Tension levelers are one of several forms of shaping equipment that can be used on metal roll and coil feeding, cutting or slitting lines. The main purpose of a tension leveler is to help either preserve or improve the uniformity and sizing of the coil material as it proceeds through a feeding, slitting or cut-to-length line.
The mechanism for this involves stressing the metal sheet through a series of rollers above and below the material, allowing the material to relieve stress and achieve shape stability along with tighter tolerances.
Tension Levelers are Not Miracle Workers
Garbage In, Garbage Out is an old saying that applies well to tension levelers as well as the entire metal coil slitting or CTL line. If the mill provides low quality coil with significant edge variances, then the tension leveler might be able to get it close to a good shape and uniformity.
The material will not be able to make the transformation into high quality, tight tolerance coil production simply because of a tension leveler. Shaping equipment, in general, will only be able to improve, but not fully repair low quality input stock coils.
Tension Levelers Need Frequent Preventive Maintenance
With multiple hardened rollers, repetitive adjusting, high vibration and high stress service, tension levelers will be a focus of the maintenance department. Keep the rolling surfaces clean.
Have the rollers reground and hardened at least once per year for light duty operations. The heavy duty toll operations could require PM on tension levelers as often as every 10 to 30 days if the production demands high quality surface finishes.
Tension Levelers Use in CTL (Cut-to-Length)
High-speed CTL lines can have the tension leveler after the shear such as is common in Europe, or before the shear for the North American lines. A leveler after the shear will need to start and stop.
The North American preference for running the leveler continuously keeps it running more smoothly and with greater consistency than the start and stop system of Europe.
Using Multiple Tension Levelers for Coil Lines
There are practical limits for leveling operation of about four times the minimum or maximum material gauge. Operators will often choose to install two tension levelers for achieving higher modification levels without unduly stressing either the leveler machine, or the coil material.
There can be a big and small leveler working in tandem.
Levelers use the actual yield strength, as opposed to the nominal yield strength. With two levelers at work, the practical limit is about 6 times maximum or minimum capability.
There is also a debate about where to place edge trim slitters relative to the tension leveler in CTL lines. Some claim the it should be after levelers for accurate width control, while others offer that the edge slitter will cause turn-down and needs to be before the leveling operation.
If there is any concern that turn-down is a possibility, a leveler after the edge slitting operation will resolve it.
Tension Assisted Leveling Lines for Heavy Gauge Material
Heavier gauge material can be run with tension assisted leveling lines more easily than plain tension levelers. These systems provide large diameter pinch rollers that put the coil under increased tensionfor passage through the levelers.
This form of processing can also be tied with a temper mill with rollers for producing hot-rolled plate coil.
Tension levelers are one of the keys to keeping the entire metal roll and coil slitting operation running smoothly. Maintaining the levelers frequently, using computer adjustment controls, and locating them for continuous operation will keep them running smoothly.