How to correctly evaluate a stone dust extraction system?

Guide to the selection of the suction wall or suction bench for the stone dust

It sometimes happens that the equipment for the suction and removal of stone dust is seen as a regulatory compliance rather than a need to protect the health of workers, and in this case the less expensive equipment is preferred.
Luckily, in most cases, those who use a dust removal equipment during the stone processing are well aware of the risks of silicosis and decide to protect themselves and its employees. In this case, even if it is not a manufacturing machine and the economic return cannot be measured directly, the investment in a good dust extraction system plays a fundamental role in any activity that produce dust during the processing and polishing of marble, granite and especially quartz agglomerates, as the stonemason is exposed to high concentrations of crystalline silica (primary cause of silicosis).
But then, how to choose a good dust collector for the marble workshop? Here’s a brief guide to the features you should focus on when choosing a suction wall, a downdraft bench or a suction booth.

Structure
As for all kind of machinery, a rugged structure is one of the main features to check. As there are rotating fans at a speed of 1,500-3,000rpm, a solid frame avoids annoying vibrations that affect the lifespan of the machine and the noise level. More than the choice of the material (stainless steel or painted or galvanized steel does not make much difference, since there are today painting and galvanizing processes that are equivalent in terms of resistance to corrosion), we must focus on the strength of the structure . When choosing your dust extractor, ask for the weight: it will give you a quick indication of the type of structure of the equipment you are buying.

Ok, the structure is fine, but a dust suction wall must remove the granite and other stones dust from the workplace. Therefore, the other two important features to consider are:
1- Capability to capture and convey the dust
2- Capability to suppress the dust

Ability to capture and suck the dust
The most obvious thing for a stone fabricator: the first step to eliminate dust is to suck it up. Very often this characteristic is erroneously associated with the m3/h stated in the nameplate data of the fan. The higher the value, the better the machine will work and the faster it will suck and clean my workplace from the dust … e.g., if the equipment fan flow rate is 15.000 m3/h, I will be able to clean a workshop of 5 mt x 10 mt x 3 mt  in 36 seconds …. Obviously, this is WRONG!
First of all, the fan has not a single m3/h value, but a values curve depending on the operating conditions. For example, a Ferrari can reach a maximum speed of 250km/h, but this value depends on the specific condition at the time of measuring: certainly it doesn’t reach it on an uphill gravel road and with 300kg on board … Therefore, every time we see a value of m3/h, it is necessary to know if it is a standard data of the fan (which doesn’t give us any real information on the equipment we are buying) or it’s a measured value of that fan on that machine in specific conditions (for example with new filters or after 8 hours of work ….).

So, how can we understand the real suction power of the equipment we are buying? First of all, we can say that no fan will be able to suck up dust if it escapes capture and settles on the ground; so the primary task of the fan is to capture the dust at its source of generation during the stone processing phase, before it settles. A parameter that can give you an indication is the speed of the air near the machine, but it is an experimental parameter that is almost never supplied and therefore it’s hard to make a comparisons between different machines. Another value that can make sense to consider is the motor power as, under the same conditions, it guarantees a higher intake depression and therefore a greater speed.
In any case, once you’ve narrowed down your choices to a few machines, the best advice we can give you is to personally test the equipment and evaluate the suction capacity, knowing that if the suppression system consists of mechanical filters, the suction power of the dust collector will diminish over time, as the filters get dirty … but we address the topic of dust suppression here below.

Capability to suppress the dust
Ok, we have evaluated a set of sturdy stone dust extraction systems able to capture all the dust we produce, and now? Well, now we need to consider the most important, and at the same time, less verifiable feature at the time of purchase: that is, what percentage of the stone dust that is captured is actually “suppressed” and not returned to the environment?
There are various systems of suppression: with internal water, with water-wall, with different types of filters (sleeves filter, pocket filter, etc ..), with cyclones or the combination of multiple systems.
Each has advantages and disadvantages and different percentages of suppression.
The mechanical filters (almost always made of fabric) are the simplest solution to reduce dust with high performance, close to 99%, but they have several drawbacks: first they get dirty, so they require more ordinary maintenance than other systems (that means constant cleaning). Moreover, despite the cleaning, the filters will lose their filtration capacity over time, and therefore they will reduce the aspiration performance of the dust collector until it will be necessary to replace them completely with a significant cost (we suggest to quantify it at the time of purchase of the machine).
The solution of wet filtration seems to be the most advantageous: using the water as a means of purification there are no filters that get dirty, so the performance of the dust collector remains unchanged over time. As a result of the suppression they produce mud, but for companies that process stone this should not be difficult to manage. However, not all the water-based systems are equally effective: for example, waterwall booths are excellent for dust from paint spraying and powder coating (that is very heavy) but they are not enough effective for the stone dust; moreover the curtain of water, and the consequent humidity, are very near to the worker.

A different wet-system is based on the water mist: once the stone dust is captured inside the suction wall or dust extraction bench, it get mixed with the drops of water so it becomes heavier and after a speed reduction it is conveyed through forced paths, that by gravity separate the dust from the air.  With this system you get to a dust suppression of 99%.

Finally, an alternative solution is to combine different systems, for example a first suppression by cyclones + a final suppression with filters. In this case you have all the advantages of a dry dust collector and a guaranteed dust reduction of 99%, but also a very limited filtering part, that considerably reduces the problems related to the filters (as mentioned, frequent cleaning, decrease in performance and costs of replacement). Obviously, systems of this type are more expansive.

Regarding the dust suppression capability, we would recommend to consider equipment with a third party certification on the dust suppression level, just because this feature cannot be checked in the nameplate data but just through an operation test on the machine, and if it is carried out by independent third-party technicians it has higher reliability.
This wants to be a quick overview on the problems related to the industrial aspiration solutions for granite, quartz and other stones dust; although not exhaustive, it can be a good starting point for choosing the dust extractor for your workshop.
In Ghines we based the design and production of our dust extraction systems on these technical evaluations, in order to protect the health of the stone fabricators.