Bucket Tooth Shell Mold Casting Method – Unit Two
As shown in the attached figure 2, the upper shell mold 5 of the bucket tooth is manufactured, the cavity between an upper metal mold 13 and a lower metal mold 14 which are horizontally placed is the cavity between the upper shell mold 5 and a box sealing shell 11, coated sand is sent into the cavity by high-pressure air, after the coated sand is heated to 280 ℃ and hardened at 320 ℃, the upper metal mold 13 is removed and replaced by an upper box 6. The quality of the shell of the upper shell 5 and the sealed shell 11 is checked, if a local shell is not formed, the precoated sand can be supplemented, and the lower metal mold 14 is used for heating or preheating for hardening. The upper box is shaped as shown in figure 3, a sprue 4 shell mold is positioned on an inner sprue shell mold, and steel shots 3 are added into an upper box body 6. After the steel shot 3 is filled in the upper box body 6, the upper opening of the upper box body 6 is scraped off, and the agricultural film 2 is covered. And connecting a vacuum port 12 of the upper box with a vacuum pump, vacuumizing, demoulding and removing the upper box from a lower metal mold 14, and finishing the operation of the upper box.
When the upper box 6 is filled with the steel shot 3, the upper shell 5 and the box sealing shell 11 with thin wall thickness are supported by the lower metal mold 14, and are not damaged by pressure. The upper box is vacuumized to integrate the steel shots, so that the steel shots do not flow, and the upper shell type 5 and the box sealing shell 11 are smoothly released from the lower metal mold 14 under the action of negative pressure. The height of the upper box is not higher than 200mm, the downward pressure of the steel shots on the shell is far lower than the upward pressure of the atmospheric pressure on the shell, and the upper box is taken as a whole under the condition that the agricultural film 2, the upper shell 5 and the box sealing shell 10 are completely airtight, so that the upper box cannot collapse.
The shell mold manufacturing and the lower box molding of the lower shell mold 10 and the box sealing shell 11 of the bucket tooth are the same as the above, and two main differences exist, namely, the lower box body 7 is used for replacing the upper metal mold 13 and then directly adding steel shots, and the lower agricultural film 8 is fully covered. Secondly, the box needs to be turned over, the position of the lower box is consistent with that of the upper box in the attached drawing 3 before demoulding, the lower box is vacuumized and demoulded, and the lower box needs to be turned over by 180 degrees and laid flat when being closed, as shown in the lower box in the attached drawing 1.
When the upper box and the lower box are combined, the sand core 9 is positioned and placed, after the upper box and the lower box are combined, a layer of quartz sand is spread on the top surface of the upper box, and the quartz sand layer plays a role in protecting the upper agricultural film 2 and preventing high-temperature molten metal from being scalded, so that the vacuum degree of the sand box is ensured, and the box collapse is avoided.
The upper box and the lower box are combined on the vibration casting platform, or can be placed on the vibration casting platform after combination, but the movement of two vacuum tubes is involved, the risk of crush is increased by multiple times of lifting, and the box combination operation is preferably carried out on the vibration casting platform. And (3) quickly pouring molten metal in a sand box in a vacuum state, starting a vibration motor when the pouring gate is full, and vibrating off the as-cast dendrite to form a core and refine as-cast grains under the high-frequency low-amplitude vibration of the molten metal. The vibration amplitude is not more than 5mm, and the vibration frequency is 50-100 HZ.
If the precoated sand is not well filled in the metal mold and the shell mold is defected in molding, the precoated sand is used for repairing after the metal mold is demoulded and before steel shots are added, so that the air leakage is ensured, and the thickness of the shell mold is reduced as much as possible. Therefore, the molding method hardly generates shell type waste products on the premise of greatly reducing the consumption of the precoated sand by reducing the wall thickness, so that the cost of the precoated sand material is greatly reduced.
When alloy steel metal liquid pours, get into bucket tooth casting die cavity through the ingate by runner 4, gating system’s shell mould thickness is thicker, can play the heat preservation effect, and the shell mould thickness of die cavity is thinner, and the shot that surrounds the die cavity can absorb heat fast, increases the super-cooled degree of metal liquid, is favorable to solidifying the nucleation, together with the vibration pouring, can reduce as-cast crystalline grain, avoids thick dendrite. And after the molten metal is solidified, stopping vibrating, and removing the vacuum from the upper box and the lower box. The sand box is wrapped by a quartz sand heat-insulating layer, and the bucket teeth are cooled slowly at a high-temperature solid state, so that cracks caused by temperature stress and tissue stress are avoided. Because the quartz sand has more heat storage, the heat-insulating layer can adopt other heat-insulating measures such as heat-insulating cotton and the like, and although the heat-insulating cotton has good heat-insulating effect, the material cost is higher.
The excavator bucket tooth produced by the molding and vibration pouring method has the advantages that the crystal grains are refined, the high-frequency quenching is carried out after the casting and cleaning, the annealing and tempering procedures are omitted, and the energy consumption of heat treatment is greatly reduced.