Bucket Tooth Shell Mold Casting Method – Unit One
The invention is applied to the field of casting, relates to shell mold casting, and is suitable for casting production of bucket teeth of wear-resistant parts of excavators.
The bucket teeth are wear-resistant castings with the largest consumption on engineering machinery excavators, the bucket teeth are required to be unified in high toughness and high hardness, the bucket teeth are mostly manufactured by alloy steel or bimetal, lost foam and resin sand are mostly adopted in a casting process, shell mold casting is rarely adopted, and the bucket teeth castings produced by the process are good in surface quality. Generally, the bucket teeth need to be subjected to heat treatment to obtain high-hardness wear resistance, and the heat treatment of the bucket tooth steel castings is divided into withdrawal pretreatment, quenching, tempering treatment and the like.
The shell mold casting is firstly carried out to manufacture the shell mold, precoated sand formed by mixture of silica sand or zircon sand and resin is molded and crusted in a metal mold plate preheated to about 280-320 ℃, two bucket tooth half-shells are buckled, the core is placed in a sand box, steel shots are added around the sand box for fixation, then metal liquid is poured, and the bucket tooth casting is formed after cooling. In order to ensure the molding strength of the shell mold, the thickness of the shell mold is generally not less than 5mm, the expensive precoated sand is large in material and high in production cost, and therefore, even if the surface quality of the bucket tooth casting is good, manufacturers adopting the shell mold are few.
Disclosure of Invention
The technical problem solved by the invention is as follows: the casting method of the bucket tooth shell is provided, the thickness of the shell is reduced, and the production cost is reduced.
The technical scheme adopted by the invention is as follows: the bucket tooth shell mold casting comprises sand box molding and pouring, wherein the sand box molding comprises the following steps: 1) and (3) upper box modeling: the precoated sand is sent into a horizontally placed metal mold cavity by high-pressure air, an upper shell mold and a box sealing shell are formed by heating and hardening, the thicknesses of the upper shell mold and the box sealing shell are not more than 3mm for reducing the using amount of the precoated sand, and the minimum thickness of the metal mold is the best. And then removing the upper metal mold, replacing the upper metal mold with an upper box body, checking the shell mold, repairing the local unformed part of the upper shell mold or the box sealing shell by using precoated sand, and ensuring that the sand box is vacuumized and airtight. And positioning a pouring gate shell mold on an inner pouring gate, adding steel shots into the upper box body, scraping the upper opening of the upper box body after the steel shots are filled, covering an agricultural film, vacuumizing the upper box, demolding from the lower metal mold and removing to finish the molding of the upper box. 2) Molding the lower box: the precoated sand is sent into a horizontally placed metal mold cavity by high-pressure air, and is heated and hardened to form a lower shell mold and a box sealing shell, so that the thickness of the lower shell mold and the thickness of the box sealing shell are not more than 3mm in order to reduce the using amount of the precoated sand, and the minimum thickness of the metal mold in molding is the best. And removing the upper metal mold, replacing the upper metal mold with a lower box body, checking a shell mold, repairing the local unformed part of the lower shell mold or the box sealing shell by using precoated sand, and ensuring that the sand box is vacuumized and airtight. And adding steel shots into the lower box body, scraping the upper opening of the lower box body after the steel shots are filled, covering a lower agricultural film, vacuumizing the lower box, demolding from the lower metal mold and removing to finish the modeling of the lower box. 3) Assembling the box: the lower box is overturned and horizontally placed on the vibration pouring table, the sand core is positioned and fixed, and the upper box is positioned and buckled with the lower box. 4) Covering with a heat insulation layer: and quartz sand or heat-insulating cotton heat-insulating layers are covered on the top surface and the periphery of the sand box. Pouring is finished on the vibration pouring table, the sand box is in a vacuum state during pouring, vibration is carried out immediately after pouring, and vibration is stopped before vacuum removal. The vibration adopts low-amplitude high-frequency vibration, the amplitude is not more than 5mm, and the frequency is 100-200 HZ.
The invention has the beneficial effects that: the thickness of the shell mold is reduced by about half, no shell mold waste is generated, and the using amount of the precoated sand is greatly reduced. The thin shell and the heat-insulating layer are combined together, so that the contradiction between the increase of the solidification speed and the reduction of the cooling speed of the casting is solved, cracks generated by temperature stress and structural stress are avoided, as-cast crystal grains are refined together with vibration pouring, the heat treatment process is simplified, and the heat treatment energy consumption is reduced.
FIG. 1 is a schematic view of a tooth-shell molding flask;
FIG. 2 is a schematic diagram illustrating fabrication of an upper shell of a bucket tooth;
FIG. 3 is a schematic view of the shape of the bucket teeth upper box;
wherein: 1-quartz sand, 2-upper agricultural mold, 3-steel shot, 4-sprue, 5-upper shell mold, 6-upper box body, 7-lower box body, 8-lower agricultural film, 9-sand core, 10-lower shell mold, 11-box sealing shell, 12-vacuum interface, 13-upper metal mold and 14-lower metal mold.
FIG. 1 is a schematic structural diagram of a bucket tooth shell molding sand box of an excavator, wherein the sand box is formed by combining an upper box and a lower box, and one box comprises two or four pieces. The lower opening of the upper box body 6 is covered by the upper shell type 5 and the box sealing shell 11 at the bottom of the upper box body, the thickness of the upper shell type 5 and the box sealing shell 11 is not more than 3mm, and the minimum thickness of the mould forming is preferably used. Go up the roof portion and cover the last mouth of box 6 by last plastic sheeting for farm use 2, go up the inside of box 6 and fill shot 3, the design has vacuum interface 12 on last box 6, and runner 4 draws out the bucket tooth casting die cavity and goes up roof portion as the gating system, and gating system’s shell mould thickness is not less than 5mm, guarantees to go up and adds sufficient intensity occasionally in the box 6. The top of the lower box is covered by a lower shell 10 and a box sealing shell 11, the upper opening of the lower box 7 is covered by the lower shell 10 and the box sealing shell 11, the thickness of the lower shell 10 and the box sealing shell 11 is not more than 3mm, and the minimum thickness of the die forming is better. The bottom of the lower box is covered by a lower agricultural film 8 at the lower opening of the lower box 7, the lower box 7 is filled with steel shots 3, and the lower box 7 is also provided with a vacuum interface 12. The vacuum ports 12 of the upper box and the lower box are connected with a vacuum pump, and the vacuum state of the upper box and the lower box is kept in the processes of box assembling and pouring of the upper box and the lower box, so that the box collapse is prevented. When the upper box and the lower box are combined, the sand core 9 is positioned and placed in the casting cavity and fixed, and the top surface and the periphery of the whole sand box are covered by quartz sand 1 after the boxes are combined.