DIN 50938-2000 Black Oxide Treatment

Coatings N02 207Textile Systems 001-en Technical Design Manual Browning DIN 50938 Page 1/1 The following standard is used at Rieter: DIN 50938: April 2000, pages 1 - 5 Black Oxide Treatment of Steel Components Requirements and Testing Recommendations and Engineering Drawing Notation: Designation for a black oxide coating following DIN 50 938 on a steel (Fe) part, process group (A) bath black oxide and post-treatment by greasing, oiling or other lubricants (T4). Release: S. Liefert DTTNS 2003-10-21 Change: . unalloyed and low-alloy steel) components with uniform black coatings while substantially retain- ing their dimensional accuracy. Previous editions DIN 50938: 1973-12. Foreword This standard has been prepared by Technical Committee Chemische und elektrochemische Überzüge of the Normenausschuss Materialprüfung (Materials Testing Standards Committee). Brünieren von Bauteilen aus Eisenwerkstoffen – Anforderungen und Prüfverfahren In keeping with current practice in standards published by the International Organization for Standardization (ISO). The purpose of this treatment is to give the material a particular appearance and to increase its corrosion resistance even without aftertreatment.220. 1987-11.V. 10772 Berlin. DIN 50017 Artificial climates in technical applications – Condensation water test atmospheres DIN 50902 Protective coatings on metals – Concepts. No. Amendments This standard differs from the November 1987 edition in that it has been harmonized with DIN EN 1403 and DIN 50960-1. This process provides iron and steel (i. DIN 50938 : 2000-04 DIN Deutsches Institut für Normung e. For dated references. Threaded articles shall be coated as agreed. however. provisions from other publications. Germany. the latest edition of the publication referred to applies.e. a comma has been used throughout as the decimal marker. the German-language original should be consulted as the authoritative text. by dated or undated reference.01 . 12. D EUTSCHE NORM April 2000 Black oxide treatment of ferrous products { Requirements and testing 50938 ICS 25. For undated references. 1 Scope This standard specifies requirements for and methods of testing black oxide coatings produced on ferrous components by a chemical reaction during an immersion process. and it has been editorially revised. subsequent amendments to or revisions of any of these publications apply to this standard only when incorporated in it by amendment or revision. These normative references are cited at the appropriate places in the text. © No part of this translation may be reproduced without the prior permission of Ref.20 Supersedes November 1987 edition. English price group 06 Sales No. application methods and surface preparation DIN 50960-1 Electroplated and chemically applied coatings – Designation and information in technical documentation DIN EN 1403 Corrosion protection of metals – Electrodeposited coatings – Method of specifying general requirements Continued on pages 2 to 5. In case of doubt. The degree of protection provided is. Berlin. Beuth Verlag GmbH. The standard does not cover semi-finished products and fasteners. 0106 has the exclusive right of sale for German Standards (DIN-Normen). low. cast iron. 2 Normative references This standard incorporates.. Translation by DIN-Sprachendienst. and the titles of the publications are listed below. The saturation of the colour obtained depends on the nature of the base metal (substrate). three-bath coating: C. DIN 50902) to which reducing agents or other reagents may have been added. the surface preparation and the composition and type of treatment bath.3 Heat treatment The heat treatment shall be designated by the following: a) the letter ‘H’. These shall be designated as follows: single-bath coating: A.5 4. e) a solidus. significant surface is an area on a product that can be touched with a ball 20 mm in diameter.2 Coating methods There are three black oxide coating methods. 4. this shall be indicated by a double solidus. expressed in °C. If a specific treatment is not required and thus need not be referred to in the designation. c) the treatment time. b) the minimum heat treatment temperature. two-bath coating: B. f) any additional symbols to denote further treatments to be carried out shall be separated by solidi and give the sequence in which the coatings are applied (see subclauses 4. c) a hyphen.2. the heat treatment. d) the chemical symbol of the base metal or the main component of the alloy. . in g/m2 A 4. NOTE: It is recommended that the standard designation of the base material follow the symbol of the base metal. 3.Page 2 DIN 50938 : 2000-04 DIN EN ISO 2064 Metallic and other non-organic coatings – Definitions and conventions concerning the meas- urement of thickness ISO 4519: 1980 Electrodeposited metallic coatings and related finishes – Sampling procedures for inspec- tion by attributes 3 Concepts 3. 4. ‘significant surface’ is defined as ‘The part of an article covered or to be covered by the coating and for which the coating is essential for serviceability or appearance’. each resulting in a different mean mass of coating per unit area (see table 1).5 C 6.1 General The designation shall include the following information: a) The word ‘coating’.*) 4 Designation 4. Table 1: Approximate mean mass per unit area of black oxide coatings Designation of Approximate mean mass per coating method unit area of coating. b) the number of this standard.3 and 4.1 Black oxide coating A thermally produced dark-brown to black oxide conversion coating produced by immersion of a component in alkaline salt solution (cf. in hours. in brackets. In DIN EN ISO 2064. Designation of heat treatment carried out for three hours at a minimum temperature of 190 °C: HT(190)3 *) Translator’s note.4).2 Significant surface Unless otherwise agreed.5 B 5. 6 Procedure 6.4 Supplementary treatments Any supplementary treatments shall be designated as in table 2. d) the quality. except for T10. by providing a suitably marked specimen). varnishes. f) details of sampling.g. the acceptable quality level or any test requirement differing from those in ISO 4519 (see clause 7). Designation of a black oxide coating on a steel (Fe) component that has not been heat-treated. with a rinse in cold water between baths. which is dependent on concentration. h) any special requirements relating to the reprocessing of discarded components. the second immersion and. b) whether heat treatment is required prior to coating (see subclause 4. If necessary. then thoroughly in cold. In some cases. first in cold. The coating time will also depend on the nature and quality of the components. regarding roughness). where necessary. the components may be preheated in water at 60 °C to 80 °C. In the case of the multi-bath methods. To prevent the temperature of the bath dropping sharply. the quality of the coating may be improved by adding other salts to the bath.g. con- centration and temperature of the solution. oxide and other impurities removed. The customer may provide the following supplementary information: g) any special requirements or conditions relating to the surface preparation of the components. optionally with reducing agents or other substances added to the bath. The condition of the bath shall be continuously checked by monitoring the boiling point. 6. oil or other lubri- cants T5 Application of wax T10 Application of water-displacing anti- corrosive agents NOTE: The symbols conform to the standard designations for supplementary treatment for electrodeposited coatings as in DIN EN 1403. i) any other special requirements (e. attachment points). the coatings will develop in immersion times of between five and twenty minutes. Depending on the composition.3). state and appearance of the base metal if they may affect the serviceability and appearance of the coating. Table 2: Designation of supplementary treatments applied to black oxide coatings Symbol Type of treatment T1 Application of paints. After coating. No other bath checks are generally needed. e) the location of unavoidable defects (e.2 Main treatment One or more coating stages shall be carried out in boiling alkaline oxidizing solution at about 135 °C to 145 °C. c) the significant surface (e. . stationary water. Page 3 DIN 50938 : 2000-04 4. the boiling point of each bath being about 5 °C higher than that of the preceding bath. the third immersion shall be carried out in separate baths. pow- der coatings or similar materials T4 Application of grease.g. the components shall be rinsed. this point shall be adjusted to the required value by carefully adding water or coating salt. but has undergone the single-bath coating process (A) and then waxed (T5): Coating DIN 50938 – Fe//A/T5 5 Order details The customer shall provide the following information: a) the designation of the coating (see clause 4). running water and finally in hot water at 60 °C to 80 °C.1 Preparation of surfaces The surfaces of the components to be coated shall be carefully degreased and any scale. The suppliers’ operating and safety instructions shall be observed when making up and using the bath. and its colour shall be uniform and as black as possible. To meet special requirements. the components or specimens shall not be aftertreated. 7 Testing the untreated coating The test to be used to assess the quality of the coating or of the bath shall be agreed on a case-by-case basis. item f)). have a surface texture as similar as possible to that of the component to be coated and have received the same treatment prior to coating. If a coated component that has not been aftertreated is wiped with a clean white cloth. after which not more than 1 % of the surface of the component tested shall be covered with rust. the samples taken shall measure at least 50 mm × 50 mm × 1 mm. they shall be treated while cold to minimize the loss of solvent by evaporation. no colour shall appear on the cloth. the minimum exposure time shall be agreed on a case-by-case basis. CH3COOH.Page 4 DIN 50938 : 2000-04 6.1 Appearance The black oxide coating shall cover the surface of the base metal evenly and completely. sharp edges shall be coated with acid-resistant paint after coating and prior to being placed in the test chamber.3.2 Procedure After coating. 7. Supplementary treatments serve to increase the degree of protection. Table 3: Minimum exposure times in DIN 50017 – KK test Minimum time with no signs Coating method of corrosion. Drying is unnecessary if there is to be an aftertreatment with hot saponifiable oil at about 120 °C. When components having highly contoured surfaces are to be tested. full immersion with amended times may be agreed. in hours A 24 B 48 C 72 The minimum exposure time shall be as specified in table 3. but dried as specified in subclause 6. Table 4: Minimum exposure times in acetic acid test Minimum exposure time.3 Drying and supplementary treatment After rinsing.2 Determining the degree of protection by exposure to a standard atmosphere The anti-corrosive effect of the coating shall be determined by suspending components or specimens that have not been aftertreated.3. If the components are to be aftertreated in water-displacing anti-corrosion agents. To prevent edge corrosion.3 Determining the degree of protection with acetic acid at ambient temperature 7. paints or similar coatings may be applied. in the DIN 50017 – KK standard atmosphere. 7. 7. except in the case of cast materials and hardened components. This test may be commenced immediately after the specimens have been dried and cooled to ambient tempera- ture. Slight changes in hue shall be ignored. in oil emulsions at 80 °C to 95 °C or with hot. There shall be no brownish or greenish spots due to an excessive concentration or contamination of the coating bath. the components shall be dried immediately in an oven at about 120 °C or in hot air. 7. Unless otherwise agreed. Coating method in minutes A 10 B 20 C 30 . but dried as described in subclause 6. Any corrosion at such points shall be ignored.1 Test solution 20 % (m/m) aqueous solution of analytical grade acetic acid. About four drops of the test solution shall then be applied to a flat area of the coated specimen or component. the samples shall be collected as specified in ISO 4519 (see clause 5. For accuracy experiments.3. be of the same material grade.3 and cooled to ambient temperature. unless otherwise agreed. molten wax. The time taken for the surface of this area to be exposed shall not be less than that specified in table 4. When components having highly contoured surfaces are tested. 1 Test solution 5 % (m/m) aqueous solution of analytical grade oxalic acid. 8 Test report The test report shall refer to this standard and include the following details: a) type and designation of coated component. C2H 2O4 . m0. 2 H 2O.5.5 g/m2. c) type and results of testing as described in clause 7.5. is less than 0. A. 7. 7.3 and cooled to ambient temperature. To determine the loss in mass of steel due to the action of the test solution containing inhibitor. for example. However. m0. 7. 7.1 Test solution Chemically pure 1 mol/l hydrochloric acid with a commercial inhibitor added. dried specimen or component shall be weighed (mass m1) after the area of the surface. The specimen or component shall then be immersed in the test solution at ambient temperature until the coating has been dissolved.2.5. Page 5 DIN 50938 : 2000-04 Table 5: Assessment of oxalic acid test Appearance of exposed Quality of coating coating area Grey with light-grey halo Inadequate Black to brownish black Good with exposed halo1) 1) Even good quality coatings may have very bright halos due to metal being exposed at the boundary of the area to which the solution was applied. of the coated part. treated for the same time as the coated component with test solution. dried and reweighed (mass m2). rinsed. is given by equation (3): Dm mA = × 10 (3) A where m is in mg and A is in cm². has been determined. C 6H 12N 14. but only dried as specified in subclause 6.5 Determining the mass per unit area 7. b) type and designation of coating. using equation (2): Dm = m 1 – m 2 + m0 (2) The mass per unit area. the inhibitor being chosen so that the loss in mass. m0. Dm. It shall then be removed. assessment shall be based solely on the area covered by the drops. uncoated test sheets or components made of the same material shall be weighed (mass m3).4. . mA.4 Determining the degree of protection with oxalic acid at ambient temperature 7.2 Procedure The coated. About three drops of the test solution shall then be applied to a flat area of the coated specimen or component. determined as specified in subclause 7. The loss in mass. if a 4 % (m/m) solution of hexamethylenetetramine. the components or specimens shall not be aftertreated. is given by equation (1): m0 = m 3 – m4 (1) The value of m0 shall be taken into account when calculating the loss in mass. in 1 mol/l hydrochloric acid is used.4. dried and reweighed (mass m4 ).2 Procedure After coating. An adequate inhibitory action is achieved. in g/m2 . After eight minutes’ exposure. the test solution shall be rinsed off with water and the affected area evaluated visually as in table 5.