Enclosures II

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Enclosures require ventilation. A well designed local exhaust system can remove a large percentage of the mist and fumes generated by an operation, keeping it away from the machine operator and concentrating it for more effective removal and disposal. Local exhaust systems are especially effective when combined with appropriately designed enclosures.

If you're looking for information on types of enclosures or retrofitting enclosures, you need Enclosures I.

On this page:

ventilation required

types of ductwork systems

ductwork design

Glossary terms:

coalescence separator

impaction separator

impingement separator

centrifugal separator

electrostatic
separator

plenum system

tapered main system

comparison of ductwork systems

ductwork design

compatibility

welded or mechanical seams

proper drainage

easy access

proper air velocity

do rates, pressures, temps need to be monitored?

limit flexible ductwork

traps for drains: static pressure, accessibility

compatibility of gaskets, sealants

What ventilation do the machine tools require?

Each workplace location should be evaluated as to

the number of machine tools in a given area

the types of operations performed

existing ventilation patterns

ceiling height

ultimate disposition of the collected MRF mist.

Consider aerosol generated by all work stations, including washers; all machine tools need to be considered together.Vapors cannot be removed from the plant air by common mist or particle removal techniques such as coalescence, impaction, impingement, centrifugal, or electrostatic separators. They can only be removed by absorption, adsorption, or condensation, for example, by scrubbers, charcoal filters or refrigeration. Smoke, depending on its nature, can often be removed by filters and electrostatic precipitators.

The airflow of local exhaust ventilation systems must be measured. Make adjustments or repairs as appropriate. Refer to Industrial Ventilation: A Manual for Recommended Practice, available from the American Conference of Governmental Industrial Hygienists, for further guidance.

What kind of ductwork system should be used for machine tool enclosures?

Exhaust ductwork from machine tool enclosures should be designed and maintained in accordance with ANSI B 11 TR 2-1997 as a guide. The ductwork should be inspected and cleaned regularly, and ductwork not in good working order should be repaired.

There are two main types of systems: the plenum system and the tapered main system. A plenum system uses a main duct of constant cross-sectional area. A tapered main system uses ducts that gradually change in cross-sectional areas to maintain a relatively consistent air velocity. Each system has its advantages and disadvantages, as shown below.

Type	Advantages	Disadvantages
Plenum	·· easy to relocate machines · easy to expand ductwork · may coalesce/condense aerosol before collection · easy to clean	· initial cost · large duct · may require duct drains
Tapered main	· lower initial cost · compact size · lower power required to operate	· difficult to relocate machines or expand ducts

How should exhaust ductwork be designed?

Exhaust ductwork should be constructed from materials that are not affected by the metal removal fluid intended for use in that system.

Exhaust ductwork should be designed with all welded seams or with mechanical seams. The use of ductwork intended for HVAC is NOT recommended.

Ductwork should be designed so as to maintain proper drainage angles to collection points.

Exhaust ductwork for metal removal machines should be designed with adequate access for maintenance, or it will rarely be cleaned.

Air velocity in exhaust ductwork should be adequate for the transport of MRF mist, but not so high that chips and MRF are also transported.

During design and construction of exhaust ductwork, consider that system flow rates, pressures and temperatures need to be monitored. You might, for example, include ports for pitot tubes and/or other instruments that can be readily opened and tightly closed after use.

Flexible ductwork may at times be necessary on some enclosures, but it should be limited in length and never used in a horizontal position.

When designing traps for ductwork drains, you must consider the static pressure of the system at the location of the drain.

All drains and traps should be accessible for maintenance. Standard plumbing traps should not be used.

MRF-compatible gaskets or sealants should be used between connecting sections of ductwork.