Hydraulic System of a Four Roll Plate Rolling Machine: Components, Circuits and Working Principles
Hydraulic System of a Four Roll Plate Rolling Machine: Components, Circuits and Working Principles
Posted by PLSON Engineering Team
Introduction
The hydraulic system is the power source of a four roll plate rolling machine. It drives the lower roll and the side rolls, holds the rolls in position under heavy rolling load, and operates the drop end that opens to release the finished cylinder. Roll positioning accuracy, repeatability, and the quality of the finished shell all depend on how precisely the hydraulic system controls these movements.
This article explains how the hydraulic system of a four roll plate rolling machine is built, which circuits it is divided into, and how each circuit contributes to rolling accuracy. It also covers the key parameters, maintenance points, and the faults that show up most often in service.
Safety first: Hydraulic systems store pressure even after the pump has stopped. Before opening any connection, checking a valve, or servicing the drop end, stop the machine, isolate the main power, and release residual pressure according to the manufacturer’s procedure. Support the rolls mechanically before working under them. Only trained and authorized personnel should service the hydraulic system, and only hydraulic oil and components approved for the machine should be used. Never defeat a pressure protection device or a safety interlock to keep the machine running.
Composition of the Hydraulic System
The hydraulic system of a four roll plate rolling machine is made up of four groups of components.
These four groups must work as one system. A correct pressure setting is useless if the oil is contaminated, and a precise valve stack cannot hold position if the oil temperature is allowed to climb.
Sandwich Valve Design
The valve group of this machine uses the sandwich valve series, also called modular or stack valves.
In a sandwich valve system, individual valves are mounted on top of each other as modules on a common manifold block. Oil passages are formed inside the block instead of being created by external piping.
Advantages of this layout
- Simple piping arrangement. Internal passages replace most external pipes and fittings, so the installation is compact and easy to follow.
- Convenient maintenance and adjustment. A valve can be removed or replaced within the stack without dismantling the whole circuit.
- Fewer leakage points. Every external joint is a potential leak; reducing the number of pipes and fittings reduces the risk.
- Lower pressure loss and cleaner response. Short internal passages limit pressure drop and help the circuit react faster.
- Easier fault finding. Because each function occupies a defined module in the stack, a problem can be traced to a specific element.
Three Circuits of the Hydraulic System
The hydraulic system of a four roll plate rolling machine is organized into three circuits, each with a defined job.
1. Overpressure Protection and Pressure Regulation Circuit
This circuit performs two related tasks: it establishes the working pressure of the system, and it protects the system from pressure that exceeds the design limit.
The pressure regulation circuit adjusts the working pressure of the system through the main relief valve. The working pressure of the system is 19.5 MPa.
How to read this
- The main relief valve is the reference point for the whole hydraulic system. Its setting determines the force available at the rolls.
- The relief valve also acts as the overpressure protection device. When pressure rises above the set value — for example, when the plate is too thick for the selected setting, or when a roll reaches a mechanical stop — the valve opens and diverts oil back to the reservoir instead of allowing pressure to keep rising.
- Because the relief valve protects both the workpiece and the machine, its setting should be verified against the machine specification and should not be adjusted beyond the specified range.
Practical note: the rolling force required depends on plate thickness, width, and material yield strength. If the required force exceeds the available force at the set pressure, the relief valve opens and the rolls stop advancing. This is a sign that the machine is being asked to exceed its capacity — not that the pressure setting should be raised beyond specification.
2. Synchronization Circuit
The synchronization circuit is the reason a four roll plate rolling machine can produce an accurate shell, and it is the circuit that most directly determines rolling quality.
Function
The synchronization circuit uses flow divider and throttle valves to provide the initial, coarse synchronization of the raising and lowering movements of the lower roll and the side rolls. Throttle valves then make fine adjustments in both the up and down direction. Displacement sensors monitor the actual position of the rolls, and closed-loop correction keeps the synchronization accuracy of the lower roll and the side rolls within ±0.05 mm.
Why two stages are used
A flow divider alone cannot guarantee accuracy, because cylinder friction, load distribution, and oil temperature all change during the rolling cycle. Position feedback is what turns a rough division of flow into a measured, repeatable position. The same applies in reverse: feedback cannot correct a badly divided flow, which is why the two stages work together.
Why ±0.05 mm matters
- Parallelism of the rolls. If the two ends of a roll are not at the same height, the roll gap is not uniform along the plate width.
- Consistent diameter and taper control. Synchronization error between the ends shows up as a diameter difference across the width of the rolled shell, or as a taper.
- Accurate pre-bending. The pre-bending stage sets the flat end length and the end curvature; if the rolls are not synchronized, the pre-bent end is not symmetric.
- Repeatability. Because the position is measured and corrected rather than assumed, the same program produces the same result on the next plate.
3. Speed Circuit
The speed circuit controls the tilting and resetting of the drop end.
The drop end is the section of the machine that swings out to allow a closed cylinder to be removed from the rolls. If the drop end moves too quickly, the motion is abrupt and can shock the structure and the hydraulic components; if it moves too slowly, the rolling cycle becomes unnecessarily long.
The speed circuit regulates the speed of this movement through a throttle valve, which restricts the flow in the circuit and allows the tilting speed to be set to a controlled value.
Points to observe
- Tilting and resetting should be smooth, without jerking or impact at the end of the stroke.
- The end position must be positively reached and confirmed before rolling resumes; rolling with the drop end not fully closed is unsafe and will damage the machine.
- The speed should be set as required by the machine specification and should not be increased simply to shorten the cycle.
How the Three Circuits Work Together
During one rolling cycle the three circuits operate in sequence and interact.
Because the circuits share the same oil supply, a fault in one can appear as a symptom in another. Low oil level, air in the oil, or high oil temperature will affect pressure regulation, synchronization, and speed at the same time. This is why oil condition and temperature should be checked before individual circuits are adjusted.
Key Parameters Summary
Maintenance of the Hydraulic System
Regular attention to a small number of items prevents most hydraulic faults.
Oil
- Check the oil level at the specified interval and top up with the approved oil grade.
- Check oil condition for darkening, emulsification, or visible contamination.
- Check oil temperature in operation; sustained high temperature shortens oil life and changes viscosity, which affects synchronization accuracy.
- Replace the oil and clean the reservoir at the manufacturer’s interval.
Filters
- Replace or clean the filter elements on schedule. A clogged element causes pump cavitation, noise, and unstable pressure.
- Inspect the suction strainer when the oil is changed.
Valves
- Keep the valve stack and manifold clean; dirt introduced during maintenance is a common cause of valve sticking.
- Check the relief valve setting periodically against specification.
- Check flow divider and throttle settings only after the oil condition is confirmed good, so that a contamination problem is not mistaken for a setting problem.
Connections and seals
- Inspect pipes, hoses, fittings, and manifold joints for leakage and weeping.
- Replace hoses that show cracking, swelling, or abrasion at the bend radius.
- Bleed air from the circuit after any repair that opens it.
Drop end
- Check the tilting and resetting motion for smoothness.
- Check the end position confirmation and the associated interlock.
- Lubricate and inspect the hinge or guide according to the machine manual.
Common Faults and What They Suggest
When more than one symptom appears together, check the shared items first — oil level, oil condition, oil temperature, and air in the system — before adjusting an individual circuit.
Conclusion
The hydraulic system of a four roll plate rolling machine is built from a hydraulic pump, a valve group, fluid connections, and hydraulic accessories, arranged as a sandwich valve stack for compact piping and convenient maintenance. It is organized into three circuits: overpressure protection and pressure regulation, synchronization, and speed.
The pressure regulation circuit sets the system working pressure at 19.5 MPa through the main relief valve. The synchronization circuit combines flow divider and throttle valves with displacement sensor feedback to hold the lower roll and side rolls within ±0.05 mm. The speed circuit uses a throttle valve to control the tilting and resetting of the drop end.
Understanding how these three circuits work together makes the machine easier to operate, easier to maintain, and much faster to troubleshoot — because the symptom usually points to the circuit, and the circuit points to the component.
For questions on the hydraulic configuration, spare parts, or technical support for your PLSON plate rolling machine, contact our engineering team.
Contact the PLSON Engineering Team for four roll plate rolling machine specifications, hydraulic spare parts, and technical support.
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📧 Eric@plsonmachine.com
🏭 Haian Industry Park, Jiangsu Province, China