Bearing Types for Lithium Battery Electrode Roll Presses
Bearings for lithium battery electrode roll press are mounted on the roll necks at both ends of the calendering rolls, and carry the very high radial load generated when the coated electrode is compressed between the rolls. Depending on the machine design, the roll neck is supported by a four-row cylindrical roller bearing, a double-row cylindrical roller bearing, a spherical roller bearing or a heavy-duty tapered roller bearing. As a four-row cylindrical roller bearing can carry radial load only, it is normally combined with a thrust bearing, such as a pair of angular contact ball bearings or a thrust tapered roller bearing, which takes the axial load and locates the roll in the axial direction. Bearings for this application have high stiffness and high running accuracy, so that the runout, roundness and parallelism of the roll are held within very close limits and the compaction density and coating thickness of the electrode remain uniform across the full width of the foil. Where spherical roller bearings are selected, they are self-aligning and can automatically adjust the misalignment caused by the deflection of the roll under high pressing force, with an allowable alignment angle of about 1°~2.5° depending on the series. These bearings can bear a large radial load, and in a thrust arrangement also the axial load and combined load; they have good anti-vibration and impact resistance as well as heat and dust resistance, and sealed versions with pre-filled grease further keep electrode powder out and reduce maintenance.
They are widely used in lithium battery electrode roll press (calendering) machines, roll press and slitting combination machines, and also in coating machines, slitting machines, winding machines and dry electrode film forming equipment of the lithium battery production line, as well as in other high-load, high-precision strip processing machinery.
Installation method: The bore of the roll neck bearing has two versions, cylindrical and tapered, and the tapered bore is 1:12 and 1:30. The tapered bore bearing is pressed onto the tapered roll neck by a hydraulic nut, and the required interference is controlled by the position of the abutment ring; it is dismounted by the high-pressure oil injection method through an oil passage drilled from the shaft centre to the fitting surface. The cylindrical bore inner ring is usually mounted with an interference fit by heating it in an oil bath to about 100 °C (in no case above 120 °C) or by an induction heater, and it can also be mounted on a tapered shaft with an adapter sleeve. After mounting, the roll body and the inner ring raceway can be ground together so that the runout of the roll is kept to a minimum. When the bearing is reassembled after cleaning, the outer ring should be turned by 90° to change the load zone and extend the service life.
Bearing Types for Lithium Battery Electrode Roll Presses
Features：Spherical roller bearings for lithium battery electrode roll press are mounted on the necks of the calendering rolls, where the coated electrode is compressed between the rolls under high pressing force. The bearing consists of an outer ring with a common spherical raceway and two rows of barrel-shaped rollers running on the double raceway inner ring, and it is supplied with a cylindrical bore or with a tapered bore so that it can be pressed onto the roll neck quickly with a sleeve.
Advantages：Because the outer raceway is spherical, the bearing is self-aligning: it automatically compensates the deflection of the roll under the high pressing force and any misalignment of the bearing seat, so the roll stays correctly aligned without any increase in friction or temperature rise. It can carry the heavy radial load of the roll pressing together with bidirectional axial load and combined load, and its large radial load capacity, anti-vibration and impact resistance suit the continuous heavily loaded running of the roll press. Sealed and grease-filled versions keep the electrode powder out of the bearing.
Spherical Roller Bearing
Features：Deep groove ball bearings are used in the auxiliary positions of the lithium battery electrode roll press — the guide rolls, tension rolls, edge-trimming units and foil path rollers that carry and align the coated electrode before and after calendering. Each bearing consists of an inner ring, an outer ring, a cage and one row of balls running in deep uninterrupted raceway grooves, and it can be supplied open, or shielded or sealed with a lifetime grease fill.
Advantages：They run with very low friction, low noise and low vibration, so the electrode foil passes through the roll press at a steady tension without marking, wrinkling or thickness fluctuation. They accommodate radial load and axial load in both directions, run at high speed, and require less maintenance than other bearing types. Because they are compact, light and economical, and easy to replace, they are a practical choice for the many small guide and tension rolls of the machine. Shielded and sealed versions are filled with grease for life and protect the rolling contact from electrode powder.
Deep Groove Ball Bearing
Features：Cylindrical roller bearings for the lithium battery electrode roll press support the calendering roll in the main loaded positions. The cylindrical rollers run in line contact with the raceways, and the inner ring and the outer ring assembly are separable, so the bearing can be fitted separately onto the roll neck and into the bearing housing.
Advantages：Line contact gives this bearing type the highest radial load capacity and the highest radial stiffness of the four, so the roll deflects the least under the pressing force and the electrode coating is compacted to a uniform thickness across the full width of the foil. Friction and heat generation stay low, which suits continuous running of the roll press. Because the ring assemblies are separable, the bearing is quick to mount, inspect and replace on the roll neck and the roll can be assembled without driving a complete bearing over a long seat. As the bearing allows axial displacement inside itself, it also serves as the floating end of the roll arrangement.
Cylindrical Roller Bearing
Features：Tapered roller bearings for the lithium battery electrode roll press consist of a cup and a cone assembly, with tapered rollers running between tapered raceways whose apexes meet at a common point on the roll axis. They are normally mounted in pairs on the roll necks, and the axial clearance or the preload is set when the roll is assembled.
Advantages：The tapered construction carries radial and axial load at the same time, so one bearing arrangement supports both the heavy radial load of the roll pressing and the axial load that locates the roll, giving a compact and rigid support for the roll neck. The clearance or the preload can be adjusted, which keeps the roll position stable and reduces axial movement under reversing or varying load, so the electrode thickness stays consistent. The cup and the cone are separate parts, which makes mounting on the roll neck straightforward, and with correct adjustment and lubrication the bearing gives a long service life in continuous heavy-duty running.
Tapered Roller Bearing
How to Select Bearings for a Lithium Battery Electrode Roll Press
On a roll press the bearing has to do three jobs at the same time: carry the very high radial load produced by the roll pressing, hold the roll accurately enough for the electrode thickness to stay uniform across the whole width of the foil, and survive continuous running in an environment full of electrode powder. Work through the steps below in order.
• Step 1 — Locate the position. The main calendering and backup roll necks carry the full pressing force and need the highest radial load capacity and stiffness. Guide, tension, edge-trimming, unwind and rewind rolls carry the web tension only, and there the priorities are speed, low friction and low cost.
• Step 2 — Decide the load direction. Pure radial load points to a cylindrical roller bearing or a deep groove ball bearing. Combined radial and axial load points to a tapered roller bearing or a spherical roller bearing. If one bearing position has to take axial load in both directions, choose a double row tapered roller bearing or a spherical roller bearing.
• Step 3 — Check the stiffness and the accuracy the roll needs. The uniformity of the electrode thickness depends on how little the roll deflects and how accurately it runs. Cylindrical roller bearings give the highest radial stiffness; tapered roller bearings give high stiffness when they are correctly preloaded; spherical roller bearings are self-aligning and therefore softer in the radial direction.
• Step 4 — Check the speed and the lubrication method. Higher speed points to a deep groove ball bearing or a cylindrical roller bearing, with oil or oil-air lubrication at the fastest positions and grease at lower speeds and in sealed bearings.
• Step 5 — Match the environment. Electrode powder, regular cleaning and temperature rise call for shielded or sealed bearings, for a suitable clearance group (C3 where the bearing runs hotter than its surroundings) and for a grease that resists contamination.
• Step 6 — Choose the mounting method. A cylindrical bore with an interference fit suits simple seats. A tapered bore of 1:12 or 1:30 with an adapter sleeve, a withdrawal sleeve or a hydraulic nut suits positions where the bearing has to be mounted and dismounted quickly and the interference has to be set precisely.
• Step 7 — Fix the service interval. Sealed, grease-for-life bearings suit positions that are difficult to reach. Regreasable or oil-lubricated bearings suit the heavily loaded, high-temperature roll necks.
Spherical Roller Bearing
Four-row cylindrical roller bearings
Deep Groove Ball Bearing
Mounting and Maintenance
Mounting
Clean the roll neck and the bearing housing bore, and check the dimensions, the roundness and the corner radii before mounting starts. A bearing with a cylindrical bore is mounted with an interference fit: press it on with a suitable mounting sleeve, or heat it in an oil bath or with an induction heater to about 80 °C to 100 °C — never above 120 °C — and keep the bearing and the seat free of dust during fitting. A bearing with a tapered bore (suffix K, 1:12; suffix K30, 1:30) is mounted directly on a tapered roll neck, or on a cylindrical or stepped roll neck with an adapter sleeve (suffix H) or a withdrawal sleeve (suffix AH). It is driven up with a lock nut or a hydraulic nut, and the drive-up is controlled by the reduction of the internal clearance, measured with a feeler gauge. Never strike a ring or a roller directly, and never press through the rolling contact.
Clearance and Preload
Set the operating clearance for the actual working temperature. Tapered roller bearings, and any arrangement of opposed bearings, are adjusted against a second bearing: the clearance or the preload is set with shims, with a lock nut on the shaft, or with the housing end cover, and a small preload makes the roll arrangement rigid and reduces axial movement when the load varies. Too little clearance makes the bearing run hot and shortens its life; too much clearance allows vibration and a variation in electrode thickness. Always use the value given by the machine maker.
Lubrication
Grease is the normal choice for shielded and sealed bearings and for lower speeds, and sealed bearings run for life without relubrication. Oil, and for the highest speeds oil-air lubrication, is used on the heavily loaded roll necks, where the oil also carries heat away from the bearing. Relubrication intervals depend on speed, temperature and contamination, and they are shorter where electrode powder is present. Never mix different greases, and never overfill a bearing.Inspection and Maintenance
Check bearing temperature, noise and vibration at regular intervals; an unexplained rise in temperature or a change in the running noise is the earliest sign of a problem. Examine the grease for hardening, water or powder contamination and renew it at the stated interval. Keep the bearing seats and the surrounding machine clean, and keep the housing seals and the drain holes clear. When a bearing is cleaned and reassembled, turn the outer ring by 90° so that the load zone moves to an unworn part of the raceway. Replace the bearing when spalling, scoring, heat discoloration or a measurable increase in clearance is found.
Dismounting
Tapered bore bearings are dismounted by the high-pressure oil injection method: oil is forced through a passage drilled from the shaft centre to the fitting surface, which releases the interference so that the bearing comes off without damage. Cylindrical bore inner rings mounted with an interference fit are removed with a puller or by heating. Never lever a bearing off by its cage or its seals.
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