How to Test Adherence Level for Enamel Coating

The adherence level of enamel coating can not be directly judged by its surface appearance. As the combination of enamel coating layer with steel is hidden inside. While Nolifrit has a very professional method to test adhesion of enamel coating.
20181013074523_16391Test Principle
Test weight generates a cavity on the enamel coating surface as the result of free fall. The enamel in this region breaks and the effect of the impact visually examined. The impact effect is scored in accordance with the following graduation scale. This result is recorded as adhesion value of the enamel.
Test Method
Impact testing instrument on the picture is used. The impact apparatus has a specific diameter with specific weight and spherical tip. The plate with enamel coating is placed on the annular metal mould.
Structural Specifications
A pipe with a length of 1 meter and an inner diameter of 21 mm is positioned fully vertically on an appropriate chassis. A channel is opened on one side of the pipe. There are various sections positioned on various heights of the pipe in order to fix the weight.
The weight of impact apparatus inside the pipe is 2kg. The tip of this apparatus is designed to be a hemisphere with a diameter 10 mm. The distance between the end of the pipe and the metal mould is adjusted in a manner so that the power of the vertical load weight will not decline.
Distance between the impact weight and metal plate to be tested is 0.75 m. The impact part is released from this position, so the impact energy is determined as 15 kj. Impact energy = Falling height X Impact weight X Gravitational constant.

The result can show the adhesion level of enamel coating with steel plate. There are mainly 5 levels as follows:QQ截图20190619101809

Hunan Noli Enamel Co,. Ltd is the leader manufacturer of enamel frit and enamel powder in China. Focused on enamel coating solutions for almost 30 years.

We have very professional laboratory and engineer to test enamel plate. Our ground coat all meet with the standard of Excellent level. Which make the quality of our enamel frit supreme and stable.

Advice for Making Enamel Mug with Rolled Edge

Enamel mug is quite popular in our daily life. It covers all the advantages of a glass or ceramic mug, but it won’t easily be broken like glass or ceramic mugs. And it can be decorated by varies of colors, which makes it colorful and beautiful, looks much better than steel mug. Also, it’s more healthy and environmental friendly than plastic mug.

Nolifrit has many customers who manufacture high quality enamel mugs with very nice appearance.

One of our customer was facing problem to make those enamel mugs. They use 0.3-0.4mm thickness steel plate. Problem comes from the edge. As picture showed, its metal body exposed on the rolled edge. not fully covered by enamel slurry when coating. This problem is very common among most of enamel mug manufacturers.

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He asked for our help and we offered our professional technical service and advice to solve this problem.

Our advice is as follows:

1– When casting the steel body, try to make the edge more curving. To make the rim more close to mug wall, like the picture showed:

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2–  There are some burrs in edge. Try to grind the burrs from sharp edge. This work should be done before welding.

3– Make mug rabbet upward when drying enamel slurry.

4—By using enamel frit with higher quality, the result could be better.

5—By using steel plate with thickness 0.5-0.6mm, the result could be better.

After taking our advice, our customer solved this problem completely and can make enamel mug with perfect edge:

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Classification of Enamel Frit (2)

Cover Coat Frit

Cover coat enamel frit is coated on the surface of enamelware. By appearance, it can be classified into white frit, colored frit, transparent frit. By features, it can be Acid resistant frit, Alkali resistant frit, Abrasion resistant frit, Microcrystal frit, optical luminescent frit. High temperature resistant enamel frit and insulative frit etc…

①White frit:

White frit can make cover coat in a white color with strong covering power. By the opacifiers used in cover coat frit, it can be classified into Titanium cover coat and Antimony cover coat. In Titanium cover coat, when Titanium dioxide is fired, it can make the surface in super white color, And its enamel layer is thin, so it can save material. It’s most widely applied in daily enamel cookware. The opacification of Antimony oxide in Antimony cover coat is not good as Titanium Dioxide, so its enamel layer is thicker. It’s usually used in cast iron bathtub or other enamelware not for food containers.

(Antimony White Frit:)

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Colored cover coat frit:

It’s made by white frit with pigment. Pigment can be added when firing or milling. Colored cover coat frit has colored Titanium frit and colored Antimony frit etc…

(Titanium Ivory Frit:)

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Transparent frit:

It has no opacifying power, and it’s transparent enamel frit. It’s usually coated on cover coat to enhances glossiness. And it’s also used as a basic frit to mill pigment together, which is called decal transparent frit.

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Enamel frit with chemical properties:

This type has Acid resistant and Alkali resistant frit. Acid resistant frit contains more than 65% silicon dioxide, it’s mainly used in chemical industrial enamel product. Alkali resistant frit contains much Zirconium dioxide and it also need silicon carbide and Titanium dioxide to enhance its Alkali resistance.

(Acid Resistant enamel frit for pipe:)

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⑤Enamel frit with mechanical properties:

It’s Abrasion resistant frit. There are two ways to improve abrasion resistance of enamel frit. One is to add Silicon Carbide, Boron Nitride worked as milling additives. Other is to micro crystallize enamel frit to gain microcrystallization enamel frit with better abrasion resistance.

⑥Enamel frit with optical properties:

Namely, luminescent enamel frit. Enamel frit with Zinc Sulfide and Cadmium Sulfide added, mainly used in enamel signage and instrument panel etc…

⑦Enamel frit with thermal properties:

High temperature resistant enamel frit can be used in more than 750℃ temperature, can bear sudden change of temperature. It can’t contain any alkali metal oxide, and it contains much (40% or more) Boric oxide and few Beryllium oxide. It also need to add some refractory materials like Aluminum oxide and Chromic oxide. High temperature resistant enamel frit mainly applied in jet parts protection or paint for nuclear power reactor.

⑧Enamel frit with electrical properties:

It’s resistor enamel frit. It has very big electrical resistivity and it’s insulative enamel frit. It’s not allowed to contain any alkali metal oxide. It’s usually used to be wire of insulating material or insulative coating material for printed circuit board.

Edge frit:

Enamel coating for the edge of enamelware. The expansion coefficient is higher than normal cover coat frit. And it has wide firing temperature range, elasticity also better. Edge frit has many colors, usually worked as decorations for the edge.

(Blue Edge Frit: )

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Classification of Enamel Frit (1)

Enamel frit can be classified into ground coat frit, cover coat frit and edge frit.

By metal body material, it can be steel enamel frit, cast iron enamel frit, Aluminum enamel frit, Copper enamel frit and Gold, Silver enamel frit etc… Among these, steel enamel frit and cast iron enamel frit is applied most widely.

By enamel material, it can be Titanium frit and Antimony frit etc…

By enamel features, it can be Acid resistant frit, Alkali resistant frit with good chemical properties. Abrasion resistant frit, Microcrystal frit with good mechanical property. And optical luminescent frit. High temperature resistant enamel frit with thermal properties etc…

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Ground Coat Frit

Ground coat frit can be directly coated on metal body. Main function is to make a tight combination(adherence) between metal body and cover coat.

By adherence promoters, it can be classified into Nickel ground coat frit, Cobalt ground coat frit, Cobalt-Nickel ground coat frit, Antimony- Molybdenum ground coat frit and compound ground coat frit etc… Cobalt-Nickel ground coat frit is most widely applied. Antimony- Molybdenum ground coat is in white color, other name white ground coat. Its cost is lowest. Usually be used for daily enamel cookware. Compound ground coat frit is mixed by many kinds of ground coat frit with specific ratio. It can improve effect of firing process, enhance adherence between enamel and metal body. Usually used to make big and thick enamel products.

(Cobalt-Nickel Ground Coat Enamel Frit:)

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Cover Coat Frit

Cover coat frit is coated on the surface of enamelware. By appearance, it can be classified into white frit, colored frit, transparent frit. By features, it can be Acid resistant frit, Alkali resistant frit, Abrasion resistant frit, Microcrystal frit, optical luminescent frit. High temperature resistant enamel frit and insulative frit etc…

(Titanium White Frit:)

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To be continued…

Enamel Coating Process

Enamel manufacturing process mainly include enamel frit manufacturing, metal body casting, enamel coating, drying, firing and testing. For art enamel, cookware, sanitary and architecture etc…It will need decorating and packaging for its good appearance and daily use; For industrial enamel, it will need to be tested then assemble.

First, coat a ground coat on a metal body which is already casted or stamping to the specific shape. After firing and cooling, then coat a cover coat(one time or many times). This is the traditional enamel coating. Ground coat is a transition layer for combination with metal body. It need strong adherence. Cover coat is coated on ground coat, which can cover the ground coat and give it a smooth and beautiful surface and stable physicochemical property. Cover coat can be divided into opacifying cover coat(white and colored) and transparent cover coat. It’s coated on the outermost layer to increase its glossiness or improve its property. Nowadays, there is a new enamel coating process, which is called direct on one time coating. It has only one coat, can be both ground coat and cover coat, only need one time to coat, and one time firing, then the products can be done.

Enamel frit manufacturing

Enamel frit is glassy state silicate or borosilicate coated on metal body. Enamel frit has seven parts, every parts have different functions. Its basic are mainly silicate, boric oxide, aluminium oxide and alkali metal oxide. Its composition can be confirmed by the metal material and end product’s requirements. It need to be accurately weighted, fully mixed, fused to specific average extent in tank, pot or rotary furnace, and after water quenching, air cooling or hot-pressing to flake(0.6-1.5mm). Then milling it(by ball or airflow milling machine) to dry enamel powder or add water to make it enamel slurry.20180825021216_74320

Enamel coating

Coat enamel powder or slurry evenly on the metal body, after firing, coat cover coat on ground coat. Coating ways can be dipping, pouring, spraying and bepowdering. Bepowdering is to sprinkle cover coat enamel powder to red hot ground coat, which makes coating and firing one process. It’s a must for making cast iron products in large size(bathtub, reactor…). Moreover, there’s electrostatic powder spray and electrophoresis coating.

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Firing

Put the coated metal body to oven, rotary or tunnel furnace and fire. Firing temperature of ground coat with borosilicate is about 820-880℃. In order to form a iron oxide layer on the metal surface which can improve the adherence between enamel layer and metal body. Firing temperature of cover coat is little lower, Antimony cover coat  can be fired in 830-850℃, Titanium cover coat can be fired in 800-850℃. In order to make cover coat good opacifying and bright color, and close integration with ground coat, strict control of firing time and condition is a must. Antimony and Titanium cover coat is especially strict on firing condition.

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Hunan Noli Enamel Co,. Ltd focus on enamel coating for almost 30 years, which makes us quite professional on enamel coating and very familiar with enamel coating process. We can completely control every process of enamel frit manufacturing and have strong technical supporting team, which makes our quality very close with Ferro and Pemco corporation. And our cost can be lower.

Natural inorganic pigments

Natural inorganic pigments are among the oldest used by humans. They first appear in the funeral preparation of human remains from 60,000 years ago, and in polychrome cave art from about 20,000 years ago. Mined in prehistory from surface deposits of clay and rock, many inorganic pigments have shown extraordinary permanence over long periods of time.

With few exceptions, inorganic pigments are combinations of a mineral element with oxygen and other elements (most often sulfur, silicon or carbon) that fall in the chemical classes known as oxides, oxide hydroxides, sulfides, sulfates, silicates and carbonates.

The pigments in this category that have been of importance to watercolor painting include:

Red earths. A large and diverse category of pigments, all made from earths (mostly clays) containing large proportions of iron oxide (the dark violet to light red hematite or everyday rust, the orange to yellow lepidocrocite, or the dark brown maghemite) that is processed and sold as natural iron oxide. The pigment color may range from a dull yellow through a dull deep yellow, dull orange, dull red or dark brown (listed either as PR102 or PBr7) to near black (PBr6). The color depends on the average particle size, the presence of manganese or other elements (which darkens and dulls the color), and whether water is chemically bonded within the iron oxide crystals. (The dull red orange to yellow hydrous oxides contain water, the maroon to dull red anhydrous oxides do not.) Although red iron oxides occur in all parts of the world and have been used as pigments since antiquity, rich deposits are currently found near Malaga, Spain (Spanish red, which has a characteristic brownish undertone) and in Ormuz, in the Persian Gulf (Persian red). Historically, European sources of yellow brown earths were mined near Leghorn or Siena (in Tuscany, Italy); these are the siennas, containing roughly 50% iron oxide and less than 1% manganese dioxide. The dark red or brown earths or umbers, containing 45%-70% iron oxide and 5% to 20% manganese dioxide, were originally imported to Europe from Turkey (via Venice), but are now mined primarily in Cyprus. (The name probably derives not from the Italian region of Umbria but from the Latin ombra or shadow, referring to the original use of dark iron oxides as shadow colors.) These earths are often “burned” (calcinated or roasted at a dull red heat) to darken them (burnt sienna, burnt umber), a technique that was probably suggested around 2000 BCE by the visible reddening or darkening of pottery after it had been fired or glazed. And natural manganese ores have sometimes been added to red earths create darker red, violet or black colors in pottery clays or glazes. (Due to growing scarcity of high quality natural deposits of iron oxides, most artists’ colors are now made from synthetic iron oxides, for example the same pigments manufactured for wood stains.)

Yellow earths. Natural earths containing silica and clay, hydrous forms of iron oxide (yellow brown limonite or the brown yellow to green yellow goethite), and traces of gypsum or manganese carbonate. Like the red iron oxides, they are found around the world and have been used as pigments since prehistory. French ochre, historically one of the best grades of limonite, contains about 20% iron oxide and is high in silica. Currently workable deposits for yellow oxides are located in the Republic of South Africa and France. Most often sold as yellow ochre (PY43) or brown ochre. Most yellow clays are normally not “burnt” as heat does relatively little to alter their color.

Green earths. Clays containing large amounts of silica and the green minerals glauconite and celadonite, consisting essentially of hydrous iron, magnesium, and aluminum potassium silicates. Color varies from a dark, grayish blue green to a dark, dull yellowish green. Completely lightfast and chemically inert, green earth or terre verte has been used around the world since ancient times. In Europe, the first documented use in paintings is in Roman frescos; it was also commonly used in the Middle Ages as an underpainting for flesh tones and shadows. Originally extracted from deposits in central Europe (today’s Czech Republic), near Verona (Italy), or in France, modern supplies come from high quality deposits in Cyprus. Most of these pigment deposits originated as marine clays. In watercolors the typical color is light valued (diluted), and paints made from the genuine pigment tend to be thin and gummy. The label terre verte is often applied to paints mixed from other inorganic pigments, typically chromium oxide green (PG17) or viridian (PG18) mixed with a red iron oxide. (See also the section on chromium compounds.)

This article comes from handprint edit released

Features of Cobalt Blue Pigment

Cobalt blue is a very important inorganic blue pigment, it has very wide applications. What’s the main feature of Cobalt Blue Pigment? Let us analyze this.

Cobalt blue pigment, also called pigment blue 28, it mainly composited by Cobalt Aluminate(CoAl2O4). According to its chemical formula, the content of Alumina oxide should be 57.63%, cobalt oxide is 42.36%.But in Cobalt blue pigment, Alumina oxide is contained about 65% to 70%, Cobalt oxide is 30% to 35%.

(Cobalt blue pigment from Nolifrit:)

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Cobalt blue belongs to spinel group, it’s cubic with spinel crystal. Cobalt blue Density ratio is 3.8~4.54g/㎝3, Covering power is 75~80g/㎝2, Oil absorption 31%~37%, Bulkiness 630~740g/L.

Cobalt blue has very bright color. it’s highly weather-proof, alkali resistant, which can bear varies of solvent and its heat resistance can be 1280℃. Cobalt blue is also a environmental friendly and nontoxic high temperature resistant inorganic pigment.

Cobalt blue pigment is mainly applied to heat resistant paint, ceramic, enamel and glass. Coloring for heat resistant industrial plastic. And it can be also the pigment for art, in this field, Cobalt blue pigment is much expensive than other inorganic pigment.

(Enamel cookware in Cobalt blue color:)

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According to the above description, let us sum up main features of Cobalt blue pigment:

Name Compositions Heat Resistance Corrosion Resistance Price Applications
Cobalt Blue CoAl2O4 1280℃ Nice Contact us to know its price Heat resistant paint, ceramic, enamel and glass

Hunan Noli Enamel Co,. Ltd is the leader manufacturer of Cobalt Blue pigment in China, Focusing on the production of Cobalt blue pigment over 30 years.

It can be widely applied in enamel coloring, and its heat-resistance can be more than 1280℃, which is approved and welcomed by most of our customers.

Heat Resistance of Cadmium Yellow Pigment

Cadmium Yellow, also called Pigment Yellow 37, is a high-performance inorganic yellow pigment. Cadmium Yellow has very bright color and strong coloring power, Stable light fastness. And it’s weather-proof, heat resistant, with no bleeding and transference. Its heat-resistance better than Chrome Yellow, of course much better than Benzidine Yellow and all of other organic pigments.

Well, How’s the Heat Resistance of Cadmium Yellow Pigment?

Pure Cadmium Yellow is a solid solution composited by Cadmium Sulfide and Zinc Sulfide. Cadmium Sulfide has two stable forms in normal temperature:

One is β—CdS, it’s cubic crystalloid; The other one is α—CdS, it’s Hexagonal crystalloid. The former one is stable in low temperature, heat-resistance is less than 500℃; The latter one is stable in high temperature, melting point: 1405℃, heat-resistance is higher than 600℃. In normal temperature to 500℃, the two crystalloids can maintain stable coexistence.

(Enamel cookware in Cadmium Yellow color:)20180811033150_59303

High temperature resistant Cadmium Yellow’s heat-resistance is depend on the ratio of cubic crystalloid β—CdS and Hexagonal crystalloid α—CdS. The more hexagonal crystalloid α—CdS contains in Cadmium Yellow, the higher its heat-resistance will be.

Hunan Noli Enamel Co,. Ltd is the leader manufacturer of Cadmium Yellow pigment in China, Focusing on the production of Cadmium pigment over 30 years.

It can be widely applied in enamel coloring, and its heat-resistance can be more than 800℃, which is approved and welcomed by most of our customers.

(Cadmium Yellow pigment from Nolifrit:)

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Porcelain Enamel Cups: What A Nice Choice in Hot Summer

Summer is usually hot, you will sweat even you do not get moved. It’s quite necessary to drink water after you sweated a lot. Then a healthy and beautify cup is a must. There are many kinds of cup in the market to choose from. For example, Glass cup, enamel cup, ceramic cup, plastic cup, stainless steel cup, etc…How to choose, is there anything need to care about?

Generally, consumers may not know which kind of material for cup is most reliable. Here we can say, glass one should be one of the best choice. Why?  Because glass contain no organic chemical material, and its surface is very smooth, easy to clean, bacteria and virus won’t survive in the glass inner wall. But glass is of high thermal conductivity, so when using a glass cup, it’s quite easy to be scalded. And it’s easily be broken when pour hot water into a glass cup.

And the colors of glass cup is very few to choose from, it has no ornamental value at all. This make us always ignore them. Do we have any other choice? Of course, that must be the enamel cup.

Enamel cup is coated with vitreous porcelain enamel. The enamel frit is milled to enamel powder and after almost 1000℃ firing, it can adhere to Its steel body. After cooling, the surface can be very smooth, it’s without any toxic material. Except for all the advantages a glass cup have. It can be also colored by inorganic pigment and decorated by enamel deco, which makes it colorful and good looking. If you own one of the follow enamel cup, will you drink more water than ever before?

Porcelain Enamel Cups

Some one would prefer plastic cup, but plastic cup should be the worst choice. As it may contain many toxic chemical material. And it can even release toxic material to the water when it filled with hot boiling water. Especially when it filled with strong acid or strong alkaline beverages, the toxic heavy metal like Pb, Hg will be dissolved to the liquid. So when using a plastic cup, you must choose the cup meet with the health standard.

Anyway, a cup with porcelain enamel coating can be the best choice for you to drink.

Porcelain Enamel Coating

From world-class raw materials and production facilities to global presence and process knowledge, we develop product solutions for your porcelain enamel coating and frit needs. Through technical know-how, we formulate specialty frit based products that meet the needs of the consumer white goods, hot water tanks, sanitary ware, cookware, and other industries. We have dedicated R&D centers and staff specialists to assist customers in achieving consistent, high quality output and increasing productivity. As an industry leader, we specialize in understanding the role of porcelain enamel coating and glass enamels across a wide spectrum of applications.

Frits are the basis and main component of an porcelain enamel coating. Each PEMCO® frit is individually designed to address the complex variables of chemistry and end use application. Quality raw materials are blended and melted to create a frit technically adapted for different applications. Our range of products is composed of ground coat, transparent, opaque and white frits that are engineered to match desired color, aspect, or effect.

We engineer PEMCO® frits into a pre-milled, ready-to-use formulation to provide customers with a powder for liquid application. The use of pre-milled products eliminates the need for costly milling equipment. Just add water and mix! One of the most successful innovations in the porcelain enamel coating industry has been the development and continued improvement of our portfolio of PEMCO® Electrostatic Powders. The advantages of electrostatic powders include automated application, elimination of hazardous waste, reduction of energy costs for milling and drying and labor costs in mill room and set up, excellent finish quality, and maximized utilization of material.

This article comes from princecorp edit released