Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-07-28
2002-07-30
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S144000, C523S143000
Reexamination Certificate
active
06426374
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to foundry binder compositions that contain a divalent sulfur compound, and/or foundry mixes where the aggregate contains a divalent sulfur compound. The foundry binders and foundry mixes are used to make foundry shapes, e.g. molds and cores. The presence of sulfur in the foundry shape facilitates the removal of foundry shapes (particularly internal cores) from the metal casting which is made by pouring molten metal into a casting assembly in which the foundry shapes are arranged. The invention also relates to a method of preparing foundry shapes, the shapes prepared, a method of making a metal casting, and metal castings by this process.
BACKGROUND OF THE INVENTION
In the foundry industry, one of the procedures used for making metal parts is “sand casting”. In sand casting, disposable molds and cores are fabricated with a mixture of sand and an organic or inorganic binder. The foundry shapes are arranged in casting assembly, which results in a cavity through which molten metal will be poured. After the molten metal is poured into the assembly of molds and cores and cools, the metal part formed by the process is removed from the assembly. The binder is needed so the molds and cores will not disintegrate when they come into contact with the molten metal.
Two of the prominent fabrication processes used in sand casting are the no-bake and the cold-box processes. In the no-bake process, a liquid curing catalyst is mixed with an aggregate and binder to form a foundry mix before shaping the mixture in a pattern. The foundry mix is shaped by putting it into a pattern and allowing it to cure until it is self-supporting and can be handled. In the cold-box process, a gaseous curing catalyst is passed through a shaped mixture (usually in a corebox) of the aggregate and binder to cure the mixture.
A binder commonly used in the cold-box fabrication process is a phenolic urethane binder. The phenolic urethane binder is mixed with an aggregate to form a foundry mix. The foundry mix is blown into pattern, typically a corebox, where it is cured by passing a gaseous tertiary amine catalyst through it. The phenolic urethane binder consists of a phenolic resin component and polyisocyanate component. Phenolic urethane binders are widely used in the foundry industry to bond the sand cores used in casting iron and aluminum. An example of a commonly used phenolic-urethane binder used in the cold-box process is disclosed in U.S. Pat. No. 3,409,575.
One of the problems with the using organic binders to form foundry shapes is that they can be too effective in binding the aggregate together. The result is that the foundry shapes are not readily separated from the metal part formed during the casting process. Consequently, time consuming and labor intensive means must be utilized to break down the binder so the metal part can be removed from the casting assembly. This is particularly a problem with internal cores, which are imbedded in the casting assembly and not easily removed.
The phenolic urethane cold-box process can be used to make cores and molds for the casting of ferrous and non-ferrous metal parts. Since iron castings are manufactured at about 1500° C., any phenolic urethane binder used in making foundry shapes, i.e. internal cores, will undergo rapid thermal decomposition at this temperature. Because of this, the internal core can be easily separated from the iron casting. This does not occur when aluminum parts are cast because aluminum castings are manufactured at about 700° C. At this lower temperature, the phenolic urethane binder does not readily decompose when the aluminum is cast, thus making complete removal of an internal core difficult.
Since light alloy casting, such as aluminum casting, is becoming increasingly used in place of iron as a means of reducing the weight of vehicle components such as engine blocks and manifolds, there is a need for developing new methods which facilitate the removal of internal cores. One method of facilitating removal of an internal core from a large aluminum casting (e.g. an engine block) or a complex aluminum casting (e.g. a water pump housing), is by baking the casting in a forced air oven at a high temperature for five to ten hours until the binder slowly decomposes. This procedure reduces productivity and requires forced air ovens and large amounts of energy. Alternatively, some aluminum castings can be violently shaken until the internal core is released. This procedure is inefficient and also reduces productivity.
Alternatives to phenolic-urethane cold-box binder systems can be used for aluminum casting that afford good core removal. For example, furan cold-box resins display excellent core removal characteristics in aluminum casting. However, furan resin binders build a tar like residue on tooling. This requires frequent cleaning, higher tooling costs, and lowers foundry productivity. See Richardson U.S. Pat. No. 3,879,339.
It is also known to use additives to improve the core removal characteristics of phenolic binders. For example, Ohashi et al, U.S. Pat. No. 4,600,733, teaches that a “disintegration assistant” composed mainly of calcium hydroxide, calcium carbonate, barium hydroxide and/or barium carbonate will promote heat deterioration of condensation resins such as phenolic shell resins. Another example is described in Japanese Abstract J.P. 60,064,744, which discloses that metal bromides promote the collapsibility phenolic shell resins. S.U. Abstract 1,316,741 discloses the use of a water glass binder in mixture with iron oxide, sulfur, and silica based refractory filler that has improved knockout. The iron oxide is added to breakdown the binder which improves the knockout capability of the mixture.
SUMMARY OF THE INVENTION
This invention relates to foundry binder compositions comprising as a mixture:
(a) an organic foundry binder having at least one component; and
(b) an effective amount of a divalent sulfur compound where said divalent sulfur compound is present in at least one component of the binder.
An effective amount of divalent sulfur compound is an amount sufficient to facilitate removal of a foundry shape from a metal casting, where the foundry shape is made from the organic binder containing the divalent sulfur compound.
The invention also relates to foundry binder systems where (a) and (b) are separate components, and foundry mixes that contain a divalent sulfur compound in the foundry aggregate. The invention also relates to a method of preparing a foundry shape, the shapes prepared, a method of making a metal casting, and metal castings prepared by this process.
The presence of sulfur in the binder composition and/or the aggregate facilitates the separation of the foundry shapes (cores and molds) from the metal part made by pouring molten metal into the foundry assembly. The effect of the sulfur in the foundry mix is particularly noteworthy when making aluminum parts with a casting assembly having internal cores. The time needed to remove the internal core from the metal part is significantly reduced which reduces cost and increased productivity.
These sulfur-containing organic binder compositions and/or foundry mixes are preferred for the cold-box process using phenolic urethane binders. Their advantages are most apparent when used to make internal cores that will be used in a casting assembly to cast aluminum parts.
BEST MODE AND OTHER EMBODIMENTS OF THE INVENTION
This invention can be used in any process, which utilizes an organic binder for making foundry shapes. For purposes of describing this invention, a foundry shape is any shape made from a foundry aggregate and organic binder that is used in a molding assembly for casting metal parts. A casting assembly is an arrangement of foundry shapes in a pattern such that a metal casting will be produced when molten metal is poured into the casting assembly and allowed to cool. An internal core is a core that is imbedded in the casting assembly. A foundry mix is a mixture of a foundry binder, and aggregate, and possibly a curing
Ashland Inc.
Cain Edward J.
Hedden David L.
Lee Katarzyna W.
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