Tribofinishing

Mechanical-chemical polishing, tumbling, tribofinishing or even trovalisation is a process which makes it possible to modify the surface condition and the edges of parts made of metal, synthetic material, ceramic, etc. by immersing them in an abrasive mixture set in motion vibratory, oscillatory, or rotating in an open or closed tank.

Process parameters

Abrasive mixture

The abrasive mixture is usually composed of three components:

• media (also called carriers, or chips) whose role is to transfer the movement of the tank to the abrasive mixture and to the parts to be treated, so as to generate the friction which is the basis of the abrasive effect. They can be of various materials (metal, polymer, ceramic, plants, etc.), shapes (cylinders. Tetragons, etc.) and dimensions (from 0.1 mm to several centimeters). They generally form the majority of the volume of the load (abrasive mixture and parts). Although they can be used several times, they undergo wear which can modify their effect or cause separation difficulties (see below), which limits the number of cycles of use.
• an abrasive in the form of powder or paste, the role of which is to amplify the effect of friction, and therefore the abrasive effect. In principle, it is not reusable because it wears out during processing.
• a liquid (water or oil) which fluidifies the mixture and limits the increase in temperature.

Equipment

Some types of equipment commonly encountered: The equipment used is characterized by the type of movement imposed on the tank and by the volume of the latter (from less than one liter to several cubic meters).

• Vibrating bowls (also called circular vibrators): for parts of modest dimensions (<100 mm) the most common equipment uses a vibratory movement imposed on a toric tank (whose axis of revolution is vertical), which generates a displacement parts and media both around the axis of the vessel, and circularly in the profile of the vessel. These tanks are often fitted with a cover to prevent water evaporation and limit splashing.
• Vibrating tanks (or linear vibrators): for larger parts (> 100 mm). the tank is often rectangular and the carriers move quickly back and forth.
• Rotating bottom centrifuges: the round tank is fitted with a rotating bottom which drives the load, while the wall fixes the brake, generating friction within it.
• Satellite centrifuges: the satellites are cylindrical or straight prismatic with a hexagonal base; they are subjected to an epicyclic movement (in a horizontal, vertical or oblique plane). In order to balance the equipment, 2 or 4 satellites are used. In certain cases, the axes of the satellites can be inclined, which makes it possible to generate more complex movements and therefore to reach areas that are more difficult to access. Finally, the main advantage of this equipment is to provide a very high working power, making it possible to reduce cycle times very appreciably. For example, Altia has thus reduced the cycle times of its deburring and polishing processes by a factor of 20.
• Deburring barrel: Dry deburring barrels are economical and ecological alternatives to wet tribofinishing processes. The parts to be treated are placed in a tank with abrasive media, most often metallic. The setting in rotation of the tank operates a mechanical treatment having the effect of deburring the edges and removing the slag. A suction and filtration system makes it possible to concentrate the ferritic dust thus generated in a separator tank, with a view to being recycled. The tank is often coated on its inner wall with an elastomeric protection which has the effect of prolonging the life of the media and considerably reducing noise emissions.

The tanks or barrels used are most often made of synthetic material (or coated), eg polyurethane or rubber.

• Magnetic centrifuges: abrasives are magnetic; due to the setting in motion of a magnetic plate, they move relative to the parts and generate polishing or deburring operations.

A variant consists in fixing the parts to the tank by an armature or pins which are themselves set in rotation; in this case, only the abrasive mixture is moving in the tank. This process, also called smuritropy, makes it possible to prevent parts from colliding with each other, sometimes causing damage to the parts.