Ultrasonic cleaning is most commonly used for cleaning metal parts but we occasionally get asked to clean a variety of other materials. Ultrasonics works best when cleaning a hard item such as a steel pipe, but what about plastic items?
Plastic is not the most favourable material for ultrasonic cleaning. There will always be cleaning action taking place in the tank, but how effective it is depends on the density of the plastic. Low density and flexible plastics such as low-density polyethylene (LDPE), actually absorb some of the ultrasonic power, lessening the cleaning action. Another big problem with this type of low-density plastic is that the items usually float on the solution meaning there isn’t total coverage and therefore not a total clean unless the parts are “held” underwater in an inverted basket.
Ultrasonic cleaning works better on harder plastics like Polyether ether ketone (PEEK) but it is still limited to what it can achieve. Ultrasonic cleaning can work really well for removing light contaminants such as the powdered releasing agent from injection moulding, but when it comes to tougher contaminants, the results can be fairly underwhelming.
If you do decide that ultrasonic cleaning is the best option for cleaning your plastic parts, here are some things you should consider:
- Does the part float? – If the answer is yes, then you will need to rig something up so it is held completely under the solution.
- How heavily contaminated is your item? – If it is completely covered in a thick oil for example, it will take longer, it may require a multi-stage ultrasonic clean, and it will need to be thoroughly rinsed with clean water at the end to make sure none of the contamination has reattached itself from the solution.
- Can your item handle the heat? – We generally operate ultrasonic tanks from 40 – 60°C. Some plastics may begin to distort when held at these temperatures for a longer period of time.
- Is the chemistry safe for your material? – Some ultrasonic cleaning chemicals may not be safe to use with plastic parts. This is especially true for solvent-based solutions.
What are the alternatives to ultrasonic cleaning then? The very best alternative if you are looking for a deep clean for plastic parts is to clean them by hand. If you are using the correct solution, your contaminant should lift straight off without much issue. For tougher contaminants, it may require a bit of elbow grease, but it can be done. If you have a large batch where hand-cleaning will take months, it may also be worth looking into spray washing (I’ve heard a dishwasher will work if you are in a pickle!).
As an ultrasonic cleaning company, it pains us to say that ultrasonics isn’t the best cleaning method for anything, but in this case, we have to hold our hands up and admit that for this application, it doesn’t quite cut the mustard. For removal of light contaminants form hard plastics, it’s worth a shot but always be aware that you may be required to do some hand-cleaning to finish them off.