Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2000-06-19
2002-03-26
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S359000, C164S360000
Reexamination Certificate
active
06360808
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to exothermic sleeve compositions comprising (a) an oxidizable metal where the oxidizable metal comprises aluminum dross, and (b) an oxidizing agent capable of generating an exothermic reaction. The invention also relates to sleeve mixes prepared with the sleeve compositions, the use of the sleeve composition to prepare sleeves, the sleeves prepared with the sleeve compositions and the use of the sleeves to prepare metal castings.
BACKGROUND OF THE INVENTION
A casting assembly typically consists of a pouring cup, a gating system (including downsprue, choke, and runner), riser, sleeve, mold, core, and other components. To produce a metal casting, metal is poured into the pouring cup of the casting assembly and passes through the gating system to the mold and/or core assembly where it cools and solidifies. The metal part is then removed by separating it from the core and/or mold assembly.
Risers or feeders are reservoirs that contain excess molten metal. The excess molten metal is needed to compensate for contractions or voids of metal that occur during the casting process. Metal from the riser fills such voids in the casting when the casting metal contracts as it cools. Thus, the metal from the riser needs to remain in a liquid state for a longer period of time, so it can provide metal to the casting as it cools and solidifies. Sleeves are used to surround or encapsulate the riser and other parts of the casting assembly in order to keep the molten metal in the riser hot and maintain it in the liquid state for a longer time.
In order to serve their function, sleeves have exothermic and/or insulating properties. Exothermic sleeves function by liberating heat. This liberated heat satisfies some or all of the specific heat requirements of the riser and limits the temperature loss of the molten metal in the riser, thereby keeping the metal hotter and liquid longer. Insulating sleeves, on the other hand, maintain the heat of the molten metal in the riser by insulating it from the surrounding mold assembly.
Typical exothermic sleeve formulations contain aluminum as a fuel, metal oxides and/or nitrates as oxidizers, and fluoride containing compounds as fluxing agents. Fluoride compounds can be organic, such as fluorocarbon polymers (U.S. Pat. No. 5,180,759) or inorganic, for example sodium fluoride, aluminum fluoride, potassium fluoride, and sodium aluminum fluoride. These fluxing agents reduce the time it takes the exothermic sleeve to ignite and improve the propagation of the exothermic reaction.
However, high fluoride levels in the sleeve can cause fish eye defects in ductile iron castings. Therefore, it is desirable to keep the fluoride level extremely low, while still maintaining a fast exotherm in the sleeve.
U.S. Pat. No. 5,180,759 discloses that the fluoride level of the exothermic sleeve mix can be kept low by using organic fluorine compounds such as Teflon. The claims of the patent suggest that fluoride amounts as low as 0.05% fluoride are effective. However, the examples in the patent do not show polytetrafluoroethylene (PTFE) levels below 1.5% as effective in promoting the exothermic reaction. This level of PTFE corresponds to a fluoride level of 1.12%, which is much higher than the 0.05% level set forth in the claims.
SUMMARY OF THE INVENTION
The invention relates to an exothermic sleeve mix comprising:
(a) an oxidizable metal where the oxidizable metal comprises aluminum dross, and
(b) an oxidizing agent capable of generating an exothermic reaction.
This invention differs from the prior art because fluorine compounds typically used as fluxing agents in exothermic sleeve mixes are not required. Instead, a source of fluorine is derived from aluminum dross, which is a by-product of the manufacture of aluminum metal. Aluminum dross contains fluoride as a minor constituent. Aluminum dross has the fluoride intimately mixed and melted with aluminum, other oxidizable metals such as magnesium, silicon and aluminum oxide. Therefore, it provides a very efficient, fast igniting, and good propagating exothermic reaction. Exothermic sleeves containing aluminum dross, fine aluminum powder, potassium nitrate, and iron oxide are particularly efficient as riser sleeves in the casting of ductile iron. The use of aluminum dross with the oxidizing metal reduces the fluoride content needed in exothermic riser sleeves to achieve faster ignition and effective propagation of the exothermic reaction. Consequently, the likelihood of producing castings with “fish eye” defects, particularly ductile iron castings, is reduced.
In most cases, the amount of fluoride in the exothermic sleeve composition can be reduced by as much as 10-20 times compared to existing commercial formulations, while still maintaining a rapid exothermic reaction. Thus, the amount of fluoride in the sleeve mix is reduced to very low levels, e.g. 0.1-0.5 weight percent, based on the weight of the sleeve composition. Although the tested formulations were designed specifically for ductile iron, the sleeve mixes can be used to make sleeves for casting other metals.
DEFINITIONS AND ABBREVIATIONS
The following definitions and abbreviations are stipulated:
Casting assembly—assembly of casting components such as pouring cup, gating system (downsprue, runner, choke), molds, core, riser, sleeve, etc., which are used to make a metal casting.
ISOCURE® cold-box binder—a two part polyurethane-forming cold-box binder where the Part I is a phenolic resin similar to that described in U.S. Pat. No. 3,485,797. The resin is dissolved in a blend of aromatic, ester, and aliphatic solvents, and a silane. Part II is the polyisocyanate component, and comprises a polymethylene polyphenyl isocyanate, a solvent blend consisting primarily of aromatic solvents and a minor amount of aliphatic solvents, and a benchlife extender. The weight ratio of Part I to Part II is about 55:45.
Exothermic sleeve—a sleeve that has exothermic properties compared to the mold/core assembly in which it is used.
Gating system—system through which metal is directed from the pouring cup to the mold and/or core assembly. Components of the gating system include the downsprue, runners, choke, etc.
Handleable—the ability of a sleeve to be transported from one place to another without sagging or breaking.
Microspheres—alumino-silicate hollow spheres such as those described in WO 97/35677.
Mold assembly—an assembly of molds and/or cores made from a foundry aggregate (typically sand) and a foundry binder, which is placed in a casting assembly to provide a shape for the casting.
Pattern—a shape used to make a sleeve.
Riser—cavity connected to a mold or casting cavity of the casting assembly which acts as a reservoir for excess molten metal to prevent cavities in the casting as it contracts on solidification.
Sleeve—any moldable shape having exothermic and/or insulating properties made from a sleeve composition that covers, in whole or part, any component of the casting assembly.
US Standard Screen Test—test to determine particle size distribution using set of sieves 8″ diameter and aperture sizes from 4 inches to 500 mesh.
BEST MODE AND OTHER MODES
The exothermic sleeve composition comprises (a) aluminum dross and (b) an oxidizing agent. The sleeve compositions are used to make sleeve mixes that contain (1) an exothermic sleeve composition, and (2) an effective amount of a chemically reactive inorganic or organic binder. The sleeve mix is shaped and cured by contacting the sleeve with an effective amount of a curing catalyst.
Aluminum dross is produced as a by-product during the processing of aluminum metal, and, as such, has a variable composition. The major components of a typical aluminum dross suitable for use in this invention are described in Table I that follows, where the weight percents are based upon the total weight of the aluminum dross composition.
TABLE I
(Components of Aluminum Dross)
Component
Weight Percent
Aluminum metal
5-35
Aluminum oxide
30-50
Total magnesium
3-5
Total silicon
3-5
Total zinc
0-1
Total copper
0-
Aufderheide Ronald C.
Twardowska Helena
Ashland Inc.
Hedden David L.
Lin Kuang Y.
LandOfFree
Exothermic sleeve compositions containing aluminum dross does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exothermic sleeve compositions containing aluminum dross, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exothermic sleeve compositions containing aluminum dross will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2822324