Carry out multi batch pouring and anatomical analysis on the shell cast crankshaft, and make corresponding adjustment and improvement:
For the three sets of shell type six crankshafts poured for the first time, no measures of adding any cold iron were taken, but 200mm gate cup was added in the three sets of gating systems. Hot metal fcd55 brand, hot metal pouring temperature: 1420 ℃, 75fesi inoculation treatment with flow, and the shell shape filled with iron shot is vibrated on the vibrating table for 120s. Unpacking inspection and analysis:
(1) the three sets are all found on the two cranks and the bottom. The iron shot is poured together with the shell casting crankshaft. After analysis:
a. The bottom iron shot is poured together with the shell casting crankshaft: it may be that the workers take the operation of pressing down when placing and fixing the mold, resulting in the fracture of the bottom. In addition, the shell may be thin and not strong enough.
b. The two plates of the shell casting crankshaft are poured together: it may be caused by the iron shot filling at the two plates is not solid, or the shell is thin and the strength is not enough.
(2) another major problem is that shrinkage porosity and shrinkage cavity are found at the crank. From its position, it is possible that the iron shot at the two plates is not fully filled, resulting in shell expansion and poor feeding. For such problems: first, improve the operation process when filling iron shot in the mold shell; The second is to place the formed cold iron at the two plates.
Through analysis, it is decided to put wedge-shaped cold iron block at the two fan plates to increase the chilling effect at the hot joints of the two fan plates, and try to pour two sets of shell type four crankshafts. After dissection, the shrinkage porosity and shrinkage cavity at the two fan plates are eliminated, but the shrinkage porosity and shrinkage cavity are serious at the lower fan plate and lower main journal of the crankshaft, the expansion is at the two fan plates, the flowing inoculant has obvious unmelted particles at the cold iron, and the bottom of the shell type leaks water. Analyze the causes:
(1) the serious shrinkage between the lower fan plate and the lower main journal is due to the blocking of the upper molten iron by the clay core of the oil plug hole
A large amount of gas is generated from the cement core of the sprue and oil plug hole and the sprue system does not play a role in feeding.
(2) the deep groove iron shot at the two panels still cannot be effectively filled and compacted.
(3) the bottom of the shell is cracked when it vibrates for a long time.
(4) during vertical pouring, the flowing inoculant fails to melt in time, resulting in the accumulation of unmelted inoculant particles at the cold iron.
Through analysis, it is decided to add three formed cold irons at the main journal of the lower fan plate, make the shell shape at the two fan plates as a whole (cancel the deep groove at the two fan plates), increase the inner gate of the lower fan plate (change from 20mm to 25mm, and change the right angle to circular arc), increase the feeding effect of the sprue system on the lower part, open the exhaust duct connected with the atmosphere at the oil plug hole core, reduce the vibration time of the mold shell on the vibrating table, and cancel the flow inoculation process. Through the above adjustment measures, trial casting and small batch production, the qualified rate of shell casting crankshaft is increased to more than 80%.
Modeling is the key link to solve the compactness of filled iron shot. In the molding, there are two stations and three times of filling iron shot, one is laying iron shot at the bottom of the sand box; The second is to pre fill 1 / 3 of the iron shot of the whole formwork after putting it into the formwork and tamp it manually; The third time is to fill the iron shot to the gate. The mold after inner cavity inspection and cleaning shall be vibrated on the vibration table. At the beginning of the test, the vibration time was about 30s. It was found that more than 90% of the cast shell casting crankshaft had water leakage at the bottom of the fan plate and between the two fan plates. After analysis, it was due to the long vibration time, the rupture of the mold shell and the insufficient compactness of the filled iron shot near the fan plate. By improving the mold shell (making an integral shell between the two plates) and exploring and adjusting the tamping time (the tamping time is controlled at 5-8s), the phenomenon of molten iron leakage during casting the crankshaft in the shell mold is basically eliminated.
The flow inoculation process was adopted in the pouring process, but it was found that due to the vertical pouring cooling, the inoculant could not be completely melted, and the inoculant particles were concentrated at the cold iron of the crankshaft, so the inoculation effect was not obvious. Therefore, it was changed to rapid pouring after inoculation in the package.