New Technology for Casting Process of Large-Section Support Rollers for Rotary Kilns

Feb 27, 2025

New Technology for Casting Process of Large-Section Support Rollers for Rotary Kilns

The support roller is one of the key components of rotary kiln equipment. It bears the rotational load of the equipment and operates under significant alternating stress. Therefore, the internal quality of the support roller casting is highly demanding, and no obvious casting defects are allowed. Taking the φ6.2/φ6.4m×90m rotary kiln support roller produced by our company for a factory as an example, the product has a net weight of 44.1 tons, made of ZG42CrMo material, with a maximum diameter of 2800mm, a height of 1400mm, and a maximum wall thickness of 830mm. It undergoes ultrasonic and magnetic particle non-destructive testing according to GB7233 Grade II and Q/HMZ402---2002 standards.
Through research on the influence of sand-coated chills on the feeding channel, a formula for the feeding channel of sand-coated chills was derived. Additionally, the traditional process was optimized using MAGMASOFT solidification simulation software, resulting in high-quality castings.
1. Traditional Process
The casting process was designed using the hot-spot circle method. The riser groove was cast solid, the upper part of the center hole was cast solid, and a full-circle sand-coated chill was set on the outer circumference. The casting process is shown in Figure 1.

Figure 1 Traditional Process of Castings

Determine the hot spot T: Calculate the casting thickness T1, the distance between the upper and lower groove bottoms T2, and the channel width between adjacent weight-reducing holes T3, and take the smallest dimension as T. Determine the height h of the 1# sand core (also called the shell core) by drawing, ensuring the theoretical feeding channel from top to bottom of the riser: L = T + (20～30)mm. Finally, determine the riser diameter and pouring height using the hot-spot circle method.
According to the traditional process, for this support roller, T1 = 830mm, T2 = 850mm, T3 = 830mm, so T = 830mm, and L is taken as 850mm. At this time, the casting weight is 61 tons, and the molten steel weight is 85 tons.
Disadvantages of the traditional casting process: The upper part of the inner hole of the support roller is cast solid, resulting in a large amount of subsequent machining, lower production efficiency, and difficulty in meeting non-destructive testing requirements.
2. Process Optimization
Actual production shows that the sand-coated chill on the outer circumference has a significant impact on the feeding of the casting. Therefore, process optimization is needed to adjust the feeding channel. Considering the large thickness of the external chill used for the casting, D = 450mm, the chill layer will have a certain thickness, which will inevitably reduce the hot spot of the support roller.
After multiple computer simulations and adjustments, an approximate formula for the actual feeding channel was derived:
L actual=T theoretical−kD + (20∼30)
Where:

L_actual: Actual feeding channel;
T_theoretical: Theoretical hot-spot circle diameter;
k: Influence coefficient of the sand-coated chill, ranging from 0 ≤ k < 1;
D: Thickness of the sand-coated chill, D = 450mm.

kD is the chill influence layer (the chill influence layer and the maximum chill influence layer are different).
T_actual = T_theoretical - kD, which is the actual hot-spot circle diameter.
It should be noted that the maximum chill influence layer thickness for the same thickness of sand-coated chill should be a fixed value. In this paper, areas with less than the maximum chill influence layer thickness are considered as the chill influence layer.
Based on the chill influence layer of the sand-coated chill on the casting, the feeding channel is adjusted, and the height of the 1# sand core is appropriately increased to save molten steel and improve production efficiency.
From the formula, it can be seen that the traditional process used for producing support rollers was based on the theoretical hot-spot calculation for the feeding channel (i.e., taking k = 0) for process design.
3. Computer Simulation
First, SolidWorks 3D software was used to model different values of k, and then MAGMASOFT solidification simulation software was used to simulate the solidification process of different models. In post-processing, the Feeding criterion was used, and by adjusting the parameters of this criterion, the internal shrinkage porosity and cavities of the casting were observed at different feeding channels, i.e., different heights of the 1# sand core.
The table below summarizes the main simulation results from MAGMASOFT. The table shows that when 0 ≤ k ≤ 0.6, there are no defects inside the casting, but when 0.66 ≤ k ≤ 1, varying degrees of shrinkage porosity and cavities appear inside the casting.
MAGMASOFT Simulation Summary Table

Figures 2 to 5 show the solidification conditions inside the casting for four different values of k. Figure 2 shows that when k = 0.8 and the actual feeding channel is 450mm, serious problems occur inside the casting; Figure 3 shows the situation when k = 0.66, where minor shrinkage porosity and cavities appear inside the casting; while when k = 0.6 and 0.4, the solidification inside the casting is good, with no defects.

Figure 2: Simulation result for k = 0.8

Figure 3: Simulation result for k = 0.66

Figure 4: Simulation result for k = 0.6

Figure 5: Simulation result for k = 0.4
4. Production Status
Using the optimized process, two support rollers of this specification were produced. The new process was designed with k = 0.4, i.e., a hot-spot diameter of 650mm and an actual feeding channel of 675mm. At this time, the casting weight is 59 tons, and the total molten steel weight is 80 tons.
Compared with the traditional process, the optimized process reduces the casting's gross-to-net ratio, saves molten steel, reduces machining workload, and improves production efficiency. Figure 6 shows the cleaned casting blank, and non-destructive testing after rough machining shows that the internal and external quality of the casting meets technical requirements.

Figure 6: Support roller blank after process optimization
5. Analysis and Discussion
(1) The chilling effect of the sand-coated chill creates an artificial end zone in the outer circumference of the support roller during solidification, reducing the feeding distance of the riser to some extent and alleviating the burden on the riser. Additionally, the 1# sand core is located in the middle of the casting, and heat is only dissipated from the lower part during solidification. This characteristic keeps the molten steel in the riser area at a high temperature for a long time, which is more conducive to the insulation of the riser. The combined effect of these two aspects maintains a good feeding channel expansion angle during the solidification of the support roller casting, facilitating the feeding of molten steel from the top to both sides and achieving directional solidification of the casting. The temperature field simulation of the casting solidification process is shown in Figure 7.

Figure 7: Temperature field simulation for k = 0.4
(2) Since the maximum chill thickness of the sand-coated chill is influenced by factors such as the chill material, molten steel pouring temperature, pouring time, casting material, and the thickness of the sand layer on the chill, it is very difficult to accurately calculate the maximum chill thickness of the sand-coated chill. However, according to the approximate calculation formula for the actual feeding channel, in the casting process design of support rollers with the same structure, it is not necessary to calculate the maximum chill thickness of the sand-coated chill. By using computer simulation and adjusting the chill influence coefficient to ensure the solidification results are within a safe range, the casting process can be optimized.

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