (nominally Al-0.53 Mq-0.54 Mn), OFHC Copper and low-carbon steel (nominally Fe-0.35%
05 Mn 0.05S C). The cast strip is preferably crystalline with a thickness of greater than 0~25 mm.
~ V-shaped grooves were introduced by sin-gle-point machining or rolling. Acetate replicas of the wheel surfaces taken after runs and samples of the as-cast strip were examined with a profilometer and compared.
ExamDle 1 - Thickness Variation Qualitatively, it is easy to see the difference in strip quality using smooth and grooved wheels. Quanti-tatively, a definitive measure of strip quality is the thickness variation over a small area, for example one square inch, of the cast product due to defects. Measure-ments with flat and point micrometers were taken on sam-ples cast on smooth wheels and those cast on grooved wheels according to the invention. The statistical difference between thickness measurements taken with flat micro-meters and those with point micrometers weighted by the nominal thickness of the material (e.g. the percent dif-ference) gives an indication of thickness variation over closely spaced regions. The similarly weighted dif-ference between flat micrometer measurements and thick-ness calculated from the weight, length, width and density ' of the material gives a similar indication but without the subjective skill required to read a point micrometer. The results in Table 1 for 25.4 cm wide strip continuously cast on a clean, 71 cm diameter drum show that the thick-ness varies by twice as much over a small region of smooth-wheel-cast aluminum strip versus grooved-wheel--cast aluminum strip. Also, the scatter in the data (e.g., the s" values) is much less for product cast on the ; 35 grooved drums.
lX905~7 . ~ .
Strip Cast on:N ~ Sm ~tc Sc Smooth Wheel 21 29.5 7.8 Grooved Wheel 2 14.0 1.4 11.5 0.2 05 6 -- -- 11.1 1.4 Where: N c number of casting experiments for which average thickness difference statisticC
were evaluated. For each experiment, sev-eral individual samples were measured.
tm = average measured thickness variation, per-cent (point micrometer vs. flat micrometer) among ~ experiments Sm = standard deviation, percent (among N exper-iments) tc = average calculated thickness variation, percent (flat micrometer vs. calculated from density~
Sc = standard deviation, percent (among N ex-periments) Numerous (typically 10 to 20) sample measure-ments of thickness with flat and point micrometers were ~ompiled to determine the average percent difference for strip from each of 21 separate strip casting trials on a smooth wheel representing different castin~ speeds, pool, 1~90~47 thickness, etc. These averages were then combined, re-sulting in an overall average, ~m~, ~ith a variability defined as ~Sm" for smooth-wheel casts.
Two separate-grooved wheel strip casting ex-05 periments were evaluated in the above manner, and also bythe similar (but easier) comparative method utilizing flat micrometer readings and ~calculated thickness" values.
Table 1 show~:
a. A direct comparison between ~tm and Sm for smooth and grooved wheels, and b. the relationship between ~tm and ~tc, and between Sm and Sc for the same materials cast on a grooved wheel.
An additional 6 experiments on a grooved wheel were evaluated by the easier ~tc method only. The results between the Wgroup of 2~ and the ~group of 6~ were statis-tically identical. By inference, we conclude that the "group of 2" and group of 6~ would have shown statis-tically identical ~tm values if these had been determined for the "group of 6n. This leads to the conclusion that the relative variability in thickness of product cast on ~grooved~ wheels is only about half of that for ma-terial cast on smooth wheels. The same conclusion results from ~tm for only rows 1 and 2 of Table 1, but the added ~tc values of row 3 make this conclusion much more certain.
Example 2 Several trials were made using apparatus such as shown in Fig. 1 with a ~smooth" wheel ~i.e. a machined surface ground through 600-grit A12O3 sanding paper then finished to a matte surface by peening with a rotating stainless steel brush~. Aluminum 3105 alloy was melted and introduced to the chilled copper drum in a thin layer by the tundish. The drum surface was moving at between 1~90S47 about 4 and 6 meters/second. A rotating wiper was used to keep the drum surface clean. A metallostatic head of about 4 inches was required to produce strip in a rather contin-uous mode. Strip quality varied, but dimples and other 05 surface defects were plainly visible in virtually all the strip.
Trials with copper and steel on smooth drums produced similar defects in cast strip.
Example 3 - Grooved Drum Castinq Additional trials were run using grooved drums.
The drums were cleaned to remove any impurities, including any lubricants or other additive. Table 2 gives the conditions of each run. A brush was fixed to clean the wheel on each rotation after release of the strip.
The grooves appear to afford a preferred site (on the lands~ for initiation of solidification and afford channels for escaping of entrained gases. Cast strip using the grooved drums showed substantially less defects on upper and lower surfaces than strip cast on smooth drums and substantially less thickness variability.
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Claims (9)
1. A method for casting a commercial quality metal sheet or strip of a thickness less than about 10 mm directly from a metal melt, which comprises:
rotating a chill wheel comprising an outer cylindrical surface having (i) axially-spaced, substantially circumferentially extending grooves with a groove density of at least about 8 grooves per centimeter (ii) substantially cylindrical flat land regions between adjust grooves and (iii) generally circumferential edges at the intersections of each land region with the adjacent grooves and passing the grooved outer cylindrical surface through a melt pool to extract a layer of the metal melt having upper and lower surfaces onto the grooved outer surface, wherein the lower surface of the metal layer directly contacts the land regions and substantially spans the grooves between the land regions and wherein the upper surface of the metal layer is unconfirmed and directly exposed to atmosphere; and withdrawing heat from the melt layer through the grooved surface to progressively solidify the melt layer from the grooved surface to the upper surface of the melt layer.
rotating a chill wheel comprising an outer cylindrical surface having (i) axially-spaced, substantially circumferentially extending grooves with a groove density of at least about 8 grooves per centimeter (ii) substantially cylindrical flat land regions between adjust grooves and (iii) generally circumferential edges at the intersections of each land region with the adjacent grooves and passing the grooved outer cylindrical surface through a melt pool to extract a layer of the metal melt having upper and lower surfaces onto the grooved outer surface, wherein the lower surface of the metal layer directly contacts the land regions and substantially spans the grooves between the land regions and wherein the upper surface of the metal layer is unconfirmed and directly exposed to atmosphere; and withdrawing heat from the melt layer through the grooved surface to progressively solidify the melt layer from the grooved surface to the upper surface of the melt layer.
2. The method of claim 1, wherein:
the metal pool is held in an open tundish having one wall defined by the outer cylindrical surface of the chill wheel, and the chill wheel is rotated in a direction to move the outer cylindrical surface upwardly through and out of the melt.
the metal pool is held in an open tundish having one wall defined by the outer cylindrical surface of the chill wheel, and the chill wheel is rotated in a direction to move the outer cylindrical surface upwardly through and out of the melt.
3. The method of claim 2, wherein the metal melt layer is cast at such a speed and delivering rate that a crystalline metal strip of thickness greater than about 0.25 millimeters is formed.
4. The method of claim 3, wherein the land regions have an average width of about 0.025-1.00 millimeters.
5. The method of claim 4, wherein a ratio of average groove width to average land region width is between 0.5 and 1.5.
6. The method of claim 4, wherein the grooves have an average depth of from about 0.025 to about 0.25 millimeters.
7. The method of claim 3, wherein the chill wheel is rotated at a peripheral speed of about 100-1000 cm/sec, the grooves have an average depth of about 0.025-0.25 millimeters and the land regions have an average width of less than abut 0.635 millimeters.
8. The method of claim 7, wherein the land regions have an average width of between about 0.025 and 0.635 millimeters.
9. The method of claim 2, wherein the contact length and thickness of the metal melt layer on the outer cylindrical surface are controlled by means of at least one weir for regulating the melt level of a section in the tundish where the melt is extracted from the melt pool.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US78678985A | 1985-10-11 | 1985-10-11 | |
| US786,789 | 1985-10-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1290547C true CA1290547C (en) | 1991-10-15 |
Family
ID=25139600
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000520270A Expired - Fee Related CA1290547C (en) | 1985-10-11 | 1986-10-10 | Direct strip casting on grooved wheels |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0243453B1 (en) |
| JP (1) | JP2632824B2 (en) |
| CA (1) | CA1290547C (en) |
| DE (1) | DE3672827D1 (en) |
| WO (1) | WO1987002284A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3721510A1 (en) * | 1987-06-30 | 1989-01-19 | Fink Gerdinand | Apparatus and method for the strip casting of steel |
| US4819712A (en) * | 1987-09-28 | 1989-04-11 | Battelle Development Corporation | Method and apparatus for continuous casting of molten metal |
| US4793400A (en) * | 1987-11-24 | 1988-12-27 | Battelle Development Corporation | Double brushing of grooved casting wheels |
| US5179996A (en) * | 1989-11-23 | 1993-01-19 | Usinor Sacilor | Process and device for continuous casting on a roll or between two rolls |
| FR2654659B1 (en) * | 1989-11-23 | 1992-02-07 | Siderurgie Fse Inst Rech | METHOD AND DEVICE FOR CONTINUOUS CASTING ON OR BETWEEN TWO CYLINDERS. |
| FR2681543B1 (en) * | 1991-09-25 | 1993-11-05 | Pechiney Rhenalu | PROCESS FOR OBTAINING A THIN STRIP OF REGULAR THICKNESS IN A CAST ON CYLINDER. |
| AU2008100847A4 (en) | 2007-10-12 | 2008-10-09 | Bluescope Steel Limited | Method of forming textured casting rolls with diamond engraving |
| EP2982460A1 (en) * | 2014-08-07 | 2016-02-10 | Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. | Apparatus and method of manufacturing metallic or inorganic strands having a thickness in the micron range by melt spinning |
| US20170326629A1 (en) * | 2016-05-16 | 2017-11-16 | Golden Aluminum, Inc. | System and method for adjusting continuous casting components |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1364717A (en) * | 1963-05-14 | 1964-06-26 | Duralumin | Method and machine for casting allowing the improvement of the surface condition and blanks obtained by this method |
| AT346001B (en) * | 1977-01-12 | 1978-10-25 | Inst Elektroswarki Patona | THROUGH FILLER |
| US4250950A (en) * | 1978-11-03 | 1981-02-17 | Swiss Aluminium Ltd. | Mould with roughened surface for casting metals |
-
1986
- 1986-10-06 WO PCT/US1986/002125 patent/WO1987002284A1/en not_active Ceased
- 1986-10-06 DE DE8686906575T patent/DE3672827D1/en not_active Expired - Lifetime
- 1986-10-06 JP JP61505718A patent/JP2632824B2/en not_active Expired - Lifetime
- 1986-10-06 EP EP19860906575 patent/EP0243453B1/en not_active Expired
- 1986-10-10 CA CA000520270A patent/CA1290547C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DE3672827D1 (en) | 1990-08-23 |
| JP2632824B2 (en) | 1997-07-23 |
| EP0243453B1 (en) | 1990-07-18 |
| WO1987002284A1 (en) | 1987-04-23 |
| JPS63501062A (en) | 1988-04-21 |
| EP0243453A1 (en) | 1987-11-04 |
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