Establishing Ultrasonic Cleaning Cycles

cleaning cycle 2Many of our posts describing an ultrasonic cleaning process contain a caveat along the lines of “with experience you’ll develop your own routine.”  And that is true because even if you clean similar parts the conditions of those parts may vary from slightly to substantially dirty.  Parts themselves react differently to cavitation action.  You’ll need more vigorous cavitation remove grease and grime from heavily soiled engine parts than to finish clean precision optics.

This post takes a brief look at variables that go into establishing an ultrasonic cleaning cycle and presents some suggestions that should help you refine your own cleaning procedures to secure the best results.

Ultrasonic Cleaning Temperatures

Cavitation action in water is most intense at 35⁰C (95⁰F).   But higher temperatures may be required to remove oils, greases, waxes and other contaminants.  This is where cleaning chemistries come into play.  Cleaning chemistries and cleaning temperatures together define the most effective ultrasonic cleaning process.  There is an upper limit, however.  Above 80⁰C (176⁰F) cavitation loses its effectiveness.  That’s why temperature controls on ultrasonic cleaners do not exceed 80⁰C.

Biodegradable cleaning formulations come with instructions including proper dilution with water and recommended cleaning temperatures.  For example, the cleaning temperature for elma lab clean A20sf for lab glassware and instruments of stainless steel, ceramics and plastics is 50 to 70⁰C.   The widely used elma tec clean A4 to remove oil, grease, combustion residues and other organic contaminants has a recommended cleaning temperature of 50 to 80⁰C.

The temperature range provides leeway.  As you “develop your routine” remember that lower temperatures consume less energy, so it is a tradeoff between cleaning time and thoroughness.

On the other hand medical and surgical instruments contaminated with blood should be cleaned at room temperature because heat causes blood to set on surfaces and becomes very hard to remove.

Ultrasonic cleaning temperatures can be controlled on Elmasonic and other cleaners available from Tovatech.  Keep in mind, however, that cavitation action in itself raises the temperature of the cleaning solution.  Cooling coils are available as an option if high solution temperatures should be avoided.

Ultrasonic Cleaning Time

It won’t surprise you that the dirtier the part the longer the cleaning cycle.  When cleaning heavily contaminated parts such as automotive gears and other products with built-up deposits take a few minutes to carefully scrape away loosely adhering deposits.  The same applies to removing grinding dust, shavings and powder residues from newly fabricated metal parts.  Not only will this shorten the cleaning cycle but it also helps prolong the effectiveness of the cleaning solution.

Here are some suggested cleaning times in our posts relating to specific products, but again referring to our caveat actual time will depend on the condition of the parts.  We also suggest that when cleaning medical and surgical instruments and implants you should be guided by the recommendations of professional associations.

Parts being Cleaned/Contaminants Removed Suggested Cleaning Time
Printed Circuit Boards/solder flux 3 to 10 minutes
Partially Disassembled Outboard Motor Engines 40 minutes
Highly Finished Parts/buffing compounds 10 minutes
Firearms/oils, powder residues/lead deposits 10-12 minutes followed by ultrasonic lubrication
Carburetors/varnish, grease and other deposits 20 minutes
Rusty Tools/rust 15 to 30 minutes
Injection Molds/burned on residues, oil, flashings 10 to 15 minutes, longer for complex molds
Dental  Instruments/blood 15 minutes

The position of parts in the cleaning solution is important and can affect cleaning time.  All surfaces must be exposed to cavitation action.  Parts with slots, blind holes and tiny crevices, and narrow aperture tubing should be positioned to allow full penetration of the cleaning solution but without “trapping” thereby keeping contaminants from draining away.  This may call for removing the basket and repositioning the parts, then continuing the process.  Slight vertical agitation such as provided by the Elmasonic Flex 1 ultrasonic cleaner and Flex 2 system combining cleaning and ultrasonic rinsing greatly assists this process.

Selecting Ultrasonic Frequency

Ultrasonic frequency in kHz produces bubbles that implode on contact with parts being cleaned thereby carrying away the contaminants.  Low

Ultrasonic frequency, time, temperature and power can be selected on the Elmasonic P ultrasonic cleaners

Ultrasonic frequency, time, temperature and power can be selected on the Elmasonic P ultrasonic cleaners

frequencies such as 25 kHz produce relatively large bubbles that implode more violently than those created at higher frequencies such as 37, 80 or 130 kHz that produce progressively gentle cleaning action.

Removing gross contaminants from robust parts such as fabricated or cast metals requires lower frequency cleaners.  Softer metals, plastics, and products with polished surfaces should be cleaned at higher frequencies.  In addition to protecting polished surfaces smaller bubbles are better able to penetrate tight areas such as seams, crevices and blind holes.

The following table provides a representative selection of ultrasonic cleaners available from Tovatech and their frequencies. Additional options are available.  Contact us for information.

Ultrasonic Cleaner Family Frequency/Frequencies
Elmasonic E and S Cleaners 37 kHz
Elmasonic TI-H Dual Frequencies 25/45 or 35/130 kHz
Elmasonic P Dual Frequency 37 or 80 kHz
Elmasonic X-tra Basic Dual Frequency 25 or 45 kHz
Elmasonic Flex 1 and Flex 2 Dual Frequencies 25/45 or 35/130 kHz

And Finally Ultrasonic Cleaning Power

Power, usually presented in watts per gallon of cleaning solution, is another variable to be considered when selecting an ultrasonic cleaning system.  Since this post is already long enough we direct you to another post on tips for selecting ultrasonic cleaner power.  As always, the ultrasonic cleaning professionals at Tovatech are ready to help.  Simply contact us to get the discussion started.

About Rachel Kohn

So how did an MIT Ph.D. end up selling refrigerators? When I figured out that a lot more scientists buy lab refrigerators than innovative leading-edge instruments. I hope that my many years of lab experience will help you find the right equipment for your work. Before co-founding Tovatech I worked in business development and project management at Smiths Detection, Photon-X, Cardinal Health, and Hoechst Celanese. And before that I spent 12 years as an R&D chemist at Hoechst Celanese and Aventis working on advanced drug delivery systems, polymer films and membranes, optical disks, and polysaccharides. Some day, eventually, I’ll make enough money to develop an innovative technology that will change the world. Read More