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 >> >>--------------------------------------------------- >>Technet Mail List provided as a service by IPC using LISTSERV 1.8e To >>unsubscribe, send a message to [log in to unmask] with following text in >>the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt >>or (re-start) delivery of Technet send e-mail to >>[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing >>per day of all the posts: send e-mail to >>[log in to unmask]: SET Technet Digest >>Search the archives of previous posts at: >>http://listserv.ipc.org/archives Please visit IPC web site >>http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional >>information, or contact Keach Sasamori at [log in to unmask] or >>847-615-7100 >>ext.2815 >>----------------------------------------------------- >> > > > -- > 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