The best compromise firstly would be not to use IPA which is a mediocre
solvent at the best of times! :-) Secondly, IPA in a US sump could be
dangerous if the energy levels were high, as it may cause increased
evaporation if cavitation occurs near the surface (e.g., with floating
contaminants forming nuclei). Thirdly, would hot IPA with no useful US
agitation be better than cold IPA with US agitation? As Doug would say,
it depends. If the contaminants were readily soluble and the article had
a fairly simple topology, I'd go for the hot solvent and no US. If the
article had a complex shape, esp. blind holes, then the US may be
better. That having been said, best results would certainly be obtained
by immersion in boiling solvent, transfer to cold solvent with US and a
final rinse in vapour phase. And even better results obtained with water!
Brian
Ingemar Hernefjord (KC/EMW) wrote:
> What is United States cleaning. Is that something you do after 4th July?
> And what is special about United States transducers,
> are they better than english?
> Erh..hmm..(cough)..hrrrm..
> Brian, if you use a solvent as agitation media, won't the lowest temperature
> theory collide with the fact that higher temperature increases the
> solubility? If we use isopropanol for flux removal, what would be the best
> compromise?
>
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis
> Sent: den 6 juli 2005 10:29
> To: [log in to unmask]
> Subject: Re: [TN] Ultrasonic Cleaner
>
>
> OK, lesson on US coming up, sorry for the simplistic didactic matter! :-)
>
> How does US cleaning work? You apply a mechanical vibration to the
> liquid, which is virtually incompressible. When the pressure rises, the
> fluid is pushed and the level rises (imperceptibly, of course). When the
> pressure decreases, minute cavities form where there are nuclei. These
> are essentially vacuums, but they do contain vapour, as well. At the
> next positive pressure, the mechanical inertia of the mass of fluid is
> too great for the cavities to be refilled. At the next negative
> pressure, the cavities which are still present form the nuclei for the
> cavitation and they thus grow bigger. After n cycles, the cavity will
> have grown to a critical size and, being essentially a vacuum, they
> collapse instantaneously (in picoseconds). This causes the vapour to be
> adiabatically compressed, resulting in an astronomical temperature rise,
> often of the order of thousands of degrees. The heat is dissipated in
> the solvent and the energy contained therein becomes a mechanical shock
> wave, a micro-tsunami if you like, and this shock wave is what scrubs
> your parts clean. The effective radius of this scrubbing action is of
> the order of µm, so you want the cavitation to occur where the dirt is.
>
> Now, the favourite place for cavitation to occur is on gas molecules
> which can be anywhere in the fluid, nowhere near the place to be
> cleaned, so the energy is wasted there. This is why the solvent must be
> degassed before use. In the case of some organic solvents, such as the
> late-lamented CFC-113, applying the US for, say, 15 minutes before
> starting to clean would degas the solvent sufficiently. Water (or
> aqueous solutions) are a horse of another colour and degassing became a
> complex procedure requiring heating and low pressures, then cooling,
> before use.
>
> What is the difference between liquid and vapour phases of a substance?
> Only the size of the molecule. In an apparently homogeneous liquid, you
> actually have some molecules in vapour phase (which is why the liquid
> evaporates, as the larger molecules happen to randomly reach the
> surface). This is also the motive power for Brownian movement. This is a
> question of the equilibrium conditions of the vapour pressure at a given
> temperature. The more molecules in vapour phase within the body of the
> liquid, the more cavitation nuclei are formed remote from where you want
> them, so the cleaning becomes less efficient.
>
> However, it doesn't stop there. The higher the temperature, the more
> vapour there is within a cavity and the lower the adiabatic compression
> during collapse, resulting in a shockwave of lesser amplitude.
>
> For the most efficient US cleaning, choose the lowest temperature
> DEGASSED solvent you can. This is why, in the traditional vapour phase
> degreaser, the US transducers are always placed in the cold sump,
> receiving the condensate from the refrigerated freeboard condensers and
> never in a heated sump.
>
> I hope this makes it clear.
>
> Brian
>
> Dehoyos, Ramon wrote:
>
>> I plead ignorance on this matter. I was taught that the fluid *had* to be heated. Could you enlighten us please?
>> Thanks Brian,
>> Ramon
>>
>>-----Original Message-----
>>From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
>>Sent: Tuesday, July 05, 2005 10:24 AM
>>To: [log in to unmask]
>>Subject: Re: [TN] Ultrasonic Cleaner
>>
>>You do realise that US cavitation becomes less effective if you heat the solvent, do you?
>>
>>Brian
>>
>>David Tremmel wrote:
>>
>>
>>>Happy 4th Everyone,
>>>
>>>I am in the market for a benchtop ultrasonic cleaner and am interested
>>>in purchasing a Branson 1510DTH (1/2 gallon capacity with a heater).
>>>
>>>It will be removing post-reflow flux residue from stencils and other
>>>equipment and will be operating 5-10 hours per day.
>>>
>>>If anyone has any experience with this model or has a suggestion based
>>>on their experience with another brand and model, please let me know.
>>>
>>>As always, I appreciate whatever feedback I receive.
>>>
>>>David
>>>Technical Manager
>>>BT Mexico
>>>
>>>_________________________________________________________________
>>>Consigue aquí las mejores y mas recientes ofertas de trabajo EE.UU.
>>>http://latino.msn.com/empleos
>>>
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