This invention relates to a method for making sand covered by bentonite by mixing discarded sand, reproduced sand or new sand or some or all of them with bentonite. Also, it relates to the sand and a method for recycling molding sand for a mold using the sand.
FIG. 2 shows a prior-art processing line for green sand. Generally, as shown in the processing line a core or a mold on which sand is attached is transmitted to another line after it is removed from a flask. After green sand is removed from a flask, part of it is transmitted to the sand processing line where it is called collected sand and again used as green sand for a casting. The sand into which a flask is broken is discarded through a collector. Part of the sand, which is discarded through the collector, is collected and used again (not shown).
Generally, a core and green sand that is attached to a mold are discharged from the sand processing line after they are removed from a flask. Also, part of the collected sand is extracted and discarded to prevent unnecessary sand of the core from being mixed with the collected sand, because of the mixing of the sand of the core. Thus, the collected sand decreases as it is sent to the green sand processing line.
Thus, regenerated sand and new sand or one of them is supplied to the green sand processing line to supplement the collected sand, and is mixed with it so that it can be used again as green sand for a molding. Also, during the mixing operation bentonite is supplemented for part of the bentonite that has been inactive because of its burning. Water is also added during that operation.
During the mixing operation of green sand for a mold, generally, active bentonite and water are supplemented so that the active bentonite may be 7xcx9c8% of the green sand and the water may be 3xcx9c4%. But the amount of water is less than 50% of the active bentonite. Also, the amount of the water in the green sand is never set to more than that amount. Thus, it is desirable that sand particles of green sand for a molding are uniformly coated by bentonite so that each may have a sufficient thickness of bentonite.
However, it is difficult for the mixing operation of the prior-art method to sufficiently cover regenerated sand and new sand or one of them with bentonite for a given period of time. Moreover, a long time is needed to make desirable green sand.
Also, by a prior-art method, part of the discarded sand that is output from the molding sand processing line is used again for sand for a core, and is thus returned to the line. Also, part of the discarded sand is used for subgrades. However, much of the sand is discarded for landfills or waste products. Recently, discarded sand is sometimes processed to be reproduced and returned to the molding line. However, this is not common. In the green sand processing line of the prior art, almost all of the green sand is transmitted to the sand processing line after it is removed from a flask. That sand is called collected sand and is used again as green sand for a mold.
In that case, a core and green sand that is attached to a mold are also discarded. Alternatively, part of the collected sand is discarded, so that the collected sand decreases as it is transmitted along the green sand processing line.
Thus, regenerated sand and new sand or one of them is added to the collected sand in the green sand processing line. During the mixing operation, active bentonite is supplemented for bentonite that is inactive because of its burning. Also, water is added. Thus, a method for recycling green sand is used so that the collected sand can be used again as green sand.
Sand particles for green sand for a mold are needed to uniformly be coated by bentonite so that each has a sufficient thickness of the bentonite. However, it is difficult for the prior-art method using the green sand processing line for recycling green sand to cover the supplementary sand that is added to the collected sand with bentonite so that it may have a given thickness. Thus, it is possible that a mold that does not have any given size or shape could be made. Thus, the available percentage of molds decreases. Also, there are other disadvantages such as that a long time is needed to mix the collected sand and supplementary sand to make given green sand, and such as that the sand that is discarded from the molding sand processing line that includes the green sand processing line cannot be efficiently used. Resource saving and environmental protection cannot be efficiently achieved.
Also, for a common mold, many points, such as the nature of green sand that contacts the surface of a mold, especially; the stability of the surface, the fire resistance, the compression strength, the size of sand particles, etc. must be considered. Substantially the same nature of the green sand is needed for insular parts.
Thus, there is a case when special sand is used for facing sand or sand for a pocket (xe2x80x9cpocket sandxe2x80x9d) that contacts surfaces of a mold or insular parts. The special sand may include synthetic mullite sand, zircon sand, chromite sand, oivine sand, etc. They have some advantages such as that the coefficient of thermal expansion is small, the fire resistance is excellent, and burning can be prevented. The special sand for facing sand and the pocket sand is mixed and processed in a line that differs from the line for common green sand.
However, the special sand is more expensive than common green sand. Also, the special sand for facing sand and the pocket sand differs from green sand that is cycled within the line in that the facing sand and the pocket sand are made by mixing reproduced sand or new sand to which no bentonite has been attached with bentonite. However, it is difficult to cover them with bentonite to have a given thickness. Also, it takes a relatively long time to perform the mixing and processing operations so as to obtain a given nature of green sand.
This invention is conceived to overcome the disadvantages stated above. One of the objects of this invention is to provide sand covered with bentonite and a method for making the sand by adding supplementary sand to collected sand and mixing and processing them in a relatively short time, so that given green sand can be made for a mold.
Another object of this invention is to provide a method for recycling molding sand by mixing discarded sand that is discharged from a line for processing molding sand with bentonite to make sand that is covered by the bentonite, and supplying it as supplementary sand to a line for processing green sand. This method allows the sand that is to be provided to the line for processing green sand to have given natures for a short time. Also, the discarded sand can be effectively used again.
Further, another object of this invention is to provide sand covered with bentonite having given nature of green sand for facing sand and the pocket sand and a method for making the sand by performing mixing and processing operations in a relatively short period of time.
To achieve the objects stated above, the method for making bentonite-covered sand of this invention includes the steps of mixing any of the reproduced sand, new sand, and discarded sand, or a combination of any or all of them with bentonite to make a mixture, and drying the mixture.
The method of this invention for making bentonite-covered sand by mixing reproduced sand and new sand, or one of them with bentonite so as to be used as sand supplement to collected sand includes the steps of mixing reproduced sand and new sand or one of them, floury bentonite, and water having a weight the same as or greater than that of the bentonite to make a mixture, and drying the mixture.
The mixture may include components of bentonite of 4-8% and water of 2% or less after the mixture is dried.
The step of drying the mixture may include a heating operation or a heating and decompressing operation.
The bentonite-covered sand of this invention is made by mixing reproduced sand and new sand or one of them, floury bentonite, and water having a weight the same as or greater than that of the bentonite to make a mixture, so that the reproduced sand and new sand or one of them is covered by the bentonite.
The method and bentonite-covered sand of this invention have the following advantages. According to a prior-art processing method, bentonite is added to supplement the bentonite that is burned during a molding process. The quantity of the bentonite to be supplemented is determined based on the sand that is to be supplied to a mixing process. In contrast, according to a method for processing collected sand of this invention, reproduced sand and new sand or one of them is mixed with at least bentonite, so that supplementary sand can previously be made for the collected sand. The supplementary sand is added to the collected sand. Thus, given molding sand for a mold can be made in a relatively short period of time.
Also, to achieve the objects, the method of this invention for recycling molding sand includes the steps of collecting discarded sand that is discharged from a sand processing line for a molding, reproducing the discarded sand that is collected and mixing the discarded sand with at least bentonite, so that bentonite-covered sand is made, and supplying the bentonite-covered sand to sand collected from a green sand processing line as supplementary sand.
Another method of this invention for recycling molding sand includes the steps of collecting discarded sand that is discharged from a sand processing line for a molding, mixing the discarded sand with at least bentonite, so that bentonite-covered sand is made, and supplying the bentonite-covered sand to sand collected from a green sand processing line as supplementary sand.
Another method of this invention for recycling molding sand includes the steps of collecting discarded sand that is discharged from a green sand processing line, reproducing the discarded sand that is collected and mixing the discarded sand with at least bentonite, so that bentonite-covered sand is made, and supplying the bentonite-covered sand to sand collected from the green sand processing line as supplementary sand.
Also, another method of this invention for recycling molding sand includes the steps of collecting discarded sand that is discharged from a green sand processing line, mixing the discarded sand with at least bentonite, so that bentonite-covered sand is made, and supplying the bentonite-covered sand to sand collected from the green sand processing line as supplementary sand.
The step of making the bentonite-covered sand may include mixing reproduced sand or the discarded sand, floury bentonite, and water having a weight the same as or greater than that of the bentonite to make a mixture, and drying the mixture.
The step of drying the mixture may include a heating operation or a heating and decompressing operation.
The method of this invention for recycling molding sand includes the steps of collecting discarded sand that is discharged from a sand processing line for a molding, mixing discarded sand that is discharged from a molding sand for a mold with at least bentonite, so that bentonite-covered sand is made, and using the bentonite-covered sand as supplementary sand for the molding sand processing line for a mold.
The method of this invention for recycling molding sand includes the steps of mixing the discarded sand that is reproduced with at least bentonite, so that bentonite-covered sand is made, and using the bentonite-covered sand as supplementary sand for a molding sand processing line for a mold.
Also, to achieve the object stated above, bentonite-covered sand can be used for facing sand or the pocket sand. It is made by covering reproduced sand and new sand or one of them with bentonite and simultaneously drying the sand, or by covering reproduced sand and new sand or one of them with bentonite and then drying the sand, so that the bentonite-covered sand is made, and by supplying the bentonite-covered sand to a mixing process.