EP2929958A1

EP2929958A1 - Method for producing silicon-containing aluminum alloy ingot

Info

Publication number: EP2929958A1
Application number: EP13863450.6A
Authority: EP
Inventors: Masashi FUKUDA
Original assignee: Showa Denko KK
Current assignee: Resonac Holdings Corp
Priority date: 2012-12-10
Filing date: 2013-11-28
Publication date: 2015-10-14
Also published as: JP5833257B2; CN104837577A; KR20150067291A; JPWO2014091939A1; US20150314367A1; CN104837577B; EP2929958A4; WO2014091939A1

Abstract

Provided is a method of producing a silicon-containing aluminum ingot capable of preventing filter clogging that requires suspension of casting, suppressing aluminum loss, and reducing a content rate of phosphorus as an impurity in the obtained silicon-containing aluminum alloy ingot. The production method of the present invention includes a water-rinsing step for subjecting a silicon mass containing phosphorus as an impurity to a water-rinsing treatment, a molten metal formation step for obtaining molten metal by introducing, into a melting furnace, an alloy material including at least the silicon mass obtained through the water-rinsing step and an aluminum material and and melting the alloy material, and a casting step for obtaining a silicon-containing aluminum alloy ingot by casting the obtained molten metal.

Description

Technical Field

The present invention relates to a method of producing a silicon-containing aluminum alloy ingot containing less phosphorus as an impurity.

Background Art

A silicon mass used as a production raw material for a continuous cast rod, etc. , of a silicon-containing aluminum alloy contains phosphorus. It is considered that phosphorus as an impurity in such a silicon mass is brought in from silica of a raw material, or from carbon used for deoxidization, in the process of producing the silicon mass.
In a case in which an ingot is cast by adjusting the aluminum alloy molten metal using such a phosphorus-containing silicon mass as a part of the raw material and the ingot is processed by rolling, etc., hole defects, etc., are generated due to phosphorus contained in the ingot. As a result, a desired strength cannot be obtained, and for example, when chemical processing is performed, uniform etching cannot be performed, resulting in a deterioration of product quality.
As a method of removing such phosphorus in an aluminum alloy, the following technologies are proposed. Patent Document 1 discloses that an aluminum alloy molten metal containing 5 ppm or more of phosphorus is subjected to a filtration treatment at a molten metal temperature of 750°C or lower to remove the phosphorus.
Further, Patent Document 2 describes that oxygen is added along with MgO to Al or Al alloy molten metal containing P as an impurity to form an oxide of the impurity P and/or a complex oxide of P and Mg, then the oxide and the complex oxide are separated to remove the phosphorus as an impurity.
Patent Document 3 describes that Mg is added to an aluminum molten metal containing P at a molten metal temperature of 650 to 850°C to form a compound of P and Mg, and also MgCl₂ is formed by injecting chlorine gas or chloride, and P in the molten metal is removed while making MgCl₂ absorb the compound of P and Mg to rise to the surface. Further, Patent Document 3 describes that Ca is added to an aluminum molten metal containing P at a molten metal temperature of 650 to 850°C to form a compound of P and Ca, and also CaCl₂ is formed by injecting chlorine gas or chloride, and P in the molten metal is removed while making CaCl₂ absorb the compound of P and Mg to rise to the surface.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: Japanese Unexamined Patent Application Publication No. 4-276031
Patent Document 2: Japanese Unexamined Patent Application Publication No. 7-207366
Patent Document 3: Japanese Patent Publication No. 3524519

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

However, each of the technologies as described in the aforementioned Patent Documents 1 to 3 had the following problems. That is, in the technology of Patent Document 1, since minute aluminum phosphide particles are also mixed, there were problems that there were phosphorus that could not be removed since the minute particles passed through the filtration filter, and that the minute particles caused clogging of the filtration filter.
Further, in the technology of Patent Document 2, since oxygen is injected into the molten metal, there was a problem that an oxidation loss of the molten metal (aluminum loss) occurred.
Further, in the technology of Patent Document 3, since a large amount of chlorine gas or chloride was injected in the molten metal, the environmental load was great, and the removal rate of phosphorus was not sufficient.
The present invention was made in view of the related technical background, and aims to provide a method of producing a silicon-containing aluminum ingot capable of preventing an occurrence of filter clogging that requires a suspension of casting, suppressing an aluminum loss, and also sufficiently reducing a content rate of phosphorus as an impurity in the obtained silicon-containing aluminum alloy ingot.

MEANS TO SOLVE THE PROBLEMS

In a silicon ingot, etc., as a silicon mass, in a stage of deoxidizing silica with carbon to form into an ingot, phosphorus exists as a phosphorus compound, etc. The inventor of the present invention found that the phosphorus as an impurity is distributed at a high concentration on a final solidified portion of the silicon ingot, etc., and especially on the surface of the final solidified portion. As a result of diligent research based on such new knowledge, the inventor found that by subjecting a silicon mass to a water-rinsing treatment before introducing into a melting furnace, the content rate of phosphorus as an impurity in the obtained silicon-containing aluminum alloy ingot can be reduced, and completed the present invention. That is, to achieve the aforementioned objects, the present invention provides the following means.

(1) A method of producing a silicon-containing aluminum alloy ingot, comprising:
- a water-rinsing step for subjecting a silicon mass containing phosphorus as an impurity to a water-rinsing treatment;
- a molten metal formation step for obtaining molten metal by introducing an alloy material including at least an aluminum material and the silicon mass obtained through the water-rinsing step into a melting furnace and melting the alloy material; and
- a casting step for obtaining a silicon-containing aluminum alloy ingot by casting the obtained molten metal.
(2) The method of producing a silicon-containing aluminum alloy ingot as recited in the aforementioned item (1), wherein,
in the water-rinsing step, after performing the water-rinsing treatment of rinsing a surface of the silicon ingot containing phosphorus as an impurity with water, the silicon ingot is crushed to obtain a plurality of crushed objects, and
the crushed object is introduced into the melting furnace in the molten metal formation step.
(3) The method of producing a silicon-containing aluminum alloy ingot as recited in the aforementioned item (1), wherein,
in the water-rinsing step, after obtaining a plurality of crushed objects by crushing the silicon ingot containing phosphorus as an impurity, a water-rinsing treatment of rinsing surfaces of the crushed objects with water is performed, and
the crushed object after the water-rinsing treatment is introduced into the melting furnace in the molten metal formation step.
(4) The method of producing a silicon-containing aluminum alloy ingot as recited in any one of the aforementioned items (1) to (3), wherein a temperature of water used for the water-rinsing treatment is 5°C to 90°C.
(5) A method of producing a silicon-containing aluminum alloy ingot, comprising:
- a molten metal formation step for obtaining molten metal by introducing an alloy material including at least an aluminum material and a water-rinsed silicon mass into a melting furnace and melting the alloy material; and
- a casting step for obtaining a silicon-containing aluminum alloy ingot by casting the obtained molten metal.
(6) The method of producing a silicon-containing aluminum alloy ingot as recited in any one of the aforementioned items (1) to (5), wherein a content rate of phosphorus in the silicon-containing aluminum alloy ingot obtained by the casting is 5 ppm or less.

EFFECTS OF THE INVENTION

In the invention as recited in Item (1), as a silicon mass as a material used in producing a silicon-containing aluminum alloy ingot, as at least a part of the silicon mass, a silicon mass subjected to a water-rinsing treatment before being introduced into a melting furnace is used. Therefore, phosphorus (including phosphorus compound) often aggregating on the surface of the silicon mass can be sufficiently rinsed and removed, making it possible to produce a silicon-containing aluminum alloy ingot in which the content rate of phosphorus as an impurity is sufficiently reduced. It becomes possible to suppress the content rate of phosphorus in the silicon-containing aluminum alloy ingot to 5 ppm or lower.
In comparison to a conventional technology using a method of separating and removing phosphorus existing in an aluminum alloy molten metal, phosphorus can be sufficiently removed. Since rinsing is done with water, the removing operation of phosphorus can be performed easily and productivity can also be improved.
Further, it is a method in which a silicon mass is subjected to a water-rinsing treatment for rinsing and removing phosphorus at a stage before being introduced into a melting furnace (at the stage before becoming aluminum alloy molten metal), aluminum loss can be sufficiently suppressed.
Further, since filter clogging that requires suspension of casting can be prevented, productivity can be further improved.
According to the invention as recited in Item (2), since the water-rinsing treatment is performed in a state of a silicon ingot, a silicon-containing aluminum alloy ingot in which the content rate of phosphorus as an impurity is sufficiently reduced can be produced.
According to the invention as recited in Item (3), since the water-rinsing treatment is performed in a state of a crushed objects obtained by crushing, a silicon-containing aluminum alloy ingot in which the content rate of phosphorus as an impurity is further reduced can be produced.
According to the invention as recited in Item (4), since the temperature of water used for the water-rinsing treatment is 5°C to 90°C, the dissolution removability of phosphorus by water-rinsing can be further improved.
In the invention as recited in Item (5), as a silicon mass as a material used in producing a silicon-containing aluminum alloy ingot, since a silicon mass that was already subjected to a water-rinsing treatment is used as at least a part of the silicon mass, it possible to produce a silicon-containing aluminum alloy ingot in which the content rate of phosphorus as an impurity is sufficiently reduced. It becomes possible to suppress the content rate of phosphorus in the silicon-containing aluminum alloy ingot to 5 ppm or lower. Further, aluminum loss can be sufficiently suppressed and filter clogging that requires suspension of casting can be prevented, which in turn can further improve the productivity.
According to the invention as recited in Item (6), a silicon-containing aluminum alloy ingot in which the content rate of phosphorus is 5 ppm or lower can be produced.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic drawing showing a part of a process of a first embodiment of a production method according to the present invention.
Fig. 2 is a schematic drawing showing a part of a process of a second embodiment of the production method according to the present invention.
Fig. 3 is a schematic drawing showing a part of a process of a third embodiment of the production method according to the present invention.
Fig. 4 is a crushed object exterior photograph showing an example of a crushed object.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

An example of a production method of a silicon-containing aluminum alloy ingot according to the present invention will be explained. The production method of the present invention includes a water-rinsing step, a molten metal formation step, and a casting step.
In the water-rinsing step, a silicon mass used as a material (a silicon mass containing phosphorus as an impurity) is subjected to a water-rinsing treatment.
In a silicon ingot, etc., as a silicon mass, in a stage of deoxidizing silica with carbon to form an ingot, phosphorus exists as a phosphorus compound. As described above, the inventor of the present invention has found that the phosphorus as an impurity is distributed at a high concentration at the final solidified portion of the silicon ingot, especially on the surface of the final solidified portion. When a molten silicon is poured into a casting mold 10, the molten silicon is cooled and starts to solidify from the vicinity of the wall surface of the casting mold, and the top surface portion of the molten silicon at the opening of the top portion of the casting mold 10 solidifies last. The aforementioned final solidified portion refers to the solidified portion that solidifies last. For example, after 95% or more of the volume of the molten silicon in the casting mold is solidified, the portion in which the remaining molten silicon is finally solidified can be defined as the "final solidified portion" (upper surface solidified portion).
In the water-rinsing step, for example, at least the surface of the final solidified portion of the silicon ingot 11 (the upper surface of the ingot 11) is rinsed with water 13 (see Fig. 1). After drying the rinsed silicon ingot 11, the silicon ingot 11 is disintegrated (crushed) to obtain a plurality of crushed objects 12, and these crushed objects 12 are introduced into the melting furnace in the next step.
Alternatively, in the water-rinsing step, the silicon ingot 11 is crushed to obtain a plurality of crushed objects 12 and a water-rinsing treatment for rinsing the surfaces of the crushed objects 12 with water 13 is performed (see Figs. 2 and 3). After removing the adhered water from the silicon crushed obj ects 12 which have gone through rinsing by drying, wiping, etc., the plurality of crushed objects 12 is introduced into the melting furnace in the next step.
It is preferable that the size of the crushed object (including powder form) is 30 cm or less in average major axis length. Among them, it is preferable that the size of the crushed object is in a range of 1 cm to 30 cm in average major axis length. In addition, in such a case, powders produced at the time of crushing may be introduced into the melting furnace together with the crushed objects of 1 cm to 30 cm in the later molten metal formation step.
In the water-rinsing treatment, it is acceptable that at least a portion of the surface of the final solidified portion is rinsed with water, or that a portion not rinsed with water remains on the surface of the final solidified portion,.
The water-rinsing treatment can be performed by spraying water 13 to a silicon ingot, crushed objects, etc. (see Figs. 1 and 2), or by immersing a silicon mass, crushed objects, etc., in water 13 (see Fig. 3). The method is not especially limited.
In a case of performing the water-rinsing treatment by spraying water on the silicon mass, it is preferable that water is sprayed from the top side in a state in which the silicon ingot is arranged with the surface of the final solidified portion facing upward. Further, in a case of performing the water-treatment by spraying water on the crushed objects, it is preferable that spraying is performed from the side direction (horizontal direction) in addition to spraying from the top side.
When performing the water-rinsing treatment, it is preferable that 100 mass parts to 1,000 mass parts of water (water for immersion or spraying water) is used for 100 mass parts of silicon mass or crushed objects. Further, the water-rinsing time is preferably set to 10 to 30 minutes.
It is preferable that the temperature of water for performing the water-rinsing treatment is 5°C to 90°C. By using water of 5°C to 90°C, the dissolution removability of phosphorus by water-rinsing can be further improved. In addition, in a case of accompanying conveyance and movement of the silicon mass in a later step, it is preferable that the temperature of the water is 40°C to 60°C. By setting it to 40°C to 60°C, safety of the operation can be improved.
By performing a water-rinsing treatment as described above, phosphorus (including phosphorus compound) that is often aggregated on the surface of a silicon mass (silicon ingot, etc.) can be sufficiently rinsed and removed.
In the molten metal formation step, an alloy material including at least an aluminum material and a silicon mass obtained through the water-rinsing step is introduced into a melting furnace to be melted to thereby obtain a molten metal. The molten metal temperature for melting is typically in a range of 770°C to 870°C.
Although the aluminum material is not especially limited, for example, an aluminum ground metal, etc., can be exemplified.
As the "silicon mass obtained through the water-rinsing step", a silicon ingot subjected to the water-rinsing step, a silicon crushed object subjected to the water-rinsing step, etc., can be exemplified.
As needed, other metal materials (copper, magnesium, etc.) other than the aforementioned two materials may be introduced into the melting furnace. Further, in a range in which the effects of the present invention are not inhibited, introducing a silicon mass which has not been subjected to a water-rinsing treatment into the melting furnace together with the "silicon mass obtained through the water-rinsing step" is not excluded depending on the intended alloy specifications. However, for the alloy specifications intended for sufficiently obtaining an impurity phosphorus content reduction effect, it is needless to say that it is desirable to not introduce such silicon mass which has not been subjected to a water-rinsing treatment as much as possible.
In the casting step, by subjecting a molten metal obtained in the molten metal formation step to casting, an ingot of an aluminum alloy containing silicon (silicon-containing aluminum alloy ingot) is obtained. By the aforementioned casting, a silicon-containing aluminum alloy ingot can be processed, or a continuous cast rod of a silicon-containing aluminum alloy can be processed. The shape of an ingot obtained by casting is not especially limited.
According to the production method of the present invention, it becomes possible to produce a silicon-containing aluminum alloy ingot in which the phosphorus content rate is 5 ppm or less (including 0 ppm) (see the later explained Embodiments 1 and 2).
The casting method is not especially limited, and for example, a semi-continuous casting method, a horizontal continuous casting method, a strip casting method, a gravity casting method, etc., can be exemplified, but any casting method may be used.
The production method of the present invention is for producing a silicon-containing aluminum alloy ingot (silicon-containing aluminum alloy cast product), and although the components other than Al and Si are not especially limited, as the aluminum alloy composition, 2000 series alloy, 3000 series alloy, 4000 series alloy, 5000 series alloy, and 6000 series alloy are suitable. Especially in the case of alloy series containing a large amount of Si, for example, 4000 series alloy is preferable since effects (effects of the present invention) are great.

Examples

Next, specific examples of the present invention will be explained, but the present invention is not especially limited to these examples.

<Example 1>

A silicon mass obtained by subjecting silica to a deoxidization treatment (phosphorus content rate 230 ppm) which was heated and melted was poured into a casting mold 10 and naturally cooled to obtain a rectangular shaped silicon ingot 11. By this natural cooling, the solidification of the molten silicon progressed from the vicinity of the outer peripheral frame section of the casting mold and the solidification was completed on the upper exposed surface. As shown in Fig. 1, in a state in which the silicon ingot 11 was kept inside the casting mold 10, the upper surface of the ingot 11 (final solidified portion) was subjected to a water-rinsing treatment for spraying water 13 of 20°C for 30 minutes.
Next, after the rectangular shaped silicon ingot 11 was taken out from the casting mold 10 and the adhered water was removed by drying, the silicon mass was crushed to obtain a plurality of crushed objects 12. Then these crushed objects 12 were introduced into a melting furnace, and an aluminum ground metal having an aluminum content rate of 99.7 mass%, a copper ground metal having a copper content rate of 99.9 mass%, and a magnesium ground metal having a magnesium content rate of 99.9 mass% were further introduced into the melting furnace and heated at 850°C to produce an aluminum alloy molten metal. Each of the aforementioned materials was introduced so that the silicon content rate became 11 mass%, the copper content rate became 4 mass%, the magnesium content rate became 0.5 mass%, and the aluminum content rate became 84.5 mass% in the aluminum alloy molten metal. The size of the crushed object was 10 cm in average major axis length.
By casting the aluminum alloy molten metal, a silicon-containing aluminum alloy ingot (silicon-containing aluminum alloy ingot) was obtained.

<Example 2>

A silicon mass obtained by subjecting silica to a deoxidization treatment (phosphorus content rate was the same phosphorus content rate as the silicon mass used in Embodiment 1) which was heated and melted was poured into a casting mold 10 and naturally cooled to obtain a rectangular shaped silicon ingot 11. By this natural cooling, the solidification of the molten silicon progressed from the vicinity of the outer peripheral frame section of the casting mold and the solidification was completed on the upper exposed surface.
Next, as shown in Fig. 3, the rectangular shaped silicon ingot 11 was taken out from the casting mold 10 and the silicon mass was crushed to obtain a plurality of crushed objects 12. Thereafter, the plurality of crushed objects 12 were subjected to a water-rinsing treatment for immersing them in water 13 of 90°C for 10 minutes. Next, after removing the adhered water from the taken-out crushed objects 12 by drying, these crushed objects 12 were introduced into a melting furnace, and an aluminum ground metal having an aluminum content rate of 99.7 mass%, a copper ground metal having a copper content rate of 99.9 mass%, and a magnesium ground metal having a magnesium content rate of 99.9 mass% were further introduced into the melting furnace and heated to 850°C to produce an aluminum alloy molten metal. Each of the aforementioned materials was introduced so that the silicon content rate became 11 mass%, the copper content rate became 4 mass%, the magnesium content rate became 0.5 mass%, and the aluminum content rate became 84.5 mass% in the aluminum alloy molten metal. The size of the crushed object was 15cm in average major axis length.
By casting the aluminum alloy molten metal, a silicon-containing aluminum alloy ingot (silicon-containing aluminum alloy ingot) was obtained.

<Comparative Example 1>

A silicon mass obtained by subjecting silica to a deoxidization treatment (phosphorus content rate was the same phosphorus content rate as the silicon mass used in Embodiment 1) which was heated and melted was poured into a casting mold and naturally cooled. By this natural cooling, the solidification of the molten silicon progressed from the vicinity of the outer peripheral frame section of the casting mold and the solidification was completed on the upper exposed surface.
Next, the rectangular shaped silicon ingot was taken out from the casting mold, and a plurality of crushed objects obtained by crushing the silicon ingot were introduced into a melting furnace, and an aluminum ground metal having an aluminum content rate of 99.7 mass%, a copper ground metal having a copper content rate of 99.9 mass%, and a magnesium ground metal having a magnesium content rate of 99.9 mass% were further introduced into the melting furnace and heated to 850°C to produce an aluminum alloy molten metal. Each of the aforementioned materials was introduced so that the silicon content rate became 11 mass%, the copper content rate became 4 mass%, the magnesium content rate became 0.5 mass%, and the aluminum content rate became 84.5 mass% in the aluminum alloy molten metal. The size of the crushed object was 10 cm in average major axis length.

By casting the aluminum alloy molten metal, a silicon-containing aluminum alloy ingot (silicon-containing aluminum alloy ingot) was obtained.

[Table 1]

	Water-rinsing treatment	Phosphorus content rate of silicon-containing aluminum alloy ingot (ppm)
Example 1	Silicon ingot was rinsed with water of 20°C	4
Example 2	Crushed objects were rinsed by immersing in water of 90°C	4
Comparative Example 1	None	25

For each of the silicon-containing aluminum alloy ingots obtained in the aforementioned manner, the content rate of phosphorus was measured based on the following measuring method. The measurement results are shown in Table 1.

The quantitative analysis of phosphorus in the silicon-containing aluminum alloy ingot was performed using an emission analyzing device ("PDA 5500 II" made by Shimadzu Corporation).
As it is clear from the table, in the silicon-containing aluminum alloy ingots of Embodiments 1 and 2 produced using the production method of the present invention, the content rate of phosphorus was sufficiently suppressed to low levels.
On the other hand, in the silicon-containing aluminum alloy ingot of Comparative Example 1 produced without using the production method of the present invention, the content rate of phosphorus was 25 ppm and the content rate of phosphorus was high.

INDUSTRIAL APPLICABILITY

Since the content rate of phosphorus as an impurity is suppressed to low levels in a silicon-containing aluminum alloy ingot produced by the production method of the present invention, it can be suitably used as, for example, 1) products or parts in which, when the content rate of phosphorus as an impurity is high, a condensed portion of phosphorus is at a risk of becoming a source of cracks when external stress is applied (specifically, for example, automobile cast parts, etc.) 2) material produced through a step accompanied by a chemical reaction by chemical etching, etc., and products or parts obtained by processing while applying external stress (rolling, extrusion, forging, etc.) (specifically, for example, foil for electrolytic capacitors, sheet material, automobile parts, etc.), but it is not especially limited to these exemplified applications.
The present invention claims priority to Japanese Patent Application No. 2012-269082 filed on December 10, 2012 , the entire disclosure of which is incorporated herein by reference in its entirety.
The terms and descriptions used herein are used only for explanatory purposes and the present invention is not limited to them. The present invention allows various design-changes falling within the claimed scope of the present invention unless it deviates from the spirits of the invention.

DESCRIPTION OF THE REFERENCE NUMERALS

11...silicon ingot (silicon mass)
12...crushed object (silicon mass)
13...water

Claims

A method of producing a silicon-containing aluminum alloy ingot, comprising:
a water-rinsing step for subjecting a silicon mass containing phosphorus as an impurity to a water-rinsing treatment;

a molten metal formation step for obtaining molten metal by introducing an alloy material including at least an aluminum material and the silicon mass obtained through the water-rinsing step into a melting furnace and melting the alloy material; and

a casting step for obtaining a silicon-containing aluminum alloy ingot by casting the obtained molten metal.
The method of producing a silicon-containing aluminum alloy ingot as recited in claim 1, wherein,
in the water-rinsing step, after performing the water-rinsing treatment of rinsing a surface of the silicon ingot containing phosphorus as an impurity with water, the silicon ingot is crushed to obtain a plurality of crushed objects, and
the crushed object is introduced into the melting furnace in the molten metal formation step.
The method of producing a silicon-containing aluminum alloy ingot as recited in claim 1, wherein,
in the water-rinsing step, after obtaining a plurality of crushed objects by crushing the silicon ingot containing phosphorus as an impurity, a water-rinsing treatment of rinsing surfaces of the crushed objects with water is performed, and
the crushed object after the water-rinsing treatment is introduced into the melting furnace in the molten metal formation step.
The method of producing a silicon-containing aluminum alloy ingot as recited in any one of claims 1 to 3, wherein a temperature of water used for the water-rinsing treatment is 5°C to 90°C.
A method of producing a silicon-containing aluminum alloy ingot, comprising:
a molten metal formation step for obtaining molten metal by introducing an alloy material including at least an aluminum material and a water-rinsed silicon mass into a melting furnace and melting the alloy material; and

a casting step for obtaining a silicon-containing aluminum alloy ingot by casting the obtained molten metal.
The method of producing a silicon-containing aluminum alloy ingot as recited in any one of claims 1 to 5, wherein a content rate of phosphorus in the silicon-containing aluminum alloy ingot obtained by the casting is 5 ppm or less.