FOCUS ON FILTRATION
Automated material handling, on the other hand, switches out finished sheets in minutes so cutting and part removal happen at the same time. While this feature increases productivity, it also makes dust collection more challenging because the collector is exposed to more cutting time. Such automation often leads to higher dust and fume loads, and a dust collector should therefore be sized to accommodate those increased loads.
Air considerations
To help optimise the operational life of filters, collection systems should have a controlled air volume to avoid pulling excess air through the system. Dust collection systems therefore often incorporate a damper on the fan to adjust for resistance changes in the filters as they become plugged. The partial closure of the damper assists the fan in pulling just the required air volume when the filters have relatively little resistance.
However, dampers are not the only way to control airflow, as adjustable-speed motors allow fan speed to be adjusted to control airflow and allow for potential energy savings.
The greater the air volume required to control the dust and fume from cutting, the larger the dust collection system that will be required. Consequently, many large cutting systems will be compartmentalised or zoned. This approach requires airflow only in the space below the cutting bed, translating to a smaller air volume and therefore a smaller dust collection system. Careful consideration should therefore be given to the static pressure required by the system, especially in large or long tables.
In other situations, the stock being cut may have existing openings that create the need to pull additional air, and dust collectors should then be designed with this extra capacity requirement in mind. Increasing the collector capacity, in this instance, helps the system to maintain the necessary downdraft velocity across all the openings for effective dust evacuation.
Finally, a collector fan should generate sufficient airflow through the cutting table to create the downdraft velocities needed to capture rising fume. Material removed during cutting produces slag, smoke and fine thermally generated particles. While slag typically drops to the bottom of the table floor, the dust collection system should be sized to generate adequate downward airflow to overcome the thermal rise, capturing smoke and fine particulate from the cutting process.
Downdraft tables are often partitioned or zoned to reduce the total airflow required to capture dust effectively, reducing the size of the collector. The collector size is then tailored based upon factors including the number of cutting heads, the cutting technology( laser, plasma, oxy-fuel etc.), the material being cut and the cutting speed and torch on-time. For larger workpieces, multiple cutting machines may be integrated within a single downdraft table.
Surface-loading media
Donaldson Downflo ® Evolution( DFE) dust collectors.
The fine particulate generated by thermal cutting applications generally requires highefficiency cartridge collectors to perform well. It is widely accepted that surface loading, fine fibre media and downward airflow patterns increase collector performance, when compared to traditional depth-loading medias.
Fine fibre media allows sub-micron particulate to build on the surface of the media, creating a barrier for dust to accumulate and be easily pulsed-off. Cartridge filter media without fine fibres has the potential to allow particulate to embed within the media fibres, resulting in increased resistance across the media and leading to reduced airflow and shorter filter life. This can necessitate more maintenance, greater energy consumption and frequent filter changes, which impacts resource demand and increases costs.
Traditional filter media enhanced with a layer of fine fibre will provide higher filtration performance for capturing fine particles from thermal cutting, compared to traditional cellulose media options. Fine fibre aids in the removal of the very fine particulate from the airstream through several filtering phenomena including interception, diffusion and impaction.
Such fine fibre therefore increase the overall efficiency of the filter media as it helps to prevent fine particles from embedding deep within the filter fibres. This forces particulate to accumulate at the media’ s surface, creating an extremely effective surface-loading filter so that it can be easily pulse-cleaned off which, depending upon use, may help extend filter life and reduce energy consumption. As the cleaning system pulses, the downward airflow assists with evacuating
fine particulate and fume from the surface of the filter media and into a storage container. If particles are not stopped on the surface, filters will depth-load. This allows fumes to enter the depth of the media, making it difficult for pulse cleaning to discharge these depth-loaded particles.
Managing multiple variables
Designing and integrating an effective dust collection system for thermal cutting is not a one-size-fits-all exercise. Many variables influence dust control system performance during thermal cutting, and a well-designed system including the ducts, fan and filtration media should take all the variables and elements into account. A well-designed system should also maintain consistent downward airflow velocity to effectively evacuate dust across a range of filter and operational cutting conditions. Considering the filtration challenges posed by thermal cutting applications, manufacturers should consult filtration experts for dustcollection solutions that help them to align their dust collection strategies with their operational priorities. n
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About Donaldson
Founded in 1915, Donaldson is a global specialist in technology-led filtration products and solutions, serving a broad range of industries and advanced markets. It solves complex filtration challenges through three primary segments: Mobile Solutions, Industrial Solutions and Life Sciences.
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