Mechanical engineers say : 80% of material failure are due to fatigue. What is fatigue? When a mechanical part is subjected to repeated load below ultimate strength but above fatigue limit. In other words : pull the handle once, no problem; pull a thousand times it breaks. That’s what occurred to iron casted handle. The upper ring which forms the pivot is split into two. I will cast a new handle, using the broken one as pattern but with a rebuilt ring carved in the mold.
There are some techniques I use for metal casting. Please note that metal casting is pretty dangerous. All of this is just for information. Dont’ use those techniques. I wont be responsible of any disaster that might happen if you try metal casting.
Molding is the operation that produce the mold cavity thank to a pattern.
Today, I’m asked for a spare part for a John Deere 4650. The front axle pivot was damaged by friction :
The aim is to obtain a part which will fit in the void and prevent further damage of the pin or the bore.
In order to built the mold we need a pattern. This is a part that look like the wanted one but is not made of the same material. In this case I use a two compounds silicone past that I force into the void. After it hardens, I’v got my pattern:
For economical purpose, the today’s part will share its mold with an other one. It is a replica of a casted part.Today’s patterns
A classical material for metal casting mold is silica sand (SiO2). Indeed it has many advantages, the first one : it’s refractory. But sand alone is not consistent. That’s why it is added with bounding agent. In this case it is oligo-clay and oil. This mixture becomes very constant when rammed in a flask, and can be recycled at 90%.
The two patterns are set into a flask and powdered with talc.
They are covered with sieved sand.
Ramming begins with fingers.
After the first contact layer, I add sand (no need to be sieved) and use the rammer.
This operation has to be performed in a spiral way, from sides to center. Otherwise the sand is not well rammed.
The operation is repeated until rammed sand level is higher than the flask. Then I use a flat rammer. A mallet will also do a good work.
I finish with leveling the sand with a corner iron.
The flask is turned over.
I carve the sand in order to found the parting line.
The sand is powdered with talc and the “drop” or upper flask is set up and filled with sand exactly the same way than the drag.
The the mold is opened in order to remove pattern and carve sprue, runners, gates, risers, vent holes…
The mod is blowed to remove sand grain, and closed.
After shake out, here are the parts, with ingots of exeding metal and patterns:
And finally, our John Deere is repaired.
Here is a little bibliography about metal casting. Mainly in french, it contains some english books.
- Le bronze d’art et ses techniques – J.P.Rama – Vial 2003
- Moulage et fonderie d’art – D.Lambert – Vial 2002
- Pour le fondeur d’alliages légers – H.le Breton – Dunod 1954
- Pour le fondeur (fonderie de fonte) – F.Ouvrard, H.le Breton – Dunod 1953
- Manuel pratique du fondeur de fonte – H.le Breton – Dunod 1966
- Précis de fonderie – L.Goujon – Béranger 1932
- Manuel pratique de fonderie – J.Duponchelle – Dunod 1923
- Fonderie, éléments fondamentaux – L.Giai-Brueri – Dunod 1983
- Fascicules technologiques du mouleur fondeur – G.Derouet – Librairie Delagrave 1927
- Traité pratique de fonderie – A.Lelong, E.Mairy – Béranger 1912
- Fonderie d’Art – D.Lavie
- Fonderie – L.Guillet – Ecole centrale des Arts et Manufacture
- Album de défauts de fonderie – G.Hénon – ETIF 1952
- Défauts de fonderie – F.Boussard – Dunod 1952
- Métallurgie structurale théorique – H.Cottrel – Dunod 1955
- Aide mémoire de métallurgie – R.Cazaud – Dunod 1964
- Métallurgie – C.Chaussin, G.Hilly – Dunod 1962
- La métallurgie – U.le Verrier – Société française d’édition d’art (date inconnue)
- La métallurgie artisanales – M.Séry, C.Moretti – Vial 2014
- Les chantiers du fer – G.dalstein – Serpenoise 2001
- Matériaux et produits refractaires – A.Granger – Béranger 1910
- Les matériaux réfractaires – J.Lachnitt – PUF 1983
- Making crucibles – V.Gingery – Gingery Publishing LLC 2003
- The colouring, bronzing and patination of metals – R.Hughes, M.Rowe – Thames & Hudson 1982
- La technique du modèle de fonderie – J.Masviel – Dunod 1927
- Cours de technologie d’atelier – volume 5 : modelage – A.Druot – Eyrolles 1941
- Guide du moulage – J.P.Delpech, M.A.Figueres – Eyrolles 2007
- L’art du mouleur – A.Tesson – Baudry 1897
- Etude de moulage type – H.Coste – 1951
- Iron melting cupola furnace – S.Chastain – 2000
- Small foundry furnaces – S.Chastain – 2002
- La fonderie amateur – T.Aspin – Pratiques d’atelier 2010
- Crucible furnace – D.Gingery – Gingery Publishing LLC 1988
- La pratique du cubilot – G.Joly – ETIF 1948
- Gas burners for foges, furnaces & klins – M.Porter – SkipJack press 2004
- C’est en forgeant… – R.Strozzini – Emotion primitive 2007
- Art et techniques de la forge – H.Bergland – Vial 2007
- Custom knifesmaking – T.Mc Creight – Stackpole books 1985
- The art of blacksmith – A.Bealer – Castle books 1995