Material Properties: Steel vs. Cast Iron for Drying Cylinders

Steel Advantages:

1. Strength and Elasticity:

   • Steel has a much higher modulus of elasticity than cast iron, allowing for better design parameters under pressure vessel safety codes.
   • Higher allowable stresses mean thinner shell walls, leading to improved heat transfer rates.

2. Heat Transfer and Efficiency:

   • Thinner shell walls in steel dryers enhance heat flow and evaporation rates, increasing production or reducing energy consumption at constant machine speed.
   • The better heat transfer allows for lower steam pressure with higher Latent Heat of Vaporization.

3. Defect Management:

   • Cast iron casting often develops pinholes that need repair, affecting paper quality. Steel dryers do not have this issue.

4. Higher Tensile Strength:

   • Steel’s ultimate tensile strength is much higher than cast iron’s, with specially developed high-strength steels offering even greater performance.

5. Heat Transfer and Lower Energy Costs:

   • Comparable thermal conductivity but better heat transfer due to thinner shells.
   • Significant energy cost savings due to reduced shell thickness and enhanced heat transfer.

6. Automation and Control:

   • Thinner steel dryers respond faster to changes in set points, improving paper quality consistency and reducing startup times after stoppages.

7. Metallization Benefits:

   • Steel Yankees & dryers can be metalized for increased surface hardness, life, and water resistance, eliminating re-grinding needs.

Safety:

1. Explosion Resistance:

   • Cast iron’s brittleness can lead to explosions under excessive pressure or load. Steel is more ductile and withstands higher internal stresses without catastrophic failure.

2. Integrity under Stress:

   • Steel shells deform but stay intact if stresses exceed the yield strength, unlike cast iron, which may explode.

Sizes Available:

Drying Cylinders:

• 1220 mm (4 feet) up to 5.1 meters, with internal machining and grooving.
• 1500 mm (5 feet) up to 5.1 meters, with internal machining and grooving.
• 1800 mm (6 feet) up to 5.1 meters, with internal machining and grooving.
• 2100 mm (7 feet) up to 5.1 meters, with internal machining and grooving.

Yankee Cylinders:

• 3048 mm (10 feet) up to 5.1 meters, without internal machining and grooving.
• 3658 mm (12 feet) up to 5.1 meters, without internal machining and grooving.
• 4267 mm (14 feet) up to 5.1 meters, without internal machining and grooving.
• 4876 mm (16 feet) up to 5.1 meters, without internal machining and grooving.
• 5486 mm (18 feet) up to 5.1 meters, without internal machining and grooving.

Summary:

Steel Dryers:

• Offer major advantages in productivity, safety, and energy costs.
• Require lower capital investment and have a lower physical weight than cast iron.
• Enable significant heat transfer improvements and energy savings due to thinner shells.
• Provide improved response times and quality consistency due to faster heat capacity changes.

Advanced Features:

• Internal machining for even shell thickness.
• Spiral ribbed internal surfaces for more heating area.
• Composite units with alloy steel cast shafts and side discs for high-speed applications.
• Surface finishes up to 0.6 to 0.9 microns.
• Stringent inspection and testing protocols to ensure quality and safety.

Advantages:

1. Energy Savings: Lower consumption due to efficient heat transfer.
2. Flexibility: Adaptable to various operational needs.
3. Investment Costs: Lower initial costs compared to cast iron.
4. Safety and Weight: Enhanced safety features and reduced weight for better operational efficiency.

Steel dryers, particularly the second-generation carbon steel fabricated drying cylinders, offer enhanced drying capacity, improved safety, energy savings, and cost benefits, making them superior to cast iron dryers for modern paper production needs.