Cold-box foundry binder systems having improved shakeout

Details Cold-box foundry binder systems having improved shakeout Cold-box foundry binder systems having improved shakeout

2002-04-05

2003-12-16

Dawson, Robert (Department: 1712)

Metal founding

Process

Shaping liquid metal against a forming surface

C164S016000, C164S526000, C523S139000, C523S144000, C523S145000, C523S147000, C523S148000, C523S466000

Reexamination Certificate

active

06662854

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to foundry binder systems, which will cure in the presence of sulfur dioxide and a free radical initiator, comprising (a) an aliphatic epoxy resin; (b) a multifunctional acrylate; and (c) an effective amount of a free radical initiator. The foundry binder systems are used for making foundry mixes. The foundry mixes are used to make foundry shapes (such as cores and molds) which are used to make metal castings, particularly aluminum castings.
(2) Description of the Related Art
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 into which molten metal is poured. The binder is needed so the molds and cores will not disintegrate when they come into contact with the molten metal. 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.
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.
The core or mold produced from the binder must maintain its dimensional accuracy during the pouring of the metal, but disintegrate after the metal cools, so that it can be readily separated from the metal part formed during the casting process. Otherwise, time consuming and labor intensive means must be utilized to break down (shakeout) the bonded sand, so that 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. Usually, mechanical energy is applied to the casting to facilitate removal. If the core does not break down sufficiently during the metal solidification and cooling stage, the core is difficult to remove and requires excessive mechanical rapping to remove it, or in extreme cases may require baking at temperatures exceeding 425° C. for extended periods to thermally degrade the core. This can result in substantial productivity losses as well as excess energy usage.
In iron or steel casting, the pouring temperature is typically around 1550° C. These high pour temperatures facilitate the break down of the core. However, in the case of light metals such as aluminum, core breakdown is compounded because of the relatively low pouring temperature of the metal. For instance, aluminum is typically poured at a temperature of around 725° C. Not only does this lower pouring temperature not facilitate core breakdown, but the aluminum casting cools quicker than a iron casting of similar dimensions, so that core breakdown is not facilitated as readily during the cooling stage of the casting. In view of these circumstances, core removal is a common problem in aluminum casting, there is a need for improved binders that will produce cores, which will not only provide good cores and castings, but will result in good core removal.
U.S. Pat. No. 4,176,114 discloses a poly(furfuryl alcohol) binder composition, which is mixed into an aggregate along with an organic peroxide (preferably methylethyl ketone peroxide, MEKP). The mixture is shaped into a mold or core and gassed with sulfur dioxide. The sulfur dioxide is oxidized by the peroxide and a strong acid generated, which polymerizes the poly(furfturyl alcohol) and hardens the mold. This binder is sold under the trade name “INSTADRAW”. The binder provides cores that are easy to remove from an aluminum castings. In fact, core removal times are significantly less than those where phenolic urethane cold-box binders are used to prepare the cores.
Nevertheless, the INISTRADRAW binder has two drawbacks. First, when the binder was actually used in a foundry, a chemically resistant poly(furfuryl alcohol) coating slowly deposited on the core box tooling. This deposit was very tough to remove, and if was not periodically removed, cores would stick in the tooling and dimensional accuracy would suffer. Secondly, the methylethyl ketone peroxide (MEKP) free radical generator had to handled as a separate part, and could only be shipped in small containers. This constituted a safety hazard if not handled properly. The MEKP catalyst was not storage stable when blended with the polyfurfuryl alcohol resin, and no other diluent for the MEKP could be found which was compatible with the system. Though this system is still sold commercially, it's commercial growth has been hindered by these drawbacks.
U.S. Pat. No. 4,518,723 discloses a binder, which is a mixture of an aromatic epoxide resin, such as bisphenol-A epoxy, blended with a multifunctional acrylate, such as trimethyolpropane triacrylate (TMPTA), and cumene hydroperoxide. This composition is mixed with an inorganic aggregate, e.g. sand, shaped, and gassed with sulfur dioxide. This use of this binder does not result in deposit formation on core box tooling during actual practice in a foundry, and was safer to use than the INSTRAWDRAW binder because the cumene hydroperoxide could be diluted in epoxy resin to form a storage-stable solution. It also made cores with much greater tensile strength with a greater variety of inorganic aggregates. This binder system, known as ISOSET® binders, is commercially successful and sold by Ashland Specialty Chemical Company. Although cores made with ISOSET binders have faster shakeout in aluminum casting operations than phenolic urethane cold-box binders, they do not have the fast shakeout characteristics of the poly(furfturyl alcohol) binders. Therefore, there is a need for binders that will produced cores with the fast shakeout characteristics of cores made with the poly(furfuryl alcohol) binder, without sacrificing the tensile properties of the cores, productivity, or the clean operating characteristics of the epoxy/acrylate system.
BRIEF SUMMARY OF THE INVENTION
The subject invention relates to foundry binder systems, which cure in the presence of vaporous sulfur dioxide and a free radical initiator, comprising:
(a) 20 to 70 parts by weight of an aliphatic epoxy resin;
(b) 10 to 50 parts by weight of a monomeric or polymeric acrylate monomer; and
(c) an effective amount of a hydroperoxide,
where (a), (b), and (c) are separate components or mixed with another of said components, provided (b) is not mixed with (c), and where said parts by weight are based upon 100 parts of binder.
The binders produce cores, which breakdown (shakeout) more easily and can be more rapidly removed from the casting. This advantage is particularly important when the castings are made from light-weight metals, e.g. aluminum. This improvement results without detrimentally affecting the tensile properties of the core or productivity.
This improvement is very significant from a commercial standpoint. The ability to remove core sand from a casting in less time boosts productivity and reduces labor costs, because, for most aluminum casters, the bottleneck in production is the core removal.
Also, the quality of the castings is improved because all of the sand from the cores used in making the casting can be removed from the casting before use. Many casting operations, such as automotive and aerospace, cannot tolerate even a single grain of sand remaining in the casting. The binders of this invention produce cores and molds which

Affiliated with

Also associated with

Rating

Cold-box foundry binder systems having improved shakeout does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Cold-box foundry binder systems having improved shakeout, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cold-box foundry binder systems having improved shakeout will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3140569