Vitreous enamel, also called porcelain enamel, was initially used throughout history to make religious and ceremonial items or high-quality jewellery. The application of vitreous enamel, or enamelling, of household items such as pots and pans, especially those exposed to high heat, dates back to the early 19th century. With the changing times and rapid development, vitreous enamel products are now used to make traditional daily-use enamelware and in many other fields.
Vitreous enamel and steel panels are now widely used to make sanitary ware, signages, modular furniture, and architectural cladding. The reason vitreous enamelled steel panels are preferred to other materials is that it combines the traditional properties of glass with the strength and flexibility of steel.
Vitreous enamels are usually richer in fluxing oxides (modifiers), and the materials are highly fritted. The enamels are made by modifying Silica (SiO2) according to the different requirements by adding various oxides. The purpose of using modifiers is to change the compound’s chemical, physical, and thermal properties. Common modifiers used are CaO, BaO, SrO, ZnO, PbO, Na₂O, etc.
To make vitreous enamel, the manufacturer starts by grading and accurately weighing the raw materials to be smelted, such as sand, feldspar, borax, soda ash, and sodium fluoride. Then, the raw materials are mixed and sieved, and made ready to be put into crucibles for firing/fritting. A 5kg batch of raw material fits into four crucibles. The raw materials are carefully placed on a kiln batt and fired after choosing the required firing program (90 mins up to 1300c or 150 mins @ 1300c). They are then tested for melt and colour and adjusted as needed.
Once done, the enamel is put into water to prevent crystallization. The material produced after this is called frit. The enamel is then grounded in a rotating porcelain ball mill to form a powder, which is graded and sieved. At the milling stage, other minerals are added to give the required properties for the final enamel.
The vitreous enamel panels are made with special grade steel, usually around 1.5mm thick that are made into tray panels with flanges between 25 and 40mm. Before applying the enamel coating, the metal surface impurities are cleaned in a degreaser or acid bath. Both sides of a panel are coated with a ground coat of enamel frits. After coating, the panels are then fired, fusing the enamel ground coat to the steel. The face side of the panel is then further coated with the enamel cover coating using frits that are used for a glossy appearance. Post the application of the main coat, the panels are fired at 830 degrees Celsius. When necessary, a 0.6mm thick galvanized balancer is added to improve panel flatness and rigidity.
Advantages of Vitreous Enamel
Vitreous enamel is a versatile material with several unique properties that make it a sustainable and economical alternative for designers.
- Variety of colours: Vitreous enamels are available in a wide range of shades that can be customized as per the requirement. When used for architectural cladding, the surface of the panels is given a glossy finish, and can also incorporate logos, designs, and signages onto the surface.
- Resistance to corrosion: The application of the enamel is done to the steel in such a way that it covers it completely, ensuring that the structural integrity of the steel is maintained. The panels do not rust even in extreme conditions.
- High-temperature resistance: The vitreous enamel panels are non-toxic and resistant to high temperatures. They can withstand naked flames or fire up to 650ºC and continuous temperatures up to 400º C.
- Durable and Low maintenance: The panels are long-lasting, scratch-resistant, and very easy to clean. Unwanted graffiti, markers, and spray paints can be easily removed using water and a mild cleaning liquid. The hard enamel surface prevents the absorption of dirt or grease, and eliminates the growth of bacteria and mould.
- Acid / Alkali resistant: Vitreous enamel is resistant to most alkalis, all acids, all organic solvents, normal detergents, all neutral saline solutions and is unaffected by kerosene.
- Sustainable: The raw materials used to produce both the enamel and the steel base are fully recyclable, as they contain no polluting substances, making enamel panels an environment-friendly material.
Types of Vitreous Enamel Panels
There are two basic panel types used majorly in architectural applications:
1.Light Gauge Panels – Originally designed as infill panels, light gauge panels are mostly used in internal cladding. The thickness of the enamelling quality steel varies between 0.5 mm and 0.7 mm.
2. Heavy Gauge Panels – These panels are used to create more complex form profiles like curves. The panels are prefabricated to the required size and shape by cutting the steel sheets and welding the edges before enamelling.
Architectural Applications of Vitreous Enamel Panels
Mass Transit and Railway Systems
Vitreous enamel panels are largely used as decorative panels for the interior facade of tunnels and subway stations. An example of this is the London Underground network, where the panels are used extensively. Transit systems in Hong Kong, Singapore, Australia, and the United Kingdom also use these panels in their stations. Companies like Ceratec and Trico design and manufacture vitreous enamel panels for mass transit and railway systems all over the world.
They are also used in airports as wall cladding, commercial shop fronts, and food court seating areas. Because of its high resistance to chemicals, vitreous enamel panels are also largely used in the laboratory and industrial environments where exposure to chemicals and other pollutants is high. They are also commonly used as high-quality cladding, doors, and partitions in public washrooms.
The Wanangkura Stadium in Western Australia is an example of a structure where architects have implemented the usage of vitreous enamel panels in the facade. The sustainable design of the stadium had to consider the harsh local climate. So the facade is made of vitreous enamel panels and a rain-screen system, mounted onto a sealed galvanized-steel inner facade. The waterproof layer protects the building from heavy rainfall. Combined with the panels, it creates a vented thermal cavity to protect the interiors against the intense heat load. The vitreous enamel surface is also highly durable; therefore, it cleans off easily and maintains a clean and appealing facade throughout the year.
Photographs, text, and graphics can be directly printed on the panels, so vitreous enamel is extensively used to make signages. Since the material is abrasion and impact resistant and it doesn’t fade, it is ideal for use in public areas. The panels are also available in multiple, bold colours that help create attractive and effective signs. Vitreous enamel panels are also used to make logos, information boards, maps, and public information displays.
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