Heat, smoke and molten metal
The product we’re currently working on features custom metal components, which has allowed me to brush up on my metallurgy. From raw shaping to surface treatment, all aspects come into play, and forms a nice break from the usual polymers.
One of the metal components is used to contain X-rays, which makes the choice of material, as well as proper process control, paramount. Steel for example blocks radiation quite well and is relatively easy to process, but you require a thick wall to block the radiation. Bronze is more efficient at blocking X-rays, but has a higher viscosity during casting compared to steel and foundries consider it a more exotic material to work with.
Casting defects such as blowholes will locally reduce the wall thickness and form a potential radiation leak. Thus these defects need to be controlled and compensated for.
One could ask: why not simply apply a lead lining if one wants to block X-rays? ROHS compliancy prevents such extensive use of lead, not to mention that applying the radiation blocking layer would be completely reliant on the quality of assembly – the latter is quite a risk, not to mention labour intensive.
Other components are oil-filled sand casted aluminium parts. Surface quality and treatment are a bit of an issue however with this (cheap) production method. The sand casting process is a manual process, so each product will be unique with its own slight blemishes. Vibratory finishes followed by sand blasting and/or glass bead blasting will aid in smoothing the surface, but may not be sufficient. Electroless nickel or galvanised chrome may be used to harden the surface and make it scratch resistant, but their cosmetic effect is limited. Unfortunately anodising for a decorative effect is not an option with sand-casted components, as it will lead to a blotchy surface. All-in-all it’s quite the learning experience.
Today I’ve been lucky enough to receive a tour of the foundry here at Non-Ferro Gieterij Oldenzaal (after reviewing samples), which has both a modern and a more traditional workshop. Out of all metal manufacturing processes I have to say that sand casting has got to be my favourite one. The process is just so raw, pure and tough. All one needs is sand as mould material held together by some wooden planks: in goes the molten metal, and out comes the desired shape. All accompanied by intense heat, sparks, smoke, and the fiery smell of burning metal that will linger in your clothes and skin for days on end: it’s awesome. 🙂