Working Principle
The abrasive held in the pressure vessel is drawn through the metering valve by compressed air (5-8 bar), carried along the hose and propelled at high velocity from the nozzle of the blast gun. The grains striking the surface produce micro-erosion, removing the unwanted layer (rust, paint, mill scale) and roughening the surface.
Applications
- Removing rust, paint and old coatings (automotive restoration, steel structures)
- Surface roughening — so that the following paint or coating keys properly
- Cleaning and exposing the aggregate of concrete surfaces
- A matt, sandblasted finish on marble and granite
- Decorative frosted surfaces on glass
- Cleaning the weld seam area before welding
- Restoration — stone facades, sculpture, antiques
Abrasive Types
| Abrasive | Hardness (Mohs) | Application | Warning |
|---|---|---|---|
| Silica sand | 7 | General cleaning, cheap | High SILICOSIS risk — a full-face respirator is essential |
| Garnet | 7-7.5 | Roughening steel and stainless steel | Safer, and reclaimed from the waterjet |
| Aluminium oxide | 9 | Hard metal, rust, moulds | Expensive but reusable |
| Glass bead | 5.5 | Light cleaning, polishing | Deforms rather than abrades the surface |
| Olivine | 6.5-7 | A low-dust alternative | Performance close to garnet |
Choosing the Grain Size (Mesh)
| Mesh | Grain Size | Effect | Application |
|---|---|---|---|
| 8-12 | Very coarse | Aggressive, deep profile | Heavy rust, concrete |
| 16-30 | Coarse | Fast cleaning | Steel structures |
| 30-60 | Medium | Standard surface preparation | Automotive, stainless steel |
| 60-100 | Fine | Delicate surfaces | Precision parts, decorative work |
| 100-500 | Very fine | Matt / bright finish | Glass, decorative sandblasting |
Pressure Setting — How High Should It Be?
- 0.5-2 bar — delicate surfaces, decorative work, glass
- 2-4 bar — standard surface preparation (automotive, stainless steel)
- 4-6 bar — general use (the standard range of the USEL EasyBlast)
- 6-8 bar — heavy surfaces (the FastBlast range), thick rust, concrete
High pressure is not always the right answer — on soft metals, delicate alloys or decorative surfaces, too much pressure causes deformation. The correct pressure should be established on a test piece.
Surface Profiles (Ra/Rz)
For paint and coatings to key properly the surface has to carry the correct roughness. ISO 8503 divides a blast-cleaned surface into three grades — but the same grade means a different roughness value depending on the type of abrasive used. The values below are for angular (grit) abrasives:
- Fine — from 25 µm to 60 µm — thin paint, delicate alloys
- Medium — from 60 µm to 100 µm — industrial paint, most applications
- Coarse — from 100 µm to 150 µm — thermal spray, heavy coatings
- With round (shot) abrasives the same grades correspond to lower values: 25-40 / 40-70 / 70-100 µm
PPE — A Matter of Life and Death
- Full-face respiratory protection (a P3 respirator or an air-fed blast hood)
- Protective clothing — long sleeves, leather gloves, steel toe-capped boots
- Ear defenders — continuous noise above 90 dB
- A ventilated cabinet — an extraction system when working indoors
- A deadman switch — the flow must stop the instant the gun trigger is released
Air Compressor Requirement
- EasyBlast (10 L vessel): 300 L/min air consumption → at least a 5.5 kW compressor + a 200 L receiver
- FastBlast (25 L vessel): 500 L/min → a 7.5-11 kW compressor + a 300-500 L receiver
- A water separator and an oil filter — moist air blocks the blast gun
- A reserve air receiver — prevents sudden pressure drops