CERACAT MAX HC Super High Capacity Filter for Very Large Iron Castings

CERACAT MAX HC Used in High Capacity Ductile Iron Applications

Jobbing  foundries making large ductile iron castings have always had some unique difficulties and requirements with regard to filtration or indeed controlling flow to reduce turbulence during the pouring process.

A similar foundry making large steel parts would generally utilise bottom pour ladles and elaborate ceramic gating systems to reduce ingate velocities whilst enabling rapid filling etc generally the iron foundry faces much tighter pressure on margin. What in theory is ‘doable’ is very often curtailed by what is most practical.  For example the volume of moulding sand/binder is kept to a minimum resulting in very little space around the mould cavity for elaborate gating.

The sheer size of some of these parts give rise to other restrictions like the limit on mould height in relation to maximum crane height to be able to pour the ladle. There are many many factors that are not always immediately apparent to someone coming up with a ‘blue sky’ optimal gating system

Stress critical parts such as wind hubs are relatively thin in section and the effects of surface defects such as Dross and other inclusions can have a major impact on fatigue life.

Many foundries making large iron parts have utilised filters to some success but there are currently limitations to what is available from suppliers.

The grey silicon carbide foam filters that are available from many suppliers are very cheap but have limitations, some suppliers rate them as useable up to 1450 deg C but in reality survival of the filter is a function of temperature and pouring time and with bigger castings these SiC filters are soon overwhelmed.

The alternative is to then look at filters developed for steel, typically zirconia filters these can  operate up to 1700 Deg C and have no issue with iron temps and longer pouring durations. However they are significantly more expensive especially in bigger sizes. Typically the maximum size available in zirconia is D200 and on a good day you will only get around 1-1.5 tonne of SG iron through this size.

A typical method employed by iron casters is to put  multiple 150mmx150mm in an array in an expanded runner bar typically at the joint line of the mould sometimes 20-30 pieces or more, but  this is a compromise and again very much limited by casting geometry.

CAT developed CERACAT MAX some years ago to fill the gap between SiC and Zirconia and allow the production of larger pieces at a much more economic price, typically in sizes up to 300mm x 300mm . However the flow rate and capacity is still similar to zirconia ie D200 is around 1-1.5 tonne. These foam filters are limited by the coarseness of the PU foam available to manufacture them and 7-10ppi is the limit.

So how do we address this need for increased capacity, how can we get higher throughput of iron through a given area of filter.

One technique that is emerging and that will see significant development is the use of additive manufacturing ie 3D printing. A simple way is to print a coarser foam precursor and then make the filter with existing  filter production technology, this we are already seeing on the market.

A more significant move will be the commercial printing of ceramic directly, we and others are investing heavily in this area and development is now moving at pace, significant benefits can be achieved but again these pieces will not be cheap and we are still some time from having items made this way commercially available.

Which brings me to our latest product CERACAT MAX HC:

A  customer of ours based in the UK embarked on making a large ductile iron flask for the containment of nuclear waste with a high specification for an iron casting. It was proving difficult to achieve. They approached us to come up with a simple, reliable way to incorporate a filter/device that could take 3-4 tonnes SG iron throughput and be placed as close to the ingates as possible. They were using ceramic gating but in a relatively simple configuration due to tight constraints in the moulding box.