How to reduce reflection for Dalian blackening treatment

Dalian blackening surface treatment is widely applied to workpieces such as mechanical parts and instrument fittings. A ferrosoferric oxide conversion film forms on steel surfaces to provide basic rust prevention and matting. Conventionally machined workpieces tend to produce specular reflection. For workpieces requiring reflection control, such as optical equipment and testing instruments, adjustments can be made in pre-treatment, blackening process parameters, sealing treatment and process control to reduce surface reflection.

Workpiece pre-treatment serves as the fundamental step for reflection control. The original surface condition directly determines the final reflectivity. Smooth substrates after polishing and precision grinding retain certain specular reflection even after blackening. During Dalian blackening processing, sandblasting, shot blasting or matte grinding can be adopted according to workpiece tolerance requirements to create uniform micro-concave-convex structures on substrates. This changes light reflection mode and converts directional specular reflection into diffuse reflection to weaken reflection. Abrasive grain size shall be well controlled. Excessively coarse grains lead to overly high surface roughness while overly fine grains deliver limited matting effect. Complete degreasing and rust removal are also required in pre-treatment. Oil contamination and oxide scale cause uneven blackening film thickness and local bright spots, increasing reflection inconsistency.

Adjustment of blackening process parameters optimizes the matte texture of the film. There are two processes: high-temperature alkaline blackening and room-temperature blackening. Oxide films generated by different processes differ in microstructure. High-temperature blackening produces densely crystallized films. The crystal morphology can be adjusted and bright areas reduced by controlling bath concentration, reaction temperature and immersion duration. For room-temperature blackening, immersion time shall be controlled to avoid substrate reflection caused by overly thin films or peeling loose films due to prolonged immersion. Bath liquid requires regular maintenance and impurity removal. Aged bath liquid results in uneven local blackening, bright streaks and reflective spots. Workpieces shall be suspended when entering the bath to prevent stacking contact, which may hinder film formation on contact surfaces and form reflective areas.

Sealing procedure affects the final reflection performance. Conventional blackening is followed by oil immersion sealing. Ordinary bright oil forms an oil film on the film surface, raising gloss and reflection. Matte sealants can be used instead for low-reflection requirements to eliminate bright surface oil films. Workpieces shall be thoroughly rinsed before sealing to remove residual blackening solution in pores, which may cause local color difference and inconsistent reflection. Water shall be fully drained after rinsing before sealing. The sealing layer maintains uniform thickness to avoid bright surfaces formed by local accumulation. For workpieces with strict reflection control, light wiping can be performed after sealing to remove excess sealant and preserve the inherent matte structure of the film.

Workpiece material and tolerance prediction require prior communication and confirmation. Some alloy steel and stainless steel materials differ from ordinary carbon steel in blackening film-forming characteristics, leading to different reflection performance under identical processes. Dalian blackening manufacturers shall confirm workpiece materials before processing and evaluate matting solutions. Attention shall be paid to precision parts. Sandblasting and grinding alter surface roughness, so dimensional allowance shall be calculated in advance to avoid damaging fitting tolerances for matting purposes. Partial masking can be adopted for workpieces with threads and precision mating surfaces. Pre-treatment and blackening are only performed on exposed areas needing matting to protect functional dimensions.

Finished product inspection and batch control ensure stable reflection performance. After processing, workpieces are visually inspected under unified light sources for bright spots and streaks. Reflectance can also be measured by instruments. For workpieces in the same batch, consistent parameters including pre-treatment abrasives, blackening temperature and sealing materials shall be maintained to reduce reflection variation between batches. Sample comparison shall be conducted regularly during processing. Any gloss abnormality triggers timely troubleshooting of bath liquid and pre-treatment procedures.

The core of reducing reflection via Dalian blackening surface treatment lies in substrate micro-roughening combined with stable film-forming processes and matte sealing schemes. Integrated management of pre-treatment, bath control, sealant selection and finished product inspection can reduce specular reflection, meeting low-reflection application requirements of instrument and mechanical fittings while maintaining the adhesion and basic protective performance of blackening films.