Note No. 1380: Michelin formula validated for D 434-94 seals (1953)

In this document

This internal note from the Citroën Central Laboratory, signed by Mr. Louvet (extension 469), is addressed to Mr. Day, based in Rennes, with a copy to Messrs. Pompon and Magès p. 117.

Subject of the note

Louvet confirms the agreement of the Michelin establishments on a modification of their D 2 rubber formula, now used for the D 434-94 seals p. 117.

The new formula

The detailed composition is given precisely:

The text specifies that the designation GRS X 485 refers to a cold-prepared GRS, corresponding to the Krylene from the Polysar company, intended to replace standard GRS p. 117. A bale of this material is to be shipped "shortly" to Rennes, and the optimal vulcanisation conditions remain to be determined by Citroën's departments p. 117.

The note finally specifies that this formula "is not restrictive" and that further tests must be continued to improve the abrasion and tear resistance of the seals p. 117.

A registration stamp dated 24 September 1953 appears at the top of the page, as well as a blue handwritten arrow pointing towards Magès' name in the list of copy recipients.

Context

GRS (styrene-butadiene rubber) was, in the 1950s, a synthetic material widely used in the automotive industry as a replacement for natural rubber, particularly for sealing parts subject to mechanical and chemical stresses.

This period corresponds to Citroën's preparatory work on the future DS, whose hydropneumatic suspension — designed by Paul Magès — relies largely on hydraulic circuits requiring seals of exceptional reliability, in contact with oils and subject to significant pressure variations.

Archivist's perspective

This document, very technical and brief, illustrates the collaborative and industrial dimension of the development of the hydropneumatic suspension: beyond the design by Magès, it was also necessary to solve, with external suppliers such as Michelin, very concrete material problems — here the exact formulation of a rubber for a referenced seal.

The presence of Magès in the copy list, indicated by a handwritten arrow, suggests that he was closely following these material issues, which were essential to the reliability of his invention p. 117.

This document is likely part of the same technical monitoring file as the folder "Theoretical study – hydropneumatic suspension 1943/44", testifying to the continuity of research between the initial design and its industrial development a decade later.