Browse Prior Art Database

Card Drying System for Solvent Cleaners

IP.com Disclosure Number: IPCOM000103696D
Original Publication Date: 1993-Jan-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 3 page(s) / 173K

Publishing Venue

IBM

Related People

Smeins, CB: AUTHOR [+2]

Abstract

Most solvent cleaners that are on today's market have poor provisions for drying circuit boards effectively. Some utilize hot recycled air with a heater and blowers, but these systems utilize high volumes and low velocity air which disturbs the solvent vapor blanket within the cleaner. This will contribute to higher solvent emissions. Today's cards are becoming larger, with many more components that are difficult to clean. To increase cleaning efficiency, today's cleaners utilize higher spray volume capacities and spray pressures. To meet volume demands, some cleaners, designed to run at 2 feet per minute, are now being operated at 6 feet per minute.

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Card Drying System for Solvent Cleaners

       Most solvent cleaners that are on today's market have
poor provisions for drying circuit boards effectively.  Some utilize
hot recycled air with a heater and blowers, but these systems utilize
high volumes and low velocity air which disturbs the solvent vapor
blanket within the cleaner.  This will contribute to higher solvent
emissions.  Today's cards are becoming larger, with many more
components that are difficult to clean. To increase cleaning
efficiency, today's cleaners utilize higher spray volume capacities
and spray pressures.  To meet volume demands, some cleaners, designed
to run at 2 feet per minute, are now being operated at 6 feet per
minute.  Standard cleaners that sprayed solvent at 30 PSI and total
spray capacity of 60 GPM, are now spraying cards at 100 PSI with a
total spray capacity of 300 GPM to clean cards properly at the
increased conveyor speeds.  At this feed rate, the wet cards and
conveyors drag out much more liquid solvent which is lost within the
work place as fugitive emissions, or recycled by returning the vapors
to a carbon-absorption unit.  The increased spray pressures and
volumes have also caused more disturbance to the vapor blankets
within the machine, which causes more solvent losses.

      Water-type cleaners have hi-temp/volume air dryers mounted on
the exit end to dry the cards.  These units add substantial length
and cost to a cleaner, and can also disturb the vapor blanket in a
solvent cleaner, resulting in more solvent losses.  Solvent cleaner
manufactures now design machines with more freeboard height which
does stabilize the vapor blanket and reduce losses at low speeds;
however, when the conveyor belt speed is increased to four or six
feet per minute, large cards with numerous components still exit the
cleaner with raw solvent evaporating from the cards.

      With the increased pressures to reduce CFCs that cause ozone
depletion, it is very critical that fugitive emissions be controlled.
Solvent vapor carbon absorption units must be used to recycle minimum
amounts to solvents.  The most effective recycling systems still lose
approximately 10-20 percent to the atmosphere.  Recent changes in the
Federal Regulations have now mandated that CFC emissions be reduced a
substantial amount to stop the ozone depletion.

      To solve the emission problems with solvent dragout on cards
exiting a solvent cleaner, the following steps were taken.  Through
numerous transvector nozzles, hi-velocity low volume dry compressed
air is directed at an angle at the exiting cards as close to the
cards as possible.  The air flow is isolated from the vapor blanket
within the cleaner by a series of brushes arranged so that they
provide baffle zones to protect the vapor blanket inside the cleaner.
These chambers prevent any cross flow of vapors that will disturb the
vapor blanket with the cleaner.  This minimizes solvent losses from
the cleaner...