Normally a vital part of any vibratory mass finishing process is the media, this could be a very strong abrasive for grinding, a cutting media for deburring or a none abrasive for polishing However, there are some components that are ideal for processing without any media. In the industry we call this technique "self processing" or "part-on-part" a special vibratory mass finishing machine that often also incorporates the drying cycle.

Not all components can be finished without media, first the components should be small and not too long, for example 0.5mm – 30mm but in the case of screw blanks, nails and rivets, the component length could be up to 150mm as the likelihood of damage to this type of (hardened) product is minimal.

Generally the components need to have some rigidity, and not damage easily. "Self processing" is not suitable for all small components, fragile or delicate and intricate parts or components with complex shapes must be finished with an appropriate media.
It is usually necessary that the components to be self processed are produced (or available) in large quantities as it is important to fill the vibratory mass finishing machine with a certain volume in order to create the precise spiral and rotation of the mass. "Self processing" will not work without the correct volume of components in the process chamber, so machine capacity is an important factor when choosing this method of finishing.
With the correct machine settings, many different types of surface finishes can be achieved, for example, deburring, polishing, and when an abrasive paste or powder is added grinding or even creating an edge radius is possible, so this type of processing method can be quite versatile.
In the same single machine it is possible to carry out multi processes, for example, descaling, pickling, polishing, inhibiting and drying. Normally at least two separate machines would be required to complete this many processes.

To optimize the process result and to run an efficient cost effective process a purpose built "space saving" machine without polyurethane lining is recommended. An integrated false bottom in the process chamber facilitates thorough draining of the liquid compound and water, as well as creating a channel that allows the hot air to flow freely and efficiently around the components during the drying cycle. Some machines have polyurethane linings for extra wear protection. This type of machine would have multiple extra large liquid drain points occasionally fitted with an air diaphragm pump to minimize drain times.
Use of a standard vibratory mass finishing machine is not recommended for "self processing".

Vibratory mass finishing machines for self processing are available in sizes ranging from 50 to 620 litre process capacity, although smaller and larger machines can be manufactured.
Components to be processed are loaded automatically into the processes chamber, (if the quantities are small they would be loaded manually). The first stage of the process cycle is normally descaling, cleaning or degreasing  typically using a liquid compound with a high Ph. This takes approximately 10 minutes. At the end of the first stage the fluids are thoroughly rinsed out of the process chamber and the next cycle begins. This stage could be polishing using a neutral compound which would normally take approximately 10 – 15 minutes. If required an inhibiting compound is added before the drying cycle starts. Each process and the drying stage are precisely controlled via a central (PLC) control console. Vibratory speeds, compound/watering metering, cycle times and drying temperature are all adjustable.
Positioned at the base of the process chamber is a pneumatically operated component discharge door that when (automatically) activated at the end of the drying cycle discharges 100% of all components preventing any mixing of different product types or sizes, ensuring complete batch integrity.

Self processing can be carried out in centrifugal disc type machines (FKS) but drying components in the same machine is not always possible.
It should be said that if "self processing" is suitable for your components it would be advisable to select a machine that has been specifically manufactured for this purpose, as this would offer the most cost effective and space saving solution.

Good Vibrations
by Paul Rawlinson
Contributing Editor MFN & Business Development Manager, Aerospace International for Rösler

Tel. +49.9533.924 647
Fax +49.9533.924 601
E-mail: P.Rawlinson@rosler.com