Thursday, August 1, 2019

Metalworking

What materials can my dust collection system collect?
Per NFPA 484 11.2.3.5, the dust collection system cannot collect materials that are incompatible with each other – such as ferrous and non‐ferrous materials. Moreover, this section states that the dust collection system must only be used to collect the material it was designed for. The collector can be changed to collect a different material (from titanium to aluminium for example) only after the system has been fully cleaned and the system has undergone a management of change to ensure it fully complies with NFPA 484.

What processes can my dust collection system serve?
Per 11.2.4.3.6, grinding operations must be served by a different collection system than one serving buffing and polishing operations. Buffing and polishing operations involve combustible materials other than the metal, such as rouge. Grinding operations create a lot of sparks; so a combined system is at a very high risk of having a dust explosion, which is a major reason to keep them separate.

AAF Recommendation:
The RotoClone LVN is an ideal collector when multiple process and/or materials are involved. Its compact size allows it to be placed close to the dust generating process, keeping the inlet ducts as short and straight as possible. Furthermore, as a wet collector, it does not require ancillary explosion protection equipment and can be located indoors. This allows an LVN to be used for each process application rather than needing multiple duct runs to multiple collectors located outside the building. Additionally, an individual LVN system is much easier to balance than a centralized dust collection system with multiple duct runs, ensuring optimal performance.

Can I recycle the air from my dust collection system?
As with location, air recirculation is dependent on the type of collection medium. For dry collectors, re-circulation is prohibited by 11.2.4.4.13.1. Wet collectors can recirculate the air so long as collection efficiency meets the authority having jurisdiction’s (AHJ) needs per 11.2.4.5.3. Where required to meet industrial hygiene exposure, an after filter housing can be used so long as the following items are included:

  • Warning signs stating the use of dry filter media
  • A differential pressure alarm set to the recommended change out pressure drop
  • The filter media must be static dissipative or conductive
  • A means to limit hydrogen accumulation to 10% of the LFL
  • A high temperature alarm set to the filter media limit

AAF Recommendation:
For applications that require filtration following a wet collector, AAF recommends a two‐stage minimum side access filter housing (SAH) with the option of a third stage for added efficiency to meet industrial hygiene needs. The SAH would be the following:

  • Stage 1 ‐ Demister housing with metal mesh filters to remove added water from the wet
    collector.
  • Stage 2 ‐ PolySeal housing with DriPak 2000 MERV 11/13 pocket filters, a synthetic‐glass filter
    that can tolerate the added moisture content and is static dissipative.
  • Stage 3 (optional) – PolySeal or LeverLock housing with either a VariSorb XL15 or DriPak 2000
    MERV 15.

A HEPA filter is not recommended since the media is mainly paper‐based and is neither static dissipative nor grounded. In order for this filtration system to comply, AAF offers an integrated controls package that includes the pressure and temperature alarms, assuring safe operation of the filter system.

Need to speak with someone about your metalworking application?

Contact AAF https://www.aafintl.com/en/power-and-industrial/contact-us