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NAK Technical Information - Shaft

For the best results from your shaft sales we must consider the shaft material, hardness, roughness, eccentricity and tolerance according to the following points.

Shaft Material

Seals perform best on a medium carbon steel or stainless steel shaft. Heat treatment or nitriding is especially recommended. To seal water at low surface velocity, stainless steel is more suitable

Shaft Hardness

In the area where the sealing lip contacts the shaft we recommend that the minimum hardness is 45 HRc. Where lubrication is doubtful, abrasive matter is present or the shaft speed is greater than 14 m/sec 55 HRc is preferred.

Shaft Roughness

We recommend the shaft be machined, preferably plunge ground, to a surface roughness of Rt = 1 to 4 mm (Ra = 0.2 to 0.8 mm), in the area of the contact surface, any machine lead are not permitted.

Shaft eccentricity

Two types of shaft eccentricity affect seal performance. They are dynamic runout (double dynamic eccentricity) and offset (shaft to bore misalignment or static eccentricity). The allowable eccentricity is referred to in figures 2 and 3.

Shaft runout

Shaft offset

Shaft speed

The shaft speed corresponding to lip material is referred to below.

Shaft speeds which may be permitted related to the rubber part material in the case of non pressure condition

Shaft tolerance

The recommended tolerances are in tables below.