Most of the free weights are made of iron.
Cast iron is moulded by pouring the liquid iron into a moulding sand to form it and allowing it to cool down. The sort of iron used is regarded to as cast iron, explicitly constructed for this reason for its low melting temperature, i.e., you do not need to warm this as much as other iron forms to convert it into liquid.
The plates are then coloured, and the paint is ideally put in the oven. This stiffens the exterior, protecting it from chipping and scratching.
Milled Weight Plates
Machined or milled Olympic weight plates are made using the cast iron technique as above. But they are slightly larger than the required sizes.
The step two for milled plates is when the machine grinds them down on the corners and faces, helping to bring the sizes and weight to the specifics. The moulds have to be remodelled after a certain number of castings have been done, resulting to discrepancies among runs. The milling process is to ensure that, despite discrepancies in the mould, you have the same shape and size of the plate.
Machining also has the advantage of eliminating flaws on the face of the weight plate, softening them out, like grinding away the unavoidable seams on cast-iron moulds. Without grinding, you can still see the seams on cast-iron goods, since the upper half of the mould must be closed over the base to hold the molten iron and enable the plates to be extracted until pressed.
With this method, the machined plates can be fairly assured to be less than 2 per cent of the weight indicated, plus or minus. Most are well below 1 per cent, but suppliers usually guarantee within 2%, so that the vast majority of plates fall within it and do not incur cost of repairs for plates not conforming to standards.
How Bumper Plates are Made
Bumpers are sturdy rubber plates with a centrally shaped iron core to cover the middle hole. They are designed for the falls from as far as overhead, for the clean-and-jark and snatch, for the 2 Olympic lifts at the weightlifting events, the Cross Fit Games and the Olympic Games.
Next, the fresh rubber is refined into a smooth consistency and cut into disks slightly larger than the wheels. The rubber is put in a mould that contains a steel core. The machine heats and condenses the rubber disk to the appropriate size defined. It’s just as plain as that!
The only move from there is to chill and check the bumper.
Some vendors use the mower anchoring method instead of simply pressing the rubber around it, which stops the mower from loosening up.
Urethane or Rubber Coated Plates
They are made of cast iron, the same as standard plates of iron. They have a urethane or rubber coating instead of finishing with a baked-on paint job. Rubber coatings appear to be thin, whereas urethane is more costly and can be a very dense coating instead of a thin coating.
These are never to be mistaken with bumper plates (previous section), which are mainly rubber and not just rubber covered. And thickly wrapped urethane plates should not be released like bumper plates, or the plate, barbell, or floor can be destroyed.