Metal Part Cleaning, Metal Impurity Removal

Metal Part Cleaning Basics

A clean metallic surface is required at various stages in metal parts production. A machined component, for example, must be cleaned before any subsequent surface finishing, such as coating or electroplating. Electroplating is particularly sensitive to surface contaminants, as they can prevent adhesion of the metal coating.

Many terms have been applied to the cleaning of metal components, and nomenclature in this area can be ambiguous or misleading. Terms such as degreasing, metal surface cleaning, ultrasonic cleaning, parts washing, component cleaning, etc. are often used interchangeably. For our purposes, we are discussing the removal of any surface contaminants on metal components that are residual to the production processes that formed them, though implied with this is the removal of any particulates that have adhered to a part surface.

The American Society for Testing and Materials (ASTM) defines six groups of contaminants: pigmented drawing compounds, unpigmented oil and grease, chips and cutting fluids, polishing and buffing compounds, rust and scale, and others. Chips and cutting fluids are the primary concern for machinists.

For any given metal part, there are several approaches on how best to clean it. We restrict ourselves here to the cleaning of components through chemical, rather than mechanical means such as sand or shot blasting. There are five factors to be considered in determining a surface cleaning method or protocol: the impurities to be removed and the nature of the part(s), cleaning solution temperature, agitation, cycle time and concentration.

1. Impurities to Be Removed
During the course of manufacture, the surfaces of metal parts usually become covered by various chemical or particulate impurities called soils. A thorough high pressure washing may be helpful in removing tramp metal particles, or grit from the components. Coatings of lubricants and greases are more problematic.

The size and weight of the parts to be cleaned are both factors. Enormous parts may have to be cleaned individually by hand; smaller parts are usually cleaned in batches by immersion in a cleaning solution (often with the help of some vibration). The geometry of the parts is also important: complex, irregular geometries with threaded holes, etc. present the greatest challenges.

2. Use High Temperatures for Stubborn Soils
For the toughest jobs, metal cleaning solutions need to be heated for effective removal of surface impurities. From room temperature to about 100°F - 110°F, incremental increases in temperature offer no cleaning benefits. Above the 100°F threshold, significant improvements in cleaning results are obtained by further elevations in temperature.

Soils based on mineral oils, waxes or stearates can be tough to remove. Their high viscosities or water insolubility lead to cleaning resistance except at elevated temperatures -- in some cases approaching 200°F. The use of cleaning solutions at high temperatures helps break down the bonds that cause soils to adhere to metal.

3. Getting All Shook Up
There are many systems used to clean metal components. Some use bath immersions or sprays coupled with agitation of the cleaning fluid or the parts. It is common, for example, to immerse a batch of parts contained in a metal mesh basket or rack into a bath of cleaning solution. For effective cleaning, the solution or the parts within it should be circulated -- the more agitation the better. To this soaking cycle, an ultrasonic wave action may be added to loosen soils in tough-to-reach internal angles, holes or threaded areas.

4. Time Is of the Essence
Today's competitive market requires more throughput per hour for every manufacturing operation, including parts cleaning.

Generally speaking, more time soaking or under a spray means cleaner parts. However, demands on production volume have instead favored the development of faster-acting cleaners, more agitation and higher spray velocities for greater impingement.

5. Concentration Is Key
Most industrial metal cleaners have a particular volumetric concentration recommended by the manufacturer for best results. If you need to clean a batch faster or more thoroughly, it does not follow that you should just increase the concentration of the cleaning solution. This is a waste of product and money. Conversely, skimping on the concentration to save on cost may also end up costing you more through the re-processing of still-contaminated parts.

Acculube's fluid specialists have decades of experience in metal cleaning techniques, and in choosing - and using - cleaning solutions that deliver the greatest benefits in cycle time, energy use, effectiveness and cost.

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