JPH0231304B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus suitable for continuously heat-treating powdered materials such as ceramic raw materials at high temperatures.

Continuous heat treatment of powdered materials at high temperatures is required in many fields. To obtain silicon carbide powder or whiskers, which have wide applications in the field of ceramics, for example, a mixture of silica powder and carbon black is heated at high temperatures, usually above 1500°C. In the prior art, this heat treatment is performed by filling the raw material mixture into individual crucibles and pushing the crucibles one after another into a Tammann furnace using a pusher. However, in such conventional heat treatment equipment, the crucible has a high breakage rate due to the pressing force of the pusher, which causes an increase in running costs. Also, complex automated equipment is required to fill the crucible and remove the heat-treated powder from the crucible.

An object of the present invention is to provide a cost-effective heat treatment apparatus that can continuously heat treat various powdered materials.

The heat treatment apparatus of the present invention includes a rotatable screw made of graphite within an outer cylinder. While the powder to be heat-treated is transferred by a screw from a supply port formed at one end of the outer cylinder to a discharge port formed at the other end, a heating means provided on the outside of the outer cylinder is used. is heated to a desired heat treatment temperature over a desired heat treatment time. Various types of heating means can be used, and for example, a Tammann tube or a graphite heater can be advantageously used. Depending on the type of powder, high-frequency induction heating may be more advantageous.

The heating time of the powder is determined by the rotational speed of the screw, assuming that screws of the same standard are used. That is, if the rotational speed of the screw is increased, the time required for the powder to pass through the heating area formed within the outer cylinder will be shortened, and the throughput per unit time will correspondingly increase.

As in the case of a normal screw conveyor, the product of the cross-sectional area of the space formed between the outer cylinder and the screw and the screw transfer speed (this is determined by the pitch and rotational speed of the screw) per unit time is Corresponds to the maximum amount of processing. If the powder is continuously supplied to the supply port in an amount commensurate with this maximum value, the space between the outer cylinder and the screw will be is always filled with powder. Even when heat treatment is performed in such a transfer mode, uniform heat treatment is possible due to the stirring effect caused by the rotation of the screw.

It is also possible to provide a supply amount control means for controlling the amount of powder supplied to the supply port per unit time. When the supply amount of powder is set to a value smaller than the maximum processing amount mentioned above by this control means, a portion of the space between the outer cylinder and the screw is filled according to the difference between the two. will remain as a space. This space serves to further enhance the stirring effect of the powder by the screw, and to facilitate the change in the shape of the powder when heat treatment changes the shape. For example, a mixture of silica powder and carbon black is used as a powder,
When producing SiC whiskers by heating this to approximately 1600°C, conventional technology involves adding a space-forming agent (for example, NaCl) to form the spaces necessary for whisker growth between the grains. However, when the device of the present invention is used under the conditions in which spaces are formed as described above, it is not necessary to add a space-forming agent. Therefore, the conventional drawback that the space-forming agent vaporized at the heat treatment temperature condenses on contact with other cooler parts essentially does not occur.

In this invention, a suitable material for constructing the screw is graphite. Graphite has the advantage of having sufficient mechanical strength and chemical stability at high temperatures exceeding the heat resistance temperature of many metals, and is easy to process into the desired screw shape. There is. Furthermore, since graphite has high thermal conductivity and surface smoothness, it is most suitable for the apparatus of the present invention, which heats a powder raw material to a high temperature, stirs it, and transfers it.

Next, an embodiment of the present invention will be described with reference to the drawings. The outer cylinder designated by reference numeral 1 in the figure is made of heat-resistant metal or ceramics and has a substantially cylindrical shape, and is arranged so that its axis is substantially horizontal. Further, an upward supply port 2 is formed at one end of the outer cylinder 1, and a downward discharge port 3 is formed at the other end.

Further, inside the outer cylinder 1, a coaxially arranged screw 4 made of graphite is housed. This screw 4 is rotatably supported by the outer cylinder 1 via a suitable bearing (not shown) about its axis, and receives power from a drive device 5 to rotate in one direction. It is designed to rotate at a high speed.

Above the supply port 2, a hopper 7 having a powder supply means, in this example a supply amount control device 6, is provided. The powder to be heat-treated is transferred to this hopper 7.
and is supplied into the outer cylinder 1 through the supply port 2 at a predetermined flow rate by the action of the supply amount control device 6. The powder supplied into the outer cylinder 1 is transferred inside the outer cylinder 1 from the supply port 2 toward the discharge port 3 by the screw 4 rotating at a desired speed, and when it reaches the discharge port 3, is discharged to the outside.

Reference numeral 8 indicates a heating means, such as a graphite heater, provided surrounding the central portion of the outer cylinder 1 in the longitudinal direction. This heating means 8 is for heating the powder material moving inside the outer cylinder 1 to a desired heat treatment temperature. While moving, it undergoes a predetermined heat treatment and is automatically discharged from the discharge port 3.

Experimental Example An experiment was conducted to heat-treat a mixture of silica powder and carbon black to obtain a uniform mixture of silica powder and SiC whiskers using a heat treatment apparatus of the type shown in the figure. The heat treatment equipment used was
A graphite screw (9 cm in diameter) is provided inside an outer cylinder 1 with a length of about 2 m from a supply port 2 to a discharge port 3 and an inner diameter of about 10 cm, and a graphite heater as a heating means 8. By length
The internal powder is heated to approximately 1600℃ over a 0.5m area.
heated to. The rotation speed of the screw 4 is set to a value that requires approximately 2 hours for the powder to move from the supply port 2 to the discharge port 3, and the supply amount of the powder raw material is
The feed rate control device 6 limits the maximum transfer rate of the screw 4 to approximately 1/2.

By heat-treating a powder consisting of 85% silica powder and the remainder carbon black under the above conditions, a mixture was obtained in which SiC whiskers in an amount equivalent to approximately 20% of the total were uniformly mixed in the silica powder. . This SiC whisker has a diameter of approximately 0.2~0.5μ and a length of approximately
It was confirmed that it was a SiC single crystal with a size of 50 μm to 150 μm.

[Brief explanation of drawings]

The figure is a schematic vertical sectional view showing a heat treatment apparatus according to an embodiment of the present invention. 1... Outer cylinder, 2... Supply port, 3... Discharge port, 4
... screw, 5 ... drive device, 6 ... supply amount control device, 7 ... hopper, 8 ... heating means.

Claims (1)

[Claims] 1. An outer cylinder having a supply port through which the powder to be heat treated is supplied and a discharge port through which the heat-treated powder is discharged at one end and a discharge port from which the heat-treated powder is discharged; a screw made of graphite, which is rotatable in the state and is configured to move the powder in the outer cylinder at a predetermined speed from the supply port side toward the discharge port side end when rotated; and the outer cylinder. A high-temperature heat treatment apparatus for powdery material, comprising a heating means for heating the powdery material moving therein to a desired heat treatment temperature.