Case Study: SCR Bus Nozzle

Process: Metal injection molding
Tensile Strength: >600 MPa (88,000 psi)
Yield Strength: >350 MPa (51,000 psi)
Density: 7.6g/cm³

SCR Bus Nozzle
2015 Grand Prize: SCR Bus Nozzle

End Use and Function

The above part is a metal injection molded (MIM) bus nozzle used in a selective catalytic reduction (SCR) system of European commercial vehicles. The nozzle performs the SCR function using urea and compressed air to reduce the NOx produced during combustion to N₂ and H₂O.

Fabrication

Made of an austenitic stainless steel (AISI HK30), the part employs a patented technology that uses a removable polymeric insert to form the highly complex internal undercut channel; a feature the fabricator deems “impossible” to achieve using conventional machining.
All internal channels are achieved through MIM, while the threads on top are machined and Micro TIG welding is used to seal the small openings left by the polymeric insert; tip flatness is achieved through a grinding operation. The part has a density of 7.6 g/cm³, ultimate tensile strength >600 MPa (88,000 psi), yield strength of 350 MPa (51,000 psi), and elongation of >10%.

Results

  • While possible to create this part without using powder metallurgy, it is estimated that fabricating the nozzle through the welding/brazing of multiple parts would have increased its cost by more than 200%.