All cast and forged aluminium must be heat treated following casting or forging to give final strength and hardness to the material. The exact process varies between Cast and Forged, but broadly there are two stages to the treatment.
The cast or forged piece is heated to around 900degF for 9-10 hours. This causes the copper in the aluminium alloy to dissolve into the aluminium, creating a what is called a “Single Phase Alloy.” The piece is then cooled rapidly by “quenching” it in water, which prevents the copper reconstituting within the alloy, thus keeping the alloy “locked” in the “Single Phase Alloy” state.Ageing Phase
Following quenching, the piece is heated to a relatively low temperature – around 350degF – for 10 hours, then allowed to cool slowly in air. During this phase, the copper and alumnium (which were thoroughly dissolved and “locked” together in the Quenching Phase) combine to form copper aluminium crystals, CuAl2. It is these crystals that give the alloy (and the piece) it’s strength.
The tricky part is to control the size of the CuAl2 crystals. For best results, the crystals are kept very small to ensure conformity within the cystal structure of the alumnium. Crystal size is carefully controlled by heating and cooling temperatures and times to give the highest strength possible from the treatment.
All our cast and forged trucks use the T-6 process to add strength to the raw aluminium.
Gravity casting is quite different to Die (Pressure) Casting used by many longboard truck manufacturers. It is more expensive to produce as fewer trucks can be made on a “tree” (which is why Sabre Cast trucks cost more), but allows the use of stronger aluminium alloys, with fewer air bubbles. The result is a stronger, less brittle finished truck.
Molten Aluminium is hand-poured into the mould – as opposed to die casting where molten metal is injected into the mould at high pressure. The mould is then inverted, allowing the pull of gravity to fill the mould cavities with molten metal. The end result is a strong, consistent cast right through the truck.
Gravity cast skateboard trucks can be cast using sand moulds (“Sand Casting”) or heat-treated steel moulds. We use Steel Moulds – a more expensive option, but we feel the precision finish that is attained is worth the extra cost. Areas that require high tolerances (pivots, kingpin holes, hanger faces etc) are CNC’d to give a precise fitting prior to heat treatment.
Gravity casting allows us to use 356 aluminium, not ADC10 or ADC 12, or 356 that has been “diluted” with ADC to reduce the viscosity of the aluminium for die casting (Commonly called “356.2″).
We use Gravity Cast 356 Aluminium in Precision Steel Moulds for our “GC” components because it is the process that gives us the best balance of strength and precision.