How to adjust the diameter of the rolling machine

In the operation of the plate rolling machine,how to roll the target diameter is the core skill and a key indicator to measure the operator's technical level.Adjusting the diameter is not simply a matter of feeling,but a systematic process based on equipment principles,material properties,and scientific methods.

1.Understand the principle

The rolling principle of the plate rolling machine can be understood as the plastic bending of the plate between the support points by the downward pressure of the upper roller.The core relationship is:
The greater the downward pressure of the rollers on the rolling machine,the greater the bending curvature of the sheet,and the smaller the diameter of the formed material.
The smaller the pressing amount of the upper roller,the smaller the bending curvature of the sheet,and the larger the formed diameter.

This relationship is the theoretical basis for adjusting the diameter.However,in practical operation,due to factors such as rebound,thickness,and material of the board,the downward pressure and diameter are not simply linearly related.

2.Systematic steps for adjusting diameter

To achieve the adjustment,please follow the following systematic steps:

Step 1:Theoretical Calculation and Initial Setting

Determine the target diameter:specify the diameter of the cylinder you need to roll.
Calculate the theoretical pressure:
For a symmetrical three roll plate rolling machine,the approximate downward pressure can be calculated through geometric relationships based on the roller shaft diameter and plate thickness.Many modern CNC bending machines have built-in calculation functions.
For empirical operations,a common method is to first set an initial downward pressure slightly smaller than the target diameter based on experience or equipment manuals.Because it is better to be shallow than deep.If the diameter is too large,it can be further reduced by pressing down,but once it is rolled over(the diameter is too small),it becomes very difficult to correct.

Step 2:Pre bending and Exam Paper

Pre bending of sheet metal:Both ends of the bending machine must undergo pre bending to eliminate straight edges.Adjust the upper roller and lower pressure to bend the length of the board at both ends,so that its curvature is basically consistent with the target curvature.The quality of pre bending directly determines the roundness and diameter consistency of the cylinder.
Test paper and measurement:
After completing the pre bending at both ends,press the upper roller down to the theoretically calculated or empirically set position,and then perform rounding.
Don't roll it straight to the end!Stop the equipment when the roll reaches about one-third to one-half of the circumference.

Step 3:Measurement,Comparison,and Fine tuning

This is a crucial step in adjusting the diameter.
Measure using a template or caliper:
Template(radian gauge):This is a commonly used and quick tool.Based on the target diameter,create inner and outer arc templates and attach them to the rolled arc surface,observing the size of the gaps.
Calipers/πruler:For workpieces with high requirements,calipers can be used to measure the chord length and chord height of the current arc,and the real-time radius can be calculated,or theπruler can be directly used for measurement.
Comparison and adjustment:
If the gap is in the upper part(suspended in the middle of the template):it indicates that the current curvature is smaller than the target curvature,that is,the diameter is too large.At this point,it is necessary to increase the downward pressure of the upper roller.
If the gap is on both sides(suspended on both sides of the template):it indicates that the current curvature is greater than the target curvature,that is,the diameter is too small.At this point,it is necessary to reduce the downward pressure of the upper roller.This situation is quite tricky and may require loosening and readjusting.
Iterative fine-tuning:After making one fine-tuning,scroll slowly again and measure at the new position.Repeat the process of"fine-tuning measurement comparison"until the template fits the curved surface and the gap is uniform.

Step 4:Complete the rounding and calibration process

Final rolling:After adjusting the diameter to fully meet the requirements,continue to complete the entire rolling process.
Rounding(optional,but crucial for quality):Even if the diameter is basically correct,the cylinder of the bending machine may still have ellipticity or local roughness.At this point,1-2'empty rolls'can be performed to homogenize the material through its plastic deformation,further improving its roundness.

3.Key factors and techniques affecting diameter adjustment

Material rebound:This is a large variable.All metals will have elastic recovery,i.e.rebound,after plastic bending.
Tip:When operating,it is necessary to have a"cornering"awareness.For materials with large rebound,you need to press the upper roller down to a position slightly larger than the target curvature,so that the rebound just reaches the target diameter.This requires accumulating experience data for different materials.
Plate thickness and material:
The thicker the plate,the greater the downforce required to achieve the same curvature,and the more pronounced the rebound.
The harder the material(the higher the yield strength),the greater the downforce required,and the greater the rebound.
Equipment accuracy and maintenance:
Ensure that the roller shafts are parallel and the transmission system clearance is normal.Old equipment may have accuracy errors,which require operators to compensate with experience.
The principle of"bigger than smaller":
For beginners,it is essential to follow this principle.First,use a smaller amount of pressure to test the paper,then gradually increase the pressure in stages and in small amounts to approach the target diameter.This is a safe method to avoid the scrapping of workpieces.
Summary:A flowchart to handle diameter adjustment
Target diameter→Theoretical calculation/empirical setting of initial downward pressure→Pre bending at both ends→Test paper(1/3 circle)→Measurement and comparison using a template→
→Diameter is too large→Increase the downward pressure→Measure again on the test paper..
→Diameter is too small→Reduce the downward pressure→Measure again on the test paper..
→Qualified diameter→Completed rounding→Rounding→Inspection
In summary,adjusting the diameter of a plate rolling machine is a dynamic and precise feedback adjustment process.It relies on scientific principles,standardized operating procedures,and the operator's accumulated judgment of the material's"feel"and"rebound"in practice.By mastering the above methods and techniques,you will be able to roll cylinders that meet the requirements stably and effectively.