A real-life approach to understanding industrial aqueous cleaning before and after nondestructive testing
By David Geis, Product Manager
When selecting an aqueous cleaner for a specific application, the sheer number of choices can be overwhelming.
There are many different methods of cleaning, many different types of equipment, and the number of different cleaner solutions can be truly daunting.
How can you be sure that you’re choosing the right method to clean your parts? The right equipment to clean them as quickly as possible? The right cleaner so that the whole process is easy and safe?
Is it really as complicated as all that? We are talking about cleaning, after all.
Everyone has experience in cleaning – doing the dishes, running a washing machine, washing the car. On the face of it, these jobs seem incredibly simple when compared to industrial parts cleaning. But the process is always the same; the only difference is in the details.
So how do we apply the knowledge you already have from everyday experience to this conundrum? As with any process, take things one step at a time.
1) Base Materials – What are you trying to get clean?
The kind of metal your part is made of makes a big difference in the kind of cleaning solution you can use, the temperature that’s best, and the amount of time you can spend cleaning.
You can understand this in simple household terms – you wouldn’t use drain cleaner to wash your clothes any more than you’d use hand soap to clean your grill. You need to choose the right cleaner for the right surface.
When dealing with industrial parts, brass and aluminum will react to cleaners differently than carbon or stainless steel. An aggressive cleanser may get hard surfaces like stainless steel sparkling clean, but etch and oxidize softer metals like copper and brass, ruining the surface. Thus, harder surfaces can handle more aggressive cleaners than softer surfaces.
The structure of the part will also influence your choices.
Just as you wouldn’t clean your windows with steel wool, you wouldn’t want to use scrubbing cleaners on fragile parts. If your parts have delicate structures, or precision surfaces, a milder cleanser and gentle application would be best. While that may mean more time spent cleaning, the alternative is potential damage to the part.
2) Soil Characteristics – What are you trying to remove?
This point follows naturally from the previous one – your choice of cleaning solution will depend on what kind of dirt you’re taking off your part. Understanding what you’re trying to remove is just as important as understanding what you’re cleaning.
Cleaning solutions are formulated with different ingredients to clean different types of soil. If you’re trying to get smudges of oil off your window, you grab the glass cleaner. If you’re trying to get grease off the stovetop, you grab a scrubbing cleanser.
In the same way, if your parts have carbonized soils and heavy greases, a caustic cleaner is needed to break the soil up and remove it. But if you’re just removing a protective coating of machine oil from a precision part, you need a mild, neutral solution.
Some cleaning solutions are designed to emulsify the soils and hold them in solution. This is similar to mixing dish soap into the grease in a pan before trying to rinse it away – the cleaner will break up the soil, pull it away from the part surface, and hold it in solution.
When using this type of cleaner, the amount of soil loading in the solution affects how well parts can be cleaned – after a while, the solution loses power and has to be dumped and replaced. If the cost of the cleaner is low enough and disposal costs are low, then this can be cost-effective. However, if the parts have a lot of soil, or the disposal costs are high, then this type of situation won’t work.
Other cleaning solutions are designed to pull soil off part surfaces, but then reject them from solution so they can be skimmed or filtered out. This extends the life of the cleaning solution, allowing it to be used again and again over time. Additional equipment is needed to filter the cleaner, and this investment must be balanced against the savings of reclaiming the solution.
3) Cleaning Method – How to get things clean?
The method you will use to clean your parts is the first thing to consider.
Think about doing the dishes: will you do them by hand or use a dishwasher? Similarly, choosing the method of cleaning will tell you what equipment you need.
If you’re doing the dishes by hand, you usually need a sink of soapy water, a sponge or brush, and enough time to scrub them clean. If there’s stuff on the dishes that won’t come off easily, you can soak them for a while and they’ll be easier to clean.
All of that’s fine if you have only a few dishes and enough time to do them. But if you have a lot of dishes, they’d get clean quicker using a dishwasher.
Thinking about this from an industrial point of view, we’ve already covered three different methods of cleaning – hand scrubbing, soaking and spray cabinets.
Hand scrubbing is just like doing the dishes, you have to physically scrub the dirt or oil off a part.
Like doing the dishes, this is fine if you don’t have too many parts at once and if they don’t take a lot of time and effort to clean.
It’s also best to use a mild cleaner, since you’re doing things by hand and harsh cleaners could be hazardous.
Hand scrubbing is the simplest cleaning method as far as equipment and setup cost, but it also has the highest operating labor costs, since all the cleaning is done by the operator.
Soaking is ideal for many small parts when you have plenty of time for cleaning.
Suspending the parts in a tank of cleaning solution, or gently swirling them in the tank, will loosen and remove dirt and oils from the surface.
For tough, carbonized soils, soaking can loosen the dirt, making it easy to brush off by hand, just like when you soak the pots and pans.
When you’re soaking parts, you can use more aggressive cleaners, since you don’t have as much exposure to the cleaner as you do when hand scrubbing.
The key thing to soaking, though, is to use enough time to make sure the part get clean.
Soaking presents a reasonable equipment and space investment to set up, but it is very simple to implement and has very low operating costs.
Agitated immersion washers are a better soaking method similar to your laundry washing machine.
When you run the washing machine, your clothes are being soaked in detergent and water, and being agitated at the same time. This movement helps to clean off dirt and oil more quickly than soaking alone will do.
Many companies provide just this type of machine for cleaning industrial parts. Some use baskets and move the parts around in the tank of cleaning solution. Others will pump solution over the parts.
Such systems cost more than straight soak tanks to set up, but significantly cut the amount of time needed to clean parts.
Ultrasonic cleaning is another soaking-type method which combines the benefits of soaking with a scrubbing action induced by sound waves in the cleaning tank.
This method can be used for precision cleaning on parts having complex surfaces, blind holes, and other features that would make normal soaking or spraying difficult.
Ultrasonic cleaning uses sound waves to create microscopic bubbles in the cleaning solution, then collapsing them back on themselves. This creates a microscopic scrubbing action all over the surface of a part that will break up and remove dirt.
Costs for setting up and running ultrasonic cleaning tanks are typically higher than agitated tanks, but often produce better results with precision parts.
A spray cabinet works best in situations where you must deal with a higher volume of parts, but you need to process them quickly.
This is like the dishwasher; parts are loaded on racks and run through a chamber where cleaning solution is sprayed on them.
This accomplishes a lot of work in a short amount of time – while a soak tank may take 30 minutes to get a part clean, a spray cabinet could be able to do it in 30 seconds.
On the other hand, foam is a major concern with spray cleaning. If you’ve ever tried to use regular dish soap in the dishwasher, you understand; a spray of cleaning solution will build up foam very quickly if it is not controlled.
Setting up a spray cleaning process can represent significant investments in equipment, space, and maintenance. However, once running the process can handle high volumes of parts in short times with consistent results.
4) Rinsing and Drying – The final cleaning steps
Heading back into the kitchen, you know from experience that the dishes aren’t done until they’re rinsed off, dried and back in the cupboard.
For aqueous cleaners, rinsing and drying are very important steps so special consideration should be given to adequate rinsing of your parts, using clean water, and adequate drying.
Neglecting the final rinse will leave cleaning solution on your parts, potentially leading to corrosion or pitting on the surfaces you just spent so much time and effort cleaning. While leaving water on the parts can lead to oxidation, rust, or mineral deposits that leave the surfaces discolored at best, and oxidized and corroded at worst.
Often, parts need to move on to other machining and processing steps after cleaning. How well you rinse and dry the parts after cleaning will translate into how well prepared the parts will be for the next step in manufacturing. If cleaning is the last step in manufacturing, then the final rinse and drying will affect the appearance of your product, and the impression it makes on your customer.
5) Spec Compliance – Do you need to comply with aerospace specifications?
Whenever you process critical parts, there are specifications that dictate what methods and materials can be used. The aerospace industry has particularly stringent specifications and codes you need to comply with in order to process and clean parts.
To satisfy these requirements, we have invested our time and effort into making sure Daraclean aqueous cleaners are approved for aerospace applications. Several of our most popular formulations carry approval according to ASTM, AMS, ARP, Boeing, Lockheed, GEAE, Pratt & Whitney PMC and Raytheon specifications and procedures.
Now we’ve covered all the bases – what we’re cleaning, what we’re trying to remove, how we’re going to do it and what specs we must comply with – hopefully you have a better understanding about how to approach industrial parts cleaning.
- Understand the material your part is made of. Understand how it can react to aggressive cleansers.
- Understand the soil you’re trying to remove from the part. Understand how the cleaning solution interacts with each one, and choose the best balance of cost to performance.
- Choose the best method for cleaning your parts – hand scrubbing, soaking, spray cleaning or ultrasonic. Understand the benefits and drawbacks of each one, and choose the best balance of cost to performance.
- Make sure the parts are adequately rinsed and dried after cleaning. Understanding how these steps affect the next processing steps in manufacturing, and the final appearance of the product to the customer, highlight the importance of rinsing and drying your parts.
- Be aware of specifications you need to comply with. If you are processing precision parts, critical components, or aerospace materials, there are many specifications for the materials and procedures that can be used. Daraclean aqueous cleaners carry several approvals and certifications for use in cleaning aerospace components and critical parts.
With the simple guidelines we’ve discussed here, you should be better able to navigate through all the different equipment and cleansers out there. If you still have questions you can check out our other blog articles on aqueous cleaners, or you can contact us for additional information or support.