FR2495190A1 - PROCESS FOR APPLYING RESISTANT PROTECTIVE EMAIL COATING TO DUCTILE FOUNDRY BODIES - Google Patents

Abstract

The present invention relates to a process for applying a protective enamel coating resistant to aggressive media, on ductile foundry bodies, in particular cast iron pipes. According to the invention, an enamel having the following composition matrix in the molten state (% by weight) is applied to the surface of the foundry body, free of a first enamel layer and pretreated in a known manner: SiO2 , 30-50; ZrO2, 1-3; B2O3, 2-10; CeO2, 0-3; Na2O, 15-20; SrO, 0-1; Bi2O3, 1-10; ZnO, 1-5; Li2O, 1-5; MnO, 0-3; TiO2, 5-15; NiO, 0.5-2; CaO, 1-5; CoO, 0.5-1; BaO, 1-5; F2, 0.5-2; Al2O3, 1-3.

Description

Method for the application of enamel coating

  resistant protector on ductile foundry bodies.

  The present invention relates to a process for the application of a protective enamel coating resistant to aggressive media, on ductile foundry bodies, particularly

cast iron pipes.

  According to the data presented in the literature (Silikatechnik 1955, 480), ductile iron (nodular cast iron) was first considered unmountable at about the same time (Petzold "Emaille" l 1950, Stuckert "Die Emailfabrikation" 194 and Mârker "Emailliertechnik" 1956), that before the application of a powder enamel resistant, it is appropriate to apply and cook first a basic enamel or first layer.A procedure in two stages is thus in this case of rigor.This procedure

  results in significant energy consumption and is expensive to

  because of the first layer of enamel to be applied and

bake.

  The object of the present invention is to improve the procedure

  conventional design so that ductile foundry bodies can also be provided with a tough enamel coating in a

  enamelling process in a single stage.

  The process according to the invention is characterized by the fact that it is applied to the surface of the foundry body, free of

  first layer of enamel and pretreated in a known manner, an enamel above

  what is the following melt composition matrix% wt% wt SiO2 30-50 ZrO2 1 - 3 B203 2 - 10 CeO2 O- 3 Na2O 15SrO O - 1 i203 1 - 10 ZnO 1 - 5 Li2O 1 - MnO 0 - 3 TiO 2 5 - 15 NiO 0, 5 - 2 CaO 1 - 5 CoO 0.5 - 1 BaO 1 - 5 F 2 0.5 - 2

A1203 1 - 3

  The characteristics taught by the invention are therefore based on the surprising constvion that, unlike the widespread spread, mentioned above, can be applied by the direct method, that is to say without prior application of a premie

  layer of enamel, a layer of enamel resistant to organic acids

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  and water of all kinds, on ductile foundries,

  in particular cast iron pipes, so that these last

  do not require, when they are placed in the ground,

  special cladding or the provision of an additional layer of protection against aggressive media. Absolutely

  independently of the energy saving by removing the

  of a first layer of enamel intended to be fired in a separate working stage, the use of nodular cast iron or spheroidal graphite pipes provided with a protective enamel coating in accordance with the method of the invention entails an essential simplification and, consequently, an economy

  of work and considerable time.

  The deposit of the enamel preferably takes place in the vertical position of the cast iron pipes or other foundry bodies of revolution, namely in particular in the form of a slip, dipping, spraying or flow. We can

  advantageously use an induction coil for drying

  age of the slip applied. The actual enameling, namely the enameling of the enamels, takes place on the foundry body in a vertical position, namely preferably also with the aid of a

  induction coil, with a predetermined temperature and speed

  born. For this purpose, the pipe is passed through the induction coil

  from top to bottom or also in the opposite direction.

  It has been found particularly suitable in the process of the invention to apply powder enamel directly to the foundry body still in the heated state. In this case, saving time is not the only very advantageous factor. Since the enamel provided by the invention has a relatively low melting temperature, it is possible to enamel the foundry body to be enamelled after heating to the temperature of adhesion.

  enamel using the clean heat of the enamel foundry body

  still present, a separate heating and cooking process

  in practice is removed and the result is a new econo-

additional energy.

  The low melting temperature mentioned above

  has a low softening range of 500 to 520C, which

  torise a united enamel fusion in a temperature range of 700 to 8000C. When the cooking time is shortened, for example

  at 1 to 3 minutes, we can also operate in the field of

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  higher temperatures up to 950.

  The enamel provided by the process of the invention is distinguished by a very low surface tension of 200 to 210 Dyn / cm. This allows rapid wetting and smooth enamel flow in a thin film range of less than 400 microns. In the

  thickness of less than 500 microns, the enamel is

  shock resistant up to 5 kp and abrasion resistant. Because of

  of the drying technology used, the vitreous powder of

  Unaltered mail is brought into fusion, so that it forms compact enamelling and smooth surface, which in no way tend to form incrustations. As a result of the intimate interlocking of the composite material (ductile iron-enamel), no internal migration of corrosion or internal rust occurs. The enamel of the invention is neutral vis-à-vis materials, especially with respect to all metals and compounds of metals or alloys. It takes

  to emphasize that the enamel of the invention is on the one hand physiological

  and toxicologically harmless and on the other hand

  in the pH range of 1-10 with respect to all organic acids.

  and waste water as well as untreated water,

  industrial water and drinking water.

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Claims (3)

  1. - Process for applying a protective enamel coating   resistant to aggressive media, on ductile foundry bodies, in particular cast iron pipes, characterized in that it is applied to the surface of the foundry body, free of a first layer of enamel and pretreated in known manner, an enamel having the following melt composition matrix:% wt% wt SiO 2 ZrO 2 1 - 3 B 2 O 3 2 - 10 CeO 2 O - 3 Na 2 O 15 SrO O - 1 Bi 2 O 3 1 - 10 ZnO 1 - 5 Li 2 O 1 - 5 MnO 0 - 3 TiO 2 5 - 15 NiO 0.5 - 2 CaO 1 - 5 CoO 0.5-1 BaO 1 - 5 F 2 0.5 - 2 A1203 1 - 3   2. - Method according to claim 1, characterized in that the enamel is applied in powder form directly on   the foundry body still in the heated state.   3. - Process according to claim 1, characterized in that an induction coil is used for drying the enamel slip applied to the foundry body and / or to   baking the protective enamel coating.