Sliding alloy for spherical bearings

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The hard chromium plating to the steel calottes used hitherto was entrusted to subcontractors and involved a long processing time plus considerable costs for the transport of these sensitive items. The new development is a special metal alloy with a distinctive surface treatment, which is marketed under the registered trademark MSA® – MAURER Sliding Alloy. Compared to the hard chromium-plated steel calottes, the bright-finish MSA® calottes have a much higher corrosion resistance. Another advantage over the earlier calottes is the fact that the sliding alloy is resistant to fluorine- and chlorine-based acid solutions, which occur in some industrial areas. The original objective was achieved as well: the entire production and surface treatment of the MSA® calottes on our own premises, which adds up to advantages in terms of production time and efficiency.

Sustainable solution thanks to long service life

In combination with the sliding material MSM® introduced in 2003, MSA® guarantees a lifetime of at least 50 years. This means that no premature and cost-intensive replacement of these bright calottes is required – even under challenging environmental conditions (moisture, flood, industrial atmospheres).

The material parameters of the new sliding alloy were tested in an accredited laboratory. MSA® proved its durability in long-term sliding tests with an accumulated sliding path of 10 000 m, a displacement velocity of 15 mm/s and a contact pressure of 60 N/mm2. No wear could be observed, nor an increase in the friction resistance. The latter even lies below the values specified for polished stainless steel or hard chrome. The corrosion resistance to DIN EN 1337-9 could also be demonstrated. The composition and surface treatment of MSA® are confidentially registered with the DIBt and MPA Stuttgart (materials-testing institute). A European Technical Approval (ETA) has been applied for.

Further modifications in the approval

In the course of reviewing the National Technical Approval (AbZ Z-16.4-436), the adoption of MSA® was accompanied by two further changes:

• an increase in the upper temperature threshold for MSM® from 48 to 70 °C,
• the inclusion of cylindrical bearings.

MSM® for high temperatures too

Since its introduction in 2003, MSM® has demonstrated its superior performance compared to PTFE with a remarkably enhanced efficiency. Even under extreme conditions it achieves a service life of at least 50 years. The special characteristics of MSM® compared to PTFE are the double contact pressure (loads of up to 20 000 tonnes), the five-fold accumulated displacement and the 7.5-fold displacement velocity.

So far, the use of MSM® was limited in the ETA to a temperature range of -50 to +48 °C. Now, in the course of the new approval, this temperature range has been extended to +70 °C, which means that MSM® can now be used in practically all climate conditions worldwide.

Cylindrical bearings

Cylindrical bearings are now included in the National Technical Approval AbZ Z-16.4-436. A cylinder instead of a calotte means that only rotations about the cylindrical axis are possible. Where constructional constraints call for this characteristic, then the result is geometrical advantages, e.g. when replacing roller bearings or in special geometrical conditions, because these cylindrical bearings are rectangular on plan and virtually any aspect ratio can be selected. Of particular advantage is the use of cylindrical bearings as sliding isolation pendulum bearings for protection in seismic conditions or to create an "elastic” support, when the pendulum movement should be in one direction only or when using two crossing pendulum bearings, different in each direction.

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