Saldatura sovrapposta: Una panoramica

1. Introduzione

Overlay welding is a process where a material with specific properties is deposited onto a weldment surface. Unlike conventional welding, its purpose is not to join materials but to create a layer with properties such as wear resistance, resistenza al calore, e resistenza alla corrosione. This technique is widely used in manufacturing and repair to restore or enhance component dimensions.

2. Metals Used in Saldatura sovrapposta

The choice of metal for overlay welding depends on the weldment’s usage conditions, saldabilità, ed efficienza in termini di costi. Common overlay welding metals include:

• Iron-Based Metals
  • Pearlite Steel: Offers good weldability and impact resistance; used for repairing shafts.
  • Austenitic Steel: High impact toughness; used in mining carts and railway turnouts.
  • Acciaio martensitico: Elevata durezza e resistenza all'usura; suitable for gears and tractor chassis.
  • Alloy Cast Iron: Resistant to heat and corrosion; used in agricultural and mining equipment.
• Nickel-Based Metals
  • Nickel-Chromium-Boron-Silicon Alloys: Excellent resistance to wear and corrosion; used in high-temperature environments.
  • Nickel Alloys with Intermetallic Compounds: Elevata durezza; suitable for severe corrosive conditions.
  • Carbide-Containing Nickel Alloys: A cost-effective alternative to cobalt-based alloys.
• Cobalt-Based Metals
  • Cobalt-Chromium-Tungsten Alloys: Maintain high strength at 650°C; commonly used in high-temperature applications.
• Copper-Based Metals
  • Includes bronze, brass, and nickel silver; suitable for bearings and valve sealing surfaces.
• Carbide Surfacing Metals
  • Used for components subject to extreme wear, such as oil well drill bits and road construction machinery.

3. Overlay Welding Methods

Several techniques are used for overlay welding, each with unique advantages:

Oxygen-Acetylene Surfacing

• Ideal for small weldments requiring smooth surfaces.
• Simple and cost-effective but labor-intensive.
• Suitable for surfacing valves, drill bits, and plowshares.

Arc Welding

• Inexpensive and versatile; commonly used for field applications.
• Produces high heat concentration with minimal deformation.
• Commonly used for repairing worn parts.

Submerged Arc Surfacing

• High efficiency and automatic operation.
• Suitable for large components, such as corrosion-resistant layers in containers.
• Requires preheating and slow cooling to prevent cracking.

Other methods include gas tungsten arc surfacing, plasma arc surfacing, electroslag surfacing, laser surfacing, and friction surfacing, each suited for specific applications.

Conclusione

Overlay welding plays a crucial role in extending the lifespan and enhancing the performance of industrial components. By selecting the appropriate material and welding method, industries can achieve cost-effective solutions for wear, corrosion, and high-temperature resistance.