Page 680 - Mastik®

Surface pressure under the screw Surface pressure when mounted
head

It is not possible to precisely define the Advantages of flange screws and
Typical application
permissible surface pressure for a par- flange nuts:
ticular type of material used to make a – less intrusion
component. The effect of the production – clamping force in the fastening during
process, the alignment of fibers in the mounting tends to remain stable
material, surface finishing and tempera- – flange products are more economic
ture changes all play a decisive role. than large washers under normal
screws and nuts (fewer fastening ele-
The following measures can help ments and quicker assembly)
reduce the surface pressure: – flange screws and nuts allow greater
– use of flange screws and flange nuts hole tolerances and so are more
– chamfered holes. Field investigations economically efficient.
have shown up to a 20% increase in – flange nuts have a better stability
permissible surface pressure. against shaking than normal screws
– through hole to ISO 273 – select a and nuts.
fine hole

Guide to the use of flat washers for screws and nuts

according to ISO 887

An overview of suitable combinations of flat washers with screws and nuts, allowing for different strength classes (hardness classes)

Washers hardness class
100 HV 200 HV 300 HV
Assigned tensile strength [N/mm ] acc. ISO 18265
2
Screws Nuts
320 640 965
Permitted reference values pressure per unit area
200-300 300-500 500-800
Property class Use of washers with corresponding hardness permitted
≤ 6.8 ≤ 6 yes yes yes
8.8 8 no yes yes
9.8 9 no no yes
10.9 10 no no yes
12.9 12 no no no
Case-hardened, thread-forming screws yes yes yes
Stainless steel, screws and nuts – yes –
Limiting conditions such as strength of component, surface structure, production process, alignment of fibers and operating temperatures must be
considered when making the selection.