Technology

Bellows 101 Videos

Welded Metal Bellows

An edge-welded metal bellows is a zero leakage dynamic seal capable of a great range of motion. The metal bellows is manufactured from sheet stock. The material of construction may be stainless steel, high nickel alloys, titanium or other alloys to suit the application requirements. The material thickness may range from 0.001” to 0.025” thick.

 

Welded Bellows Technology

  • GTAW & CO2 laser welding
  • Thickness (0.001 to 0.025 inches)
  • Sizes, diameters (0.125 to 23 inches)
  • Round and non-round
  • Materials
    • Stainless steels
    • High nickel alloys
    • Titanium
  • Mass spectrometer leak tight
    • 1 × 10-10 std cc/sec He capability 
(1 cc in 320 years)
  • Zero leakage dynamic seal

Bellows Performance

  • Bellows should mostly work in compression, 20% extension max. For maximum life, always work in compression
  • Nested height of bellows should have a minimum of .002” between max weld bead size for 3 ripple configuration
  • Avoid imposing lateral offset while axial stroking.  Severely degrades life
  • Max pitch 1/3 of span
  • Bellows free length will typically stabilize at 15 to 25% of as welded length

Bellows Configurations

Nested Ripple

  • Long stroke capability
  • Compact nested length
  • Good linearity
  • Moderate pressure capability
  • High cycle life

Flat Plate

  • Limited stroke capability
  • Excellent linearity
  • Good pressure capability
  • Excellent effective area control

Crescent

  • Good stroke capability
  • Compact nested length
  • Good linearity
  • Good pressure capability

Welded Bellows Capabilities

Zero leakage through a range of motion in extreme operating conditions

  • Axial Deflection
  • Angular Deflection
  • Lateral Deflection

Bellows Performance Parameters

Spring Rate

  • Function of  material thickness, material type, cross-sectional geometry, pitch, span and number of convolutions
  • +/- 5% material thickness equates to +/- 10% change in spring rate in ripple geometry

Effective Area

  • 2D Area of bellows exposed to pressure differential
  • Function of OD/ID and installation geometry

Life

  • Function of deflection and pressure (membrane) stresses
  • Variables in life determination include:
    • Spring Rate
    • Pressure Differential
    • Stroke/Convolution
    • Bellows Span
    • Material Fatigue Strength