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Slide 20 of 69

Notes:

    The "Perkomatic" is tested to 500,000 operations to ensure it meets current and proposed legislation. To achieve this number of cycles has meant the design has become highly refined and the choice of materials has been critical. An example of this is the end and anchor plates which secure the "Perkomatic" to the door and the door frame respectively. The twin chains which connect the hydraulic cylinder mechanism in the door to the anchor in the frame pass through the end plate rubbing against it every time the door opens and closes.
    Brass stampings were chosen for the end and anchor plates because it was discovered during testing that steel end plates wore more quickly. Steel was found not to have the self lubricating and low friction properties of brass and only had a life of 10,000 operations before failure, 2% of that required and easily achieved by brass.
    The life of forged steel end anchor plates may have been extended by surface treatments required to prevent corrosion and give an aesthetic appeal. There was concern however that the chains would abrade any decorative finish exposing bare untreated metal leaving it susceptible to corrosion and high mechanical wear. These concerns combined with the strong possibility that particles from a degrading finish could enter the hydraulic system causing premature failure and the fact that steel forgings were marginally dearer without a protective finish than brass stampings, which needed no finish, eliminated steel from further investigations.
    In conclusion brass which is an apparently expensive material is in component form very cost-effective as a machined stamping, because of its excellent formability, machinability and corrosion resistance. These features combined with its bearing and mechanical properties make it an ideal material for architectural building products as Perkins and Powell have demonstrated with their Perkomatic concealed door closer.