Polyamide beads and method for the production thereof
Certain polyamide beads or granules are useful as a sustaining material for underground natural or artificial cracks of the earth's crust essentially employed for the extraction of hydrocarbons such as crude oil or natural gas; such polyamide beads have a spherical or ellipsoidal shape and have a surface free of concave portions, advantageously having a uniform shape, and having a mean diameter lower than or equal to 1.7 mm and a porosity lower than 0.1 ml/g, and are produced using a particular cutting device/extruder.
1. An apparatus for the production of polyamide beads, the apparatus comprising a granulating device including an underwater pelletizer which comprises:
one means of cutting;
a die comprising die holes having a diameter from 0.3 mm to 1.7 mm;
one means for feeding, wherein the means of feeding comprises a single-screw or twin-screw extruder combined with a gear pump, at a nominal feed pressure ranging from 70 bar to 250 bar, a polyamide or polyamide-based composition to the cutting means through the die holes, including means for controlling the pressure such that the polyamide or polyamide-based composition is fed into the die holes with establishment of at least 80% of the nominal feed pressure no later than 5 seconds after the start of the feeding of the die holes with thus molten polyamide or polyamide-based composition; and
a fluid circuit comprising means for controlling a temperature of a cooling liquid at a temperature ranging from 70° C. to 100° C.
2. The apparatus as defined by claim 1 , wherein the means of feeding comprises a means for controlling a throughput of the polyamide or polyamide-based composition in the die from 3 kg/h to 15 kg/h per hole.
3. The apparatus as defined by claim 2 , wherein the means for controlling the throughput of the polyamide or polyamide-based composition controls the throughput of the polyamide or polyamide-based composition in the die from 5 kg/h to 12 kg/h per hole.
4. The apparatus as defined by claim 1 , wherein the means of cutting comprises a rotating knife driven by a rotary drive at a rotational speed of from 3,000 rpm and 6,000 rpm.
5. The apparatus as defined by claim 1 , wherein the polyamide beads are of substantially spherical or ellipsoidal shape, a surface of which does not comprise concave portions, having an average diameter less than or equal to 1.7 mm and a porosity measured according to the mercury porosity measurement method of less than 0.1 ml/g.
6. The apparatus as defined by claim 5 , wherein the polyamide or polyamide-based composition comprises a reinforcing filler and/or a bulking filler.
7. The apparatus as defined by claim 6 , wherein a weight concentration of the reinforcing filler and/or the bulking filler ranges from 5% to 90%, with respect to the total weight of the polyamide or polyamide-based composition.
8. The apparatus as defined by claim 5 , wherein the polyamide beads have an average diameter ranging from 0.8 mm to 1.5 mm.
9. The apparatus as defined by claim 8 , wherein the polyamide beads have an average diameter ranging from 0.9 mm to 1.3 mm.
10. The apparatus as defined by claim 6 , wherein the reinforcing filler and/or the bulking filler is selected from the group consisting of glass fibers, aramid fibers, ceramic fibers, mineral fibers, clays, kaolin, silica, alumina, molecular sieves, glass beads, ceramic beads, fillers and plant fibers.
11. The apparatus as defined by claim 5 , wherein the polyamide is selected from the group consisting of polyamide 6, polyamide 6,6, polyamide T6, polyamide 4,6, copolyamides of these polyamides and semi-crystalline semi-aromatic polyamides.
12. The apparatus as defined by claim 11 , wherein the polyamide is polyamide 66 or copolyamide 6,6/6.
13. The apparatus as defined by claim 5 , wherein the polyamide or polyamide-based composition further comprises additives selected from the group consisting of additives for stabilization to oxidation and to light, pigments, dyes, mattifying agents, flame retardants, plasticizers and crosslinking agents.