| Grain-oriented electrical steel is a kind of silicon-iron soft magnetic material with high magnetic susceptibility and low iron loss.It is widely used as core materials for large motors and power transformers.However,the insulation property of the magnesium silicate layer which coats on the surface of grain-oriented electrical steel cannot meet the needs of the large and medium transformers.Thus,an insulation coating needs to be coated on the surface of magnesium silicate layer.At present,the chromic anhydride which usually used in the insulation coating solution of electrical steel is harmful to human body and environment.Therefore,the study of new chromium-free or low-chromium phosphate coating solution becomes one of the trends for grain oriented electrical steel.In addition,the phosphate insulation coating is light color with weak covering property.So,the dark treatment of grain-oriented electrical steel insulation coating is also urgently needed to be solved.In this dissertation,the effects of combined addition of ammonium tungstate and chromic anhydride on the properties of phosphate insulation coating and grain-oriented electrical steel are studied.It is shown that,with gradually increasing the addition amount of ammonium tungstate in the composite additive,the wettability of coating solution first enhances and then decreases.After coating,the interlamination resistance and lamination factor of grain-oriented electrical steel first increases and then decreases,and the iron loss first reduces and then increases.With the combined addition of 1.0wt%ammonium tungstate and 1.5wt%chromic anhydride in the insulation coating solution,the wetting angle of the coating solution on electrical steel substrate is the smallest which means the best wettability of the coating solution.At the same time,the formed insulation coating is dense and smooth with a good adhesion on the substrate,and there is a diffusion area of?0.7?m in combination with the magnesium silicate layer.Furthermore,the humidity resistance of the insulation coating is not significantly changed compared with the coating with only chromic anhydride addition in the solution.The lamination factor and the interlamination resistance of the coated grain-oriented electrical steel are 97.1%and 18021?·mm2 respectively.The values of the iron loss and magnetic induction intensity are 1.113W·kg-1 and 1.872T respectively.The effects of combined addition of ammonium tungstate and boric acid on the properties of phosphate insulation coating and grain-oriented electrical steel are studied.It is shown that,with gradually increasing the addition amount of boric acid in the coating solution,the wettability of the grain-oriented electrical steel phosphate coating first enhances and then decreases.After coating,the interlamination resistance and lamination factor of grain-oriented electrical steel first increases and then decreases,the magnetic induction intensity shows a monotonically decreasing trend,and the iron loss first reduces and then increases.With the combined addition of 0.5wt%ammonium tungstate and 2.0wt%boric acid in the insulation coating solution,the wetting angle of the coating solution on electrical steel substrate is the smallest which means the best wettability of the coating solution.At the same time,the formed insulation coating is dense with good adhesion and humidity resistance,and there is a diffusion area of?0.5?m in combination with the magnesium silicate layer.The lamination factor and the interlamination resistance of grain-oriented electrical steel are 98.2%and 19366?·mm2 respectively.The values of the iron loss and magnetic induction intensity are 1.155 W·kg-1 and 1.876T respectively.Finally,the effects of water-soluble inorganic colorants additivity in the coating solution with chromic anhydride on the properties of phosphate insulation coating and grain-oriented electrical steel are studied.The results show that,with the addition of 4.76wt%inorganic colorants in the chromium-containing phosphate insulation coating solution,the obtained insulation coating powder and the coated grain-oriented electrical steel have the darkest color.At this additive amount,the Hunter whiteness value of new insulation coating powder is 27.71 and the Hunter whiteness value of the coated electrical steel is 29.50.While without the inorganic colorants,the Hunter whiteness value of insulation coating powder is 43.08 and the Hunter whiteness value of the coated electrical steel is 44.26.Furthermore,the addition of inorganic colorants not only darkens the color of the obtained insulation coating,but also slightly improved the properties of the electrical steel compared with that of the sample without the addition of inorganic inorganic colorants. |
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