The conditions that the shelf pretreatment process should have

The conditions that the shelf pretreatment process should have are as follows: 1. Normal temperature: A shelf factory pretreatment line does not have heating facilities, and only allows normal temperature treatment. 2. Strong adaptability: It is required that the degreasing liquid and the derusting liquid can handle two materials at the same time; the phosphating liquid should have the advantages of good room temperature performance, fast reaction rate, wide process range, high stability, and uniform and meticulous film thickness. 3. Simple and easy: it must meet the existing process layout and realize a simple process flow. The process flow is as follows: degreasing → washing and pickling → surface adjustment → phosphating → water washing to optimize the pretreatment process (1) Improve the quality of pretreatment before phosphating: room temperature has a greater impact on the pretreatment, especially heavy oil pollution at room temperature for degreasing Poor results have become a key link affecting the quality of pretreatment. For this reason, the normal temperature degreasing and two-in-one degreasing and rust removal matching process are used to make up for the lack of normal temperature degreasing. The amount of degreasing agent at room temperature is 40g/L, TAL (total alkalinity) is 40-50 points, FAL (free alkalinity) is 25-30 points, and room temperature, 15-30min (until the oil is removed). The test shows that the oil removal rate of this agent is about 97% (weighing method). The two-in-one degreasing and rust removing liquid is composed of 12% H2SO4, 50% HCl, and 5g/L additives. The treatment process is normal temperature and 30 minutes. Its characteristics: ①The processing rate is fast and the quality is good. Wetting agent and degreasing agent have better wetting, penetrating and dispersing functions, which are beneficial to the contact of rust remover with the surface of steel, so that the rust remover can quickly reach the interface between the substrate and the oxide scale, thereby speeding up the degreasing and rust removal rate. At the same time, the complexing agent can prevent the black film on the surface of the workpiece and make it smooth. ②Long service life. The complexing agent can slow down the growth rate of iron ions in the solution and prolong the service life. ③Good operating conditions. Surfactant has the effect of suppressing acid mist. The concentration of the two rust removers is appropriate, which not only ensures the rust removal rate, but also reduces the escape of acid mist. (2) Screening of phosphating agents with good performance: A shelf factory tried several commercially available phosphating agents, but they gave up due to unstable quality. Instead, CZ99-03 (7) room temperature zinc phosphating agent The quality of the pre-treatment is obvious, and the production can be stabilized, which is quite popular with manufacturers. CZ99-03 (7) Phosphating agent is divided into A agent, accelerator, neutralizer, etc. Agent A (1:20): du003d1.56～1.57 (28℃), TAu003d820～830, FAu003d110～120; Dosage for tank preparation: Agent A is 50ml/L, neutralizer is 6.0～6.5ml/ L, accelerator is 2.5ml/L; process parameters: TAu003d30-40, FAu003d2.5-4.0, accelerator 1-2 gas point, 20-30℃, 15-30min. This agent has the advantages of stable bath, wide process range and good adjustability. (3) Improve the process flow: the phosphating defect of the cavity beam makes the welding seam easy to yellow and yellow water flows in the cavity, which is caused by the imperfect process flow. The solution is to increase the neutralization process after pickling (replace the neutralization liquid with degreasing solution) and the sealing treatment after phosphating (use the closed tank after phosphating the washing tank, and directly after phosphating the ultra-low chromium passivation 30s) , This is good for improving the corrosion resistance of the phosphating film.