Process and Apparatus for Sorting Reusable Pieces of Raw Material

Abstract

The invention relates to a process and an apparatus for sorting reusable raw-material pieces (5) which are moved continually in conveying direction (2) by a transport means (1), where the chemical composition of the raw-material pieces (5) is analyzed by laser-induced breakdown spectroscopy (LIBS) and automated sorting of the raw-material pieces (5) is implemented depending on the composition found, where the raw-material pieces (5) in a first step are subjected to a plurality of first laser pulses (6) in order to remove surface coatings and/or contaminants from the raw-material pieces (5), and in a second step, one or more second laser pulses (7) are directed at those locations of the raw-material pieces (5) from which the surface coatings and/or contaminants have been removed, with exposed material of the raw-material pieces (5) being converted by the second laser pulses (7) into a plasma, where the laser (3) used for the first and second laser pulses (6, 7) is the same, and the area of the raw-material pieces (5) over which the first laser pulses (6) are moved and which is freed from surface coatings and/or contaminants is greater than the area of the raw-material pieces (5) that is embraced by the second laser pulses (7), the focal diameter and the focal point of the laser beam being kept constant between the first and second laser pulses (6, 7). In this way it is possible, utilizing only one laser, to achieve undistorted analysis of the composition of the raw-material pieces (5) and to perform sorting in dependence on said analysis.

Claims

1. A process for sorting reusable raw-material pieces (5) which are moved continually in a conveying direction (2) by a transport means (1), where the chemical composition of the raw-material pieces (5) is analyzed by laser-induced breakdown spectroscopy (LIBS) and automated sorting of the raw-material pieces (5) is implemented depending on the composition found, where the raw-material pieces (5) in a first step are subjected to a plurality of first laser pulses (6) in order to remove surface coatings and/or contaminants from the raw-material pieces (5), and in a second step, one or more second laser pulses (7) are directed at those locations of the raw-material pieces (5) from which the surface coatings and/or contaminants have been removed, with exposed material of the raw-material pieces (5) being converted by the second laser pulses (7) into a plasma, where the laser (3) used for the first and second laser pulses (6, 7) is the same, wherein the area of the raw-material pieces (5) over which the first laser pulses (6) are moved and which is freed from surface coatings and/or contaminants is greater than the area of the raw-material pieces (5) that is embraced by the second laser pulses (7), the focal diameter and the focal point of the laser beam being kept constant between the first and second laser pulses (6, 7).

2. The process as claimed in claim 1, characterized in that wherein the area of the raw-material pieces (5) which is freed from at least one of said surface coatings and said contaminants and is greater by at least the focal diameter and positional tolerances than the area of the raw-material pieces (5) that is embraced by the second laser pulses (7).

3. The process as claimed in claim 1, wherein the areas of the raw-material pieces (5) that are to be freed from at least one of said surface coatings and said contaminants are embraced singly or multiply by the first laser pulses (6) depending on the nature and thickness of at least one of the surface coatings and the contaminants.

4. The process as claimed in claim 1, wherein the first laser pulses (6) are guided along at least two dimensions over the areas of the raw-material pieces (5) that are to be freed from at least one of said surface coatings and said contaminants.

5. The process as claimed in claim 1, wherein the focal diameter of the laser beam is between 60 and 140 μm.

6. The process as claimed in claim 1, wherein a pulse length of the first and second laser pulses (6, 7) is 20-200 ns.

7. The process as claimed in claim 1, wherein the plasma generated by the second laser pulses (7) is a thermal plasma.

8. The process as churned in claim 1, wherein the laser (3) is a solid-state laser.

9. The process as claimed in claim 1, wherein the laser is a fiber laser.

10. The process as claimed in claim 1, wherein the raw-material pieces (5) are moved with a speed of >0.1 m/s in the conveying direction.

11. The process as claimed in claim 1, wherein the raw-material pieces (5) are steel-scrap pieces.

12. The process as claimed in claim 11, wherein the steel-scrap pieces are galvanized steel-scrap pieces.

13. The process as claimed in claim 1, wherein the raw-material pieces (5) are nonferrous-metal-scrap pieces.

14. The process as claimed in claim 1, wherein the first laser pulses (6) are directed at raw-material pieces (5) which are further back in the conveying direction (2), and the second laser pulses (7) are directed at raw-material pieces (5) which are further forward in the conveying direction (2), there being a continual alternation between the subjection of raw-material pieces (5) that are further back in the conveying direction (2) to first laser pulses (6) and of raw-material pieces (5) that are further forward in the conveying direction (2) to second laser pulses (7).

15. An apparatus for implementing a process as claimed in claim 1, having a laser (3) which is capable of generating first laser pulses (6) for detaching surface coatings and contaminants from raw-material pieces (5), and second laser pulses (7) for converting exposed material of the raw-material pieces (5) into a plasma, a spectrometer for analyzing the light emitted by the plasma, transport means (1) for moving the raw-material pieces (5) in the conveying direction (2), a control unit which controls the pulse energy, pulse duration, and pulse frequency of the laser (3) and which moves the first laser pulses (6) over an area of the raw-material pieces (5), and frees said area from at least one of said surface coatings and said contaminants, said area being greater than the area of the raw-material pieces (5) that is embraced by the second laser pulses (7), and which keeps constant the focal diameter and the focal point of the laser beam between the first and second laser pulses (6, 7), and a sorting unit which automatedly assigns the raw-material pieces (5) to one or more target fractions depending on the composition found.

16. The process as claimed in claim 1, wherein the pulse length of the first and second laser pulses (6, 7) is 60-120 ns.

17. The process as claimed in claim 1, wherein the raw-material pieces (5) are moved with a speed of >2 m/s in the conveying direction.

Description

[0055] The invention is elucidated in more detail by means of the appended FIG. 1. This FIGURE shows a transport means 1, on which a multiplicity of raw-material pieces are moved in conveying direction 2. In order to simplify the illustration, the raw-material pieces 5 here are arranged relatively regularly on the transport means 1, although in practice this is usually not the case. The transport means 1 is a conveyor belt which is driven by rollers 4. At the end of the conveyor belt there is a series of collecting containers A, B, C, R, in which the raw-material pieces 5 are collected according to composition, to allow them to be used again subsequently. In this case, the collecting containers A, B, C are collecting containers for re-use of the raw-material pieces 5, whereas the collecting container R is a residuals collecting container which collects those raw-material pieces 5 which are not amenable to further use or for which no compositional analysis was possible.

[0056] Sorting into the collecting containers A, B, C, R takes place in dependence on the composition found for the raw-material pieces 5. This is done by means of a laser 3, which generates laser pulses, a distinction being necessary between cleaning pulses 6 and analysis pulses 7. A particular piece 5 of raw material is subjected first in each case to cleaning pulses 6 and subsequently in each case to analysis pulses 7. The control unit ensures that the analysis pulses are directed at those locations on the raw-material pieces 5 at which removal of material by cleaning pulses 6 has taken place beforehand. For this purpose, the control unit takes account of the situation of the raw-material pieces 5, the speed of the transport means 1, and the guidance of the cleaning pulses 6 and of the analysis pulses 7.

[0057] Correspondingly, a meaningful determination of the composition of the raw-material pieces 5 is possible with the aid of the analysis pulses 7. The analysis pulses 7 coming from the laser 3 convert parts of the piece 5 of raw material into the plasma state; the compositional analysis takes place by means of a spectrometer, not shown here, which captures the light emitted by the plasma. The process is therefore one of LIBS (laser-induced breakdown spectroscopy); the respective composition of a piece 5 of raw material can be determined from the light captured by the spectrometer. Subsequently, a control unit, again not shown here, ensures that the particular piece of raw material analyzed is assigned to the correct collecting container A, B, C, R.