Technology
Bridge Conveyor and Web Handling Systems in Corrugating Lines
Technical guide to bridge conveyors and web handling in corrugating lines, covering tension control, storage capacity, and impact on board quality.
The bridge conveyor (also called the incline conveyor or overhead bridge) is a critical but often overlooked section of a corrugating line. It transports the single-face web from the single facer to the double backer while providing buffer storage and tension control.
Bridge Conveyor Function
The bridge serves three essential purposes
1. Transport — Moves single-face web from single facer to double backer
2. Buffer Storage — Accumulates web when double backer runs slower than single facer
3. Stabilization — Allows moisture equilibrium before second liner bonding
Without adequate bridge storage, speed mismatches between single facer and double backer cause frequent web breaks and production stops.
Bridge Configurations
Incline Bridge (Standard)
Single-face web travels upward at 15-30 degree angle
Gravity-assisted tension control
Storage capacity: 30-60 meters of web
Most common on 3-ply and 5-ply lines
Lower cost, proven design
Horizontal Bridge
Web travels horizontally between facer and backer
Used when building height is limited
Requires more floor space
Common in retrofit installations
Multi-Level Bridge (5-Ply and 7-Ply)
Multiple bridge sections for complex line layouts
Separate bridges for each single facer section
Web combining sections for multi-wall board assembly
Higher storage capacity for multi-facer coordination
Web Storage and Accumulation
The bridge must store enough web to absorb speed differences
Single facer may run 5-15% faster than double backer during normal operation
Storage needed for order changes, splice events, and brief stops
Insufficient storage: Web breaks, production interruptions
Excessive storage: Board moisture changes, adhesive setting issues
Typical Storage Capacity
Entry-level lines: 20-40 meters
Standard lines: 40-80 meters
High-speed lines: 60-120 meters
Tension Control
Proper web tension through the bridge is essential
Too low: Sagging web, misalignment, wrinkles at double backer entry
Too high: Web breaks, stretched flutes, delamination risk
Tension controlled by: Dancer rolls, pneumatic brakes, speed differential
Electronic tension control on high-speed lines
Impact on Board Quality
Moisture Equilibrium
Single-face web has moisture gradient after single facer heating
Bridge transit time allows moisture redistribution
Typical transit: 15-60 seconds depending on line speed and bridge length
Too short: Moisture imbalance causes warping after double backer
Too long: Adhesive may begin setting before double backer application
Adhesive Setting
Single-face adhesive begins gelatinizing during bridge transit
Gel temperature must be reached before double backer for proper bond
Bridge length must match adhesive setting speed and line speed
Instant-setting adhesives (Xuegong) allow shorter bridges at higher speeds
Web Alignment
Guide rolls and edge sensors keep web centered
Misalignment at double backer entry causes edge defects
Regular inspection of guide roll condition and sensor calibration
Common Problems
Web Breaks in Bridge
Insufficient storage during speed mismatch
Excessive tension from brake misadjustment
Solution: Increase storage capacity, recalibrate tension control
Board Warping
Insufficient bridge transit time for moisture equilibrium
Solution: Increase bridge length or reduce line speed
Edge Curling
Uneven tension across web width
Solution: Check guide rolls, edge sensors, roll stand alignment
Excessive Dust
Normal at high speeds — requires dust extraction
Accumulated dust affects sensors and web tracking
Maintenance
Daily: Check web tracking, inspect belt/chain condition, clean sensors
Weekly: Lubricate bearings, check dancer roll operation, inspect guide rolls
Monthly: Calibrate tension sensors, check drive motor condition, inspect structural integrity
Bridge Design for Boiler-Free Lines
Xuegong boiler-free lines with instant-setting adhesive can operate with optimized bridge lengths
Faster adhesive setting allows shorter transit times
Higher single facer speeds (up to 300 m/min) require adequate storage
Lower operating temperatures reduce moisture gradient severity
Contact Xuegong for corrugating line bridge configuration recommendations.
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