Mechanical Joining Elements Protection from Weld Spatter and Paint Adhesions for Internal and External Threads TL188

Mechanical Joining Elements Protection from Weld Spatter and Paint Adhesions for Internal and External Threads TL188

Descriptors: Nuts, Bolts, Weld Spatter, Weld Splatter, Protection from Damage

Scope

This standard defines the requirements for all-around coating of internal and external threads,

holes and steel bolts, which was applied to avoid improper assembly on the assembly lines due to

adhesions of primer coats applied in the electrical process

weld spatter during welding of parts with internal threads, external threads, bores and bolts.

It applies with limitations for the use of threaded parts with special requirements such as

*ambient temperatures > 90° C

*waxed components

*components made of Mg

*M6 and M8 threads

*electrical connections (Nycote as insulator)

1.1 Notes

Under these basic conditions, Nycote-coated nuts or screws should only be used after testing by

the appropriate engineering department, since the coefficients of friction change with temperature.

As a precaution, to avoid low head coefficient of friction, self-locking screws can be used in con

nection with Nycote-coated nuts. Alternatively, stamping nuts (VW 604 35), for example, can be

used in case of negative evaluations.

2 Designation (Specifications in Drawings)

Coated TL 188-Ny

3 Requirements

3.1 Basic Specifications

Approval of first supply and changes according to VW 011 55.

Avoidance of hazardous substances acc. to VW 911 01.

The coater must document the quality of the coated parts by means of statistical process control

(SPC).

All contractual materials or parts or those required by the purchase order must correspond exactly

in every respect to the approved samples. No changes may be made to the composition of the

material or in manufacturing without prior notification and consent of the releasing party. The pur

chaser has the right to take random samples of incoming shipments and to test these for confor

mity with the specification. Only components that are true to gage size may be used as testing nuts

or bolts.

3.2 Material

3.2.1 Base Material of the Screw/Nut/Bolt/Bore

Acc. to drawing

3.2.2 Screw Surface Protection

Acc. to drawing

3.2.3 Coating

3.2.3.1 Material

PFA colorless (white)

3.2.3.2 Coating Length, Area and Thickness

The coating must be applied to the contact surfaces of the interior threads of nuts, threaded plates,

bores and to the contact surfaces of the exterior threads and bolts. The coating should have a

uniform, continuous appearance, with no drops, streaks and flaking areas.

Based on the different processing methods in the plants, the thickness of the coating on the thread

tip or the thread base can be different. However, the screwing and unscrewing torques must be

guaranteed (see Table 1).

If not otherwise indicated on the drawing, the coating position and the coating area should corre

spond to the following limitations:

The coating on parts with external threads should extend to the thread runout for parts with a

shank and over the entire thread length for parts with threads approximately up to the head. There

must be no coating adhering to the head and the adjacent or load-bearing surfaces of bolts, the

hexagonal surfaces of the nuts and their adjacent or load-bearing surfaces, the weld rings, points

or projections, surfaces and all head surfaces of welded screws, bolts and nuts.

In order to guarantee the function, the coating must completely cover the starting phase of the

threads on the side of the nuts to be welded.

3.3 Torque/Testing Force

To test a batch, a minimum of 10 randomly selected parts are required. The permissible thread-in

torque (Table 1) and the calculated pre-load forces per VW 011 26-1 and VW 011 26-2 are the

criteria.

For testing the parts, standard test washers are used as load-bearing surfaces, as well as phos

phatized and oiled nuts and bolts that are of approximately equal strength. The test parts must be

inspected for proper gage size. The values of the thread-in torques must correspond to the specifi

cations in Table 1. The maximum thread-in or running torques can be somewhat higher for screws

or nut surfaces that are not true to gage size. For quality problems, the results with true to gage

size phosphatized and oiled surfaces apply.

The testing force of the nuts must correspond to the requirements per EN 20 898-2 and EN ISO

898-6.

Torque preload measurements are taken with calibrated load cells or friction

4 Test

Torque preload measurements are taken with calibrated load cells or friction test stands, for example. The friction radii of the screw mates must be defined or mathematically adjusted according the

specifications per VW 011 26-1. If the specifications are kept, the specified limits per VW 011 26-1

must be achieved.

5 Referenced Standards

VW 011 26-1 Joining, Tightening Torques for Screw Connections

VW 011 26-2 Joining, Tightening Torques for Screw/Bolt Assembly Beyond the Elastic

Limit

VW 011 55 Vehicle Supply Parts, General, Approval of First Supply and Changes

VW 911 01 Environmental Standard for Vehicles, Vehicle Parts, Materials, Operating

Fluids, Avoidance of Hazardous Substances

DIN EN 20 898-2 Mechanical Characteristics of Joining Elements; Part 2: Nuts with Defined

Testing Forces; Coarse Thread (ISO 898-2: 1992)

DIN EN ISO 909-6 Mechanical Characteristics of Joining Elements; Part 6: Nuts with Defined

Testing Forces; Fine-Pitch Thread