Scale Removal - Tumbling

Equipment like coffee machines, hot water heaters, boilers and other commercial and industrial equipment that use hot water eventually shows a build-up on the parts. This residue is the deposition of the salts and minerals in the water on the surfaces.

If not removed, this scale can become quite thick and affect the performance of the equipment  The heat will not transfer efficiently from one area to another and holes and pipes will start to get blocked. Stripping down the scale, especially on smaller parts and in internal areas can be accomplished quite efficiently with vibratory tumbling.

Hard Water Scale Removal

Tumbling the parts with the proper media and compound can make a huge difference. Common sense would be to use as abrasive a media as possible to strip off the scale. But this is not always to best way.

The part on the left was tumbled with an abrasive Ceramic Media and a general purpose tumbling compound. This is a traditional deburring process and did knock-off some of scale (see oblong area in the middle of the part). The bulk of the residue wasn't touched and if the part was left too long in this type of process, the threads, edges, holes, etc on the part may have been worn down so that the part was out of tolerance.

The part on the right (which looked the same as the one on the left before tumbling), was tumbled with a polishing Ceramic Media. While this was a much less abrasive process, the appropriate compound, Kramco 1030 Mild Acid Cleaner, was used to soften, dissolve and then remove the scale. Because this was a polishing media, the part came out bright and clean with no wear on critical areas of the part.

Water Spots on Copper

Copper is a soft metal that is easily oxidized and stained (note previous post re: green color of Statue of Liberty). Stamped copper parts need to be deburred and cleaned prior to further use in most manufacturing processes.



This picture shows a portion of a copper component of an electronics part. The stamping and cleaning process (part on the left) shows light burrs and clearly visible water spots and staining.

In order to get a clean part for proper electrical contact, the part on the right was vibratory tumbled. The customer wanted a short cycle time and was not interested in a polished or bright surface finish. A Ceramic Angle Cut Triangle was used in order to deburr the outside edges as well as the ID of the holes and other features. The media and parts were tumbled in a compound solution of the Kramco 1030 Mild Acid Cleaner to remove the oxidation and water spots. The end result was a clean, smooth surface finish that met the customer's requirements. The total cycle time in the tumbler was only 15 minutes.

Dry Tumbling with Corn Cob Grit

Stamped, cut, machined and otherwise processed parts often contain cutting oils and lubricants and need to be cleaned. These parts also have burrs and sharp edges that may need to removed.

The steel parts pictured on the left are dirty and have light burrs that need to be removed. A typical process would simply demand a mass finishing, tumbling process with a Ceramic Media to degrease the parts and remove the burrs in a wet process. The challenge with these parts is the shape - long, flat parts. In a wet process these parts will stick together to form 'sandwiches' and will not be cleaned and will resist deburring.

The solution is to dry tumble the parts with Corn Cob Grit. The Corn Cob Grit media will remove and absorb the soils (note clean, brighter parts on right). In a barrel tumbler, with a high ratio of parts to media, the part-on-part tumbling action will remove the burrs. The Corn Cob Grit can be separated from the parts efficiently with a simple wire mesh screen. The dry tumbling process also eliminates the need to dry the parts so they are immediately ready for any further processing.

Clean & Polish Steel Tubes

Cutting steel tubing can produce heavy burrs on the edges and if done wet can lead to rusting on the surface of the parts (picture below).

Rusted Steel Tube

Prior to polishing the steel, the part must be deburred and cleaned. The oxidation (rust) will lead to pitting on the surface so an appropriate abrasive media must be used to create a smooth surface finish. Vibratory tumbling the parts with a general purpose Ceramic Media is typically aggressive enough to deburr the edges and remove any pitting from the rust (see left on picture below).

Clean (L) and Polish (R)

After the tube was tumbled with a Ceramic Cylindrical Wedge (a good shape for round tube parts), the steel tube was polished with a polishing Precision Ceramic Sphere. This porcelain-type round ball will significantly improve the surface finish and produce a bright polish on the part (see right on picture above). This part is now ready for producing an even higher, mirror-like finish using further mass finishing steps or hand buffing.

Removing Oxidation With Tumbling

Many metals (aluminum, copper, iron, steel) are attacked by air to create undesirable surface oxidation. While oxidation can be beneficial and protect the surface (note the green color of the Statue of Liberty) often this oxidation needs to be removed. While abrasive blasting is highly recommended for this process, large quantities of small parts can be difficult to blast one at a time.

Vibratory or barrel tumbling the parts in an abrasive or polishing media can quickly and effectively remove oxidation and prep a surface for further processing. In combination with the appropriate chemical compounds choosing the right type of media is important. Using an abrasive media will typically produce a clean, matte surface finish. Polishing media will enhance the compound cleaning action to leave a bright surface finish.

A mild acid cleaner designed for tumbling is an ideal choice for gentle oxidation removal. While more aggressive acids (mineral acids like muriatic) will also remove oxidation, care should be taken not to attack the underlying metal. In a pinch, a quick additive to use would be something like vinegar (acetic acid), citric acid or oxalic acid products (consumer bar cleaners).