Setting Realistic Parts Cleanliness Specifications | Technology

By chiron99
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Cleaning operations remove large volumes of oil, coolant, dirt, chips, or debris from manufactured parts. Each application has its own set of challenges and individual requirements. Filtration, bath life, heat, chemicals used, part orientation and spray pressures all contribute to the effectiveness of the cleaning process and the repeatability of those results.

The evolution of the part cleaning industry has advanced from using subjective cleanliness specifications like white gloves to definable, measurable objective specifications. This has helped make the task of cleaning parts a science controlled by soil weight limits and particle size limits, rather than arbitrary visual inspection.

As these objective specifications have developed, however, the level of cleanliness to be achieved in each specification has grown more stringent than is necessary for some applications. Generally, parts must be cleaned to a specification and some form of measurability has to be built into the process. Brake parts require a certain level of cleanliness and exhaust pipes require one as well. They do not however, require the same level of cleaning in order to allow a vehicle to safely operate. Common sense needs to prevail and realize that braking mechanisms need cleaner parts than exhaust manifolds.

In addition, many current cleanliness requirements have been instituted that are not only needlessly stringent but also difficult to achieve and impossible to qualify.

When qualifying a part's cleanliness level, weight is the most common means used to determine the level of clean achieved. A part is washed off with an alkaline chemical and water. That part still has some soil on it. The cleaned part is then taken to a lab and sprayed down with a solvent to make sure all of the soil is removed. That sprayed solvent is then strained through a filter patch, dried and weighed. That weight measures the cleanliness level by measuring the soil still on the part after washing with water.

Another method of objectively determining cleanliness is by the measurement of a particle's dimension. It is in this particle measurement where some cleanliness specifications go beyond what is reasonable or even achievable. A particle's size below a certain level cannot be measured across all three dimensional axis. Even if it could be done, there is no way to guarantee any specification that requires a particle be limited in size by height, length, and width can be reached due to filtration limitations. All particles can "letter box" through filter media.

For example, a particle specification can be 20 micron in size. That means no particle can be accepted if it is above 20 micron in any of the three dimensions. If a 10 micron filter is used, one would think that would be safe. This is not so. A particle that is 5 micron in width by 5 micron in height by 150 micron in length can slide through any 10 micron filter.

Particle size can be used to determine cleanliness, but realistic expectations need to be understood when setting cleanliness goals that are achievable.

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