Capture of cutting fluid aerosols (article written by the CARSAT)

The success of a project to set up a collection system is not limited to defining the suction flow rate and the filtration system. Other important elements must be taken into account and defined in the specifications (design of the premises, design of the machines concerned, nature of the pollutant, design of the ductwork, energy costs, aeraulic balance of the workshop, monitoring and maintenance of the installation, etc.) in order to integrate a future high-performance and sustainable extraction system for the company.

USI+, located in Ayse, Haute-Savoie, is specialised in the screw-machining of technical and machined parts.

In 2019, this company of 62 employees has integrated a new industrial site in Ayse. As soon as the requirements for the design of this new building were defined, the installation of centralised suction networks for cutting fluid aerosols was included in the project.

The manager, aware of the importance of protecting the company's employees from oil mists, opted for a centralised extraction system with filtered air rejected to the outside of the building. The 75 digital machining centres in the production hall were connected to this system.

According to the initial project, the installer had integrated a simple connection to the suction of the machining chambers of the machines (main emission).

After several weeks of operation and discussions with USI+, additional connections were made to the chip removal circuits (secondary emissions) of five machines that still had significant oil mist emissions, with a suction rate of around 300 m3/h per connection.

In connection with the use of whole lubricating oil, a combustible product, each machine machining titanium is equipped with an automatic fire extinguishing system and a "fire-stop" valve on the suction ducts in order to avoid any propagation of a fire to the entire suction network.

After a preliminary study of the machines to be equipped (recent digital centres entirely enclosed), the supplier proposed the installation of two centralised networks to connect all the machines spread throughout the workshop.

The filtration units and the 30 kW fans were placed in dedicated technical rooms. The unit, which is particularly suitable for aerosols from cutting fluids, consists of three filtration stages: two coalescence (self-draining) filtration stages and a HEPA (High Efficiency Particulate Air) filtration stage (finish) of class H13 (99.95% efficiency rate for 0.3 µm size particles).

A differential pressure gauge (per filter unit) allows monitoring of the clogging status of the filters.

The chosen system also has a low impact on the noise level in the workshop and in the environment (property limit) by the installation of silencers.

The workshop is also equipped with low speed fresh air reintroduction systems (supply air speeds of less than 0.4 m/s at the workstations) through textile ducts, 1120 mm in diameter and 28 to 35 metres long each, positioned in the ceiling, in order to compensate for the volumes of air extracted.

Based on data from the supplier of the extraction system, the air conditioning contractor installed Roof Tops (four compact air-to-air units with integrated heat pumps) on the roof for the treatment of fresh air, incorporating a heat exchanger (active thermodynamic recovery) connected to the discharge ducts of the oil mist filtration units.

This system compensates for the 36,000 m3/h of extracted air, limits the loss of calories linked to the extraction of air to the outside in winter and reduces the cooling needs of the workshop, in particular by evacuating the calories produced by the machines in summer.

In order to guarantee the durability of the aeraulic and filtration performances of the existing networks, the installer carries out an annual visit to carry out the preventive maintenance and the periodic checks provided for by the regulations (checking the state of the installation elements, measuring the air flow rates/speeds at characteristic points of the extraction networks). The service provider also carries out measurements, using a particle counter, to check the filtration efficiency.