Cleaning metal and plastic parts using an ultrasonic cleaner.
In my quest to find the best and easiest way to clean parts when shopping a pinball machine, I finally bought an ultrasonic cleaner. It’s a fantastic tool: an excellent way to clean parts and make them look like new, without spending hours on manual labor. I let it run while I shop a pinball machine, processing small batches as I disassemble parts. This saves a lot of time, since cleaning happens while I’m still removing components, rather than being a separate task afterward.
If you frequently shop pinball machines and want top-notch results, this machine is a must-have!
I’d heard about ultrasonic cleaners for years—mostly good things, especially how well they remove grime from plastic parts like star posts. But they were considered specialized equipment, mainly used by jewelers, and not easy (or cheap) to find. I usually cleaned parts in the dishwasher, which gives decent results and is easy. Sometimes I soaked plastic parts in a strong cleaning solution and scrubbed them manually with a brush. So I wasn’t urgently looking for a new method.
Then I dropped off my Gottlieb Majorettes pinball machine for repairs at Henk De Jager. Ramon and Henk showed me another Gottlieb woodrail they had just shopped. Many parts looked brand new, including the star posts and pop bumper components (plastic skirts and metal rings). I had tumbled the metal star posts on my machine and achieved similar results, but their plastic parts looked even better. Seeing that convinced me to invest in an ultrasonic cleaner.
Nowadays, many shops offer these machines for home use, and prices have dropped significantly.
How does an ultrasonic cleaner work ?
As the name suggests, an ultrasonic cleaner uses ultrasound to clean parts. Simply put, ultrasonic waves (which you can’t hear) cause the cleaning fluid to vibrate rapidly. This creates microscopic bubbles that implode. The energy released loosens dirt from the surface of the object, making it easier to remove.
Guidelines in using an ultrasonic cleaner
- Parts must be fully submerged in the cleaning fluid.
- Heavier objects take longer to clean, as they absorb more energy. It’s better to run small batches than fill the tank completely.
- Group similar parts together—don’t mix lightweight plastic star posts with heavy metal components.
- If a part is too large for the tank, place it in a separate container (like Pyrex), submerge it in cleaning fluid, and place that container inside the tank. Fill the rest of the tank with fluid to ensure proper operation. Cleaning may take longer due to the extra mass.
My machine has a timer that runs up to 480 seconds (8 minutes). I usually run it for the full duration. If parts aren’t clean yet, I give them another cycle. The machine emits a high-pitched sound, not pleasant to hear all day, but the results are worth it!
After cleaning, dirt may remain on the surface or dissolve into the fluid. It’s crucial to immediately rinse parts with clean water. If you leave them in the dirty solution, floating debris can reattach and dry onto the surface. Rinsing prevents this.
Some parts may look clean right out of the tank. Dirt like thick grease may not dissolve but will no longer adhere to the surface, it wipes off easily. Be aware that ultrasonic waves can break down some types of glue. Also, be cautious with painted pinball plastics, especially older ones: the artwork may come off, leaving only clear plastic.
What cleaning solution to use in an ultrasonic cleaner
The manual for my machine recommends distilled water. While this works for delicate items like jewelry or glasses, it’s not effective for the typical grime found on pinball parts. I tested several solutions to find one versatile cleaner suitable for both metal and plastic.
If you’re cleaning only one type of material (e.g., brass, chrome), there may be better specialized solutions. Some people use a sequence of vinegar, baking soda, and water for brass parts.
My first test was dishwasher soap. It helps a bit—anything that breaks surface tension aids cleaning, but it’s not ideal. Manufacturers advise against it, as it foams excessively and isn’t strong enough to remove stubborn dirt.
You can buy dedicated ultrasonic cleaning fluids, including ones for PCBs, but they’re often expensive, especially with shipping costs. I wanted an industrial, non-foaming cleaner. I found a great one at Makro (Metro in the UK): less than 5euro for 5 liters. It’s strong, dilutable, and works well on both metal and plastic. The new packaging layout is shown below.
When shopping for industrial cleaners, look for labels indicating less than 5 percent soap content. Also check for warnings about compatibility with certain metals. Never use flammable liquids in ultrasonic machines.
It seems Metro / Makro has changed the packaging to this new layout.
I dilute the cleaner 1:1 with water, and it works brilliantly. I recently shopped my Cyclone pinball machine, and every part I cleaned came out looking brand new: star posts, plastic components, small metal parts. I’m genuinely impressed!
I should have bought this machine years ago!
Health risks of ultrasonic cleaners
Ultrasonic cleaners are generally safe for home and industrial use, but precautions are necessary. The energy and potential risks increase with the unit’s power (Hz and dB). Be especially careful with large industrial models.
Ultrasound doesn’t travel well through air or heavy mass. Keeping the lid closed and placing the unit on a sturdy table provides sufficient protection. Avoid touching the unit or fluid while it’s running. If you need to reposition an object, turn the machine off first.
Use common sense—sound waves can transfer through mass into nearby liquids. Don’t run the machine next to a fish tank, for example.
Ultrasonic cleaning compared to a tumbler
I used to clean metal parts with a tumbler. So how do the two compare?
An ultrasonic cleaner isn’t a replacement for a tumbler, it’s a complementary tool. Each has its strengths. Tumblers clean and polish metal; ultrasonic cleaners only clean. However, ultrasonic cleaners are more versatile: they work on both metal and plastic.
Tumbled metal parts often need post-cleaning, as they’re covered in corn media dust that’s hard to remove manually. That’s where ultrasonic cleaners shine.
A good workflow is:
- Use the ultrasonic cleaner to remove dirt and grease.
- Tumble the parts to polish them.
- Run them through the ultrasonic cleaner again (with water) to remove fine dust.
If I had to choose between the two, I’d pick the ultrasonic cleaner. It works on plastic, saves time, and delivers excellent results. I’m extremely happy with it—everyone should get one!
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