New Technology for Casting Process of Thick Sectional Wheels for Rotary Kiln

The supporting wheel is one of the key parts on the rotary kiln equipment. It bears the rotating load of the equipment and works under the condition of large alternating stress. Therefore, the internal quality of the casting of the supporting wheel is high, and obvious casting defects are not allowed. Take the φ6.2/φ6.4m×90m rotary kiln supporting wheel produced by our company as an example. The net weight of the product is 44.1t, the material is ZG42CrMo, the maximum diameter is 2800mm, the height is 1400mm, the maximum wall thickness is 830mm, according to GB7233 Class and Q/HMZ402-2002 for ultrasonic and magnetic particle non-destructive testing.

Through the research on the influence of sand-filled cold iron on the feeding channel, the author derives the formula of sand-filled cold iron feeding channel, and at the same time, the MAGMASOFT solidification simulation software is used to optimize the traditional process and obtain high-quality castings.

Traditional craft

The casting process is designed by the hot pitch method, the groove is cast under the riser, the upper part of the center hole is cast, and the outer circle is provided with a full circle of cold iron. The casting process is shown in Figure 1.

Figure 1 Traditional casting process

The hot section T is determined: the casting thickness T1, the distance T2 between the bottom and bottom surfaces of the upper and lower grooves, and the channel width T3 between the adjacent two weight reducing holes are respectively calculated, and the smaller size is T. Determine the height h of the 1# sand core (also called the shell core) by drawing, and ensure the theoretical feeding channel of the riser from top to bottom: L=T+(20~30)mm. Finally, the diameter of the riser and the height of the casting are determined by the thermal pitch method.

According to the traditional process, the supporting wheel T1=830mm, T2=850mm, T3=830mm, then T=830mm, L takes 850mm, at this time the casting gross weight is 61t, and the molten steel weight is 85t.

Disadvantages of the traditional casting process: the upper part of the inner hole of the supporting wheel has more casting parts, the later machining volume is large, the production efficiency is low, and it is difficult to meet the requirements of non-destructive testing.

2. Process optimization

The actual production shows that the outer circular sand cold iron has a great influence on the feeding and shrinking of the casting, so it is necessary to optimize the process for the adjustment of the feeding channel. Considering that the thickness of the outer cold iron used in the casting is large, D=450mm, the chill layer will have a certain thickness, which will inevitably reduce the hot section of the roller.

After many computer simulations and adjustments, the author derives an approximate formula for the actual feeding channel, namely

L actual = T theory - kD + (20 ~ 30)

Where L is actually - the actual feeding channel;

T theory - theoretical thermal pitch diameter;

k —— influence coefficient of sand-cold cold iron chilling, value range

0≤k<1;

D——The thickness of the cold iron in the sand, D=450mm.

kD is the cold iron chilling influence layer (the chilling influence layer and the maximum chilling influence layer are different).

T actual = T theory - kD, which is the actual thermal pitch diameter.

It should be noted here that the maximum thickness of the chilled layer of the same type of sand-filled cold iron should be a fixed value. In this paper, the area smaller than the thickness of the maximum chilling effect layer is regarded as the chilling influence layer.

According to the chilling influence layer of the sand-cold cold iron on the casting, adjust the feeding channel and appropriately increase the height of the 1# sand core, thereby achieving the purpose of saving steel liquid and improving production efficiency.

It can be seen from the formula that the pallets produced by our company in the past using traditional crafts are calculated according to the theoretical hot section to calculate the feeding channel (ie, taking k=0).

3. Computer simulation

Firstly, Solidworks 3D software is used to model the different conditions of k value. Then, MAGMASOFT solidification simulation software is used to simulate the solidification process of different models. In the post-processing, the Feeding criterion is used, and the parameters are adjusted to observe different feedings. The channel is the shrinkage and shrinkage of the inside of the casting at different heights of the 1# sand core.

The attached table is a summary of the main simulations of MAGMASOFT. It can be seen from the table that when 0≤k≤0.6, there is no defect inside the casting, but when 0.66≤k≤1, there are different degrees of shrinkage and shrinkage defects inside the casting.

MAGMASOFT simulation summary table

Figures 2 to 5 show the solidification inside the casting when k takes four different values. Figure 2 shows that when k is 0.8 and the actual feeding channel is 450mm, serious problems occur inside the casting; Figure 3 shows the case where the k value is 0.66, and there are tiny shrinkage and shrinkage defects inside the casting; At 0.4 o'clock, the internal solidification of the casting is good, and no defects are generated.

Figure 2 Simulation results at k = 0.8

Figure 3 Simulation results at k=0.66

Figure 4 Simulation results at k = 0.6

Figure 5 Simulation results at k = 0.4

4. Production status

Two pieces of the specification roller were produced by the optimized process, and the new process was prepared by taking k=0.4, that is, the diameter of the hot section was 650 mm, and the actual feeding channel was 675 mm. At this time, the gross weight of the casting was 59t, and the total weight of the molten steel was 80t.

Compared with the traditional process, the optimized process reduces the gross net ratio of the casting, saves the molten steel, reduces the machining workload, and improves the production efficiency. Figure 6 shows the blank body of the cast after cleaning, and the non-destructive testing after roughing shows that the internal and external quality of the casting meets the technical requirements.

Figure 6 Process optimized roller blank

5. Analysis and discussion

(1) The chilling effect of the cold-cold cold iron makes the outer circle area of ​​the supporting wheel form an artificial end zone during the solidification process, which reduces the feeding distance of the riser to a certain extent and reduces the burden of the riser. In addition, the 1# sand core is located in the middle part of the casting, and only heats from the lower part during solidification. This feature makes the molten steel in the riser part of the supporting wheel maintain the high temperature state for a long time, which is more conducive to the heat preservation of the riser. The combination of the above two aspects enables the roller casting to maintain a good expansion angle of the supplementary passage during the solidification process, which facilitates the feeding of the upper molten steel to both sides and achieves the sequential solidification of the casting. The temperature field simulation of the casting solidification process is shown in Fig. 7.

Figure 7 Temperature field simulation at k = 0.4

(2) Because the maximum chilling thickness of cold iron outside the sand is affected by the cold mold material, the pouring temperature of the molten steel, the pouring time, the material of the casting and the thickness of the cold mold sand layer, it is necessary to accurately calculate the maximum cold iron outside the sand. The chill thickness is very difficult. However, according to the approximate calculation formula of the actual feeding channel, in the casting process design of the same structure of the supporting wheel, it is not necessary to calculate the maximum extremely cold thickness of the cold-cold cold iron, and the chilling influence coefficient is adjusted by computer simulation to ensure the solidification result. Within the safe range, the casting process can be optimized.

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