Rolling Cones on a Four Roll Plate Rolling Machine: Roll Adjustment Techniques
Rolling Cones on a Four Roll Plate Rolling Machine: Roll Adjustment Techniques
Posted by PLSON Engineering Team
Introduction
Rolling a conical shell — commonly called a cone, a conical shell, or a reducer — puts higher demands on the operator than rolling a cylinder. The adjustment of the rolls directly determines the quality of the finished cone, the scrap rate, and the production efficiency.
This article examines the two practical approaches to taper adjustment on a four roll plate rolling machine: moving the rolls with hydraulic cylinders, and controlling the roll position precisely through a CNC system. It then compares the two methods and sets out the factors that decide which one suits a given workshop.
Safety first: Roll adjustment and taper setting are carried out with the machine under power and with hydraulic pressure applied. Stop the machine and isolate the power before inspecting limit switches, sensors, cylinders, or valve blocks. Hydraulic circuits store pressure after the pump stops — release residual pressure before opening any connection. Never reach between the rolls or into the tooling area while the machine is running, and never disable a guard interlock or a safety device to shorten the setting procedure. Only trained and authorized personnel should adjust the rolls or the control parameters.
Why Conical Rolling Differs from Cylindrical Rolling
In cylindrical rolling, the roll gap is uniform across the full width of the plate, and every point along the plate passes through the rolls at effectively the same condition. The plate bends into a cylinder with a constant radius.
In conical rolling, the finished shell has a large end and a small end. The circumference varies continuously across the width of the plate, so the required curvature varies with it. To produce that variation, the roll gap must not be uniform: it has to be larger at the end that will form the large diameter and smaller at the end that will form the small diameter.
This is the single most important point to understand before adjusting anything: a cone is not produced by bending the plate harder. It is produced by making the bending condition uneven along the width of the plate.
How a Four Roll Machine Forms a Cone
A four roll plate rolling machine has four rolls: one upper roll, one lower roll, and two side rolls. The four rolls work together to bend and roll the plate.
When rolling a cone, the decisive factor is the relative position of the rolls — specifically:
- The two side rolls are set at different positions. Instead of being symmetrical, one side roll is set closer to the centre line than the other, so the curvature imposed on the plate is different at the two ends.
- The upper roll is offset relative to the lower roll. A lateral offset skews the bending line relative to the plate, which combines with the asymmetric side roll setting to generate a tapered roll gap.
- The plate is fed at an angle. The plate edge is deliberately not parallel to the roll axis. Without this, the roll gap varies but the plate still tends to roll as a cylinder, or rolls with a skew.
The hydraulic cylinders are the power source that moves the rolls into these positions, which is why the accuracy with which they can be positioned and held determines the accuracy of the cone.
Method 1: Hydraulic Cylinder Roll Adjustment
In this method, hydraulic cylinders push the rolls to the position required for the taper. Two parameters are adjusted: the stroke of the cylinder, which sets position, and the pressure, which sets force.
Stroke (position) adjustment
The stroke of the hydraulic cylinder is normally adjusted through limit switches or position sensors. These devices monitor the distance the roll has travelled and send a signal when the preset position is reached, which stops the cylinder.
Pressure (force) adjustment
The pressure is normally adjusted by changing the output pressure of the hydraulic pump or by fitting a pressure reducing valve in the circuit.
Force matters for a different reason than position. At the large end of the cone the plate presents a different resistance than at the small end, and as the cone develops, the load distribution across the machine changes. If the clamping force is too low at that stage, the plate can slip; if it is too high, the plate can be marked, the ends can be over-compressed, or the roll can deflect. Because of this, position and force have to be set together, not independently.
Practical sequence for setting a taper hydraulically
Limits of manual hydraulic adjustment
- The setting must be re-established for every new cone size, which costs time on each changeover.
- The two sides are adjusted independently, so an asymmetry between them is easy to introduce and hard to notice before the part is measured.
- Repeatability depends heavily on the operator and on the accuracy of the switches or sensors.
- Fine adjustment during the pass is limited, because the cylinders are positioned before the pass rather than controlled continuously through it.
Method 2: CNC Control of Roll Position
A CNC system controls the roll position and the motion path accurately, which allows different tapers to be rolled without rebuilding the setting by hand each time.
Composition of the CNC system
A CNC system normally consists of a computer, a controller, and actuators.
How the adjustment works
The CNC system receives the input parameters — such as the taper, the plate thickness, and the other part data — automatically calculates the required roll position and the motion path, and issues commands to the actuators, such as the hydraulic cylinders and proportional valves, to make the adjustment.
The adjustment process is automatic: the operator enters the part data, and the system establishes the roll positions and controls the movement through the pass.
Advantages of CNC taper control
The storage and traceability function is often underestimated. Being able to call up the exact parameters used for a previous order means the next identical cone starts from a known-good setting instead of from a fresh trial.
Comparing the Two Methods
Neither method is universally better. The hydraulic method gives a lower entry cost and is adequate where cone sizes rarely change and the tolerance is moderate. The CNC method pays back where cones are produced repeatedly, where sizes change often, or where the tolerance and traceability requirements are strict.
Other Factors That Affect Cone Accuracy
Roll adjustment is necessary but not sufficient. Cone accuracy also depends on:
- Plate support and alignment, including how the plate is fed and held during the pass
- Plate thickness and material variation, which changes the required force and the springback
- Springback, which must be allowed for on the final pass, especially for large end diameters
- Roll diameter and machine configuration, which limit what geometry the machine can produce
- Number of passes and the pre-bending of the ends, since a cone cannot be corrected after the ends have been pre-bent incorrectly
- Hydraulic oil temperature, which affects positioning repeatability and therefore the taper
- Tooling and roll condition, including wear and surface condition
Choosing the Right Method
When selecting a taper adjustment method, the decision should consider the production requirement, the cost budget, and the technical level available in the workshop.
Continuing to optimize the taper adjustment method is how a workshop moves toward more efficient, more accurate, and more reliable cone production.
Maintenance Points for Taper Rolling
Conclusion
Rolling a conical shell on a four roll plate rolling machine depends on creating a deliberately uneven bending condition across the width of the plate — through the relative position of the upper roll, the lower roll, and the two side rolls, combined with the correct plate feed angle.
Hydraulic cylinders provide the force and the position for that setting. The stroke is normally adjusted through limit switches or position sensors, and the pressure through the pump output or a pressure reducing valve. This approach has a lower entry cost, but the setting must be re-established for each new cone size and the repeatability depends on the operator.
A CNC system takes the same adjustment further: it receives the input parameters, calculates the roll positions and the motion path automatically, and commands the cylinders and proportional valves to carry out the adjustment. The result is simpler operation, faster adjustment, higher accuracy, reduced manual intervention, and data storage that makes previous settings reusable and traceable.
Choosing between them comes down to production demand, cost budget, and the technical level available — and to how often the cone size changes and how tight the tolerance is. Optimizing this choice is one of the most direct ways to improve both cone quality and production efficiency.
If you are rolling cones and want advice on whether CNC roll control is worth it for your mix of work, contact our engineering team with your typical cone sizes, plate thickness, and required tolerance.
Contact the PLSON Engineering Team for four roll plate rolling machine specifications, CNC control options, and technical support.
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📧 Eric@plsonmachine.com
🏭 Haian Industry Park, Jiangsu Province, China