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Showing posts with label Monolithic refractories. Show all posts
Showing posts with label Monolithic refractories. Show all posts

Benefits of using Steel Fibers and Organic Fibers in Refractory Castables and Monolithics

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One of the most effective ways of improving the mechanical and thermal properties of refractory castables and other monolithic refractories is adding in suitable proportions of stainless steel fibers (SS) and organic fibers to the castable respectively.

Steel Fibers
Steel fiber reinforced refractory castables are very resistant to the tendency of the material to fall apart on thermal cycling. Stainless steel fibers greatly improve the flexural strength of the castable. And this added increase in ductility contributes significantly to the thermal shock and spalling resistance of the material. The fibers generally used are in size varying between 0.1 to 0.4 mm2 in cross-section & 20-40 mm in length. For monolithic SS is used either high chrome or high chrome nickel steels available in the market with different grades. One reason commonly reported that the thermal shock resistance of castables is greatly increased through addition of SS fibers because these fibers act as crack arresters, preventing cracks propagating. This is also possible that the microcracks caused by a mismatch in thermal expansion coefficients of matrix and fibers dissipate energy from larger cracks propagating as a result of thermal stress. However percentage of these fibers added becomes important because of two reasons as it has a direct impact on the fluidity of the castable, then it may also cause mixing difficult due to fiber-balling when added beyond 3% by volume. Another critical factor will be the maximum application temperature for the castable that those fibers present in the castable can resist oxidation (since these fibers can not perform beyond their melting temperature).

Organic Fibers

An effective means for improving the explosive spalling resistance of a castable is to add organic fibers to the formulation. It has been reported that the composition & concentration of fibers are not as important as melting temperature of the fiber, since these fibers after melting increase permeability at certain temp. & thereby reducing the explosive spalling tendency of the castables. The fibers generally used for this purpose are Polypropylene fibers, Polyester staple fibers, etc.

Here is one reference (work) of benefits of using refractory composition containing both stainless steel fibers and organic fibers. Because of these different advantages it have been found that both organic and SS fiber reinforced refractory castables provide substantial increase in service life and therefore, a considerable reduction in refractory maintenance cost and furnace down-time.
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Nomenclatures and Terminologies of Monolithic Refractory Products based on their setting or installation methods

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The following terminologies which have been given for different type of Monolithic Refractory products are based on and therefore, can be related to their lining process or installation methods. Read our previous article

Castables

These are dry mix hydraulic compositions of graded refractory aggregates with a suitable bonding material, Fillers & (/or) special Additives. On addition of the prescribed quantity of water to these compositions, a wet concrete-like mass is produced which forms useful castables. Ceramic bond is developed when the same is fired at a certain high temperature.
Type of Castables -

  • Conventional Castable.
  • Low Cement Castables (LCC).
  • Ultra Low Cement Castable (ULCC).
  • No Cement Castable (NCC).
  • Light Weight Castables.
  • Self Flow Castables (SFC).
  • Insulating Castable.

Coating Mass

These are the Refractory materials especially made for coating on the working surface of the lining having a thin thickness.

Fettling Mass

It is a material which is deposited on the worn out areas of banks and bottom of Electric Arc Furnace (EAF) in hot condition. These are normally applied by shoveling and by using a Fettling Machine.

Gunning Compound or Gunning Mass

Gunning Masses are also unshaped refractory materials (Products) made after blending graded refractory grains with suitable bonding agents and are installed with a Gunning Machine.

Type of Gunning Compounds -

  • Dry Gunning
  • Shortcreting
  • Flame Gunning

Injection Mass

These are the refractory materials that can be injected into a furnace in the slurry state.

Mortar

Powdered or finely ground refractory preparation which becomes plastic and trowel able when tempered with water and is suitable for laying and bonding refractory bricks.

Patching Mass

These are powdered refractory materials mixed with water and/or added with a binder, and with adequate plasticity that can be patched in a place.

Plastic Refractories / Mass / Plastics

Refractory materials tempered with water and/or added with a binder, which has adequate plasticity to be rammed into a place.

Ramming Mass

Ramming Masses are the ready-mix of refractory materials usually tempered with water, that can not be extruded but that has suitable properties to permit ramming into a place to form a monolithic structure.

Type of Ramming Masses -

  • Dry Ramming Mass
  • Wet Ramming Mass

Spraying Mass

These are refractory mix consisting of fines and additives which are installed with a Spraying Machine (can also be applied with a Gunning Machine).

Related articles

Type of Monolithic Refractories - Monolithic Refractory Products

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What are Monolithic Refractories?

Monolithic refractories or Monolithics are those, which have no definite shape. In other words these are the refractories which can be moulded or can be given any shape as per requirement. Because of this reason, these products are also known as the ready-refractories and can be used as such on the site to repair or build a furnace. Monolithics consists of graded Refractory aggregates, Binders, Fillers & (/or) special Additives for modification of properties.

Type or Classification of Monolithics:

The classification and nomenclatures of monolithics have been done on the basis of more than a single criterion.

Based on Physical State

1. Powdered state - Castable, Mortar and Ramming Mass.
2. Mud state - Plastics.
3. Paste state - Coating Mass.

Based on Setting Method

1. Hydraulic setting - Castables.
2. Air setting - Mortars, Plastics.
3. Chemical setting - Plastics, Ramming Masses.
4. Ceramic (Heat) setting - Mortars, Plastics, Ramming Masses.

Based on Installation Method

1. Trawling and Pouring - Castable, Mortar.
2. Ramming - Ramming Mass.
3. Gunning - Gunning compound, Castable.
4. Vibrating - Castables.

The Terminologies of the different type of Monolithic Refractories will be discussed in another article: