JP2006007536A - Extruded product drying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for drying an extruded product, which can dry an extruded product of an iron-containing powder to which an organic binder is added without causing explosion, and develop the strength of the molded product after drying.
In a method in which an organic binder is added to an iron-containing powder and kneaded, and then the kneaded product is extruded by an extruder and the molded extrudate is dried. After low temperature pre-drying in an atmosphere in the range of 80 to 100% and normal temperature to 60 ° C., in an atmosphere in which the relative humidity is 60% or less and the temperature is 150 ° C. from the temperature at which low temperature pre-drying is performed. This is dried, and the extruded product after this drying is cooled.
[Selection] Figure 1

Description

The present invention relates to a method for drying an extrudate for producing a high-strength extrudate that can be used in a steelmaking and steelmaking process by drying an extrudate obtained by extruding iron-containing powder generated in an ironworks or the like. About.

Conventionally, as a method for forming dust or the like generated at an ironworks or the like, a fired pellet method, which is an effective means for obtaining a strong molded product, has been used. However, since this method requires heat energy to develop the strength of the molded product, particularly from the viewpoint of energy saving, in recent years, the molded product by non-firing molding method using cement or a water-soluble organic binder as a binder is used. Manufacturing methods have been put into practical use. Here, when cement is used as a binder, it must be cured in the atmosphere for several days before the molded product can be used, and a large site is required for curing the molded product, and further handling to the site is required. There is a problem that the transportation cost for (conveying) becomes enormous.
Therefore, in order to eliminate the need for a vast site as in the case of using cement and to eliminate the handling of the molded product, the molded product is forcibly dried using an organic binder as a binder.

However, immediately after molding the molded product, the molded product is not strong enough to be easily disintegrated. In particular, when drying is performed immediately after molding, the molded product explodes, making it difficult to dry immediately after production.
Therefore, Patent Document 1 proposes a method of performing drying at less than 150 ° C. so that carbon and volatile residues, which are foaming components that expand due to firing, are not consumed due to oxidation or volatilization when drying lightweight refractories. Has been. In this way, an attempt was made to prevent explosion during drying of the molded product by applying a drying method with a drying temperature of less than 150 ° C. to drying the molded product.

JP-A-60-103057

However, for molded iron-containing powders using organic binders, even when dried at less than 150 ° C., the molded product will explode, making it impossible to produce molded products with the desired strength. It was.

The present invention has been made in view of such circumstances, and is capable of drying an iron-containing powder-extruded product to which an organic binder has been added without causing explosions, and exhibiting the strength of the molded product after drying. It aims at providing the drying method of a molded object.

In order to achieve the above object, the present inventors have conducted various tests, and as a result, the humidity was set in the range of 80 to 100% and the temperature was set in the range of room temperature to 60 ° C. or less at the initial drying stage. It has been found that by performing drying inside, the occurrence of cracks in the molded product can be suppressed and the strength can be expressed in a short time, and the present invention has been completed.

The means 1 is a method of adding an organic binder to an iron-containing powder and kneading, and then extruding the kneaded product with an extruder and drying the formed extrudate.
The temperature at which the relative humidity is 80% or less and the temperature is 60% or less, the relative humidity is 60% or less, and the temperature is the temperature at which the low temperature preliminary drying is performed. To 150 ° C. in the atmosphere within the range, and the extruded product after the main drying is cooled.
In the drying method of the extruded product described in Means 1, the organic binder includes any one or more of a starch binder, lignin, polyvinyl alcohol, and the like.
Moreover, as an extrusion molding machine, for example, a conveying pipe in which a screw for conveying a kneaded material from upstream to downstream is conveyed, and a gold provided at a downstream end of the conveying pipe. A conventionally well-known thing etc. which have a type | mold can be used, and it can shape | mold to a predetermined shape by extruding a kneaded material from a conveyance pipe through a metal mold | die.
Then, the surface layer portion is cured while suppressing the moisture from being removed from the central portion of the extruded product by the low temperature preliminary drying, and the moisture of the central portion of the extruded product is removed by the main drying, so that the entire extruded product Dry.

Here, in the low temperature pre-drying, when the relative humidity of the atmosphere for drying the extruded product is less than 80%, the moisture in the central part of the extruded product is rapidly and greatly removed, and the surface of the extruded product is cracked. May occur. On the other hand, when the relative humidity exceeds 100%, water droplets are generated on the surface of the extruded product, and this moisture is absorbed by the extruded product, so that the surface layer portion of the extruded product cannot be cured.
Therefore, in order to cure without causing cracks in the surface layer portion of the extruded product, it is preferable to set the lower limit of relative humidity to 85% and the upper limit to 95%.
In addition, in the low temperature pre-drying, by controlling the temperature of the atmosphere in which the extruded product is heated and cured within the range of normal temperature (for example, 15 to 20 ° C.) to 60 ° C., the occurrence of cracks in the extruded product is suppressed. Furthermore, it can be prevented.
Therefore, in order to dry the extruded product with high productivity in a short time and to suppress or further prevent the occurrence of cracks, the lower limit of the ambient temperature should be 30 ° C., further 40 ° C., and the upper limit should be 55 ° C. preferable.

In the main drying, when the relative humidity of the atmosphere for drying the extruded product exceeds 60%, the moisture contained in the extruded product cannot be reduced to the target moisture content, resulting in the strength of the extruded product. Absent. Even if the strength can be increased, the time required for drying becomes longer and the productivity becomes worse. In addition, in this drying, since the objective is to dry an extrusion molding, the lower limit of relative humidity is not set.
However, in order to extremely reduce the humidity, dehumidifying equipment is required. Therefore, it is preferable that the humidity is unnecessary, that is, about 30% or more. In order to increase the strength of the extruded product after the main drying and increase the productivity, it is preferable to set the relative humidity of the main drying atmosphere to 50% or less, and further to 40% or less.
Further, in the main drying, the temperature of the atmosphere in which the extruded product is dried is set within the range of 150 ° C. from the temperature at which the low temperature pre-drying is performed, so that the extruded product is dried while the extruded product is dried. Oxidation heat generation of iron components inside can be prevented.
Therefore, in order to dry the extruded product with high productivity in a short time and to develop the strength of the molded product after drying, the lower limit of the ambient temperature is 100 ° C., the upper limit is 150 ° C., and further 140 ° C. Is preferred.

Means 2 is the drying method of the extruded product according to Means 1, wherein the organic binder is starch, and the low temperature predrying is performed for 10 minutes while maintaining a preset temperature within the temperature range from the normal temperature to 60 ° C. Do it above.
The starch binder has different alteration temperatures depending on the production method, but it may be α starch or β starch that has been heated to about 90 ° C. to be gelatinized.
Further, since the extruded product is dried while maintaining the temperature in the low temperature preliminary drying, the entire surface layer portion of the extruded product can be uniformly heated and cured.
Here, by setting the temperature holding time in the low temperature pre-drying to 10 minutes or more, preferably 15 minutes or more, more preferably 20 minutes or more, cracks are generated in the surface layer portion of the extruded product even in the main drying. The extruded product can be dried without any problems. In addition, in the low temperature pre-drying, since it is only necessary to heat and cure the surface layer portion of the extruded product, the upper limit value of the temperature holding time is not set, but for example, in consideration of productivity etc., it is 30 minutes or less. It is preferable to set.

The means 3 is the drying method of the extruded product according to the means 1 and 2, wherein the main drying is performed by sequentially raising the temperature in a temperature rising pattern in which the temperature is set in advance.
In the method for drying an extruded product described in the means 3, for example, there are the following temperature rising patterns.
(1) In the initial stage of the main drying, the temperature is rapidly increased from the temperature of the low temperature preliminary drying to near 150 ° C., and then the temperature is maintained.
(2) From the initial stage to the final stage of the main drying, the temperature is gradually increased continuously or intermittently from the temperature of the low temperature preliminary drying to around 150 ° C.
(3) The temperature of the low temperature preliminary drying is maintained from the initial stage to the middle stage of the main drying, and the temperature is rapidly increased to about 150 ° C. from the middle stage to the final stage of the main drying.

Means 4 is the drying method of the extruded product according to means 1 to 3, wherein the moisture of the extruded product cooled after the main drying is 1% by mass or less.
In the drying method of the extruded product described in the means 4, when the water content of the molded product exceeds 1% by mass, the produced molded product may not be able to obtain the intended strength.

In the present invention, the inside of the extruded product is dried by main drying after the surface layer portion is heated and cured while suppressing the loss of moisture from the extruded product by low temperature preliminary drying, so that an organic binder is added. The extruded product of the iron-containing powder can be dried without causing explosion, and the strength of the molded product after the main drying can be expressed.

In particular, since the drying method of the extrusion molding according to claim 2 uses starch as the organic binder, it is possible to produce a molding with enhanced binding strength at a low cost. In addition, since the low temperature preliminary drying is performed for 10 minutes or more while maintaining a predetermined temperature, the extruded product can be dried without causing cracks in the surface layer portion of the extruded product in the main drying.

In the drying method of the extruded product according to claim 3, since the main drying is performed by sequentially raising the temperature in accordance with a preset temperature raising pattern, it can be removed by gradually increasing the amount of evaporation of water, and cracks and the like are generated. No drying can be carried out.

In the drying method of the extruded product according to claim 4, since the moisture of the extruded product cooled after the main drying is 1% by mass or less, the molded product which does not collapse at the time of use can be obtained.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is an explanatory view of a method for drying an extruded product according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing the influence of relative humidity and temperature at the time of low temperature pre-drying on the manufactured product. is there.

As shown in FIG. 1, the method for drying an extruded product according to an embodiment of the present invention includes adding a starch binder (an example of an organic binder) to an iron-containing powder and kneading, and then extruding the kneaded product. This is a method of extruding by a machine (not shown) and drying the formed extrudate. This will be described in detail below.

First, a starch binder (α-starch) and water are added to and kneaded with iron-containing powder having converter dust (OG dust) and dust collection dust (dry dust) generated in an ironworks to produce a kneaded product. In addition, the particle size of the iron-containing powder to be used is, for example, about 0.5 mm or less, and the amount of water to be added is, for example, 10 to 20% by mass (for example, 10 to 20% by mass) of the moisture content of the extruded product formed by the extruder. In the present embodiment, adjustment is made to be about 15 to 16% by mass).
The kneaded product is supplied to the extruder at a predetermined amount, for example, a rod-like extrusion molding having a diameter of about 10 to 20 mm (16 to 17 mm in the present embodiment) and a length of about 30 to 40 mm. Manufacturing things.

This extrudate is dried using a dryer 10 shown in FIG.
Inside the dryer 10, a conveyance path 11 is provided from the upstream side to the downstream side, and an endless net 13 of the net conveyor 12 is movably disposed in the conveyance path 11. Further, the dryer 10 is divided into 11 blocks A to K from the upstream side to the downstream side, and the temperature and humidity can be set for each block. In addition, the conveyance speed of the extrusion molding by the net | network 13 of the net conveyor 12 is set so that the passage time of each block may be about 5 to 10 minutes (6 minutes in this Embodiment), for example.

Each of the blocks A to K is provided with a heat exchanger 14 that uses steam heat at the top, and heat blown downward via a damper (not shown) that adjusts temperature and humidity is below the net 13. It is collected by the window box 15 located.
Thereby, after the extrudate inserted from the supply port 16 of the dryer 10 is placed on the moving net 13, it is transported at a predetermined speed in the transport path 11 of the dryer 10. Drying is performed while passing through the atmosphere in which the temperature and humidity are set for each block of K and discharged from the discharge port 17 of the dryer 10.

Here, the temperature and humidity for each of the blocks A to K will be described.
Each block of AC of this dryer 10 is a part for performing low temperature pre-drying of the extrusion molding, each block of D to J is a part for performing main drying of the extrusion molding after the low temperature pre-drying, and a block of K is The extrudates after the main drying are cooled.
The low temperature preliminary drying performed in each of the blocks A to C is important in order to develop the strength of the molded product, and the humidity and temperature were set based on the following results.

First, as the low-temperature pre-drying of the extruded product, the relative humidity was 60% (■), 80% (♦), and 95% (▲), and the drying temperature (initial drying temperature) was in the range of 40 to 100 ° C. Thereafter, the powder ratio of the molded product which was dried and cooled under conditions of a relative humidity of 60% or less and a maximum temperature of 150 ° C. was investigated.
As shown in FIG. 2, as the relative humidity was decreased, the powder ratio of 5 mm under (−5 mm) was increased, that is, the obtained molded product was easily explosive. In particular, when the relative humidity was 60%, the result that the powder rate increased by 2 mass% or more was obtained compared to the case where the relative humidity was 80%.
Further, as the drying temperature was increased from 40 ° C., the powder rate tended to increase, and in particular, the result was that the powder rate increased rapidly at the drying temperature of 60 ° C. as a boundary.

From the above, in order to suppress the occurrence of cracks and produce a high-strength molded product, low-temperature pre-drying is performed in an atmosphere in which the relative humidity is in the range of 80 to 100% and the temperature is in the range of room temperature to 60 ° C. I decided to do it. Note that the temperature of the atmosphere can be gradually increased from room temperature to 60 ° C., for example, or can be further increased after being rapidly increased from room temperature to about 50 ° C. and held for a predetermined time.
Moreover, since this low-temperature preliminary drying is to heat and cure the surface layer portion of the extruded product, in order to perform stable drying, a temperature within the above-described range (preferably in the range of 40 ° C to 60 ° C). (Predetermined temperature) is preferably 10 minutes or longer (in this embodiment, about 18 minutes).

Next, main drying is performed in which the extrusion-molded product that has been subjected to the low-temperature pre-drying is dried almost completely in the blocks D to J of the dryer 10.
Each of the blocks D to J has a relative humidity set within a range of 60% or less, and has an atmosphere within a range of 150 ° C. from the temperature at which the low temperature preliminary drying is performed. Note that the temperature of the main drying is a preset temperature increase pattern, for example, from the initial to the end of the main drying, from the low-temperature pre-drying temperature (for example, 60 ° C.) to 150 ° C. continuously or intermittently gradually. Raise the temperature.

As described above, by using the dryer 10, the extruded product charged in the dryer 10 is a block of A to C. In each block, the whole is heated and dried.
The extruded product thus dried is cooled to room temperature with a K block. The moisture contained in the cooled molded product is about 1% by mass or less (in this embodiment, 0.5% by mass or less, and further 0.3% by mass or less).
By the above method, the formation of cracks can be suppressed, and a molded product having high strength that can be used in the iron making and steel making processes can be produced in a shorter time than before.

As described above, the present invention has been described with reference to one embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and is described in the claims. Other embodiments and modifications conceivable within the scope of the above are also included. For example, a case where the drying method for an extruded product of the present invention is configured by combining some or all of the above-described embodiments and modifications is also included in the scope of the right of the present invention.
Moreover, in the said embodiment, although the case where a starch binder was used as an organic binder was demonstrated, it is also possible to use another organic binder, for example, lignin or polyvinyl alcohol.

It is explanatory drawing of the drying method of the extrusion molded product which concerns on one embodiment of this invention. It is explanatory drawing which shows the influence of the relative humidity and temperature at the time of low-temperature predrying with respect to the manufactured molded object.

Explanation of symbols

10: dryer, 11: transport path, 12: net conveyor, 13: net, 14: heat exchanger, 15: window box, 16: supply port, 17: discharge port

Claims (4)

In the method of adding an organic binder to the iron-containing powder and kneading, then extruding the kneaded product with an extruder and drying the formed extrudate,
The temperature at which the relative humidity is 80% or less and the temperature is 60% or less, the relative humidity is 60% or less, and the temperature is the temperature at which the low temperature preliminary drying is performed. To 150 ° C., and drying the extruded product after the main drying, and cooling the extruded product. The method for drying an extruded product according to claim 1, wherein the organic binder is starch, and the low temperature preliminary drying is performed for 10 minutes or more while maintaining a preset temperature within the range of the normal temperature to 60 ° C. A method for drying an extruded product. 3. The method for drying an extruded product according to claim 1, wherein the main drying is performed by sequentially raising the temperature in a temperature rising pattern set in advance. Drying method. The method for drying an extruded product according to any one of claims 1 to 3, wherein moisture of the extruded product cooled after the main drying is 1% by mass or less. Drying method.

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