Key points for construction of high temperature refractory materials for industrial furnaces

Industrial kiln lining materials generally use refractory and thermal insulation materials with light weight, high strength and good thermal insulation performance. This can reduce the weight of the kiln itself, save energy and protect the environment. The construction of high-temperature castable refractory materials should be adapted to local conditions. Depending on the type and location of the kiln, as well as the size of the maintenance area, the choice of construction method is also different; a reasonable construction method should be selected.

Preparation work before refractory castable construction

Before constructing high temperature castable refractory materials, the following preparations should be completed:

• Make a test block and calculate the amount of water to be added. Construction can only be carried out when the test block meets the design requirements.
• Check the corrosion of the steel shell and remove rust on the surface of the steel plate shell that is in contact with the castable.
• Check whether the frame is firmly supported. The surface of the formwork should be planned and coated with a layer of varnish to prevent the formwork from absorbing water and facilitate the removal of the formwork.
• To mix the castable, a forced mixer must be used. All mixing tools must be clean. Add water and mix well. Unload and use only after the material is completely homogeneous.

Construction steps for different parts of refractory castables

The construction steps of different parts of refractory castables are as follows:

The packaging of preliminary refractory castables is usually 25KG/50KG woven bags. When using, first take out a small bag of binder from each bag, then open it and pour the castable into the mixer. Dry mix for 3 to 5 minutes to mix evenly, then add water to the good castable and stir. The water must be clean water. The amount of water added should be based on the ratio provided by the manufacturer. The amount of water added should be accurately weighed. Generally, the amount of water added is between 8% and 15%. The specific amount of water added is based on the experience of the workers on site and is added appropriately. The castable must be stirred evenly after adding water, generally about 3 minutes, and can be slightly adjusted according to the site.

Construction steps of insulation layer castable

When pouring lightweight castables for the insulation layer, manual spreading and tamping should be used to prevent particle separation and increase the packing density. When the thickness is greater than 100mm, the required thickness should be poured at one time, otherwise the layers will peel off and leave expansion joints.

Construction steps of castables in high temperature areas

When pouring heavy castables into the fire surface, they should be compacted by mechanical vibration to eliminate the internal air. When compacted manually, it should be uniform and dense, but it should not be rolled, because after rolling, the cement slurry will flow back upwards and the surface will be more dense. If it is dense, the internal moisture will not evaporate easily and cracks will easily appear. To prevent the water from evaporating too quickly, it should be covered after construction to keep it moist for maintenance.

Construction steps of thermal insulation castables in corner transition section

When pouring refractory castables in the corner transition section, a layer of plastic board should be laid to isolate the contact surface with the insulation blanket/cotton/board/brick to prevent the insulation brick/board/cotton from absorbing water. Refractory castables with difficult corners can be poured by self-flowing method. The material has good fluidity, and the tamping time should not be too long to prevent particle separation and excessive moisture from returning upward, which may cause cracks due to moisture evaporation. For some parts with a structural thickness of only a few centimeters, plastic should be used for coating. Pay attention to welding claw nails or tortoise shell mesh on the repair parts before construction. Fill the steel mesh with plastic so that there are no gaps and it must be dense. The density cannot be increased. When applying, the plastic should be spread out and smoothed with a wooden trowel until the surface is rough. To prevent cracking, the plastic surface can be smoothed with an iron trowel.

Precautions for construction of high temperature castable refractory materials

During the construction of castable refractory materials, the following matters should be noted:

• Use a vibrator or shaker to vibrate and tap every corner to make sure no bubbles are forced out and there are no holes.
• The castable should be prevented from bursting and peeling due to the rapid increase in temperature during the oven process. When mixing the castable, all foreign matter in the mixture should be removed, clean water must be used, and the amount of water added should be strictly controlled. The mixed material should be used up within 30 minutes.