Casting Process of Flywheel and Table Lost Foam for 65 Tons High Speed Punch


1 Brief description and technical requirements of castings

The flywheel is a part used to store energy and balance the load on a high-speed punch. The maximum outer diameter is Ø820mm, the outer ring thickness is 210mm, the middle spoke thickness is 140mm, and the part weight is 620Kg. Hand-cut white mold, casting blank parts are fully processed, there shall be no obvious casting defects on the processing surface, and dynamic balance shall be less than 50g.

The platen is a device used for punching machine tightening on a high-speed punching machine. The maximum outline size is 750 mmX350mmX140mm and the actual weight is 415Kg. The cast blank parts need to be fully processed, in which a tightening groove with a depth of 20mm is required to be processed on a large plane.

The material of the two castings is HT300, which belongs to the large thick-walled castings of high grade gray cast iron. It is an important part of the punching machine, with large force load and continuous operation of punching. The internal structure is required to be dense, and the casting shall be cut open for inspection without shrinkage and porosity. The weight and volume of castings are large, and the quality requirements are high, so it is difficult to manufacture them by lost foam casting. There are many problems to be overcome in the white area, yellow area and black area.

2 Casting process scheme

The riser design of the casting is shown in Figure 1. The operation of adding cold iron and riser ring is shown in Figure 2.

 

Fig.1 Design of casting riser

 

Fig. 2 Operation of adding chilled iron and riser ring

Design of 2.1 Runner

These two castings have large volume and high height, and both adopt stepped gating system to ensure rapid filling of castings, uniform cooling and local overheating due to heat concentration.

Size of flywheel gating system: sprue: 1100 × 40 × 40mm; Runner: 800 × 40 × 40mm; Ingate: 15 × 50 × 60mm (height) × 2.

Size of table pan gating system: sprue: 1000 × 40 × 40mm; Runner: 300 × 40 × 40mm; Ingate: 15 × 50 × 60mm (height) × 4. (Note: The riser shall be open, and the height of the sprue and sprue cup shall be flush with the riser.)

Design of 2.2 riser

The contraction tendency of molten iron is large, and the success or failure of replenishment is an important factor to ensure the density of the tissue, so the open riser is used. On the other hand, the riser of cast iron is difficult to clean, so the contact area should be controlled. Otherwise, even if the replenishment is successfully cleaned up, it is a difficult problem.

The riser of gray iron is calculated according to 15% ~ 20% of the actual weight of the casting. The diameter is based on the empirical value D = 1.5 times the thickness of the hot section or the diameter of the inscribed circle. For these two castings, the design of the riser neck is particularly important, which involves the problem of feeding effect and later cleaning cost. The contact between the riser neck and the casting is 60mm wide and 300mm long. The height of the variable diameter is 70mm, and the right angle of the variable diameter part needs to be rounded too much.

3 Casting of flywheel and table plate

3.1 appearance

In order to ensure the overall size of the casting and the strength of the white mold, and reduce gas generation and carbon deposition, the white mold selects a 19g/L white mold cutting model with a shrinkage rate of 1% and a processing capacity of 8mm.

When making models and runners, foam continuity must be considered. The foam continuity is poor, and there are gaps between the foam beads after cutting, which causes the coating to penetrate, and the slag defect will appear after processing. Apply repair cream to the parts with large gap of foam beads on the model, and the way of sticking newspaper can be considered for those with large area. Especially in the runner part, due to the high flow rate of molten iron, if the continuity of the white mold is poor, the coating will be washed seriously, so it must be treated.

In addition, the right angles of all gating systems and models should be polished into rounded corners. There is stress at the right angles. The coating here is not good, the coating is thin, and the strength is low. It is easy to crack in the pouring process, and the tendency of box collapse and sand sticking is large.

The gate and riser system of the white mold adopts hot glue bonding to ensure firm bonding on the premise of using less glue as far as possible, and there is no batch seam to prevent the paint from infiltrating and causing slag inclusion.

3.2 coating

The casting time of these two castings is long, and the inner wall of the coating system is seriously washed, and the coating must ensure sufficient high temperature strength. To prevent the molten iron in the flow process inside the runner, part of the coating on the inner wall of the coating peeling off, resulting in the processing surface of the coating defects.

Coating permeability is also an important indicator of the normal casting and casting quality. The coating has good air permeability, the gas generated by the combustion of the foam can be discharged from the cavity in time, the pouring is smooth, and the flow resistance of the molten iron is small. Black smoke and oily substances produced by the combustion of the foam are adsorbed to the outside through the coating.

To sum up, the coating adopts the RO-HT type of coating prepared by the coating factory of Ruiou Company. In order to improve the high temperature strength and air permeability, 3% silica sol and 15% quartz powder for 100 purpose are added to the coating. The coating has the advantages of good strength at low temperature and high temperature, good air permeability, anti-sand sticking, environmental protection, etc., and fully meets the requirements of production and use.

Due to the large casting, the paint is painted three times, and the total thickness is about 2mm. The temperature of the drying room is 52~56, and the humidity is less than 20. The first and second drying time is at least 8h, and the third drying time is more than 12h to ensure that the coating is dry. During the drying process, bumping should be avoided, and deformation should be considered when placing. The flywheel should be placed horizontally, and the table plate should be placed sideways or upright when it is longer.

3.3 styling

The maximum outline size of the casting is 820 × 210mm thick, so we choose a sand box with a size of 1200 × 1200 × 1400mm to ensure the amount of sand eaten and the quality of the casting. The sand adopts 20/40 purpose jewel sand, which has the advantages of good air permeability, high fire resistance and good fluidity.

The two castings are simple in structure and vibrate layer by layer with sand. This kind of thick, large and high grade gray iron has a large shrinkage tendency. In order to eliminate shrinkage and realize simultaneous solidification, external cold iron is placed in the upper part of the casting during the box burying process. Note that the cold iron must be dry and rust-free, and the thickness of the cold iron is 2/3 of the wall thickness of the hot section. In order to prevent the cold iron from running away during the earthquake, the cold iron should be placed after the sand layer is compacted. When adding sand to the root of the riser, place an iron ring. The diameter of the iron ring is 100mm larger than the diameter of the riser. Fill the middle of the iron ring and the riser with thermal insulation materials. The thermal insulation materials are mixed in advance. The mixing method uses coal ash plus 5% sodium bentonite plus 15% sodium silicate to fill the iron ring. After tamping, the eyes are blown dry with carbon dioxide to form strength. The material density is realized by adding cold iron and heat preservation riser. Then film, cover with sand and wait for pouring[1].

3.4 melting and pouring

For smelting HT300 grade molten iron, in order to ensure the material quality and mechanical properties, lower carbon equivalent is selected. The detailed design composition is shown in Table 1. 75SiFe is used for inoculation, 0.6 for inoculation in tapping groove and 0.1 for inoculation in pouring flow. The tapping temperature is 1480~1490 ℃, and the pouring temperature is 1420~1430 ℃.

Table 1 Requirements for chemical composition of castings

During the pouring process, the flow shall not be cut off. After the small iron flow is recognized and the runner is opened, rapid pouring shall be steadily added and rapid filling shall be carried out. After the molten iron enters the runner, immediately use the cutting gun to point the riser and open the upper exhaust channel. After pouring, wait for 20s and add iron liquid at the riser. The riser shall be sprinkled with thermal insulation agent and covered with aluminum silicate board for thermal insulation.

4 Turn over the box to clean

Photographs of the castings after cleaning are shown in FIGS. 3 and 4.

 

Fig.3 Photograph of the casting after turning over the box

  

Fig. 4 Photo of Casting Shot Blasting

5 Summary

After the casting is processed, there are no defects on the processing surface, and after cutting, there are no defects such as shrinkage holes and dirt inside, and the two castings are successfully cast.

The success or failure of the lost foam casting process should be considered comprehensively, and it is never so simple. Casting requirements, casting process, casting material, human operation, material, environment, experience and other factors will affect the quality of castings, and each link is linked. Only by thoroughly mastering the contents of all links of lost foam can we produce qualified castings. If there is any mistake in any link, there will be quality problems.

References

[1] Li Zengmin. Adaptation conditions of lost foam casting and applicable countermeasures for defect resolution [EB/OL]. Hundred casting network http:// www. baizhuwang/news/show-12211.html,2014-08-25

 

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