For the steel structure engineering with diaphragm for a period of time, there are inevitably some adherents on its surface, such as rust, dirt, dust, old paint film, etc. Before painting the steel structure surface, if these attachments are not removed completely, they can be temporarily covered after painting, but because they play the role of isolation, the adhesion between the coating and the component matrix will be seriously reduced, and the paint film will fall off prematurely, resulting in the reduction of the corrosion resistance of the surface coating, which will not play the protective role of the coating. Therefore, before painting the component surface, the attachments on the steel structure surface shall be thoroughly cleaned.
In the construction of steel structure maintenance project, the surface cleaning mainly includes the removal of old paint film. In the process of derusting, due to the limitation of construction conditions, the commonly used methods are as follows:
1. Manual derusting
This method is to use scraper, blade, hammer, wire brush and other steel tools to remove dirt by hand, and to use abrasive cloth, sandpaper and grinding wheel to remove dirt, so that the surface of the component is basically oil free, rust free and burr free. Because of its convenience, simple equipment, low labor cost, and not limited by the size of construction site conditions, this method is often used in steel structure maintenance engineering. Its main disadvantages are poor working conditions, low working efficiency, incomplete rust removal and poor quality assurance. Therefore, when using this method to remove rust in Han Dynasty, the management personnel should emphasize the quality requirements.
2. Mechanical derusting
In order to improve the quality and efficiency of derusting. In order to improve the working conditions of the construction personnel, a large number of small-scale wind-driven or electric equipment have been used in the steel structure derusting work. The main derusting methods of the equipment are as follows:
(1) angle grinder: this kind of small pneumatic equipment is mainly used to clean the flat area. It can use sandpaper, grinding wheel and wire brush as required.
(2) needle beam rust remover: this small pneumatic equipment is generally equipped with 30-40 needle bundles, which can be adjusted with different working surfaces, mainly suitable for bending, narrow, uneven and seam.
(3) single head cold air gun: this small pneumatic equipment is also called zinc knocking. It uses the impact force of the shovel head to remove the rust. The diameter of the shovel head is generally 25-40mm, and it can impact 1000-6000 times per minute, which is suitable for relatively narrow places.
3. Sand blasting
Sand blasting can be used to remove rust in projects that can be shut down for construction and maintenance. The rust on the top surface of steel structure members shall be removed by sandblasting machine to expose the true color of metal. A better sandblasting machine can automatically screen out the fine powder of the spurted stone yellow sand, iron sand or iron shot, prevent the dust from flying, and reduce the impact on the health of the operator. This method can remove rust thoroughly. The efficiency is also high, which has been widely used in developed countries. It is an advanced rust removal method.
4. Remove rust with pickling paste
A special pickling paste for rust removal can be purchased on the market. The method of use is to apply the pickling paste on the surface of the component under the coating, with a thickness of about 1-2mm. After a proper time of rolling, peel off a small piece of pickling paste to check the rust removal. If the surface of the component shows the true color of metal, peel off the pickling paste, wash with water, and thoroughly remove the residual acid. Except for some special cases, this method has been rarely used.