Detailed explanation of the process flow of electroless nickel plating
Pre processing: laying a solid foundation
Oil removal, as the primary task of pre-processing, aims to thoroughly remove oil stains from the surface of the workpiece. The presence of oil stains is like a stubborn "barrier" that seriously hinders the close contact between the plating solution and the surface of the workpiece, thereby affecting the quality and adhesion of the coating. For this, we can adopt various effective methods for oil removal. Organic solvents can quickly remove oil from the surface of workpieces due to their ability to quickly dissolve oil stains; Chemical degreasing cleverly utilizes the saponification effect of alkaline solutions and the emulsification effect of surface active substances to thoroughly decompose and remove oil stains. For example, in practical operation, we can immerse the workpiece in a chemical degreasing solution containing sodium hydroxide, sodium carbonate, and other components. After a period of treatment at an appropriate temperature, the oil stains will be effectively removed.
Rust removal is also an indispensable step in the preliminary treatment. The presence of rust layer not only affects the aesthetics of the coating, but may also cause problems such as blistering and peeling of the coating. Common rust removal methods include mechanical rust removal and chemical rust removal. Mechanical rust removal involves using methods such as sandblasting and polishing to remove the rust layer from the surface of the workpiece through mechanical force; Chemical rust removal involves a chemical reaction between an acid solution and the rust layer to dissolve and remove the rust layer. For example, using hydrochloric acid or sulfuric acid solution to acid wash the workpiece can quickly and effectively remove the rust layer, but the acid washing time and temperature need to be strictly controlled to prevent excessive acid washing from causing damage to the workpiece.
Polishing can make the surface of the workpiece smoother and smoother, as if putting a delicate "coat" on the workpiece. This not only helps to improve the uniformity and glossiness of the coating, but also enhances the adhesion between the coating and the workpiece. The commonly used polishing methods include mechanical polishing, chemical polishing, and electrochemical polishing. Mechanical polishing involves using polishing wheels and other tools to polish the surface of the workpiece; Chemical polishing uses chemical reactions to dissolve the microscopic protrusions on the surface of the workpiece, thereby achieving a smooth effect; Electrochemical polishing is the process of making the surface of a workpiece smooth through electrolytic action in a specific electrolyte.
Water washing runs through all stages of the pre-treatment process, acting as a diligent "cleaning guard" to promptly remove impurities and chemical agents remaining during the processes of oil removal, rust removal, and polishing, ensuring that the surface of the workpiece remains clean at all times. Each water wash must be thorough and thorough to avoid any adverse effects of residual substances on the subsequent nickel plating process.
Acid washing activation: Activate surface activity
Acid pickling activator, as the "magic potion" of this process, usually consists of a specific ratio of acid and additives. The acid pickling activator formula applicable to workpieces of different materials also varies. For example, for steel workpieces, commonly used acid pickling activators may contain components such as sulfuric acid and hydrochloric acid; For aluminum alloy workpieces, a specialized acidic solution is required to avoid excessive corrosion of the workpiece.
When performing acid washing activation operation, it is necessary to strictly control the soaking time and temperature. Generally speaking, the soaking time is usually around 2-3 minutes, and the temperature is adjusted reasonably according to the specific activator formula and workpiece material. If the soaking time is too short or the temperature is too low, it may lead to poor activation effect and insufficient surface activity of the workpiece; On the contrary, if the soaking time is too long or the temperature is too high, it may cause excessive corrosion to the surface of the workpiece, affecting its performance and quality.
Plating process: Perfect deposition of nickel layer
Temperature, as one of the key factors in the plating process, has a significant impact on the rate of nickel plating reaction and the quality of the coating. Generally speaking, the optimal temperature range for electroless nickel plating is between 85-92 degrees Celsius. Within this temperature range, the nickel plating reaction can proceed at an appropriate rate, ensuring both production efficiency and stable coating quality. If the temperature is too low, the nickel plating reaction rate will significantly slow down, and may even cause the reaction to stop; If the temperature is too high, it may make the plating solution unstable, causing problems such as plating solution decomposition, which seriously affects the quality of the coating.
Loading ratio, which is the ratio of the surface area of the workpiece to the volume of the plating solution, is also a parameter that needs to be strictly controlled during the plating process. A reasonable loading ratio is generally between 0.5-1.5 square decimeters per liter. If the loading ratio is too large, the nickel ions and reducing agents in the plating solution will be rapidly consumed, leading to an imbalance in the composition of the plating solution and a decrease in the quality of the coating; If the loading ratio is too small, it will cause waste of plating solution and increase production costs.
Stirring plays an important role as a "mediator" during the plating process. Moderate light stirring can make the temperature and composition distribution in the plating solution more uniform, ensuring that the nickel plating reaction can be carried out uniformly on all parts of the workpiece surface, thereby ensuring the consistency and uniformity of the coating. At the same time, stirring can also promote the escape of hydrogen gas, prevent hydrogen gas from accumulating on the surface of the workpiece to form bubbles, and affect the quality of the coating.
Filtering is like installing a "precision filter" for the plating solution, which can timely remove impurities and suspended solids in the plating solution. In the plating process, a cyclic filtration method is usually used, and the pore size of the filter is generally controlled between 1-8 microns, and it needs to have high temperature resistance of 100 degrees Celsius and acid resistance. By regularly filtering the plating solution, the service life of the plating solution can be effectively extended and the quality of the coating can be improved.
During the plating process, it is also necessary to closely monitor the changes in the composition of the plating solution. As the nickel plating reaction continues, the main salts, reducing agents, and other components in the plating solution will be continuously consumed, resulting in a gradual slowing down of the plating rate. At this point, supplements A and C can be added based on the amount of bubbles, according to A: C = 1: Add in a ratio of 1, and follow the principle of small amounts and multiple times. For every gram of nickel metal consumed, 10 milliliters of each of A and C needs to be added. When a large amount of A and C need to be replenished, the plating should be stopped by cooling down first, then the supplement should be added and stirred thoroughly to ensure that the composition of the plating solution is balanced before continuing with nickel plating.
The inspection and maintenance of equipment cannot be ignored. In the process of electroless nickel plating, the plating tank, heating device, stirring equipment, filtering equipment, etc. are all subjected to certain pressure and corrosion. Therefore, it is necessary to regularly inspect these devices to see if there are any damage, leaks, or other issues. For problems discovered, timely repair or replacement should be carried out to ensure the normal operation of the equipment. At the same time, it is necessary to regularly clean and maintain the equipment to extend its service life.