How to Calculate Load and Power for Symmetrical 3-Roll Plate Bending Machine

Introduction

The load on plate roll bending machines is substantial, necessitating high strength in their components. This is critical to ensure the machine’s durability and performance under heavy operational conditions.

In today’s competitive market, reducing the cost of plate rolls is crucial. This requires designing the machine with both accuracy and reliability to maintain quality while minimizing expenses.

To design a roll bending machine effectively, it is essential to first perform a comprehensive force analysis. This analysis provides the fundamental parameters needed for designing each part of the machine, ensuring that all components can withstand the operational stresses they will encounter.

Additionally, calculating the driving power of the main drive system is vital. This calculation is crucial for designing the main drive system and selecting an appropriate motor, ensuring the machine operates efficiently and effectively.

Therefore, performing a detailed force analysis and accurately calculating the driving power are critical steps in the design process of a roll bending machine.

This post outlines a method for calculating the force capabilities of a symmetrical three-roll bending machine. This method can also serve as a reference for other types of plate rolling machines, providing a foundational approach to their design and optimization.

Force Analysis

2.1 Maximum torque required for a cylinder rolling

When the plate rolling machine is working, the steel sheet should be rolled into the steel pipe.

At this time, the stress of the material has reached the yield limit.

Therefore, the bending stress distribution on the tube section is shown below the figure (b), and the bending moment M of the section is:

In the above formula,

• B, δ – The maximum width and thickness of rolled steel sheet (m)
• σ_s – Material’s yield limit (kN • m^-2)

Fig.1 Stress distribution of roll bending

When considering the deformation of the material, there is reinforcement, and the reinforcement coefficient K is introduced to modify the equation (1), namely:

In the above formula,

• K – reinforcement coefficient, the value can be K = 1.10~1.25, when the result for δ/R is big, then take the biggest value.
• R – Neutral layer’s radius of the rolling plate (m)

2.2 Force Condition

When rolling steel plate, the force condition is shown as below figure. According to the force balance, the supporting force F₂ on the roll plate can be obtained via the formula:

In the above formula,

• θ – The angle between defiled line OO1 and OO2,

• α – Lower roller center distance (m)
• d_min – Min diameter of plate rolling (m)
• d₂ – Lower roller diameter (m)

Fig.2 Force analysis of roll bending

Considering that the thickness of the plate δ is far less than the minimum diameter of the rolling tube, the radius R of the neutral layer is around 0.5d_min, in order to simplify the calculation, the above equation can be changed to:

According to the force balance, the pressure force F₁, which is generated by the upper roller, acting on the rolling plate is:

Calculation of driving power

3.1 Lower roller drive moment

The lower roller of the plate rolling machine is the driving roller, and the driving torque on the lower roller is used to overcome the deformation torque T_n1 and the friction torque T_n2.

In the process of steel plate rolling, the deformation capabilities stored in AB section of the steel plate (see Fig 1a and Fig 2) is 2Mθ, the costed time is 2θR/V (V is rolling speed).

The ratio is equal to the power of deformation torque T_n1, namely:

Therefore,

The friction torque includes the rolling friction torque between the upper and lower roller and the steel plate, and the sliding friction torque between the roller neck and the shaft sleeve, which can be calculated as follows:

In the above formula:

• f – Coefficient of rolling friction, take f = 0.008m
• μ – Coefficient of sliding friction, take μ = 0.05-0.1d₁,
• d₂ – Upper roller & lower roller diameter (m)
• D₁, D₂ – Upper roller & lower roller neck diameter (m)

The size is not yet accurate in the design phase, the value can take D_i = 0.5d_i (i=1, 2). The lower roller drive torque T equals the sum of the deformation torque T_n1 and the friction torque T_n2.

3.2 Lower roller driven power

Lower roller driven power is:

In the above formula:

• P – Driven power (m • KW)
• T – Driven force moment (KN • m)
• n₂ – Lower roller rotation speed (r • min^-1), n₂=2V/d₂ (V is rolling speed)
• η – transmission efficiency， η=0.65-0.8

The power of the main motor can be obtained from the value of P.