The armor plate and profiled bar for welding manufacture of the gantry crane are pretreated before welded. The armor plate and profiled bar are not allowed to weld if they aren’t pretreated.
(1)removing the impurity which cling to the surface of armor plate, and removing the grease etc. dirt by thinner, for example sulphate or corrosive salts , using the clear water to wash and blow drying  by compressed air.
 (2) removing cleanly the oxide scale,rust or other impurity by throwing ruster or sand blasting method, and then clearing  armor plate’ surface cleanly by vacuum cleaner or depurative compressed air. The quality must reach Sa2 1/2 grade(Rusting grade and derusting grade of armor plate surface before painting  in GB8923-88)
8. Oil paint
(1). After derusting, the time interval  which the primer are painted on the metal surface shouldn’t exceed 6 hours. 
(2) the primer is total two hand which adopts “702 zinc rich epoxy primer”,  the first hand is used as mainted primer, the dry coating thickness is 20μ±5μ; and the second hand is used as antirust primer, the dry coasting thickness is 35μ±5μ. The middle painting adopts “cloud iron epoxy primer”, airless spraying 1 hand, and dry coasting thickness ≥45μ±5μ. And the topcoat adopts “Chlorinated Rubber topcoat” , 1 hand , and dry coating thickness≥70μ±5μ.
The topcoat painting of crane should be uniform, meticulous, bright ,full and color consistency , and it shouldn’t be rough, leak painting , fault painting , wrinkle , pinhole  and severely etc.  tearing.
 (3).customer can decide the color of crane’s surface painting. If the customer doesn’t have special requirement, the manufacturer can refer to the rules of JB2299《Mining engineering, lifting the transport machinery products paint colors and safety signs》，as for the inner wall of room for electric equipment  and inner wall of the box structure, the topcoats are whit.
(4).the 1 hand antirust primer should be painted the inner of close box body. The primer type is as same as above mention, the dry coating thickness≥35μ。
(5) all of the surface of mechanical parts should be painted light-gray if there don’t have special requirement.
 (6) the inner surface and parts’ surface without processing of reducer box should be painted milk yellow oil resistant enamel or other oil resistant coating.
(7)grease cup, chock ,lubricating system, hydraulic pressure tube, air pressure tube etc. symbol parts and preventing-loosing device such as button and fast rotary parts without preventing-loosing device, coupling, spoke and web plate, all of them should be painted red topcoat paint.
 (8)according to JB2279-78 “Mining engineering, lifting the transport machinery products paint colors and safety signs”, the warning sign part of outside of crane which is very easy to cause colliding such as lifting hook, the surface of rotationable tail counterweight box should be painted safety sign(yellow alternate with black, the angle between the inclined strip and horizontal plane should be 45°.)