Material Properties and Benefits of Steel Dryers

Advantages of Steel over Cast Iron:

1. Strength and Design Efficiency:

   • Steel has a much higher modulus of elasticity and allowable stress compared to cast iron, allowing for thinner shell walls in pressure vessel design. This results in higher heat transfer rates.
   • Thinner shell walls in steel result in higher heat flow, leading to increased evaporation rates. This can either boost production rates at constant energy input or reduce drying energy if machine speed remains constant.

2. Improved Heat Transfer and Energy Savings:

   • Although cast iron and steel have comparable thermal conductivity, the thinner steel shell ensures better heat transfer.
   • The reduced shell thickness and higher heat transfer efficiency enable the use of lower steam pressure for drying, leading to energy savings.
   • Grooved internal surfaces of steel shells increase the overall heating area, enhancing conductivity and reducing total energy consumption.

3. Durability and Maintenance:

   • Steel dryers do not develop pinholes during casting, unlike cast iron, which requires repairs and can affect paper quality.
   • Steel Yankees and dryers can be metalized to increase surface hardness, lifespan, and water resistance, eliminating the need for re-grinding and reducing the risk of chatter problems.

4. Safety:

   • Steel dryers perform better under excessive internal stresses. If stresses exceed the yield strength, the steel shell may deform but remain intact, while a cast iron shell might explode.
   • The higher tensile strength of steel makes it more suitable for high-stress applications, ensuring safer operation.

Design and Technical Specifications:

• Design Parameters:

  • The box body is an airtight attenuation pond with overflow holes and an oblique stock-inlet to reduce stock retention.
  • The inlet taper manifold consists of tapered and rectangular manifolds with a pressure balance observing pipe.
  • Distribution elements include a three-step diffuser made of organic glass integral casting.
  • Double holy roll head box with spiral helix holes driven by worm reduction with TEFC motor for optimal evenness.
  • Upper-lip regulator for precise adjustments, and a fixed lower lip.
  • Injection spray pipe made of stainless steel.

• Material of Construction (MOC):

  • Inlet pipes, side walls, upper parts, bottom beam, upper-lip frame, and bottom lip are made of stainless steel.
  • Stepped hole diffuser made of PMMA.
  • Holy roll made of stainless seamless steel tube (304).
  • Micro-adjuster made of cast aluminum.

Head Box Controlling System:

• Control Parameters:

  • General pressure, liquid level, and stock speed/wire speed ratio controlled by pressure and differential-pressure transmitters.
  • PLC regulating loop for pressure head and level control.
  • Roots blower and pulp distributing fan pump VFD for stock approach quantity and air-blast control.

• Control Accuracy:

  • Level control within ±1mm.
  • General pressure fluctuation within ±0.5%.

Sizes Offered:

• Drying Cylinder:

  • Diameter: 1220 mm (4 Feet) to 2100 mm (7 Feet)
  • Face Length: Up to 5.1 meters
  • With internal machining and grooving.

• Yankee Cylinder:

  • Diameter: 10 Feet (3048 mm) to 18 Feet (5486 mm)
  • Face Length: Up to 5.1 meters
  • Without internal machining and grooving.

Summary:

Steel dryers offer major advantages over cast iron in terms of productivity, safety, and energy costs. The reduced shell thickness of steel dryers decreases thermal resistance and increases heat transfer, leading to higher drying capacity. Steel dryers also provide substantial energy cost savings and lower capital investment compared to cast iron dryers. The steel dryers are designed for high-speed applications, ensuring even thickness, minimal unbalance, and high precision. Additionally, steel’s superior strength and safety features make it the preferred material for modern drying cylinders.

Advantages of Steel Dryers:

• Energy Saving: Lower energy consumption due to efficient heat transfer.
• Flexibility: Suitable for various production needs and speeds.
• Investment Costs: Lower initial costs compared to cast iron.
• Safety and Weight: Safer operation and lighter weight reduce overall system strain and energy consumption.