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Bimetallic barrel head for processing corrosive metals and a method of manufacture thereof

IP.com Disclosure Number: IPCOM000012407D
Publication Date: 2003-May-05
Document File: 7 page(s) / 802K

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The IP.com Prior Art Database

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5711366: PATENT [+5]

Abstract

In accordance with the present invention, components of the barrel assembly may be manufactured from a Ni-based superalloy body (i.e. substrate) with a Co-based liner applied to all surfaces that could come into contact with the processing alloy. The Ni-based superalloy body provides high-temperature strength, and ductility. The application of a low C content, Co-based, crack free liner on any melt channel surface protects the Ni-based shell against contact with molten processing alloy. Similarly, the application of a high C content, Co-based coat, applied to sealing surfaces provides for proper sealing by preventing high-temperature yielding and also protects Ni-based superalloy against contact with the processing alloy.

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Bimetallic barrel head for processing corrosive metals and a method of manufacture thereof

Background

    An injection molding system for processing of semi-molten or molten alloys, such as with a thixomolding process as generally described in United States patents 4,694,881 and 4,694,882, requires that the components of a barrel assembly of an injection unit have the properties of sustained high temperature strength and resistance against corrosive attack by the processing alloys. A typical thixomolding processing alloy is AZ91D Magnesium alloy, with a nominal composition of 8.5% Al, 0.75% Zn, 0.3% Mn,
0.01% Si, 0.01% Cu, 0.001% Ni, 0.001 Fe, and the balance being Mg (also referred to herein as Mg-9%Al-1%Zn). A typical barrel assembly for a thixomolding injection unit includes a barrel and barrel head, the barrel head is retained on the discharge end of the barrel with a number of bolts. The construction and operation of a typical thixomolding injection unit and barrel assembly is described in United States patent 6,494,703. To meet the stated requirements of strength and resistance to corrosion, the barrel head is typically made of a tool-steel, such as DIN 1.2888 or VOLVIC 10, and the bolts made of Ni-based superalloy, such as INCONEL 718, that provide high-temperature strength. However, due to the fact that the coefficient of thermal expansion of the bolts is larger than that for the barrel-head steel it is necessary to re-torque the bolts of the barrel head once it has reached processing temperature in order to maintain a sealing arrangement at the barrel- barrel head interface. Conversly, when the barrel assembly is subsequently cooled to ambient temperatures the bolts shrink more than the barrel head, that without loosening

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cause large tensile stresses to develop within the stretched bolts that may eventually cause premature failure.

Detailed Description

    In accordance with the present invention, components of the barrel assembly may be manufactured from a Ni-based superalloy body (i.e. substrate) with a Co-based liner applied to all surfaces that could come into contact with the processing alloy. The Ni- based superalloy body provides high-temperature strength, and ductility. The application of a low C content, Co-based, crack free liner on any melt channel surface protects the Ni-based shell against contact with molten processing alloy. Similarly, the application of a high C content, Co-based coat, applied to sealing surfaces provides for proper sealing by preventing high-temperature yielding and also protects Ni-based superalloy against contact with the processing alloy.

     In an embodiment of the invention, a barrel head is proposed that is manufactured of a Ni-based superalloy, such as INCONEL 718, the melt-channel surface coated with low C content, Co-based compact (crack-free) and ductile layer, such as STELLITE 21. The seal surfaces of the barrel head are also to be coated with high C content, Co-based layers, s...