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Metal & Plastic Manufacturing Devices
SIALON CERAMICS DIE-CAST SLEEVES
Figure 2: Photo of a Sialon Sleeve
Overview
Sialon die-cast sleeves boast long product life in addition to
excellent molten metal heat-retention properties and extrusion
stability. These sleeves were first developed in 1986 and they
have been steadily improved. In recent years, the use of large-scale
sleeves of 2,000 tons-3,000 tons (This tonnage refers to the clamping
force of the die cast machine.) has been increasing.
Because automobiles have become lighter to preserve the environment and conserve energy, many auto parts, including engine blocks, have been converted to aluminum. Therefore, aluminum alloy forging has been on the increase. Many of these parts are manufactured using die casting. Although die casting offers the advantage of high productivity, it often causes problems with quality, such as defects in the internal cavity of products and products with chill fracture layers. The task for R&D is to improve these areas.
To improve the quality of die-cast products, a variety of methods to improve forging conditions, starting with molds, have been suggested. However, it has proven very difficult to surpass the molten metal heat-retention properties and extrusion stability offorded by inside the sleeve of conventional die casting. The reason for this is, because the die-cast sleeve is made of steel, the heat energy of the intruded molten metal is greatly leached, and the temperature of the molten metal, especially that which comes into contact with the inside face of the sleeve, is greatly reduced, resulting in potential chill fracture layers. During extrusion, the product is fractured at the tip and chill fracture layers are formed' Athereby resulting in defects. In addition, to prevent seizing between the tip and the sleeve, a large amount of tip lubrication must be used. As a result, a large volume of combustion gas from said lubrication is produced in the internal cavity.
As a result of the above, there is a strong demand in the die-casting industry for sleeves with excellent heat-retention properties and that use little lubrication but feature excellent extrusion stability. For this reason, for some time (since around 1975), the suggestion has been put forth that a ceramic product should be developed for use in die-cast sleeves. For quite some time, this idea could not be put into practice due to the insufficient strength, toughness and heat resistance of ceramics. Finally, Hitachi Metals succeeded in developing and put to practical use a die-cast ceramic sleeve by using Sialon, which offers excellent strength, toughness and heat resistance.
Next, we would like to introduce the form and function (features) of Sialon sleeves.
Because automobiles have become lighter to preserve the environment and conserve energy, many auto parts, including engine blocks, have been converted to aluminum. Therefore, aluminum alloy forging has been on the increase. Many of these parts are manufactured using die casting. Although die casting offers the advantage of high productivity, it often causes problems with quality, such as defects in the internal cavity of products and products with chill fracture layers. The task for R&D is to improve these areas.
To improve the quality of die-cast products, a variety of methods to improve forging conditions, starting with molds, have been suggested. However, it has proven very difficult to surpass the molten metal heat-retention properties and extrusion stability offorded by inside the sleeve of conventional die casting. The reason for this is, because the die-cast sleeve is made of steel, the heat energy of the intruded molten metal is greatly leached, and the temperature of the molten metal, especially that which comes into contact with the inside face of the sleeve, is greatly reduced, resulting in potential chill fracture layers. During extrusion, the product is fractured at the tip and chill fracture layers are formed' Athereby resulting in defects. In addition, to prevent seizing between the tip and the sleeve, a large amount of tip lubrication must be used. As a result, a large volume of combustion gas from said lubrication is produced in the internal cavity.
Figure 1: Position of
Die-cast Sleeve
As a result of the above, there is a strong demand in the die-casting industry for sleeves with excellent heat-retention properties and that use little lubrication but feature excellent extrusion stability. For this reason, for some time (since around 1975), the suggestion has been put forth that a ceramic product should be developed for use in die-cast sleeves. For quite some time, this idea could not be put into practice due to the insufficient strength, toughness and heat resistance of ceramics. Finally, Hitachi Metals succeeded in developing and put to practical use a die-cast ceramic sleeve by using Sialon, which offers excellent strength, toughness and heat resistance.
Next, we would like to introduce the form and function (features) of Sialon sleeves.
Structure
Figure 2 shows
a an exterior view photo, and Figure 3 shows cross-sectional view.
The structure of the sleeve is cylindrical and split into an internal
and an external layer. The internal layer is a Sialon cylinder, and
the external layer is made of a specialized alloy. The internal Sialon
sleeve's functions include heat retention and seizing resistance.
The external specialized alloy sleeve serves to protect the Sialon
from external forces, such as load. The internal and external sleeves
are shrunk to fit together to form one unit.
Figure 3: Cross-Sectional
View of a Sialon Sleeve
Features
What follows
is a comparison of Sialon die-cast sleeves and conventional steel
die-cast sleeves.
(1) Superior Molten Metal Heat Retention
Results of both testing and actual application show increased heat retention by 10-40°C and the temperature decrease of the molten metal in the vicinity of the sleeve shows little decrease. As a result, there is lower incidence of the development of chill layers and, therefore, lower incidence of the development of chill fracture layers in the internal cavity of the mold, thereby reducing defective output.
(2) Superior Extrusion Stability
Because Sialon does not react to molten aluminum, there is very little seizure onto the internal face of the sleeve. As a result, there is little sliding drag from the tip, yielding high extrusion stability and allowing a substantial reduction in the volume of lubricant used. In practical application, the volume of lubricant was reduced by 1/5 to 1/2. As a result, the volume of combustion gas produced by the lubricant is reduced, not only reducing defective output caused by the gas but also improving the air quality of the plant.
(3) Long Life
In practical application, Sialon die-cast sleeves were shown to have lifetimes 2-5 times as long as conventional steel sleeves.
(1) Superior Molten Metal Heat Retention
Results of both testing and actual application show increased heat retention by 10-40°C and the temperature decrease of the molten metal in the vicinity of the sleeve shows little decrease. As a result, there is lower incidence of the development of chill layers and, therefore, lower incidence of the development of chill fracture layers in the internal cavity of the mold, thereby reducing defective output.
(2) Superior Extrusion Stability
Because Sialon does not react to molten aluminum, there is very little seizure onto the internal face of the sleeve. As a result, there is little sliding drag from the tip, yielding high extrusion stability and allowing a substantial reduction in the volume of lubricant used. In practical application, the volume of lubricant was reduced by 1/5 to 1/2. As a result, the volume of combustion gas produced by the lubricant is reduced, not only reducing defective output caused by the gas but also improving the air quality of the plant.
(3) Long Life
In practical application, Sialon die-cast sleeves were shown to have lifetimes 2-5 times as long as conventional steel sleeves.
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