Pickling sheet is a cost-effective product between cold-rolled sheet and hot-rolled sheet. It is widely used in the automotive industry, machinery industry, light industrial appliances and stamping parts of various shapes, such as beams, sub-beams, rims, spokes, carriage panels, fans, chemical oil drums, welded pipes, electrical cabinets, fences, Iron ladder etc. Has broad market prospects.
We will introduce the technical process of the pickling process and the comparative advantages of laser cleaning.
1. Metal pickling process
1.1 Pickling principle
A surface process in which an acid solution is used to remove oxide and rust from the surface of steel, usually in conjunction with a prefilm. Generally, the parts are immersed in sulfuric acid and other chemical agent solution to remove the oxide film on the metal surface. It is the pre-treatment or intermediate treatment of electroplating, enamel, rolling and other processes. Also known as wet cleaning.
The main pickling processes are immersion pickling, jet pickling and acid paste rust removal.
The main acids used are sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, hydrofluoric acid and mixed acid.
1.2 Process flow
Hanging metal parts → chemical deoiling (conventional alkaline chemical deoiling or surfactant deoiling) → Hot water washing → water washing → First step pickling → water washing → Second step pickling → water washing → Transfer to the next process (such as: chemical coloring → recovery → water washing → hardening treatment → water washing → closed treatment → water washing → drying → finished products)
1.3 Common defects
Oxide pressing: Oxide pressing is a surface defect formed during hot rolling. After pickling, it is often black spot-like, long strip pressure, rough surface, generally feel, and sporadic or dense. It is often caused by the imperfect heating process, descaling process and rolling process of pickling.
Oxygen spot (surface landscape painting) : refers to the spot-like, linear or pitted morphology left after the oxidation sheet on the surface of the hot roll is washed off. The essence is that the oxidation sheet on the surface of the hot rolled strip is not cleaned, and it is pressed into the matrix after subsequent rolling and highlighted after pickling. The appearance is affected, but the performance is not affected.
Macula: Yellow spots appear on local or whole board surface, which cannot be covered after oil coating, affecting the appearance of product quality. The main reason is that the surface activity of the strip steel just out of the pickling tank is high, and the rinsing water fails to play a normal role in rinsing the strip steel. The spray beam and nozzle of the rinsing tank are blocked, and the Angle is not equal.
Under-pickling: The strip surface is not clean and sufficient to remove local oxidation iron sheet, the surface is gray black, fish scale or transverse water ripple markings. It is related to the acid process, mainly because the acid concentration is insufficient, the temperature is not high, the strip steel running speed is too fast, the strip steel can not be immersed in the acid and other reasons.
Pickling: the strip surface is often dark or brown black, showing blocky, flaky black spots or macula, the surface is generally rough. The cause is the opposite of under-pickling.
1.4. Environmental pollution
The main pollutants in the production process are the cleaning wastewater produced by the washing process at all levels, the dust produced by the sandblasting process, the hydrogen chloride acid mist produced by the pickling process, and the waste tank liquid, waste residue, waste filter element, raw material empty barrel and packaging waste produced by the pickling, bleaching, phosphating, neutralization and rust prevention process. The main pollutants are hydrogen chloride, pH, SS, COD, BOD? , ammonia nitrogen, petroleum, etc.
2. laser cleaning process
2.1 Cleaning principle
With laser energy through the surface of the object, 100 femtoseconds or so in the matter of the electron absorption energy vibration, the surface of the matter to produce plasma; After 7-10 picoseconds, the electron energy is transferred to the lattice, which makes the lattice vibrate. After 10 picoseconds, the object starts to produce macroscopic temperature, and the local materials irradiated by the laser begin to heat up, melt and vaporize, so as to achieve the purpose of cleaning.
2.2 Cleaning process and effect
Compared with pickling method, laser cleaning process is very simple, without pretreatment, can be cleaned at the same time to remove oil, remove oxidation layer and rust. Just turn the device on and clean it.
Laser cleaning can reach the highest industrial cleaning level of Sa3; There is almost no damage to the hardness, hydrophilicity and hydrophobicity of the material surface. More thorough than pickling.
3. the comparative advantages of laser cleaning
3.1. Process flow and operation requirements
Compared with more than a dozen pickling methods, laser cleaning has achieved the most simplified process, basically achieved a step in place. Greatly shorten the cleaning time and material loss.
Pickling method has strict requirements on the operation process: the workpiece must be thoroughly removed from oil, in order to ensure the quality of rust removal; Control the concentration of acid washing solution to avoid the corrosion of the workpiece caused by the high concentration of acid; Control the temperature according to the process specification, so as not to cause corrosion to the workpiece and equipment; The pickling tank gradually deposited sludge, blockage heating pipe and other control devices, need to be removed regularly; In addition, it is necessary to pay attention to pickling time, jet pressure, operation sputtering, exhaust equipment and so on.
Laser cleaning in the early setting of parameters can realize the fool operation or even automatic unmanned operation.
3.2 Cleaning effect and environmental pollution
In addition to the stronger cleaning effect, laser cleaning has an advantage of greater fault tolerance:
The operation of pickling method often causes oxygen spots, yellow spots, redness and blackness due to mistakes, and the rejection rate is high.
The droplet laser experiment has proved that even if the laser cleaning is supersaturated, it still has a strong metallic luster and does not produce hydroxide and other pollutants, which will not affect the next welding and other processing methods.
Laser cleaning will not have waste liquid waste residue and other environmental pollution, is the most green cleaning way.
3.3 Unit cost and conversion cost
Pickling requires chemical agents as consumables, so the unit cost is composed of equipment depreciation + consumables cost;
Laser cleaning does not require additional consumables in addition to the purchase of equipment. Unit cost is equipment depreciation;
Therefore, the larger the cleaning scale, the longer the years, the lower the unit cost of laser cleaning.
The formation of pickling production line requires a complex process, and the ratio of acid cleaning agents of different metal materials is not the same, so the conversion production line requires a large conversion cost, and the metal materials cleaned in the short term are single and cannot be changed flexibly.
There is no conversion cost in laser cleaning: the same cleaning machine can realize the effect of cleaning steel plate one minute and cleaning aluminum alloy the next minute after switching software parameters. Convenient for enterprises to implement JIT flexible production.
