What should be paid attention to when using sandblasting machine for surface treatment of precision parts?

When the surface treatment of precision parts is carried out by sand blasting machine, the process parameters and operation details should be strictly controlled to avoid the damage of dimensional accuracy, surface quality or material properties caused by sand blasting. The following are key considerations:

I. Selection of Equipment and Abrasives

Sandblasting machine type

Negative pressure or suction sandblasting machine is preferred: this kind of equipment has low sandblasting pressure (usually 0.2-0.4MPa) and mild impact force, which is suitable for micro-removal or finishing of precision parts to avoid dimensional deviation or surface damage caused by high pressure.

Avoid high-pressure pressure sandblasting machine: too high pressure (> 0.6MPa) may cause deformation, out-of-tolerance size or micro cracks of parts (such as thin-walled parts and slender shaft parts).

Abrasive type and particle size

Abrasive hardness: Choose abrasives (such as alumina, glass beads, nylon sand) with hardness lower than that of parts materials, so as to prevent hard abrasives (such as silicon carbide and emery) from scratching the surface or causing excessive local material removal.

Granularity control:

Rough machining (deburring and derusting): 80-120 mesh abrasive can be selected to quickly remove surface defects.

Finishing (finishing and sub-polishing): Choose 150-240 mesh or finer abrasives (such as 280 mesh glass beads) to ensure uniform surface roughness (Ra 0.8-1.6μm) and avoid excessive sandblasting leading to tolerance deviation.

Abrasive cleanliness: Use dry, oil-free and impurity-free abrasives to prevent surface contamination of parts or nozzle blockage.

Second, the process parameter control

Sandblasting pressure

Recommended pressure for precision parts: 0.1-0.3MPa, and the critical pressure (i.e., the lowest pressure that can just remove surface defects) should be determined by trial spraying to avoid uneven treatment caused by pressure fluctuation.

Pressure stabilization measures: use a pressure stabilizing valve to control the air source, and regularly check the air pressure stability of the air compressor.

Sandblasting distance and angle

Distance: the nozzle is kept at a distance of 100-150mm from the surface of the part. Too close distance may easily lead to local excessive sandblasting; If the distance is too far, the efficiency will be reduced and the surface treatment will be uneven.

Angle: The angle between the nozzle and the surface of the part is 45-60, so as to avoid vertical sand blasting (excessive impact) or too small angle (abrasive rebound and accumulation).

Sandblasting time

Time-limited processing: the single-station sandblasting time (such as 10-30 seconds/face) is controlled by the timing device to avoid the size deviation caused by long-time sandblasting in the same area.

Dynamic inspection: Spot check regularly during machining to observe the surface state (such as roughness and gloss) and adjust the time parameters in time.

Third, the parts clamping and protection

Clamping mode

Special fixture: design custom fixture to fix parts, to avoid position deviation or local over-treatment caused by hand-held sandblasting. The fixture should ensure the stability of the parts and not block the surface to be machined.

Isolation of soft materials: use soft gaskets such as rubber and silica gel to separate parts to prevent indentation or collision damage (such as thin-walled shells and gear parts) during clamping.

Non-processing area protection

Sealing or shielding: use rubber plugs, adhesive tapes or special shielding tools to protect the precise parts such as threaded holes, mating surfaces and sealing surfaces, so as to prevent abrasives from entering the interior or damaging key surfaces.

Cleaning of blind holes: After sandblasting, compressed air (0.5-0.7MPa) should be used to thoroughly purge the residual abrasives in the gaps and blind holes of parts to prevent the abrasive residues from affecting the assembly or service performance.

Fourth, the environment and operating specifications

environmental requirement

Temperature and humidity control: the humidity in the sand blasting room should be lower than 60%, so as to avoid moisture absorption and caking of abrasives or rusting of parts (especially corrosive materials such as aluminum alloy and titanium alloy).

Dust filtration: equipped with high-efficiency dust removal system (such as filter element dust collector), to ensure that the dust concentration in the working environment is less than 10 mg/m, so as to avoid dust affecting the health of operators and the accuracy of equipment.

Operator training

Work with certificates: Operators should be familiar with equipment performance, process parameters and tolerance requirements of parts, and work after training and assessment.

Handle with care: Rough operation is strictly prohibited. Use soft tools (such as plastic tweezers and rubber gloves) when loading and unloading parts to avoid bumping and scratching.

Five, quality inspection and subsequent treatment

Surface detection

Roughness measurement: use a roughness meter (such as stylus or optical) to detect the machined surface to ensure that it meets the requirements of the drawings (such as Ra≤1.6μm).

Dimensional accuracy check: use a three-coordinate measuring instrument or projector to check the key dimensions (such as aperture, shaft diameter and mating surface) to prevent the size from exceeding the tolerance caused by sandblasting.

Subsequent treatment

Cleaning and degreasing: immediately after sandblasting, use alcohol, acetone or special cleaning agent to remove oil stains and abrasive residues on the surface to avoid corrosion or influence the adhesion of subsequent coatings (such as electroplating and painting).

Anti-rust treatment: for steel parts, phosphating, electroplating or anti-rust oil can be applied; Aluminum and magnesium alloy parts can be anodized or chemically passivated to prevent oxidation corrosion.

Six, special parts matters needing attention

Thin-walled parts/slender shafts

Sand blasting with low pressure (0.1-0.2MPa) for a short time, combined with rotary tooling, can make the parts evenly sanded to avoid local stress concentration leading to deformation.

Complex inner cavity parts

Dry ice sand blasting or liquid sand blasting (water-sand mixing) is preferred to avoid solid abrasive residue; If solid abrasives are used, it is necessary to design special tooling to sand blast from multiple angles to ensure that there is no dead angle in the inner cavity.

Rework of plated/coated parts

Control the pressure and time of sandblasting, aiming at just removing the old coating, to avoid excessive exposure or damage of the substrate, and re-test the bonding force after rework.

summary

The core principle of sandblasting for precision parts is * * "precise control and minimum damage" * *, and the whole process control of equipment selection, parameter optimization, clamping protection and process detection is needed to ensure that the surface treatment effect matches the precision requirements of parts. It is suggested that small batch trial processing should be carried out first, and the feasibility of the process should be verified before mass production, and the first piece inspection and regular sampling inspection system should be established to reduce quality risks.