Iron Melt Flow in Thin Walled Sections Cast in Vertically Parted Green Sand Moulds

Shortage of resources can be expected to become more wide spread in the future. Furthermore the focus on the environmental aspects will also be intensified. Today the clearest example is the large attention on the fuel consumption of cars. Many different approaches can be made to reduce the fuel consumption and pollution of passenger cars, trucks etc. The engine design can be optimized for higher efficiency, the wind resistance can be reduced, combinations of combustion engines and electrical power can be used etc. But no matter which approach is taken, parts have to be used for building the vehicles. I.e. reducing the weight of the needed parts is a general way of saving fuel, applicable together with all other means of saving fuel.
Even though iron castings have been used in cars from the first car ever build, a big potential still exists for optimizing iron cast parts from a weight-saving point of view. This can be done by designing parts with thin walled sections and building stiffness into the parts via ribs, hollow section etc. Processing of parts with thin walled sections becomes hence important.
Detailed analysis of melt flow in a conventional bottom filling gating system and in thin sections have been made via videos of the metal flow. Conventional bottom filling gating systems are shown to give relatively low control over the melt flow. The result is flow patterns being able to change radically from mould to mould due to minor fluctuations in the pouring
conditions. At this type of gating system it is very difficult to avoid pressure shock waves. The pressure shock waves can be initiated at two different stages of the filling. If the gating system contains a dead end and the cross sections are completely filled behind the melt front, a pressure shock wave will be initiated by the hammer effect when the melt reaches the dead
end of the runner. Pressure shock waves can also be initiated when the last air pocket in a partly filled runner is closed. The pressure shock waves result in disintegrating melt surfaces.
Flow in thin walled sections is not only important when casting thin walled parts, as thin plate shaped ingates are used for casting many parts. This is illustrated with a brake disc. 6 layouts have been made. The filling sequences have been recorded on video. The trials show the difficult task to design a bottom filling system generating no splash during the initial filling and
obtaining a balanced filling. When calm flow is wanted, normally the runners are designed to give low velocities. But to secure calm flow, pressure shock waves also have to be avoided. When pressure shocks are avoided and runners with good control over the melt are used, relatively high velocities can still result in calm flow with coherent melt fronts. Conventional types
of gating systems have been used for 5 of the 6 layouts. The flow patterns in these systems are to a large degree controlled by the relative sizes of the dynamic and braking forces acting on the melt and not solely by the geometry of the runners. A non-conventional gating system has also been tested. The system gives a high degree of control over the flow, the balance
between the dynamic and braking forces have only little influence on the flow patterns.
An exhaust manifold with 2 mm wall thickness has been cast utilising a developed stream lined gating system. The manifold is cast with no visible defects coming from the filling. The very stream-lined gating system gives uniform flow patterns from mould to mould compared to what is seen for conventional gating systems. This means, the conventional types of gating
systems investigated in this work, cannot be recommended for castings with high demands to the quality, as the variation in the filling patterns can be very large from mould to mould and hence the stability of the quality will be affected.