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Fins- Most Important Component For Tube Making

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After strip is formed into round shape, inner fibres of tube come closer and outer fibres fall apart. if such a tube is welded then it will be a very weak welding, as both surfaces of open tube will not be matching. For this reason round shape is made to pass through fin pass rolls. There are 2 to 3 stands depending upon tube size, gauge and mill design. Fin conditions the strip edges for proper welding. Its functions are -

  • Guiding the edges of strip
  • Squaring the edges for butt welding
  • Directing the tube to squeeze rolls for perfect welding

Fin should be wear resistanr & tough. Best raw material for Fin is AISI-D2.

 

C  = 1.50  
 Si   = 0.40   Mn = 0.40
Cr = 12.0  Mo = 0.90   V   = 0.70

Edges of strip strike and rub fin on both sides.
Recommended hardness is 56/58 HRC.
Next best Raw Materials for Fin are Cr-V / Ni-Cr Steel with hardness 56/58 HRC.
In India Fins are also made from AISI-D3 & SAE-52100 having hardness 56/58 HRC.

Recommended tolerances on Fin are -

Outer diameter
=  
± 0.1 mm
I.D.
= G-7
Keyway Width = + .1 / + .4
Keyway Depth = + .2 / + .5
Keyway corner radius 
=  2.0 R
Thickness
=  ± 0.02 mm
Bevel
=  ± 30’
Bevel Diameter
= ± 0.5 mm
 P.C.D. on holes
=  ± 1.0 mm
  =  
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