A Brief Discussion on the Room Temperature Blackening Process and Application of Conveyor Accessories Chain Plates

A Brief Discussion on the Room Temperature Blackening Process and Application of Conveyor Accessories Chain Plates

Compared with the traditional alkaline high-temperature blackening process, the room temperature blackening process has many advantages such as stainless steel material variety constraints, energy saving, high efficiency, non toxicity, simple equipment, convenient operation, low environmental pollution, and low cost, which have attracted widespread attention. However, there are still many shortcomings in the black liquor produced by various products sold in the market for more than 10 years, such as the stability of the black liquor, the fineness, adhesion, and corrosion resistance of the generated outer film, which have constrained the production and application of room temperature blackening process to varying degrees. This article combines the years of production practice of conveyor accessory manufacturers, taking the room temperature blackening process of conveyor accessory chain plates as an example, to analyze and discuss the process control and improvement methods in the production and application of chain plates, in order to better promote the use of this process, improve economic and social benefits.

1. Black process flow of conveyor accessory chain plate

The room temperature blackening process for conveyor accessory chain plates generally includes the following four processes:

(1) Basketing - degreasing and rusting - flushing - room temperature blackening - flushing - rinsing with active water - changing baskets - soaking in dehydrated rust proof oil.

(2) Basket loading - degreasing and rust removal - flushing - room temperature blackening - flushing - weak alkali neutralization - rinsing - basket replacement - immersion in dehydrated rust proof oil.

(3) Basket loading - degreasing and rust removal - flushing - room temperature blackening - flushing - passivation closure - boiling water dehydration - basket replacement - immersion in engine oil.

(4) Basket loading - degreasing and rust removal - flushing - room temperature blackening - flushing - closing passivation - drying - basket replacement - immersion in closing paint.

In the above process, the post-processing steps go from simple to complex, with an increase in cost and a corresponding improvement in product quality. The general product application process (1) can meet the quality requirements. For special and demanding parts, subsequent processes can be selected, or a certain process can be freely added or removed according to the part requirements. Compared with alkaline blackening process, although the pre-treatment and post-treatment processes in the process flow are the same, the former has stricter requirements. It is necessary to ensure complete oil and rust removal before blackening, and it is necessary to use dehydrated rust proof oil or high-temperature engine oil to turn off after blackening. The process of blackening the conveyor accessory chain plate at room temperature depends on customer requirements. Generally, process (2) can be used for general requirements, while process (4) can be used for strict requirements.

2. Conveyor accessories chain plate oxidized black at room temperature

(1) Process operation requirements

The composition of blackening solution mainly includes main salt, oxidant, complexing agent, stabilizer, and wetting agent.

Mix the blackening solution and water into the working tank according to the required proportion, and mix evenly.

① Add water first and then add the solution. Good water quality is required because high hardness water or contaminated water can easily form poor film layers or unstable solutions.

② Except for parts, all other utensils that come into contact with the solution can only be made of materials such as plastic, ceramics, or titanium. Metal objects such as iron, copper, and aluminum will react with the solution, seriously affecting the service life and stability of the solution.

③ Solution concentration control of working fluid: high concentration, short film formation time, high film quality induction function, but light color, cost addition, mainly manifested as a large amount of effective ingredients carried out by the workpiece and a large number of side reaction products; Low concentration, dark color, extended time required for film formation, decreased film quality induction function, but also reduced cost. The stability of the solution improves, mainly manifested as a small amount of effective ingredients carried out by the workpiece and few side reaction products. In practical application, the quality ratio of black liquor to water is often chosen as 1:3 or 1:4, depending on the product. Regarding the conveyor accessory chain plate, a concentration of 1:3 is selected for manufacturing.

(2) Fundamental operation

Quickly immerse the conveyor accessory chain plate, which has been cleaned and is free of oil stains and rust spots, into the blackening working solution, and intermittently lift it up and down to ensure that all parts are fully in contact with the solution. After soaking for 4-8 minutes, remove it and rinse it clean with tap water.

(3) Key points of control

① Parts installation and hanging

Use specialized hangers or hooks to suspend and oxidize black parts, which works well. This method forms a film layer with uniform thickness and common color due to the abundant contact between the solution and the surface of the workpiece, resulting in extremely low adverse phenomena. Regarding the conveyor accessory chain plate, a dedicated hanging fixture is used for hanging, which prevents the stacking and accumulation of flat parts and improves the quality of blackening at room temperature.

Small parts or workpieces that are not suitable for this method (such as various hardware components) can be impregnated using the basket or barrel method. However, it should be noted that intermittent oscillation or rolling should be carried out during the blackening process to ensure sufficient contact between the parts and the solution, and to prevent or reduce the stacking and accumulation of parts. Attention should be paid to the appropriate loading capacity, as excessive loading can cause workpieces to stack and accumulate, making them difficult to disperse. Workpieces should not come into contact with the solution, resulting in uneven film layers; Additionally, prevent vigorous mixing. The intense mechanical conflicts and collisions caused by intense mixing can easily lead to the detachment of the regenerated film layer, which not only affects the quality of the film layer, but also causes solution pollution and accelerates aging.

② Blackening moment

The blackening time is short, the film layer is not continuous, the film growth is incomplete, the film layer is too thin, and there are flower spots; Extending the blackening time, the thickness of the blackening film is increased, and the corrosion resistance and wear resistance are improved, but the data consumption is large, and the cost is correspondingly improved. When the blackening time exceeds 15 minutes, the function of the blackening film actually decreases, and excessive black oxides appear on the surface. The remaining parts are loose and have poor adhesion. Therefore, the longer the blackening time, the better the blackening effect. Regarding the conveyor accessory chain plate, a 1:3 dilution solution is selected, and the reaction time is controlled within 4-8 minutes.

③ Blackening temperature

Temperature also has a certain impact on the speed and quality of blackening film formation. The film-forming rate of room temperature blackening includes blackening rate and phosphating rate. The temperature has little effect on the blackening rate, but has a significant impact on the phosphating rate. In principle, black liquor can be used at 5-45 ℃, but when the temperature is below 10 ℃, the reaction speed is slow, the blackness and uniformity are poor, the phosphating speed is slow, the adhesion of the black film is low, and sometimes even floating ash occurs. At this point, the response time should be extended. When the temperature is above 40 ℃, the reaction speed is too fast, the membrane adhesion is poor, and the stability of the blackening solution is significantly reduced. The addition of sediment increases the production cost of blackening. Regarding the conveyor accessory chain plate, the blackening temperature should be controlled between 15-35 ℃.

④pH

Low pH, strong oxidizing power, rapid film-forming reaction rate, high acidity, high iron dissolution, and sludge accumulation. During the reaction process, there is an upward trend in pH. When pH>3, the reaction rate is slow, the membrane layer is not continuous, and the appearance is not ideal. It indicates the aging of the solution and requires the addition of concentrated solution to adjust pH. Regarding the conveyor accessory chain plate, the pH should be controlled between 2.0 and 2.5.

⑤ Raw materials

Regarding steel raw materials, there is no selection for black liquor; But for cast iron parts, the concentration of black liquor should be diluted; For medium and low carbon steel, medium concentration black liquor can be used; For high carbon steel and alloy steel, it is required to have a thicker black liquor.