baking oven at about 55 to 65 u00b0 c for about 10 to 15 minutes the anodizing technology may be a known method in this field for example it may be carried out by placing a substrate into an electrolyte as anode and a steel plate is used as cathode the electrolyte includes sulfuric acid solution with a concentration of about 100 to 200 g l and aluminum sulfate of about 5 to 10 g l the dc power voltage may be about 10 to 15 v and the anodizing time may be about 20 to 40 minutes in some embodiments the substrate may be pre treated before anodizing the pretreatment may include the steps of the substrate is placed into a solution of degreasing powder with a concentration of 30 50 g l at about 50 70 u00b0 c for about 3 8 minutes and then the degreasing powder solution on the substrate surface is removed by water the above dewaxed and degreased substrate is placed into a mixed acid solution with a concentration of about 650 750 g l phosphoric acid and about 150 250 g l sulphuric acid for chemical polishing for about 3 7 seconds after polishing the substrate is immediately transferred into water to.