Accelerating Ultrasonic Cleaning

Question:

I am working on a cleaning application for die casting parts (valve bodies of automatic transmissions, many cavities, very intricate form). The problem: the parts are covered with a sticky layer of graphite, because the casting company uses the graphite to facilitate the release of the parts from the molds after the casting process. I already tried to clean the parts with an ultrasonic cleaner (the medium used was a water/soap solution approximately 200:1 at 60°C). The results were not bad. The problem is that the cleaning process took about 20 min, and I am already at the temperature limit (because of the dimensional accuracy of some bores). Could you recommend a chemical that supports the ultrasonic cleaning and accelerates the process? That chemical should not be too acidic/alkaline, because the process is handled manually by an operator. M.A.

Answer:

It sounds like the part you are working with is limiting your possible cleaning options. The primary factors that affect the cleaning process are the chemical of choice, its concentration, time, temperature and agitation. By systematically working through each one of these factors, it may be able to achieve a higher degree of cleanliness.

Temperature: As you stated, you are at the maximum temperature for this part, so this variable should remain fixed at 60°C.

Agitation: You are doing the right thing by using the ultrasonics in this application. It is a good application for the blind holes and recesses on your part. There are a couple of items that you can check. One would be the frequency. A high frequency ultrasonic would not be as effective as a lower frequency ultrasonic in this application. You should be in the range of 20-50 kHz. Also, make sure the bath is degassed prior to use. Heat the bath for at least an hour or two prior to use to drive off dissolved gasses that will decrease the cavitation efficiency of the ultrasonics. Time: I am sure you do not want to go beyond 20 minutes here, but it may be worth doing a couple experiments to see what effect time has on the cleaning results.

Cleaner and concentration: Before abandoning the current cleaner, it may be worth trying it at a higher concentration. Running any cleaner at 0.5% by volume is very low. I would try it at a significantly higher concentration (5–10%) before giving up on it completely. If you are still dissatisfied with the cleaning result, you will probably then want to talk to your chemical supplier to see if they have anything more effective. If not, other suppliers can be found in the 2005 Products Finishing Directory and Technology Guide or at www.pfonline.com/suppliers.html.