anti-corrosion coating for the steel box to provide technical reference.

On the city anti-corrosion coating steel box girder bridges construction technology
Over engineering example, introduced anti-corrosion coating technology steel box girder construction techniques, quality testing standards and results achieved project example, anti-corrosion coating for the steel box to provide technical reference.
    [Key words] city bridge; steel box girder; corrosion; Painting
    [Article ID] 1672-7045 (2011) 12-0064-04 [CLC] U445.7 +3 [Document code] B
    1 Project Overview
    Length of a Bridge bridge 734.5m, single-hole span of 300m, the two inclined steel box arch, curved steel box girder bridge, and the bridge deck boom tilt rods. Among them, the steel box section, a total of 30 full-bridge segments, the maximum weight of 137t, the smallest segment weight 120t. Currently, the steel girder is easily eroded by the external environment, in order to prevent corrosion of steel box girder, to molybdenum plating normal function of the bridge, the construction of the bridge after its anti-corrosion coating process is necessary. Therefore, in this bridge design, the outer surface of the steel box girder metal coating, paint coating; steel box inside surface using hand-held spray gun for primer finish benefits sweeping sand nap; against corrosion at weld and paint damage sand-blasting, sand blasting preferably Sa2.5 level, paint coating, anti-corrosion design life of ≥ 30 years.
    Two anti-rust coating steel box girder construction points
    2.1 Pre-construction preparation
    2.1.1 rust
    Steel box before painting should be strictly in accordance with "steel surface before painting Rust grades and preparation level" (GB8923) the relevant requirements, the use of throw (spray) pill machinery to rust, so rust grade requirements to Sa2 .5 ~ Sa3 level.
    2.1.2 Control Coating construction environment
    Before the operations, should be strictly controlled coating construction environment. General requirements for steel box girder surface temperature 5 ℃ ~ 35 ℃, relative humidity ≤ 85%, open-air ≤ 85%. All painting is not allowed in the fog, rain environment, the construction of wind speed ≤ 15m / s.
    2.1.3 paint selection and characteristics and requirements
    The choice of paint to prevent corrosion of steel box girder is essential and should be selected based coating technology. Paint and its specific characteristics are shown in Table 1.
    Subject to enter the construction site when the paint should be strictly in accordance with the construction specifications check mark, model, name, color, batch number, production date, quantity and production certification, etc., and to indicate the kinds of paint (including uses, such as primer, paint, paint), to ensure compliance with construction specifications.
    Meanwhile, the paint into the construction site, the construction schedule in batches into the inventory should be, and should be stored in the painting area 50m outside the outer security coffers. In addition, the use of paint should be commensurate with the longest shelf life, extended not be used.
    2.1.4 Construction Equipment
    Construction equipment including air compressors, sandblasting machine, spraying machine, fan, heating machine, etc., and construction equipment in place should be prepared before use, installation and commissioning work to ensure their safe operation.
    2.2 Construction blasting
    (1) Blasting shall, before the steel box girder polished surface treatment, such as the acute angle of the surface of the steel edges, corners, etc. polished into R ≥ 2.00mm above the arc, and remove the steel slag, pinholes, burr. In polished before doing ventilation, dehumidification and dust and other measures, and then use pneumatic grinder for grinding.
    (2) construction blasting, due to the unique characteristics of the blasting machine and steel corrosion requirements, etc., should be used for angular grit abrasive and grit size should G14 ~ G18, the particle diameter is preferably 1.0mm ~ 1.7mm, hardness HRC40 ~ HRC50, and shall no oil, dust and damp without caking, no soluble salts.
    (3) construction blasting process parameters: sandblasting gun nozzle air pressure ≥ 0.7MPa; blast from 100mm ~ 300mm; blasting angle 60o ~ 70o; sandblasting nozzle diameter 8mm ~ 10mm.
    (4) blasting operations, the jet surface should be evenly; sandblasting the surface should be no oil, no rust, no corrosion, oxide, no paint, etc.; sandblasting steel base surface should be a solid color, roughness should reach Rz40μm ~ Rz80μm.
    2.3 Thermal spray aluminum construction
    After blasting operations shall be conducted in 4h arc thermal spray aluminum construction.