For these applications, Spieth offers locknuts with (scalable) corrosion protection individually tailored to the customer's requirements - in various coating types and in stainless steel. Spieth has examined the corrosion resistance and functionality of the individual versions in extensive salt spray tests in accordance with DIN EN ISO 9227-NNS in the research laboratory. Based on the detailed results, customers can be advised even more specifically and better with regard to the optimum corrosion protection for their particular application.

Scalable corrosion protection

Due to the ecological disadvantages and the restrictions on compatibility with the REACH regulation for coating materials, both the availability of and demand for components with yellow chromating will decrease. In some areas, this type of coating is even prohibited. As a result, more and more customers are signaling a need for products that meet these special corrosion protection requirements.

Spieth has now expanded its range and offers locknuts in various coatings (blue chromate, zinc-nickel) as well as stainless steel versions, which demonstrate very high resistance in salt spray tests. Precision nuts with "scalable" corrosion protection are available for mechanical and plant engineering, tailored to demanding applications and also available in special designs.

Illustration: the functional principle of the adjusting nut. © Spieth machine elements

Each corrosion-protected locknut is based on the proven Spieth principle: according to the company, the ability to set the thread backlash to zero ensures optimum alignment on the thread, the best possible locking values and high breakaway torques. This should also be accompanied by high axial rigidity, very good concentricity properties and greater functional reliability, even with heavy loads and high dynamics. The locknuts are suitable for high speeds, offer high axial run-out accuracy, less wear and are quick and precise to install.

Tough test conditions in the test

In an extensive series of salt spray tests in accordance with DIN EN ISO 9227-NSS, the manufacturer tested locknuts in various coating variants through to stainless steel locknuts, both with and without clamping screws, for corrosion and functionality. An extremely corrosive environment was simulated in "fast motion" for a total of 8 x 20 nuts. The maximum test duration was 1,000 hours. Intermediate tests were carried out at seven time intervals, after which nuts were removed: after 96 hours, 192 hours, 336 hours, 432 hours, 504 hours, 672 hours and 1,000 hours.

The corrosion test in such a "time-lapse" cannot, of course, be a 1:1 reproduction of the respective installation situation in the corrosive environment of the customer application, but it does provide a detailed indication of how the product would behave in the respective coating variants over a defined period of time. This makes it easier to estimate which product is suitable for the installation situation and in which version.

Adjusting nut available in various galvanic or chemical coatings and in stainless steel. © Spieth machine elements

The evaluation is carried out according to precisely defined evaluation criteria in accordance with DIN EN ISO 10289 (degree of protection _Rpundappearance _RA) at a very high level of competence. After seven time intervals, the percentage defect area (according to protection grade _Rpundappearance _RA) is differentiated and the degree of deterioration is assessed in detail. For this purpose, the condition of the end faces, holes and bolts are examined in the laboratory. Locknuts with a base metal corrosion or defect area of >50 percent do not pass this test - they do not meet the high standards set by Spieth. This is because a key aspect of the evaluation is that the source of the corrosion formation (end face, holes, clamping screws) was precisely localized and analysed for the various combinations tested - locknuts with and without clamping screws - in order to make appropriate optimizations, such as the use of other screws.

Based on the test series with over 150 tested components, very detailed statements can now be made about the corrosion behavior of the individual coating types and designs.

Stainless steel locknuts last over 1,000 hours

The stainless steel adjusting nut showed no base metal corrosion in the salt spray test after 1,000 hours. © Spieth machine elements

The winner of the test series is the stainless steel locknut. In the salt spray test, even after 1,000 hours under the harshest environmental conditions, it still showed no base metal corrosion and no significant defect areas - the clamping screws, the axial and radial bore as well as the end face and the functionality of the locknut were all in order.

Stainless steel locknuts are indispensable in extremely corrosive environments or in the food industry. However, appropriately coated locknuts are often sufficient and are then the more economical solution. The results for blue chromated locknuts with blue chromated screws were 192 hours. Zinc-nickel locknuts with blue chromated screws lasted up to 432 hours. All coatings offer at least the corrosion protection that customers are familiar with from Spieth products with yellow chromating.

Exact tolerances: layer thickness and materials matched

Each coating changes the tolerance of the locknut due to the corresponding coating thickness. The precisely defined thickness of the subsequent coating is therefore already taken into account during the manufacturing process at Spieth. The coating and materials of the locknut are precisely matched to the requirements, resulting in precision products with the lowest manufacturing tolerances and the best dimensional accuracy. "By optimizing our processes, the results show very little variation. The layer thicknesses and the materials used are very precisely defined," explains Dr. Heiko Alxneit, Head of Product Management at Spieth. "It is very important to us to offer customers a range of product alternatives that meet Spieth's high quality standards and also offer a significant increase in corrosion protection, such as the stainless steel version."