By adopting a riser design appropriate to the moulding technique, foundries may expect to improve casting yield and reduce riser contact areas – without fibre contamination in the mould.
Experts at ASK Chemicals gave their answers to questions put to them and they were first published in Foundry Management & Technology.
Q: Is it possible to use the high-efficiency riser systems commonly used with iron castings
instead for steel castings?
A: Yes, high-efficiency riser systems commonly used for iron can be employed with steel castings,
creating many advantages for the operator and the foundry. However, there are a few important details to bear in mind about this application.
First, to review the relevant details of the application, recall that a riser (sometimes referred to as a feeder) is a reservoir built into a metalcasting mould to prevent cavities from forming during solidification as a result of shrinkage. Most metals are less dense in liquid form than solid, so a casting may shrink as the metal cools, which may result in a void at the final point of solidification.
The Exactcast KMV mini-riser is a lightweight design adaptable to a range of moulding types. This versatile riser can be fitted with a spring pin or simply placed directly on the casting. And, It’s a highly exothermic solution available in a fluorine-free formulation
The optimal riser system depends on the current moulding system in use by the foundry. If the foundry employs a high-pressure, horizontally parted green sand system, ASK Chemicals’ Exactcast Optima riser would provide the best solution.
If the foundry employs a no-bake moulding system, ASK Chemicals’ Exactcast KMV riser would provide the best solution. With these solutions in place, the operators would recognise the following improvements over traditional fibre riser systems:
1) Improved yield due to mini-riser feeding efficiency
2) Reduced riser contact areas, reducing finishing and grinding costs and
3) No fibre material contamination in the moulding system.
Additionally, ASK Chemicals’ Optima riser creates a perfect residue-free moulding with improved compaction and a clean, clearly defined breaker edge directly on the casting. Steel casting temperatures can be significantly higher when compared to iron castings. This higher temperature profile demands higher refractoriness from the exothermic feed mixture. ASK Chemicals’
Exactcast product line has developed special, high-refractory formulations to meet these requirements.
Another factor to be recognised is that steel castings typically have significant volume requirements. ASK’s KMV and Optima risers are effective in addressing this need. These products reduce riser volumes by 50% or more, allowing current melt production to be used in other casting applications.
An important criterion in the foundry’s selection of a riser are the process costs associated with removing risers from the cooled casting. A traditional riser system requires lancing or cutting tools. The KMV risers’ reduced contact areas and Optima’s cleanly defined breaker edges allow risers on steel castings to be knocked off easily with a hammer. This adds value to the casting while reducing metal loss with foundry operations.
Additionally, due to the solidification morphology of steel alloys, riser necks may require larger contact areas. ASK Chemicals’ KMV and Optima risers can be used with full contacts or varying breaker strategies where larger contacts become necessary.
For further details contact ASK Chemicals on TEL: 087 057 7635 or visit www.ask-chemicals.com
