High-Humidity Paper Mills: Reliable Power in Pulp Mist and Steam

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:

Key insight: The dryer section is a mixed hazardous area​ — motors must carry both gas (Ex) and dust (Ex tD) certifications.

• 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):