GB1047256A - - Google Patents

Abstract

1,047,256. Removing stains from stainless steel. DIVERSEY (U.K.) Ltd. June 27,1963 [July 23, 1962], No. 25581/63. Heading C7E. A method of removing stains from the surface of stainless steel comprises contacting the stained surface with a stain conditioning aqueous solution comprising a strong basic material, and an ammonium, alkali metal or alkaline earth metal hypobromite (and optionally hypochlorite ions), and thereafter washing the so conditioned stained surface with an aqueous acidic solution having a concentration of acid sufficient to remove the stain and give a bright shiny appearance without substantially dulling or etching the surface. The strong basic material, e.g. 10-450 g/l, may be NaOH, KOH, Na 2 CO 3 or alkali metal silicates. The hypobromite, e.g. sufficient to provide 0.1- 100 g/1 hypobromite ions may be added to the solution as (a) the hypobromite itself, or (b) by combining the strong basic material with Br 2 or a Br providing material such as tetramethylammonium chlorodibromide, or (c) by combining an alkali or alkaline earth metal bromide with an alkali or alkaline earth metal hypochlorite or a compound which produces hypochlorite ions in water. Examples of hypochlorite producing compounds are chloramine T, dichloramine T, chloramine B, Ca(ClO) 2 , chlorinated Na 3 PO 4 , Na or K dichloroisocyanurate, dichloro-or trichloroisocyanuric acid, di-or tri-chloromelamine and dichlorodimethylhydantoin. Bromides which can be used are NaBr, KBr, CaBr 2 , BaBr 2 , MgBr 2 , NH 4 Br and amine hydrobromide salts such as triethanolamine HBr. Alkali metal Ortho- or polyphosphates may be included in the conditioning solution. Example 9 is of preparing a conditioning solution by adding NaBrO 3 and NaBr to H 2 O, and then adding c. HCl and NaOH. The acid of the washing solution, e.g. 10-200 g/l concentration of acid may be HC1, H 2 SO 4 , perchloric, phosphoric, sulphamic, HNO 3 tartaric, acetic, gluconic, citric, maleic, lactic or hydroxy acetic. Both the conditioning and acid washing solutions may be used at 120‹F to the boiling temperature. The method may be used in removing heat stains or in removing stains from equipment which had been spray cleaned with aqueous caustic solution and then used in the processing of milk. The stain conditioning solution may be sprayed on to the stained surface and be recirculated. Dry admixture compositions are specified for preparing stain conditioning solutions.