How to extract array from json on Angular

I'm not sure I understand you, but I'll try.

is it the right why to define my object?

It should be:

export class ImpiantoModel {
  nomeImpianto: string;
  descrImpianto: string;
  posizione: string;
  dati_status: string;
  unita_misura: string;
  vel_attuale: number;
  vel: Array<string>;
  orario: Array<string>;
}

(But I have to confess, I don't know why model and not an interface)

How can I use the array "vel" and "orario"?

What do you mean?

How can I print (access) the array "vel" of machine with "nomeImpianto" = "MFL1"

const thisContainsTheDataFromVel = whereYourDataIsStored['ImpiantiProva'].find((item) => { item['nomeImpianto'] === 'MFL1'})['vel'];

and how can I copy the array "vel" on new array?

UPDATE after reading your comment under this answer:

I took code from your example and added what you are missing. I made it so it can be more reusable (it can be enhanced even more, but I hope you understand the code and do what you need).

copyArray(data, targetValue) {
  const mfl1Data = data.find((item) => item['nomeImpianto'] === targetValue);

  if (mfl1Data) {
    return mfl1Data.vel;
  }

  return [];
}

getdata2() {
    this.http.get<ImpiantoModel[]>(this.myUrl)
      .subscribe(
        data => {
          this.variableToStoreIn = this.copyArray(data, 'MFL1');
          data.forEach(item => {
            this.sub$.next(item);
          });
        });

    return this.sub$;
  }

CopyArray finds the data and returns it. If you don't want it like this, but just set a value of some property to the value of vel array then you can change it to:

copyArray(data) {
      const mfl1Data = data.find((item) => item['nomeImpianto'] === targetValue);

      if (mfl1Data) {
        this.yourVariable = mfl1Data.vel;
      }
    }

If this answer is sufficient, please consider to mark it as the best answer, thank you.

According to your model classes, your JSON is wrong. You should have something like this:

{ "ImpiantiProva": [
        {
        "nomeImpianto":"MFL1",
        "descrImpianto":"Multifilo 1",
        "posizione":"Place1",
        "dati_status": "true",
        "unita_misura": "m/s",
        "vel_attuale": 11.5,

        "vel": [
            {
                "vel": 24.5 
            },
             {
                "vel": 13.6
            }
            ...
        ],
        "orario": [
            {
                "orario": "17.05"   
            },
             {
                "orario": "17.06"
            }
            ...
        ]
        }
    ]
}

Your model expects ImpiantoModel.vel and ImpiantoModel.orario to be arrays of objects. In your JSON response one is an array of numbers and the other of strings.

An if you want to use it in an HTML template, considering that you have a class attribute in your .ts file like this:

private impiantoModels: ImpiantoModel[];

You could do something like this inside your .html template:

<div *ngFor="let impModel of impiantoModels">
    ...
    <div *ngFor="let v of impModel.vel">
        <p>{{v.vel}}</p>
    </div>

    <div *ngFor="let o of impModel.orario">
        <p>{{o.orario}}</p>
    </div>
</div>