Use of Graphite in Refractory: Burning or using

 Graphite is a natural limited resources. Because of its unique properties like flaky nature, non wettability with liquid metal and high thermal conductivity along the axis, used in Refractory. Anti oxidant is used along with graphite during manufacturing of refractory to take care of oxidation. But a portion of graphite is burned in the furnace, which can be avoided.

Graphite or Carbon is used largely together with silicon carbide in ramming masses and castables. The function of carbon is prevent premature oxidation of silicon carbide in these refractory products. Depending the time and temperature the carbon is oxidized resting only the SiC to protect the product . If SiC is also oxided then we will have erosoin or ling wear. In consequency the life will be shorted.

Natural graphite consisting of clay material is utilized for the production of refractory blocks, crucibles,sheaths,high temperature lubricant and it is also used as a lining material for ramming the tapholes,and the colloidal graphite is used as mould release compound in foundary practice. Besides which it is also used as reductant for the reduction of metal oxides to produce metals which means it is useful during burning also. In recent years there have been efforts to increase the oxidation resistance of graphite by the addition of anti-oxidants to the surface graphite particles. As against the natural graphite the synthetic and pyrolytic graphite are very pure and highly crystalline substances and because of their outstanding high temperature thermal, electrical conductivity and high thermal strength they are used used in specialised applications such as electrical commutation, spectral elecrodes, heating element,high purity crucibles,thermal seals, metal matrix composites.  

Improvement of refractory life and performance

Improve your Refractory Life and Performance by following 3 steps

Nothing counts like the 'performance'. Getting or giving a better performance is one thing which everyone tries to do. Reasons obvious! For getting better performance of refractories from an installation (lining) i.e. an improved refractory life, one must take care of the following three simple but very important things:

1. Proper Selection of Refractories.
2. Proper Installation - Laying of Refractory Bricks.
3. Proper Operation Practice.

Selection of Refractories

Though there are specific refractories for different applications, operation practices lead to certain criteria on which, depends the refractory life. As such these need to be properly considered. Customers should disclose the actual operating practices and conditions so that some important properties, required to such conditions can be taken care during the selection of refractories as well as during the manufacturing stage of such refractory bricks, castables, and mortars. Among various physical, chemical, thermo-chemical and thermo-mechanical properties of Refractories, there are a few properties which can change significantly performance of refractories. These are called Key Properties. For ensuring better performance, quality and of course, refractory life these key properties should be tested.

Installation - Laying of Refractory Bricks

Depending on the method of application or installation there has to be a set of guidelines in respect to laying of refractory bricks, their dimensions, selection of mortars, expansion joints and many other minute but very important things. So from case to case basis the supplier of refractories should specify this properly and also ensure that the methods are actually being followed. Transportation, handling, timely arrival of refractory bricks, mortars, skill of masonry work, proper equipment for application e.g. mixer machine for castable, vibrator for installation, forma etc. are very important. Maintaining proper expansion gaps, correct dimension (size) of bricks and monolithics, fixing anchors etc. all are very important to achieve better life of refractories. Once the laying job and other installation of refractories are over, the initial heating of the lining before starting the actual operation is of prime importance. Customers should demand the initial heating schedule from the refractory supplier.

Operational Practices

Proper operation is not only important for getting right quality output but also, help in getting the optimum refractory life, less downtime, maximum availability of the furnace and thus, the benefit of lower cost of refractories per tone of finished product. Customers must be aware of the reasons which can damage the refractories arising because of improper operations. During the training of the furnace operators, apart from the method of the furnace operation etc. they must be given some knowledge regarding the proper usage and importance of refractories also.

how to minimize/stop the erosion in high alumina bottom pouring sets, without much cost increase.

One can try magnesia - carbon refractory coating over the high alumina bottom pouring sets. The coating can be applied using carbonaceous adhesives.

Using BP set manufactured by small companies then probable cause of this erosion can be lower alumina content than specified or using a low melting clay as binder to reduce firing temperature. Total alumina can be checked by sending sample to any reputed lab for chemical testing. However for checking low melting matrix, you have to test hot MOR or RUL property of the sample. In case of low melting matrix, it will fuse at steel temperature and will not hold the grains, so more erosion. So buy only from manufacturers who have high temperature kilns to make fire proper grade of BP sets.

 Reduced oxygen content in the steel will be better for the refractories. I recall a case where the customer "killed" the steel in the ladle with some aluminum prior to casting. It is costly to measure oxygen but will give good information if you can do this.