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Did a Metal Inner Cover Fail During Batch Annealing? Take These Steps

You might be looking for ways to improve your annealing cycle. While there are many variables to batch annealing furnaces, one of the logical places to explore first is the metal inner cover. They are an important component of the batch annealing process, maintaining atmospheric integrity during the annealing.

Premature failures can cause a host of issues by interfering with the product inside and causing downtime in the steel, brass or copper making process. Understanding why inner covers fail and exploring ways to extend their life can help minimize production disruptions.

In the simplest terms, inner covers fail due to metal fatigue. The specifics of how, when and why vary because there are many different inner cover designs and several heating methods – but what we discuss here is generally universal.

Metal Inner Cover

Side Wall Failures: After many cycles and old age, the side wall of an inner cover will often fail. Additionally, vertically corrugated units can bulge until they interfere with the furnace.

Cracking or Warping of the Seal: This is another area that can develop issues due to thermal stressing. Near the bottom of the inner cover during the annealing cycle, there is a temperature transition zone from hot to cold; This action will cause thermal stresses in the material that leads to cracking, warping and then failure.

Inner covers require eventual replacement, but there are certain design elements that can enhance heat transfer and lifespan.

Straight Wall vs. Corrugated Sidewalls

The purpose of the corrugated inner cover is to provide increased surface area, promoting better heat transfer; however there is a tradeoff. They require constant care and observation to ensure their retaining bands do not break, leading to the eminent bulge.

We’ve published a full article on why vertically corrugated inner covers are falling out of favor, and you can read more here

Cracking and Warping Correction

Selecting the proper material designed for your specific operation is an important step in addressing sidewall failure as well.

Addressing the cracking of the base requires selecting a combination of materials whose thermal characteristics can help reduce the effects of thermal stresses.

With careful thought put into the design of your replacement inner cover, it’s possible to greatly extend its life expectancy. For example, we’ve seen instances of proper material selection, routine maintenance and planned outsourced repair work that have kept inner covers in operation for 20 years. Make sure you start to discuss design options sooner rather than later so you can be prepared for a smooth transition.

Metal Inner Covers 2

Alloy Engineering manufactures batch annealing equipment and a number of related products. To learn more, contact us here or call us at 440.243.6800.

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