Since dryer sections require use of high temperatures and pressures, they must be treated with caution. The nature of the dryers' function and required operating care make it important that they be given close attention in the mill safety program. The key to dryer section safety is to keep operating personnel from getting into dangerous areas or unsafe positions, especially while the dryers are operating. If unsafe conditions exist, the dryers must be shut down until the condition is corrected.
Machine tenders and other mill personnel with work assignments in the dryer section must be given complete safety instructions and continued refresher courses so they “think safety” and will be on guard against potential hazards. They should be carefully instructed on the proper use of equipment and potential dangers of the steam systems, high pressures and high temperatures associated with dryer operation. Also, adequate barriers, footwalks platforms and signs should be installed at appropriate locations to protect and warn personnel of the potential hazards.
Valmet recommends that a trained and responsible person be designated at each mill to oversee safe operation, maintenance and inspection programs for dryers.
Be aware of the following conditions:
- Felts and felt seams should be inspected at least once a shift on high speed machines and during all clothing changes. Should a felt seam part due to fatigue or wear, serious damage could occur.
- Some steam fit designs can be hazardous if not protected by a guard due to exposed rotating journal flange, capscrews or bolt heads. The guard must completely cover the rotating parts that provide the seal between the rotating dryer and the stationary piping that supplies the steam to the dryers and carries away the condensate from the dryers. It is recommended that the guard be constructed from solid sheet metal as opposed to expanded metal plate, to provide protection against a sudden escape of steam.
- Loose balance weights, siphons and other debris that may be inside the dryer cylinder can cause severe erosion that may result in shell failure. If detected during routine inspection, the loose items must be removed. If erosion is excessive, the dryer should be replaced or at least run at lower pressures.
- Loose plates on manholes and clean-out holes must be reported so repair work can be scheduled immediately.
- Rope systems should be continually inspected. Ropes that have become dislodged or show signs of wear should be replaced.
Maintenance safety in the dryer section
When performing maintenance or service in the dryer section, the following safety rules must be observed:
- Use proper lockout/tagout procedures on all drives and controls before performing maintenance. Accidental start-up may injure personnel.
- Release pressure from steam, water and air lines before disassembly. Hot steam or high water and air pressure may be dangerous to personnel in the area.
- Valve off or blank off steam and condensate piping before entering the dryer for maintenance. Use adequate ventilation inside of the dryer along with low voltage lighting. Also, make certain that a standby person is posted by the manhole entrance to observe and communicate with workers inside the dryer at all times. For complete requirements regarding entry into confined spaces, refer to the mill's and Valmet's Confined Space Entry procedures and the applicable confined space safety regulations which govern your operation.
- Inspect slings and cables for worn or weak spots before using them. Keep all personnel away from under machine components when lifting to prevent injury in case the slings, cables or hoists should break.
- Use lift points as specified by the manufacturer. Where provisions have been made for lifting eyes to be screwed into a tapped hole, make certain that the eyebolt is tightened to the shoulder and that the eye is parallel to the lifting plane to prevent breakage.
- Tie slings securely when attempting to lift machine components. When using two crane hooks, lift the component evenly. Rapid shifting of out-of-balance pieces could be hazardous.
- Do not depend on hydraulic or pneumatic drives or components to hold equipment in a raised position while performing maintenance. Pin, chain or block the equipment in the raised position as a precautionary measure.
- Use proper stops when applying hydraulic removal equipment to bearings, heads, gears, etc. These items may travel at a high rate of speed once they have loosened from the fit.
- All condensate and steam lines must be insulated to prevent possible burns to personnel.
- Never weld repair cast iron dryers. Contact Valmet for dryer cylinder maintenance procedures.
- Valmet recommends inspecting the inside of dryer cylinders every 2 to 3 years. Loose balance weights, siphons and spoiler bars must be secured. Examination must be made for erosion to the shell inside diameter which is caused by condensate channeling or loose equipment. Seriously eroded dryer components must be replaced.
- Loose plates on manholes and clean-out holes must be reported to mill supervision who should arrange for immediate repair.
- Dryer outside diameters should be checked each year for doctor wear. Dryer shells which are pressurized must be replaced or derated if worn too thin to be safe.
- Dryer head to shell leaks should be repaired immediately. Capscrew failures may result due to stress corrosion cracking when contaminated by steam system additives. Capscrews in a leak area should be checked ultrasonically to detect cracks. For additional information contact Valmet.
- Dryers subjected to severe paper wraps or felt wrecks should be carefully examined. These accidents can overload journals and shells and may cause cracks.
For more information on dryer section safety and maintenance, contact your Valmet representative.