Do cylinder heads have the same narrow CGI specification requirements as cylinder blocks?


Shareholder, name withheld

In general, the CGI specifications for passenger vehicle or commercial vehicle cylinder blocks and heads are the same. CGI is formally defined as having 0-20% nodularity which, in practice, corresponds to a stable production range of approximately ± 0.004% magnesium. Also, as cylinder heads incur higher thermal loading than cylinder blocks, it is preferable to produce the heads in the low-nodularity region (<10%) to optimise the heat transfer. This provides an advantage for the SinterCast technology as the patented magnesium fade simulation allows the SinterCast foundries to safely operate in the low-nodularity region without the risk of flake graphite formation.

The use of CGI for cylinder heads is initially included in the second wave of the Five Wave scenario, and also as a potential sixth step. Initially, in the second wave, CGI will be applied to commercial vehicle cylinder heads in the 8-20 litre size class. These large engines have high combustion temperatures and forces, and large cylinder bore diameters that require stiff heads that can span the bore without deformation. In the potential sixth step, CGI may also be applied to diesel engine cylinder heads for passenger vehicles where the continuous increase in loading threatens to exceed the durability limit of the current aluminium heads.

The possible exception to the 0-20% nodularity requirement in cylinder heads is in the large industrial power generation engines (>250 mm bore diameter). In these low speed engines, mechanical strength is often more important than heat transfer. For these engines, some OEMs may specify a higher/larger nodularity range, or even ductile iron. However, in the high volume passenger vehicle and commercial vehicle sectors, a narrow specification of CGI with low-nodularity will be preferred to optimise heat transfer, castability and machinability.