Rotamat - Consistent Bulk Small Part Coating

If you're looking to coat large quantities of small parts, your processing options are fairly limited. Chain-on-edge or dip-spin are popular but can have heavy operator involvement or difficulty producing a consistent coating thickness over the surface of some part geometries.

Enter the Rotamat, a machine/process from Walther Trowal. Popular for coating small components throughout Europe, this technology has become more prominent in the U.S. It combines a rotating barrel similar to that found on a mass finishing machine but with paint spray guns.

The process works by spinning randomly oriented small parts beneath the spray nozzle or nozzles, enabling even coating coverage on all areas of the parts. The workpieces gently tumble over each other in the rotating drum. The resulting intensive mixing effect evenly exposes the workpieces to the spray pattern of the spray gun at different angles – a pre-condition for an even coating thickness. This process works on various part geometries but is especially well-suited for parts with crevices. An example is Phillips head screws, where the head might tend to clog with the coating material in a dip-spin operation.

The unique drum shape and the adjustable rotary speed ensure an optimum tumbling and mixing of the workpieces. The drum inclination is infinitely adjustable within a certain angle and can, thus, be precisely adjusted to different workpiece shapes. The ideal angle of inclination for the various coating processes is determined by processing trials and then stored in the machine controls. Different drum sizes for different part volumes are available. Exchanging one drum with another is easy and requires very little time. This allows the Rotamat to be adapted quickly to different batch sizes or coating processes. If required, the inside of the drums can be lined with a 3S-coating. In addition, the inside of the cover and the drum housing can be coated with an anti-adhesion material.

Once the coating process is completed, the drum is mechanically tilted downward to gently discharge the finished work pieces, which are now ready for the next production step.

Another feature of the Rotamat is the weight scale to measure the coating applied. Every batch is monitored for the weight of the coating applied, ensuring consistency from batch to batch.

The Rotamat system can handle parts of about 4 inches in diameter. Process parameters, including barrel angle and rotation speed, air temperature and flow, and spray parameters, must be developed for each part size, weight, and configuration, but once a process is developed, the machine's PLC provides automated process control. Although the Rotamat barrel looks similar to a typical tumbling barrel, its elliptical cross-section is designed to throw parts riding near the outside edge of the drum into the center and under the machine's spray guns.

In a typical process, parts are loaded and started tumbling slowly. They're heated until they reach the desired processing temperature, then sprayed to develop multiple, very thin layers of the coating material being applied. Coatings can be solvent- or water-based, and the process has been proven with lacquers, epoxies, and a variety of water-based paint materials, as well as rust preventatives, lubricants, and other materials.

Once the desired coating thickness has been achieved, the machine heats prefiltered inlet air to 300°F to speed drying. Exhaust air is removed from the drum with a suction fan, and the drum can then be tilted downward for easy part removal. Parts with coatings that require higher cure temperatures can be post-processed using any desired curing technique.

If needed, the barrel's internal surface can be cleaned using special media supplied by Walther. But, if processors run consistent batch sizes, there should be very little need for barrel cleaning.

In addition to decorative coatings, the Rotamat can be used to apply anti-blocking agents to reduce the coefficient of friction of small parts. A typical application in this area is the PTFE coating of sealing o-rings used in many assemblies in the automotive and other industries. The Rotamat technology also works to prepare part surfaces for applying adhesives, such as rubber to metal bonding, and for coating parts for electrical insulation. Examples of applications include coating ferrite cores, core discs for small electric motors, aerospace fasteners, screws, buttons, rivets, springs, buckles, plastic toy pieces, elastomeric sealants for lithium batteries, and more.

Please contact Walther Trowal for more information or to process samples.