RU2451566C2 - Cast band with low surface roughness, method and device for its production - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: thin cast band has, at least, one microstructure selected from the group including polygonal ferrite, acicular ferrite, Widmanstatten pattern, bainite and martensite. Proposed method comprises forming the band in clearance between casting rolls, applying mix of water and oil on hot rolling stand rolls, passing thin cast band at temperature below 1100°C through hot rolling stand from said rolls through entire stand in atmosphere with oxygen content lower than 5%.

EFFECT: surface roughness under 1,5 mcm and scale thickness under 10 mcm, reduced rack formation.

28 cl, 5 dwg

Description

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to cast tape manufactured on a twin roll casting machine, to a method and apparatus for manufacturing such a cast tape.

In a two-roll casting machine, molten metal is introduced between two horizontal casting rolls that rotate in opposite directions, which are cooled so that the metal crusts harden on the surfaces of the moving rolls that come together to form a gap between them and to obtain a product in the form of a hardened tape fed down from clearance between casting rolls.

The term “gap” as used herein refers to a common area in which the casting rolls are closest to each other. The molten metal can be cast from the ladle through a metal supply system including a casting device and a central nozzle located above the compression gap to form a molten metal casting bath supported on the casting surfaces of the rolls above the gap and elongated along the length of the gap. This casting bath is usually limited between the refractory side plates or baffles held in sliding connection with the end surfaces of the rolls to limit the two edges of the casting bath.

Cast steel tape, located in a twin roll casting machine, is removed from the gap at a very high temperature of about 1400 ° C or higher. If it is exposed to a normal atmosphere, it will form very quickly scale due to oxidation at such high temperatures. Therefore, it is planned to create a sealed casing under the casting rolls for receiving the hot tape through which the tape passes on the way from the casting machine, while the sealed casing contains an atmosphere that prevents the oxidation of the tape. An oxidation inhibiting atmosphere can be created by injecting a non-oxidizing gas, such as an inert gas such as argon or nitrogen, or exhaust gases from combustion, which can be reducing gases. Alternatively, the casing may be sealed against oxygen-containing atmosphere during operation of the casting machine. The oxygen content in the atmosphere inside the casing is then lowered during the initial casting phase due to the oxidation of the tape removing oxygen from the sealed casing, as disclosed in US Pat. Nos. 5,762,126 and 5,959,608.

It is known to hot roll cast tape produced on a twin roll casting machine in a hot rolling mill after the tape leaves the casting machine to form a thin tape. It is generally understood that a combination of a rolling mill and a two-roll casting machine is necessary for the manufacture of a tape with a given cross-sectional profile.

However, as it turned out, if the tape is cast at a standard casting speed of 80 m / min and then hot rolled in a hot rolling mill with a 16% compression in a hot rolling mill, a relatively high surface roughness of 6 to 8 microns Ra with surface microcracks. Figure 1 is a photomicrograph showing a typical surface roughness of such a cast and hot rolled strip exiting from a hot rolling mill and from a twin roll casting machine. In the direction of rolling from left to right, micrographs show a clear influx on the surface of the tape (20-30 microns). The cause or reasons for this surface roughness may be a shift on the surface of the tape caused by welding of the tape to the surface of the work roll of the rolling mill, imprinting of the surface texture of the work roll on the surface of the tape and / or other factors. Moreover, microcracks on the surface of the cast tape proved to be a problem. It is possible to reduce microcracks by reducing the casting speed and heating rate of the tape, but it is economically inefficient to implement these conditions during tape production.

The microstructure of the products in the form of a hot rolled strip is essentially 100% equiaxed grain ferrite. However, in the manufacture of cast tape on a twin roll casting machine, previous experience was that the microstructure is a large grain of polygonal ferrite, needle ferrite and Widmannstätt structure. Typically, the microstructure was 30–60% of polygonal ferrite and 70–40% of the Widmannstätt structure and needle-like ferrite. With such a microstructure, the typical surface roughness was 4–7 microns Ra (average).

A thin cast tape having at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstett structure, bainite and martensite, with a surface roughness of less than 1.5 microns Ra (average) and a scale thickness of less than 10 microns, was carried out through steps including:

a) preparing a twin roll casting machine having laterally arranged casting rolls forming a gap between each other, and a hot rolling mill having work rolls and backup rolls adjacent to the twin roll casting machine,

b) forming a thin cast tape in the gap between the casting rolls of a twin roll casting machine,

c) applying a mixture of water and oil on the work rolls of the hot rolling mill,

d) passing a thin cast tape at a temperature of less than 1100 ° C through a hot rolling mill while applying a mixture of oil and water on the work rolls,

e) conducting a thin cast tape from the rolls through a hot rolling mill in an atmosphere with less than 5% oxygen to form a cast tape having at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstätt structure, bainite and martensite, the surface roughness is less than 1.5 microns Ra (on average) and the scale thickness is less than about 10 microns.

Thin cast steel tape is also provided with reduced surface roughness below 1.5 microns Ra through steps including:

a) preparing a casting machine for manufacturing tapes having two casting rolls and a gap between them;

b) preparing a metal supply system capable of forming a casting bath between the casting rolls above the compression gap with side barrier walls at the ends of the gap to limit the casting bath;

c) preparing a hot rolling mill next to a casting machine for manufacturing tapes having work rolls with work surfaces defining a gap therebetween, through which the tape is rolled;

d) preparing spray nozzles located adjacent to the work rolls and capable of delivering a mixture of water and oil to the work rolls;

e) introducing molten steel between the two casting rolls to form a casting bath supported on the surfaces of the casting rolls and limited by the indicated first side barrier walls;

f) rotation in the opposite direction of the casting rolls to form cured metal crusts on the surfaces of the rolls and cast steel tape in the gap between the rolls of these crusts;

g) spraying a mixture of oil and water when the tape enters the hot rolling mill;

h) rolling the cast tape between the work rolls of the hot rolling mill to produce a cast tape having a surface roughness of less than 1 micron Ra.

Thin cast steel tape with a reduced surface roughness of less than 1.5 microns Ra is also manufactured at stages including:

a) preparing a casting machine for manufacturing tapes having casting rolls and a gap between them;

b) preparing a system for supplying metal capable of forming a casting bath between the rolls above the gap with lateral barrier walls next to the ends of the gap to limit said casting bath;

c) preparing, next to the casting machine, for casting the tapes of a hot rolling mill having support rolls and work rolls with work surfaces, forming a gap between them, through which the hot tape is rolled;

d) preparing spray nozzles located upstream of the work rolls and capable of spraying a mixture of water and oil on the backup rolls;

e) introducing molten steel between the two casting rolls to form a casting bath supported on the surfaces of the casting rolls and limited by the indicated first side barrier walls;

f) rotation in the opposite direction of the casting rolls to form cured metal crusts on the surfaces of the casting rolls and cast steel tape in the gap between the casting rolls of crusts;

g) spraying a mixture of oil and water when the cast tape enters the hot rolling mill;

h) rolling the cast tape between the work rolls of the hot rolling mill to produce a cast tape having a surface roughness of less than 1.5 microns Ra.

A thin cast tape may have a surface roughness of less than 1.0 microns Ra, or less than 0.7 microns Ra, or less than 0.5 microns Ra, or less than 0.4 microns Ra.

A thin cast tape may have a scale thickness of less than 7 microns or less than 4 microns.

Cast tape can be passed through a hot rolling mill at a temperature of less than 1050 ° C while applying a mixture of oil and water on the work rolls.

A thin cast tape may have a scale thickness of less than 7 microns or less than 4 microns.

A mixture of oil and water can be sprayed onto work rolls.

A mixture of oil and water can be applied to the backup rolls.

A mixture of oil and water may be from less than 5% oil to form a thin cast tape with a low surface roughness of less than 1.5 microns Ra.

A method for manufacturing a thin cast tape having at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstett structure, bainite and martensite, a surface roughness of less than 1.5 microns Ra and a scale thickness of less than about 10 microns, and The method includes the steps of:

a) preparing a two-roll casting machine having laterally arranged casting rolls forming a gap between each other, and a hot rolling mill having work rolls and backup rolls near the two-roll casting machine,

b) forming a thin cast tape in the gap between the rolls of a two-roll casting machine,

c) applying a mixture of water and oil on the work rolls of the hot rolling mill,

d) passing a thin cast tape at a temperature of less than 1100 ° C through a hot rolling mill while applying a mixture of oil and water on the work rolls,

e) conducting a thin tape from the casting rolls through a hot rolling mill in an atmosphere with less than 5% oxygen to form a thin cast tape having: at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstett structure, bainite and martensite, surface roughness less than 1.5 microns Ra and scale thickness less than 10 microns.

There is also a method of manufacturing a thin cast steel strip with a reduced surface roughness below 1.5 microns Ra, the method includes the steps of:

a) preparing a casting machine for casting tapes having two casting rolls with a gap between them;

b) preparing a system for supplying metal capable of forming a casting bath between the casting rolls above the gap with lateral barrier walls at the ends of the gap to limit said casting bath;

c) preparing, in the vicinity of the casting machine for manufacturing a strip of a hot rolling mill, having work rolls with work surfaces defining a gap therebetween in which the hot tape is rolled;

d) preparing spray nozzles adjacent to the work rolls and capable of delivering a mixture of water and oil to the work rolls;

e) introducing molten steel between the two casting rolls to form a casting bath supported on the surfaces of the casting rolls and bounded by said first side barrier walls;

f) rotation of the casting rolls in the opposite direction for the formation of cured metal crusts on the surfaces of the casting rolls and cast steel tape in the gap between the rolls of these crusts;

g) spraying a mixture of oil and water when the tape enters the hot rolling mill;

h) rolling the cast tape between the work rolls of the hot rolling mill to produce a cast tape having a surface roughness of less than 1 micron Ra.

A method for manufacturing a thin cast steel sheet with reduced surface roughness below 1.5 microns Ra is also provided, the method comprising the steps of:

a) preparing a casting machine for the manufacture of tapes having two casting rolls forming a gap between themselves;

b) preparing a system for supplying metal capable of forming a casting bath between the casting rolls above the gap with lateral barrier walls near the ends of the gap to limit said casting bath;

c) preparing, next to the casting machine, for manufacturing a tape of a hot rolling mill having support rolls and work rolls with work surfaces defining a gap therebetween, through which the hot tape is rolled;

d) preparing spray nozzles located upstream of the work rolls and capable of spraying a mixture of water and oil on the backup rolls;

e) introducing molten steel between the two casting rolls to form a casting bath supported on the casting surfaces of the casting rolls and limited by the indicated first side barrier walls;

f) rotation in the opposite direction of the casting rolls to form curable metal crusts on the surfaces of the casting rolls and cast steel tape in the gap between the casting rolls of crusts;

g) spraying a mixture of oil and water when the cast tape enters the hot rolling mill;

h) rolling the cast tape between the work rolls of the hot rolling mill to produce a tape having a surface roughness of less than 1.5 microns Ra.

The method may include applying a mixture of oil and water by spraying it onto work rolls, for example, spray nozzles.

The nozzle spray rate can be between 10 and 30 gallons (1 gallon = 3.785 L) per minute.

A mixture of oil and water can be applied to the work rolls by applying it to the backup rolls.

The method may include the manufacture of cast tape at a speed above 80 meters per minute.

The rolling temperature may be below 1100 ° C, or below 1050 ° C, or below 900 ° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The operation of the shown two-roll foundry machine in accordance with the present invention is described with reference to the attached drawings, on which:

figure 1 is a photomicrograph showing a typical surface roughness of a cast tape after hot rolling;

FIG. 2 is a schematic illustration of an installation for casting a thin tape having a hot rolling mill for controlling the shape of the cast tape; FIG.

FIG. 3 is an enlarged cross-sectional side view of the foundry machine of the thin strip casting machine shown in FIG. 2;

4 is a block diagram showing a system for applying a mixture of oil and water on the rolls of a hot rolling mill;

5 is a graph of the average surface roughness for a thin cast steel strip for a series of swimming trunks 2613 made using the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The casting and rolling installation shown includes a twin roll casting machine, designated as a whole, 11, which makes a thin cast steel strip 12, which passes along the line through the guide table 13 to the stand 14 with pulling rollers. After exiting the stand 14 with pulling rollers, a thin cast tape 12 enters the hot stand rolling mill 15 and passes through the stand 15, which includes support rolls 16 and the upper and lower work rolls 16A and 16B, while the thickness of the tape decreases. The tape 12 after leaving the rolling stand 15 enters the discharge roller 17, where it can be forcedly cooled by water jets 18 and then pass through the stand 20 with pulling rollers, including two pulling rollers 20A, to the winding device 19.

The twin roll casting machine 11 includes a main frame of the machine that supports two laterally arranged casting rolls 22 having casting surfaces 22A and forming a gap between them. During the casting period, the molten metal is supplied from a ladle (not shown) to the casting device 23, through a refractory cup to a removable intermediate casting device 25 (also called distribution tank or adapter) and then through a metal supply nozzle 28 (also called a core nozzle) - between the injection rolls 22 above the compression gap.

The molten steel is introduced into the removable intermediate casting device 25 from the casting device 23 through the outlet of the refractory cup. The casting device 23 is provided with a locking rod and a slide gate (not shown) for selectively opening or closing the nozzle outlet and for efficiently controlling the flow of molten metal from the casting device 23 to the casting machine. The molten metal flows from the removable intermediate casting device 25 through the outlet and possibly, but not necessarily, into the feed nozzle 28 and through the feed nozzle 28.

The molten metal thus supplied to the casting rolls 22 forms a casting bath above the gap supported by the surfaces of the casting rolls 22A. This casting tub is bounded at the ends of the rolls by two side barrier walls or plates which are applied to the ends of the rolls by two pushers (not shown) including hydraulic cylindrical devices connected to the side barrier walls. The upper surface of the casting bath (usually called the meniscus level) may rise above the lower end of the feed nozzle 28 so that the lower end of the feed nozzle is immersed in the bath.

The casting rolls 22 are internally cooled by the supplied water from a tank (not shown) and rotated in the opposite direction by drive devices (not shown) so that the metal crusts solidify on the moving surfaces of the casting rolls and come together at the gap to make a thin cast tape 12, which is fed down from the gap between the casting rolls.

Under the twin roll casting machine 11, the cast steel strip 12 extends inside the sealed casing 10 to the guide table, which guides the tape to the stand 14 with pulling rollers, through which it is removed from the sealed casing 10. The sealing of the casing 10 may not be complete, but sufficient to provide control atmosphere and oxygen access to the cast tape inside the casing 10, as will be described below. After exiting the pressurized casing 10, the tape can be passed through other pressurized casings after the stand 14 with pulling rollers, including stand 15 for hot rolling.

The casing 10 is formed by several separate wall sections that are joined together in various sealing joints to form a continuous casing wall. These sections include a first wall section 41 near the twin roll casting machine for enclosing the casting rolls 22 and a wall covering section 42 extending downwardly under the first wall section 41 to form an opening that is sealed to the upper edges of the waste box 40. The seal 43 between the box 40 for metal waste and the wall 42 of the casing may be formed in the form of a seal of the type "knife and sand" around the hole in the wall 42 of the casing, which can be created and broken when the vertical movement of the box 40 for metal waste relative to the wall 42 of the casing. A seal 43 is formed by raising the metal waste box 40 so that the blade flange penetrates the sand grooves to create such a seal.

This seal 43 may be broken by lowering the metal waste box 40 from its operating position to prepare for movement from the casting machine to the position for unloading metal waste (not shown). The metal waste box 40 is mounted on a carriage 45 provided with wheels 46 that roll along the rails 47, while the metal waste box can be moved to a position for unloading the metal waste. The carriage 45 is equipped with a set of motor screw jacks 51, which serve to lift the box 40 for metal waste from the lowered position, where it is removed from the wall 42 of the casing, to an elevated position where the knife flange penetrates the sand to form a seal 43 between the two parts.

The sealed casing 10 may also have a third wall section 61 located near the guide table 13 and connected to the frame of the stand 14 with pulling rollers, which includes two pulling rollers 50. The third wall section 61 of the casing 10 is sealed by means of sliding seals.

Most wall sections 41, 42, and 61 of the casing may be provided with refractory bricks from the inside. The waste box 40 can also be lined internally with refractory bricks or refractory lining. Thus, the entire casing 10 is sealed before the casting operation, thereby restricting oxygen access to the thin cast tape 12 when it passes from the casting rolls 22 through the stand 14 with pulling rollers and stand 15 for hot rolling. Initially, the tape can absorb all the oxygen in the space of the casing 10, forming a thick scale on the original section of the tape. However, the tightness of the casing 10 limits the access of oxygen to it from the surrounding atmosphere to a value that is lower than the amount of oxygen that can be absorbed by the tape. Thus, after the initial start-up period, the oxygen content in the casing 10 will remain reduced, thereby limiting the availability of oxygen for oxidation of the tape 12. Thus, the formation of scale is suppressed to a thickness of less than 10 microns without the need to continuously supply reducing or non-oxidizing gas to the casing. Of course, reducing or non-oxidizing gas can be supplied through the walls of the casing. However, in order to avoid thick scale during the start-up period, the casing 10 can be cleaned by blowing just before the start of casting, in order to reduce the initial oxygen level in it, thereby reducing the time interval for stabilizing the oxygen level in the casing as a result of the interaction of oxygen during oxidation of the tape passing through the casing. Thus, as an example, the casing may conveniently be cleaned, for example, with nitrogen gas. It turned out that a decrease in the initial oxygen content to levels of 5% will limit the formation of scale on the tape at the exit from the casing 10 to about 10-17 microns even during the initial phase of launch. In an embodiment of the present invention, a thin cast steel strip has a scale thickness of less than about 10 microns, or a scale thickness of less than 7 or 4 microns during continuous casting.

At the start of foundry operations, an imperfect tape of short length is made when stabilization of the casting conditions occurs. After the continuous casting is stabilized, the casting rolls 22 are slightly moved apart from each other and then shifted again to break off this front end of the tape in the manner described in Australian Patent 646981 and US Pat. No. 5,287,912 to form a clean front end of the subsequent thin cast tape 12. Poor quality the material falls into a metal waste box 40 located underneath the casting machine 11, and at this time a swivel apron 38, which usually hangs down from the hinge 39 to one side of the casting machine, as shown in FIG. 3, rotates across the outlet of the casting machine to direct the clean end of the thin cast tape 12 to the guide table 13, where the sheet is fed to the stand 14 with pulling rollers. The apron 38 is then retracted back into its overhanging position, as shown in FIG. 3, which allows the tape 12 to pass through the loop 36 under the injection molding machine, as shown in FIGS. 2 and 3, before it enters the guide table 13. The guide table 13 includes a series of support rollers 37 for supporting the belt before it enters stand 14 with pulling rollers. The rollers 37 are arranged in the form of an ordered structure extending from stand 14 with pulling rollers in the opposite direction under the casting machine and bending downward to smoothly receive the tape and direct it from the loop 36.

A twin roll casting machine may be of the kind shown and described in detail in US Pat. Nos. 5,184,668 and 5,277,243 or in US Pat. No. 5,488,988. Reference may be made to these patents for structural details that are not part of the present invention.

The cage 14 with the pulling rollers includes two pulling rollers 50, responsive to the interference exerted by the cage 15 for hot rolling. Therefore, the tape is able to hang in the form of a loop 36 when it passes from the casting rolls 22 to the guide table 13 and into the cage 14 with pulling rollers. The pull rollers 50 thus provide an interference barrier between the loosely hanging loop and the interference of the belt downstream in the processing line. The pulling rollers 50 also stabilize the position of the tape on the feed table 13, which feeds the tape into the stand 15 for hot rolling.

From the stand 14 with pulling rollers, a thin cast tape 12 is supplied to the stand 15 for hot rolling, including the upper work roll 16A and the lower work roll 16B. As shown in FIG. 4, a preferred embodiment of the present invention includes spraying a mixture of water and oil on the surface of the support rolls 16 downstream. The oil tank 100 is equipped with a heater 101 to maintain the oil at a temperature of approximately 50 ° C, but its heating is optional. The heated oil is transported along the oil supply lines 103 by pumps 102 with constant capacity to the static mixers 104, where the heated oil is mixed with water.

Water is supplied from the source 110 to the water collectors 111 for cooling the belt and in line 112 for supplying water to the rolls of the rolling mill. The first part of the water is supplied to the collectors 18 for spraying cooling water to cool the hot strip 12 after it leaves the stand 15 for hot rolling. Typically, water pressure is reduced by a pressure regulator 113 to approximately 40 psi. About 10 to 30 gallons per minute of water is supplied to each static mixer 104, in which water is mixed with about 4 gallons per hour of heated oil.

The mixture of oil and water is then applied to the surface of the support rolls 16 downstream (in the direction of movement of the thin cast steel tape 12, shown by arrow 120) by means of oil-water nozzles 71. Alternatively, the mixture of oil and water can be applied to the cast tape 12 in the area of capture by the rolls , can be applied on the surface of the backup rolls 16 downstream or on the work rolls 16A, 16B.

Preferably, the temperature of the thin cast steel strip 12 in the hot rolling stand 15 is less than 1100 ° C., more preferably less than 1050 ° C., and most preferably less than 900 ° C. It is also preferred that the temperature of the thin cast steel strip in the hot rolling stand 15 be higher than 400 ° C.

Static mixers 104 are standard conventional commercially available devices. Other types of mixers may be used provided they are capable of mixing oil and water well.

In one embodiment, the oil and water mixture is supplied at a flow rate of 5-30 gallons per minute at 40 psi to the backup rolls 16. Typically, the oil and water mixture is supplied to the backup rolls at this embodiment at a flow rate of about 10-20 gallons per minute, with 15 gallons per minute is a suitable value. A mixture of oil and water may include less than 5% of the oil, and in one embodiment, it comprises 4 parts of oil per 600-1800 parts by volume of water. Oils may be less than 2 or 1% of the mixture. The oil is supplied for mixing with water, typically at a rate of less than 15 gallons per minute.

Figure 5 shows the average surface roughness (Ra) in microns for a thin cast steel strip 12 made using the present invention. As can be seen in figure 5, the average surface roughness is noticeably lower than about 0.66 - about 1.5 microns when adding a mixture of oil and water, as described above.

In one embodiment, the present invention includes the manufacture of a thin cast steel strip using the mixture of oil and water described above to produce a thin cast steel tape at a speed of more than 80 meters per minute.

Although the invention has been described with reference to some embodiments, those skilled in the art will appreciate that various changes and substitutions by equivalents can be made without departing from the scope of the present invention. In addition, many modifications can be made to adapt a particular situation or material to the present invention without departing from its scope. Therefore, it is understood that the invention is not limited to the specific embodiments disclosed, but that it will include all embodiments falling within the scope of the appended claims.

Claims (28)

1. A thin cast tape having at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstett structure, bainite and martensite, the average surface roughness is less than 1.5 microns and the scale thickness is less than 10 microns, and made by stages including:
a) preparing a twin roll casting machine having laterally arranged casting rolls forming a gap between each other and a hot rolling mill having work rolls and backup rolls next to the twin roll casting machine,
b) forming a thin cast tape in the gap between the casting rolls of a twin roll casting machine,
c) applying a mixture of water and oil on the work rolls of the hot rolling mill,
d) passing a thin cast tape at a temperature of less than 1100 ° C through a hot rolling mill while applying a mixture of oil and water on the work rolls, and
e) conducting a thin cast tape from the casting rolls through a hot rolling mill in an atmosphere with less than 5% oxygen when forming a thin cast tape having: at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstett structure, bainite and martensite, the surface roughness is less than 1.5 microns on average and the scale thickness is less than 10 microns. 2. The tape according to claim 1, while the tape is passed through a hot rolling mill at a temperature of less than 1050 ° C while applying a mixture of oil and water on the work rolls. 3. The tape according to claim 1 or 2, in which the average surface roughness is less than 1.0 microns. 4. The tape according to claim 3, in which the average surface roughness is less than 0.7 microns. 5. The tape according to claim 4, in which the average surface roughness is less than 0.5 microns. 6. The tape according to claim 1, in which the thickness of the scale is less than 7 microns. 7. The tape according to claim 6, in which the thickness of the scale is less than 4 microns. 8. The tape according to claim 1, wherein the mixture of oil and water is sprayed onto work rolls. 9. The tape according to claim 1, wherein the mixture of oil and water is applied to the work rolls by feeding this mixture of oil and water to the backup rolls. 10. The tape according to claim 1, wherein the mixture of oil and water contains less than 5% oil, while the tape has a low surface roughness of less than 1.5 microns. 11. A thin cast steel strip with a reduced average surface roughness of less than 1.5 microns, made in stages including:
a) preparing a casting machine for the manufacture of tapes having two casting rolls with a gap between them,
b) preparing a metal feed system capable of forming a casting bath between the casting rolls above the gap with side barrier walls at the ends of the gap to limit said casting bath,
c) preparing, next to the injection molding machine, a hot rolling mill strip having work rolls with work surfaces defining a gap therebetween in which the hot tape is rolled,
d) preparing spray nozzles adjacent to the work rolls and capable of delivering a mixture of water and oil to the work rolls,
e) introducing molten steel between the two casting rolls to form a casting bath supported on the surfaces of the casting rolls and limited by said side barrier walls,
f) rotation in the opposite direction of the casting rolls to form cured metal crusts on the surfaces of the rolls and cast steel tape in the gap between the casting rolls of these crusts,
g) spraying a mixture of oil and water when the tape enters the hot rolling mill and
h) rolling the cast tape between the work rolls of the hot rolling mill to produce a cast tape having an average surface roughness of less than 1.5 microns. 12. The tape according to claim 11, produced at a speed of 80 m cast tape per minute. 13. The tape according to claim 11, while the rolling temperature is less than 900 ° C. 14. The tape according to claim 11, wherein the spraying speed of the nozzles is from 10 to 30 gallons per minute. 15. The tape according to claim 11, in which the average surface roughness is less than 0.7 microns. 16. The tape according to clause 15, in which the average surface roughness is less than 0.4 microns. 17. Thin cast steel tape with an average surface roughness of less than 1.5 microns, made in stages, including:
a) preparing a casting machine for casting sheets having two casting rolls with a gap between them,
b) preparing a metal feed system capable of forming a casting bath between the casting rolls above the gap with side barrier walls at the ends of the gap to limit said casting bath,
c) preparing, next to the casting machine, a strip for casting a hot rolling mill having support rolls and work rolls with work surfaces defining a gap between the work rolls through which the hot tape is rolled,
d) preparing spray nozzles located upstream of the work rolls and capable of spraying a mixture of water and oil on the backup rolls,
e) introducing molten steel between the two casting rolls to form a casting bath supported on the surfaces of the casting rolls and limited by the indicated first side barrier walls,
f) rotation in the opposite direction of the casting rolls to form cured metal crusts on the surfaces of the casting rolls and cast steel tape in the gap between the casting rolls of crusts,
g) spraying a mixture of oil and water when the cast tape enters the hot rolling mill and
h) rolling the cast tape between the work rolls of the hot rolling mill to produce a cast tape having an average surface roughness of less than 1.5 microns. 18. The tape according to claim 17, wherein the production speed of the cast tape is more than 80 m per minute. 19. The tape according to claim 17, wherein the rolling temperature is below 1100 ° C. 20. The tape according to claim 17, wherein the rolling temperature is below 1050 ° C. 21. The tape according to claim 20, while the rolling temperature is below 900 ° C. 22. The tape according to claim 17, wherein the spraying speed of the nozzles is from 10 to 30 gallons per minute. 23. The tape according to 17, in which the surface roughness is on average less than 0.7 microns. 24. The tape according to claim 17, wherein the mixture of oil and water contains less than 5% oil. 25. The tape according to 17, in which the thickness of the scale on the surface is less than about 7 microns. 26. A method of manufacturing a thin steel strip having at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstett structure, bainite and martensite, the average surface roughness is less than 1.5 microns and the thickness of the scale is less than 10 microns, including :
a) preparing a twin roll casting machine having laterally arranged casting rolls forming a gap between each other and a hot rolling mill having work rolls and backup rolls next to the twin roll casting machine,
b) forming a thin cast tape in the gap between the casting rolls of a twin roll casting machine,
c) applying a mixture of water and oil on the work rolls of the hot rolling mill,
d) passing a thin cast tape at a temperature of less than 1100 ° C through a hot rolling mill while applying a mixture of oil and water on the work rolls and
e) passing a thin cast tape from the casting rolls and through a hot rolling mill in an atmosphere with less than 5% oxygen when forming a thin cast tape having at least one microstructure selected from the group consisting of polygonal ferrite, needle ferrite, Widmannstett structure, bainite and martensite, the average surface roughness is less than 1.5 microns and the scale thickness is less than 10 microns. 27. A method of manufacturing a thin cast steel strip with a reduced average surface roughness of less than 1.5 microns, including:
a) preparing a casting machine for the manufacture of tapes having two casting rolls with a gap between them,
b) preparing a system for supplying metal capable of forming a casting bath between the casting rolls above the gap with side blocking walls adjacent to the ends of the gap to limit said casting bath,
c) preparing, in the vicinity of the casting machine for the manufacture of tapes, a hot rolling mill having work rolls with work surfaces defining a gap therebetween in which the hot tape is rolled,
d) the preparation of spray nozzles located next to the work rolls with the possibility of feeding a mixture of water and oil on the work rolls,
e) introducing molten steel between the two casting rolls to form a casting bath supported on the surfaces of the casting rolls and limited by said barrier walls,
f) rotation in the opposite direction of the casting rolls to form cured metal crusts on the surfaces of the rolls and cast steel tape in the gap between the casting rolls of these crusts,
g) spraying a mixture of oil and water when the tape enters the hot rolling mill and
h) rolling the cast tape between the work rolls of the hot rolling mill to produce a cast tape having an average surface roughness of less than 1 micron. 28. A method of manufacturing a thin cast steel strip with an average surface roughness of less than 1.5 microns, including:
a) preparing a casting machine for the manufacture of tapes having two casting rolls with a gap between them,
b) preparing a metal feed system capable of forming a casting bath between the casting rolls above the gap with side barrier walls at the ends of the gap to limit said casting bath,
c) preparing, next to the casting machine for the manufacture of tapes, a hot rolling mill having support rolls and work rolls with work surfaces defining a gap between the work rolls through which the hot tape is rolled,
d) preparation of spray nozzles located upstream of the work rolls with the possibility of spraying a mixture of water and oil on the backup rolls,
e) introducing molten steel between the two casting rolls to form a casting bath supported on the surfaces of the casting rolls and limited by said side barrier walls,
f) rotation in the opposite direction of the casting rolls to form cured metal crusts on the surfaces of the casting rolls and cast steel tape from these crusts in the gap between the casting rolls,
g) spraying a mixture of oil and water when the cast tape enters the hot rolling mill and
h) rolling the cast tape between the work rolls of the hot rolling mill to produce a cast tape having an average surface roughness of less than 1.5 microns.

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