Metal founding – Process – Including recycling of process material
Reexamination Certificate
2002-07-03
2003-02-11
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Including recycling of process material
C164S412000
Reexamination Certificate
active
06516863
ABSTRACT:
BACKGROUND
In foundries, metal is poured into molds which are fabricated from special mixes of sand and special-purpose bond/adhesive compositions. This invention addresses apparatus and methods for making, using, and recycling the sand mix. The invention specifically addresses use of particulate bond materials which remain in particulate form when mixed with water, and apparatus and methods for controlling dust which may be generated in the process of making and using such sand mixes.
In making the sand mix, sand is mixed with water, and with the bond material. The bond material is a finely-powdered mixture of e.g. bentonite clay, coal, and a combination of compatibilizers, stabilizers, wetting agents, and the like.
In conventional sand preparation, the sand mix is generally made up in a mullor. In general, a mullor is a special purpose mixing tank. Sand and bond material are metered into the mullor at specified ratios or rates. Water is added to the tank in defined quantity. A typical charge to the mullor is comprised primarily of return sand, with make-up quantities of fresh bond material and fresh sand, in combination with sufficient water to bring the resultant water content of the mix to the desired level.
A mix motor or the like rotates mixing paddles and/or wheels inside the mullor to mix the respective components placed therein. The mixing of sand in the mullor can be either a batch process or a continuous stream process. The exiting sand is preferably tested against a standard, and adjustments to the dry or wet ingredients currently in the mullor are made in response to results of those tests of completed product which have recently exited the mullor.
Typical bond material is a finely powdered particulate material, so fine as to easily become airborne as dust in a gaseous environment such as the air inside the mullor. Such particulate bond material is in general smaller than 200 mesh, and is typically added to the mullor in dry form, and thus is susceptible to becoming air borne until such time as the respective particles become wetted with the water. Indeed, that wetting process is part of the function of the mulling operation. In general, the mullor should accomplish the tasks of uniformly dispersing the fresh sand and fresh bond material, and substantially wetting all bond and sand particles.
In general, the sand particles tend to be relatively hydrophilic while the bond material particles tend to be relatively hydrophobic. Thus, the water tends to be more attracted to the relatively larger sand particles than to the relatively smaller bond material particles whereby the relative tendency for wetting sand particles with a given batch of water is greater than the relative tendency for wetting bond particles with the respective batch of water. Namely, absent an excess of water, the water is selective in tending to wet sand surfaces more readily than bond material surfaces, thereby running the risk that a significant fraction of the bond particles may not be wetted. Accordingly, one of the objects of this invention is to increase the fraction of the fresh bond particles which are effectively wetted by the water.
Typically, freshly-added bond material is fed into the mullor as a stream of dry particles, e.g. transported pneumatically or dropped by gravity into the mullor receptacle. As the dry particulate bond material enters the mullor receptacle in the conventional manner, a fraction of the bond material can and does become entrained in the air through which the bond material passes as the bond material drops to either the bottom of the tank or to a mass of sand, water, and/or other bond material already in the tank. In addition, to the extent bond material lands on underlying dry material already in the mullor, e.g. relatively dry return sand or previously added and still-dry bond material, the dropping dry bond material particles land on the bond material particles on the surface of such underlying material are free to become air-borne upon sufficient agitation or other disturbance, whether solid, liquid, or gaseous agitation. Indeed, so long as such small particles are not wetted, the particles readily go air-borne upon even mild agitation, much like edible grain flours.
Accordingly, one of the primary sources of dust in foundry operations is dry, or relatively dry, particulate bond material in the sand system. A first mechanism for such dust to become air-borne is bond material which becomes dispersed in the air inside the mullor as the bond material is added to the mullor, and as the bond material is in general being mixed with the sand and water. Since bond material, sand, and water are repeatedly or constantly being added to the mullor, and discharged from the mullor, there is an ongoing flow of air into the mullor, and out of the mullor. If no controls are placed on flow of such air, much of the air which exits the mullor will pass to ambient, and will carry with it substantial quantities of air-borne particulate bond material pollution.
Accordingly, it is well known to provide dust collection apparatus as part of a sand system, for capturing particulate material which becomes entrained in the air in the mullor and in other parts of the sand system. Indeed, typical foundry sand systems generate waste particulate bond material amounting to about 25 percent to about 50 percent by weight of the particulate make-up bond material fed to such sand systems, as it is common that such quantity is eventually collected in the dust collection system.
In addition to providing for addition of make-up quantities of bond material, provisions are also conventionally made for addition of make-up quantities of sand. Sand can be lost e.g. as dust. However, the usefulness of the sand is degraded with use. Accordingly, there is a need to routinely and regularly remove used sand from the sand system and to replace such used sand with fresh sand, or regenerated sand. As used herein, “regenerated sand” refers to sand which has been removed from the sand system use cycle, and which has been regenerated by e.g. washing, removal of non-sand materials, sizing, and the like.
It is common for the sand system to be operated on a positive replacement basis, wherein sand is routinely removed from the system, and replaced by adding sand at e.g. the sand mixing stage of the sand system. While sand can be selected for removal according to a number of factors, it is common to pass the sand through sizing screens at the work stations where the sand molds are broken away from the cast metal parts, and to remove any chunks of sand which do not pass through the sizing screens. In addition, it is common to deposit the return sand in one or more surge tanks, and to remove from the system any sand which accumulates in the surge tanks above a pre-set volume level.
Such accumulation can occur, for example, where the sand mix prepared at the sand mixing station contains a first pre-determined fraction of return sand and a second pre-determined fraction of fresh make-up sand. Where the quantity of the fresh make-up sand is greater than the quantity of sand lost in use of the sand system, the overall quantity of sand in the sand system potentially increases by the difference. It is such difference which represents the quantity of sand which is removed from the surge tanks, thereby to balance the quantity of sand leaving the sand system with the quantity of sand entering the sand system at the sand mix process.
A second locus for generation of such air-borne bond material, e.g. as dust, is in the sand return system, especially at the entrance to the sand return system.
In general, material so collected in a dust collection system which is connected to a such sand system cannot be economically recycled into the sand system, and is thus sent to land fill as waste. Such waste adds to the cost of the process, in that (i) bond material purchased for the purpose of making sand mix is sent to land fill either prematurely before utility of such bond material is exhausted, or without ever being used at all as part o
Lin Kuang Y.
New Ideas, LLC
Wilheim Thomas D.
Wilhelm Law Service
LandOfFree
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