Which Carbide Do I Need?

At Carbide Industries, calcium carbide production in different sizes (grades) is all we do. Generally speaking, the different grades of carbide that we make correspond to different reactivities of the carbide. For example, we produce fast-acting carbide powder that is injected into molten iron to combine with and remove sulfur. We also supply carbide in a slower-reacting nut size to add to the stream of molten metal when the steelmaking furnace is tapped. The carbide reduces oxides and returns iron and metal alloys to the steel that would otherwise be trapped in the slag, but does not react so fast that the steel overflows its ladle.

The best way to choose which grade you need is to contact us. Our industry experts have decades of experience specifying carbide grades for different applications and optimizing processes in many industries.

Carbide for Metallurgy

Calcium carbide is a powerful and effective chemical reducing agent, and can also be used as a source of energy. Nowhere is this more evident than in the field of metallurgy, where it is used in several ways to reduce costs.

In modern steelmaking operations, the need for lower sulfur steels demanded by modern continuous casting operations and specialty applications has increased calcium carbide's appeal as a hot metal desulfurizer or as a modifier to the slag to increase desulfurization efficiency.

In addition, the reaction of carbide with oxides produces a large amount of heat that is highly retained in the process. This has efficiency implications for ladle metallurgy, but moreover carbide provides major cost savings as a source of energy and productivity improvement in the steelmaking furnace.

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Carbide for Chemistry

Calcium carbide is converted into acetylene in a controlled reaction with water using an apparatus called a generator. Acetylene, which has the chemical formula C2H2, is an extremely useful hydrocarbon due to the energy that is locked up in the triple-bond between the carbon atoms. This energy is then released and utilized in different ways by our customers for a variety of industrial purposes.

An acetylene cylinder for cutting and welding purposes is perhaps the most recognizable use, but many important chemicals are derived from acetylene.

When carbide is reacted with water to produce acetylene, it produces calcium hydroxide, itself a useful chemical. Having a pH of 12.4 and a ready reactivity with sulfur, it is widely used for acid neutralization, pH modification of soil, and for the cleaning of sulfur emissions from industrial processes and power generators.

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Desulfurization (direct)

In modern steelmaking operations, the need for lower sulfur steels demanded by modern continuous casting operations and specialty applications has increased calcium carbide's appeal as a hot metal desulfurizer.

As late as 2002, most blast furnace iron was desulfurized in the torpedo car as shown above. In the integrated steel mill, this practice has now been largely replaced by the use magnesium to remove an initial amount of sulfur in the transfer ladle, and the use of carbide as a steel ladle deoxidizer and slag conditioner to obtain the final sulfur specification.

In ductile iron foundries, liquid iron must be desulfurized before specialized inoculation treatments can be employed. This desulfurization is frequently performed by feeding granular forms of calcium carbide onto the surface of the liquid iron, which is contained in specially designed mixing units.

Purity and particle size are the key parameters for optimum effectiveness in these applications. Particle sizing is carefully selected to provide maximum contact with carbide particles without incurring excessive dust losses.

Carbide Industries manufactures three standard sized products for ductile iron desulfurization, generally within the range of 8 to 80 US-mesh (2.5 to 0.2 mm). In addition, two patented specialty products are available to meet specific customer requirements. These specialized products are formulated to help eliminate the retention of unreacted carbide in the resulting desulfurization slags and also to minimize slag odor.

For subsurface injection, a powdered carbide is manufactured by ball milling selected sizes of carbide to less than 140 US-mesh (<105 microns). The milled carbide can then be custom blended with a wide range of other powder additives, such as lime, limestone, and fluorspar to meet customer specified formulations. The milled carbide is treated with special additives to significantly improve flow characteristics.

Because of their reactivity, calcium carbide powders are manufactured, mixed, loaded, and transported in either 20 ton pressure differential trailers or 90 ton railcars, under an inert nitrogen atmosphere.

Slag Conditioning

Carbide is an essential tool for the removal of unwanted iron oxide from furnace slag that is carried into the ladle during tapping. When added to the liquid metal stream, or to the ladle after tapping, a coarser grained carbide reacts with the oxides and recovers iron and expensive alloys that otherwise would have been lost. Furthermore, left untreated, these oxides can interfere with the downstream steel refining operation by inhibiting desulfurization, oxidizing ("fading") alloy additions, and attacking refractories.

Although aluminum, ferrosilicon, silicon carbide, and even coke have also been used for this purpose, calcium carbide has proven to be more economical, more efficient, and more reproducible in its effects. This is due to the fact that unlike the other materials, calcium carbide produces CO gas which uniformly distributes and mixes the carbide while foaming the slag; does not require a balancing lime addition as do silicon-based additives (in fact every pound of carbide adds about one pound of lime); reacts exothermically (producing heat) to not chill the slag; and under typical conditions does not dissolve in steel producing practically no carbon pick-up, no unexpected deoxidation, and nearly 100% utilization.

For this application, Carbide Industries can provide the grade size of calcium carbide that best meets the requirements of a particular application. Standard sizes range from 0.5" x 0.25" (13 mm x 6.5 mm) to 10 x 40 US-mesh (2 mm x 0.4 mm). For increased ease of application, these grades are available in smaller 2 1/2 and 5 gallon containers, in addition to the conventional 55 gallon drums and 2.5 ton bulk flo-bin containers.

In every case, consistent carbide purity and sizing are of special importance, especially with respect to oversize and fines.

Furnace Injection

Carbide has the unique ability to react only with metal oxides without adversely affecting steel chemistry, adding significant amounts of energy to the process. In the electric arc furnace (EAF) the energy produced during the oxide reduction is accompanied by the production of heated lime particles and CO gas which assist in retaining the heat generated while adding to the ability of EAF slags to foam.

In addition, since most of the slag that is generated in the EAF is not tapped into the ladle, all of the benefits of oxide reduction and alloy recovery that are well-known in ladle metallurgy are available to the EAF on a much larger scale.

The result is a much more energy-efficient, faster, higher yield, and higher alloy recovery EAF process.

For furnace injection, Carbide Industries produces carbide in a size range suitable for pneumatic transport to the furnace, where it is blown into the furnace with inert gas. Carbon injection ports that are marketed by several companies are entirely suitable for carbide injection. Carbide Industries LLC has also certified pneumatic equipment vendors that have the know-how to manufacture the tranport equipment. (Pictured is a MOCA pneumatic injector/transporter modified for use with calcium carbide produced by More s.r.l.)