Special handling materials: Size reduction of soft, fusible solids is often done on steam-heated rolls and roll crushers. Which of the following is typically processed this way to avoid gumming or smearing?

Introduction / Context:
Some materials soften, smear, or gum up conventional grinders. For such thermoplastic or fusible materials, controlled heating (or cooling) plus specific milling arrangements are used to obtain a manageable fracture behavior and avoid clogging screens.

Given Data / Assumptions:

• Steam-heated rolls provide a controlled temperature surface.
• Goal is to nip and flatten brittle–plastic solids without smearing.
• Target material is soft and fusible.

Concept / Approach:
Waxes and certain resins soften and smear at modest temperatures. Using heated rolls or roll crushers allows forming thin, cooled flakes or controlled-size particles after pressing. Waxes are classic examples: heating maintains a workable consistency and prevents clogging; subsequent cooling and flaking give a granular product.

Step-by-Step Solution:
Identify fusible candidates: waxes and some thermoplastic resins.Heated rolls mitigate smearing and allow controlled thickness sheeting then breaking.Among options, waxes are the textbook case for steam-heated roll processing.

Verification / Alternative check:
Process handbooks cite roll/crusher handling of waxes, bitumen-like materials, and certain resins with heat control to avoid agglomeration.

Why Other Options Are Wrong:

• Resins: some are handled similarly, but waxes are the clearer canonical example.
• Gums: typically handled in solution; dry grinding is problematic.
• Hard rubber and quartz: require different, more robust comminution methods.

Common Pitfalls:
Attempting to grind waxes in high-energy mills at room temperature, leading to dangerous heat build-up and smeared screens.

Final Answer:
Waxes