Porcelain Enamel Coatings

Porcelain enamel coatings have their origins in ancient times when they were mainly used for decorative and ornamental purposes. From the industrial revolution onwards, these coatings have started to be used also as functional layers, ranging from home applications up to the use in high-technological fields, such as in chemical reactors.

The excellent properties of porcelain enamel coatings, such as fire resistance, protection of the substrate from corrosion, resistance to atmospheric and chemical degradation, mainly depend and originate from the glassy nature of the porcelain enamel matrix itself. On the other side, the vitreous nature of porcelain enamel coatings limits their application in many fields, where mechanical stress and heavy abrasion phenomena could lead to nucleation and propagation of cracks inside the material, thus negatively affecting the protective properties of this coating. Many efforts have been made to improve the abrasion resistance of enamelled materials.

On this regard, researchers showed encouraging results and proposed many different improvement approaches. Now it is possible to obtain porcelain enamels with enhanced resistance to abrasion. Differently, the investigation of the mechanical properties of porcelain enamel coatings remains a poorly studied topic. In the literature, there are interesting methodological ideas, which could be successfully applied to the mechanical study of enamelled materials and could allow to have further insights on their behaviour. Thus, the path that should be followed in the future includes the mechanical characterization of these coatings and the search for new solutions to address their brittle behaviour.

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Porcelain Enamel Powder in the 21st Century

With the invention of powder coating about 60 years ago, a lot of work began in the coatings and finishing industries to leverage this new technology. The porcelain enamel industry was an early adopter of electrostatic powder coating, but a lot of development was required from both the material and equipment aspects. By the 1980s, porcelain enamel powder coating was taking place in many factories, primarily for flatware but also in several lines for cavities, like ovens and dishwashers.

The physics of powder coating of porcelain enamel powder for metal is the same as for traditional powder paint, although there are some differences in behavior, etc. One of the most noticeable is the transfer efficiency; porcelain enamel powder for metal is about 40 percent efficient, so much more powder travels through the recovery system in comparison with traditional powder paint. Additionally, porcelain enamel powders for metal are often applied in a thicker film; usually six to eight mils.

Almost all of the electrostatic dry powder porcelain enamel application is for major appliances; for exterior parts it is usually a two coat/one fire process, and for interior (non-appearance) parts it is a one coat/one fire process. In two coat/one fire processing, the first coat is a special ground coat enamel powder for metal(designed to adhere to the steel) which is applied to a thickness of one to two mils, directly followed in a second application booth with a cover coat (for the final color of the part) at a thickness of five to seven mils. Both layers are melted/cured at about 1500 degrees Fahrenheit in a single pass through the furnace. Firing times are typically dependent on the thickness of the metal; for successful enamel coatings the time at peak temperature is two to three minutes.

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Inorganic cadmium pigments VS. organic cadmium pigments

Organic cadmium pigments are based on carbon chains and rings. While some contain inorganic elements as stabilizers, organic cadmium pigments are defined primarily by this factor. These strong carbon chains also make them highly stable.

Carbon-based cadmium pigments are derived from animals, vegetables or synthetic organic chemistry. While traditional cadmium pigments were typically created using flora and fauna, the majority of modern cadmium pigments are created through synthetic organic chemistry. Synthetic organic cadmium pigments are most commonly derived from aromatic hydrocarbons including coal tars and other petrochemicals.

Organic cadmium pigments are marked by the following qualities:

  • Color quality: While most organic cadmium pigments are considered transparent, their tonality is
    unparallelled. Organic cadmium pigments are characterized by bright, rich colors. They often
    provide powerful tint strength despite their transparency.
  • High prices: Organic cadmium pigments tend to be more expensive to produce, especially
    synthetic organic cadmium pigments. Synthetic cadmium pigments require a great deal of chemical
    processing to produce, increasing the cost by volume.
  • Varying lightfastness: There are many different varieties of organic cadmium pigments, but most
    of them tend to hold up poorly when exposed to light. While some can resist light and
    heat exposure well, many will fade over time.

Organic cadmium pigments tend to be less popular in most industries compared to inorganic cadmium pigments, with
the exception of artists’ paints. However, organic cadmium pigments are frequently used on a lesser scale
in combination with inorganic cadmium pigments as this method improves the color quality of a product.

Different types of enamel powder coating and their applications

Different types of enamel powder coating have different chemical and physical properties —corrosion resistance, performance when exposed to UV, etc.— but no enamel powder coating provides all the protection a structure needs. That’s why assets are coated with one or more enamel powder coating types to form a total protective coating system, or a system providing all the chemical, physical and galvanic protection required to protect the substrate from its environment.

Selecting a enamel system for your application: Weighing price and performance

Enamel powder coating systems provide steel structures with long-term protection against their environment. To do this, the enamel powder coating system must be well-equipped to handle the environmental conditions of its environment, whether that’s heat, sunlight, contact with chemicals or constant abrasions.

The prevailing service environment —along with factors such as cost, accessibility of the asset, expected labor costs, desired service life of the enamel powder coating system— will dictate which enamel powder coating system is best-suited for your application.

For designers or owners looking for a short list of enamel powder coating systems suited for their application and budget, calling a enamel powder coating contractor like us is a good place to start. Enamel powder coating selection happens on a case by case basis, and we can evaluate the specific needs of your application, offering several systems that could work based on our decades of experience in the industry.

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Cadmium Yellow Pigment

Cadmium Yellow pigments are the most durable yellow, orange and red inorganic pigments commercially available. They have excellent chemical and heat stability and can be used in chemically aggressive environments and durable applications without color fade.

Cadmium zinc sulfide pigments were developed in response to the need for stable, lighter shades of cadmium yellow. Cadmium and zinc salts of the same anion are used to form the pigment with up to about 25% zinc content.

Origin and History

When first introduced, there were few stable, bright pigments in the yellow to red range, with stable orange and bright red being very rare. The cadmium yellow pigments eventually replaced compounds such as mercury sulfide (vermilion) with improved lightfastness.

Cadmum sulfide was suggested as a pigment in 1819 by Stromeyer, but it was not commercially available until 1840s due to scarcity of metal required for its production.

Source

About half the consumption of cadmium, which is about 2,000 tons annually, is used to produce colored cadmium yellow pigments. The principal pigments are a family of yellow/orange/red cadmium sulfides and sulfoselenides as well as compounds with metals other than cadmium.

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Enamel Powder For Metal

ENAMEL SUPPLEMENTS – For Medium Temperature Enamels for Copper, Gold, Silver, Low Carbon Steel, Window Glass, Stained Glass, Bulls-eye and Spectrum Glass, Effetre (Moretti), 400 Series Stainless Steel and Pottery (A.K.A. Ceramics)

Enamel Powder for Metal

A series of vitreous enamel powder for metal which fuse slightly below 1200ºF. Mix with your favorite painting medium.

The enamel powder for metal will attach to glass at 1250 degrees F. They will gloss between 1300 and 1400 degrees. F. They may be taken up to 1450 degrees F. without loss of color. Firing times and temperatures are only guides. Your actual experience may indicate the firing may need to be more or less time and temperature.

You may want to vent your kiln as it heats up to allow for any painting medium fumes to escape kiln.

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Advances in Porcelain Enamel Technology

Porcelain is made from baked clay

Porcelain itself is a ceramic material made from a type of white clay called kaolin, plus feldspars, quartz, steatite, and other rocks. To make regular porcelain, the whole mixture is baked at 1300-1400 degrees. Porcelain enamel is made when the porcelain is melted together with a stronger metal. This makes porcelain enamel cookware both light and strong, with low porosity, so it is naturally non-stick.

Pay attention to porcelain coatings

Oddly enough, though, some companies seem to want to coat their porcelain enamel cookware with chemical non-stick coatings or to use potentially toxic heavy metals and other compounds in glazes and in the enamel mixture. It pays to be picky about porcelain enamel cookware and to ask questions of manufacturers if it’s not clear what they use in their pots and pans.

Unlike somewhat terrifying porcelain dolls that could be extras in a Stephen King movie adaptation, porcelain enamel cookware is a fun addition to the kitchen. That’s because it is available in a variety of colors and does not fade or peel when used according to instructions. My advice, though, would be to avoid porcelain enamel in reddish tones and to favor those that are blue, given that some Le Creuset models with a red tone have tested positive for lead and cadmium. The Signature Enameled Cast Iron Braiser (in a blue shade like Marseille or Marine) from Le Creuset is a good option for one-pot meals (View on Amazon).

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Process for vitreous enamel coating

Those skilled in the enameling art have tried for years to produce multi-colored articles wherein the colors are overlapping or adjacent to each other by vitreous enamel coating and in a single firing operation, however, the best that has been accomplished before my invention is the production of articles which may have more than one color thereon, provided that such colors do not touch each other, or provided they are not overlapping or superimposed one on the other. .As heretofore practiced, the manufacture of multi-colored vitreous enameled articles has been carried out by a separate firing for each color when it is necessary to overlap or superimpose one color upon another. In the manner in which the colors have been applied in the past, if separate firings are not accomplished, then the finished article will be full of blisters and enamel defects and if separate firings are accomplished the finish will not be uniform, but will be stepped up, each subsequent color coating being higher than the last. Also every time a color coat is fired the color fades out so that the first color applied has changed to an undesirable shade after repeated firings and the colors lose the desired brilliance. Furthermore, there is a limit to the number of firings to which the first coat applied can be subjected, so that the prior process has serious limitations.

In the enameling art, as heretofore practiced, coatings averaged about 1% ounces per square foot of surface, (dry weight); some coatings may run as low as 1 ounce or may go as high as 1% ounces per square foot. The vitreous enamel coating in the present practice should pass through a 40 to 60 mesh screen and in some cases, such as for silk screen work, they are put through a screen as fine as 200 mesh.

A further object of my invention is to produce a multi-colored vitreous enameled article, or one having different hues, shades and different color tone in one firing and having a substantially smooth surface thereon free from blisters and blowholes and other enamel defects.

Another object of my invention is to reproduce vitreous enameled products of various colors, which may be superimposed, one upon the other, by a printing press. My invention generally comprises a wet enameling process wherein I start with a. metal base upon which one ground coat and one or two cover coats of enamel have been applied, this ground coat being a vitreous enamel coating 16 fused to the metal base. I then may apply a fine “wash coating” of frit over the surface to which other colors are to be applied; this wash coating may contain some coloring matter or it may be white. In the wash coating just referred to and in subsequent frits and colors applied to the article thereafter, the particles in the frit and coloring matter may be, and preferably are, of a size to belong to the class of dispersoids; that is, the solution is such that the particles range in size from 0.1 micron to one milli-micron, a micron being equal to .00003937 inch.

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Process Development of Porcelain Powder Material

When used with pigment white, Porcelain Powder achieves the look, feel, and texture of a porcelain casting.

  • Use Porcelain Powder with flesh-toned dyes to duplicate one of a kind dolls and sculptures
  • Use to make a part heavier
  • Mix ½ of the total amount of powder into both A and B sides before mixing A and B together

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Synthetic industrial inorganic pigments

Synthetic industrial inorganic pigments are created through chemical manufacturing rather than by grinding and washing clays or minerals taken directly from the earth. The techniques for producing these substances on an industrial scale were developed after 1800, making them the first modern synthetic pigments of importance to artists.

The amazing story of these early industrial inorganic pigments is well told in Philip Ball’s Bright Earth. Nearly all synthetic inorganic pigments were discovered or identified in the grand European flowering of inorganic chemistry that occurred in the century after 1750, when European industries sponsored intensive minerological and metallurgical research, and early chemists isolated and identified many new metallic elements — cadmium, cobalt, chromium, zinc, manganese, magnesium, and so on. (These new puzzle pieces helped John Dalton to formulate modern atomic theory in around 1805.) Several synthetic inorganic pigments still used today, including iron blue, cobalt green, cobalt blue and zinc oxide, were discovered prior to 1800.

These manufactured pigment compounds generally have excellent chemical purity and color consistency, and are cheaper to buy and available in larger quantities than natural inorganic pigments. With very few exceptions, all inorganic pigments used in artists’ paints today are industrially manufactured. (Some dry powder natural inorganic pigments are available from specialty pigment retailers.)

As an artist, your primary concern is to understand the generic attributes of these industrial inorganic pigments across different manufacturers and different pigment hues (chemical or crystal variations) — that is, to see paints as physical substances rather than as “colors”. For example, the violet and blue ultramarines are typically granulating and moderately transparent; the many lemon yellow to deep red cadmiums are all powdery, permanent, opaque and quite staining; compounds made with mercury are poisonous and fugitive. The historical information can also help you to understand the rapid expansion in artists’ pigments that occurred in Europe between the 18th and 19th centuries.

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