Group standard TL 233Issue 2016-10 Class. No.:50223Descriptors:corrosion protection, surface protection, zinc, aluminum flake, zinc flake, base coat, top coat, organiccoating, t330, t350, t630, t650Non-Electrolytically Applied Zinc Flake Coatings with an Organic Top Coat Surface Protection RequirementsPrefaceIn contrast to the surface protection (Ofl) types specified in Technical Supply SpecificationTL 180 1) and TL 245 2), this TL describes a coating system which ensures the functional character‐istics of components, e.g., the color and/or corrosion protection, additionally by means of a consis‐tent organic top coat with a greater coating thickness.For new designs, if fasteners with a metric ISO thread are used, the use of surface protection types as per TL 180 1) (black) or TL 245 2) (silver) is preferred.For spring clamps on fuel hoses, coatings as per TL 134 3) must be used.Previous issuesTL 233: 1982-09, 1983-02, 1991-05, 1992-06, 1993-11, 1998-02, 2003-09, 2003-11, 2010-11, 2016-09ChangesThe following changes have been made to TL 233: 2016-09:–Correction in attachment 1 of appendix A "Released surface protection systems"1)TL 180 – Non-Electrolytically Applied Zinc Flake Coatings with a Black Top Coat; Surface Protection Requirements2)TL 245 – Non-Electrolytically Applied Zinc Flake Coatings; Surface Protection Requirements3)TL 134 – Non-Electrolytically Applied Zinc Flake Coatings with Organic Coating for Increased Corrosion Protection Requirements;Requirements and TestingAlways use the latest version of this standard.This electronically generated standard is authentic and valid without signature.The English translation is believed to be accurate. In case of discrepancies, the German version is alone authoritative and controlling.Page 1 of 10All rights reserved. No part of this document may be provided to third parties or reproduced without the prior consent of one of the Volkswagen Group’s Standards departments.© Volkswagen Aktiengesellschaft VWNORM-2015-07d Q U E L L E : N O L I SPage 2TL 233: 2016-10ScopeThis standard defines requirements and tests of surface protection types comprising non-electrical‐ly applied zinc flake coatings, with an additional organic top coat, on iron materials.The coating systems as per this standard can be used at temperatures up to a maximum of 180 °C.Because, with proper pretreatment, no risk of hydrogen embrittlement arises as a result of the coating process, this coating is also suited as corrosion protection for hardened and high-strength steel parts with tensile strength values ≥ 1 000 MPa or surface hardness values > 320 HV (Vickers hardness). The individual coats are applied primarily using a dip-spinning method.Coatings as per this standard are not suited for components with an electrically conducting function (e.g., ground connections).Designation Depending on the protection class and on the lubricant content (see table 1), a distinction is made between four surface protection types for the coating system as per this standard, which are desig‐nated with the following codes as per the specifications in Volkswagen standard VW 13750, sec‐tion "Designation":Ofl-t330Ofl-t350Ofl-t630Ofl-t650Requirements Appearance of the top coat, lubricant additive, and protection classThe surface protection types of the coating system must meet the requirements specified in table 1.The released protection systems are listed in appendix A.Table 1 – Appearance, lubricant additive, and protection classa)If a silver appearance of the top coat is required, the code for the surface protection type is expanded with the addendum "silver."This applies to other color specifications as well.Basic requirementsApproval of first supply and changes as per VW 011551 2 33.1 3.2Page 3TL 233: 2016-10Avoidance of hazardous substances as per VW 91101.At least ten parts (depending on size) are required for complete testing. For the initial-sample re‐lease of small parts, ≥ 50 kg of specimens must be produced (e.g., for fasteners).Unless certain sections of a part marked in the drawing are excluded from the surface coating, the entire surface of the parts must have the required surface protection with the specified properties.The protective coatings must not have any pores, cracks, damage, or other flaws impairing corro‐sion protection and/or the specified appearance. The coating systems must firmly adhere to the base metal and must not peel off or crack under elastic deformation.The coating system must be free of any flaws and excess material that have a negative impact on the part's function. The production process must be designed and controlled in such a way that the use properties of the finished part are not impaired.If the coated components are properly installed, the coating must not be damaged in any way that would negatively affect the function and/or would reduce the specified corrosion protection.For metric ISO threads as per VW 11611, after the coating process, the zero line for outer threads must not be crossed, and the zero line for inner threads must not be undershot. For fasteners with a metric thread, the coefficients of friction as per VW 01129 must be complied with (applies only to Ofl-t330 and Ofl-t630).Because the coating temperatures may have effects on the properties of materials, it must be checked whether coating can be carried out using solvent-based or water-based zinc flake coat‐ings, depending on the component. The baking temperature for solvent-based zinc flake coatings is usually 200 °C to 250 °C. A temperature of 300 °C is necessary for water-based zinc flake coat‐ings. The requirements in the drawing or master data list always apply to the coated component.The selection of manufacturer and surface protection types, as well as the coating method, must be agreed upon with the appropriate department in each case (e.g., GQL-M, N/GQ-L, I/GQ-L) on a part-specific basis before use.Requirements for mechanical fastenersFor mechanical fasteners with the following characteristics, the coating system must be released on an application-specific basis:–Parts with a metric ISO thread ≤ M8 with specific requirements regarding the loosening tor‐ques of the connection if temperatures > 80 °C occur–Outer threads ≤ M6 and inner threads –Force applied by triple square as per VW 01043, < N8–Hexalobular socket as per VW 01048, < T30–Hexagon socket, nominal size < 5 as per DIN 475-1 or product standards –Cross recess as per DIN EN ISO 4757, < H3Base metalThe surface of the base metal being coated must be bright. The surface must be cleaned to ensure that it can be coated. For hardened and high-strength steel parts with tensile strength values > 1 000 MPa, alkaline or mechanical cleaning (e.g., by abrasive blasting) must always be carried out before the coating process.The application of fine-crystal zinc phosphating (coating weight of 1 g/m 2 to 3 g/m 2) is permissible.3.3 3.4Page 4TL 233: 2016-10Coating system Composition of the dry filmComposition of the dry film: See the International Material Data System (IMDS).Coating layers Layer structure of the coating systemThe coating system consists of a base coat (inorganic zinc flake coating) and a top coat (organic coating).NOTE 1: The required number of layers also depends on the coating method and on the coating material.Base coatThe base coat consists of an inorganic matrix with at least 70% zinc flakes and up to 10% alumi‐num flakes by mass. The use of zinc with a globular structure is permissible. The use of zinc dust is prohibited.3.53.5.1 3.5.23.5.2.1 3.5.2.1.1Page 5TL 233: 2016-10Top coatTop coat without lubricantThe organic epoxy resin coating without lubricant must contain a maximum of 5% lubricant (PTFE)by mass.Top coat with lubricantThe organic epoxy resin coating must have 25% to 30% lubricant (PTFE) by mass.Total thickness of the coating system Requirements for Ofl-t330 and Ofl-t350The minimum coating thickness is 6 µm (of which 3 µm must be the inorganic zinc flake coating).The coating thickness must not exceed a maximum of 25 µm.Requirements for Ofl-t630 and Ofl-t650The minimum coating thickness is 10 µm (of which 6 µm must be the inorganic zinc flake coating).The coating thickness must not exceed a maximum of 25 µm.ExceptionsFor threaded parts, the specifications apply only to the head, or to face surfaces and wrench bear‐ing surfaces.If more stringent corrosion protection requirements (compared to the basic requirements) areagreed to in the drawing or master data list, then greater coating thicknesses are also permissible (e.g., for spring clamps).Tests Adhesion and ductility of the coating system Cross-cut test Procedure as per DIN EN ISO 2409; requirement: characteristic value ≤ 1When performing the cross-cut test, a spacing of 1 mm must be maintained between cuts.NOTE 2: For small components or those with complex geometry, a single-blade manual cutting tool is preferred. If no cross-cut test can be performed due to the component's size or geometry, a single cut or two intersecting cuts are permissible. If even a single cut cannot be made, only the tape test as per section 4.1.2 must be carried out.Tape testA scribing line based on DIN EN ISO 17872 must be applied if the component dimensions allow for this. After this, adhesive tape with a bond strength of (10 ±1) N per 25 mm of width is used. This tape is firmly pressed by hand onto the surface and then pulled off with a sudden motion perpen‐dicular to the surface. The coating must not peel off over a large area when the tape is removed 3.5.2.1.2 3.5.33.5.3.1 3.5.3.2 3.5.3.3 44.14.1.1 4.1.2Page 6TL 233: 2016-10(particle diameter ≤ 1 mm). Small particles of the coating adhering to the tape are permissible (≤ 5% of the test surface).NOTE 3: Suitable adhesive tape for this test is, e.g., tesaband 4657 4).Ductility testThe coating must not flake off when springs are expanded or compressed as intended, or when spring washers are bent during assembly, or when spring clamps are opened to their maximum diameter.Coating thickness The coating thickness is measured using a microscopic method as per DIN EN ISO 1463 and DIN EN ISO 2064; the location of the measuring points and tolerance zone positions for threaded parts with a metric ISO thread are specified in DIN EN ISO 10683.NOTE 4: For bulk products, the edge areas constitute a weak point; a check on the existing edge coverage in the microsection is recommended.Testing corrosion properties Neutral salt spray test General informationThe neutral salt spray test must be performed as per DIN EN ISO 9227.For bolts and nuts, the test requirements apply only to the head, face surface, and/or wrench bear‐ing surfaces. For threaded parts and thread-like parts, e.g., tap-end studs, they apply to the face surfaces. Less stringent requirements apply in the threaded area. These are specified in list items1. to 4. below.1.Evaluation of coating corrosion (applicable to all surface protection types)After 120 h, coating corrosion up to a maximum degree of change S5 as per DIN 34804 is per‐missible, with and without thermal conditioning (heat aging in recirculated air) for 96 h at 180 °C.Coating corrosion is not evaluated in the area of threads.2.Evaluation of base metal corrosion for Ofl-t330 and Ofl-t350 (interior)After 240 h, no base metal corrosion and no corrosion creepage along the scribe line must oc‐cur, with and without thermal conditioning (heat aging in recirculated air) for 96 h at 180 °C.A less stringent requirement of 120 h applies in the threaded area.3.Evaluation of base metal corrosion for Ofl-t630 and Ofl-t650 (exterior)After 480 h, no base metal corrosion and no corrosion creepage along the scribe line must oc‐cur, with and without thermal conditioning (heat aging in recirculated air) for 96 h at 180 °C.A less stringent requirement of 240 h applies in the threaded area.4.Evaluation of base metal corrosion for spring clamps (Ofl-650)4.1.3 4.2 4.34.3.14.3.1.1 4)tesaband 4657 is the manufacturer's product designation, produced by tesa SE.This information is only intended for informational purposes for the users of this in-house standard. This does not signify an en‐dorsement of the mentioned product by the Volkswagen Group. Equivalent products may be used if it can be verified that they lead to the same results.Page 7TL 233: 2016-10Unless surface protection as per TL 134 5) is required, the following applies:The parts must be opened to their maximum diameter five times using spring-clamp pliers be‐fore the start of the salt spray test.For pre-opened spring clamps without a clip, the contact points for the pliers and the latching areas are exempt from the evaluation.After 720 h, no base metal corrosion and no corrosion creepage along the scribe line must oc‐cur, with and without thermal conditioning (heat aging in recirculated air) for 96 h at 180 °C.NOTE 5: For reliable fulfillment of corrosion protection specifications, a coating system with at least two base coat layers and two top coat layers is usually necessary for spring clamps.Testing in the condensation atmosphere with constant humidity (CH)Testing in the CH standard atmosphere as per DIN EN ISO 6270-2Requirement: After 240 h, there must not be any blisters or other coating detachments, and no base metal corrosion. After subsequent acclimatization for 24 h at (23 ±2) °C, the requirements specified in section 4.1 must still be met.Resistance to test media The test for resistance to test media is only required for the release of new coating systems. This test is usually carried out on coated test sheets (see table 2 for the test scope). As part of the initial sample inspection, it is also permissible to verify the resistance to test media with a certificate is‐sued by the coating material manufacturer.Testing is carried out as per the relevant part of standard series DIN EN ISO 2812. The evaluation is performed as per DIN EN ISO 4628-1. For test media and requirements, see table 2.4.3.2 4.4 5)TL 134 – Non-Electrolytically Applied Zinc Flake Coatings with Organic Coating for Increased Corrosion Protection Requirements;Requirements and TestingPage 8TL 233: 2016-10Table 25Applicable documentsThe following documents cited in this standard are necessary to its application.Some of the cited documents are translations from the German original. The translations of Ger‐man terms in such documents may differ from those used in this standard, resulting in terminologi‐cal inconsistency.Standards whose titles are given in German may be available only in German. Editions in other languages may be available from the institution issuing the standard.TL 52146Central Hydraulic System Fluid; Lubricant RequirementsTL 52185Reference Engine Oil SAE 5W-30 for Testing of Compatibility with Re‐spect to Elastomer Materials; Lubricant RequirementsTL 766Brake Fluid; Material RequirementsTL 774Ethylene-Glycol-Based Coolant Additive; Materials RequirementsTL 788Diesel Fuel; Fuel RequirementsVW 01043Multipoint Socket Profile; Drive Shape for Threaded PartsVW 01048Hexalobular Socket Profile; Drive Shape for Threaded PartsVW 01129Limit Values for Coefficients of Friction; Mechanical Fasteners with Met‐ric ISO ThreadsVW 01155Vehicle Parts; Approval of First Supply and ChangesPage 9TL 233: 2016-10 VW 11611Metric ISO Thread; Limit Dimensions with Protective Coating for MediumTolerance Class; External Threads 6gh / Internal Threads 6HVW 13750Surface Protection for Metal Parts; Surface Protection Types, Codes VW 91101Environmental Standard for Vehicles; Vehicle Parts, Materials, Operat‐ing Fluids; Avoidance of Hazardous SubstancesDIN 34804Fasteners - Change of appearance of black surfacesDIN 475-1Widths across flats for bolts, screws, valves and fittingsDIN EN 228Automotive fuels - Unleaded petrol - Requirements and test methods DIN EN ISO 10683Fasteners - Non-electrolytically applied zinc flake coatingsDIN EN ISO 1463Metallic and oxide coatings - Measurement of coating thickness - Micro‐scopical methodDIN EN ISO 17872Paints and varnishes - Guidelines for the introduction of scribe marksthrough coatings on metallic panels for corrosion testingDIN EN ISO 2064Metallic and other non-organic coatings - Definitions and conventionsconcerning the measurement of thicknessDIN EN ISO 2409Paints and varnishes - Cross-cut testDIN EN ISO 2812Parts 1 to 5: Paints and Varnishes – Determination of Resistance to Liq‐uidsDIN EN ISO 2812-3Paints and varnishes - Determination of resistance to liquids - Part 3:Method using an absorbent mediumDIN EN ISO 2812-4Paints and varnishes - Determination of resistance to liquids - Part 4:Spotting methodsDIN EN ISO 4628-1Paints and varnishes - Evaluation of degradation of coatings - Designa‐tion of quantity and size of defects, and of intensity of uniform changesin appearance - Part 1: General introduction and designation system DIN EN ISO 4757Cross recesses for screwsDIN EN ISO 6270-2Paints and varnishes - Determination of resistance to humidity - Part 2:Procedure for exposing test specimens in condensation-water atmos‐pheresDIN EN ISO 9227Corrosion tests in artificial atmospheres - Salt spray testsPage 10TL 233: 2016-10Appendix A (informative)Released surface protection systemsCoating materials will be added to appendix A when the supplier demonstrates to the person re‐sponsible in each case, by means of tested parts and inspection reports, that its coatings meet the requirements in TL 233. The Volkswagen Group reserves the right to perform counter-checks. Released protection systems are listed in attachment 1 of appendix A.。