VOL. 9 November ISSUE YEAR 2008
in Vol. 9 - November Issue - Year 2008
State-Of-The-Art Blasting Technology For Increasing Efficiency In Foundries
Figure 1:High-performance turbine featuring a sturdy housing made of manganese steel. State-of-the-art design reduces assembly times.
Figure 2: Turbine wheel of the high-performance turbine: Few wear parts and easy assembly reduce overheads
Figure 3: The AGTOS magnetic wind sifter with two magnetic drums separates sand and abrasive reliably
Figure 4: Functional diagram of the magnetic wind sifter with two magnetic drums
Figure 5: loaded blast holders being transported into the continuous overhead rail shot blast machine
Figure 6: Work pieces after shotblasting
Fig 7: steel mill shot blast machines in tandem operation
To gain a competitive edge in the industry, new methods can be linked with well-known procedures. For castings finishing, AGTOS combines robust blasting technology with state-of-the-art electronics to radically increase a foundry’s efficiency. The emphasis is placed on details that create decisive advantages in terms of operation and maintenance.
The heart of each shot-blasting machine is the turbine, with a great variety of types available. Differences can be found in the construction, i.e., the design of the units as well as the technical characteristics and the material of wear parts.
The AGTOS high performance turbine is a rugged aggregate structure that is extremely efficient due to a reduced number of wear parts and a high abrasive flow rate, which brings down the maintenance cost (Figure 1). The patented shot-blast turbines are equipped with six blades, on one side attached to a single disc. For assembly, normal tools are sufficient; the blades are simply plugged on, thereby saving time (Figure 2). Compared to other turbines, the blasting wheel only has six blades instead of eight or more. Moreover, the distance bolts which are required for double disc wheels are not needed anymore. The spare part costs are already reduced by the low number of wear parts. In addition, there are fewer components disturbing the flow of the abrasives (no velocities), which improves the blasting result at the same power consumption levels.
Equipping the turbines with frequency converters permits applications that were until now reserved to production in a less rough environment. Frequency converters allow for an adjustment of the rotational speed, carrying a number of advantages. For certain work piece groups individual programs can be provided in order to achieve surface qualities defined previously. Another advantage is that different surfaces and dimensions can be treated differently using the same abrasives. If required, AGTOS turbines can be operated with an abrasives granulation of up to 3 mm. Thus, even large-sized plants can be finished where there are large distances between the turbines and work pieces.
Large abrasives diameters are also useful when treating thick-walled, sanded work pieces. The sand is removed quickly and efficiently. When shotblasting more delicate work pieces, the surface may be damaged because of the high impact force of the blasting compound. With the alternative of decreasing the motor rotation of the turbine continuously, however, optimum treatment of delicate work pieces is possible (Figure 3). It is not necessary then to change the type of abrasives.
Intelligent blasting technology
The trend in foundries is definitely towards automation and saving labour. The handling of machines has to be simplified, and units often work fully automatically. During the change of loadings with new work pieces the blasting technology has to be adapted without difficulties. Therefore the unit has to “recognize on its own” which blasting program is needed. For this purpose, coded hangers are the solution. The coding unit collects certain data of the work piece hangers. A special blasting program is assigned to a specific coding, so the shotblasting machine is automatically adjusted to the current blasting job. Blasting times, rotational speed and movements of the hangers (e.g. oscillation) in the unit are varied as previously defined. Not only does the coding have an influence on the working sequence in the blasting machine, but a temperature detection system allows that excessively hot work pieces are, for instance, conveyed through a cooling section.
Separation of sand and abrasives
Sand drastically increases wear and tear in blasting machines, which is why it is vital to eliminate it from the shotblasting process to the greatest possible extent. AGTOS meets these requirements with its magnetic air separation system especially designed for foundries. Not only does the principle play a major role, whereby abrasives and sand pass two magnetic rollers (Figure 4), but the correct dimensioning of the component is also significant. A fine veil of abrasives and sand guarantees a successful separation and ensures a continuously high surface quality.
Dust has an even greater impact on wear and tear than abrasives. This mainly refers to the wear parts of shotblasting machines. Apart from turbine wear parts, such as blades, impellers, control cages, and the wear lining, the lining of the entire shot blast machine also suffers. It is, therefore, very important to separate these fine particles from the blasting compound by means of a professional adjustment system. The air stream within the abrasives reclamation unit has to be adjusted to remove fine grains and dust. Moreover, optimum cleaning of the exhaust air is a vital prerequisite for success.
AGTOS uses a special filtering material for the suction of dust during the blasting process in foundries. The aim is to further decrease the harmful quantity of fine dust particles. Special cartridges which minimize the adherence of dust and therefore offer the best cleaning quality provide optimum air pollution control. In the past, foundry air streams were allowed to escape into the open air. Nowadays it is possible to clean the air to such a degree that it can be returned to the workshop. This alone will save the foundry heating energy, made possible by a special secondary filter unit. Almost all fines are absorbed by downstream filter mats. Emission values of less than 0.15 per cent per m3 of dust can be reached and pose no health hazard to humans.
User-friendly maintenance of filter units
The replacement of filter cartridges often represents a very time-consuming and harmful job due to the dusts. The AGTOS engineers have taken foundry practice into consideration. Novel drawers simplify the exchange of cartridges. Thanks to this innovative system the cartridges are removed from the filter unit from the outside to be replaced within a clean environment. During installation the cartridges are automatically positioned accurately and always fixed with the correct contact pressure.
The clock actuated filter control activates the compressed air diaphragm valves placed above the filter cartridges. There are two different cleaning possibilities. Conventional filter units are cleaned by continuous blows of compressed air at pre-selected time intervals. However, the filtering material is also subjected to stress during cleaning. As this method provokes unnecessary cleaning impulses, the filtering material is often put under needless stress. AGTOS generally applies a more efficient means of cleaning control.
The filter cartridges are cleaned in dependence on the differential pressure, which means that the pressure is measured and compared before and after passing the filter cartridges. A cleaning impulse is only triggered off when the difference exceeds a preset value. The individual compressed air valves for the cleaning of the filter cartridges are triggered by means of a PLC unit at the control cabinet of the shotblasting machine.
These technical developments incorporate comprehensive know-how derived from many decades of experience in the field of foundry surface technology. Combined with a state-of-the-art approach, it results in a trend setting concept.