VW TL 188 Mechanical Fasteners - Protection Against Weld Spatter and Paint Residues for Internal and External Threads

The standard “VW TL 188 Mechanical fasteners - Protection against welding spatter and paint residue for internal and external threads” developed by the Volkswagen automobile company describes the requirements for the all-around coating of parts containing internal and external threads, bolts and holes made of steel. This coating is applied on assembly lines to prevent faulty assembly due to:

• Remains of primer coat applied using the electro-coating method
• Weld spatter caused by welding parts containing internal or external threads, bolts and holes

It is only valid to a limited extent for the use of gear parts with special requirements. For example,

• Ambient temperatures up to 90 degrees (due to the effect on the coefficient of friction)
• Waxy components
• Components made of magnesium
• Thread sizes M6 and M8 (due to critical rake angle, VW 01129 standard should be consulted)
• Electrical connections
• B/screws with adhesive bonding and compression coating.

With these prerequisites, nuts or bolts/screws coated with a coating for weld spatter and paint residue protection may only be used after testing by the relevant department, as the friction coefficients change with temperature. As a precautionary measure, RIPP bolts can be used with BSSL coated nuts to avoid low friction coefficients. Alternatively, if the evaluation results are negative, for example, drilling nuts and blind rivet nuts as well as drilling screws and blind rivet screws can be used.

The requirements in this standard are specified as follows:

• Initial supply and approval of changes must comply with the VW 01155 standard.
• Avoidance of hazardous substances must comply with the VW 91101 standard.
• The coating operator must document the quality of the coated parts through statistical process control.
• All materials or parts required by the contract or order must conform in all respects to the approved samples.
• No changes in the composition of the material or in production may be made without the prior notice and approval of the persons responsible for this standard. Only components suitable for the measurement dimension shall be used as test nuts or screws/bolts.
• Compliance with tooth friction coefficients in the range of 0,07 to 0,13 is mandatory. Testing must be carried out in accordance with the VW 01129 standard.
• The temperature of the part to be coated is a maximum of 15 degrees for a short time (≤ 400 s) during the deposition of the all-over coating and must be taken into account for the component geometry. As a result, the corrosion resistance is reduced.
• Permitted coating materials are: PFA (perfluoroalkoxy alkane) colorless and FEP (fluorinated ethylene propylene) colorless
• Permitted coating materials are stored in the Volkswagen Polymer Laboratory if required.
• The coating shall be applied to the mating surfaces of the internal threads of nuts, toothed plates and holes, and to the mating surfaces of the external threads and bolts. The coating shall have a smooth and continuous appearance and shall be free of drips, streaks or flaking spots.
• Due to different processing equipment, the thickness of the coating on the tooth crown or tooth root may be different. However, the screwing or screwing working torque must be met.
• Unless otherwise specified on the drawing, the coating layer and coating area must comply with the following restrictions:
  • The coating on externally threaded parts should extend along the entire length of the tooth for threaded parts, up to the tooth ridge for shafted parts and nearly to the head.
  • The coating shall not adhere to the head and adjacent or load-bearing surfaces of bolts, the hexagon surfaces and adjacent or load-bearing surfaces of nuts, weld rings, points or protrusions or surfaces, and any head surfaces of welded screws, bolts and nuts.
  • It is important for the coating to completely cover all the threads up to the thread entry on the side of the nut to be welded, in order to ensure its function.
• To test a batch for torque, at least 10 randomly selected parts are needed. The test criteria are the thread friction coefficients measured according to the permissible screw or screw operating torques VW 01129 standard.
• For testing, washers equivalent to DIN EN ISO 16047, phosphated and oiled nuts and screws/bolts of equivalent strength are used as load-bearing surfaces. The devices tested must be tested for suitability for the measuring device. The values ​​of the screwing or screwing operating torques must comply with the specifications in table 1.
• In case of quality problems, the results on phosphated and oiled surfaces suitable for the measuring device are valid.
• In order to launch a new product, torque and friction coefficient tests as well as material analysis must be performed and documented.

Among the numerous tests, measurements, analyses and evaluations our organization has carried out for businesses in various sectors, our organization also provides testing services defined in the standard “VW TL 188 Mechanical fasteners - Protection against welding spatter and paint residues for internal and external threads” with its trained and expert staff and advanced technological equipment.