Parts cleaning can be complicated

Almost all machined parts coming out of a machine tool are covered in some type of metalworking fluid residue. Depending on the next step in a part’s life, a certain amount of cleaning is in order. A major factor in determining the type of necessary cleaning is the degree of cleanliness specified by a customer. Other considerations include the workpiece material, the type of debris to be removed and the level of complexity for part features.

“It really depends on which stage of the manufacturing process you’re on,” said Sandro Siminovich, director of sales for Ecoclean Inc., Southfield, Michigan.

Cleaning parts generally involves a combination of cleaning time, a solution and the solution temperature. The two main drivers of solution chemistry are the debris, or soils, that must be removed and the workpiece material. Some materials, such as aluminum, brass and bronze, can be harmed when cleaned with an incorrect solvent. And some cleaning agents can affect post-machining processes, such as plating, said Bernie Santerre, manager of
outside sales and business development for Graymills Corp., Broadview, Illinois.

The rotation silo is a parts cleaner that features indexing rotation and ultrasonics to enhance batch cleaning of parts with complex geometries that might be prone to nesting. Image courtesy of Miraclean Ultrasonics

“The right machine also needs to factor in load size and throughput goals,” said Cheryl Larkin, Northeast regional sales manager for Miraclean Ultrasonics, Ashville, New York.

Finding the right parts cleaner ultimately can be just as complicated as the cleaning process itself.

The Cleaning Process

To select an appropriate cleaning agent, the maxim “like dissolves like” applies. If a shop uses a nonpolar cutting fluid, such as mineral oil or grease, a solvent might be the correct choice. When ultrasonic cleaning, for example, chips and particles, which are polar contaminations, no longer adhere to a part after the oil or grease is removed and are carried away by the cleaning action.

The ultrasonic process uses ultrasound, usually 20 to 40 kHz, to agitate a fluid. Ultrasonics introduces microscopic bubbles into a cleaning solution. They implode and take the soil with them. The bubbles travel wherever a solution goes, making ultrasonics suitable to clean parts with complex geometries and apertures.

Water-based detergents also effectively break the soil bond when properly matched to substrates and soils based on the pH level, solution concentration and temperature.

The higher the temperature, the better, Siminovich said. Solvent-based machines typically work with a temperature of about 65.6° C (150° F) during the liquid phase. With vapor degreasing, the temperature is about 121.1° C (250° F). For water-based cleaning, the temperature is usually about 37.8° to 48.9° C (100° to 120° F).

Increasing cleanliness requirements and achieving consistent cleaning results are common demands, he said.

Two main criteria measure how clean a part must be: the visible particle size and weight, which are measured in microns and milligrams, and the invisible surface tension, which is measured in millinewtons per meter or by contact angle and indicates how much of a chemical is left on a surface.

“At Miraclean,” Larkin said, “we build for a variety of industries, and each customer’s cleaning requirement is unique.”

She said requirements range from visual inspection and particle counts to water break tests and black light or white glove inspections.

The Cleaning Systems

Finding the right parts cleaning machine or system is “shockingly complicated,” said Tom Kucklick, applications specialist at Graymills.

A batch machine is widely used to simultaneously clean a large number of small parts, which are placed in trays or baskets and go into one or more tanks depending on the number of stages. With a single-chamber machine, parts go inside the chamber, and the entire process takes place inside.

One of the most common forms of parts cleaning is ultrasonic cleaning. It can be used with just water, but adding a cleaning agent appropriate for the part to be cleaned and the type of soiling present enhances cleanliness.

The simplest form of water-based ultrasonic cleaning consists of a standard-size heated tank, such as one measuring 304.8 mm × 304.8 mm (12″×12″). Parts go into a basket, which a user lowers into a tank that contains chemistry. The amount of time needed to clean them is calculated through trial and error. Parts then are rinsed. Some operations use a second tank for rinsing. Others just rinse parts in a sink and blow off excess water by hand with a compressed air hose.

A large facility that deals with heavily soiled items, such as injection molds or remanufactured automotive parts, might need a bigger parts washer that offers more mechanical cleaning action. That may require an ultrasonic tank that heats water and has a platform that agitates up and down. Those parts also must be rinsed and inhibited or dried.

An installation by Graymills involved an aggressive pre-wash, an ultrasonic wash, rinsing and drying. However, less than 10% of the company’s cleaning systems have multiple stages.

The DMD232 (left) is a small, manual drum-mount washer. The 500 (right) is a small, manual tank washer.
Both have a pump for low-pressure spray washing. Image courtesy of Graymills

Conversely, most of Miraclean Ultrasonics’ systems are automated and have multiple stages for parts that require a high level of cleanliness, such as those for the medical device and aerospace industries.

Kucklick said he also has been seeing more automated parts cleaning, which necessitates proper communication among various pieces of production and cleaning equipment. Most are still manual or semi-automatic, whereby an operator is present at the beginning and end of a cycle but not through the entire period. In addition, there has been a fairly constant shift from solvents to water-based cleaners, especially in locations with strict environmental regulations, such as California, but solvents can be more cost-effective.

All of Ecoclean’s cleaning machines also dry parts.

“Is it always necessary?” Siminovich said. “Nope, but it does make sense to have a drying stage. There’s a blow-off dry process where hot air inside the machine will blow-dry the part. Vacuum dry is more effective because it will remove all of the contamination from the parts. With blow-off drying, that process can reintroduce contamination onto the parts because when you’re blowing air around the part, there’s a risk of sending the particles back onto the parts.”

Depending on the process, cleaning time can vary widely. An equipment supplier typically helps a customer determine which process is needed and how to set up a proper cleaning system for it.

Make an Informed Decision

When looking for a parts washer, an end user must have some information ready for a supplier.

“I get calls all the time,” Kucklick said. “People tell me they are milling X number of parts, and they give me the length, width and height. They’ll say there’s a mixture of coolants and chips that need to be removed before the parts go to a plating process or an anodizing process. With a request like that, we first ask what process they currently have in place.”