Grinding wheels are classified largely by the bonding agent that holds the abrasive grains together, and each bond type has its own hardening/curing process. This question concerns the silicate bond.

Silicate-bonded wheels are made as follows:

• Abrasive grains (e.g., aluminium oxide) are thoroughly mixed with sodium silicate (water glass) which acts as the bond.
• The mix is packed and moulded (tamped) into the required wheel shape.
• The moulded wheel is dried to drive off moisture and is then baked/fired at a moderate temperature (roughly 250–300°C) for many hours. This controlled firing sets and hardens the silicate bond into a rigid but relatively mild-acting matrix.

Because the bond is not fully vitrified, silicate wheels are comparatively soft-acting and release grains readily, making them useful where a cool cutting action is needed (for example, grinding edge tools without burning them). Hence the correct method is controlled firing at moderate temperature.

Why the other choices are wrong: low-temperature drying without any firing would leave the sodium-silicate bond weak and incompletely set — firing is essential to harden it. Chemical polymerization at room temperature describes the curing of resinoid (bakelite/phenolic) bonds, not silicate bonds. High-pressure forging of abrasive particles is not a wheel-making route at all — abrasive wheels are moulded and bonded, never forged like metal.