Loka Refractories - Are you familiar with castable refractory? If not, you're in luck because this article will add to your knowledge about this material.

As discussed in the article Monolithic Refractory: Definition, Strengths, and Types, castable is a monolithic refractory that mixes raw materials and chemical binder using water and then forms it using a mold/cast.

Chemical binders that are often used are high alumina castable (HAC), hydratable alumina, and colloidal silica. Adding a chemical binder will form a ceramic bond after heating. Castable, which is also commonly called concrete refractory, is commonly used to coat furnaces, kilns, and so on.

Alumina and alumina silicate castables have been registered as SNI (Indonesian National Standard) products with SNI number 15-0809-2001. The two types of castable are classified as follows.

Classification of Alumina and Silicate Alumina Castable 

1. Regular Castable

Regular castable has a hydraulic cement and CaO content of less than 2.5%. There are two types of regular castable based on MOR (Modulus of Rupture), namely normal type (MOR ≥ 300 psi) and high strength type (MOR ≥ 600 psi). Permanent linear shrinkage should not exceed 1.5% at fuel temperature.

2. Low Cement Castable

Castable with CaO content between 1-2.5%.

3. Ultra Low Cement Castable

Castable which has a CaO content of between 0.2-1%.

4. No Cement Castable

Castable which has a CaO content of less than 0.2% and comes from aggregates.

5. Insulating Castable

Insulating castable has the main function of producing thermal insulation. This type of castable has low density, low thermal conductivity, and has lower mechanical strength than ordinary castable. Permanent linear shrinkage should not be more than 1.5% at fuel temperature.

In addition, there are types of castable which are grouped based on the bonding process as follows.

Types of Castables based on Bonding Process

- Castables that harden at dry temperatures 

Strong bonds and dense materials will be formed from the reaction of refractory grains with matrix materials in aqueous media. The matrix in question is refractory cement and phosphate.

- Castable which hardens at high temperatures

A strong bond is formed between the refractory grains and the matrix in the form of ceramic bond (clay) so that hardening occurs at relatively high temperatures.

Source: - Gupta, O.P. 2018. Elements of Chemical Process Technology. New Delhi: Khanna Book Publishing.

Loka Refractories - Based on their shape, refractory materials are classified into shaped/brick refractory, unshaped/monolithic refractory, and fibrous material.

 A brief explanation of the classification has been presented in a previous article entitled Refractory Classification: What Are Refractory Shapes?. In this article, we will focus on the explanation of monolithic refractories. 

Want to add more insight of monolithic refractories? Check out the explanation from the definition to the type of product.

What is Monolithic Refractory? 

Monolithic refractory, is a heat and flame resistant material that does not go through the process of forming by a press machine as well as burning before it reaches the consumer.

That's what makes this material do not have a definite shape, meaning that monolithic refractory can be formed or casted as desired when applied. 

The Strengths of Monolithic Refractory over Shaped Refractory 

One of the other forms of refractory is shaped refractory as opposed to monolithic, it has a definite shape. Compared to shaped, monolithic has several strengths including: 

1. The absence of a regular connection is the weak point of shaped refractory products; 

2. Faster to use and easier to handle and transport; 

3. Better coverage to reduce downtime during maintenance; 

4. Saving storage space because it does not have a definite shape; 

5. More heat efficient; 

6. More resistant to spalling or corrosion; 

7. Has greater volume stability. 

Application of Monolithic Refractory 

Application of monolithic refractories are done by spraying, ramming, casting, or molding. This type of refractory is generally applied to fill gaps and adhesive refractory stones and linings.

Types of Monolithic Refractories

 1.       Castable

Castable is a type of refractory that mixes raw materials and chemical binder using water and then forms it using a mold/cast. Chemical binders that are often used are high alumina castable (HAC), hydratable alumina, and colloidal silica.

Adding a chemical binder will form a ceramic bond after heating. Another form of castable is Insulating castable which has the main function of producing thermal insulation. This type of castable has low density, low thermal conductivity, and has lower mechanical strength than ordinary castable.

2.       Plastic Refractories

Plastic, is a monolithic refractory which is applied using a rammer without the need to prepare it first. Plastic refractories are distributed wrapped in polyethylene in a hard condition and form blocks.

3.       Ramming mix

Ramming mix, which is a granular refractory which is strengthened by a ceramic bond arrangement after being heated. This material is similar to plastic refractory but harder. Just like plastic refractory, ramming mix is ​​applied using a pneumatic rammer.

4.       Mortar

Mortar is a material used as the adhesive of refractory bricks in a refractory lining. Initially, mortar did not include shaped nor unshaped refractory. There are three types of mortar, namely heat-setting, air-setting, and hydraulic setting.

5.       Gunning

Gunning mix, which is a monolithic refractory material which is applied by spraying it on the surface or wall using various tools in the form of an air placement gun.

       6.         Slinger mix

Slinger mix, namely material that is applied using a slinger machine.

      7.       Patching and Coating Materials

This material has properties similar to mortar, but the grain size is more controlled making it suitable for patching and coating.

      8.       Light-weight castables

Refractory material produced by mixing hydraulic cement, a light and porous raw material, and water. Light-weight castables are molded and applied to the lining of furnaces, kilns, and so on.

Source:

- The Technical Association of Refractories, Japan. 1998. Refractories Handbook. Tokyo: The Technical Association of Refractories, Japan.

- Gupta, O.P. 2018. Elements of Chemical Process Technology. New Delhi: Khanna Book Publishing.