May 2021 Volume 3

MATERIALS

Forge Furnace Refractory Lining: Material SelectionMatters By Patrick Laskey

Whether you are building a new furnace or relining an existing piece of equipment, refractory material selection is important. Not all refractory materials are created equally. Each product is specifically engineered for certain applications. Yet, choosing the right refractory for an application is not the whole story. It is true that refractories are ceramic materials used in high- temperature applications. However, when choosing a material, you should also consider the manufacturing process and failure mechanisms that may be encountered such as impact, abrasion, chemical attack or mechanical abuse. Installation techniques are very important to ensure that the physical properties that are expected, are obtained, and the life of the refractory lining is not compromised. Common Reasons for Refractory Failures in a Forge Furnace The chemical makeup and particle sizing of refractory materials make a big difference in the physical properties. Let’s look at a few failure mechanisms and how you should design your furnace lining to prevent failure: Temperature: Refractory materials are rated for different in-service temperature usage. Care must be taken so that you do not melt the refractory or cause shrinkage in ceramic fiber products. Temperature will break down the bonds in the refractorymaterial, causing failure. Burner flame impingement will melt refractory. Chemical Attack: Analyze the chemicals in the process and choose a refractory material that is inert to the reactions. If you are experiencing a chemical attack, you may notice blotting of the refractory materials causing it to crumble. Also, oxides may form causing a glassy look or a washing effect. In this case, the refractory material structure is being attacked causing a premature failure. Mechanical: Scale forms on steel. When the scale falls off the steel, it can penetrate cracks in the refractory lining causing the working hearth to be pushed apart. Expansion needs to be designed in refractory joints in high-scale areas. Impact/Abrasion: When designing for impact or abrasion, determine where force is being exerted. Then, choose a high cold crush material with large aggregate installed with an engineered anchoring system that will absorb the impact or abrasion without destroying the refractory lining. Material Selection and Installation Experience Matters You may be thinking, “I did not know refractory material selection and installation was so important.” So, what should you expect from your refractory supplier?

1. Remember the Farmers Insurance commercial, “We know a thing or two because we have seen a thing or two.” Your refractory contractor should have experience in many different industries and applications. So, they are familiar with different materials and installation techniques. 2. A refractory lining should be engineered and designed to meet your specific production and business requirements. A 3D model may be provided to aid you in seeing and understanding why different materials are installed in the hearth, walls and roof of the furnace. The installer should also work with a lot of refractory manufacturers so they can help you choose the best product and the best price to meet your needs. 3. When there is a refractory failure, the contractor should be able to perform a root cause failure analysis using a variety of tools including a visual inspection, samples sent for chemical analysis, samples sent for destructive testing and thermal imaging to assess the integrity of the refractory lining

Exhibit 1: Box Furnace Refractory Side View History and current operating parameters play important roles when designing a refractory lining for a forge furnace. The client and contractor must look at the complete system to understand the furnace dynamics. Important questions to ask may include: what material is being processed, what is the operating cycle length and temperature, what materials have been used in the past and how did they perform? It is equally as important to understand what is not going well. Is the refractory experiencing flame impingement from the burners? Is the furnace over/under pressurized? Are there areas

36

FIA MAGAZINE | MAY 2021