Gốm sứ industry bearings are a specialized group of rolling bearings — including spherical roller bearings and high-temperature cylindrical roller bearings — engineered to withstand high temperatures, abrasive dust, and severe impact loads across the production chain for ceramic tiles, sanitary ware, and technical ceramics.
The ceramics industry imposes three simultaneous technical challenges: kiln temperatures reaching 1,200 °C, continuous silicon-based abrasive dust that causes wear, and impact loads from hydraulic pressing systems. According to SKF Application Guide — Ceramics Industry, more than 60% of unscheduled kiln shutdowns originate from incorrectly selected bearings due to improper clearance or thermally incompatible greases. This article analyzes each critical bearing location, optimal bearing codes, and practical maintenance protocols — grounded in ISO 281:2007, ISO 15243:2017, and engineering catalogs from FAG/Schaeffler.
What are gốm sứ industry bearings?
Ceramic production lines comprise five main equipment clusters: roller kilns, ball mills, hydraulic presses, drying conveyor systems, and glazing lines. Each cluster generates distinct bearing requirements in terms of bearing type, internal clearance, and lubrication strategy.
Bearing selection for ceramics is classified by four critical factors:
| Factor | Typical Range | Bearing Requirement |
|---|---|---|
| Operating Temperature | 80–250 °C (up to 300 °C near kiln zones) | Clearance C4/C5, silicone or PFPE grease |
| Load Type | Heavy + impact loads (mills, presses) | SRB or TRB single/double arrangement |
| Dust & Abrasive Particles | Silicon, alumina, ceramic glaze | Labyrinth seals, IP6X rating |
| Speed Range | 10–1,500 rpm (low to medium) | Roller bearings more efficient than deep-groove balls |
Bearing nomenclature follows ISO 15:1998: bore diameter d, outer diameter D, width B, internal clearance (C2/C3/C4/C5), and cage/seal suffix. Engineers must decode the full suffix string — for example, 22320 E1 C4 M specifies not merely "22320 spherical roller bearing" but also C4 clearance and bronze cage for elevated-temperature operation.
Roller kiln bearings — thermally rated C4/C5
Roller kilns operate continuously 24/7 with firing zones reaching 1,100–1,200 °C. Bearings supporting the kiln rollers are located outside the direct heat zone but radiant and conducted heat through the shaft raises bearing temperature to 150–250 °C under normal conditions — and up to 300 °C when cooling systems degrade.
At 200 °C, a standard C3 deep-groove bearing loses 60% of its designed clearance due to asymmetric thermal expansion between inner ring, outer ring, and shaft. Result: uneven load distribution, accelerated surface fatigue, and bearing life reduction of 40–70% relative to initial ISO 281:2007 calculations.
Standard bearing selection for roller kiln shafts:
| Location | Bearing Code | d × D × B (mm) | C (kN) | Clearance | Notes |
|---|---|---|---|---|---|
| Kiln roller Ø60 | 22312 E1 C4 | 60 × 130 × 46 | 285 | C4 | Operating temp 150–250 °C |
| Kiln roller Ø80 | 22316 E1 C4 | 80 × 170 × 58 | 510 | C4 | Higher load zones |
| Kiln roller Ø100 | 22320 E1 C4 | 100 × 215 × 73 | 760 | C4 | Main firing zone |
| High-temperature zone | 22316 E1 C5 | 80 × 170 × 58 | 510 | C5 | Measured bearing temp > 250 °C |
Why C4 instead of C3? Clearance C4 (radial clearance 35–52 µm for size 22316) compensates for thermal expansion when the inner ring heats faster than the outer ring. Using C3 (25–38 µm) at 200 °C is equivalent to running with negative clearance — the bearing preloads internally and seizes prematurely.
Lubricating grease must handle minimum operating temperature of 220 °C: SKF LGFP 2 (PFPE base, rated to 260 °C), FAG Arcanol TEMP110 (continuous 200 °C), or silicone NLGI 2 grease rated to 250 °C. Relubrication interval: 500–800 hours, with grease quantity G = 0.005 × D × B. For 22316: G = 0.005 × 170 × 58 = 49 grams per cycle.
Ball mill bearings — heavy-load SRB
Ball mills grind raw materials (clay, kaolin, feldspar) to particle sizes of 20–40 µm. The main shaft carries enormous radial loads from the rotating mill drum (5–50 tons) and impact loads from grinding media. Operating speeds are low, 15–40 rpm, making static load rating C₀ — not dynamic rating C — the determining specification.
Spherical roller bearings (SRB) are the only practical choice: self-aligning capability (±2°) compensates for shaft deflection from the heavy drum, and radial load capacity is 3–5 times that of a deep-groove bearing of equivalent size.
Typical ball mill bearing specifications deployed in Vietnam:
| Mill Capacity | Main Shaft Bearing Code | d × D × B (mm) | C (kN) | C₀ (kN) |
|---|---|---|---|---|
| 5–10 tons/batch | 23132 CC/C3 W33 | 160 × 270 × 86 | 1,180 | 1,700 |
| 10–20 tons/batch | 23140 CC/C3 W33 | 200 × 340 × 112 | 1,870 | 2,800 |
| 20–40 tons/batch | 23156 CC/C3 W33 | 280 × 460 × 146 | 3,350 | 5,600 |
Suffix W33 denotes oil grooves and supply holes in the outer ring — mandatory for circulating oil systems on large mills. ISO VG 220 or VG 320 mineral oil, filtered to 10 µm absolute, replaced every 4,000 operating hours.
Common error: substituting a deep-groove ball bearing 6220 C3 (C = 112 kN) for a spherical roller bearing 23120 C3 (C = 390 kN, C₀ = 585 kN) because "sizes appear equivalent." The load rating differential is 3.5×: the ball bearing fails in 2,000–3,000 hours instead of 15,000–20,000 hours.
Clearance C3 is standard for ball mills. Operating temperature typically 40–80 °C; shaft-to-bore fit H7/k6 reduces clearance by 15–25 µm — C3 compensates precisely for this interference. ZVL 23132 CC/C3 W33 delivers dynamic load rating C = 1,180 kN and static C₀ = 1,700 kN, adequate for a 10-ton mill with significantly competitive pricing versus SKF/FAG.
Hydraulic press bearings — combined thrust + radial
Hydraulic presses form ceramic blanks under biaxial loading: axial force (pressing force) up to 2,000–8,000 kN when the die closes, plus radial loads from the ram weight and coupling geometry. Single deep-groove bearings lack sufficient axial capacity — the solution is a matched pair: spherical roller bearing (SRB) for radial loads plus thrust spherical roller bearing (TSRB) for axial loads.
Standard main-shaft arrangement for a 3,000 kN ceramic press:
- Fixed end (axial constraint): 29420 E (TSRB, d=100, D=210, B=67 mm, C_axial = 1,400 kN, C₀_axial = 4,900 kN) — carries pressing force
- Free end (axial float): 22220 EK/C3 (SRB, d=100, D=180, B=46, C=365 kN) — carries radial load, accommodates thermal growth
| Specification | 29420 E | 22220 EK/C3 |
|---|---|---|
| d × D × B (mm) | 100 × 210 × 67 | 100 × 180 × 46 |
| Radial dynamic rating C | 560 kN | 365 kN |
| Axial dynamic rating C_a | 1,400 kN | — |
| Static rating C₀ | 4,900 kN | 600 kN |
| Clearance | Standard | C3 |
Installing TSRB 29420 E requires initial axial preload of at least 1% C₀ = 49 kN to prevent roller skidding during light-load operation. Without preload, rollers accelerate suddenly when load is applied — surface slip (skidding) generates friction, leading to rapid wear within 500–1,000 hours.
Press lubrication typically uses EP lithium-complex NLGI 2 grease. For 29420 E: G = 0.005 × 210 × 67 = 70 grams. Relubrication interval 1,500–2,000 hours or monitored by vibration — using SKF TKSA 41 or equivalent to measure acceleration-based vibration per ISO 10816-3:2009.
Drying conveyor bearings — sealed, high-temperature idlers
Drying conveyors transport unfired ceramic pieces through a thermal chamber at 80–180 °C before kiln entry. Idler roller bearings operate in a combined environment: elevated temperature, silicon dust, and moisture vapor from damp clay in the initial stage. This location has the highest failure rate in the ceramic line due to difficult regreasing access and irregular maintenance cycles.
Idler roller bearing requirements for drying conveyors:
- Double-contact seals or labyrinth-type non-contact seals — blocking silicon dust ingress
- Grease rated for minimum 180 °C with water-resistance properties
- C3 or CM (modified clearance) clearance to accommodate daily thermal cycling
Common drying conveyor idler bearing codes:
| Roller Shaft | Bearing Code | d × D × B (mm) | C (kN) | Seal Type | Max Temp |
|---|---|---|---|---|---|
| Ø30 mm | 6206-2RS C3 | 30 × 62 × 16 | 19.5 | 2RS (sealed) | 120 °C |
| Ø40 mm | 6208-2RS C3 | 40 × 80 × 18 | 29 | 2RS (sealed) | 120 °C |
| Ø50 mm | 6210-2RS C3 | 50 × 90 × 20 | 35.1 | 2RS (sealed) | 120 °C |
| Ø50 mm, high-temp | 1210 ETN9 C3 | 50 × 90 × 20 | 21.6 | Open + labyrinth | 180 °C |
Pre-sealed bearings (2RS) suit drying conveyors at modest temperatures (≤ 120 °C) because factory-packed grease delivers service life of 8,000–12,000 hours. However, when temperature exceeds 120 °C, polyurea or silicone grease replaces standard lithium grease — and open bearings with labyrinth seals allow replenishment when required.
Recommended grease: SKF LGFP 2 (PFPE base, rated 260 °C) or FAG Arcanol TEMP110 (rated 200 °C). Avoid standard lithium NLGI 2 above 120 °C — grease thins, exudes from the bearing, and causes complete dry-running within 200–500 hours.
Practical maintenance schedule: inspect 6208-2RS C3 on an 80–100 °C conveyor every 8 hours of operation using an infrared thermometer gun. Outer ring temperatures exceeding 90 °C (ΔT > 20 °C above ambient) signal need for relubrication or load verification.
ZVL versus SKF for ceramics
Vietnam's ceramic industry primarily sources bearings from two channels: SKF/FAG for integrated imported equipment (Sacmi kilns, Siti B&T systems from Italy), and ZVL or other Tier 1 manufacturers for domestic equipment and field replacements.
Brand comparison for ceramic applications:
| Brand | Example Code | Ceramic Application | Strengths | Considerations |
|---|---|---|---|---|
| SKF | 22316 E/C4 | Kilns, mills | Extensive catalog, full suffix range | Highest pricing |
| FAG (Schaeffler) | 22316-E1-C4 | Kilns, OEM Italy installations | OEM compatibility (Sacmi/Siti) | Premium pricing |
| ZVL | 22316 C4 | Kilns, mills | ISO 9001 EU manufacturing, competitive pricing | Narrower suffix availability |
| NTN | 22316 EAD1/C4 | Kiln applications | Optimized contact geometry | Limited local inventory |
| Timken | 22316YMW33C4 | Large mills | High-strength rollers | Focused on large-capacity markets |
ZVL manufactures in Slovakia under ISO 9001 and DIN standards — bearing steel sourced from EU mills, tolerances equivalent to SKF. ZVL 22316 C4 delivers dynamic load rating C = 510 kN and static C₀ = 735 kN — identical to SKF 22316 E/C4. Differentiation lies not in material quality but in suffix range breadth: SKF offers VA405 and VA406 suffixes for ultra-high temperature (>250 °C) applications where ZVL equivalents are not yet cataloged.
Practical recommendations:
- Kiln zones 150–250 °C, standard shafts: ZVL or SKF both qualify — verify C4/C5 suffix only
- Italian turnkey equipment (Sacmi, Siti B&T): prioritize FAG or SKF to ensure OEM warranty alignment during commissioning
- Field replacement mills and conveyors: ZVL 22xxx C3/C4 fits well with meaningful operational budget savings versus SKF/FAG
Real-world scenario
At a ceramic tile plant in Binh Duong province, maintenance technicians recorded three unscheduled kiln stoppages in six months — each time the kiln roller shaft seized, requiring 8–12 hours of downtime for bearing replacement and realignment.
Investigation revealed the plant was operating 22316 C3 bearings throughout the kiln roller assembly — including the primary firing zone where temperatures sustained 220–240 °C. Clearance C3 (25–38 µm) was exhausted completely at 200 °C, causing the bearing to run with negative preload and seize after 2,000–3,000 operating hours.
Implemented solution:
- Replace all 22316 C3 with 22316 C4 (clearance 35–52 µm) in zones exceeding 150 °C
- Upgrade grease from LGMT 2 (rated 120 °C) to LGFP 2 (rated 260 °C) near kiln zones
- Install bearing outer-ring temperature sensors at eight critical locations — alert threshold ΔT > 25 °C above ambient
- Increase vibration inspection frequency from quarterly to monthly per ISO 10816-3:2009
Results after 12 months: zero unscheduled kiln shutdowns. Bearing service life increased from 2,500 hours to 11,000 hours — estimated savings of 180 million VND/year from eliminated replacement costs and downtime. Initial upgrade investment (C4 bearings, PFPE grease, temperature sensors) recovered within 3 months of operation.
The critical variable was not bearing brand but correct clearance suffix for actual operating temperature. Both SKF and ZVL 22316 C4 performed identically in this scenario.