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Wrapper roll (also written as wrapper roller) is the core auxiliary component of hot & cold strip coilers in steel rolling lines, widely installed around the coiler mandrel. It is a hydraulic pressure roller set specially designed to assist the coiling of steel strip, aluminum strip and other metal strips.

Wrapper Roll

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Main Structure & Layout

A standard underground coiler is equipped with 3 wrapper rolls (WR1, WR2, WR3) arranged circumferentially around the mandrel in sequence from the strip feeding direction:
  • WR1 & WR2: Close to each other, bear the main bending and wrapping task for the strip head;
  • WR3: Relatively far from WR2, mainly provides auxiliary guiding and eliminates strip elastic rebound.
Each wrapper roll assembly consists of roll barrel, bearing housing, swing arm, hydraulic cylinder, position sensor and pressure detection unit. Most modern models adopt hydraulic servo control with AJC (Auto Step Control / Auto Jump Control) system.

Core Working Functions

  1. Bend and wrap strip head
     
    When the strip head comes out from pinch rolls, wrapper rolls press the strip tightly against the expanding mandrel, forcing the flat strip to bend into a circular shape and complete the initial coil forming, which solves the problem that thin metal strip cannot wind around the mandrel by itself due to elastic recovery.
  2. Stabilize coil shape during coiling
     
    Continuous contact pressure maintains uniform strip tension, prevents loose coil, edge warping and irregular coil outer diameter, improving the roundness of finished steel coils.
  3. AJC automatic stepping protection
     
    As the coil diameter increases layer by layer, the AJC system automatically lifts the wrapper roll for a short distance when the strip head passes, avoiding hard impact between strip head and roll surface, effectively reducing surface indentation and scratch defects on strip products.
  4. Supplementary tension support
     
    Cooperate with pinch rolls to maintain stable strip tension in the coiling area, guarantee smooth high-speed coiling for hot rolling, pickling, galvanizing and continuous annealing lines.

Service Conditions & Material Requirements

Wrapper rolls operate under harsh comprehensive loads: high temperature (hot rolling up to 700–900℃), continuous heavy pressure, frequent impact and high-speed friction with metal strips.
  • Roll barrel base: Forged alloy steel or high-chromium cast steel;
  • Surface treatment: Hardfacing overlay, thermal spray or laser cladding to enhance wear resistance, heat resistance and anti-stripping performance, extending service life sharply.

Application Scope

  • Hot strip rolling underground coiler;
  • Cold rolling mill recoiler;
  • Continuous processing lines: pickling, galvanizing, color coating, slitting, tension leveling lines;
  • Non-ferrous metal processing: aluminum strip, copper foil coiling equipment.