Technical Field

The present invention relates to a rotary device for treating molten metal. In particular, the present invention relates to a rotary device for removing unwanted impurities from molten metal, such as dissolved gas and solid inclusions.

Background

For casting applications (in particular casting of non-ferrous metals such as aluminium or aluminium alloy), the molten metal must be treated before casting - typically by one or more of the following processes: i) Degassing and inclusion removal - The presence of dissolved gas in molten metal can introduce defects in the solidified product and may detrimentally affect its mechanical properties. Hydrogen has a high solubility in liquid aluminium which increases with melt temperature, but its solubility in solid aluminium is very low which can lead to gas pores in the solidified casting. Gas may also diffuse into voids and discontinuities (e.g. oxide inclusions) resulting in pores or blister formation during the production of castings or other products made from aluminium or aluminium alloys. ii) Grain refinement - The mechanical properties of the casting can be improved by controlling the grain size of the solidifying metal. iii) Modification - The microstructure and properties of metal alloys can be improved by the addition of small quantities of certain ‘modifying’ elements such as sodium or strontium. Modification increases hot tear resistance and improves alloy feeding characteristics, decreasing shrinkage porosity. iv) Cleaning and alkali removal - Significant concentration of alkali elements can have an adverse effect on alloy properties, and so these alkali elements need to be removed or reduced. The above treatment processes may be carried out individually or simultaneously by a variety of methods and equipment.

Degassing of molten metal is typically conducted using a rotary degassing unit, which flushes the molten metal with fine bubbles of a dry gas. The gas can be inert, such as argon or nitrogen, or reactive, such as chlorine or hydrogen or may be mixtures thereof. The rotary degassing unit typically comprises a hollow shaft to which a rotor is attached. In use, the shaft and rotor are rotated and gas is passed down the shaft and dispersed into the molten metal via the rotor. As the gas bubbles rise through the melt, hydrogen diffuses into them and is ejected into the atmosphere when the bubbles reach the surface. The rising bubbles also collect solid inclusions and carry them to the top of the melt, where they can be skimmed off. In addition to introducing gas to remove hydrogen (and oxide inclusions), the rotary degassing unit may also be used to inject metal treatment agents into the melt through the shaft together with the inert gas, or through a tube adjacent to the shaft. Examples of rotary devices for use in rotary degassing units are the “XSR rotor” described in W02004/057045, the “FDR rotor” described in W02009/004283, and as described in DE202013102823.

The geometry of the rotors is important, since it has a direct effect on the time needed for the metal treatment to be completed. Existing products have complex configurations and intricate shapes in order to provide desirable metal treatment rates.

Rotors for treating molten metals, such as aluminium, magnesium, copper and relevant alloys have traditionally been manufactured by machining a solid block of graphite into the desired shape. However, machining can be a difficult and costly process and is not well suited to producing intricate shapes - particularly on interior surfaces of the rotor, since line-of-sight access is required for the drilling tool. Machining also limits the selection of materials that the rotor can be made from, since the drilling tool may be unable to bore through more durable or more abrasive ceramic materials. Such machining processes are often relatively expensive and/or slow, with a subsequent effect on unit price.

Rotors for use in molten metal treatments are typically consumable products. The harsh conditions of the molten metal limits the number of times a rotor can be re-used before it needs to be replaced. Extending rotor lifetimes would have cost savings for end users who consume fewer rotors. Longer service periods also minimises downtime due to maintenance and rotor replacement, which has further positive effects on cost and productivity.

The present invention intends to resolve or mitigate one or more of the above problems with respect to rotors for use in molten metal treatments.

Summary of the invention

According to a first aspect of the invention, there is provided a rotor for use in the treatment of molten metal. The rotor may comprise a roof. The roof may have a central axis. The roof may comprise a plurality of peripheral cut-outs. The rotor may comprise an intermediate plate. The intermediate plate may extend axially from the roof. The intermediate plate may comprise a plurality of sides having arcuate portions. The rotor may comprise a plurality of blades extending axially from the intermediate plate. The intermediate plate may be directly adjacent to, and contiguous with, the roof.

In use, the rotor may be oriented such that the roof is above the intermediate plate and blades. It would be understood that the rotor may be used at other angles.

The plurality of sides may delimit the intermediate plate e.g. radially. The arcuate portions of the plurality of sides may be concave. In context, the arcuate portion is concave when the centre of the arcuate portion is closer to the central axis of the rotor (e.g. compared to the ends of the arcuate portion or to a straight side).

The roof and/or the plate may extend radially from the central axis and have a thickness in the axial direction. The roof may be approximately disc-shaped. The roof may be configured to extend radially beyond the ends of the intermediate plate and/or blades, for example, the roof may have a radius (i.e. measured from the axis) greater than or equal to the equivalent dimension of the intermediate plate and/or blades. In some embodiments, the roof may have a radius equal to the radius or length of the intermediate plate and/or blades at their largest point. As would be understood, the radius of the roof is intended to refer to the distance between the axis and the roof’s outermost edge, not the peripheral cut-outs. Where the plate and/or blades have a non-circular cross-section, the term ‘radius’ is intended to mean the distance from the axis to the point on the plate and/or blades which is furthest from the axis. For example, the intermediate plate and/or the blades may extend up to the edge of the roof (i.e. the radially outer edge). In a preferred embodiment, the intermediate plate and the blades have the same radius at their largest point. The roof may have a diameter of 100-300mm, 125-275mm, 150- 250mm, or approximately 200mm. The roof may have a thickness in the axial direction of 20-50mm, 25-45mm, 30-40mm, or approximately 35mm. It will be understood that end points of the ranges herein can be combined in any combination. The roof has a top surface and a bottom surface spaced by its thickness. The top surface of the roof may be flat, or approximately flat. The top surface may be curved or comprise a curved region adjacent to a central shaft. The bottom surface of the roof may be flat.

The plurality of peripheral cut-outs may comprise at least six cut-outs, preferably at least eight cut-outs, preferably at least nine cut-outs. The number of cut-outs is preferably a multiple of the number of blades. The number of cut-outs is preferably at least twice and/or at maximum six times the number of blades. For example, if the rotor comprises three blades, the number of cut-outs is preferably six, nine, twelve, sixteen or eighteen.

The peripheral cut-outs may have an arcuate or semi-circular shape in the horizontal cross-section. The horizontal cross-section means that the plane is parallel to the base or, in other words, the “cutting” plane is perpendicular to the axial direction. The peripheral cut-outs may extend through the thickness of the roof (e.g. axially). The peripheral cut-outs may extend through the entire thickness of the roof. The peripheral cut-outs may be spaced apart around the perimeter of the roof. The peripheral cut-outs may be spaced equally around the roof, or alternatively, clusters of cut-outs may be provided around the roof. In some embodiments, the full circumference of the roof is provided with cut-outs e.g. to provide a scalloped outer surface.

The intermediate plate may be located between the roof and the blades. In such embodiments, the roof may be located between the shaft and the intermediate plate. The intermediate plate may extend directly from the roof. The intermediate plate may be contiguous with the roof. The intermediate plate may extend axially from the roof such that there is no separation or spacing between the roof and the intermediate plate. The roof and the intermediate plate may be integrally formed. The bottom surface of the intermediate plate may be flat. The top surface of the intermediate plate may be totally contiguous with the bottom surface of the roof. The roof and intermediate plate may comprise a central aperture therethrough e.g. for fluid communication with a fluid supply.

In some embodiments, the rotor comprises no radial holes or radial apertures. As used herein, a radial hole or aperture is one which extends through the rotor, for example, by being surrounded or substantially surrounded on all sides by portions of the rotor, and which comprises an opening on a radial outer surface. In particular, the roof and intermediate plate may comprise no radial holes or apertures. The intermediate plate and/or roof may be configured such that there are no radial holes or apertures located between the intermediate plate and roof.

The rotor may comprise a chamber defined by (at least) the intermediate plate and an internal surface of the blades. For example, the chamber may be defined axially by the intermediate plate and radially by an internal surface of the blades. The chamber may be axially delimited by the intermediate plate in one direction and may be open in the opposite direction. For example, the lower surface of the intermediate plate may form the upper surface of the chamber. The chamber may be radially delimited by the blades and may be partially open radially. For example, the blades may be located radially outwards of the chamber e.g. the radially innermost surface of the blades may define the chamber. In some embodiments, the chamber does not extend beyond and/or between the blades. The central aperture may open into the central chamber. The internal surface of at least one of the blades may be curved e.g. to define a nominal cylindrical chamber. The chamber may have a nominal radius of 20 to 60mm, 25 to 55mm, 30 to 50mm, or 35 to 45mm. In context, the nominal radius is measured from the central axis to the internal surface of the blades. The central chamber may have a width or a nominal radius greater than the width or radius of the central aperture. For example, the central chamber may have a nominal radius at least 2 times, 2.5 times, 3 (or greater) times that of the central aperture. The cross-sectional area of the chamber may be greater than the cross- sectional area of the central aperture. In such embodiments, the blades do not extend inwardly as far as the central aperture. Preferably, the rotor comprises a single chamber. As used herein, the chamber is not considered to be a radial hole or aperture since its primary opening is axial and since there is no lower physical bound to the chamber. In one series of embodiments, the intermediate plate comprises three sides connected by three corners or ends. The corners may define a pointed end or edge or alternatively, the ends may be flat or rounded. The intermediate plate may have an approximately triangular or truncated triangular cross-section (e.g. viewed axially). Preferably, each corner or end comprises one of said plurality of blades, although in some embodiments, each corner or end may comprise at least one of said plurality of blades. The rotor may have C3 rotational symmetry. In alternative embodiments, the intermediate plate may comprise, 4, 5, 6 or a greater number of sides and corners or ends.

The plurality of sides of the intermediate plate may each comprise a pair of straight portions separated by one of said arcuate portions. The pair of straight portions may be coplanar. In some embodiments, the corners or ends have an internal angle of 60°. In embodiments wherein the ends are flat or rounded, the internal angle of the adjacent sides (i.e. the straight portions) of the intermediate plate may be 60°. In some embodiments, the corners or ends may have an internal angle of 40 to 80° or 50-70°, and the straight portions may be angled relative to each other.

The blades may have a cross sectional shape the same as the adjacent portions of the intermediate plate. The blades may have a height of 10-50mm, 15-45mm, 20-40mm, 25- 35mm, or 30mm. In some embodiments, the blades do not extend radially beyond the intermediate plate and/or roof.

The peripheral ends of the blades may be tapered and may form a pointed, flat, or rounded edge or end. In some embodiments, the flat or rounded edge or end may thus approximately form a trapezium shape (when viewed axially). They may be located, axially, between cut-outs in the roof. They preferably extend, radially, up to the lateral surface of the roof (e.g. the circumferential or peripheral outer edge or surface of the roof).

In some embodiments, the roof may be provided with one or more vanes. The vanes may extend axially from the roof, toward the shaft and away from the intermediate plate.

In some embodiments, the roof, intermediate plate, and plurality of blades are integrally formed such that the rotor is contiguous. In some embodiments, the rotor is made from an isostatic pressed refractory material. In some embodiments, the rotor may be moulded from a mouldable refractory material. In the present context, moulding is intending to include casting processes. Any refractory material which is suitable for isopressing may be used, such as refractory mixtures comprising metal oxides, carbides, or nitrides. In some embodiments, the rotor is made from graphite, alumina, alumina silicate, carbon- bonded alumina, carbon-bonded ceramics, clay-bonded graphite, silicon alumina nitride, fused silica, silicon carbide, zirconia, or any mixture thereof.

According to a second aspect of the invention, there is provided a rotary device comprising the rotor described herein and a shaft. The rotor may be provided at one end of the shaft. The shaft and rotor may be integrally formed such that they are contiguous.

In some embodiments, the roof of the rotor is provided with engagement means for attachment to the shaft of the rotary device. The engagement means may comprise a threaded wall which allows the rotor to be screwed onto a complementary thread on an end of the shaft. Alternatively, the engagement means may comprise a recess in the roof of the rotor which is configured to have a complementary size and shape to an end of the shaft, such that the rotor can attach to the shaft by a push-fit mechanism or using a suitable refractory adhesive such as expanding refractory foam adhesive (for example, Cera Foam produced by ZYP Coatings, Inc). Alternatively, the engagement means may comprise a locking mechanism. In one series of embodiments, the engagement means comprise bayonet connectors.

The roof may be configured such that it has an upper surface obliquely angled relative to the shaft. The roof may be configured to be thicker in a region immediately adjacent to the shaft. The roof may taper such that it reduces in thickness towards its peripheral surface.

The shaft may be hollow and/or tubular. The shaft may be in fluid communication with the central aperture in the roof and intermediate plate.

The rotor or the rotary device of the preceding aspects may be formed from an isostatic pressed refractory material. Alternatively, the rotor or rotary device may be formed from a moulded refractory material. In some embodiments, the rotor or rotary device may be formed from a combination of isostatically pressed and moulded components. According to a third aspect of the invention, there is provided a method of treating molten metal. The method may comprise immersing the rotor, and optionally part of the shaft, of the rotary device into the molten metal. The method may comprise rotating the rotor. The method may comprise passing one or more molten metal treatments through the rotary device and into the molten metal via the rotor. The molten metal may comprise molten aluminium, magnesium, copper, or alloys thereof.

The method may comprise rotating the shaft to rotate the rotor. The method may comprise rotating the rotor at 100 to 500 rpm, or 150 to 450rpm, 200 to 400 rpm, 250 to 350rpm, 300rpm, or any combination thereof. In a preferred embodiment, the method comprises rotating the rotor at 250 to 450 rpm. The method may comprise stirring the molten metal for a 1 to 10 minutes, 2 to 8 minutes, 3 to 6 minutes or 4 to 5 minutes.

The molten metal treatments may comprise passing a gas through the rotor and/or rotary device. The gas may comprise an inert gas, such as argon and/or nitrogen, or a reactive gas, such as hydrogen and/or chlorine. In some embodiments, mixtures of gases may be used. The gas may be supplied at a flow rate of 5 to 50 litres per minute, or preferably 10 to 30 l/min. The gas may be supplied at a flow rate of around 20 litres per minute.

In some embodiments, the molten metal treatments may comprise a powdered or granulated metal treatment. The powdered or granulated treatments may be any chemical treatment used to support the degassing of the liquid metal. The rotor may be used for mixing applications, such as stirring chips in a melting furnace.

Brief Description

Embodiments of the invention will now be described with reference to the following drawings, in which:

Figure 1 is a perspective view of a rotary device;

Figure 2 is a perspective view of the rotary device of Figure 1 ;

Figure 3 is a side view of the rotary device of Figures 1 & 2;

Figure 4 is a graph comparing the torque of two rotor designs; and

Figure 5 is a graph comparing the degassing efficiency of two rotor designs. Specific Description

Figures 1 to 3 show a first embodiment of a rotary device 10. The rotary device 10 comprises a rotor 11 connected to a shaft 20. The shaft 20 is tubular and has a central passageway 16A extending the length thereof. The rotary device 10 defines an axis A which extends centrally through the length of the shaft 20, central passageway 16A and the rotor 11 . The shaft 20 has a flared end where it connects to the rotor 11 with a curved surface to ensure a smooth transition between outer surface of the shaft 20 and the rotor 11.

The rotor 11 is formed in approximately three layers, with a roof 12 adjacent to the shaft 20, an intermediate plate 13 extending axially from the roof 12, and three blades 15 extending axially from the intermediate plate 13. The roof 12 is approximately disc shaped (i.e. it has an approximately circular shape in the horizontal cross-section) and has a thickness in the axial direction A. The roof 12 is provided with a series of cut-outs 18 in its outer (i.e. peripheral) surface which extend axially through the thickness of the roof 12. The cut-outs 18 are arcuate and have a curved cross-section when viewed axially and a depth in the radial direction relative to axis A. In other words, the cut-outs 18 are arcuate and have a curved shape in the horizontal cross-section and a depth in the radial direction relative to axis A.

As best shown in Figure 2, the intermediate plate 13 has an approximately triangularly shaped cross-section formed from a series of sides 13a which join at corners 13b. Each side 13a has a pair of straight portions 13c separated by arcuate portions 14 extending radially into the sides 13a thereof. The peripheral ends (i.e. the radially outermost ends) of the blades 15 and the intermediate plate 13 taper to a sharply pointed edge or corner 13b. In the depicted embodiment, the intermediate plate 13 is sized such that the corners of the plate 13b are positioned at the peripheral edge of the roof 12, although in other embodiments, the corners may be spaced away from the peripheral edge of the roof 12. The central aperture 16 opens to the centre of the intermediate plate 13, thus providing a continuous passage through the rotor 11 from the shaft 20.

From each corner 13b of the intermediate plate 13 is a blade 15, which extends axially away from the intermediate plate 13 and roof 12. The blades 15 have a cross-section area (as seen in the horizontal cross section) equal to the immediately adjacent region of the intermediate plate 13, such that the blades 15 extend continuously from the intermediate plate 13. The shape of the blade 15 is thus defined by the corners 13b, straight portions 13c and part of the arcuate portions 14 of the intermediate plate 13. The surface of the blades 15 closest to the central axis A is curved and partly defines a round chamber 17 beneath the intermediate plate 13 and between the three blades 15. The chamber 17 is thus open through spaces between the respective blades 15.

The corners 13b and leading edge of the blades 15 have an angle of 60° such that the straight portions 13c are coplanar. In alternative embodiments (not shown), the corner angles may be different, such that the straight portions 13c of each pair are angled relative to each other. Similarly, the size of the arcuate portions 14 can be provided in a range of lengths and depths (i.e. radially).

The rotor 11 and shaft 20 are made from refractory materials and can be formed by isostatic pressing or by moulding (including casting). The rotary device 10 shown in Figures 1 to 3 is formed as a single integrally formed component. In alternative embodiments, the rotor 11 and shaft 20 are formed as separate pieces and connected together. The shaft 20 can be provided with a connecting portion, such as a screw- threaded portion or push-fit arrangement. In such embodiments, the rotor 11 may be provided with a socket with a corresponding connecting portion, such as a corresponding screw threaded portion or push-fit socket.

In use, the rotary device 10 can be secured in a Rotary Degassing Unit having a motor and a gas supply, and inserted into a container of molten metal. The gas can be passed down the hollow shaft, through the rotor 11 and the central aperture 16 and into the chamber 17, while the rotary device 10 is driveable by the motor to rotate about the axis A. The rotation of the rotor 11 disperses the gas blown into the chamber 17 as the gas rises through the molten metal. Without wishing to be bound by theory, it is believed that the peripheral cut-outs 18 in the roof 12 act upon the gas bubbles which rise through the molten metal. In particular, peripheral cut-outs 18 collect the bubbles as they rise from the chamber 17 and, due to the rotation of the rotor 11 , throws the bubbles radially from the rotor 11 . This leads to an especially effective distribution of the bubbles throughout the molten metal. Furthermore, the chamber has been found to increase the retention time of gas bubbles below the rotor e.g. the internal faces of the blades slow and prevent some of the bubbles from being thrown radially b the rotation of the rotor. This is believed to increase the mixing between the gas and the molten metal, and thus improves the purging effect of the gas upon the molten metal.

Water modelling results

The performance of various rotor designs was tested by water modelling, in a full size crucible fitted with a baffle plate. The crucible was filled with 220 litres of water at 16°C and the rotor immersed until 190mm from the bottom of the vessel. Water has similar viscosity characteristics to molten aluminium, and is therefore a useful proxy to indicate the performance of a rotor in molten metal.

Two rotor designs were compared: (A) a design according to the invention as shown in Figures 1 to 3 and (B) a commercially available rotor by the present applicant (the XSR™ rotor) as described in W02004/057045.

Stirring power

Torque measurements were carried out at different rotation speeds, to compare the relative stirring power of each rotor design. The experiments were repeated at least three times in total and a mean average value calculated.

The torque measurement results are shown in Figure 4, which is a graph of torque (N m) vs rotation speed (rpm). At all rotation speeds, rotor designs A exhibited higher torque than comparative design B. Greater torque has been found to lead to smaller bubbles of gas being introduced through the rotary device. The smaller bubble sizes lead to an increase in surface area and lower rising speed of the gas bubbles which increases the gas residence time in the melt and thus improved degassing of the liquid metal in use.

Degassing efficiency

An oxygen meter was immersed in the water, towards the top of the crucible. Rotor designs A and B were each rotated at 300rpm and 400rpm and the time taken for the oxygen level to reach a minimum plateau was measured. Oxygen dissolved in water exhibits similar behaviour to hydrogen dissolved in molten aluminium, so this test gives a useful measure of degassing efficiency in molten metal. The degassing results are shown in Figure 5, which is a graph of oxygen level (mg/L) vs time (s). The rotor design according to the present invention (Ex. A) exhibited significantly faster oxygen removal from the water than comparative Ex. B at both 300rpm and at 400rpm. An improved degassing rate is desirable for reducing treatment times and increasing throughput at the foundry. Furthermore, the improved rate at lower rotational speeds is particularly desirable for minimising the wear on both the rotary devices but also the rest of the rotary degassing units, thus minimising maintenance costs and downtime.

Aluminium melt testing results

Visual Observations

The rotary device was immersed in 400kg liquid aluminium at 720°C to a depth of 200mm from the bottom of the vessel. A baffle was fitted to the degassing unit adjacent to the shaft of the rotary device, gas was supplied at varying flow rates through the rotary device, and the rotor was rotated at varying speeds. Visual observations of the melt surface were recorded in Table 1 to determine acceptable working conditions for the rotary device.

Table 1

The visual observations determined that the working window for the rotor is between 250 and 450 rpm with a gas flow rate through the rotor of 10 - 20 l/min. Typically, a relatively calm melt surface is desirable to avoid negative effects. Large bubbles are indicative of poor mixing and low bubble surface area and thus gas efficiency. Turbulent surfaces are also more likely to re-dissolve impurities which have floated out of the melt. A small vortex can lead to faster degassing rates and better mixing efficiency, but larger vortexes lead to greater air and oxide entrainment, and thus a balance must be struck for greatest efficiency.

The working window for the rotary device utilises lower rotation speeds and lower gas consumption than existing commercial rotary devices. The lower rotation speeds are desirable due to reducing the wear on the RDU and on the rotors themselves, thereby increasing the working life of the rotary device.

Degassing efficiency

Reduced pressure testing (RPT) can be used to identify the density index (DI) of a metal sample. RPT is an inexpensive and effective way to determine hydrogen levels in aluminium and thus control the gas porosity. A sample of the aluminium is taken from the melt and immediately placed under a vacuum dome of a Reduced Pressure Tester. The sample is allowed to solidify under vacuum for approximately 4 minutes (i.e. at 8 kPa of pressure). Solidifying under vacuum expands the volume of hydrogen gas approximately ten times greater than solidification at normal atmosphere allowing measurement and evaluation of gas levels in the melt.

To test the hydrogen degassing efficiency of the rotor in liguid aluminium, a series of tests were carried out. The rotary device was immersed in 400kg liguid aluminium at 720°C to a depth of 200mm from the bottom of the vessel. To act as a baseline, the liguid aluminium was first upgassed for 4 minutes with a combination of 15 l/min of a mixed gas comprising 30% hydrogen and 5 l/min inert gas and with a rotor speed of 400rpm. The aluminium was then degassed using the rotary device according to the rotation speeds and gas flow rates in Table 2. A sample was withdrawn, the density index (DI) was calculated, and the process repeated under new degassing parameters. The testing was repeated using a new aluminium sample and the average recorded in Table 2. The DI of the upgassed aluminium was measured periodically and the average calculated to be 12.6%.

Table 2

The density index (%) is calculated using the formula: DI ™ where p _atm

Patm and pskPa are the densities of the samples measured in g.cm" ³ solidified at atmospheric and 8 kPa pressure respectively.

The data shows that the rotor was found to be highly effective at degassing the aluminium melt, even at low rotation speeds and low gas flow rates.

The inventors have found that the rotors of the invention are as effective or more so compared to commercially available rotors at lower rotation speeds and/or lower gas consumption. Without wishing to be bound by theory, it is believed the arcuate portions of the intermediate plates are effective at increasing the area of the plate and of better accelerating the melt and better distributing the gas-melt mixture. The blades and the cut-outs in the roof are also believed to increase the torque imparted by the rotor. As noted previously, greater torque is believed to produce smaller bubbles of gas with a higher surface area and thus improving degassing efficiency. The combination thus provides a rotor with high torque, which produces bubbles with a longer residence time, and which is also very effective at mixing the melt. Furthermore, the rotors are easier to manufacture than commercially available rotors, which require 3-axis machining and are thus limited to materials such as synthetic graphite. The simple design can be produced, for example, by isostatic pressing or moulding/casting without requiring complex machining processes, and in some embodiments, using 2-axis machining. This permits the use of alternative materials such as clay graphite or castable refractory materials which are far more durable than synthetic graphite. The result is an increase in rotor lifetimes and a decrease in maintenance leading to productivity improvements.