Originally carried out entirely by hand, the production is nowadays entrusted to a range of machines which have automated the various stages of the job, from the muller (or batch mixer) for the preparation of the sand, right up to the movement of the finished castings.
Sand castings are made using expendable moulds, hence each mould is used only once and is destroyed at the end of the process when the finished casting is extracted.
Roldo produces castings based on patterns supplied by the customers, with whom there is a 360° collaboration. A continuous dialogue with the clients is the key to satisfying their requirements within the fastest possible timeframe.
The company uses permanent patterns made of wood, metal or plastic, but if the customer supplies only the drawings, it relies on trusted partners who will produce the patterns.
Any eventual modifications are in any case feasible simply by contacting the company to work out the best deal for the production of the desired sand castings.
Over the years the staff has perfected the preparation process, which is done by hand and which envisages various phases. Once positioned the pattern and placed the clamps, the pre-prepared sand is introduced and then compressed. Then the air vents are prepared, the mould is closed up and the pattern is extracted.
Given the delicacy of the extraction process, and the danger that if it is done incorrectly can cause damage to the mould, the team removes the dust from the surface of the pattern with lycopodium flash dust, a white insulating powder which acts as a separator.
In cases where cavities are required inside the casting, the process workers place cores in the correct locations and move the clamps on to the next section. Once the mould structure has been finalized, the risers are put in place and the tapping runners assembled in such a way that the spaces inside the mould are filled in the correct direction and speed. Then it’s the turn of the ladle, the pouring header funnel (which receives the molten metal) and the ducts through which the metal flows into the mould.
Then the pouring begins where the molten metal flows from the crucible into the mould. Once the metal has been poured, it is given time to solidify – which in the case of aluminium is not very long -and once this has happened, the moulds can be unclamped and the casting extracted.
Once they have cooled, the castings are transferred to the finishing department for the removal of sprues, runners and any eventual flashing.
Shell castings are made from permanent moulds which are made from alloys and – in contrast to sand casting – can be re-used many times before they have to be replaced. For this reason, shell casting lends itself to series production (generally of small to medium size items) while sand casting is preferable for larger pieces produced in smaller numbers. Shell moulds are usually made from steel or cast iron, and due to the absence of sand in the mould-making process, the resulting castings have a smoother and more uniform surface as compared to sand castings.
Just like for sand castings, shell castings pass through the finishing department, where any excess metal is removed, even though – given the uniformity of the surfaces of these castings – the process is much simpler and quicker than for sand castings.
Depending on the customer’s requirements the castings can be delivered in either finished or unfinished form. In the first case, the “cleaning” of the casting takes place internally. In addition to sandblasting and grinding off, there is also a shotblasting option to smooth casting surfaces off.
For customers who would prefer “reworked” castings, this service is provided thanks to the long-standing partnership with local precision engineering companies. By working closely with companies in the immediate area, delivery times can be brought down even for reworked pieces, thus making customers life much simpler.
Further to aluminium we also produce brass and bronze castings for both industrial and artistic applications. In the past, on commission, we have also ventured into casting cast iron and lead, the latter being used in the production of keels for small boats.
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