Michelin note no. 1377: D 434-94 seals and replacement of Vulkacit AZ with Santocure (10 Sept. 1953)

In this document

This technical note no. 1377, dated 10 September 1953 and stamped as received on 11 September 1953, is addressed by a correspondent signed "Mr. LOUVET" from the Michelin Central Laboratory in Clermont-Ferrand, to the attention of Mr. BOUSSUS, with a copy to "E.C. Mr. MAGES" — a mention underlined with a handwritten arrow p. 115.

D 434-94 seals and the D2 formula

The document recalls that the D 434-94 seals (referenced E 40I2I0-E 653-3802), manufactured by Michelin, have shown "good resistance in use". The formula for the D2 mixture, communicated in January 1952 (note HT 5172 of 12.1.52), is detailed: GRS-X 845, zinc white, CK4 black, stearic acid, paraffin, sulphur, Vulkacit AZ and mercapto-benzo-thiazole, with autoclave curing for 40 minutes at 134°C p. 115.

The "D2 Clichy" adaptation

In April 1953, the Clichy factory, having been unable to procure all the original constituents, adapted the formula (CK-3 black replacing CK-4), with the other components being identical p. 115-116. The text specifies that these seals "seem to date to give good results" p. 116.

The replacement of Vulkacit AZ

The core of the note is the substitution proposal: Vulkacit AZ, deemed an "accelerator unstable over time" and "currently unobtainable in fresh condition", must be replaced by Santocure, described as a "stabilised form similar to Vulkacit AZ". The new formula is given (Santocure at 1.1, in place of the Vulkacit-Mercapho pair), with vulcanisation remaining "to be determined" p. 116.

The author finally asks for the recipient's opinion on the quality of this new formula compared to the D2 mixture, and proposes, in a final handwritten note, a meeting in Clermont if a "direct conversation" is preferred p. 116.

Context

In the 1950s, Michelin was a close industrial partner of Citroën for rubber and elastomer issues, materials essential for the seals and flexible elements used in particular in hydraulic and suspension systems. Vulkacit AZ and Santocure are rubber vulcanisation accelerators, used to control the setting and resistance of mixtures.

Archivist's perspective

This document illustrates a little-known but essential facet of the engineering work carried out around Paul Magès: the material and chemical development of the components necessary for the systems he designed, here simple seals, the reliability of which nevertheless conditions the proper functioning of larger mechanical assemblies.

The mention "E.C. Mr. MAGES" p. 115 confirms that Magès was a direct recipient of or involved in this technical exchange with Michelin, revealing the closeness of the collaboration between the Citroën teams and the Central Laboratory of Clermont-Ferrand.

This document is likely part of a continuous work of developing rubber components for Citroën's needs, of which other traces can be found in the same folder, such as the Summary of folder 41-59, which specifically mentions rubber and technical developments related to hydropneumatic suspension.