The paper industry is often underestimated as "low-risk," but reality tells a different story. Dryer sections operate at 80–95°C with 85%–95% relative humidity year-round, while airborne fiber dust, rosin mist, and hydrogen sulfide gas are ever-present.
In 2024, a major paper mill in South China experienced a shutdown when an IP55 motor in the dryer section accumulated condensation inside its terminal box, causing phase-to-phase arcing that ignited fiber dust. The 48-hour outage cost over 3 million RMB. Root cause: inadequate ingress protection and no condensate drainage design.
Per GB 50058-2014:
|
Area |
Classification |
Primary Hazards |
|---|---|---|
|
Pulping pit (underground) |
Zone 21 (dust) |
Dry paper scraps, fiber dust clouds |
|
Headbox area |
Zone 2 (gas) |
Rosin vapor, formaldehyde |
|
Dryer section |
Zone 22 (dust) + Zone 2 (gas) |
Fiber dust, trace H₂S in steam |
|
Coating preparation |
Zone 21 (dust) |
Calcium carbonate, starch dust |
Key insight: The dryer section is a mixed hazardous area — motors must carry both gas (Ex) and dust (Ex tD) certifications.
Ex tb IIIC T125°C Db ← Dust protection (Group III, conductive dust, max surface temp 125°C)
Ex db IIB T4 Gb ← Gas protection (Group IIB, T4 temperature class)
Float-type automatic drain valve at housing bottom — discharges accumulated water automatically
Valve material: 316L SS + PTFE gasket, acid/alkali resistant
Terminal box tilted ≥5°, with drain hole at lowest point to prevent pooling
Stator winding: Class H insulation (180°C); temperature rise evaluated per Class F (105K limit)
Impregnating varnish: hydrolysis-resistant polyesterimide resin, passing 1,000-hour dual-85 test (85°C / 85% RH)
Slot wedges and tie cords: high-temperature aramid fiber — no moisture absorption or deformation
Housing exterior: epoxy zinc-rich primer + polyurethane topcoat (total film thickness ≥ 200 μm)
Fan cover and blades: 304 SS or reinforced nylon — no rust debris falling into airflow path
Nameplate: laser-etched stainless steel, rivet-mounted (no adhesive)
Grease: high-temperature complex lithium grease (range -20°C to 160°C)
Pressure relief channel in bearing housing to prevent grease expansion into windings
V-ring rubber seals on both drive and non-drive ends to block steam ingress
Third-party lab simulation of paper machine dryer environment (90°C / 95% RH / 10 mg/m³ fiber dust, 2,000-hour continuous run):
|
Test Item |
Standard IP55 Motor |
This Explosion-Proof Motor |
Acceptance Criteria |
|---|---|---|---|
|
Insulation resistance (hot) |
12 MΩ |
380 MΩ |
≥ 50 MΩ |
|
Terminal box condensate volume |
15 mL/day |
0.3 mL/day |
≤ 1 mL/day |
|
Bearing temperature rise |
55 K |
38 K |
≤ 45 K |
|
Housing corrosion area (after 2,000h) |
8% |
< 0.5% |
≤ 3% |
|
Application |
Recommended Model |
Key Features |
|---|---|---|
|
Dryer section (high temp/humidity) |
Ex tb IIIC T125°C + Ex db IIB T4 |
Auto drain valve, Class H insulation, SS fan |
|
Pulping area (heavy dust) |
Ex tb IIIC T125°C Db |
Dust-sealed shaft extension, reinforced filter screen |
|
Coating room (wet + dusty) |
Ex tb IIIC T125°C Db + anti-corrosion coating |
Fully enclosed, PTFE seals |
Người liên hệ: Mr. Alex Yip
Tel: +86 2386551944