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Cleaning Solutions for Old Clocks

Collectors who clean their own old clocks or provide a service for owners of vintage clocks may find an investment in a benchtop ultrasonic cleaner to be a great time saver (no pun intended). Ultrasonic cleaners are available in a variety of sizes suitable for both hobbyists and owners of antique clock repair services. The value of sonic cleaning clock mechanisms is that cavitation action produced by the cleaner’s ultrasonic transducers reaches every clock component immersed in an ultrasonic cleaning solution formulated for the job. Dried lubricants and dirt accumulations are quickly and safely blasted away by the implosion of millions of minute cavitation bubbles.

Ultrasonic Cleaner Selection for Old Clocks

Ultrasonic cleaners come in a range of sizes and features.  Let’s look at size first.  A key consideration is the size of the cleaning basket used to fully immerse clockworks in the cleaning solution, especially if the movement is cleaned as a unit. Basket dimensions, not internal dimensions of the cleaning tank, are the important criteria. For example, basket dimensions of the 1-gallon capacity Elmasonic SH100EL ultrasonic cleaner are 7.5 x 4.1 x 3 in. deep. If you clean disassembled parts these can be placed in the optional cleaning basket or optional fine screen immersion baskets.

Ultrasonic cleaner features are important.  The 37 kHz frequency Elma SH-EL series, available in 13 sizes, has what is called a “sweep” mode.  This is especially important when cleaning materials such as brass because it provides a homogenous distribution of sonic action throughout the cleaning solution. Sweep avoids what are called hot spots and dead zones. By way of explanation hot spots are areas with a high concentration of cavitation bubbles, i.e. a stronger ultrasonic effect. If the ultrasonic cleaning is too intense this can cause etching on delicate parts with fine features, on polished surfaces, on soft metals, or on thin metal layers. Dead zones are areas where there is no cavitation, i.e. no cleaning.

A degas mode is useful when preparing fresh cleaning solutions because it drives off trapped air that slows the cleaning process.  Auto-degas is recommended if the solution has not been used for a period of time.

Heaters and timers are self-explanatory.  The SH-EL series has controls to indicate set and actual cleaning solution temperature and has an auto-start feature that initiates sonic cleaning when the set temperature is reached.  It can also be manually started. Cleaning time can be set up to 30 minutes with remaining time shown or continuous with an auto shutoff after 12 hours.

Cleaning solution chemistry is likewise important.  Ask us for biodegradable elma tec clean N1, a liquid neutral concentrate for gently cleaning various metals to remove oil, grease, dust and other contaminants.  A recommended dilution is to 5% with water at a temperature of 60?C (140?F). To avoid potential rusting of steel parts such as springs and verges ask us for elma-KS to provide temporary corrosion protection until parts are dried and lubricated. Add 0.05 to 0.5% to the bath and to rinse water before drying.

A Cleaning Cycle for Old Clocks

As we say in many of our posts, with experience you’ll develop your routine.  Here’s a suggested start:

Fill the tank half full of water, add the correct amount of cleaning solution concentrate and elma-KS for a full tank and then fill the tank.  Place the lid on the tank, turn on the ultrasound and activate the degas mode to mix and degas the solution.  This should take about 10 minutes.

Position the clockworks or disassembled parts in the basket(s).  If you disassemble the clockworks try to avoid parts contacting each other.

Set the temperature at 60?C and the timer for 5 minutes.  Turn on the unit.  Sonic action and the timer will start when the temperature is reached. Then lower the basket into the solution and replace the lid to reduce noise and evaporation.

At the end of the cycle remove the basket and place it on the inverted lid to drain.  While the clockworks are hot and flash dry you may want to speed drying using a hair dryer.

The clockworks are now ready for lubricating and reassembly.

Contaminants that float to the surface should be skimmed off and set aside for later disposal.  When cleaning time extends it is time to replace the solution.  Drain the tank and dispose of the solution according to local regulations, rinse the tank following the instruction manual then prepare and degas a fresh batch.

Contact the ultrasonic cleaning experts for additional information on ultrasonic cleaners and cleaning solution formulations.


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