Basic Know-hows about Refractory Materials

Basic Know-hows about Refractory Materials

Raw Materials and Their Distribution

Refractory minerals are used to make crucibles, saggers, pushing plates, among other kiln furniture, because they can add strength and improve chemical and slag resistance, which hence helps refractory materials to prolong their service life. Refractories products are generally divided into basic, neutral and acidic groups, based on the type of refractory environment the product has been designed for and hence the minerals used.

Minerals that we commonly use for refractories include alumina, bauxite, graphite, kaolin, magnesia and zirconium, etc. China, blessed with favorable mineral resources, is a leading producer of numerous refractory minerals.

◎Alumina

Alumina grades that we commonly utilize in manufacturing refractories are calcined, white fused and tabular alumina as well as Brown Fused Alumina (BFA), also a type of specialty calcined alumina. In general, refractory alumina are produced from Bayer alumina feedstock. Global capacity for refractory alumina is fairly balanced between Asia, Europe and North America.

◎Bauxite

Bauxite can be applied for the manufacturing of alumina, which is what it is widely used for, and for producing cement, serving as slag conditioning as well as for refractoreis. World supply of refractory-grade bauxite is fairly limited, particularly for the export market. The main producers of refractory bauxite are based in China, and the country accounts for over 85% of production. Therefore, we, as a Chinese manufacturer, are able to produce all kinds of refractories upon your request.

◎Graphite

Graphite is used in refractories as a source of carbon. We mine graphite in the form of amorphous, flake or vein graphite, which is then applies in refractory production. However, people nowadays are able to synthesize graphite in the form of electrodes from calcined petroleum needle coke, which is crushed, shaped and carbonized over a six-month period. Refractories have consumed an estimated 70% of natural graphite output. The main producer is China. We also produce graphite crucible for steel, gold melting, iron, and alumina, etc., with a steady supply of natural graphite.

◎Magnesia

Magnesia is produced in three forms: caustic calcined (CCM), dead burned (DBM) and fused (FM). The latter two are commonly used as the raw materials for refractories. DBM and FM grades are typically used in basic refractories combined with graphite, dolomite, alumina, or chrome during manufacturing. Asia has been the largest producer (principally from China). Europe has also accounted for a significant amount of refractory magnesia production. Almost all DBM and FM produced have been consumed for refractories, although some output of FM is used in electrical-grade magnesia (EGM) for heating elements.

◎Kaolin

Kaolin is typically used in neutral or acid refractories as an aluminosilicate source, where alumina levels of 30-70% are required. Keep it in mind that when an alumina content of above 70% is desired, bauxite and specialty calcined aluminas are more suitable.The U.S. has been the world’s largest kaolin producer, and China is also a leading contributor to world kaolin production.

◎Zirconium

Zirconium can be used in a variety of refractory products, mainly in the form of zircon, zirconia or alumina-zirconia-silica. Zircon is generally used in acidic refractory environments, while zirconia-based refractories are considered to be basic.

Different Kilns

Kilns are insulated chambers that use fuel or electricity to reach high temperatures for firing or melting some products of high temperature resistance. There are different types of kiln to fire different materials. For example, there are kilns designed specifically for ceramics, glass, metal, brick, metal clay, and enamels. As a long-standing company, our company is ready to provide a wide span of refractories for different kilns.

◎Contemporary Types of Kiln

Kilns have been used for over thousands of years and gradually people have developed the following types of kilns that are more commonly used nowadays.

Broadly speaking we can classify kilns that are used by modern potters in two broad ways. The first one is based on how the kiln is heated. Some kilns are heated by electricity while Other kilns are heated by burning fuel, known as fuel-burning kilns. The fuel used are combustible materials includingnatural gas, propane, wood, and sawdust, etc.

The other distinction is whether a kiln is continuous or intermittent. Most smaller kilns are intermittent or periodic kilns, mainly used by individual potters. These kilns are loaded with ware, turned on, heated, allowed to cool, and then unloaded. By contrast, continuous kilns stay on. The ware is loaded onto a moving platform and travels through one side of the kiln and out the other. The kiln stays hot and the ware cools as it leaves the kiln. These kilns are more typical of commercial or industrial settings where very large amounts of ceramics are being made.

◎Gas Kilns

Gas kilns use either natural gas or propane. The kiln consists of a chamber that is insulated with fire bricks. Heat is introduced to the chamber by burner ports at the base of the kiln. Burner ports are basically opening through which lit gas passes. Gas kilns either have an updraft or a downdraft design.

◎Electric Kilns

Electric kilns are more recenlty develped and more and more favored.They are especially popular amongst hobby potters, and small scale pottery and ceramics outfits.

◎Raku Kilns

Raku is a particular approach to firing, which involves removing the pottery from the kiln when it is red hot. The pottery is then put in a closed container of some kind, along with some combustible material like paper. The combustible material burns when it makes contact with the hot ware.

Because the fire is happening in a closed container, a reduction atmosphere is formed. This creates certain characteristic raku effects on the pottery glaze. The container can be as simple as an inverted steel bucket. Just as long as it can withstand the heat from the pottery and flames. Mostly raku is made in gas-burning kilns. A common choice for raku is propane gas. Raku kilns come in all shapes and sizes.

◎ Car Kilns

Some types of kiln have a static base. With these kilns, the door is positioned on the base and locked in place. The chamber of the kiln is static, and the base of the kiln moves. And the ware travels through the kiln on a car. Some car kilns are huge industrial-sized kilns, known as tunnel kilns.