Common problems and solutions of blackening surface treatment process in Dalian

1、 Overview of Blackening Surface Treatment Process

Dalian blackening surface treatment is a common metal surface treatment process, which forms a dense oxide film on the metal surface to achieve the purpose of corrosion prevention, aesthetics, and improved wear resistance. This process is widely used in fields such as mechanical parts, automotive components, and hardware tools. Blackening treatment is mainly divided into two process routes: high-temperature blackening and room temperature blackening, each of which has its specific application scenarios and technical requirements.

2、 Common problems and solutions for blackening treatment

1. Uneven blackening on the surface

Problem manifestation: The surface of the workpiece exhibits uneven colors, spots, or stripes.

Root cause analysis:

Incomplete pre-treatment results in residual oil stains, rust, or oxide scale on the surface

Uneven solution concentration or large temperature fluctuations

The workpiece is placed too tightly, resulting in poor local contact

Solution aging or contamination

Solution:

Strengthen the pre-treatment process to ensure thorough oil and rust removal

Regularly stir the solution to maintain uniform concentration and temperature

Reasonably design hanging fixtures to ensure the spacing between workpieces

Regularly check the composition of the solution and replenish or replace it in a timely manner

For large workpieces, spraying can be used instead of soaking

2. Poor adhesion of black film

Problem manifestation: The black film is prone to peeling off, and the black substance can be wiped off with a cotton cloth.

Root cause analysis:

Insufficient activation of metal substrate surface

Blackening time too short or temperature too low

Imbalance in the proportion of solution components

Improper post-processing (such as incomplete cleaning)

Solution:

Add acid washing activation steps to enhance the surface activity of the substrate

Adjust process parameters (extend processing time or increase temperature)

Regularly check the composition of the solution and replenish the consumed chemicals

Improve post-processing technology to ensure thorough cleaning and drying

If necessary, a closed processing procedure can be added

3. White spots or redness appear on the surface

Problem manifestation: After blackening, white spots or reddish areas appear locally on the surface.

Root cause analysis:

Incomplete pre-treatment and residual alkaline substances in local areas

Water quality issues (such as high hardness)

The solution contains impurity ions

Insufficient rinsing leads to residue crystallization

Solution:

Strengthen water washing after pre-treatment to ensure neutrality

Rinse with deionized water or softened water

Regularly filter the solution to remove impurities

Increase the frequency and duration of rinsing

After discovering white spots, rework can be carried out

4. Black film has poor corrosion resistance

Problem manifestation: The blackened workpiece shows rusting phenomenon in a short period of time.

Root cause analysis:

The black film is too thin or not dense

Insufficient post-processing closure

The environmental humidity is too high

Inappropriate blackening process parameters

Solution:

Adjust parameters such as blackening time and temperature to obtain a thicker film layer

Sealing treatment with rust proof oil, wax or resin

Control the humidity of the storage environment

For high demand workpieces, secondary blackening can be considered

Choose a higher quality blackening agent formula

5. The solution ages quickly

Problem manifestation: The short service life of the solution and frequent replacement lead to increased costs.

Root cause analysis:

Unbalanced consumption of solution components

Excessive accumulation of impurity ions

Excessive processing capacity

Improper temperature control

Solution:

Establish a regular solution testing system and supplement as needed

Install filtering device to remove impurities

Control the processing capacity per unit time

Accurately control the temperature of the solution

Adopting segmented processing technology to extend the lifespan of the solution

3、 Suggestions for optimizing blackening process

1. Optimization of pre-treatment process

Pre treatment is the key to blackening quality, and it is recommended to adopt the standard process of "degreasing → water washing → acid washing → water washing → activation". For complex workpieces, ultrasonic cleaning process can be added; For materials prone to hydrogen embrittlement such as high carbon steel, the pickling time and temperature should be controlled.

2. Key points of process control

Establish a strict process parameter control system, including:

Temperature control: ± 2 ℃ accuracy

Time control: determined based on the material and size of the workpiece

Concentration monitoring: Regular titration analysis

PH control: maintain a stable range

3. Improvement of post-processing technology

Post processing is crucial for the durability of blackening film, and it is recommended to use:

Three stage countercurrent rinsing system

Hot air drying (60-80 ℃)

Rust proof oil immersion (temperature 40-50 ℃, time 3-5 minutes)

Add drying process if necessary

4. Equipment maintenance and management

Regularly clean the tank to prevent sedimentation and accumulation

Check the heating system and temperature control device

Maintain good ventilation in the workshop

Establish equipment maintenance records

4、 Precautions for Blackening Treatment of Special Materials

1. Blackening of stainless steel

The difficulty of blackening stainless steel is relatively high, and attention should be paid to:

Using specialized stainless steel blackening agent

Pre treatment requires thorough removal of passivation film

Control the oxidation of the solution

May require electrolysis assistance

2. Blackening of aluminum alloy

Common problems with blackening of aluminum alloy:

Poor adhesion of film layer

uneven color

Solution corrodes the substrate

Solution:

Adopting alkaline blackening process

Strictly control the time (usually 1-3 minutes)

Add a closed process for post-processing

3. Blackening of cast iron parts

Blackening characteristics of cast iron parts:

Easy to cause pore pollution

Surface roughness affects blackening effect

Uneven color caused by graphite phase

Response measures:

Add sandblasting treatment before blackening

Extend pre-processing time

Adopting high-temperature blackening process

The quality control of blackening surface treatment process requires the management of the entire process from raw materials, pre-treatment, process control to post-treatment. By analyzing the causes of common problems and taking targeted measures, the quality and stability of the blackening film can be significantly improved. Meanwhile, with the increasing demand for environmental protection, the development of low pollution and high-efficiency new blackening processes will become the future direction of development. Enterprises should establish a sound quality control system and regularly train operators to ensure the stability and reliability of the quality of blackened products.