Process control and stability are critical aspects to regulated medical device and aerospace processes.  It is important to ensure that a process has input and output variable limits which are defined and fully tested during process design, Equipment Qualification (IQ), Operational Qualification (OQ) and Process Qualification (PQ) validation testing.  Setting up a proper DOE (Design of experiments) to test these limits is also important as it result of the DOE will give statistical confidence intervals of the limits.

Being that operators and employees perform various process operations different no matter how instructed in work instructions, the variation of operators must also be captured during process qualification (PQ) validation.  An automated system typically eliminates many of the operator variability in the manufacturing process and this process “input” elimination also allows for tighter process output controls.

For example, in our automated passivation system, the elimination of relying on an operator to move the parts basket from stage to stage ensures that the parts remain in the appropriate (wash, rinse, acid passivation, etc) solutions for the process defined times and in accordance with the proper ASTM A967, AMS2700, etc specification.  If a parts basket is immersed in the acid passivation solution too short or long duration, the passivation can likely fail and be outside specification limits.

Naturally any water that comes out of a pressurized water supply will contain dissolved gases and these gases need to be removed or degassed from the solution for maximum ultrasonic cleaning performance.  The reason for removal is gases are easier to compress than liquids; therefore, when the ultrasonics cavitate the solution, some of the cavitation energy is absorbed by the gases.  

Degassing solution is easily achieved by either letting the solution sit out for number of hours.  This is why a glass of water tastes “different” when first out of the faucet vs. drinking it hours later.   Running the ultrasonics in a tank will expedite the degas process significantly typically down to 5-10 minutes.  Keep in mind solution only needs to be degassed when first dispensed from a pressurized supply.

Although 5-10 minutes is much shorter than hours achieved by letting the solution sit, 5-10 minutes is still too long to wait for our automated cleaning and passivation systems to degas each time the solution is pumped from the storage tank to the process tank.  Our system feature a fast-degas feature at the start of the ultrasonic cycle which allows the solution to degas in a matter of seconds vs. minutes.

The fast degas feature can be heard in the video below (note high pitch of ultrasonic degas and tuning amplified for video demonstration)

How to tell if a solution is degassed or not?

Solution de-gases by simply releasing the dissolved and entrapped air in solution.  During a degas process with ultrasonics,  fine bubbles will suddenly appear and begin to rise to the surface of solution (similar to that seen after first pouring a glass of beer) This implosion or cavitation of solution with dissolved gases can result in high pitched audible sound from the ultrasonic tank until the solution is degassed as heard in the video above.

Once a solution or fluid is degassed either by letting it sit, ultrasonic cavitation energy, or heating, it does not need to be degassed again unless the solution replaced with new fluid.

 

Desiccants are used to absorb the water found in humid conditions to reduce or eliminate condensation. It can also be added directly to liquids to absorb the water content from the fluid.  We are used to seeing the small white bags of desiccant found in packaging for everything from shoes to electronic equipment.  Most of this desiccant is silica – typically in gel form.  Other common substances used as desiccants are activated charcoal and calcium chloride.

The desiccant used in vapor degreasers is 3 Angstrom Molecular Sieve, small pellets of zeolite clay. Like all desiccants, the zeolite clay adsorbs water from the solvent, and may be reused by baking it dry. Desiccants are most often used in a vapor degreaser if the solvent contains an alcohol. This is often the case with solvents used for defluxing processes on soldered boards and leads. Water found in the separator extracts the alcohol from the solvent and in turn the water and alcohol is absorbed by the zeolite clay. If a degreaser is operated in a very humid environment a desiccant may be need to effectively remove the water from the solvent.

A Rotary Drum Parts Washer is essentially a large “inside-out” screw.  Small parts are fed into the opening and the continuous rotation or tumbling of the barrel causes the parts to travel along this auger from one end of the barrel to the other.  As the parts travel through the inside of the barrel they pass through a wash area, a rinse area (or areas) and finally drying areas.

Small perforations in the side walls of the barrel allow the cleaning solution and rinse(s) to envelope the parts.  In addition, high powered spray jets spray on the parts during both wash and rinse cycles to provide even greater cleaning action.  Finally, the action of the parts traveling along the auger causes a tumbling action of the parts so that not only the aqueous cutting fluids are cleaned from the parts, but also small particulates are brushed off and drained away.

Once the parts are completely washed they travel through the dryer area of the barrel where a combination of heat and blowing air dry them before they are transported out the end of the barrel for final packaging.  These rotary drum parts washers are ideal for stamped parts, die-cast parts, cold heated parts and many more parts where high volume throughput are required.

If you’ve ever been wearing glasses as you walked into an air-conditioned building on a hot summer day, you already have a good understanding of part of the Vapor Degreaser process works. (For those in colder northern climates, walking outside while wearing glasses on a cold winter day is an even better example)

A vapor degreaser has two tanks (sumps) of solvent inside.  One boils the solvent (boil sump) which creates a vapor or mist of the solvent. The second sump (ultrasonic sump) is heated but not to the boiling point and is used as the second cleaning stage.  The vapor degreaser also has bands of cooling coils inside just above the level of the sumps. These coils cause the vapor to return to a liquid state and fall back into the sump.  The effect is like small “clouds” of the solvent are formed between the top of the sumps and the cooling tubes.

As parts at room temperature are lowered through the cooling area into the vapor, the vapor from the boil sump condenses on the parts just like moisture in the air does on your glasses in the examples above.  This condensation contains the solvent that dissolves the oils on your parts, and the beading action creates droplets which run across the surfaces of the parts and fall back into the boil sump. The parts are then moved to the ultrasonic sump which contains heated but non-boiling solvent.  This allows the parts to be lowered into the sump so that any blind holes or internal features are also thoroughly exposed to the solvent.

Finally parts are raised into the cooling coil area to allow the solvent to quickly dry and and then raised through a second layer of freeboard coils near the very top of the vapor degreaser that insure complete drying and the recapture of the solvent from the parts.

The below video demonstrates the process:

There is an old saying when it comes to parts cleaning: “Like dissolves like”.

This comes from the world of chemistry, and is really quite a simple and useful phrase to remember. In chemistry molecules are described as being polar or non-polar. (Think north and south pole on the Earth)  Polar molecules have a polarity that causes them to attract other molecules that have polarity, while non-polar molecules do not.

Water is a polar molecule.  Oil is not.  At the molecular level this is why “oil and water don’t mix”.  Chemically they are dissimilar and cannot absorb each others molecules.  By contrast salt IS polar; this is why you can dissolve salt in water.

So when should you use aqueous cleaning and when should you try cleaning with solvents? Solvent based cleaning systems (like Vapor Degreasers) are used when you need to clean true oils from your manufactured parts.  Aqueous Cleaning Systems are used to clean water based materials from your parts.

There are three ways that spotting can occur:
  1. If there is soil introduced with the rinse (ie: contaminants in the DI bath),
  2. If soil is introduced in the air stream (ie: either present in the atmosphere and blown onto the parts or circulated from the air supply into the heater and blown onto the parts), or 
  3. If soil is left as residue from the wash process (this could either be soil that was originally on the parts and not completely washed off or it could be residue from the cleaning chemistry that is not completely rinsed off).

When parts are washed the parts themselves, as well as the basket they are in, carry some of the wash with them into the rinse tank. This “drag out” means that the rinse solution has to be constantly replaced or will simply become less and less clean over time. The biggest issue is not that the parts will be rinsed off, but that when the parts are withdrawn from the rinse tank, they may have soil redeposited on them. Once the parts are dried this soil can cause spotting on the surface of the otherwise clean parts. A second rinse bath produces a much cleaner final product by rinsing off the soil that is redeposited during the first rinse.

Often times, the second rinse tank includes a heated facility water inlet which constantly overflows the second rinse tank with small amounts of water to ensure water cleanliness.  The second rinse tank overflow is sent to rinse tank 1 and then rinse tank 1 overflows to drain.  This cascade overflow process ensures constant water quality over time no matter the amount of drag out on the parts and baskets.