JPS59542B2 - Iron powder for hand warmers made from reduced pellets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to iron powder for hand warmers, particularly to iron powder for hand warmers manufactured using reduced pellets whose main raw materials are fine ore and dust.

Recently, pocket warmers that utilize the oxidation heat of iron powder have come into use.

For a hand warmer that utilizes the heat of chemical reaction, it is desired that the heat generation temperature be as high as possible and the duration be long.To achieve this, generally porous reduced iron powder or dense and relatively Atomized iron powder with a small surface area has been heat-treated to activate the particle surface. Furthermore, since the calorific value is low when the total iron content is low, it has traditionally been thought that it is preferable for both reduced iron powder and atomized iron powder to have as much total iron content as possible. High purity iron powder with an iron content of 98% or more is used.

The present invention uses low-grade reduced iron powder made from reduced iron manufactured by a direct iron manufacturing method as the iron powder for such a hand warmer, instead of using expensive and high-purity iron powder. be.

According to the present invention, it is possible to use low-grade iron powder with a total iron content of 65 to 95% for hand warmers, and it is possible to supply reduced iron powder for hand warmers at low cost and in large quantities industrially. can.

By the way, when actually manufacturing a pocket warmer, iron powder, oxidizing agent,
A heat insulating agent is mixed and packaged, but after a while after storage, hydrogen is generated in the bag at the same time as the iron powder oxidizes, deforming the package and causing the package to collapse, reducing the product value.

The present inventors have elucidated the cause of hydrogen generation, and based on this, have taken the following measures to prevent hydrogen generation. First, the reduced iron pellets used in the present invention are manufactured in a rotary kiln.

Reduction of iron oxide such as iron ore or dust proceeds according to the following reaction formula using Co gas generated by the gasification reaction of the added carbon material. FeO+ Co→Fe+ CO2...
... (1) CO2+C→2CO... (2
) The reduction is carried out at a temperature below 1100°C.

Reduced iron and carbonaceous material (coke) discharged from the kiln are cooled in a cooler and then magnetically separated. The obtained reduced iron pellets usually have a particle size of about 12n and are used for blast furnace charging or as a replacement for scrap. When high-grade iron ore is used as the raw material for reduced iron pellets, the purity of the reduced iron is high and the total iron content and metallized iron content are over 85%, but when using blast furnace dust as a raw material, In case, total iron content is 65-80%, metallic iron content is 60%
Only ~75% of the amount is obtained.

The present inventors have devised a method of further drying and pulverizing these pellets and utilizing them as iron powder for hand warmers.

That is, the pellets discharged from the kiln are cooled by putting them into a cooler or underwater, but in the present invention, in order to reduce the moisture content of the reduced pellets, the reduced pellets are forcibly dried, then pulverized, and then put into a pocket furnace. Used as iron powder.

The reason why it is necessary to reduce the water content in the iron powder for hand warmers of the present invention is considered as follows.

The reaction in which reduced iron powder is reoxidized is caused by oxygen and water, and the following reaction can be considered. As a summary of the formula, 1Fe++Bi indicates an iron ion vacancy.

In particular, when iron is ionized in the reactions of formulas (3) and (8), H2O may be decomposed and H2 may be generated. Generally, hand warmers are manufactured by enclosing an oxidizing agent or oxidizing promoter such as H2SO4 or NaCl, and a heat insulating agent such as ash or sawdust together with iron powder or separately.

The outer bag is made of paper laminated with resin film on both sides or one side. Therefore, if the iron powder ionizes or oxidizes and generates hydrogen after packaging but before the bag is torn and used, the gas will fill inside the bag, deforming the bag and causing the load to collapse during storage. In addition to causing
When considering an oversized pocket warmer, it can even be dangerous. It is thought that this generation of hydrogen can be prevented by reducing the water content in the iron powder, as can be seen from the above reaction formula.

In reality, several tens of grams of iron powder are used in one bag of hand warmers, so if we consider the maximum, it is conceivable that more than 100 CC of hydrogen will be generated.

In addition, the iron powder conventionally used as iron powder for hand warmers is subjected to finishing reduction treatment in an atmosphere containing hydrogen during the final finishing process, so the iron powder contains a small amount of hydrogen.

On the other hand, in the case of reduced iron pellets according to the present invention, only the reduction treatment using solid carbon material (coke) is performed (types 1 and 2).
, there is no chance of hydrogen contamination.

Next, regarding the pulverization process, it is preferable to pulverize as strongly as possible to make it into a fine powder.

The reason for this is thought to be as follows. Usually, a pocket warmer is used by holding the outer bag by hand.

At this time, oxidative heat generation occurs locally, and the temperature first rises, and then the whole body becomes hot. As a hand warmer, one with a high heat generation temperature and a long heat generation time is preferred. In addition, in order to maintain the rising temperature, highly active iron powder is required to react quickly. From this, it is considered that the finer the particle size, the more active the iron powder is, and the greater the strain created by the crushing process.
For the above-mentioned reasons, it is necessary to pulverize the material into a fine powder. In the present invention, the material is finely pulverized to 100 meshes or less. This is because pulverizing more than that causes problems such as the particle shape becoming spherical and pores within the particle being closed, the pulverization cost being increased, and handling becoming difficult. Further, purity will be described.

Iron powder for hand warmers manufactured from reduced iron pellets is
Unlike conventional iron powder for powder metallurgy, there is a considerable difference between the total iron content value and the metallic iron value, and it is characterized by containing a considerable amount of FeO or Fe3O4. It is thought that this unreduced iron oxide (or partially re-oxidized iron) changes into a higher-order stable oxide when the temperature initially rises when it is used as a hand warmer. In fact, it has been discovered that even iron powder with a not so high metallization rate (ratio of metallic iron content to total iron content) exhibits a large amount of heat generation. It goes without saying that a high total iron content is required in order to perform high-temperature heating and long-term heating.

The iron powder for hand warmers of the present invention has a chemical composition of iron powder after pulverization of 65% to 95% of total iron content (T-Fe) and 65% to 95% of metallic iron content (M-Fe).
) 60 to 90%, a metallization rate of 90% or more, and a reduction loss of 5% or less.

The reduction weight loss is expressed as the weight loss rate when heated at 1050° C. for 1 hour 1 H2, and indicates the oxygen or vaporized components of the oxide that is reduced at this temperature.

Now, taking a reduction loss of 5% as an example, most of it is FeO
Assuming that the amount of oxygen is 23%, the amount of FeO is 23%.

If the rest is all metal iron, it will be 77%, and the total amount of iron at this time corresponds to 95% (18%+77%), so the metallization rate will be 'γrf.

Therefore, there is a difference of 9% from the metallization rate of 90% or more as claimed in the claims, which means that oxides or vaporized components may be contained in addition to iron by this amount.

Next, examples will be shown.

Table 1 shows reduced iron pellets (average particle size of each pellet: 12 m).
1L) to obtain iron powder for hand warmers.

Symbols A-C mainly consist of converter dust with high iron quality (T-F
e63.8%, coke blending ratio 20%, reduction temperature 120
0°C), D and E are mainly made of somewhat poor quality blast furnace dust and sludge (T-Fe43.5%,
Coke blending ratio 20%, reduction temperature 1200℃),
F and G are made from high-grade iron ore (T-Fe67.4%,
Coke blending ratio 25%, reduction temperature 1200. C). The drying conditions are usually air-cooled (or water-cooled) and then air-dried.
Since the content is ~2%, in the example of the present invention, the reduced pellets were dropped into water after being discharged from the kiln, and after being rapidly cooled, they were forcedly dried at 200'C and 30mm using a heavy oil burner.

This method resulted in a moisture content of 0.1% or less. As for the pulverization conditions, a vibrating mill was used, and A was set to -48 mesh coarse powder in order to examine the influence of particle size. B-G is -10
It was ground to 0 mesh, and there was no difference in particle size between B and G. Table 2 shows the chemical composition, metallization rate, and reduction weight loss of the iron powder for hand warmers produced in this way (1050% in hydrogen atmosphere).
℃, weight loss after heating for 1 hour), particle size distribution, and maximum exothermic temperature when these iron powders were actually made into a hand warmer.

The maximum exothermic temperature was measured by the following method.

Each of the iron powders A to G was wrapped in an inner bag, surrounded by an oxidizing agent, and then tested using a hand warmer in which the outer periphery of the oxidizing agent was surrounded by an outer bag.

The iron powder is 15 gr, and the oxidizing agent is commercially available Cairo ash powder with a concentration of 5 to 10 gr. impregnated with sulfuric acid aqueous solution 15 to 209 of
Wet Cairo ash whose pH value was adjusted to 4.0 to 6.0 was used. The inner bag was open at one end and was made of a thick non-breathable synthetic resin film, and the outer bag was made of paper laminated with a synthetic resin film with numerous pinholes on both sides or one side. . The outer bag of this pocket warmer was vigorously rubbed by hand for several minutes to mix the iron powder in the inner bag and the oxidizing agent on the outside, and the maximum exothermic temperature at this time was measured. Regarding the influence of iron powder particle size on the maximum exothermic temperature,
A is a coarse powder ground to -48 mesh and contains about 80% +100 mesh.

B is 100 mesh pulverized powder. Since the chemical components of A and B are almost the same, the difference in maximum exothermic temperature with A (5B) is considered to be simply due to the particle size.A is T-Fe,
Although the M-Fe content is quite high, the degree of heat generation is low. Therefore, it is necessary to set the grain size to -100 mesh.
Next, as for the influence of chemical components, B (in 5C, C
has lower M-Fe and more FeO than B.

Therefore, the value of the metallization rate is low, and on the contrary, the value of reduction loss is high. In this way, the difference between T-Fe and M-Fe is 1
When the value of the metallization ratio is 0% or more and 85% or less, the heat generation effect becomes poor. A similar tendency is seen in T- than in B and C.
It is also observed in D and E, which have a slightly lower Fe content. D and E have slightly lower exothermic temperatures overall than B and C. As shown in E, those with lower M-Fe values and metallization ratios of 85% or less have worse heat generation effects. Note that even if the value of T-Fe is low as in D, it can be said that there is a considerable exothermic effect if the metallization rate is 90% or more and the reduction loss value is 5% or less.

On the other hand, iron powder produced from reduced pellets made from high-grade iron ore tends to have high values for both T-Fe and M-Fe, and especially high exothermic temperature values for F. Furthermore, as for the influence of the moisture content in iron powder, B, D, and F iron powders that have been force-dried to a moisture content of 0.1% or less do not generate hydrogen even if they are stored for a long time after manufacturing a pocket warmer. There was almost no deformation of the bag.

As explained above, in the present invention, the particle size is set to 15 m7!L or less, since it is not economical to granulate it if the particle size is 16m77!L or more using a magnetic material of +5 mm by the direct iron manufacturing method.

Claims (1)

[Claims] 1 Reduced pellets with an average particle size of 5 to 15 mm are soaked in water at 0.1
% or less and then pulverized to 100 mesh or less, the iron powder has a total iron content of 65 to 95%, a metallic iron content of 60 to 90%, and a metallization rate of 90% or more,
Iron powder for hand warmers, characterized by a reduction loss of 5% or less.