Principle of powder galvanizing technology

Place the galvanizing agent and steel parts in the galvanizing furnace and heat them to about 400 ℃, and the active zinc atoms penetrate into the steel parts from the surface to the inside. At the same time, the iron atoms diffuse from the inside to the outside, forming zinc-iron intermetallic compounds on the surface of the steel parts, namely the powder galvanizing layer. The powder galvanizing layer is formed by the diffusion reaction of zinc and iron, and its main component is δ phase (FeZn17). δ phase contains 7%~11% (mass fraction) Fe, has good density and toughness, and its corrosion resistance is not lower than that of hot-dip galvanizing layer. The hardness is about 250HV and has good wear resistance.

Powder galvanizing process

Powder galvanizing is to bury the workpiece with cleaned surface in a sealed container filled with galvanizing agent, heat it to below the melting point of zinc (419.4℃), keep it warm for a certain period of time, and then cool it to room temperature with the furnace. Powdered zinc infiltrants usually consist of zinc powder, inert powder, activator, etc. The thickness and quality of the zinc-diffused layer are mainly related to the heating temperature, insulation time, agent composition and zinc-diffused method. The characteristics of powdered zinc-diffused are: the infiltration layer is relatively uniform, no hydrogen embrittlement and deformation will occur, and it is suitable for workpieces with complex shapes, such as fasteners, springs and pipes.

The performance of powdered zinc-diffused products is good, and in summary, they have the following characteristics:

● Strong corrosion resistance: Corrosion and rust are the natural enemies of steel materials. It is estimated that about one-tenth of the world's steel production is lost to corrosion and rust. Practice has proved that in a variety of environments such as marine atmosphere and harsh industrial atmosphere, the corrosion resistance of the zinc-diffused layer is better than that of hot-dip galvanizing, electroplating and stainless steel. In the same industrial atmosphere, stainless steel corrodes for 600 days and the surface is covered with rust spots, while the surface of the zinc-diffused product is not rusted after more than 1,600 days of corrosion.

● Good wear resistance and scratch resistance: The surface hardness of the zinc-dip coating can reach Hv250-400, while the surface of hot-dip galvanized and electro-galvanized parts is pure zinc, and the coating hardness is only about Hv70. Therefore, the wear resistance and scratch resistance of zinc-dip coating are much better than those of hot-dip galvanizing and electro-galvanizing.

● The production is basically pollution-free: Under normal circumstances, the pre-treatment of zinc-dip coating production only uses shot blasting machines to remove rust and oil, and uses bag dust removal, which can meet the national third-level standard. Electricity or natural gas is used as the main energy source in production, and low-nitrogen circulating combustion smokeless emission technology is adopted. Powder zinc-dip coating technology is solid zinc-dip coating, and no zinc vapor is generated. The workpiece and the additive are infiltrated and separated in a closed device, which does not pollute the surrounding environment.

● The zinc consumption is relatively low: the zinc consumption of hot-dip galvanizing is about 100 kg per ton of product, while the powder zinc-dip coating is only about 30 kg, accounting for only 30% of hot-dip galvanizing. In addition, there is no zinc pot corrosion, which is a long-standing problem of hot-dip galvanizing.

● Composite protection can be achieved after painting: the zinc layer of the zinc-diffused product is uniform and has a first-level bonding strength with the paint. The corrosion resistance of its composite protective layer is better than that of hot-dip galvanizing, electro-galvanizing and zinc-diffused layers.

● The mechanical properties of steel parts treated by zinc-diffusion do not affect the material: the temperature of zinc-diffusion treatment is 40 to 180°C lower than that of hot-dip galvanizing. At this temperature, the hydrogen atoms absorbed into the steel matrix have diffused and escaped. Therefore, there is no harm of hydrogen embrittlement in the application, and the disadvantage of mechanical properties of some high-strength parts such as springs being reduced due to high treatment temperature can also be avoided.

Composition of complete equipment of hot-diffusion zinc-diffusion line (multi-element powder infiltration line)

● Main equipment: pre-treatment [carbonization degreasing, ultrasonic spray degreasing cleaning machine; shot blasting (sand blasting) rust removal], zinc-diffusion furnace; post-treatment (ash separation, water washing, grinding, phosphating, passivation, sealing, drying).

● Environmental protection equipment: environmental protection feeding and discharging machine, environmental protection separation screen, dust control dust collector.

● Central automation, informationization, and intelligent control system (composed of host computer (HMI), PLC, field instruments, etc. Among them, the automation system PLC mainly completes communication, data collection, important logic control, etc. The host computer plays a role in centralized monitoring and management.)

Suggestions for production line equipment selection:

● The heating furnace can use electricity, natural gas, and liquefied petroleum gas as energy.

● The zinc-dipizing charging barrel is round, hexagonal, and square, with an inscribed circle of 0.6-2.6 meters in diagonal diameter and a charging barrel length of 1-13 meters.

● The capacity is determined by the volume of the zinc-dipizing charging barrel and the shape of the workpiece: 80% of the charging barrel volume is the maximum furnace loading capacity, the length of the zinc-dipizing charging barrel minus 10CM is the longest workpiece of the zinc-dipizing piece, and the width of the zinc-dipizing charging barrel minus 6CM is the widest width of the zinc-dipizing piece.

● The post-processing production line can be operated manually: remote control crane, automatic mesh belt (plate chain) passivation closed line, automatic door hanging passivation closed line, automatic catenary passivation closed line, and automatic suspended rail passivation closed line.

● According to the investment, manual operation, semi-automatic logistics and control system, and fully automatic logistics control system can be selected.

Our company specializes in providing complete sets of hot-dip galvanizing lines (multi-element powder infiltration lines)

● Our company is committed to the research and development of high-quality equipment and the goal of reducing customer use costs. We specialize in providing advanced technology, stable and reliable, high-efficiency energy-saving, safe and environmentally friendly, easy to use, automated, and intelligent hot-dip galvanizing complete sets of equipment; supporting pre- and post-processing equipment; supporting environmental protection equipment, mature processes, and raw materials for production.

● Turnkey project for whole-plant planning, scheme design, equipment manufacturing, installation, commissioning, and process technology guidance and training for customer construction projects.

● Professionally provide the necessary equipment for anti-corrosion treatment of bridge-affiliated steel structures that meet the requirements of CRCC certification rules (carbonization and oil removal device, shot blasting machine, multi-element powder infiltration agent batching device, multi-element alloy co-infiltration furnace, infiltration agent and infiltration parts separation device, passivation and sealing treatment line, etc.).

Performance and application of hot-dip galvanizing

The performance advantages of infiltration products determine its wide application and significant benefits. Such as railway system, highway system, electric power, communication, construction, ocean, bridge, shipbuilding industry, chemical industry, petroleum, metallurgy, power generation, outdoor steel structure and fasteners, etc., used for bridge support anti-fall beam embedded steel plate, box beam contact network pillar embedded parts, high-strength bolts, ordinary fasteners, crossarms, iron towers, non-standard hardware, electric porcelain base, metal pipes, plumbing appliances, automobiles, engineering machinery parts, hardware parts, malleable cast iron scaffolding, spikes, electric locomotive pulleys, highway guardrails and fasteners, anchor chains and high temperature resistant parts anti-corrosion treatment, its economic benefits are very considerable. Powder zincizing technology can create huge economic and social benefits, plus the benefits of improving resource utilization and protecting the environment, the contribution of powder zincizing technology is very significant.