What role do different types of abrasives play in sand blasting?

In sand blasting, the type, hardness, shape and particle size of abrasive directly affect the machining effect, including surface roughness, cleanliness, material removal efficiency and the risk of parts damage. The following are the classification, characteristics and specific functions of different types of abrasives:

A, according to the material classification and function

1. Metal abrasives

Common types: steel grit, steel shot, stainless steel shot, aluminum shot and copper shot.

Hardness: 40-65 HRC (adjustable by heat treatment)

Shape: spherical, angular (such as steel wire cutting pills)

Main functions:

High-strength cleaning and derusting: used to remove welding slag and oxide scale of steel structures and castings (such as anti-corrosion pretreatment of ships and bridges).

Surface strengthening: surface compressive stress is generated by shot blasting or sand blasting to improve the fatigue strength of parts (such as shot peening of gears and springs).

Roughening treatment: angular steel grit can quickly form a rough surface (Ra 25-100μm) and enhance the adhesion of the coating (such as thermal spraying pretreatment).

Precautions:

It is easy to rust, so it needs to be stored dry or used with antirust agent;

Not suitable for precision parts, avoiding excessive impact and deformation.

2. Mineral abrasives

Common types:

Natural minerals: quartz sand, garnet sand, emery (silicon carbide)

Man-made minerals: brown corundum (alumina), white corundum (high purity alumina) and black corundum.

Hardness:

Quartz sand (Mohs hardness 7), garnet (6.5-7.5)

Corundum (9-9.5 HRA, second only to diamond)

Shape: polygonal, with wide particle size range (20 mesh-320 mesh)

Main functions:

Efficient material removal:

Coarse-grained corundum (20-60 mesh) is used for removing burrs of castings and cutting stones;

Fine-grained corundum (120-240 mesh) is used for deburring metal parts and polishing dies.

High hardness surface treatment: Silicon carbide (hardness is second only to diamond) is used for sand blasting of cemented carbide and ceramics, which can remove quenching layer or oxide film.

Stone and glass processing: quartz sand and garnet sand are used for glass sanding (forming frosting effect) and stone carving.

Precautions:

Dust contains free silicon (such as quartz sand), so it is necessary to strictly control the dust concentration in the working environment to prevent silicosis;

Soft materials such as aluminum alloy and copper alloy, which have high hardness and are easy to scratch, should be carefully selected.

3. Plastic/resin abrasive

Common types: nylon sand, polyester sand and polyurethane sand.

Hardness: Shore hardness 80-100A (similar to rubber to hard plastic)

Shape: spherical, cylindrical, polygonal

Main functions:

Precision treatment of soft materials:

Deburring aluminum alloy die castings (such as mobile phone middle frame and automobile wheel hub) to avoid scratching the surface with metal abrasive;

Clean the burrs of plastic parts (such as gears and shells) to maintain dimensional accuracy.

Surface finishing: Fine-grained nylon sand (200-400 mesh) can be pretreated before mirror polishing to form a uniform matte surface (Ra 0.4-1.6μm).

Cleaning of electronic components: used for dust removal of PCB boards and semiconductor packages, without conduction and electrostatic adsorption.

Precautions:

Poor high temperature resistance (usually < 100℃), not suitable for high temperature workpieces;

Abrasive is easy to age, so it needs to be screened regularly to remove debris.

4. Glass/ceramic abrasives

Common types:

Glass beads: ordinary glass beads, borosilicate glass beads (impact resistance)

Ceramic beads: aluminum silicate ceramics, zirconia ceramic beads.

Hardness:

Glass beads (5-6 HRC); Ceramic beads (60-70 HRC)

Shape: spherical (roundness ≥95%)

Main functions:

Surface finishing and strengthening:

Glass beads (80-200 mesh) are used for matte treatment of aluminum alloy and stainless steel to form uniform diffuse reflection surfaces (such as tableware and bathroom parts);

Ceramic beads (such as zirconia beads) are used for high strength shot peening, such as surface stress optimization of aero-engine blades.

Deburring of precision parts: the impact of spherical abrasive on the hole edge, groove bottom and other parts is more uniform, avoiding excessive cutting caused by angular abrasive (such as deburring of gear tooth surface).

Precautions:

Glass beads are easy to break and produce dust, which needs to be replaced frequently;

Ceramic beads have high cost and are suitable for high value-added parts (such as aerospace parts).

5. Special abrasives

Dry ice particles:

Function: Low-temperature sand blasting can remove oil stains and coatings without residue, which is suitable for the repair of precision electronic equipment and cultural relics (such as circuit board glue removal and dirt removal on the surface of ancient buildings).

Walnut sand/corncob:

Function: natural organic abrasive with low hardness (similar to plastic), used for cleaning carbon deposits in automobile engines and food-grade equipment (such as the inner wall of beer cans).

Sponge sand:

Function: resin coated quartz sand has both cutting force and buffering property, and is used for ship anti-corrosion sand blasting (reducing steel plate damage) and wood surface treatment.

Second, according to the shape classification and function

Typical shape abrasive machining effect characteristics applicable to the scene

Spherical glass beads and ceramic beads have soft impact and high surface finish, and are not easy to scratch. Precision parts are polished and shot peened.

Angular steel sand and corundum sand have strong cutting power, high material removal efficiency and high surface roughness. Derusting, deburring and roughening are carried out.

Cylindrical/strip steel wire shot cutting and nylon column have strong directional impact, which is suitable for deep holes, groove inner surface treatment of gear inner holes and engine cylinder block sandblasting.

Sheet/fibrous aluminum pellets and copper sheets have low impact force and are suitable for thin layer material removal or surface texture processing, aluminum alloy surface wire drawing and circuit board coating peeling.

Three, according to the particle size classification and function

Application scenario of typical mesh processing effect in particle size range

Quick removal of thick oxide scale with coarse granularity of 20-60 meshes, welding slag, sand cleaning of raw-edge castings and steel pretreatment.

Deburring and roughening of ordinary parts with medium particle size of 80-150 mesh and medium roughness surface (Ra 12.5-3.2 μ m) before painting.

Finishing and Electroplating Pretreatment of Fine-grained 180-320-mesh Precision Parts with Fine Matte Surface (Ra 1.6-0.4μ m)

Surface polishing of optical elements and medical instruments with ultra-fine granularity of more than 400 meshes and close to mirror effect (Ra ≤ 0.2 μ m)

Four, the core principles of abrasive selection

Hardness of matching parts materials:

Abrasive hardness ≤ hardness of parts materials (such as nylon sand for aluminum alloy and glass beads for stainless steel) to avoid scratches;

When strong derusting is needed (such as steel parts), corundum sand with hardness slightly higher than that of the base material can be selected.

Requirements for controlling surface roughness:

Angular and large-size abrasive for rough machining; Spherical and fine-grained abrasives for finishing.

Avoid pollution and residue:

Organic abrasives (such as walnut sand) or stainless steel pellets for food and medical industries;

Insulating abrasives (such as nylon sand) are used in electronic industry to prevent electrostatic damage.

Balance between cost and efficiency:

In mass production, wear-resistant and recyclable abrasives (such as steel grit) are preferred;

Choose disposable abrasives (such as glass beads) for precision parts to avoid cyclic wear of debris.

summary

Abrasive is the "tool" of sand blasting, and its characteristics directly determine the processing quality. When selecting, factors such as parts materials, surface requirements, processing efficiency and environmental safety should be considered comprehensively, and the best scheme should be determined by trial spraying if necessary. For example:

Aluminum alloy wheel hub: deburr with 80-120 mesh nylon sand, and then polish with 200 mesh glass, giving consideration to accuracy and beauty;

Aviation titanium alloy blades: 60 mesh zirconia ceramic beads are used for shot peening to improve fatigue resistance;

Circuit board maintenance: Dry ice particles are used to remove the residual solder paste on the pad without physical contact damage.