Phosphating Process for Forklift Bearings and Its Advantages

Phosphating, when used as a protective treatment, involves thick-film phosphating with a film thickness exceeding 20 µm. The typical coating weight ranges from 10 to 30 g/m², or even higher, to achieve superior protective performance. After the phosphating process, forklift roller bearings are often immersed in oil, grease, or wax to further enhance their corrosion resistance.

1. Slow Phosphating Process

The phosphating solution is made of zinc dihydrogen phosphate, manganese dihydrogen phosphate, or iron dihydrogen phosphate, possibly in combination with free phosphoric acid. Since no oxidizing agents are involved, the concentration of Fe²⁺ ions increases as the treatment area grows, causing more precipitation. The treatment time typically lasts 40 to 60 minutes.

2. Accelerated High-Temperature Phosphating

Adding agents like NO₃⁻ or ClO₃⁻ to the phosphating solution can significantly reduce the treatment time. These agents help maintain a consistent level of Fe²⁺ in the solution by facilitating the oxidation of iron and the reaction with acid to generate hydrogen ions. Even though the zinc content in the solution may initially decrease, it remains stable throughout the process, and the composition of the phosphating film doesn’t vary noticeably with the treatment area.

Phosphating solutions containing accelerators also produce fewer precipitates than non-accelerated solutions. The corrosion resistance of the phosphating film remains unchanged, and the life of the solution is prolonged. Regular testing and replenishing of the solution during production are essential to maintain a consistent quality of the phosphating film. Forklift roller bearings can be placed in the tank using rollers.

Functions of Surface Phosphating Treatment

1. Enhanced Corrosion Resistance: The phosphating film, although thin, acts as a non-metallic, non-conductive isolating layer, turning theforklift roller bearing's surface from a good conductor into a poor conductor. This prevents the formation of micro-galvanic cells on the surface and effectively stops the corrosion of the coating.

2. Improved Adhesion Between Substrate and Coating: The phosphating film tightly bonds with the forklift roller bearing, forming a solid structure. Additionally, the film's porous nature allows the coating to penetrate these pores, bonding more securely to the phosphating film, which enhances adhesion.

3. Provides a Clean Surface: Phosphating films can only form on metal surfaces free from oil and rust. Therefore, forklift roller bearings treated with phosphating offer a clean, uniform, oil-free, and rust-free surface, ensuring better coating adhesion and performance.

4. Improves Cold Working Performance: The phosphating process improves the material’s ability to undergo cold working, such as bending or forming.

5. Improves Surface Friction: The treatment improves the friction properties of the surface, which enhances the sliding characteristics of the forklift bearings.

Phosphating Process Parameters

• Temperature: Ambient temperature
• Specific Gravity: 1.38 - 1.50
• Color: Green

Phosphating Solution Composition

• Phosphating Liquid: 2.4% - 4.8%
• Accelerator: 0.06%
• Total Acid Value: 14 - 30 points
• Free Acid: 0.6 - 1.4 points
• Accelerator: 0.8 - 4 points
• pH Value: 2.5 - 3.5
• Phosphating Time: 8 - 20 minutes

Testing Methods

• Total Acid Value: Take 10 ml of the working solution, add distilled water to 50 ml in a conical flask, then add 3-5 drops of phenolphthalein. Titrate with 0.1N sodium hydroxide until the solution turns pink. The amount of sodium hydroxide used is the total acidity.
• Free Acid: Take 10 ml of the working solution, add distilled water to 50 ml in a conical flask, then add 3-5 drops of bromothymol blue. Titrate with 0.1N sodium hydroxide until the solution turns light blue. The amount of sodium hydroxide used is the free acidity.
• Accelerator: Fill a fermentation tube with working solution, add 3-4 grams of ammonium sulfamate, and wait until no further reaction occurs. Accurately read the parameters.
• pH: It is recommended to use precision test paper for measurement.

Solution Preparation (for 1000L)

1. First, add 1/4 of the water to the phosphating tank.
2. Add 0.06 kg of calculated accelerator.
3. Add water until it reaches 3/4 of the tank, then add 48 kg of the calculated phosphating solution.
4. Finally, add water to fill the tank to 1000L.
5. Test the total acidity and free acidity, and adjust using sodium hydroxide or sodium carbonate to reach the standard parameters.

Note: When adjusting with sodium hydroxide or sodium carbonate, dissolve them completely in water before slowly adding the solution to the phosphating tank while stirring.

For more info, feel free to contact QIBR.