DD262474A1 - PROCESS FOR COATING COMPOUND ELEMENTS FOR TUBES WITH CUTTABLE CORROSION PROTECTION - Google Patents

Abstract

The invention relates to a method for coating connecting elements for pipes with cuttable corrosion protection coatings. The protective layers of organic material serve to protect pipe fittings against corrosion and incrustation even after a mechanically cutting treatment (tapping) under continuous load by aqueous media up to 100C. A mixture of 1 part by weight of phenolic resin, 2 parts by weight of epoxy resin and 8.5 to 9.5 parts by weight of a pigment, filler, solid additive mixture is applied in several layers, intermediately hardened at temperatures of about 180 ° C. and quenched at 210 ° C.

Description

Characteristic of the known state of the art

Metallic articles, if they are to be subjected to continuous long-term exposure to water, aqueous solutions or other nonaqueous media at normal temperature or elevated temperature, are usually made of such metals which are resistant to corrosion and incrustation. Such metals are e.g. Lead, copper, brass, zinc casting, etc. Here it is not difficult to perform a cutting after treatment, such. B. cut an internal or external thread.

If the objects are made of iron, steel or cast steel, corrosion and incrustation can be expected in a short time, unless suitable metals are applied as coatings by hot dipping, galvanic coating, etc. Galvanization is particularly often carried out, but undergoes a potential reversal at a constant temperature of more than 6O ⁰ C compared to aqueous solutions, ie the iron material is electrochemically to the anode and then destroyed by corrosion even faster than without this zinc coating. A damaged protective layer of an electrochemically noble metal, z. As brass, even at a temperature below 60 ⁰ C lead to a similar destruction of the base metal.

Also, organic protective layers are suitable for the corrosion protection of ferrous materials under the conditions described and are used in some cases for the inner coating of pipes. Are the long-term acting wet temperatures not above 60 or 7O ⁰ C, then z. B. polyethylene coatings used for internal protection of pipes. At higher temperatures, it is preferably baked enamels based on epoxy resin, epoxy / phenolic resin or furfurol resin combinations or catalytically curing epoxy resin layers. The very temperature resistant silicone resin coatings are not resistant to simultaneous wet stress. Occasionally, inorganic coatings are used, for. However, such coatings are very hard and brittle.

An additional problem occurs that means a great deal of restriction in the choice of coating materials when a subsequent cutting treatment is required, eg. B. if an external or internal thread is cut into this coating, as in fasteners, such as fittings, etc., is necessary.

In these cases, the organic coatings are either relatively easy to cut, such as thermoplastics and zinc-rich coating materials, but at temperatures above 60 or 70 ⁰ C for the reasons mentioned no longer applicable. Phenol / epoxy resin based stoving coatings are also capable of withstanding higher wet temperature loads, but are either too brittle in the conventional way for cutting operations and therefore give faulty thread cuts that provide corrosion points of attack, or are in one case provided with a certain inappropriate special pigmentation.

It can therefore be stated that for a long-term stress in o. G. Within the temperature range of 70 to 100 ° C in principle organic coating materials fail, provided that the requirement for a thread cutting is connected. There is a technological gap in this case. This fact is reflected i.a. By contrast, special plastic couplings are now being offered for internally plastic-coated tubes, making any metallic or organic coating superfluous at all (Infotech 2/87, TPS Technitube Röhrenwerke GmbH, Customer Information Magazine, pp. 12-15), i. a special construction of the pipe ends to be connected allows the storage of internal and external threads not touched by media. However, these connections are relatively complicated.

Object of the invention

The aim of the invention is to reliably protect pipe connection elements even with a continuous action of water, aqueous solutions and non-aqueous media at a temperature up to 100 ° C against corrosion and instruction and at the same time to offer the possibility of a cutting after treatment, eg. As the cutting of connecting threads with high thread precision at an economically acceptable degree of wear of the cutting tools to allow.

-2- 262 Presentation of the essence of the invention

The object of the invention is to provide an organic coating which can be subjected to a cutting mechanical machining with good thread quality and a long-lasting protection of metallic surfaces against water, aqueous solutions and non-aqueous liquid or gaseous media up to 100 ° C. Continuous load against corrosion and incrustation guaranteed.

This organic coating should be applicable to fittings inside and / or outside by the usual application methods, such as spraying, dipping, flooding and electrostatic spraying.

It has been found that in contrast to the previous findings that a layer in which a ratio of 1 part by weight Resol type phenol resin (solid) to 3 parts by weight of epoxy resin (solid) offers the best properties against simultaneous corrosive and mechanical stress, the object of the invention is soluble with a coating having a mixing ratio of 1: 2 parts by weight of said solid resins. These coatings also contain 8.5 to 9.5 parts by weight of pigment, fillers and solid additives having an average density of 3.5 ± 0.3 g / cm ³ and are applied in multiple layers, cured at temperatures of about 18O ⁰ C and at temperatures finally cured to 210 ⁰ C.

embodiments

In the following, the importance of the ratio of the main components of the coating material in the mechanical stress solid coating and the resistance to the media at a continuous temperature of up to 100 ° C will be set forth.

The preparation of the coating materials is carried out in the usual manner for the paint manufacturing technology using about 50% resin solutions and use of solvents such. As ethyl glycol, butanol, xylene, etc. The coating is applied for the intended purpose in 4 to 6 layers with a total layer thickness of about 200μιτι. The respective intermediate curing after each layer is carried out for 1 h at 18O ⁰ C, the final curing for 1 h at 200 to 210 ⁰ C.

table

Sample No. Mass ratio A: B: C average density of the pigment-filler mixture (g / cm ³ ) Total layer thickness (μιη) (number of layers) 1 1: 2: 7.9 3.69 240 (6x) 2 1: 2: 6.7 3.36 120 (6x) 3 1: 2: 1.7 3.36 160 (6x) 4 1: 2: 8.3 3.36 160 (5x) CJL 1: 2: 14.4 3.36 130 (4x) 6 1: 2: 9.6 3.36 1104X) 7 1: 2: 9.2 3.36 200 (6x)

In the table mean:

A = phenol resin (solid) of the low-condensation type resol (eg Phenodur 678 U, Scadeform L9, KSE resin of VEB Kunstharze Mattstedt

B = high molecular weight epoxy resin (solid) (eg Araldit 6097, 6099.7097, Epikote 1007, 1009 etc.) C = mixture of pigments, fillers and solid additives whose particle diameter is less than 20μηη and whose average density is 3.5 ± 0 , 3g / cm ³ (eg, titanium dioxide, chromium oxide, silica, bentone, etc.)

Table (continued)

Sample No. Surface smoothness (grades) Luchtbeständigkeit (h) Mechanical workability (grades) Remarks 1 4 > 2000 5 6 layers possible 2 2 250 2 low layer structure 3 2 100 2 inconsistent in hot water 4 2 80 , 3 porous, tends to break CJI 4 40 3 strong tearing

Surface smoothness (grades) Light resistance <h) Mechanical workability (grades) -3- 262 474 Sample No. 3 200 1 Remarks 6 1 > 2,000 1 Coating to the 4th layer well, then uneven 7 smooth, non-porous coating

Grades: 1 = best value smooth coat, low incrustation or sharp cut edges and little wear on cutting tools

5 = worst value rough layer, relatively very strong incrustation or partially brittle fracture at cutting edges and unacceptably high wear of the cutting tools

In the luchtprüfung mentioned in the table, the coating material with the specified number of layers and total layer thickness is applied to a closed metal tube on one side, which is traversed by cooling water inside. The coating is on the outside and is flushed for the specified number of hours until bubbles, cracks or detachments of condensing water vapor occur.

Claims (1)

A process for coating of connecting elements for pipes with corrosion and inkrustationsschützenden, to water, aqueous solutions and non-aqueous liquid or gaseous media up to 100 ⁰ C resistant coatings that are subsequently mechanically cutting machined from phenolic and epoxy resin and pigments, Filler, solid additive mixtures, characterized in that a mixture of 1 part by weight resole phenolic resin, 2 parts by weight of epoxy resin and 8.5 to 9.5 parts by weight of solids from pigments, fillers and solid additives having an average density of 3.5 ± 0, 3g / cm ^{3 applied} in several layers, cured at temperatures around 18O ⁰ C and finally cured at temperatures up to 210 ⁰ C. Field of application of the invention The invention relates to the coating of fasteners for pipes (fittings) with an organic protective coating, which can still be subjected to a cutting mechanical machining after the order and against water, aqueous solutions and non-aqueous media even with continuous exposure to temperatures of up to 100 ⁰ C from corrosion and incrustation protects.