Sandblasting
Colloquially sandblasting ( English sandblasting, abrasive blasting ), general technical term: compressed air blasting with solid blasting media , one understands the surface treatment of a material or workpiece (blasting material) by the action of blasting media, e.g. B. sand as an abrasive against rust, dirt, paint, scale and other impurities or for surface design by matting.
Process description
A strong air jet is generated using compressed air, which takes the blasting media (e.g. sand but also blast furnace slag, glass granulate, corundum, steel, plastic granulate, nutshells or soda with different degrees of fineness; see blasting technology ) from a collecting container and accelerates it. The abrasives then hit the surface to be treated together with the air jet at high speed. Due to the mostly abrasive effect of the blasting agent, undesirable components of the surface, such as rust or paint, are detached and carried away.
The remaining blasting debris is either disposed of (disposable blasting media - EwSM) or processed in a cycle - a small amount of blasting debris remains as waste - and used again after replacing the coarse blasting media (reusable blasting media - MwSM).
Because of the silicosis caused by the fine dust, quartz sand is no longer permitted as an abrasive in most countries. There are also more suitable materials for different purposes. Depending on the blasting media used, blasting work is always associated with more or less extremely high mechanical and dust loads, which affect the blasting material, e.g. B. with already partially or pre-assembled system components, can lead to considerable damage. There is no such thing as dust-free blasting with air. But there are water + air-based blasting processes, whereby the dust is bound by the water, so-called dust-free sandblasting (or dustless blasting ).
Effect of abrasives
Sandblasting is used to remove natural or foreign impurities (solid or loose) from surfaces and / or to roughen or mattify the surface. Sandblasting is used both in the construction industry (substrate / surface preparation before e.g. coating or bonding work on steel or concrete) and in metalworking. In addition to removing paint and thin, low-strength layers (including small plaster residues) on metals or concrete, sandblasting is also used to clean plastics. This process is also used to matt glass or stone. A distinction is made between disposable (slag) and reusable (steel / chilled cast iron), artificial (steel / chilled cast iron, glass beads) and natural (garnet sand) as well as abrasive (sand, corundum etc.) and non-abrasive (e.g. CO 2 pellets for dry ice blasting , CO 2 snow for snow blasting) abrasives. The choice of the abrasive or the blasting process depends on the desired effect, as well as the surface to be processed or the type of contamination. The abrasive used and the grain size determine the surface structure after processing. The results of blasting work also depend on the air pressure and the amount of air at the blasting nozzle. When derusting, removing rolled skin or thick coatings and roughening a steel structure, an air pressure of at least 8 bar is required for efficient radiation, whereas when matting stone or sweep blasting (light roughening with minimal material removal, e.g. on Hot-dip galvanizing) much lower pressures are sufficient. The impact speed has a decisive influence on the result.
Individual abrasives (not exhaustive):
- Slag blasting media (EwSM)
- Inexpensive disposable blasting media made from waste products from various smelting processes, which have a good abrasive effect due to their sharp-edged fracture pattern, but are sometimes very dusty. Ferrite-free possible.
- Corundum (MwSM)
- a sharp-edged ferrite-free abrasive. Because of the high price preferably for ferrite-free metal surfaces in the circuit for removing paints or coatings and for surface preparation. With a corresponding grain size, a very rough surface can be achieved.
- Garnet sand (EwSM or MwSM)
- a less sharp-edged natural, ferrite-free abrasive. Low dust generation, high abrasive effect and good price-performance ratio. Can be used as disposable and reusable abrasives.
- Plastic (EwSM or MwSM)
- Ferrite-free, a less hard and sharp-edged blasting agent for gentler surface treatment, but less abrasive. When using plastic granulate, less dust is generated.
- Ceramic beads
- With ceramic bead blasting, for example, rolled metal surfaces are roughened / refined or cutting edges rounded according to customer requirements .
- Glass beads (EwSM)
- ferrite-free, by blasting with glass beads (technical term: glass bead blasting), a small plastic deformation is achieved, which creates a desired residual stress in the workpiece and thus increases the surface hardness and fatigue strength (see also shot peening and work hardening ) The surface is less roughened than by that Blasting with sand or corundum, but rather matted.
- With such glass beads, a glass bead arc can be created , a curved or circular visible color spectrum similar to a rainbow .
- Glass granulate
- Ferrite-free, glass granulate blasting has proven itself in stripping paint from body parts , in which sharp-edged glass particles remove a tough, elastic layer from a hard surface.
- Dry ice and snow (EwSM)
- the dry ice blasting and snow blasting methods are considered non-abrasive, which means that the surfaces to be treated are cleaned very gently. The abrasive itself does not leave any debris behind. Very complex because of the necessary technology.
- Chilled cast iron or steel (cast), angular or round (MwSM)
- Reusable abrasives for large-scale use. With different grain shapes suitable for different purposes.
- Classic: Automated removal of mill scale and scale without roughening raw profiles with large, round steel grains by the steel dealer before delivery.
The blasting media are mostly inert and therefore not themselves harmful to health or the environment. However, it often looks different with older coatings ( red lead or tar ), which are blasted.
Areas of application
The development of sandblasting technology has evolved significantly over many years and now offers a good solution for almost every application. The areas of application are very diverse, especially in industry:
- Cleaning of machines, motors, containers, molds and systems
- For use in concrete renovation for derusting the reinforcement and for roughening and cleaning concrete surfaces
- Cleaning of facades, masonry, frameworks
- For rust removal, paint stripping and stripping of steel structures
- For roughening the surface in preparation for painting
- Decorative sandblasting
- Structuring of glass plates for use in the microsystems technology by micro sand-blasting (microfluidic channels for producing microreactors or through holes for fluidic coupling of a microchip to its environment)
- Textiles (Controversial and in some countries banned method of treating jeans in order to achieve a worn effect, which can lead to the formation of silicosis in textile workers due to dust containing quartz .)
Types of blasting guns / systems
Various types of blasting guns or systems are offered.
- Sandblasting blower for use in blasting cabins as stand-alone devices for smaller parts.
- Centrifugal wheel blasting systems for sheet metal or profile steel or as cabins without conveying the blasting material for z. B. Moldings
- Sandblasting blower for use on large components, both for use in special blasting rooms and for outdoor use.
- Injector blasting guns with suction of the blasting agent from pressureless containers
- the so-called cup guns from the hardware store for DIY use, also based on the injector principle
See also
- High Frequency Impact Treatment : hammering process for weld seam treatment
- Bristle Blasting
Individual evidence
- ↑ Ökotest: Jeans & Co. processing ban ( memento of the original from November 8, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Declaration of Bern: Sandblasting: Deadly danger in jeans production
