Mechanical conveyors — “scrapers” division:\nWhich of the following does NOT belong to the scraper-type conveyors group?

Introduction / Context:
Scraper-type conveyors move bulk solids by dragging or scraping them along a trough using flights or chains. Knowing which common machines fall into this category helps in shortlisting equipment for sticky or granular materials, especially when horizontal or inclined transport is required inside process plants.

Given Data / Assumptions:

• “Scraper” implies flights/drag elements contacting solids in a trough.
• We compare flight/drag devices against elevators and screw/ribbon devices.

Concept / Approach:
Flight and drag conveyors employ scrapers attached to chains to pull material along; these are archetypal scraper conveyors. Ribbon (helicoid) conveyors are a screw-conveyor variant and are not scraper-chain devices. Bucket elevators are vertical lifting machines using buckets on belts or chains and are not classified as scraper conveyors. Therefore, among the choices, the clear non-scraper is the bucket elevator.

Step-by-Step Solution:

Verification / Alternative check:
Standard equipment taxonomies separate scraper/drag conveyors from elevators and screw conveyors in vendor catalogs and handbooks.

Why Other Options Are Wrong:

• Flight conveyor: classic scraper.
• Drag conveyor: classic scraper (chain-drag).
• Ribbon conveyor: not a scraper but also not an elevator; still not the best answer vs. elevator. The bucket elevator is unequivocally non-scraper.
• Scraper chain in trough: definitionally a scraper.

Common Pitfalls:
Confusing screw and scraper mechanisms; screws convey by helical rotation rather than dragging with flights.

Final Answer:
Bucket elevator