Strength analysis and cooling water system research of continuous casting tension and leveling machine

Abstract: For the R9m, cross-section 170±30mm billet continuous casting machine tension leveler, the strength of the tension leveler structure was checked and improved using the cosmosworks finite element analysis plug-in of SolidWorks. The cosmosfloworks fluid analysis plug-in of SolidWorks was used to perform flow and heat exchange simulation on the cooling water system of the tension and straightening machine, which solved the problems of dead water and small water flow in the cooling water system. Testing costs are minimized and product quality is improved.

Keywords: Tension and straightening machine; strength; cooling water; flow; heat exchange

Preface

The tension and leveling machine studied in this article is a clamp-type frame structure, which is mainly composed of a frame, a clamp rod, a pressing arm, a hydraulic cylinder, an upper and lower roller assembly, a motor, a reducer, an insulated water jacket, and a cooling water system. As shown in Figure 1. The upper and lower rollers of the blanking machine are both transmission rollers, while the straightening machine only has the upper roller transmission. Each action of the pressing device is completed by a hydraulic cylinder.

Finite element (static) analysis

The strength of the tension and leveling machine directly determines its work safety, which in turn affects the dimensional accuracy and quality of the cast slab. Therefore, strength analysis of tension leveling machines has important practical significance.

Figure 1 Main components of tension and leveling machine

1. Frame 2. Clamp rod 3. Press down arm 4. Hydraulic cylinder 5. Upper and lower roller assembly 6. Motor 7. Reducer 8. Insulated water jacket 9. Cooling water system

Stress conditions of tension and leveling machine

In the design of the tension leveling machine, in order to overcome the drawing resistance and the force on the tension roller when installing the dummy bar, a certain positive pressure must be exerted on the roller. After calculation, it can be seen that the positive pressure is the largest when the dummy bar is installed, so only the situation when the dummy bar is installed is analyzed.

When installing the dummy bar, the dummy bar moves upward, the friction resistance is downward, and the downward force is downward, so the force of the pull roller when installing the dummy bar is

Fr=rAρg(μ0sin(a)-cos(α)+1)=12911.26 N

In the formula, g=9.8m/s²; A is the cross-sectional area of the dummy bar, A= 192.67cm²; R is the basic arc radius of the casting machine R=900cm; ρ is the specific gravity of the dummy bar material, ρ=0.0078kg/cm³; α is the limit position of the dummy head and the maximum wrapping angle of the pull roller, α=80°; μ0 is the friction coefficient within the secondary cooling device, μ0=0.15.

Since there are two pairs of pull rollers, the force on the upper roller of the pair of pull rollers is F’r=F/2=6455.63N.

The positive pressure on the roller is N=F’/μ₁=161390.75N. In the formula, μ₁ is the friction coefficient between the roller and the dummy bar, μ₁=0.04.

From a structural point of view, there is a leverage relationship between the pressing force of the hydraulic cylinder and the pressing force of the pull roller. Then the pressing force of the hydraulic cylinder

P=Nb/a=105421.51 N

In the formula, a is the distance from the oil cylinder to the rotating shaft, a=842mm; b is the distance from the roller center to the rotating shaft, b=550mm.

The friction force F on the roller is 6455.63N. Considering the balance, the torque of the roller is M=Fr/1000=1129.74N·m

In the formula, r is the radius of the roller, r=175mm.

Finite element analysis

Establish the geometry of the tension leveler and compress the reducer and motor to simplify the model.

Material property preparation

The parts (except rollers) are made of plain carbon steel, and the rollers are made of alloy steel.

Define fixture

Select the lower surfaces of the six bottom panels of the rack as fixed geometry.

Apply external load

The pressure applied to the upper and lower rollers is 161390.75 N, the friction force is 6455.63 N, and the torque is 1129.74 N·m; the pressure applied to the hydraulic cylinder piston is 105421.51 N. Apply a pressure of 105421.51N to the bottom of the hydraulic cylinder, ignoring the circumferential force (cancel each other). Apply a pressure of 3000N to the reducer positions at the upper and lower roller ends (because the reducer has been compressed), as shown in Figure 2.

Meshing

Figure 2 Schematic diagram of force loading of tension and leveling machine

Set the mesh density close to good and apply mesh control to local refinement.

Result analysis

Figure 3 is the equivalent stress diagram. It can be seen from Figure 3 that the two areas with relatively large stress are the upper panel of the clamp rod pressed down by the piston rod, and the edge of the pin hole and the pin shaft at the hinge between the clamp rod and the frame. The maximum equivalent stress occurs in the latter region, about 210.3 MPa. The material is Q235, the yield strength σ=235MPa, and the safety factor n=1.5 is selected, then the allowable stress [σ]=σ/n= 235/1.5=156.7MPa. Obviously, the allowable stress is less than the calculated maximum equivalent stress, which poses a safety hazard. Therefore, improvements must be made. Taking into account the stress concentration on the edge of the pin hole, the edge of the pin hole is rounded. In order to increase the strength of the pin, the material of the pin is changed to alloy steel. The upper panel of the clamp rod pressed down by the piston rod also has safety risks. A support plate is added below it while ensuring its stiffness requirements, as shown in Figure 4.

Figure 3 Equivalent stress distribution diagram

After calculation again, the maximum equivalent stress is significantly reduced and is close to 148 MPa. The maximum equivalent stress is less than the allowable stress. Therefore, the improved design is safe and the strength of the tension leveler meets the working requirements.

Figure 4 Improved clamp rod

Fluid (cooling water system) analysis

Since the tension and leveling machine works under high-temperature radiation for a long time, all parts of the equipment of the tension and leveling machine must be effectively cooled and protected to prevent high-temperature creep of equipment components and increased drawing resistance. Conducting flow and heat exchange analysis on the cooling water system of the tension leveler can help improve the waterway structure and thereby extend the service life of the tension leveler.

The cooling water system of the tension and leveling machine in this project includes: the bearing seat and the upper and lower rollers are cooled by water; the lower arm and clamp rod are cooled by water; and the reducer is cooled by water. The insulated water jacket covering the red hot casting billet is passed through water for internal cooling; the rack is passed through water for internal cooling. The water-cooling rack also functions as a water distribution tank. The inlet and outlet pipes of all water cooling components are connected to the rack. There is only one water inlet pipe and one outlet pipe on the rack, which facilitates rapid replacement of the entire tension and leveling machine and improves the continuous casting operation rate.

Flow analysis

Basic settings

The simulation type is set to allow heat conduction, including between solids and solids, and between solids and fluids. The fluid is set to water, and the solid material is selected to be plain carbon steel.

Boundary conditions

Set the flow rate of the water inlet to 3.6 kg/s and the pressure of the water outlet to 601325 Pa.

Result analysis

To ensure the smooth flow of water, no stagnant water or too small flow rate in key waterways is allowed. Because neither of the above can take away heat in time, the water temperature will rise, affecting the cooling effect.

The first position: stagnant water appears at the front end of the clamp rod return chamber, as shown in Figure 5.

Figure 5 Schematic diagram of dead water appearing at the front end of the clamp rod return chamber

Treatment method: Change the connecting water pipes of the left and right bearing seats from the front end of the bearing seat to the rear end of the bearing seat, so that the cooling water of the bearing seat flows in and out from the front end of the clamp rod to overcome the dead water phenomenon at the front end of the clamp rod.

Second position: There is stagnant water in the backwater cavity of the rack, as shown in Figure 6.

Figure 6 Schematic diagram of stagnant water in the backwater cavity of the rack

Treatment method: Move the reducer on the frame and the cooling water inlet and outlet of the lower roller as far away from the center of the bearing seat as possible.

Third position: A rectangular tube at the upper end of the rear of the insulated water jacket’s water inlet chamber has 1 water inlet hole and 2 water outlet holes. Only the water outlet hole close to the water inlet hole discharges water, and the other water outlet hole does not discharge water, resulting in stagnant water in the pipe, as shown in Figure 7. The water return chamber also has the same problem.

Figure 7 Schematic diagram of stagnant water in a rectangular pipe

Treatment method: Reduce the diameter of the two water outlets of the rectangular pipe.

Fourth position: From the density of the flow trace, it can be seen that the water flow into the pressure lower arm is greater than the water flow into the insulating water jacket. The main reason is that the diameter of the two water pipes is the same, and the pressure loss of the pressure arm pipe is small, so a large amount of cooling water enters the return water chamber through the pressure arm. However, in fact, the insulated water jacket is directly baked by the cast billet and requires a large amount of cooling water for cooling. However, the pressing arm is not directly baked, so the amount of cooling water can be reduced, as shown in Figure 8. Treatment method: Change the diameter of the water inlet and outlet of the push-down arm from the original 1in to 0.75in, so as to ensure the water inlet of the insulated water jacket.

Figure 8 Flow trace diagram of the pressing arm and insulating water jacket

Heat exchange analysis

The water temperature of the overall heat exchange water circuit changes very little, so there is no need to analyze it. Only the temperature rise of the insulating water jacket is relatively large, so only the thermal analysis is performed on the insulating water jacket. In fact, most of the heat released by the casting billet is heat exchanged in the insulated water jacket.

It should be noted that in order to realize the heat exchange between the billet-air-insulating water jacket-water, the insulating water jacket needs to be placed in an assumed empty box to achieve heat transfer of hot air.

Basic settings

The simulation type is set to allow heat conduction, including between solids and solids, and between solids and fluids. The fluids are set to air (default) and water, and the solid material is selected to plain carbon steel.

Fluid region

Set up a flow sub-region for water.

Boundary conditions

Set the air flow environment pressure to 101325 Pa.

Set the flow rate of the water inlet to 1 kg/s and the pressure of the water outlet to 601546 Pa.

Set the heat source

Set a certain length (1700 mm) of billet as the heat source, define the heat 60 kJ/s and the temperature 1000°C.

Result analysis

The water temperature change trend is reasonable. The water temperature has increased by up to 6.5°C from normal temperature, and is within the range of 6°C to 10°C, which meets the design requirements, as shown in Figure 9.

Figure 9 Cooling water temperature distribution diagram

Conclusion

(1) Through the strength analysis of the R9 m tension leveler, the weak points of the structure were found. That is, the panel on the upper part of the clamp rod pressed down by the piston rod, as well as the edge of the pin hole and the pin shaft at the hinge of the clamp rod and the frame. Therefore, targeted improvements were made and the design was optimized to ensure the safety of the tension and leveling machine.

(2) Through the flow simulation of the cooling water system of the R9 m tension leveler, the reasons for the dead water in some waterways and the low flow rate of key waterways were found out, and the treatment methods were proposed. A heat exchange simulation was conducted to determine the rationality of the overall waterway design of the insulated water jacket. This work helps to improve the water path structure of the cooling water system, thereby extending the service life of the tension and leveling machine.

Share on facebook
Facebook
Share on twitter
Twitter
Share on linkedin
LinkedIn
Share on pinterest
Pinterest

High-quality equipment and parts manufacturer for continuous casting

cover picture-COPPER MOULD TUBE PDF

Special product design, please send specific data and drawings to our mailbox or form.

Products