JP2002180109A - Ferrous powder material and manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferrous powder material with which grinding swarf can be effectively recycled and also to provide its manufacturing method. SOLUTION: A flocculent agglomerate B which contains grinding swarf of ferrous metal and grinding fluid containing oil and water is compacted to prepare a brittle compact C where the grinding swarf in a fibrous state is roughly sheared and excess water and oil are removed. The brittle compact C is pulverized to shear the grinding swarf more finely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based powder material and a method for producing the same, and more particularly, to a technology for effectively utilizing ground metal chips of an iron-based metal.

[0002]

2. Description of the Related Art Chips generated when grinding ferrous metals such as bearing steel and carburized steel (hereinafter used as a concept including polishing, superfinishing and lapping) are grinding fluids containing water and oil. And a flocculent (fibrous) aggregate containing abrasive grains and the like. Since this flocculent aggregate contains a large amount of pure iron, it has been attempted to reuse it as, for example, a steelmaking raw material. However, since this flocculent agglomerate contains a large amount of water, if it is put into a blast furnace as it is, the water causes a problem of bumping (steam explosion). Therefore, it is conceivable to remove the water in the flocculent aggregate by centrifugation or the like.In this case, the oil contained in the flocculent aggregate is also removed together with the moisture, and the flocculent aggregate naturally generates heat. Pure iron, which is a component of grinding chips, is transformed into iron oxide. For this reason, in order to reuse this as a steelmaking raw material, it is necessary to reduce it, and the use of a reducing agent increases costs.

[0003] In addition, since the above-mentioned ground chips to which the oil component adheres hardly adhere to each other, it is difficult to solidify to a desired strength even if the flocculent aggregate is compression-molded. Further, the flocculent agglomerate containing a large amount of ground cuttings of an iron-based metal having a carbon content of 0.2% by weight or more has a large springback at the time of compression. It is difficult to solidify strongly. Therefore, even if the compression-molded flocculent aggregate is put into a blast furnace, it flies up while scattering and is mostly collected by the dust collector. Furthermore, since the fibrous ground chips contained in the flocculent aggregate are difficult to be crushed by a hammer mill or the like, the flocculent aggregate cannot be finely sheared into powder. For this reason, it is also difficult to process the flocculent aggregate into briquettes or the like. Therefore, the actual state is that the flocculent aggregate is disposed of by a waste disposal contractor without being reused.

On the other hand, in a steel manufacturing process such as a melting process, dust containing iron and heavy metals is generated.
This is collected as dust collection dust (OG dust) (see, for example, JP-A-7-97638). However, if this dust is put into the blast furnace as it is, it will fly up while scattering and be collected again by the dust collector, so it is landfilled without reuse.

[0005]

However, such landfill disposal is not preferable from the viewpoint of effective utilization of resources. In addition, there is a problem that the environment is deteriorated and the disposal cost is high. In particular, dust collected contains heavy metals, so it is necessary to landfill it as a special industrial waste, and there is a problem that the disposal cost is higher. The present invention has been made in view of the above problems, and an object of the present invention is to provide an iron-based powder material capable of effectively reusing grinding chips and a method for producing the same. It is another object of the present invention to provide an iron-based powder material capable of effectively reusing dust collected together with grinding chips and a method for producing the same.

[0006]

The iron-based powder material of the present invention for achieving the above object is a powdered material containing an iron-based powder and an oil component, wherein the ground chip of the iron-based metal has an oil content and a water content. A brittle compact obtained by compression-molding a flocculent aggregate containing a grinding fluid containing (a) is crushed (claim 1). According to the iron-based powder material configured as described above,
Oxidation of pure iron, which is a component of the iron-based powder, is prevented by the contained oil. In addition, since the flocculent aggregate is obtained by compression molding and pulverized, the iron-based powder becomes fine.

The iron-based powder material may further contain a solidification aid (claim 2). In this case, the iron-based powder material can be solidified to a desired strength and shape only by compression molding. . The solidification aid is preferably at least one selected from rice bran, molasses, starches, quicklime, colloidal silica, sodium silicate, aluminum phosphate, vinyl acetate sludge, asphalt emulsion, and bentonite (Claim 3). ), Whereby solidification can be made firmly despite the oil content.

The iron-based powder material may further contain coke (claim 4). In this case, the iron-based powder material can be solidified firmly by compression molding. In this case, it is preferable that coke is contained in an amount of 5 to 50% by weight (claim 5), so that the coke can be further solidified.

The iron-based powder material may further include dust collected in a steel manufacturing process (claim 6). In this case, the dust collected is reused together with the grinding chips. be able to. Further, in this case, it is preferable that the dust collection contains 10 to 30% by weight (claim 7), whereby the dust can be compression-molded to a desired hardness.

The method for producing an iron-based powder material according to the present invention comprises:
Compression molding of flocculent agglomerates containing grinding chips of iron-based metal and grinding fluid containing oil and water, brittleness in which fibrous grinding chips are roughly sheared and excess water and oil are removed It is characterized in that a compact is obtained, and the brittle compact is pulverized to further finely shear the ground swarf to obtain a powder material containing an iron-based powder and an oil component. According to the manufacturing method of the iron-based powder material configured as described above, the compression molding of the flocculent agglomerates makes it possible to easily coarsely shear the fibrous ground cutting chips, which have conventionally been difficult to shear. In addition, since the fibrous ground chips are rough-sheared in advance, the ground chips can be easily and effectively sheared in the step of pulverizing the brittle compact. For this reason, fine iron-based powder can be obtained easily and reliably. Furthermore, since each of the above-described steps is performed while retaining the oil content contained in the grinding fluid, it is possible to prevent oxidation of pure iron, which is a component of grinding chips.

In the method for producing an iron-based powder material, a solidification aid may be mixed during or after the pulverization of the brittle compact (claim 9). An iron-based powder material that can be solidified into a desired strength and shape can be obtained. As the solidification aid, rice bran,
It is preferable to use at least one selected from molasses, starch, quicklime, colloidal silica, sodium silicate, aluminum phosphate, vinyl acetate sludge, asphalt emulsion, and bentonite (claim 10). Nevertheless, an iron-based powder material that can be easily and firmly solidified can be obtained. In addition, the solidification auxiliary is 2
Preferably, it is mixed in an amount of up to 30% by weight (claim 11), whereby an iron-based powder material that can be further solidified can be obtained.

In the method for producing an iron-based powder material, coke may be mixed during or after pulverizing the brittle compact (claim 12). In this case, the coke is strongly compressed by the coke. A possible iron-based powder material can be obtained. Also, in this case, the solidification aid is added to 1
Preferably, it is mixed in an amount of 10 to 10% by weight (claim 13), whereby an iron-based powder material that can be easily and stably solidified can be obtained. Further, the coke is preferably mixed in an amount of 5 to 50% by weight (claim 14). In this case, an iron-based powder material which can be more compactly formed can be obtained.

In the method for producing an iron-based powder material, dust collected during the steel production process may be mixed with the brittle compact during or after the pulverization (claim 15).
In this case, an iron-based powder material containing dust collected can be obtained. In this case, it is preferable that the dust collection dust is mixed in an amount of 10 to 30% by weight.
6) Thereby, an iron-based powder material that can be compression-molded to a desired hardness can be obtained.

In the method for producing an iron-based powder material, the flocculent aggregate is used in which the water content is adjusted to a range not exceeding 50% by weight and the oil content is adjusted to a range not exceeding 10% by weight. Is preferable (claim 17). This facilitates handling such as transportation of the floc and the like, and allows easy and appropriate removal of excess moisture and oil content of the brittle molded body only by compression molding.

In the method for producing an iron-based powder material, the brittle compact has a moisture content of 2 to 12% by weight and an oil content of 1 to 12% by weight.
It is preferably adjusted to 5% by weight (claim 18). In this case, the brittle molded body can be solidified to an appropriate hardness, and the oxidation of pure iron, which is a component of the grinding chips, can be effectively prevented by the minimum residual oil content. . Further, as the grinding chips, those containing 0.2% by weight or more of carbon may be used (claim 19).
The effect of the springback is eliminated, and rough shearing can be effectively performed by the compression molding.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a process chart showing a method for producing an iron-based powder material according to an embodiment of the present invention. In the production of the iron-based powder material A, first, the flocculent aggregate B (see FIG. 1 (a)) of the swarf generated when grinding the ferrous metal is pressed and compressed, and Aggregate B
Preliminarily adjust the contents of water and oil, which are components of the grinding fluid contained in the above. The pressurization and compression of the flocculent aggregate B is performed, for example, by a pair of rolls 2 while being conveyed on a belt conveyor 1.
It is performed by being sandwiched between them (see FIG. 1 (b)). However, there is a method of adjusting the water content and the oil content by simple air blowing or air compression. At this time, the flocculent aggregate B
Means that the oil content is not more than 50% by weight and the oil content is 1
It is preferable to adjust each of the amounts so as not to exceed 0% by weight, so that handling such as transportation and storage of the flocculent aggregate B becomes easy.

Next, the flocculent agglomerate B, whose content of water and oil is adjusted, is compression molded by, for example, pressing using a molding die 3 to obtain a brittle molded body C (see FIG. 1 (c)). ). By this compression molding, the spiral fibrous ground chips contained in the flocculent aggregate B are roughly sheared. Also,
Excess water and oil are removed, and the water content of the brittle molded product C is adjusted to 2 to 12% by weight, and the oil content is adjusted to 1 to 5% by weight. Thereby, it is possible to effectively prevent the oxidation of pure iron, which is a component of the grinding chips, with a minimum residual oil content. In addition, since the water content of the flocculent agglomerate B was previously adjusted to a range not exceeding 50% by weight and the oil content thereof not exceeding 10% by weight in the previous step, the brittle molded product C was
Of water and oil can be easily and appropriately adjusted only by compression molding. The brittle molded body C
Is formed in a shape that is easy to handle, such as a column, a sphere, and a prism, and is hardened to such a degree that it does not collapse when transported to the next step.

Next, the brittle compact C is put together with the solidification aid D into a mixer (or Henschel mixer) 5 equipped with a rotary blade 4 and equipped with a rotary blade 4 and pulverized (see FIG. 1 (d)). Thereby, the grinding chips of the brittle molded body C are further finely sheared (finish shearing), whereby an iron-based powder material A containing pure iron, an oil component and a solidification auxiliary agent D can be obtained (FIG. 1 (e)). The major axis of the iron-based powder is about 3 to 1000 μm. When the brittle molded body C is ground, the fibrous ground cuttings in the brittle molded body C are rough-sheared in advance, so that they can be finish-sheared without any trouble. If the fibrous ground chips in the brittle compact C are not subjected to rough shearing, it takes a long time to grind them with a mixer (or Henschel mixer) 5 with a chopper,
It is not economically advantageous, and it is also difficult to obtain fine iron-based powder.

Examples of the solidifying aid D include molasses such as rice bran and sugarcane, starches such as potato starch and corn starch, quicklime, colloidal silica, sodium silicate, aluminum phosphate, vinyl acetate sludge, asphalt emulsion and bentonite. One or two or more selected from the following are preferably used. It is preferable that such a solidification aid D is contained in an amount of 2 to 30% by weight. In particular, the rice bran and molasses are very suitable as the solidification aid D because they effectively act on the solidification of the iron-based powder material A and are inexpensive. In addition, when the asphalt emulsion is kneaded and then separated into asphalt and water, caking is generated and the strength is developed.
As the asphalt emulsion, an anionic asphalt is preferably used.

Since the iron-based powder material A obtained as described above always holds a part of the oil of the grinding fluid even during machining, the oxidation of pure iron as a component thereof is effectively prevented. I have. For this reason, by solidifying by, for example, compression molding, it can be suitably reused especially as a briquette material for a steelmaking raw material.

In the step of pulverizing the brittle compact C, the dust collected and generated in the coke and steel making process together with the solidification aid D is charged into a mixer (or Henschel mixer) 5 equipped with a chopper. May be. In this case, the brittle compact C was 50 to 70% by weight, coke K was 5 to 50% by weight, and dust collected was 10%.
It is preferable to mix the solidification aid D at a ratio of 1 to 10% by weight. Thus, an iron-based powder material A containing pure iron, coke, dust collection dust, and a powder of the solidification aid D can be obtained. In particular, in this production method, the coke is 5 to 50% by weight, and the
Since each of 0% by weight is mixed, the iron-based powder material A that can be solidified more firmly can be obtained. Further, since the mixing ratio of the dust collection dust is set to 10 to 30% by weight, the iron-based powder material A that can be solidified to a desired hardness can be easily obtained. As the dust collection dust, for example, iron (total Fe) generated and collected in a steel making process is 10 to
Those containing 55% by weight are used.

FIG. 2 is a process chart showing an example of a method for producing a briquette G for a steelmaking raw material using the iron-based powder material A. In manufacturing the briquette G, first, a predetermined amount of the iron-based powder material A is compression-molded using, for example, a roll-type molding machine or a cylinder-type molding machine 6 (see FIG. 2A).
An almost pillow-shaped briquette F containing a large amount of pure iron is obtained. During the compression molding of the iron-based powder material A, the iron-based powders to which the fats and oils are adhered can be solidified by the solidification aid D and the moisture in the iron-based powder material A to be solidified. . In particular, the water content of the iron-based powder material A is 5-6.
In the case of using one containing 4% by weight of rice bran and 2% by weight of molasses, and one containing 7 to 15% by weight of water and 2 to 10% by weight of vinyl acetate sludge, briquette F solidified more firmly is used. Obtainable. In addition, the "substantially pillow shape" is a shape having a rounded peripheral portion and a gradually increasing thickness from the peripheral portion toward the central portion, and an oval shape.
It is a shape including almond shape, rugby ball shape, etc.,
By forming into such a shape, it is possible to obtain a briquette F that is strongly resistant to a compressive load and hardly collapses, and is hard to be partially damaged at corners or the like.

Then, air at room temperature or cooled is blown onto the briquette F immediately after compression molding to rapidly cool it (see FIG. 2 (b)). Thereby, the briquette F can be easily and stably solidified. Thereafter, the briquette F is cured (dried) to remove the water content (see FIG. 2 (c)), whereby a briquette G for a steelmaking raw material can be obtained (see FIGS. 2 (d) and 3). . It is preferable to carry out this curing for about two days because the water content can be surely removed.

Since the briquette G obtained as described above is a porous material obtained by solidifying the iron-based powder material A, the water content can be easily and reliably removed by curing. For this reason, there is no possibility that bumping or soaring and discharge will occur even if the blast furnace is directly charged into the blast furnace. In addition, since the molding and curing are performed in a state in which a part of the oil of the grinding fluid is held, the oxidation of pure iron is effectively prevented.
For example, for a briquette G manufactured using flocculent aggregate B containing ground cuttings of bearing steel (SUJ-2), 70
It has been confirmed that it contains pure iron by weight or more. Therefore, the melting yield is as high as 90% or more, and it can be provided as a high quality steelmaking raw material to a steelmaker for a fee. Moreover, it is easy to carry and other handling in solid form.

The above-described method for producing the iron-based powder material A is particularly suitably applied to the reuse of ground chips containing 0.2% by weight or more of carbon. Such grinding chips have a large springback and are difficult to solidify. However, by applying the compression molding of the present invention shown in FIG. The powder can be roughly sheared effectively. As a typical example of the ground chips containing 0.2% by weight or more of carbon, ground chips of bearing steel can be given.

The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the brittle compact C is pulverized and the solidification aid D, coke and dust collection dust are mixed at the same time. But the brittle compact C
May be mixed with the powder obtained by pulverizing the solidifying aid D, powdered coke and dust collection dust. Further, the solidification aid D, coke and dust collection dust may be selectively mixed. Further, the solidification aid D, coke, and dust collection may be carried out without mixing. In this case, an iron-based powder material A composed of an iron-based powder and an oil component is obtained. It should be noted that the iron-based powder material A can be reused as an additive material such as a powder material for a sintered metal or a resin or the like for a magnetic material, in addition to the briquette G for a steelmaking material.

[0027]

As described above, according to the iron-based powder material according to the first aspect, since it is a fine material containing a large amount of pure iron,
It can be reused as briquettes for high-quality steelmaking raw materials and powdered raw materials for sintered metals, which contributes to environmental preservation and reduces the disposal cost of grinding chips.

According to the second aspect of the present invention, since the iron-based powder material contains a solidification aid, it can be solidified to a desired strength and shape only by compression molding. For this reason, the reuse of the grinding chips can be further promoted. According to the iron-based powder material of the third aspect, the solidification aid is selected from rice bran, molasses, starches, quicklime, colloidal silica, sodium silicate, aluminum phosphate, vinyl acetate sludge, asphalt emulsion, and bentonite. Since it is at least one kind, it can be solidified firmly despite containing oil. For this reason, the reuse of the grinding chips can be further promoted.

According to the fourth aspect of the present invention, since the iron-based powder material further contains coke, it can be solidified firmly by compression molding. According to the iron-based powder material of the fifth aspect, since coke is contained in an amount of 5 to 50% by weight, it can be further solidified by compression molding.

According to the iron-based powder material according to the sixth aspect, the collected dust can be solidified and reused together with the grinding chips, thereby contributing to environmental protection and reducing the disposal cost of the collected dust. be able to. According to the iron-based powder material according to claim 7, the dust collection dust is 10 to 30% by weight.
Since it is included, compression molding can be performed to a desired hardness.

According to the method for producing an iron-based powder material according to the present invention, it is possible to easily coarsely shear the fibrous ground cutting chips, which have conventionally been difficult to shear, by the compression molding of the flocculent aggregate. it can. In addition, since the grinding chips have been coarsely sheared in advance, in the step of pulverizing the brittle molded body,
The ground chips can be easily and effectively sheared. Furthermore, since each of the above-described steps is performed while retaining the oil content contained in the grinding fluid, it is possible to prevent oxidation of pure iron, which is a component of grinding chips. Therefore, a fine iron-based powder containing a large amount of pure iron can be obtained easily and reliably.

According to the method for producing an iron-based powder material according to the ninth aspect, a solidification auxiliary agent is mixed at the time of pulverizing the brittle compact or after the pulverization. It is possible to obtain an iron-based powder material that can be converted. For this reason, the reuse of the grinding chips can be further promoted. According to the method for producing an iron-based powder material according to claim 10,
As the solidification aid, at least one selected from rice bran, molasses, starches, quicklime, colloidal silica, sodium silicate, aluminum phosphate, vinyl acetate sludge, asphalt emulsion, and bentonite is used. Regardless, an iron-based powder material that can be easily and firmly solidified can be obtained. For this reason, the reuse of the grinding chips can be further promoted. According to the method for producing an iron-based powder material according to claim 11, the solidification aid is used in an amount of 2 to 3 times.
By mixing at 0% by weight, it is possible to obtain an iron-based powder material that can be solidified even more strongly.

According to the method for producing an iron-based powder material according to the twelfth aspect, it is possible to obtain an iron-based powder material that can be solidified very strongly by coke. According to the method for producing an iron-based powder material according to claim 13, 1 to 10
By mixing by weight, an iron-based powder material that can be easily and stably solidified can be obtained. According to the method for producing an iron-based powder material according to the fourteenth aspect, since coke is mixed in an amount of 5 to 50% by weight, an iron-based powder material that can be more compactly formed can be obtained.

According to the method for producing an iron-based powder material according to the fifteenth aspect, the collected dust can be solidified and reused together with the grinding chips, which contributes to environmental protection and
The cost of disposing of dust collection dust can be reduced. According to the method for producing an iron-based powder material according to the sixteenth aspect, the dust-collected dust is mixed at 10 to 30% by weight, so that an iron-based powder material that can be solidified to a desired hardness can be easily obtained. .

According to the method for producing an iron-based powder material according to the seventeenth aspect, the flocculent aggregate is adjusted to have a water content not exceeding 50% by weight and an oil content not exceeding 10% by weight. Since the above-mentioned material is used, handling such as transportation of the flocculent aggregate is facilitated, and excess moisture and oil content of the brittle molded body can be easily and appropriately removed only by compression molding.

According to the method for manufacturing an iron-based powder material according to the eighteenth aspect, the brittle compact is adjusted to have a water content of 2 to 12% by weight and an oil content of 1 to 5% by weight. It is possible to solidify to an appropriate hardness, and it is possible to effectively prevent the oxidation of pure iron, which is a component of the grinding swarf, with a minimum amount of residual oil. According to the method for manufacturing an iron-based powder material according to the nineteenth aspect, even for grinding chips containing 0.2% by weight or more of carbon having a large springback, the influence of the springback is eliminated and compression molding is effectively performed. Coarse shearing is possible.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for producing an iron-based powder material according to an embodiment of the present invention.

FIG. 2 is a process chart showing a method for producing briquettes from an iron-based powder material.

FIG. 3 is a partially cutaway perspective view of a briquette.

[Explanation of symbols]

 A Iron-based powder material B Cotton-like aggregate C Brittle molded body D Solidification aid G Briquette

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Mitsuma Matsuda 3-5-8 Minamisenba, Chuo-ku, Osaka-shi Koyo Seiko Co., Ltd. (72) Yoshihiro Kiyoo 3-58 Minamisenba, Chuo-ku, Osaka-shi Koyo Seiko Co., Ltd. (72) Inventor Shoichi Kashino 3-5-8 Minamisenba, Chuo-ku, Osaka-shi Koyo Seiko Co., Ltd.F-term (reference) 4K001 AA10 BA14 BA22 CA26 CA29 CA49 4K018 AB07 AB10 BA14 BA20 BC12 BD10 CA11

Claims (19)

[Claims] 1. A powder material containing an iron-based powder and an oil component,
An iron-based powder material obtained by pulverizing a brittle compact obtained by compression-molding a flocculent aggregate containing iron-based metal grinding chips and a grinding fluid containing oil and moisture. 2. The iron-based powder material according to claim 1, further comprising a solidification aid. 3. The solidification aid is at least one selected from rice bran, molasses, starches, quicklime, colloidal silica, sodium silicate, aluminum phosphate, vinyl acetate sludge, asphalt emulsion, and bentonite. 2. The iron-based powder material according to 2. 4. The iron-based powder material according to claim 1, further comprising coke. 5. The iron-based powder material according to claim 4, wherein said coke contains 5 to 50% by weight. 6. The iron-based powder material according to claim 1, further comprising dust collected in a steel manufacturing process. 7. The iron-based powder material according to claim 6, comprising 10 to 30% by weight of said dust collection dust. 8. A flocculent aggregate containing iron-based metal grinding chips and a grinding fluid containing oil and moisture is compression-molded, whereby the fibrous grinding chips are roughly sheared and the excess water and oil content is reduced. Iron-based powder material characterized by obtaining a brittle compact from which is removed, grinding the brittle compact to further finely shear the ground cuttings, and obtaining a powder material containing an iron-based powder and an oil component Manufacturing method. 9. The method for producing an iron-based powder material according to claim 8, wherein a solidification aid is mixed during or after the pulverization of the brittle molded body. 10. The solidification aid includes rice bran, molasses, starches, quicklime, colloidal silica, sodium silicate, and the like.
The method for producing an iron-based powder material according to claim 9, wherein at least one selected from aluminum phosphate, vinyl acetate sludge, asphalt emulsion, and bentonite is used. 11. The method for producing an iron-based powder according to claim 10, wherein the solidification aid is mixed in an amount of 2 to 30% by weight. 12. The method according to claim 11, wherein said brittle molded body is crushed or crushed.
The method for producing an iron-based powder material according to claim 8, wherein coke is mixed. 13. The method for producing an iron-based powder according to claim 12, wherein 1 to 10% by weight of a solidification aid is mixed. 14. The method according to claim 12, wherein the coke is mixed in an amount of 5 to 50% by weight. 15. The method according to claim 15, wherein the brittle molded body is crushed or crushed.
The method for producing an iron-based powder material according to claim 8, wherein the dust collected in the steel production process is mixed. 16. The method for producing an iron-based powder material according to claim 15, wherein the dust is mixed with 10 to 30% by weight. 17. The iron-based powder material according to claim 8, wherein said flocculent aggregate is adjusted to a water content not exceeding 50% by weight and an oil content not exceeding 10% by weight. Manufacturing method. 18. The method for producing an iron-based powder according to claim 8, wherein the water content of the brittle compact is adjusted to 2 to 12% by weight and the oil content is adjusted to 1 to 5% by weight. 19. The method for producing an iron-based powder material according to claim 8, wherein said ground swarf contains at least 0.2% by weight of carbon.