JPH0623413B2 - Resin coated reduced iron pellets - Google Patents

Description

TECHNICAL FIELD The present invention relates to resin-coated reduced iron pellets.

2. Description of the Related Art The Midrex method, the Hill method, the Fior method, and the like are widely known as direct reduction steelmaking methods for directly reducing iron ore using a reducing gas. The Midrex method and the Hill method are methods for obtaining reduced iron by solidifying massive or powdery iron ore into pellets having a diameter of about 5 to 20 mm, introducing this into a reducing furnace, and introducing a reducing gas. . The reduced iron pellets usually have a porosity of about 50%, and have a drawback that they are relatively easily pulverized by friction between the pellets and that they are easily oxidized by water absorption.

On the other hand, in the steel manufacturing method such as the fior method, since natural lump or powdery ore is used as it is, it is inexpensive, but on the other hand, the product is powdery or sponge-like, so that moisture absorption and oxidation are easily caused. Therefore, in this method, the reduced iron produced is hot-compressed again (for example, 770 to 780 ° C.) to obtain a porosity of 20 to
Used as a 30% briquette for storage or transportation. Although this briquette has an iron-like uniform surface in appearance, it still has a water absorption rate of 3 to 5%, which causes oxidation, corrosion, and bumping during melting. In order to prevent this water absorption phenomenon, US Pat. No. 3,573,959 describes a method of impregnating the briquette pores with a resin and curing the resin by the heat of the briquette itself to seal the pores. ing. The resin used here is an alicyclic olefin, a cyclic olefin, a diolefin, a triolefin, etc., and it is described that a mixture containing an oligomer of cyclopolyene is particularly preferable, and a steam cracking suffer residue is particularly suitable. Is stated. These are generally
It has a low viscosity and is considered to be polymerized and sealed by the heat of the briquette itself in the briquette pores.

However, the technique in which the pores of the briquette seal the pores and prevent water absorption is not useful for preventing water absorption and reducing pulverization of the reduced iron pellets. The reason is that reduced iron pellets have significantly higher porosity than briquette and are more brittle than briquette, and in general, the temperature of the pellet itself after resin impregnation is not high enough to polymerize polyenes. .

When a resin as described in U.S. Pat. No. 3,573,959 is used for coating reduced iron pellets, the impregnated amount of the resin is significantly increased at a temperature at which polymerization is possible, which is not profitable. In addition, the coating thickness on the surface of the pellet becomes thin, and the wear resistance decreases. Further, when the temperature is low, a separate heating step for accelerating the polymerization of polyenes is required, and a dryer for elementally unfavorable metal salts is required.

British Patent No. 2129708 describes a method using paraffin wax, but paraffin wax has a problem in strength and is not necessarily useful for preventing pulverization.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention provides the above-mentioned problems of reduced iron pellets, namely,
It is an object of the present invention to solve the problems that it is easily pulverized and that it easily rusts due to water absorption, and that it is extremely dangerous when water-absorbed reduced iron pellets are thrown into an electric furnace or the like to cause bumping of water. Further, it is achieved by using a coating agent having a higher strength than that of paraffin wax.

Means for Solving Problems The present invention has a viscosity at 200 ° C. of 1 to 10000 cp.
s, and a reduced iron pellet having a polyolefin resin coating layer having a softening temperature of 60 to 195 ° C.

The reduced iron pellet used in the present invention is obtained from the Midrex method, the Hill method, etc., and usually has a porosity of about 5
0-60% by volume, water absorption 12-15% by weight (saturated in water), apparent specific gravity 3-4, particle size 5
It is a substantially spherical pellet of about 20 mm. These are obtained by bringing unreduced iron pellets obtained by pelletizing iron ore into contact with a reducing gas in a reducing furnace.

The resin used to coat the reduced iron pellets is a polyolefin resin having a specific viscosity. Examples of the polyolefin resin include polyethylene, polypropylene, modified polyethylene, and the like.
The above polyethylenes are suitable.

The viscosity of the polyolefin resin suitable for the present invention at 200 ° C. is 1 to 10000 cps, particularly 10 to 7000 cps, and the softening temperature is 60 to 195 ° C., especially 80 to 120.
It is preferably in ° C.

If the viscosity of the polyolefin resin is greater than 10,000 cps, the resin coating on the surface of the reduced iron pellets will be uneven,
More resin is required to prevent water absorption. This is extremely uneconomical.

Further, if the resin viscosity is less than 1 cps, it becomes difficult to maintain the resin at an appropriate viscosity, the resin penetrates into the pores of the reduced iron pellets, and the pellets are porous with a porosity of about 50%. When this is dipped in molten polyolefin or the like for coating, the polyolefin penetrates into the inside of the pores of the pellet and is consumed for blocking the pores, so that the amount of resin adhering to the pellet surface is reduced. As a result, the abrasion resistance and pulverization resistance of the treated pellets are reduced. Further, the purpose of the present invention is to coat the surface of the pellet, and it is not always necessary to block the pores and voids.

Therefore, it is economically desirable to select a viscosity that does not allow the resin to penetrate deep into the pores.

The use of polyolefin enables formation of a high-strength coating with a smaller amount than paraffins.

The polyolefin is preferably brought into contact with the reduced iron pellets in the absence of a solvent so as to be higher than its effective melting point, preferably 2 to 3 ° C. higher than the softening melting point, and the viscosity at the time of contact is kept at least 80 to 90 cps It is desirable to adjust the temperature of the polyolefin or the reduced iron pellets.

Although contact between the polyolefin and the reduced iron pellets can be performed by dipping, spraying, etc., the dipping is uniform, but the amount of adhesion is large and the spray lacks uniformity. After holding, kneading is performed by rotation or the like.

An example of a method for producing reduced iron pellets coated with a polyolefin resin is shown in FIGS. 1 to 4.

FIG. 1 is a schematic sectional view of an apparatus for producing a polyolefin-coated reduced iron pellet of the present invention, FIG. 2 is a left side view of the apparatus of FIG. 1, FIG. 3 is an II sectional view and FIG. The right side view is shown. The rotary drum (1) is rotatably installed by a rotary support base (3) which is rotated by a motor (2), and is heated by a heater (4) provided on the outer surface of the drum. A carbon ring (5) is installed on the left side of the drum so that the heater can be energized when the drum rotates.
It is connected to the power supply by the brush (6). The electric power supplied to the heater is controlled by the slider box (7) according to the temperature inside the drum. The adjustment of the temperature and the supplied power may be manual, but can be easily managed by a computer. (10) indicates an insulator, A indicates an ammeter, and V indicates a voltmeter. A supply port (8) for supplying reduced iron pellets, a lid (9), and an inert gas (for example, nitrogen gas) supply valve (10) are provided on the right side surface of the drum. A blade (11) is provided inside the drum.

After charging reduced iron pellets and a polyolefin resin for coating the pellets from the supply port and completely replacing the air inside the drum with an inert gas, the valve (10) and lid (9) were completely sealed and the drum was closed. Heat with a heater while rotating. Since the rotation of the pellets is obstructed by the blades,
The resins that are in good contact with each other and melted by heating adhere uniformly. By adjusting the resin melting point and the internal temperature, it is possible to select the viscosity of the resin in an appropriate range, without the resin penetrating inside the reduced iron pellets,
It can be evenly attached to the surface.

The amount of polyolefin adhering to the reduced iron pellets was 0.1% of polyolefin per 100 parts by weight of reduced iron pellets.
-4 parts by weight, especially 0.3-3 parts by weight are suitable. 0.
If it is less than 1 part by weight, the coating thickness becomes insufficient, and conversely 4
It is only uneconomical to use more than parts by weight.

As described above, according to the present invention, it becomes possible to apply uniformly to the surface of the porous reduced iron pellets while suppressing suction as much as possible, and it is possible to supply the resin-coated reduced iron pellets that do not cause oxidation, pulverization, breakage, or the like. It will be. The present invention can also be applied to briquettes.

Hereinafter, the present invention will be described with reference to examples.

Example 1 100 kg of reduced iron pellets (porosity 55%, water absorption 15%)
In a drum and heated to 50 ° C under a nitrogen gas atmosphere,
2 kg of a polyethylene resin having a molecular weight of 1400 and a softening point of 83 ° C. was put into this, and the temperature of polyethylene was kept at 120 ° C. to rotate the drum at 40 rpm for 3 minutes. The obtained polyethylene-coated pellets were left outdoors for one month, and changes in metallization rate, water absorption rate during rainfall, rotational strength, and drop strength were observed. The results are shown in Table-1.

Metallization rate: Measured by wet analysis based on JIS-M-8202.

Water absorption rate: 100g of sample when it rains with an average rainfall of 2mm / hr
Was exposed for 5 hours, the water adhering to the surface was absorbed by the paper, and then weighed immediately and calculated.

Rotational strength: Measured based on JIS-M-8712.

Drop strength: Measured based on JIS-M-8711.

Example 2 100 kg of reduced iron pellets (porosity 55%, water absorption 15%)
In a drum and heated to 50 ° C under a nitrogen gas atmosphere,
2.5 kg of polyethylene resin with a molecular weight of 5000 and a softening point of 110 ° C is kept at 130 ° C for 3 minutes and the drum is rotated at 40 rp.
Rotated at m. The obtained polyethylene-coated pellets were observed in the same manner as in Example 1 for changes in metallization rate, water absorption rate during rainfall, rotational strength, and drop strength. The results are shown in Table-1.

Comparative Example 1 100 kg of uncoated reduced iron pellets were exposed outdoors for 1 month,
In addition to investigating changes in metallization rate, water absorption, rotational strength, and drop strength during rainfall were observed. The results are shown in Table-1.

Comparative Example 2 Reduced iron pellets (porosity 55%, water absorption 15%) 100 kg
Liquid diolefin (trade name: QUINTOL MW5
00) 5 kg of 100 parts by weight plus 8 parts by weight of cyclopentadiene was spin-coated at room temperature for 3 minutes, but after 30 minutes it was still tacky and the temperature was raised to 200 ° C. for drying. All were absorbed inside the pellets and almost no coating effect was observed.

Comparative Example 3 Reduced iron pellets (porosity 55%, water absorption 15%) 100 kg
Was heated to 90 ° C., held in a wire net, immersed in molten paraffin wax (liquid temperature 120 ° C .; softening point 68 ° C.) for 5 seconds, and the rotational strength and drop height were measured. The results are shown in Table-1
Shown in. The coating amount was 5.8%.

Comparative Example 4 Reduced iron pellets (porosity 55%, water absorption 15%) 100 kg
Is heated to 50 ° C., 2 kg of paraffin wax having a softening point of 68 ° C. is kept at 100 ° C., and the drum is rotated at 40 rpm for 3 minutes.
I rotated it. The rotation strength and the drop strength of the obtained paraffin wax-coated pellets were measured. The results are shown in Table-1.

EFFECTS OF THE INVENTION The resin-coated reduced iron pellets of the present invention are less susceptible to oxidation, have a smaller water absorption amount, and are less likely to be dusted. Therefore, the reduced iron pellets can be easily stored and transported. Also, compared with paraffin wax and coated pellets, high wear strength can be obtained with a small amount of use.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a reduced iron pellet manufacturing apparatus of the present invention, FIG. 2 is a left side view of the apparatus of FIG. 1, FIG. 3 is a sectional view taken along line I-I, and FIG. 4 is a right side view. (1) …… Rotary drum, (2) …… Motor (3) …… Rotary support, (4) …… Heater (5) …… Carbon ring, (6) …… Brush (7) …… Sliderax , (8) …… Supply port (9) …… Lid, (11) …… Vane (10) …… Inert gas supply valve.

Claims (3)

[Claims] 1. A viscosity at 200 ° C. of 1 to 10000 c
ps and reduced iron pellets having a coating layer made of polyolefin resin having a softening temperature of 60 to 195 ° C. 2. The pellet according to claim 1, wherein the polyolefin resin is a polyethylene resin having a molecular weight of 1000 or more. 3. The pellet according to claim 1, wherein the coating amount of the polyolefin resin is 0.1 to 4 parts by weight per 100 parts by weight of reduced iron pellets.