Lost foam castings are currently manufactured through a single or simple lost foam casting production line. Usually, 1-2 sets (for molding) of three-dimensional vibration tables, several-10 special sand boxes, sand box hoisting or sand box simple conveyor lines with roller (track) roads are set up in the foundry, and dry sand is naturally cooled or equipped with a simple sand cooling device, plus a vacuum system and sand and dust screening equipment.
Principles of layout of lost foam casting production line
The lost foam production line is generally divided into two areas: the white area and the black area. The working environment in the white area is relatively good, and it is usually a separate workshop. The black area is also an independent workshop. The layout problem of the lost foam casting production line is mainly to master the following principles: The equipment layout is as compact as possible. Make full use of the spatial location. The main equipment and each auxiliary equipment should minimize the connection distance. In addition, the layout of the equipment can be considered in combination with logistics channels and safety issues.
The lost foam casting production process is a large-flow production line composed of multiple sets of equipment. Reasonable production line layout can save part of the cost generated by the connection between equipment and equipment, reduce unnecessary project waste, shorten the distance of workshop logistics channels, improve production efficiency, reduce production costs, effectively utilize resources, and even extremely reasonable production line layout is conducive to the full play of the production process. (The distance of the white area after the paint dries, the shape of the molded part, the distance from the black area medium frequency furnace to the pouring line, etc.).
Problems and improvement methods faced by the processing technology of lost foam castings
Porosity will appear when the local air pressure in the lost foam casting exceeds the metal tension. High air pressure can easily cause more or less spherical pores in the condensed metal. Porosity generally appears on or close to the forged surface. The diameter range is from needle size to holes with a diameter of 6.35mm or larger.
Porosity is usually distinguished from shrinkage defects because of the smooth surface of the hole edge. The causes of pore defects are excessive moisture in the coating, organic sediment of the model or adhesive, poor surface bonding of the model beads, and gas in the metal.
The residual metal or iron beans are small spherical metal particles that are not melted and are trapped in the casting. Iron beans are usually spherical, sometimes covered with a layer of carbonaceous chemical residues, and are usually related to porosity defects.
Iron bean defects can also be observed in traditional casting processes. Iron beans are condensed when the metal enters the mold, but cannot be re-bonded to the metal after the mold is filled. Due to the flow of the metal during filling, the front edge of the flowing metal can also form spherical metal.
Complex sand boxes are divided into bottom discharge type and side discharge type, which are generally five-sided vacuum and six-sided vacuum internal solid types, which can achieve an effective air pressure field when the casting is vacuum packed in the sand box, so that the cast full box casting is well-formed, without defects, and easy to unload sand.
For some castings with simple shapes and low requirements for the precision of the air pressure field during pouring, a simple sand box can be used, which is generally a dump type, divided into three-sided vacuum, four-sided vacuum, five-sided vacuum and other external fixed types, mainly designed according to the actual situation of the customer.
The order of acceptability of casting materials is roughly: steel castings-non-ferrous metals-carbon structural steel-ductile castings-high carbon steel and carbon steel; according to the preparation in advance, it will not cause the process test and adjustment cycle to be too long.
The size of the casting is mainly considered in the application range of the relative equipment. The more complex the casting structure, the more it can reflect the advantages and economic benefits of the lost foam casting process. For the situation with narrow inner wall passages and partitions in the structure, it is necessary to conduct experiments in advance before using the lost foam process before investing in manufacturing.