The jet technology is a field of surface engineering , are steered in the blasting agent at high speed (up to 160 m / s) on the workpieces. Compressed air , hydraulic fluids , electrostatic or electromagnetic fields as well as centrifugal wheels are available as energy sources . In addition to various machine types and setting parameters, the blasting result essentially depends on the type of abrasive selected.
Frequently when is rays a material by beam machining sought. However, certain blasting processes can also serve to solidify or structure the surface or remove liquid or viscous contaminants without detaching solid material.
Various processing goals of blasting technology :
- Clean, Ent -temperature oxidation , Ent rust , paint stripping, stripping (Engl. Stripping )
- Core removal and desanding of castings and molds
- Surface hardening ( shot peening , Eng. Shot-peening )
- Deburring , (by shot blasting or sandblasting )
- Roughening in preparation for painting, preservation
- Matting, structuring, surface finishing
A wide variety of materials are used as blasting media, depending on the task. The criteria are price, purpose (rust removal, graffiti removal on walls, etc.), material, material thickness and the required surface roughness. Other types of systems may be required depending on the abrasive. A selection of abrasives:
- Glass beads
- Garnet sand
- Dry ice (see dry ice blasting )
- Steel shot
- Steel balls
- Wire grain
- Bronze gravel
- Blast furnace slag
- Calcium carbonate granules
Compressed air blasting with solid abrasive
Low pressure blasting
Compressed air jets with reduced air pressure. This process is suitable for the gentle restoration of surfaces of various types with all commercially available granulates - especially for the construction industry as well as for stonecutters and restorers.
The low-pressure blasting offers the following possible uses:
- Blasting or processing surfaces, facades and monuments
- Concrete renovation and corrosion protection
- Blasting of writings, gravestone design and cleaning
- Restoration of wood and furniture
- Fire damage restoration
- Removal of graffiti and antifouling paint from ships and boats
- Sweep blasting of sensitive surfaces (e.g. hot-dip galvanizing) with minimal material removal and low mechanical stress.
High pressure water jets
With high-pressure water jet systems , pure, clear water up to 4,000 bar is jetted through a nozzle onto the workpiece to be processed. This makes it possible to remove soft materials in a way that is gentle on the workpiece. For harder materials such as steel , (armored) glass or ceramics , a powder made of hard material, such as garnet sand, is added to the water jet . This powder is called abrasive because the material removal is very similar to abrasion .
Blasting with water has the following advantages:
- no deformation, since no " peening effect " occurs
- Very little material removal from the base material, as no abrasive is used (if you work without abrasive)
- environmentally friendly, the process water can be used in a closed circuit
- Subsequent cleaning of the workpieces from dust or abrasive residues, as with sandblasting, is not necessary
- no abrasion wear
- Corrosion protection agent can be added.
Nowadays this process is used in many branches of industry for a wide variety of applications. Like for example:
- Removal of thermal coatings (e.g. plasma coatings )
- Clean weld seams of slag residue
- Remove sand or ceramic residues from cast parts
- Paint stripping of a wide variety of workpieces
- Cutting of sheets and foils
Shot peening / compaction blasting
Shot-peening is a process in which internal compressive stresses are induced in the surface of a metallic workpiece to increase the service life, mainly by shot peening .
When the treated components are loaded, the compressive stresses induced in the surface layer (up to a depth of approx. 0.2 mm) must first be relieved by the tensile stresses occurring, which considerably reduces the risk of fatigue cracks during operation.
If all blasting parameters such as impact angle, blasting time and blasting pressure (compressed air blasting), ejection speed of the blasting media, type of blasting media and degree of surface coverage are strictly adhered to, the service life of many workpieces such as gear parts, drive and crankshafts, springs, turbine blades or, in general, turbine elements and many more increases. The flow of blasting media is monitored magnetically or by weighing devices, depending on whether metallic or non-metallic blasting media is used. An important point in shot peening or compression blasting is abrasive recycling, which sorts the abrasive according to shape and size.
Vacuum suction jets
In contrast to conventional blasting methods, where the particles or blasting media are accelerated with compressed air , suction blasting uses suction devices to accelerate the blasting media . The process therefore takes place exclusively in negative pressure . As a result, the process is absolutely free of dust and sparks: removed particles, including the blasting agent, are sucked off directly by the air flow and filtered in the vacuum cleaner.
Systems for blasting technology
Trough conveyor systems
Troughed belt blasting systems are suitable for batch processing of drum-compatible workpieces. Optimal results are achieved with the smallest, sensitive plastic parts as well as with large, massive workpieces. The batch system can be expanded to a fully automatic system using appropriate peripheral devices.
- Wire belt conveyor systems
Wire belt conveyor systems are ideally suited for the all-round and comprehensive blast-technical processing of flat as well as voluminous and complex workpieces in a continuous process. With several centrifugal wheels attached around the housing (both vertically and horizontally inclined), even very complicated workpieces that have pockets or undercuts can be processed comprehensively.
- Loop belt conveyor systems
In the case of continuous loop belt systems, cams arranged on the loop belt bars cause a continuous, helical, positively guided workpiece transport through the blasting space, which makes such a system particularly suitable for blasting bulk material with small dimensions.
- Troughed belt conveyor systems
Troughed belt conveyor systems are a variant of the continuously operating blasting systems with fully automatic workpiece treatment. Both bulk goods and workpieces with more complex geometries can be processed in one system.
- Continuous roller conveyor systems
According to its design, the roller conveyor system is particularly suitable for long, flat workpieces. The workpieces (sheets, pipes or profiles) pass through the pre-chamber, blasting chamber and post-chamber of the system one after the other on a roller conveyor. The centrifugal wheels attached to the cabin housing allow all-round, comprehensive and reliable machining of the workpieces.
The processing spectrum of these wheel blasting systems with single-arm robots ranges from deburring and surface finishing to shot peening of impact-sensitive workpieces of different dimensions. The design also includes defining the size, performance and technical parameters of the robot used, as well as defining the transport system.
Drum blasting systems
Drum blasting systems are particularly suitable for the economical and reliable processing of workpieces of small to medium size, which should not be blasted in a troughed belt or other conveyor belt system or in small baskets because they are either too small, too flat or too light or theirs Quantity exceeds the capacity of the system.
Complete preservation systems consist of a conveyor system, a pre-dryer, the roller conveyor blasting system, the painting machine and a subsequent post-dryer. Depending on the application and local conditions, various roller conveyors, traveling grids, cross conveyor systems or the like can be used as transport systems. A heated pre-drying unit also allows the processing of material stored outdoors. The primer layer applied by the automatic painting machine is dried off by the downstream dryer so that the workpieces can be removed immediately for further processing at the outlet of the system. The waste heat from the pre-dryer can be used to save energy.
Overhead conveyor systems
The use of an overhead blast machine is recommended for sensitive and non-drum-compatible, heavy or large-volume workpieces. They are hung on workpiece carriers for processing and driven into the system.
The workpieces are continuously guided through the blasting area on the rotating table. This ensures even blasting.
Tube blasting systems
This blasting machine allows the blasting of pipes or round steel in a continuous process.
Ceramic blasting systems
Process for the stripping of adhering material residues and worn engobes from kiln furniture. In the past, this was often done in several steps (wet grinding, washing, drying, sandblasting), which was extremely time-consuming and costly. Blasting systems reduce the stripping process to just one work step. Crack formation during firing due to diffused moisture is excluded by this dry processing.
- Hansgeorg Hofmann, Jürgen Spindler: Process in coating and surface technology . 2nd Edition. Carl Hanser Verlag , 2010, ISBN 978-3-446-42378-7 .
- Andreas Momber: Blast Cleaning Technology . Springer, London, 2008, ISBN 978-3-540-73644-8 .
- Fritz, Schulze: Manufacturing Technology , 11th Edition, pp. 408–415.