The plastic abrasives

General points
New plastic products, "soft abrasives", are continuously developed nowadays. Despite a cost much higher than the classical abrasives, they allow reaching, in many areas, some performances that other abrasives (such as plants) could not obtain in the past.

The products
Several plastic shots can be used for projection.
- polyamide
- chlorure de polyvinyle
- polycarbonate
These products, generally obtained through a raw material cut,
are presented under the cylindrical or cubic form.
- real density: from 1,1 to 1,2
- apparent density: from 0,6 to 0,7
- hardness: Shore D from 70 to 75
- granulometry: from 0,5 to 2 mm

Uses
These abrasives, with a low hardness, non-polluting, practically hard-wearing, are well adapted to the removing of rough patches, the light cleaning of small parts made of light alloys, plastic parts or bakelite. With a high cost, they are reserved for the treatment of high added value parts such as the contactors, the transistors, the printed circuits and the micromechanical parts (see chart uses).
They are generally used in automatic machines, with compressed air projection, but can be projected in blast wheel machines for some applications (see chart compatibilities).
The pulverization of an antistatic liquid in the recycling circuit is essential.
After 50 to 70 hours of use, the cylindrical or cubic grains tend towards the spherical shape.

The plastic medias

General points
The plastic medias were created in the United States in the 80's to replace the vegetal abrasives for paint stripping operations on planes.
The plastic medias are made of synthetic particles issued from polymerized resins. They are under the form of monochrome or polychrome angular grains, odourless and non-flammable.
There are two qualities of plastic medias:
- Grade A: "blank" media obtained through the crushing of "composite elements", sieved, graded and treated antistatic, whose hardness are controlled.
- Grade B: "scraped" media obtained through the crushing of various "recycled objects" made of composite.

Features
- family: acrylic (thermoplastic)
- form: angular
- real density: 1,15 to 1,52 (according to hardness)
- apparent density: 0,75
- hardness: 3 to 4 Mohs,
- granulometry: from 0,2 to 1,7 (60-80 to 12-16 Mesh)
- classifications: 2 quality levels and 6 types (see chart classification)
- specifications: (military) norme MIL P 85891 (A)

Uses
The main application of plastic medias is the origin of the paints stripping in the aeronautics. The product can strip, on a selective, way, some paints on parts made of light alloys, titanium, magnesium, stainless steel and composites. It can remove one or several paint coats without attacking or altering the under-coats or the support surface.
It does not damage the surrounding areas such as windows or chromium, and does not leave dangerous particles in the electric equipments, in the braking systems or the motors.
It can be used in other industries and applications such as the navy, the coachwork, the chemical industry, the food industry, the electronics, the nuclear technology, the moulding, etc.. (see chart uses).
The plastic media can be used each time the dimensions, the geometry and the surface finish of the parts must not be modified.
It cleans but does not polish. It removes neither dust, nor tartar.
It is mainly used with compressed air, pressure or suction projection equipments, fixed in automatic machines or sleeves stations, or moving and manual in free jet cabins. The choice of hardness and granulometry will be done, in most cases, after a test with a specialist because there are too many parameters to take into account.