N38A SR1

Teile-Bestellvorschrift; Schrauben mit Oberflaechenueberzug Replaces 01.92 edition

1 Application

This order specification applies to steel screws and threaded parts with surface coating only in combination with the N38A Order Specifications Group SR … (from SR2.1) and, if required, Group SF … as well as Bosch Norm N31A SR …

Not applicable for

2 Type

2.1 Product class

Product class A per DIN ISO 4759-1 and DIN 267-2, unless otherwise specified.

2.2 Threads

Metric ISO threads per DIN 13-1 to DIN 13-25, unless otherwise specified.

Tolerance range 6g applies to normal case and 6e for any special case for the thread profile before application of a surface coating (protective coating thickness > 7μm).

Threads with surface coating must not exceed the zero profile 6h.

3 Technical specifications

3.1 Surface coating

The surface coating must be applied with a coating thickness and durability per the following Bosch Norm for each specification

For screws with standard threads ≥M2.5 and lengths up to 5d the coating thickness at the measuring points (approximately the center of the head surface or the curved section) must be 4 to 7 μm. The coating thickness and the durability should be approximately equal at the first thread and at the measuring points. For screw lengths above 5d up to 10d, not more than 10% of tested screws may show isolated rust spots on the shank after the corrosion test. (up to max. Ri2 per N42AP 015). If the shank is exposed to an unprotected corrosion attack, special agreement is required for the corrosion protection quality for screws with length above 10d.

For other corrosion protection methods, the durability and distribution of minimum coating thickness over the length of the screw must be agreed upon separately and the tendencies listed in the above sections must be taken into consideration. 3.2 Screws with strength cla sse s from 8.8 as well as ca se-hardened, surface-hardened and nitrate-treated scre ws with surface coating.

Due to increased risk of delayed hydrogen embrittlement:

-The screws must be manufactured from a material that is particularly suitable for electrolytic surface coating protection.

Annealing of screws from strength classes 8.8 to 12.9 must generally be tempered at about 500?C; however, at least at the

tempering and test temperatures per N38A SR2.2:

- It is not permissible for screws of these strength classes to be subsequently electrolytically treated, which were based on material and heat treatment originally not meant for electrolytical surface finish.

Technical responsibility: FV/PLO1 and FV/PLM3

CF4.05.021 Rev. 3. 07/26/00

June 1996 N38A SR1 Page 2 of 2 -Residual stress due to heat treatment must be reduced as much as possible before pickling and/or electrolytic treatment.

-Only approved galvanizing process per N67F 800 00/3 is permissible for bolts of strength classes 8.8 (D-parts, R-parts per classification) 9.8, 10.9 and 12.9, which are to be electrolytically galvanized.

-Special measures must be taken during manufacturing to guarantee that no damaging hydrogen content appears in the screws (see N67F 800 00/3)

-Screw fractures or cracks are not permissible during stress test performed per N41AP 926;

-The stress test need no longer be performed for 8.8 screws if the screw manufacturer/supplier has provided evidence that at least 20 delivery lots (in case of new suppliers, 20 electrolytically manufactured batches) successively have

been delivered without embrittlement and no complaints.

-For 8.8 screws marked as D or R screws (or R3 screws, if calibration per N12A L13 is specified)and for 8.8 screws smaller than M4, the stress test must be done per N42AP 926;

-For 10.9 screws from suppliers who have proven through an audit an adequate QA system in electrolytic processing and hardening must show stress testing per N42AP 926 for only every 10th shipment to Bosch. However, evidence must be provided prior to this, that at least 20 delivery lots have been supplied successively (for new suppliers at

least 20 electrolytically manufactured batches) free of embrittlement. For D and/or R scre ws (or R3 screws, if

calibration per N12A L13 is specified) and screws smaller then M4 proof of stress test per N42AP 926 must be

enclosed with every shipment.

-For each shipment of 12.9 screws as well as casehardened and nitrated screws, proof of stress testing per N42AP 926 must be enclosed.

3.3 Combi-screws with locked up washers

Technical specification per N38A SF2 and SF3 apply to locked up components.

3.4 Galvanized screws with the additional specifications per N67F 300 25

These screws must be waxed (so-called slip coating) to reduce the friction and to narrow the distribution.

3.5 Minimum break force and test force

Independent of the specified coating thickness of a surface coating, the screws must be manufactured in a way that the minimum break force and test force comply per DIN EN 20898-1

(Minimum break force = average nominal stress x minimum tensile strength,

Test force = average nominal stress x testing load)

Applicable Norms

N42AP 015

N42AP 926

N67F 300 25

N67F 800 00/3

N67F 821 69

N67F 821 70

N67F 821 71

N67F 821 72

Additional applicable Bosch Norms are specified in preceding Order Specification (e.g. N38A SR2. or N38A SF..) is

Norms N31A SR.. and, if applicable, as specified in the drawings.

Previous editions

08.91; 01.92

Changes

Order Specification was completely revised.

CF4.05.021 Rev. 3. 07/26/00