What are the common problems in room temperature blackening

What are the common problems in room temperature blackening

1. Uneven blackening film layer

Causes: 1. The work piece is not clean when degreasing; 2. The cleaning is not thorough; 3. The work piece overlaps. 

Remedy: 1. Strengthen the degreasing and increase the flushing with water; 2. After degreasing, wash with hot water and then rinse with cold water; 3. Shake the workpiece, consider from the fixture.

2. The surface of the parts is loose and the bonding force is not strong

Reasons: 1. The blacking time is too long or too short. 2. There are residues on the surface of the part. 

Remedy: 1. Strict process and proper control of time. 2. Strengthen the pre-treatment of blackening.

Third, the blackening film is light in color

Causes: 1. The blackening time is too short; 2. The ingredients are insufficient.

Remedy: 1. Extend the blackening time; 2. Adjust or replace the solution.

4. Poor gloss and rust spots

Causes: 1. Too much water in the dehydrated oil; 2. Short dehydration time for parts.

Remedy: 1. Exclude water, check dehydrated oil or replace; 2. Extend dehydration time.

5. The firmness is worse than alkaline bluing

Causes: 1. The blackening has not been completely effected; 2. The oxide layer of the parts has not been removed.

Remedy: 1. Leave it for one day after it turns black before use; 2. Strengthen the treatment before it turns black.

6. The workpiece has variegation. The unoiled workpiece can be washed with water and reissued for 0.5-1 minutes.

7. Rework of unqualified products. Use 10% dilute nitric acid to remove the black film and then blacken it again.