| 摘要 |
PURPOSE:To enhance the close adhesiveness to polyolefin, by applying mechanical descaling to the inner surface of a steel pipe prior to zinc/calcium phosphate treatment and subsequently performing pickling by hydrochloric acid under a specific condition. CONSTITUTION:Mechanical descaling is applied to the inner surface of a steel pipe by sending a grinding material such as grid or sand into said steel pipe along with compressed air and subsequently applying pickling treatment with hydrochloric acid to said steel pipe. The treatment condition at this time is set so that iron content is 70-160g/l, the concn. of hydrochloric acid is 5-15%, a pickling time is 1.5-10min and liquid temp. is 10-60 deg.C. By performing the mechanical means for removing scale and short-time pickling with hydrochloric acid in combination as mentioned above, the adhesive strength of direct polyolefin lining after zinc/calcium phosphate treatment can be enhanced.
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