Care spraying and shotcrete: extending service life intelligently

What is care spraying?

Care spraying, also known as gunning or shotcrete, is a process for applying refractory material to worn lining surfaces by means of compressed air. Unlike a complete relining, it does not renew the whole lining but applies material specifically to the worn areas. The method is considerably faster and more economical than a complete replacement and in many cases can be carried out during planned maintenance shutdowns without significantly affecting the production schedule.

When is the right moment?

The timing of care spraying largely decides how successful it is. If it is sprayed too early, the economic benefit is small, because the remaining service life of the original material would still have been sufficient. If it is sprayed too late, the spray material can no longer bond reliably to the damaged substrate. The optimum moment is usually when 40 to 60 per cent of the lining has been consumed. At this point the wear is already clearly measurable, but the substrate surface still offers enough structure and integrity for the spray material to bond well.

Dry versus wet spraying process

In practice, two fundamentally different processes are used. In the dry spraying process, the dry spray material is conveyed through a compressed-air hose to the nozzle tip, where it is mixed with water and thrown against the surface. The process allows high application rates and is particularly suitable for large areas and thick applications. The disadvantage is a higher rebound, that is, material that does not stick to the surface and ends up as waste.

In the wet spraying process, the material is mixed with water before it is conveyed to the nozzle. The result is a more uniform material quality with lower rebound, though with a lower application rate and greater demands on the conveying equipment. The choice of process depends on accessibility, the desired application thickness, the type of material and the project-specific boundary conditions.

Quality assurance in care spraying

• Surface preparation: loose parts, slag deposits and contaminated layers have to be removed completely before the spray material is applied
• Temperature control: the substrate surface has to be cooled to below 80 degrees Celsius so that the spray material can set chemically
• Layer build-up: several thin layers achieve better adhesion and material quality than a single thick application
• After-treatment: once sprayed, the material has to be dried in a controlled way before the furnace is heated up again. The drying curve depends on the binder system used
• Documentation: layer thicknesses, quantity of material and the areas treated are documented so that the progress of wear can be tracked across several campaigns

At SBS Refractory Service we carry out care spraying with our own experienced specialists and state-of-the-art conveying equipment. Our teams are familiar with the specific requirements of different furnace types and can build up an even, firmly bonded sprayed layer even in confined conditions. The combination of regular damage analysis and targeted care spraying is one of the most effective strategies for maximising plant availability while minimising refractory costs.