Benutzer:JurecGermany/Glass-lining

Dieser Artikel ist im Entstehen und noch nicht Bestandteil der freien Enzyklopädie Wikipedia.

Solltest du über eine Suchmaschine darauf gestoßen sein, bedenke, dass der Text noch unvollständig sein und Fehler oder ungeprüfte Aussagen enthalten kann. Wenn du Fragen zum Thema hast, nimm Kontakt mit dem Autor JurecGermany auf.

This article summarises the technical applications of the material "glass-lined steel or technical enamel". General applications are described in the article glass lining.

Engineered glass linings are used in technical applications, for example in the construction of highly acid-resistant pressure vessels, which are deployed in chemical and pharmaceutical process engineering. Typical equipment includes agitated reactors, storage tanks and recipient vessels (e.g. tanks to catch a distillation product or tanks to store media for a process engineering procedure), columns, pipes and pipeline parts as well as numerous glass-lined components, which are necessary to make these types of equipment complete.

In the case of these types of equipment, measuring up to 120,000 litres in volume, the whole of the inner surface in contact with the product is coated with a glass layer between 1.4 and 2 mm in thickness and fired several times. The quality criteria of this technical enamel are stipulated in ISO 28721-1 (previously DIN EN 15159-01:2006 , formerly DIN 28063). Usually the equipment is designed to be "pore-free", that means that the several square metres of the vessel's inner surfaces should be completely free from defects in the glass layer. "Technical enamel" is high quality glass which in terms of thermal shock resistance, impact strength and especially corrosion resistance is optimised for a broad pH range. Like all types of glass, technical enamel is extremely resistant in an acidic environment. Because of the chemical properties of the silicates it is less resistant in the alkaline range.

A technical enamel coating always comprises one to two layers of base enamel and up to five layers of cover enamel. The latter gives the enamel chemical resistance and the required operational properties. Fine-grained steel (such as P275 NH, P265 GH) is used as a base material which is restricted in terms of carbon content and manganese content. The required quality, layer thickness and flawlessness of the enamel layer should be achieved for economic reasons with a minimum number of layers of cover enamel. There are two renowned manufacturers of glass-lined equipment in Germany. Pfaudler_Werke GmbH in Schwetzingen has been constructing glass-lined equipment in Germany for 100 years. With 170 years in the tradition of technical enamel, THALETEC GmbH in Thale in the Harz mountainsHarz uplands originated from the former ironworks in Thale (EHW Thale).

In the meantime, it is also possible to coat components produced using "Selective Laser Sintering" or "Selective Laser Melting" additive manufacturing process, see Video on Youtube.

Glass-lined pressure vessels and process engineering equipment

view into a glass lined reactor with a turbo-mixer

Bundesarchiv Bild 183-M0902-0130, Leipzig, Herbstmesse, Autoklaven: Glasslined reactor oft he former Eisenhüttenwerk THALE, EHW Thale shown on the Leibzig trade show in 1973

Standardisation and compatibility

Glass-lined process engineering equipment is defined and standardised in a number of DIN, EN and ISO standards. This allows the user, irrespective of the original manufacturer of the equipment, to make use of a greater number of suppliers for spare parts, reglassing and for the delivery of accessories, such as seals etc. In this way individual manufacturers can ensure compatibility with existing components without restriction. Companies in Germany which offer such spare parts include, for example, Thaletec in Thale in the Harz region.

Accessories for glass-lined equipment

These include, for example:

• baffles

• heat exchangers

• Dip pipes

• agitators

• manholecovers

• manholeprotection rings

• Bottom outletvalves with dynamic sealing of the valve tappet using bellow

• Glass-lined pumps

Glass-lined storage tanks

Large volume tanks for storing liquid manure, water and other solids and liquids are constructed from individual panels (glass-lined metal sheets measuring up to 2 ×2 m). These tanks are not pressure vessels.

Glass-lined pipelines

Glass-lined pipes and pipelines are used in the chemical and pharmaceutical industries and in the drinking water supply. In the chemical and pharmaceutical industries pipelines with a nominal diameter of up to 200 mm are coated internally with several layers of glass in order to obtain a sufficiently and chemically resistant anti-corrosive protective layer. The material used for the pipelines is usually a carbon steel such as P235 G1TH (formerly St35.8). For the drinking water supply pipelines made of cast iron are used, which are coated inside with just one layer of glass.

Reglassing

Reglassing is the process of renewing a glass coating.

Special engineered glass linings

Glass linings for processes in the pharmaceutical industry

Engineered glass linings for processes in the pharmaceutical industry are mostly white or light blue in colour which facilitates observation of the processes during the reaction and makes it easier to inspect the cleaned equipment (For an example, see Abbildung im Artikel).

Engineered glass linings with an antibacterial effect

One special development is a glass lining with an antibacterial effect, which contains small amounts of silver particles. The effectiveness of Silber as a bactericidal agent is available as a high quality surface enamel coating for specialised applications in biotechnology and for other fields in which the risks of contamination by viruses and micro-organisms have to be reduced.

Abrasion-resistant glass

Especially in agitated tanks in which suspensions of solids are stirred, this can lead to abrasive wear (hydroabrasion). In this way the glass lining can be worn by the sliding or impact processes in which the glass lining is progressively worn away. Specialised compositions of the glass can significantly improve the wear resistance to an extent compared with normal engineered glass linings:

• In the case of "semi-crystalline glass" crystallising deposits in the glass matrix improve wear-resistance compared with conventional glass.

• Enamels which are fired with nanoscale, carbide-like hard materials in an oxygen-free atmosphere, result in a dramatic improvement in wear because the embedded hard materials (e.g. carbide) provide significantly higher resistance to wear than the amorphous glass matrix. The glass matrix serves merely as a carrier for the embedded materials. The wear resistance of such a glass lining is then particularly high if the size of the abrasive particles is greater than the coating thickness of the (softer) amorphous glass matrix.

Electrically conductive glass linings

Glass linings are an electrical insulator but can become conductive by the addition of metals. To this end, chemically-resistant metals such as platinum, silver or gold are used which are distributed in the glass matrix.

There are alternatives, semiconductor materials are another possibility, to ensure conductivity in an otherwise non-conductive enamel coating. To this end, the semiconductor materials are distributed in the glass matrix and using a specially adapted firing process arranged in network-like structures in the glass matrix. Consequently, enamel coatings manufactured in this way generally have better chemical resistance to corrosive attack than those with embedded metallic particles.

Glass linings for polymerisation processes

Since glass-lined surfaces are particularly easy to clean and also has non-stick properties, it has been used for decades in the manufacture of Polymer, for example of Polyvinylchlorid (PVC). Corresponding chemical reactors are coated with a special "poly-enamel". As Polymerisation usually takes place exotherm, in such polymerisation equipment it depends upon the exothermic reaction heat being effectively dispersed. Therefore the glass lining of such equipment is usually "thin", i.e. thickness in the region of 1.1 mm maximum. Thus the heat transfer resistance of the vessel wall is minimised because of the glass lining. Since polymerisation is seldom corrosive, the reduced thickness of the layer has no influence on the operating life of the equipment.

In order to ensure the thermal transfer specifically during cooling of the polymers (exothermic reaction), often glass-lined heat exchangers are used which are fitted as baffles into the glass-lined equipment and can improve the thermal transfer performance by a factor of 3 and more compared with conventional jacket cooling.

glass lined heat exchanger for chemical applications

Glass-linings for bio-corrosive processes

Specialised glass-linings are particularly resistant to bio-corrosive attacks, such as could occur from fungi, sponges or bacteria. The phenomenon known as "Biofouling" is inconceivable for surfaces coated with special biocorrosion-resistant enamel, compared with the conventional enamel coating. The corresponding enamel coatings for biocorrosive processes can also be produced in such a way that they can also have an antibacterial and germicidal effect (see above under "Technical enamels with an antibacterial effect").

View into a gless lined reactor glassed with a glass-linging that is suited for bio-corrosive proesses

Glass linings for flue gas heat exchangers or Luftvorwärmer

Economiser in a power station, made of glass lined pipe bundles

There are corrosive exhaust fumes in the exhaust gas flows from conventional fossil fuel power stations (see Economiser), in coal-fired power stations or in waste incineration plants. These exhaust fumes cool down so much in glass-lined heat exchangers (below the dewpoint), that corrosive liquids such as sulphuric acid form. Special glass linings are modified in such a way that they are particularly resistant to exposure to sulphuric acid. Compared with the usual chemical enamels, such glass linings designed specifically for sulphuric acid applications are up to 30–40 % more resistant, i.e. they have a correspondingly smaller corrosion rate. Similar types of glass linings are available for the construction of glass-lined equipment and are used for plants processing sulphuric acid.

Other technical applications

Architectural enamel

Enamelled boards are used in architecture for wall cladding. Enamelled panels can be easily cleaned and have a high quality appearance. As a general rule, architectural enamel coatings are used on steel sheets with a thickness of 1 to 2 millimetres, or on float glass. The enamel can be applied by screen printing, digital printing, roller coating or other methods. Another option is to apply the enamel slurry using a spray gun or brush. Then the component is fired. One application where this is used is for cladding the walls of road tunnels with enamelled panels, the benefits of which include easy cleaning and being non-flammable.

enamelled wall picture colose to the train station inThale/Harz

Enamelling of sanitary ware

Baths and shower trays as well as washbasins made of enamelled steel are considered to be hygienic, easy to clean and robust sanitary ware and provide an alternative to heavy cast iron baths and the subsequently developed plastic baths. In enamelling baths and shower trays made of steel industrial plants are used, comprising two major manufacturing units: pressure forming technology and enamelling. In the former process titanium steel is pressed into shape in large presses and in the second process an enamel coating is applied to the steel. This is a glaze made of glass, quartz, borax, soda and water. The top coat in the preferred colour is sprayed on and then fired in a furnace.

Enamelling of "white goods"

"White goods" denotes household products such as cooker lids, the visible surfaces of washing machines or fridges. The name is therefore based on the traditional colour for such products. Enamel is used to coat surfaces for hygienic, tactile and visual reasons as well as being easy to clean.

Enamelling of household goods

Enamelled pottery in grijs gewolkt (grau gewölkt) made in the dutch DRU fabriek

Traditionally found in "Grandma's kitchen" were enamelled pots, pans and other items in daily household use. Such items were used almost everywhere in the past because of the lack of other corrosion-resistant materials. Only with the advent of stainless steel and especially, plastics did enamelled household goods become less common. As good quality enamels for pot and pans are particularly suitable for those with allergies, enamel cookware has meanwhile made a comeback in the modern kitchen. Cast iron pots, roasting pans and frying pans were traditionally protected against corrosion with just a thin, black matt enamel coating. The good roasting and cooking properties, however, are also available in coloured cast iron enamels.

Chipping of enamelled household goods – harmless

Enamelled crockery can suffer damage over its life, so-called chipping. This chipping can be caused, for example, by a knock or impact affecting the enamelled part. In the case of thin enamelled sheets, such as crockery, the enamel can be damaged down to the steel so that it is no longer protected from corrosion. As enamelled crockery is usually made of a non-corrosion resistant carbon steel, the crockery can rust at the damaged site. Because of the composite layer between the enamel and the steel created during firing, rust cannot spread to the enamel layer which is still intact close to the damage and thereby will not lead to progressive chipping of the enamel. Chips on the outside of a pot or pan are completely harmless, but look unappealing. In principle, chipping in modern high quality enamels is only possible with brute force. Nowadays, the enamel coating is much thinner and more flexible than in the last century.

In individual cases there is also spontaneous flaking, which resembles fish scales. Such damage is caused by hydrogen escaping from the metal if the structure of the metal does not meet the demands of the enamelling process. These fish scales are designated as hydrogen faults and thus are attributable to the steel. The worst thing about these effects is that, for the most part, they may not occur immediately during or following production but may take as long as several months to do so. They can be avoided by the careful choice of the sheet steel grades used, so that only those grades meeting the standards set with guaranteed enamelling outcomes are used.

Emailschaden an einem Geschirrteil. Chipping oft he glass at the edge.

Weblinks

• Technical enamel (PDF; 1,9 MB) DEV

References

[[:Category:enamel]] [[category:lining material]]