1. Introduction
The transition toward dry battery electrode (DBE) manufacturing is one of the most significant shifts in modern energy storage production. Unlike traditional wet coating methods, the dry process eliminates solvent recovery, reduces factory footprint, and enables thicker, higher-energy-density electrodes — essential for solid-state batteries and next-generation Li-ion cells.
At the heart of this technology lies multi‑roll continuous calendering, a mechanical compaction process that transforms loose dry powder into a self‑supporting film with precise thickness and density.
But achieving micron‑level uniformity under hundreds of kilonewtons of rolling force is impossible without advanced actuation and control. This is where hydraulic systems — specifically hydraulic cylinders, hydraulic pumps, and hydraulic control systems — become the backbone of modern calendering equipment.
In this article, we examine the dry electrode process, explain multi‑roll calendering, and detail how high‑performance hydraulics from manufacturers like Riverlake enable reliable, high‑precision production.
2. What Is the Dry Electrode Process?
The dry electrode process (also called solvent‑free electrode manufacturing) consists of three main steps:
- Dry mixing – active material, conductive carbon, and a PTFE‑ or polymer‑based binder are blended in powder form.
- Fibrosis or shear mixing – high‑speed mixing causes the binder to form a fibril network (a “dry paste” or “mastication”).
- Calendering into freestanding film – the fibrillated powder is fed into a calendering stack, where multiple roller pairs compress it into a continuous, self‑supporting electrode film (typically 50–300 µm thick).
The film is then laminated onto a current collector (Cu or Al foil) — again without solvents.
Why dry process matters
- No solvent recovery → 30‑50% lower energy consumption
- No drying oven → smaller factory footprint
- Thicker electrodes → higher volumetric energy density
- Compatible with sulfide/oxide solid electrolytes → essential for all‑solid‑state batteries
Major battery manufacturers (Tesla, CATL, BYD, and many startups) are actively developing dry electrode lines.
3. Multi-Roll Continuous Calendering Explained
3.1 What Is Calendering in Battery Context?
Calendering compresses the electrode coating (or dry film) to a target porosity and thickness, improving electronic conductivity and adhesion to the current collector.
3.2 Single vs. Multi‑Roll
- Single‑pair calender – limited reduction ratio; high risk of film cracking if compression is too aggressive.
- Multi‑roll continuous calender – the material passes through 2 to 5+ rolling gaps in sequence, each with progressively smaller gap and/or different roll diameters.
A typical arrangement:
- Pre‑calender: large‑diameter rolls, high force → initial compaction.
- Intermediate rolls: further densification.
- Finish calender: final thickness setting with micron‑level gap control.
The multi‑roll approach allows gradual plastic deformation, reduces internal stress, and enables higher line speeds (30–80 m/min) without film defects.
4. Why Hydraulics Are Indispensable for Multi‑Roll Calendering
Calendering dry electrode film imposes extreme requirements:
| Parameter | Typical value |
|---|---|
| Linear load (force per width) | up to 2000 kN/m |
| Total roll separating force | 200–1000+ kN |
| Thickness tolerance | ± 1–2 µm |
| Roll gap adjustment resolution | ≤ 1 µm |
| Force control stability | ± 0.5 % |
Electric ball screws or pneumatic cylinders cannot meet these demands reliably over long production runs. Hydraulic systems provide the necessary combination of:
- High force density
- Stiff force‑vs‑stroke characteristics
- Continuous modulation under dynamic loads
- Long service life in dusty factory environments
5. Role of Hydraulic Cylinders, Pumps, and Control Systems
5.1 Hydraulic Cylinders – The Force Actuators
In a multi‑roll calender, large‑bore hydraulic cylinders are mounted at both ends of each roll journal. Their function:
- Apply precise, adjustable roll separating force (or closing force, depending on frame design).
- Accommodate thermal expansion of the rolls.
- Provide overload protection via pressure relief.
Key requirements for dry‑electrode calendering:
- Low friction seals to avoid stick‑slip (critical for micron‑level gap control)
- High side‑load resistance (roll bending forces are significant)
- Optional position feedback (built‑in magnetostrictive sensors)
Manufacturers like Riverlake offer cylinders specifically designed for continuous industrial applications, with bore sizes from 40 mm to over 200 mm and custom mounting configurations for roll stacks.
5.2 Hydraulic Pumps – The Power Source
Calender hydraulic systems typically use variable‑displacement axial piston pumps with pressure‑ or load‑sensing control.
Why piston pumps?
- Ability to generate 250–350 bar continuously
- High volumetric efficiency (>95%)
- Low noise and pulsation (important for force stability)
A typical calender hydraulic power unit (HPU) includes:
- Main pump (often redundant, N+1)
- Accumulator bank to dampen pressure ripples
- Filtration (3–5 µm absolute) to protect servo valves
- Oil cooling circuit (dry calendering generates significant heat due to high friction)
Riverlake’s hydraulic pumps range from fixed gear pumps for simple applications to high‑pressure piston pumps for demanding constant‑force or constant‑gap control.
5.3 Hydraulic Control Systems – The Precision Brain
The control system is where the “magic” happens. Two primary control modes are used in multi‑roll calendering:
Mode 1: Constant Force Control
- The controller maintains a setpoint roll force regardless of material thickness variations.
- Used in pre‑calendering stages to achieve target density.
- Implemented via proportional pressure‑reducing valves or servo‑proportional valves reading force sensors (load cells).
Mode 2: Constant Gap (AGC) Control
- The controller maintains a fixed roll gap (e.g., 120 µm), automatically adjusting force as material stiffness changes.
- Essential for final thickness precision.
- Uses a closed loop: position sensor (cylinder mounted) → PID controller → servo valve → cylinder.
Advanced systems integrate both modes, switching seamlessly (e.g., force mode until gap sensor reaches threshold, then hold gap).
Digital hydraulic controls also enable:
- Real‑time gap profiling (crown correction)
- Tapered gap (wedge) compensation
- Data logging for statistical process control (SPC)
Riverlake hydraulic control systems include proportional/servo valve manifolds, PLC‑ready controllers, and user‑friendly HMI — all packaged for easy integration into calendering lines.
6. Practical Example: A 5‑Roll Dry Electrode Calendering Line
Consider a typical dry‑film production line for solid‑state battery anodes:
| Station | Rolls | Hydraulic function | Control mode |
|---|---|---|---|
| 1 (pre‑calender) | Ø500 mm | Force up to 800 kN | Constant force |
| 2 (intermediate) | Ø400 mm | Force 600 kN, gap start‑up | Force → gap handover |
| 3 (finish) | Ø300 mm | Gap 80 µm ± 1 µm | AGC constant gap |
Each of the 10 cylinder positions (5 rolls × 2 ends) is independently controlled by its own servo valve and cylinder pressure/position sensors, coordinated by a central PLC with hydraulic manifold.
Total installed hydraulic power: 30–50 kW.
Without high‑quality hydraulic components, defects such as thickness variation, wavy edges, or pinholes would render the dry electrode film unusable.
7. Why Component Quality Matters: Downtime Risk in Dry Electrode Lines
A dry electrode calendering line typically runs 24/7. Any hydraulic failure stops the entire line, causing:
- Hours or days of scrap
- Loss of film continuity (requiring re‑threading, often very difficult)
- Potential roll damage (if force is lost unevenly)
Therefore, reputable OEMs and battery gigafactories choose industrial‑grade hydraulic components from proven suppliers like Riverlake , not generic low‑cost alternatives.
Riverlake’s product range is specifically engineered for continuous heavy‑duty applications:
- Cylinders with chrome‑plated piston rods (corrosion resistance against binder residues)
- Pumps with extended bearing life (L10 > 20,000 h)
- Control systems with redundant pressure transducers and diagnostic LEDs
8. Conclusion
The dry electrode process, enabled by multi‑roll continuous calendering, represents a paradigm shift in battery manufacturing — eliminating solvents, reducing energy, and unlocking solid‑state battery potential.
However, the mechanical heart of this process is the hydraulic system. From massive cylinders that apply tons of roll force, to high‑response pumps that deliver steady flow, to intelligent control systems that maintain micron‑level gaps — hydraulics make dry calendering industrially viable.
For equipment builders and battery cell manufacturers seeking reliable, precision hydraulics, Riverlake offers a complete portfolio of hydraulic cylinders, hydraulic pumps, and hydraulic control systems purpose‑built for continuous calendering and other high‑force rolling applications.
As the battery industry scales dry electrode production into terawatt‑hour volumes, the demand for robust, accurate, and efficient hydraulics will only grow. Choosing the right hydraulic partner is not a detail — it is a strategic decision.
