Considerations on the Heat Transfer through Minimal Clearance-Glass Molding

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  • 微小すき間の伝熱-ガラス成形についての考察
  • ビショウ スキマ ノ デンネツ ガラス セイケイ ニ ツイテ ノ コウサツ

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In forming glass material with a metal mold, the heat is transferred from the material to the mold mainly through conduction. In this operation, the minimal clearance between the hot glass and the mold is important. The minimal clearance was studied using polyethylene glycol in place of the hot glass, and the followong results have been obtained:<br>(1) When two metallic surfaces come into contact with each other, a clearance of air layer is formed, the size of which depends upon the roughness of the metallic surfaces from the viewponit of heat transfer coefficient.<br>(2) In filling polyethylene glycol into the gap of two metallic surfaces, the clearance is filled up with polyethylene glycol, leaving no air layer, as long as the surface roughness is not too large. The clearance remains nearly unchanged even if the metallic surfaces are coated with such parting agent as graphite.<br>(3) In actual glass forming, a clearance really exists as seen from the heat transfer, and since its size is larger than it is considered from the surface roughness, the clearance is surmised to be formed by the air that is left behind during forming.

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