Cold Rolled Sheet 


Vitreous Enameling Sheet
Application Considerations
The production of Vitrenamel Sheet requires attention to processing details by both the steel manufacturer and the customer who applies the vitreous enamel coating. The steel manufacturer has to meet the requirements with respect to carbon content and its distribution, the annealing practices and other in-house steelmaking practices that are known to influence the enamelability. The customer has to apply good practices with respect to cleaning the steel before applying the frit, the application of the frit, and the high temperature firing process used to convert the loose powder frit into a hard vitreous coating.

Outgassing and fishscale are the major difficulties associated with enameling. The types of outgassing that are influenced by the steel are those caused by carbides and hydrogen. Generally, carbides are easily controlled and do not cause many problems. However, if the carbides are close to the steel surface, the carbon can combine with oxygen to form carbon monoxide or carbon dioxide gases. These gases can then cause a rough enamel surface.

Hydrogen-related outgassing is a more common problem. This problem is related to steel's increasing solubility for hydrogen when heated to high temperatures. During the frit-firing process, hydrogen may be introduced into the steel from moisture in the atmosphere or in the enamel frit. As the part cools, the hydrogen solubility in the steel decreases and is released from the steel surface. If the frit is still fluid, the escaping hydrogen gas will pass through the frit without causing any problems. However, if the enamel coating has become fairly viscous, the exiting gas can cause a rough surface on the finished vitreous coating.

Fishscale is also related to hydrogen that has entered the steel during the firing process. If the hydrogen does not escape while the frit is still fluid, but is trapped between the steel and hardening frit, eventually the internal pressure can reach such high values that the hard enamel coating is fractured. The surface roughness is known as "fishscale". 

To assure good performance of the finished product, other issues need to be attended to during application of the vitreous coating. These include:

1.	Warpage - Product distortion that occurs during firing. Usually, it relates to the residual stresses in the formed part.
2.	Sag - Dimensional instability experienced by the steel part during firing at high temperature. The purchased steel can impact this behavior.
3.	Strength after Fire - During the firing process, the steel may be prone to changes that adversely affect the strength of the finished part. Strength-after-fire- can be improved by assuring that the correct steel grade is selected to match the requirements during the firing cycle.

Enameling steels can be joined using a variety of joining processes. These include resistance welding, arc welding, laser welding, and mechanical fastening. The effects of each of these joining practices needs to be addressed carefully by the end user for each end application. Also, the specific type of frit used during the manufacturing process can impact the performance in the weld area; thus, evaluation of the performance of welded areas should be investigated whenever a new type of frit is used 

Typical Applications Application Considerations Tolerances