MATERIALS USED FOR COMPONENTS OF HX RANGE MODERN TURBOCHARGERS

Of course the materials used in modern turbochargers and the HX range in particular have been gradually further developed, thoroughly tested and used following the demand of higher boost pressures and resulting high temperatures encountered, driven by progressing emissions standards up to Euro/Tier 5 and 6.

Therefore the performance diesel world now can benefit from the latest developments and material improvements of turbocharger components used in the latest state of the art units.

Common fact is that for the turbo manufacturer, the choice of materials is always a balance of cost effectiveness, technical- and materials properties requirements for a given modern application and commercial viability of the total value package.

Below you will find some basic details on materials used in current HX range major components, technical/material requirements and possible options and features following the latest developments:

COMPRESSOR HOUSINGS 

Material used is cast aluminum, various alloys, gravity die cast or sand cast.

Technical/material requirements are ductility to ensure impact resistance, plus ease of machining.

COMPRESSOR WHEELS (IMPELLERS)

Material used is cast aluminium, casted by a variant of investment casting process, using rubber formers and plaster moulds to allow production of wheels with back curved blades.  

Technical/material requirements are fatigue strength, elevated temperature strength, creep resistance, corrosion resistance. Sensitive to balance groove shape and damage/defects.

For special high pressure applications temperatures can exceed the creep limits of cast aluminium, where ‘billet’ (machined from solid wrought aluminium) impeller,  if available for that particular model and inducer size, must be used (please refer to separate chapter ‘Billet Impellers’  for extensive details and comparisons with cast compressor wheels).

BEARING (CENTRE) HOUSINGS

Material used is grey (flake) cast iron (pearlitic),shell mould cores to provide positional accuracy of bearing location and seals, shell mould or sand cast outer, machined by a combination of milling, turning, drilling, tapping, honing, complex geometries.

Technical/material requirements are good castability, ease of machining, rigidity and thermal stability.

BEARINGS MATERIALS AND THRUST COMPONENTS

Please refer to Central section in chapter ‘How a turbo works’. Also please check the separate chapter regarding Thrust bearings.

SHAFT + TURBINE WHEEL ASSEMBLIES                                                                                             

Materials used are a high nickel super-alloy (like Inconel 713C) turbine wheel to withstand high exhaust temperatures (up to 760 degrees C for standard applications, high boost- up to 1050 C in most Truck- and Tractorpulling applications), investment cast, blade profile machined. Friction welded to a forged steel shaft. Sensitive to balance grooves and defects/damages.

Technical/material requirements are fatigue strength, elevated temperature strength, creep- and corrosion resistance.

TURBINE HOUSINGS

Materials used are cast iron (spheroidal graphite cast iron / ferritic) or Ni-resist.

Greensand mold, sand core, profile machining to match turbine wheel blade shape, operation temperatures identical and as mentioned at Shaft + turbine wheel assemblies.

Technical/material requirements are impact resistance (ductility), oxidation resistance, high temperature strength, thermal fatigue resistance, ease of machining

BALANCING

(for your information Core assembly or CHRA (means: centre housing rotating assembly) is the complete turbocharger without both the end housings)

                                    

Why do turbochargers need to be balanced?

                       

All high speed machinery needs to be balanced to fine limits. In the case of the turbocharger this has traditionally been achieved by careful balancing of individual components, which normally ensures an adequate level of balance for heavy duty applications, typically large diesels.

The diesel performance and tractorpulling turbocharger has a more demanding requirement, because of the high rotational speeds and vibrations around the maximum allowed rotor-speed, defined for the model used.

For these reasons the diesel performance turbocharger requires balancing to much finer limits and this cannot be achieved by balancing of individual components alone .

The solution to this problem is to achieve a more precise state of balance which can only be attained by balancing the complete core assembly (CHRA) over a speed range close to the maximum operating speed of the unit using professional balancing equipment.