How to Choose Cast Iron for Enamel

Cast iron can be used to make high quality enamel cookware, bathtub, stove grill in our daily life and even enamel pumps in industrial area. They are playing a more and more important role in enamel coating industry.

(Cast iron enamel cookware and stove grill)

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(Cast iron enamel bathtub)

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How to choose suitable cast iron for enamel? Nolifrit can help you to make decision!

Chemical analysis: To achieve the best enamel coating effect on cast iron, the following limiting values of the main elements in cast iron should be kept:

No Element Symbol Contents(%)
1) Carbon, total C 3.20-3.40
2) Carbon, combined C max. 0.20
3) Silicon Si 2.50-3.25
4) Manganese Mn max. 0.45
5) Phosphorus P 0.25-1.00
6) Sulphur S max. 0.12
7) Chromium Cr max. 0.05
8) Copper Cu max. 0.10
9) Molybdenum Mo max. 0.05
10) Nickel Ni max. 0.10
11) Titanium Ti max. 0.05
12) Vanadium V max. 0.05
13) Tin Sn max. 0.10

The silicon content plays an important role. Low silicon contents, below 2.5 %, are slowing down the ferritisation process so that it is not finalized after the enamelling process has been completed. An elevated outgassing, due to the conversion of perlite, causes pores and pin holes during the final stage of firing.

Because of the perlite stabilizing effect, manganese contents more than 0.45 % should be avoided. They lead to an embrittlement and to a formation of strong stresses in the composite material cast iron / enamel.

Particularly critical for the enamel coating are the trace elements Chromium, Molybdenum, Nickel, Titanium and Vanadium if the above mentioned maximal concentrations are exceeded. Consequently the perlite is that much stabilized, that only an incomplete composition to ferrite takes place during enamelling. It leads to a fluctuating expansion behaviour of the casting, depending upon its wall thickness.

The sulphur content is in particular to consider by applying the wet enamelling process for cast iron. Sulphur contents up to max. 0.12 % in general do not cause defects.

Higher sulphur contents can lead to severe difficulties in the enamelling because of the diffusion of sulphur towards the cast iron surface. During the hot process the velocity of oxidation is that much increased, that the thereby formed quantities of iron oxide cannot be absorbed by the enamel.

The formation of stresses within the composite system cast iron / enamel is mainly, under consideration of different designs, a matter of the structure of the cast iron. After the casting process the structure must be pearlitic, not cementitic.

For the enamel coating process the surface of the cast iron has to be clean and free of burned in sand. Its medium roughness should not exceed 300 microns.

For cleaning the cast iron prior to enamelling only angular shot blasting material on the basis of cast-steel or chilled cast iron has been proved. Both grades are having the essential hardness and edge stability (Vickers-Hardness HV above 650). Fractionated corundum also is very well suitable.

Spray enamel coating in wet process

Spray enamel coating is to compress air to spray enamel slurry or powder to body metal. Spray enamel coating in wet process is prevented first, then in the mid of 20th century, dry powder spray is prevented, it’s to use electrostatic adsorption to let enamel powder adhere on body metal. There’re mainly 2 ways of spray enamel coating in wet process: handwork spraying and automatic machine spraying.

1, Handwork spraying

Handwork spraying can be applied to almost all product, especially for those which has very elaborate line and pattern for decorations and with very complex shape. The weakness for handwork spraying is low efficiency, high labor strength for the workers. And the quality of final products depends much on workers’operation proficiency

For spray enamel coating in wet process, the caliber of spray gun can be adjusted according to types of enamelware and property of enamel slurry. Enamel slurry can be supplied by cup on spray gun or peripheral express tank. For product with little usage amount and need to change frequently, the cup on spray gun is suitable. For example, enamel cookware which always need to coated with patterns in many colors for decorations. When the using amount of enamel slurry is very huge and with single type, peripheral express tank will be better. For example, stove grill, cast iron cookware with single color and big architecture panels. For these, enamel slurry in express tank will easily sink, so the enamel slurry inside need to be swigged constantly to keep its balance, to prevent any bad effects due to the sink of enamel slurry.

To achieve better atomization effect, enamel slurry for spray enamel coating in wet process should be finer, but also need to pay enough attention to the quality after drying and firing. To prevent cracking and shrink of enamel surface. The specific gravity of enamel slurry better be higher. As with higher specific gravity, spraying time can be reduced. For single faced coating, required coating thickness can be attained as long as spray gun passed it for few times.

2, Automatic machine spraying

For big objects, automatic machine spraying should be applied.

The products will be horizontally hanged and pass through a channel with many spray gun around. Spraying can be done automatically when the product passed through.

Enamel pots should be placed on the transmit line and sprayed with many spray guns. Every spray gun should be adjusted with suitable anger and be fixed. To coating every face of product with required standard. When product pass through the scope that the spray gun can reach, except to go forward, it should also turn around, to ensure full coating. Enamel slurry supply system of automatic spraying machine usually include express tank, tube, liquid level control, and filter sieve etc…supply system will transport enamel slurry to spray gun. Traditional supply system is express tank, it can be used for store and also offer high express to transport. Then develop to store tank with diaphragm pump together. This makes it more convenient for continuous enamel slurry supply or change enamel slurry types and easy to clean after work.

Dipping enamel coating in wet process

Wet process enameling is to coat enamel slurry to metal body. There are mainly 3 ways for wet process enameling: dipping, spraying and flow coating. First, let’s know about dipping enamel coating.

Dipping is the most primitive and easy way in enamel coating. It’s fit for product in single color. If metal body is small and with simple shape, we just need to dip it in enamel slurry and take it out after it adsorb enough enamel slurry, then wipe off redundant enamel slurry. If metal body is complicated, we will need turn it in enamel slurry and swing, turn or hook it to wipe off redundant enamel slurry. To achieve a uniform enamel coating .

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The specific gravity and stop flow of enamel slurry is of crucial importance. Need to be measured constantly. When the stop flow of enamel slurry is low, it will need stop flow additive to adjust. For metal body with different sizes and complexities, there’re also different requirements for its specific gravity and stop flow.

1, For small product with complex shape. Specific gravity and stop flow of enamel slurry should be higher. The quality of enamel coatingdepends more on the worker’s operant level

2, For big product with simple shape. specific gravity and stop flow of enamel slurry can be lower. For the production of this product, dipping and swing can be done by one worker and other assistant works done by another operator. By this, enamel coating process is dispersed by specific workers, which makes enamel coating with high quality and more stable and the physical exhaustions of workers is also divided.

3, For product with multiple coating and firing, ground coat thickness need to be as thin as possible, to reduce the problems that happen in subsequent process. Especially for the product with decal, as the problem will mostly appear in decal firing. Traditional tools and facilities for enamel dipping is very simple, mainly include jar, pliers, grill. For products need special handle on the edge, there’re also special tools, such as: side wipe rubber, rolling case and plate. Those tools are all customized without any standard model for it.

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In reasonable enamel coating process, enamel slurry should be coated on metal body with uniform thickness. It will make big difference to final product’s property. Also will affect the quality and appearance of enamelware.

Cobalt Blue Frit

The four shades of cobalt blue frits produces, this ranks as the second lightest. cobalt blue frit is well suited for small blown work, as well as sculpture when a medium transparent blue is desired. Cobalt blue frits can take a lot of heat and can be worked in a wide range of flame settings. Stay out of reducing flames to prevent dulling or gray streaking to occur. Though the color is extremely intense, be sure to stay out of reducing flames to prevent any dulling or graying.

This article comes from northstarglass edit released

The Virtues of Vitreous Enamel

More than 500 years ago, the English chronicler Robert Fabyan described the science and art of vitreous (porcelain) enameling on metals, a practice that was already 15 centuries old. Today, vitreous enamel art is as vibrant as then. The industry of enameling metal panels, which blossomed in the 1800s and 1900s, had receded but is enjoying a resurgence thanks to new technological developments.

The Science of Vitreous Enamel: Boric Oxide Is Required

Vitreous enameling—the fusing of a thin layer of glass to a metal base—is virtually impossible to achieve on large areas unless the glass has a high (up to 25%) boric oxide content. From the day of its invention, enamel has been used to beautify metal objects, and once the technology had developed to allow its application to large pieces, its durability and protective power could be exploited.

Traditionally, an enamel surface is two coats, base and cover, each of which had to be applied and fired separately. But in the 1970s, the so-called 2C/1F process—two coats, one firing—was perfected. This technique decreases energy usage and process times dramatically. With advances in frit technology, the need for steel pre-treatment by pickling and nickel plating became unnecessary. As a result, effluent disposal costs and potential environmental risks are mitigated.

Enamel Glaze: Versatile and Beautiful

As a surface coating, especially iron and steel, vitreous enamel is unassailable. Highly durable with a long service life, it resists scratching and chemical marring. It is easy to clean, and therefore, very hygienic.

Microwave Mismatches

Microwave ovens are usually lined with plastic, stainless steel, or a painted surface. Okay for the basic process, but since integrated functions such as a grill, air circulation, and steam heating have been added, temperatures in the chamber can rise to 572°F (300°C) or more. Higher temperatures can result in staining, yellowing, and distortion. If an enamel lining is used, these faults are avoided altogether.

An added bonus is that because enameled steel has half the thermal conductivity of stainless steel, it actually improves food quality. This lower conductivity means less energy usage for the same cooking effect, shorter cooking times, and more vitamins retained in the cooked food.

This article comes from borax edit released

Function of Milling Additives for Enamel

Milling additives is very important part for porcelain enamel coating. There’re mainly four key materials to be used as milling additives for enamel coating. They are: Clay, Quartz, Sodium Nitrite and Borax. So what’s their function?

Nolifrit will give your answer:

1, Clay

The main function of clay is to make enamel slurry of suspension property, enhance the mechanical strength of dry powder body, at the same time expand the firing temperature range of enamel frit.

The usage amount of clay for daily enamel ground coat and cover coat is about 6-8 for every 100 enamel frit(weight ratio). Transparent frit about 5-6.5, industrial acid resistant ground coat will need about 10, industrial cover coat about 3-3.5, there is no clay needed for cast iron cover coat.

Impurities contains in clay will affect its quality. For example, organics will bring bubbles, pores and black dots defects on enamel surface. Iron oxide will make titanium white cover coat become yellowish so reduce its whiteness. For acid resistant blue enamel cover coat, Impurities contains in clay will make SiO2 and Al2O3 contents changed, then affect its acid resistance feature.

When Clay is over used, it will make enamel surface rough, reduce its glossy and acid resistance feature.

Hunan Noli Enamel Co., Ltd can supply high quality enamel clay. It’s all imported from one of the most professional clay manufacturer Müllenbach & Thewald GmbH, Germany. We are their agency of in China. Their MT-500/E,510/E,530/E series is especially designed forenamel coating, which has very good dispersibility and pausibility, which need less water in milling process.

2, Quartz

Only used in ground coat, using amount about 5-10. It will make enamel frit with higher fire-resistance and enhance chemical and thermal stability of enamel slurry.

We can produce 5,000 MT quartz powder every year, with very stable quality and competitive price.

3, Sodium Nitrite

Usually applied in ground coat, using amount is about 0.2-0.5(weight ratio). Main function is to prevent the rusty spot after enameling. It can also stop flow. But when over used, it will make firing temperature range of enamel frit become narrow, then boiling will happen when firing.

4, Borax

Mainly used in ground coat, using amount is about 0.5. It can prevent rust, decrease burned spot. Over using will cause boiling or burning when firing.

How to Prepare Ready to Use Enamel Powder

Ready-to-use enamel powder are basically mixed by several kinds of enamel frits and milling additives after ball milling. It mainly contains frits, clay, electrolytes, refractors and pigments. Ready-to use enamel powder can be divided into two types.

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Complete Ready-to use enamel powder: The grinding process for this enamel powder is completely finished. It can be used just by stirring in a mixer.

Preparation:

1. Put sufficient amount of water into the mixing vessel. The mixer with a high shear force is recommended.

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2. Add ready-to-use enamel powder gradually into the mixing vessel until the demanded enamel density is reached. Baume can be used instead of a vessel with fix volume, since it is easier to operate.

3. Stir or ball mill for 10 – 15 minutes. If submersion enamel is going to be used, mixing for overnight is recommended to achieve the enamel stability.

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4. Sieved the prepared enamel slurry by a 80 mesh sieve and then it becomes ready to use.

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Partial Ready-to-use enamel powder: The grinding process of this enamel powder is partially completed. This enamel powder should be grinded by the user in a mill up to the demanded fineness.

Preparation:

1,Put enamel powder into a mill.

2,Add sufficient amount of water into the mill.

3,Grind the enamel powder up to the demanded fineness.

4,Discharge the enamel slurry and after adjusting its suspension feature, the enamel powder is ready to use.

Features of Cadmium Red Pigment from Nolifrit

Cadmium red pigment is the compound of Cadmium Sulfide and Cadmium Selenide(3CdS•2CdSe). Usually, The ratio of Cadmium Sulfide is 55%, Cadmium Selenide 45%.

Chemical Name Cadmium red pigment
Chemical Compositions Cadmium Sulfide, Cadmium Selenide
Pigment Index No. Pigment red 108
CAS No. 12214-12-9
Shape Red powder
Crystal form Hexagonal crystalline, Cubic crystalline.
Temperature resistance(max) 900℃

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Cadmium red pigment has very bright color. It’s of high temperature resistance, alkali resistance, light resistance, and atmospheric resistance. With strong coloring power and covering power, the color pattern of Cadmium red pigment can range from yellow, red to purple. The more Cadmium Sulfide(CdSe) contained in Cadmium red pigment, the darker its red color will be.

Cadmium red pigment can be applied in high temperature resistant paint. It also can be used in enamel, ceramic, glass, plastic, art pigment, print ink, paper, leather, colored sand architecture material and electric material, etc…

(Steel enamel cookware in Cadmium red color:)

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(Le Creuset Cast iron enamel cookware in Cadmium red color:)

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

As the sense of environmental protection enhanced in recent years, more and more small manufacturers of Cadmium red pigment have to stop their production, which makes Nolifrit the only and best choice for Cadmium red pigment. As our production is based on factories on west border areas in China, so there’s no worries for environmental pollution.

Cadmium red pigment produced in Nolifrit is very cost-effective, the price is half of the current international brand. Much cheaper than Ferro and Pemco(Prince).

Nolifrit once had a meet with the world’s top one brand of colored cast iron enamel cookware Le Creuset in the 24th International Enamellers Congress in Chicago. Le Creuset showed the strong interests in our Cadmium red pigment series. They are quite willing to build up the long term cooperation with us. If you are also one of the enamel cookware manufacturer like them, you can contact with us, we will send you our best offer for our enamel pigments.

 

Ceramic porcelain frit

An ISO 9001:2001 certified ceramic porcelain frits manufacturer, we follow stringent guidelines for our supplier selection, porcelain frit technology and technical service standards.

We offer both leaded and no lead porcelain frit varieties available as transparent porcelain frits, glossy porcelain frits and matt porcelain frits designed specifically for double fast firing, single-fired monoporosa and porcelain stoneware ceramic coating applications.

Our specialty porcelain frits are ideal for ceramic coatings used in architectural ceramics, building ceramics, dinnerware and ceramic arts.

This article comes from ferro edit released

How to Test Acid Resistance Level for Enamels

The applications of acid resistant enamel coating is more and more widely, especially in mid and high level market. It’s not only applied in industrial area, where chemical resistance and long lasting durability against the elements is key, but also in our daily life, like enamel cookware and enamel water heater tank.

How to test acid resistance level for porcelain enamel coating?

Nolifrit follows a very serious and effective testing method for this.

Testing Reagent:

15% citric acid is used in this test. It’s reacted on the enamel coating surface and the result can be seen by virtual observation.

Testing Step:

1, Place some drops of citric acid liquid on enamel coating surface.

2, Cover the dropped enamel coating surface for 15 minutes.

3, Wash the test plate, to do the follow tests:

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A, Visual Inspection

To inspect the two enamel coating areas directly by eyes. If there is obvious difference between the acid applied area and the regular enamel coating surface, the result is negative.

B, Pencil Test( dry)

Two parallel lines are drawn between the acid applied enamel coating area and the regular enamel coating surface by a pencil. Two lines are swabbed by a dry towel. If it is harder to swab the acid applied enamel coating area than the regular enamel coating area, the result is negative.

C, Reflection Test:

A light source is reflected on the acid applied enamel coating area and the regular enamel coating area. If there is a dim reflection on the acid applied enamel coating surface, the result is negative.

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D, Pencil Test( wet)

The test in item B is applied by a wet towel. If it is harder to swab the acid applied enamel coating area than the regular enamel coating area, the result is negative.

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

We have many kinds of enamel frit and enamel powder (ready to use powder and electrostatic powder) with high acid resistance level AA. They are widely used in enamel cookware, enamel storage tank, GGH(gas gas heater) and heater exchangers.