Bao bì nhựa Industry Bearings: Codes & Applications

Bearings for the plastic packaging industry are a group of rolling-element components — chiefly ball bearings for high-speed shafts and cylindrical roller bearings for heavier loads — selected to operate in blown-film machines, printing presses, slitting lines, and laminating machines — where the combination of high speed, varying temperatures, and frequent cleaning creates challenges that standard industrial bearings cannot reliably address.

Vietnam's plastic packaging industry produces over 3.9 million tonnes of product per year, with plants concentrated in Binh Duong, Long An, and Hanoi Vietnam Plastics Association, Industry Report 2023. Equipment runs 20–22 hours per day on continuous production schedules, making bearing service life a direct determinant of unplanned downtime costs. A single unscheduled stop on a blown-film line can waste 8–15 million VND in raw material and overtime labor alone.

Characteristics of plastic packaging bearings

Plastic packaging covers three main segments: rigid packaging (PET bottles, PP containers), flexible packaging (PE film, OPP film), and composite packaging (multi-layer laminated film). Each segment uses different equipment with distinct bearing requirements.

The common thread is hygiene pressure. Machines handling food or pharmaceutical packaging materials must be cleaned with strong chemical detergents at each production shift. Bearings must withstand high-pressure water, cleaning chemicals, and retain their grease film after each wash cycle.

Core technical requirements:

Standard C0/CN clearance bearings are typically inadequate for heated extrusion shafts. C3 or C4 clearance — 12–28 µm larger than standard depending on shaft size — compensates for thermal expansion when the steel shaft rises from ambient to 80–100°C during operation.

Blown-film and blow-molding machines: extrusion shafts and clamp units

Blown-film PE machines and PET blow-molding machines are the foundation of flexible and rigid packaging production. Extrusion screws carry axial load from molten plastic back-pressure — up to 200–400 bar depending on screw diameter — while rotating continuously at 30–150 rpm.

Extrusion thrust position: Paired tapered roller bearings or thrust bearings handle pure axial load. Common codes:

• 32216 (d=80, D=140, B=26 mm, C=118 kN, C₀=140 kN) — 80 mm extrusion shaft, mid-size blown-film machine
• 32220 (d=100, D=180, B=49 mm, C=290 kN, C₀=400 kN) — 100 mm extrusion shaft, large blown-film machine
• 51316 (d=80, D=140, B=44 mm, thrust only, C₀=450 kN) — single-direction thrust position

Gearbox and reducer positions: Combined radial plus axial load. Two 32220 TRBs in face-to-face arrangement absorb forces from both directions.

Blow-molding clamp unit: The guide shafts handle impact loading when the mold opens and closes 1,200–2,400 times per hour. Bearing 6309 C3 (d=45, D=100, B=25 mm, C=52.7 kN) with 2RS seal prevents grease contaminating the mold zone.

The most common failure mode on extrusion shafts is spalling caused by axial overload when the plastic melt is too viscous. Symptom: abrupt noise increase at frequencies above 1 kHz when measured with a vibration sensor. Early detection per ISO 10816 allows scheduling replacement during a cleaning shift rather than an emergency stop.

Regreasing quantity for 32220 extrusion shaft: G = 0.005 × D × B = 0.005 × 180 × 49 = 44 grams, interval 1,500 hours with lithium complex EP2 grease.

Flexo and gravure printing machines: print cylinder precision

Flexographic (flexo) and gravure printing are the two dominant decoration technologies for flexible packaging. Print cylinders rotate at 200–600 rpm with radial load from doctor blade pressure and nip pressure between the printing plate and film. Radial runout above 3–5 µm produces visible color misregistration in 8–10 color jobs.

Bearings for print cylinders must simultaneously deliver: (1) low radial runout (P5 accuracy or better), (2) resistance to organic solvents in inks, (3) cleanability.

Typical print cylinder bearing codes:

• 6205 2RS/P5 (d=25, D=52, B=15 mm, C=14.8 kN) — small print cylinder, 600 mm wide flexo machine
• 6308 C3/P5 (d=40, D=90, B=23 mm, C=32.5 kN) — medium print cylinder, 1,200 mm wide gravure machine
• NU2208 E (d=40, D=80, B=23 mm, C=56 kN) — keyed print cylinder requiring axial adjustment

The P5 designation matters more than many engineers realize. P5 bearings have tighter fitting tolerances and lower runout limits per ISO 492: radial runout ≤ 3 µm for a 6308 P5, versus ≤ 10 µm for a standard 6308. On an 8-color print line, this difference determines the reject rate for color misregistration.

Lubrication for print cylinders has special requirements: colorless, odorless grease (food-grade if food packaging), with no risk of ink contamination. NSK Molykote EM-30L or SKF LGFP 2 (food-grade, NSF H1) are appropriate choices per NSK Technical Report: Bearing Application Guide, 2022.

Slitting and cutting machines: high-speed blade shafts

Slitter-rewinders and die-cutting machines cut film at 300–800 m/min. Blade shafts rotate at 1,500–4,500 rpm depending on diameter. Circular blades require shaft runout of ≤ 5 µm — if this is exceeded, the cut line becomes wavy and the film tears rather than cutting cleanly.

Slitter main shaft bearings:

• 6306 C3 (d=30, D=72, B=19 mm, C=22 kN) — small blade shaft, thin-film slitter
• 6308 C3 (d=40, D=90, B=23 mm, C=32.5 kN) — medium blade shaft, most common
• 7308 BECBP (d=40, D=90, B=23 mm, C=40.5 kN, 40° contact angle) — high-speed main shaft with axial thrust from helical blades

Angular contact bearing 7308 BECBP is appropriate when the blade shaft carries both radial cutting load and axial thrust from helical-cut blades. Grease speed limit: 9,000 rpm — adequate for high-speed slitters.

Rewind shaft: Self-aligning ball bearing (SABB) 2205 ETN9 (d=25, D=52, B=18 mm) compensates shaft misalignment when rewinding is uneven. Thin OPP film (12–20 µm) is particularly sensitive to shaft deflection — the self-aligning bearing reduces bending stress on the shaft.

Plastic film dust — especially BOPP and PET — is the primary cause of premature bearing wear on cutting machines. Hard plastic particles 20–80 µm in size penetrate standard dust seals and act as an abrasive. Solution: labyrinth seal combined with an external dust shield (dust guard) on the bearing housing, not a simple 2RS seal alone.

Laminating machines: heated roller bearings

Laminators bond multiple film layers — PE/PET/aluminum foil — to create composite flexible packaging for food and pharmaceutical use. The heated roller (nip roller) operates at 60–140°C, rotates continuously at 20–100 rpm under 5–15 kN radial nip pressure.

The thermal challenge: a temperature gradient from the roller core (140°C) to the bearing position (typically 60–80°C after cooling) creates non-uniform thermal expansion. Standard C0/CN clearance bearings seize when the shaft heats up — C3 or C4 clearance is mandatory.

Typical heated roller bearing codes:

• 22220 EK/C3 (d=100, D=180, B=46 mm, C=365 kN, C₀=530 kN) — main heated roller, handles high nip force FAG/Schaeffler Industrial Bearing Solutions Guide, 2023
• 23022 CC/C3 (d=110, D=170, B=45 mm, C=380 kN) — laminating shaft with misalignment ≤ 2°
• 6220 C3 (d=100, D=180, B=34 mm, C=122 kN) — locating bearing on the drive end

Floating/locating arrangement is mandatory for heated rollers longer than 600 mm. The locating end uses a ball or tapered roller bearing fixed in both axial directions. The floating end uses a cylindrical roller bearing (NU or N series) that allows the shaft to expand thermally without generating axial stress.

High-temperature grease is non-negotiable for positions where bearing temperature exceeds 80°C. Standard lithium grease loses its lubrication properties above this point. For bearing positions exposed to heat above 80°C: use calcium sulfonate complex grease (SKF LGHP 2, NTN FMF-C3) or high-temperature polyurea grease (FAG Arcanol TEMP90). Per NTN Industrial Bearing Technical Reference, 2021: relubrication intervals at elevated temperatures should be reduced by 50% compared to ambient-temperature baseline.

Brand comparison: ZVL and SKF for plastic packaging

The two brands that appear most frequently in Vietnamese plastic packaging plants are ZVL (Slovakia) and SKF (Sweden), alongside FAG (Germany) and NSK (Japan). Each brand has specific strengths suited to different equipment segments.

ZVL Slovakia manufactures at its EU plant to ISO 492 standards with full DIN/ISO certification. The product range covers ball, tapered, and spherical roller bearings — all common codes used in packaging applications. Steel metallurgy and heat treatment quality are equivalent to Japanese and German brands. Particularly well suited for:

• Extrusion shafts and gearboxes on blown-film machines (32216, 32220)
• Medium radial-load positions on slitters and laminators (6308, 6309)
• Rewind shafts and light-load bearing positions (6205, 6206)

Competitive European pricing compared to Japanese and German alternatives allows many plants to reduce maintenance costs without sacrificing equipment service life.

SKF is strongest in applications requiring high precision and specialty configurations:

• P5 precision bearings for high-accuracy print cylinders
• Food-grade bearings (LGFP 2) for food-contact packaging equipment
• Integrated vibration monitoring systems (SKF Axios) for automated production lines

For mid-capacity blown-film and laminating equipment — the most common configuration in Binh Duong and Long An — ZVL represents the best balance between quality and operating cost. For high-precision print cylinders or equipment requiring NSF H1 food-grade certification, SKF or FAG is the more appropriate choice.

Real-world case study: PE blown-film line

At a flexible packaging plant in Binh Duong producing PE food-packaging film, a 1,200 mm three-layer blown-film line experienced recurring extrusion main shaft bearing failures every 6–8 months. Bearings in use before the investigation: imported with no traceable origin or ISO certification.

Failure analysis revealed three concurrent problems:

1. Wrong clearance: Tapered roller bearing 32220 CN (standard clearance) seized after 4 hours of warm-up. Extrusion zone temperature of 95°C caused the shaft to expand and completely eliminate the CN clearance.
2. Wrong grease: Standard grease liquefied above 80°C and lost its lubrication film.
3. No monitoring: No vibration measurement points — failures were only detected when the machine stopped completely.

Solutions implemented:

• Replaced 32220 CN with 32220 C3 (ZVL) at the thrust position; 6309 C3 at secondary bearing supports
• Replaced standard grease with FAG Arcanol TEMP90 (rated to 120°C operating temperature)
• Installed 4 wireless vibration sensors at the four main bearing positions
• Set vibration alert threshold at ≥ 7.1 mm/s (ISO 10816 Zone C) and emergency stop threshold at ≥ 11.2 mm/s (Zone D)

Results after 18 months of operation: zero unplanned stoppages. The 32220 C3 bearing reached 12,000 hours before first replacement — twice the previous average service life. Maintenance cost fell substantially compared to the prior 6–8 month emergency replacement cycle.

Key lesson: internal clearance is not a secondary specification — for a heated extrusion shaft, selecting the wrong clearance is the root cause of 60–70% of early bearing failures in plastic packaging plants.