A smelting pot is the container used to melt ore and other ingredients into a liquid that can be poured into molds to be given a working shape. Commonly created from very heavy cast iron and lined with brick, ceramic tile or some other type of heat barrier, the pot is able to withstand extreme heat for many smelting cycles without burning through or weakening. Heated in various matters, the smelting pot is often hung from large lugs cast into the sides of the pot. These lugs provide a tipping location that allows the pot to be tilted and poured. The pots often include a heavy lid or cover to aid in the fast heating of the contents.
Some of the smaller smelting pot designs are placed on or above a heating element to melt the contents. Commonly an electric or natural gas heating element will be used to bring the pot up to temperature. Some very small, single-use pots are simply placed on a small burner and heated until the contents can be poured into a sand mold. When using this type of pot, it is extremely critical that no water be in the vicinity of the smelting pot. One drop of water into a very hot pot of molten metal can cause the pot to explode and empty itself on everything and anyone in the vicinity.
Larger, industrial-size designs use a number of methods of heating the contents with electricity in one form or another being the method of choice for many pots. One design uses a coiled electric element to create the required heat to allow the smelting to be accomplished. Alternating electric current (AC) is applied to the heating coils, which begin to heat similar to an element in an electric kitchen oven. Many of these electric-powered smelting pot assemblies use a water-cooled design to eliminate overheating of the heating element.
The most common type of smelting pot in large industrial operations uses carbon rods charged by electric current to create super-high temperatures similar to a carbon arc torch or welder. The carbon rods create heat to the contents of the pot, creating a molten liquid that must have impurities skimmed from the top of the liquid metal prior to pouring the material into a mold. Limestone is commonly added to molten iron to bring the impurities to the surface. Workers use long steel ladles to pull the impurities from the top of the molten liquid.
What Are Smelting Pots Made Of?
Smelting pots can be made up of several different materials and often consist of multiple layers. The key part of designing a smelting pot is that it has to be able to withstand extremely high temperatures from both inside and outside the pot. Today, the most common material used to form the outer layer of these pots is heavy cast iron. In the past, some smelting pots were made of thick clay, but these ceramic pots did not last as long and would at times burst during the smelting process causing serious injury to the smelters. There have also been bone smelting pots discovered at archaeological digs, but again, bone pots would not have been as durable as the cast iron ones of today.
The second layer, the inner layer of the pot, is usually made of brick or ceramic tiles. Brick and certain ceramic tile can usually withstand the temperatures of the molten liquids created in the smelting process better than the cast iron alone can withstand them. Basically, the inner layer acts as a heat barrier for the smelting pot itself. The inner layer has to be replaced fairly often as it gets worn away and melted over time. The tighter fit the inner layer is, the better its endurance to the liquified metals. Any cracks or spacing weaken the barrier and allow the extremely hot liquid metals to access the cast iron pot and could begin to melt the pot in the same fashion.
How Hot Does a Smelting Pot Get?
Smelting pots reach different temperatures based on the metal that is being smelted at the time. To figure out the heat required for a smelting pot, one must first determine the metal to be smelted and its melting point. For example, the melting point of nickel is around 2651 °F. This is one of the highest melting points that can be smelted as it is difficult to maintain that temperature without breaking the pot itself. Lead smelting is much easier as it has one of the lower metal melting points at 621.5 °F. Here is a list of some of the more commonly smelted materials and their melting points.
Once a person knows the melting point of the ore needed to create the metal, then in the smelting process, that ore needs to be heated beyond that melting point. This means that the smelted metal and the smelting pot will reach temperatures that are even higher than the known melting point.
Melting point temperatures vary greatly from metal to metal, but the bottom line is that they are all too hot for the human hand to safely touch. Protective equipment is a must when smelting due to these high temperatures and the chemical process of smelting itself. Briefly touching bare skin to a smelting pot or the molten ore inside can immediately lead to third, fourth, fifth, and even sixth-degree burns depending on how long the exposure is. Even a few seconds of direct contact could be enough to kill a person. For this reason, thick leather gloves, leather aprons, and specialized grasping instruments are necessary. Wearing eye goggles and heavy masks to protect from accidental splashes as well as the toxic fumes sometimes produced is also incredibly important.
What Is the Difference Between Melting and Smelting?
Though the words differ by only one letter, the processes of melting and smelting are entirely different. Melting is the process of anything solid converting into a liquid. Smelting, on the other hand, is the process of heating ore to very high temperatures in order to melt it and obtain the purest form of metal from it. Melting can apply to a variety of materials as well including metals, while smelting only works for metals. Smelting requires temperatures beyond the simple melting points for each different metal whereas the melting process takes place at the exact melting point of that metal.
In some ways, smelting can be thought of as a purer melting process for metals. Smelting takes the original ore and refines it and melts it down to form the most genuine substance possible. Melting simply changes the state of the substance though and does not necessarily remove any impurities that might be present in the material. Melting also only takes one step, as the molecules of a solid substance loosen to become a liquid form of that same substance. Smelting requires at least two distinct steps: the roasting or heating step to liquefy the ore and the reducing step to remove the excess oxygen and purify the metal.