Bao bì giấy Industry Bearings: Codes & Applications

Bearings for the paper packaging industry are industrial rolling elements — ball bearings with C3 clearance and spherical roller bearings for heated rolls — that carry combined loads of high heat, moisture, and paper dust, installed in corrugating machines, flexo printers, die-cutters, and folder-gluers across the corrugated board and premium paper packaging production chain.

Vietnam's paper packaging industry operates thousands of production lines in Binh Duong, Dong Nai, and Long An. Premature bearing failure is the most common cause of unplanned downtime — a single shutdown on a double facer corrugator takes 4 to 8 hours, equivalent to 80–200 million VND in lost output. Selecting the correct bearing code, internal clearance, and lubrication schedule for each position is the most direct preventive measure available.

Definitions and technical requirements specific to paper packaging

Paper packaging covers two main product groups: corrugated board (corrugated cardboard) and folding carton (flat paperboard). Each has its own production equipment, but both create three common challenges for bearings:

High operating temperatures. The heated rollers on corrugating machines reach 180–200°C at the surface. Heat conducted to the bearing mounting position typically stabilizes at 70–100°C. Standard C0 clearance bearings are squeezed tight by thermal expansion, generating secondary heat buildup and surface spalling. C3 clearance is mandatory for all positions with direct thermal exposure.

Moisture and steam. The steam shower that conditions the liner paper creates a continuous steam environment. Standard mineral-base grease becomes diluted and washes out quickly. Polyurea or lithium complex grease with high protection ratings (EP2, NLGI 2) achieves 2–3 times the service life of standard grease in this environment, per SKF Rolling Bearings Catalogue 2018.

Paper dust and starch adhesive particles. Cellulose dust from cutting operations and starch from glue applicator rolls creates abrasive particles sized 10–50 µm — small enough to pass through standard seals. FAG/Schaeffler Industrial Guide 2023 recommends enhanced seals (2RS or RS1) combined with supplemental labyrinth seals at positions near the gluing mechanism.

Corrugating machine bearings: heated rollers and high-speed shafts

The corrugator is the heart of the corrugated board production line. A typical 2.5 m wide corrugator has 4 to 6 pairs of corrugating rolls, each internally steam-heated at 6–8 bar pressure. Surface roll speed reaches 150–300 m/min on modern production machines.

Corrugating rolls

Corrugating rolls are the most demanding position on the machine. Requirements: heavy radial load from corrugating flute mesh pressure (15–40 kN depending on width), roll surface temperature 160–180°C, and speed n = 400–800 rpm. Spherical roller bearings (SRB) are the global standard choice for this position.

22220 EK/C3 (d=100, D=180, B=46 mm, C=365 kN, C₀=490 kN): Suitable for corrugating rolls in machines 1.4–1.8 m wide. Self-aligning angle of ±1.5° compensates for frame deflection caused by non-uniform thermal expansion. Grease speed limit: 2,200 rpm. Mount with HM220T lock washer plus KM20 locknut. Regreasing quantity: G = 0.005 × 180 × 46 = 41.4 grams, every 600 hours.

22322 E1/C3 (d=110, D=240, B=80 mm, C=620 kN, C₀=850 kN): For corrugators 2.2–2.5 m wide with higher pressure loads. Grease speed limit: 1,800 rpm. Requires SNL 522 housing with additional external V-ring seal due to the high-moisture environment.

Preheating drums

Preheating drums rotate more slowly (50–150 rpm) but reach 200°C at the surface, and carry significant axial load from paper web tension of 1–3 kN. Paired tapered roller bearings (TRB) handle this combined loading well.

32220 (d=100, D=180, B=49 mm, C=290 kN, C₀=340 kN): Mount back-to-back (DB) to cancel bidirectional axial load. Clearance adjusted with 0.1–0.3 mm shims. Li-complex EP2 grease, replaced every 800 hours.

Pull rolls and tension rolls

Pull rolls and tension rolls carry lighter loads (500 N to 3 kN) but run at high speed (600–1,200 rpm) and must run extremely smoothly. 6308 C3 (d=40, D=90, B=23 mm, C=32.5 kN) is the most common code for 40 mm shaft diameter. 6310 C3 (d=50, D=110, B=27 mm, C=48 kN) for 50 mm shafts. Both use 2RS seals to exclude paper dust.

Flexo printing machine bearings: precision rollers

Flexographic printing machines print directly onto corrugated board or flat carton sheet. Bearing requirements are fundamentally different from corrugators — lower load, but radial runout must stay below 3 µm to maintain print quality, and speeds can reach 300–500 m/min on high-speed machines.

Printing cylinders

Print cylinders carry contact pressure of 0.5–2 kN at 300–600 rpm. Bearing requirement: P5 (ABEC 5) or P6 (ABEC 6) accuracy, runout ≤ 3–5 µm. Small-bore DGBB with tight tolerances are the standard.

6205-2RS P5 (d=25, D=52, B=15 mm, C=14.8 kN): For print cylinders with 25 mm shaft. Factory-filled silicone or polyurea NLGI 2 grease, sealed for life. Replace at scheduled 4,000-hour intervals rather than waiting for failure — this prevents print vibration marks from emerging.

6305-2RS P5 (d=25, D=62, B=17 mm, C=17.8 kN): For higher-load print cylinders needing greater C value on the same 25 mm shaft.

Anilox rolls

The anilox roll is a laser-engraved ink metering roll — it may weigh 50–200 kg and rotates at 200–400 rpm. Requirements: radial load 2–8 kN, resistance to ink solvents and UV wash, low runout. Spherical roller bearings of medium size handle the load better than DGBB at this position.

22208 EK (d=40, D=80, B=23 mm, C=106 kN): Self-aligning ±1°, high C rating within a compact envelope. Nitrile seal resists ink solvents. Replace grease every 1,200 hours or after each deep machine wash.

Support and conveyor rolls

The sheet conveyor from the printer to the die-cutter has 10–20 small support rolls with 20–30 mm shaft diameter under very light loads (< 500 N). 6204-2Z (d=20, D=47, B=14 mm, C=12.7 kN) is the common choice — metal shield (2Z) resists dust better than rubber seals at 1,000–2,000 rpm on these low-load rolls.

Die-cutting machine bearings: cam mechanisms and impact loads

Die-cutting machines stamp and cut corrugated board sheets to box shape. Load profile: intermittent, with heavy impact at each cutting cycle. Cutting frequency ranges from 30 to 100 cycles per minute, and each cycle generates 20–80 kN impact force depending on box dimensions.

Eccentric cam mechanism

The eccentric cam converts rotary motion into the reciprocating motion of the cutting head. Bearings here carry cyclic impact loading — they require high dynamic load capacity and must resist fretting between contact surfaces.

22216 EK/C3 (d=80, D=140, B=33 mm, C=240 kN, C₀=305 kN): Self-aligning compensates for frame deflection; C3 is mandatory because impact loading generates secondary heat buildup. Mount on a 1:12 tapered shaft with KM16 locknut and MB16 lock washer. Verify mounting torque with a calibrated torque wrench — 180 Nm.

32216 (d=80, D=140, B=33 mm, C=260 kN): Tapered roller bearing alternative when significant axial load exists from cam shaft misalignment. Mount in X-arrangement (DX), axial clearance adjusted to 0.05–0.15 mm.

Platen guide shafts

The cutting head slides on four guide shafts. Each shaft carries eccentric load of 5–15 kN and requires high perpendicularity. Linear bearings LM40UU are common here — if converting to roller design, 6208 C3 (d=40, D=80, B=18 mm, C=22.5 kN) suits 40 mm shafts.

Sheet feeder rolls

The sheet-feeding mechanism uses rubber rolls and support shafts. Load is light (< 1 kN) but sheet-feeding accuracy is critical — misalignment over 1 mm ruins the cut position. 6205-2RS (d=25, D=52, B=15 mm, C=14.8 kN) is the most common code for 25 mm shafts at this position.

Folder-gluer bearings: conveyors and folding arms

The folder-gluer folds and glues boxes from flat die-cut blanks. The machine is 6–12 m long and runs at 100 to 600 boxes per minute. Bearings are distributed across dozens of positions: the main conveyor, folding arms, glue pressure rolls, and bundling mechanisms.

Main conveyor

The main conveyor transports boxes along the full machine length. The drive roll carries load from belt tension (200–800 N) and box friction. Typical shaft diameter is 30–50 mm.

6206-2RS (d=30, D=62, B=16 mm, C=19.5 kN): For 30 mm shafts. The 2RS seal blocks paper dust and glue vapor. Sealed for life — replace every 3,000–5,000 hours. Many modern gluers use UCF206 flanged bearing units for fast swap-out without realignment.

6208-2RS (d=40, D=80, B=18 mm, C=22.5 kN): For 40 mm shafts on higher-load drive rolls.

Folding arms and bars

The folding mechanism applies 50–200 N folding force to box edges at high speed. Small bearings (outer diameter 25–40 mm) mount on folding pins. Requirements: quiet running, absolutely sealed to prevent glue contamination of printed surfaces.

6000-2RS (d=10, D=26, B=8 mm, C=4.6 kN): For small folding pins with 10 mm diameter. Speed to 2,000 rpm. Replace in groups of 5–10 every 6 months (low cost, preventive approach).

6002-2RS (d=15, D=32, B=9 mm, C=5.6 kN): For 15 mm folding pins, commonly used on Bobst and Heidelberg folder-gluers.

Glue pressure rolls

Glue pressure rolls contact hot-melt adhesive at 120–150°C. This is the combined heat-and-adhesive-contamination position — standard rubber seals harden and crack after 500–800 hours.

6203-C-2HRS (d=17, D=40, B=12 mm): PTFE seal, rated to 160°C, resistant to hot-melt adhesive. Replace every 2,000 hours or when glue penetration into the bearing raceways is detected.

Brand comparison: ZVL and SKF for corrugated packaging

The two most common brands in Vietnamese paper packaging production lines are ZVL (Slovakia) and SKF (Sweden). FAG/Schaeffler and NSK are also present, primarily in imported printing machines supplied as matched sets.

ZVL Slovakia

ZVL manufactures at its Považská Bystrica plant in Slovakia to ISO and EN standards. The product range includes a full suite of SRB (22xxx series), DGBB (62xx, 63xx), and TRB (302xx, 322xx) bearings with C3 clearance.

Strengths for the paper packaging industry:

• SRB 22220 EK/C3 and 22322 E1/C3 for corrugator rolls — consistent quality, dimensional tolerances meeting ISO grade 6 (equivalent to SKF Explorer line)
• Stable supply through Vietnamese distribution channels — stock available in both Hanoi and Ho Chi Minh City
• Competitive European pricing versus SKF Explorer or NSK HPS, fitting strategies to reduce maintenance cost without lowering technical standards

SKF

SKF Explorer line is the performance reference for corrugators. SKF EXPLORER 22220 EK/C3 is specified as OEM by many corrugator machine builders (Fosber, BHS, Isowa).

Strengths: comprehensive technical documentation, online life calculation tool, technical after-sales service. Best when plants need ISO 281 life calculations verified for new capital investments.

Practical reality: many packaging plants in Binh Duong use ZVL for pull rolls and preheating drum bearings (replaced frequently) while retaining SKF for the primary corrugating roll shafts (replaced infrequently, but failure is very costly). This tiered approach optimizes cost without compromising reliability at the critical positions.

Real-world case study: corrugating roll shaft failure

At a corrugated board plant in Binh Duong province, a 2.2 m wide corrugator stopped suddenly in the middle of a production shift during its eighth month after a batch bearing replacement. Unusual noise from the left bearing housing of the B-flute corrugating roll appeared about 20 minutes before the stoppage, but the operator did not report it immediately.

Determined root cause: The replacement bearing for 22322 had been ordered as 22322 E — omitting the /C3 suffix. Standard C0 clearance at 85°C operating temperature became negative after three weeks of operation. The roll surface showed flaking concentrated in the load zone — characteristic of overload from excessive tightness.

Damage assessment: 6 hours of downtime, bearing and shaft alignment inspection. Estimated production loss: 120 million VND.

Corrective and preventive actions:

1. Established an approved parts list (APL) — entering C3 explicitly in the part number, prohibiting purchasing without the C3 suffix for thermally exposed positions
2. Trained operators to recognize unusual noise — immediate reporting protocol, not waiting until end of shift
3. Installed temperature sensors on housings at both main corrugating roll positions, alerting above 95°C
4. Implemented vibration monitoring per ISO 10816-3:2009 — measured baseline immediately after installation and tracked trend, not just absolute thresholds, to detect degradation 4–8 weeks before failure

After 12 months of applying these measures, the plant recorded zero unplanned bearing-related shutdowns. Maintenance cost fell 18% from timely scheduled replacement rather than emergency repairs.