Steel, 1.7227 (42 CrMoS 4 V)
tempered to tensile strength
Rm = 1220 ... 1400 N/mm2
fine turned and slide ground
GEOMET 500-treated G0
The influence of a washer on the quality of the screwed connection is very often underestimated. With washers GN 6339, high quality preloaded screwed connections can be established.
A high static clamping force can be reached avoiding loss of tension.
At a specified preloaded clamping force it is often possible to use thinner bolts. This can result in a better ratio between clamping distance and bolt diameter to minimise the danger of failure.
The case hardened smooth bolt head/screw contact face leads to a lower and more constant friction co-efficient even when continuous clamping and releasing operations are required.
Washers GN 6339 are only suitable for machine construction bolts of classes 8.8 / 10.9 / 12.9, and not for steel bolts DIN 6914.
The outside diameter d2 of the lower type refers to washers DIN 125 / ISO 7089, and the higher type to washers DIN 7349.
This dimension is, together with the chamfer angle α 70° and the inside diameter d1, the most important dimension of these heavy duty washers. Diameter d3 is actually, even in the lower tolerance range, larger than the max. contact under head diameter on a bolt. This will ensure that the chamfer of d3 of the hardened washer will not be pressed into the underhead radius causing an indentation on the bolt which would damage the bolt.
The inside diameter d1 is kept as small as possible ensuring that the bolt is inserted centrically into the washer. The choice of a matching pair of bolt and washer with least radial clearance is important in order to avoid a mismatch between chamfer diameter d3 and the max. contact area diameter of the bolt head.
This relatively large angle is necessary when using hexagon headed bolts to avoid interference with the chamfer face diameter d3 of the washer
The extended chamfer edge F, as seen from d3, and d1 create an edge that provides the smallest radial clearance towards the transition from bolt shank to head.Even with the minimum chamfer angle of α = 68° and the smallest dimensions for d1 and d3, this radial clearance is sufficient for all bolts according to DIN EN.
This is the height of the cylindrical part of the internal diameter d1, h should be as high as possible in relation to the pitch of the thread of the bolt.
Washers GN 6339 are higher when compared with DIN washers (exception: DIN 7439 which is equal to the high type).A larger thickness leads to a stronger washer. As a result, bearing in mind the chamfer d3, a minimum height is established which ensures that the bolt thread will not be damaged when the bolt is tightened.
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