JPH0554403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an extrusion molding method, and particularly to an extrusion molding method for improving the dimensional accuracy of molded bodies and the yield of molded bodies.

<Prior art and its problems> Various molding methods are used to mold inorganic materials such as ceramics into complex shapes. For example, in the molding of honeycomb-shaped ceramics used as catalyst carriers,
The panel lamination method, paper dipping method, pipe bundling method, extrusion method, press method, mold method, etc. are known, but the extrusion method in particular allows the production of various shapes depending on the shape of the die, and it also allows for continuous molding. This is considered the most effective method possible.

However, in this extrusion method, clay (a clay-like material that is mainly composed of inorganic materials and is fired into a product), which belongs to the category of viscoelastic fluid, flows out from the die, so the extrusion molded body is A so-called Barus effect occurs in which the cross-sectional dimension is larger than the flow path cross-sectional dimension of the mouthpiece. If this is a thin and complex shape such as a honeycomb, this effect not only reduces dimensional accuracy but may also cause deformation. In order to reduce this Barus effect, the length l and diameter d of the mouthpiece flow path must be
One possible method is to increase the ratio l/d and decrease the flow velocity, but it is almost impossible to completely eliminate the bulge and this is not a fundamental solution to improving dimensional accuracy.

Furthermore, since the green body formed by molding the clay into a predetermined shape is an elastoplastic fluid, depending on the shape of the molded body, it may deform due to its own weight until it dries and hardens. For example, in the case of a honeycomb shape, the rib thickness and shape are limited depending on the characteristics of the molded body.

Additionally, when a molded product is dried, cracks are likely to occur due to slight non-uniform shrinkage. Therefore, a vacuum freeze-drying method typified by Japanese Patent Application Laid-Open No. 49-36708 has been considered. According to this method, the frozen water directly changes from a solid state to a gas and scatters (sublimation), so that it can be dried uniformly and in a short time. However, in the freeze-drying method, when the green body is frozen, volumetric expansion occurs due to the phase change of water from liquid to solid, which may cause cracks to occur in the green body. Therefore, it is necessary to carefully examine the freezing conditions.

On the other hand, some inorganic raw materials, such as transition Al ₂ O ₃ typified by γ-alumina (Al ₂ O ₃ ), may have hydraulic properties depending on the manufacturing conditions, and therefore require a relatively large amount of moisture. In the case of extruders required for There is a problem that extrusion molding becomes impossible. For this reason, as seen in Japanese Patent Publication No. 57-57247, in the case of hydraulic γ-Al ₂ O ₃ , fatty acids, aromatic compounds, polymer compounds, paraffin compounds, etc. are added to prevent hydration. However, it has been experienced that the temperature of the clay may rise due to frictional heat during kneading, accelerating hydration hardening and making extrusion molding impossible.

<Objective of the Invention> An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques and to provide a method for molding and drying molded bodies with high precision dimensions with good yield.

<Summary of Means> In short, the present invention cools the cylindrical part, the conical part, and the mouth part of an extrusion molding machine to bring the clay into freezing and solidifying conditions in the mouth channel, and continuously produces a frozen molded product. This paper proposes a means for obtaining a dry molded body by feeding and then performing a vacuum operation.

<Example> Fig. 1 shows the configuration of an apparatus necessary for freeze extrusion molding. The equipment includes a push mill 1, an auger machine 2
(Auger: spiral cone) (column ring part) A molding machine consisting of a taper barrel 3 and a mouthpiece (mouthpiece part) 4, an auger cooling jacket 6, and a taper barrel cooling jacket 7
and a refrigerator system for supplying coolant to the base cooling jacket 8. The functions of each component will be explained below.

The clay used for frozen extrusion molding is the same as the clay for extrusion molding, and is made by adding a binder, a binder, and a ceramic powder raw material.
A lubricant, water, etc. are added and the mixture is sufficiently kneaded using a kneader (kneading machine) or the like. This is further put into a bag mill (kneading machine) 1 and sent to an auger machine (conical end extruder) 2 while being kneaded. At this location, the temperature of the clay rises slightly above room temperature due to frictional heat from kneading. In the auger machine, the clay is made to flow toward the taper barrel 3 and the mouthpiece 4 while applying pressure.

Here, the clay is cooled by the coolant flowing through the auger cooling jacket 6, and the temperature of the clay in the tapered barrel is controlled to be slightly higher than the freezing point, ie, close to 0° C. when water is used. As the coolant, ethyl alcohol (freezing point: -114°C), calcium chloride, etc., which are normally used in refrigerators, etc., are used.

Further, the taper barrel shown in the drawing can be used with a pressure that reaches a maximum of about 10 to 150 kg/cm ² . Lowering the molar freezing point of binders, etc.
Along with the supercooling phenomenon, the freezing point will drop to some extent.

If the clay reaches the freezing point at this point, the clay will freeze at the inlet of the die, making it impossible to extrude. The factors that control the clay temperature are clay properties, coolant temperature, coolant flow rate (flow rate), etc.
To lower the temperature, the coolant temperature may be lowered and the coolant flow rate may be increased; to increase the temperature, the conditions may be reversed.

Quantitatively, the temperature of the coolant needs to be maintained at 0°C, although it is not specified here because it varies greatly depending on the characteristics of the extruder, etc.

Specifically, the temperature of the clay is controlled by installing a thermocouple at a position where it comes into contact with the clay, and feeding back the temperature to the control box, controlling the rotation speed of the auger screw and the temperature of the coolant (which also controls the refrigerator 9). ), this is done by adjusting the flow rate of the supplied coolant.The installation positions of thermocouples are, for example, their locations and symbols.
Indicated by T ₁ to _{T 6} .

Next, the clay cooled to nearly 0° C. in the tapered barrel portion 7 is sent to the die 4 for molding.

(100 as shown in Clasius Clapeyron's formula
The freezing point decreases by 0.73℃ for a pressure increase of Kg/ ^cm2 ). Here, the cap 4 is cooled to a temperature below which the clay freezes under normal pressure. High pressure (usually 30 to 150 kg/cm ² ) is applied to the clay at the mouth of the mouth and at the position slightly below the mouth of the mouth.
Due to the so-called Clasius Clapeyron effect, the freezing point drops and the clay does not freeze. However, when the clay is subjected to the extrusion force of the auger screw and is pushed out of the system through the nozzle, the pressure on the clay is suddenly released, causing the freezing point to rise. The clay is frozen just before passing through the die and exiting the system, and is extruded while maintaining the shape of the die.

If water is used to prepare the clay, the solidification of the clay will be -6°C due to the lowering of the molar freezing point and the supercooling phenomenon.
Occurs between -1°C. For this reason, the temperature of the coolant inside the base cooling jacket must be kept at -10°C or lower. Strictly speaking, in order to freeze the clay just before the outlet of the die, the diameter and flow rate of the die flow path, the properties of the clay,
Adjust the coolant temperature according to the extrusion speed, etc.

Molded objects obtained by freeze extrusion have higher precision than those extruded in an elastoplastic fluid state without producing the bulges (Barus effect) characteristic of extrusion. Moreover, it does not deform during handling and transportation.

Further, the continuously extruded frozen molded product is cut with a hot wire or the like, and then placed in a vacuum chamber as it is and subjected to vacuum freeze-drying. The degree of vacuum varies depending on the shape of the molded product, and in the case of a honeycomb-shaped product with a large surface area compared to its volume, it may be relatively low and 0.1 mmHg or less. Conversely, if the surface area is small compared to the volume, the radiant heat from the outside will dominate compared to the latent heat of sublimation, so there is a risk of thawing if the drying rate is not increased, so the drying rate should be at least 0.1 mmHg. It needs to be lowered even further. On the other hand, by depositing gold with low emissivity on the inner surface of the vacuum chamber, radiation from the outside can be minimized, and even a round bar can be used with a vacuum of about 0.1 mmHg.

Therefore, when implementing the present invention, the degree of vacuum is 0.1 mmHg.
It is preferable to specify the following.

Since the sample in this case has already been frozen, cracks during freezing that can occur when freeze-vacuum drying an elastoplastic fluid are avoided, and a dried product can be obtained quickly and with high yield simply by reducing the pressure without cooling. be able to. In addition, when drying an elastoplastic fluid molded product, it sometimes deforms due to its own weight until it hardens, but in the case of frozen molded products, the problem of deformation is almost nonexistent because the moisture sublimes from solid to gas during drying. do not have.

The above-described freeze extrusion molding method can be applied to all ceramic raw materials, but it is particularly effective when producing hydraulic raw materials such as γ-Al ₂ O ₃ . Figure 2 shows 10 parts by weight of methylcellulose, 3 parts by weight of glycerin, and 100 parts by weight of γ-Al ₂ O ₃ .
It shows the change over time in the penetration degree (a numerical value indicating the hardness of the clay) at each temperature for clay mixed with 50 parts by weight of water. As can be seen from this figure, if a normal extrusion method is used, exothermic hardening may occur due to frictional heat, making extrusion impossible. Therefore, by using the freeze extrusion molding method of the present invention, it is possible to absorb the frictional heat generated within the molding machine and obtain a frozen molded product in the same way as with non-hydraulic raw materials.

<Effects of the Invention> By using the freeze extrusion molding method of the present invention, the following effects can be obtained.

(1) At the mouthpiece outlet, the ceramic clay is completely frozen, resulting in good dimensional accuracy and no deformation during handling.

(2) By placing the frozen molded product in an insulated vacuum container, a dried product without deformation can be obtained quickly and with a high yield.

(3) By molding a hydraulic raw material by this freezing extrusion molding method, it will not become impossible to extrude due to hydration hardening.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a freezing extrusion molding apparatus according to an embodiment of the present invention, and Fig. 2 shows the results at various temperatures of clay made by adding a rehydration inhibitor to hydraulic γ-Al ₂ O ₃ and kneading it. FIG. 3 is a diagram showing changes in penetration over time in FIG. 1...Patsugumil, 2...Ogre Machine, 3...
... Taper barrel, 4 ... Mouthpiece, 5 ... Molded object, 6
... Auger cooling jacket, 7 ... Tapered barrel cooling jacket, 8 ... Mouth cooling jacket, 9 ...
... Refrigerator, 10 ... Coolant cooling loop, 11 ...
Coolant tank, 12... Coolant supply pipe, 13...
Coolant recovery pipe, 1... Clay inlet.

Claims (1)

[Scope of Claims] 1. In a method of extruding clay by adding and kneading an inorganic raw material with a binder, a lubricant, etc. as the main component, the clay in the column ring part of an extruder is heated just above the solidification point of the liquid component. A method for freezing and extruding clay, which comprises cooling the clay flowing through the extruder nozzle to a temperature below the freezing point of the liquid component to extrude the clay. 2 The extruded clay is placed in a container that can be maintained at a temperature that will not thaw, and the pressure inside the container is set to 0.1.
2. The method for freezing and extrusion molding of clay according to claim 1, wherein the extrusion molded product is dried under reduced pressure to below mmHg.