Porcelain Enameling 101

 

Porcelain is a glass-based, inorganic coating with high-luster properties that significantly strengthens the temperature and chemical resistance of metal substrates. Porcelain, also known as vitreous enamel, is widely used across hundreds of cast iron and metal coating applications and can be found on the majority of major appliances in the United States. Porcelain is often specified for its superior durability and limitless variety of color options and high luster finishes.

Porcelain enameling offers:

  • High quality aesthetics
  • Enhanced mechanical and physical properties of metal substrates
  • Corrosion and abrasion resistance
  • High temperature resistance
  • Wide range of high luster color options

COMPOSITION

Development of porcelain enamel begins as a mineral blend similar to that used for producing common glass. This mixture is fired at a very high temperature to form a glass that is quenched to form granulated particles called frit. The frit is combined with fine oxide pigments oxide, electrolytes and other additives and milled to fine suspension to form enamel mill.

APPLICATION & FIRING

The wet enamel mill is sprayed onto a metal substrate such as cast iron grate and fused to the substrate through thermal processes by heating it to 1500 °F. During the fusion process, an inseparable bond forms between the porcelain and the substrate resulting in a completely unique chemical finish that does not peel, flake or rust.  Porcelain Industries offers in-house specialty enamel formulations that can significantly enhance the mechanical properties of metal substrates at the lowest cost possible.

Mechanical Properties


Porcelain enamels have one of the highest lubricities of any coating. The low amount of friction combined with high erosion resistance makes porcelain enamels ideal for the following applications:

  • Water lubricated bearings
  • Pipe linings
  • Shower stalls/bathtub bottoms
  • Packages chutes
  • Screw conveyors
  • Food processing equipment

Hardness of porcelain enamels can increase depending on the strength of their substrate. Porcelain enamels typically match the hardness of a plate of glass. Hardness does not vary greatly between different compositions or thicknesses. According to common hardness scales, porcelain enamels rankings are:

  • Mohs Scale: 3.5 – 6.0
  • Knopp Scale: 149 – 560
  • Sward Rocker Rating: 100
  • Unaffected through the range of pencil hardness scratch tests

Porcelain enamels can be very strong depending on the formulation, the substrate and design of the part. Generally, unless the substrate is permanently deformed, porcelain enamel will not fracture. While it is difficult to predict a universal level of impact resistance, customized formulations can be developed to meet specific levels of impact resistance needs.

  • Porcelain enamel will not fracture due to impact unless the base metal is permanently deformed.
  • Due to its high compressive strength - in the range of 20,000 psi. - porcelain enamel is rarely damaged or crushed at the point of impact.

As a rule, porcelain enamels have higher abrasion resistance than even the strongest organic coating. Porcelain often outperforms the abrasion resistance properties of metal substrates. Because of their high level of abrasion resistance, porcelain enamels are often used on:

  • Bunker/silo discharge chutes
  • Coal chutes
  • Water lubricated bearings
  • Screw conveyors
  • Chalkboards

Flexibility is important in porcelain coatings because the flexibility range impacts the integrity of the coated product. Thin porcelain enamel coatings have the best flexibility, while all coatings have approximately the tensile strength of the metal substrate.

  • A 10-mil steel sheet coated with two, 5 mil thick coats of enamel ships in 12-inch diameter coils with no damage.
  • Enamels applied at 1.5 mil to 4 mil thick steel sheets do not show damage after deformity at a radius of 1.5 in.
  • The modulus of elasticity of porcelain enameled steel is 10 x 10^6.

Porcelain Coating Application Process

Years of research and development in cast iron and steel substrates have helped us develop a highly consistent, cost-effective substrate application process. We've eliminated the risk of distortions caused by high heat firing process and can develop custom tooling designs eliminate to keep high heat at bay.

Process steps:

A porcelain enamel is considered "white" if it has a light reflectance of at least 65%.