WE CLAIM:
1. A cleaning plant for cleaning rolled metal strips provided with a superficial layer
of oxide, the plant comprising
- unwinding means (1) for unwinding at least one coil of rolled strip;
- pickling means (5) for pickling said rolled strip;
- measuring means (4, 4') for measuring the thickness of the superficial layer of oxide, arranged between said unwinding means (1) and said pickling means (5); characterized in that said measuring means (4, 4') consist of at least one laser source cooperating with a fiber optic spectrometer, defining a LIBS system (Laser Induced Breakdown Spectroscopy) also adapted to analyze the composition of the oxide and the concentration of the constituents of the oxide.

2. A cleaning plant according to claim 1, wherein at least one scale breaking device (3) is provided between the unwinding means (1) and the pickling means (5).
3. A cleaning plant according to claim 2, wherein said measuring means (4', 4) are arranged between the at least one scale breaking device (3) and the pickling means (5) or between the unwinding means (1) and the at least one scale breaking device (3).

4. A cleaning plant according to claim 2, wherein there are provided first measuring means (4'), arranged between the unwinding means (1) and the at least one scale breaking device (3), and second measuring means (4) arranged between the at least one scale breaking device (3) and the pickling means (5).
5. A cleaning plant according to any one of claims 2 to 4, wherein there are provided weight sensors (2) to weigh the amount of scales detached from the strip by means of the at least one scale breaking device (3), and preferably there are provided suction devices, possibly aided by brushing devices, to collect the oxide detached so as to weigh it.
6. A cleaning plant according to any one of the preceding claims, wherein, in each area of the plant where there are provided said measuring means (4', 4), at least one measuring means (4', 4) is arranged above the rolled strip feed line and at least one further measuring means (4', 4) is arranged below the rolled strip feed line.

7. A cleaning plant according to any one of the preceding claims, wherein there is provided a processing unit (7) for processing measurement data originating from said measuring means (4) and adjusting operational parameters of said pickling means (5).
8. A cleaning plant according to any one of the preceding claims, wherein there are provided optical detection means (6) for detecting the strip cleaning level, arranged downstream of said pickling means (5).
9. A cleaning plant according to claim 8, wherein said processing unit (7) is configured to process strip cleaning level data originating from said optical detection means (6), and possibly further adjust said operational parameters.

10. A cleaning plant according to any one of the preceding claims, wherein said pickling means (5) comprise at least one chemical pickling tank, or dry pickling systems, or dry pickling systems followed by at least one chemical pickling tank, or first dry pickling systems followed by second dry pickling systems.
11. A cleaning plant according to claim 10, wherein said dry pickling systems are laser pickling devices and/or mechanical pickling devices, preferably rotating abrasive brushes.
12. A cleaning plant according to any one of the preceding claims, wherein said fiber optic spectrometer is adapted to measure the presence of oxygen while the laser of said laser source penetrates the rolled strip towards the non-oxidized base material.
13. A cleaning plant according to claim 12, wherein there is provided a software, installed in the LIBS system and adapted to calculate the thickness of the superficial oxide layer, defined by the depth of the layer of eroded material, by means of the laser source, at the erosion time t in which said fiber optic spectrometer starts to detect the absence of oxygen, the erosion rate by means of the laser being known.
14. A method for cleaning metal strips, performable by means of a plant according to any one of the preceding claims, comprising the following steps:

a) unwinding at least one coil of rolled strip by means of the unwinding means (1);
b) measuring the thickness of the superficial layer of oxide of the rolled strip by means of the measuring means (4, 4');

c) pickling said rolled strip by means of the pickling means (5);
wherein in step b) the measurement of the thickness of the superficial layer of
oxide is performed, together with an analysis of the composition of the oxide and
of the concentration of the constituents of the oxide, by means of at least one laser
source associated with a fiber optic spectrometer, defining a LIBS system (Laser
Induced Breakdown Spectroscopy);
and wherein said fiber optic spectrometer measures the presence of oxygen while
the laser of said laser source penetrates the rolled strip towards the non-oxidized
base material, and the thickness of the superficial layer of oxide is equal to the
depth excavated in the rolled strip, by means of the laser source, when said
spectrometer will detect the absence of oxygen.
15. A method according to claim 14, wherein, when there are provided
- at least one scale breaking device (3) between the unwinding means (1) and the pickling means (5);
- first measuring means (4'), arranged between the unwinding means (1) and the at least one scale breaking device (3);
- second measuring means (4) arranged between the at least one scale breaking device (3) and the pickling means (5);
- optical detection means (6) for detecting the strip cleaning level, arranged downstream of said pickling means (5);
- and a processing unit (7) for processing measurement data, originating from said first measuring means (4') and said second measuring means (4), and strip cleaning level data, originating from said optical detection means (6);
the method, after the step a), provides of:
- measuring the thickness of the superficial layer of oxide of the rolled strip by means of the first measuring means (4');
- processing, by means of the processing unit (7), measurement data originating from said first measuring means (4'), and adjusting operational parameters of said at least one scale breaking device (3);
- descaling the rolled strip by means of said at least one scale breaking device (3);
- measuring the thickness of the superficial layer of oxide of the rolled strip by means of the second measuring means (4);

- processing, by means of the processing unit (7), measurement data originating from said second measuring means (4), and adjusting operational parameters of said pickling means (5);
- pickling said rolled strip by means of the pickling means (5);
- detecting the rolled strip cleaning level by means of the optical detection means
(6);
- processing, by means of the processing unit (7), strip cleaning level data,
originating from said optical detection means (6), and possibly further adjusting
said operational parameters.
16. A method according to claim 14 or 15, wherein the measurement of the thickness of the superficial layer of oxide is performed in 15s-=-20s.