Types of Carbon Enhancers

There are many materials that can be used as carburizers for cast iron, including artificial graphite, calcined petroleum coke, natural graphite, coke, anthracite, and mixtures made from these materials.
1. Artificial graphite
Among the various carbonization agents mentioned above, the best quality is artificial graphite.
The main raw material for manufacturing artificial graphite is high-quality calcined petroleum coke in powder form, in which asphalt is added as a binder, and a small amount of other auxiliary materials are added. After various raw materials are mixed together, they are pressed into shape and then treated in a non oxidizing atmosphere at 2500-3000 ℃ to graphitize them. After high-temperature treatment, the ash content, sulfur content, and gas content are significantly reduced.
Due to the high cost of artificial graphite products, most of the artificial graphite carburizers commonly used in foundries are recycled materials such as chips, waste electrodes, and graphite blocks from the manufacturing of graphite electrodes, in order to reduce production costs.
When melting ductile iron, artificial graphite is the preferred carbon additive for improving the metallurgical quality of the cast iron.
2. Petroleum coke
Petroleum coke is currently a widely used carbon additive.
Petroleum coke is a by-product obtained from refining crude oil. Crude oil is often subjected to pressure distillation or vacuum distillation to obtain residual oil and petroleum asphalt, which can be used as raw materials for manufacturing petroleum coke. After coking, raw petroleum coke is obtained. The production of raw petroleum coke is less than 5% of the amount of crude oil used. The annual production of petroleum coke in the United States is about 30 million tons. The impurities in raw petroleum coke are high and cannot be directly used as a carbonization agent. It must first undergo calcination treatment.
There are various types of petroleum coke, including sponge like, needle like, granular, and fluidized.
Sponge like petroleum coke is produced by delayed coking method. Due to its high sulfur and metal content, it is usually used as fuel during calcination and can also be used as a raw material for calcining petroleum coke. Calcined sponge coke is mainly used in the aluminum industry and as a carbon additive.
Needle shaped petroleum coke is produced by delayed coking method using raw materials with high aromatic hydrocarbon content and low impurity content. This type of coke has a needle like structure that is easily broken, sometimes referred to as graphite coke, and is mainly used to manufacture graphite electrodes after calcination.
Granular petroleum coke is in the form of hard particles and is obtained by delayed coking method from raw materials with high sulfur and asphaltene content. It is mainly used as fuel.
Fluid petroleum coke is produced by continuous coking method in a fluidized bed, with fine particles, non directional structure, high sulfur content, and low volatile matter.
The calcination of petroleum coke is to remove sulfur, moisture, and volatile components. Calcining raw petroleum coke at 1200-1350 ℃ can turn it into essentially pure carbon.
The largest user of calcined petroleum coke is the aluminum industry, with 70% used to manufacture anodes for reducing bauxite. Approximately 6% of calcined petroleum coke produced in the United States is used as a carbon additive for cast iron.
3. Natural graphite
Natural graphite can be divided into two types: flake graphite and microcrystalline graphite.
Microcrystalline graphite has a high ash content and is generally not used as a carbonization agent for cast iron.There are many varieties of flake graphite: high carbon flake graphite needs to be extracted by chemical methods, or heated to high temperatures to decompose and evaporate the oxides in it. This type of flake graphite has low production and high price, and is generally not used as a carbon enhancer; Low carbon flake graphite has a high ash content and is not suitable for use as a carbonization agent; The main carbon additive used is medium carbon graphite, but the amount used is also not large.
4. Coke and smokeless coal
During the process of electric arc furnace steelmaking, coke or anthracite can be added as a carbonization agent during the loading process. Due to its high ash and volatile content, induction furnace melting of cast iron is rarely used as a carburizer.
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