The short answer
As a general rule, choose a horizontal (rotating-disc) spiral accumulator for narrower, thinner strip and moderate storage needs; it is compact and needs less floor space. Choose a floor-type spiral accumulator for wider or thicker strip, or when you need more storage. There is no fixed dividing line that fits every project: with the same strip width, a different material strength, line speed or coil-change time can lead to a different answer. At InGen MillTek, our engineers evaluate strip width, thickness, material strength, line speed and required storage length, and then specify the type and diameter in the technical proposal.
In our catalogue, horizontal accumulators range from 2 to 6.5 m in diameter and floor-type accumulators from 4 to 20 m. The actual diameter depends on strip width, thickness, material and required storage, and the final configuration is set in the project's technical proposal.
The key difference: how they are driven
Both designs store strip by winding it on edge into a spiral. The difference is what turns and what provides the power:
- Base: on a horizontal accumulator the whole disc rotates and the outer ring is fixed. On a floor-type accumulator the base does not rotate.
- Drive: a horizontal accumulator uses one main motor that turns the disc through a reducer and a large open gear. A floor-type accumulator drives its outer horizontal rollers in groups; the usual design has one geared motor per group, with one group left undriven, and the inner horizontal rollers are idle. For heavy, thick strip, a floor-type unit can use one large motor with a central drive instead.
- Strip path: on both, strip enters tangentially at the outer ring and leaves near the center. On a horizontal accumulator, the strip makes a U-turn at a ring of upright rolls into the inner ring and is pulled up through an inclined exit roller at the center.
- Role of the feeder: on a horizontal accumulator, the feeder pushes strip onto the rotating disc. On a floor-type accumulator, the feeder mainly threads the strip; once enough loops are formed, the pinch rolls open and the driven outer rollers pull the strip in.
- Winding method: a horizontal accumulator already works on the outside-in, U-turn principle, so it is not divided into fixed and variable accumulators. A floor-type accumulator is built as either a fixed accumulator or a variable accumulator.
- Speed control: on both designs, storage and feeding use variable-frequency drives (VFDs).
- Footprint: a horizontal accumulator is compact. A floor-type accumulator has a larger diameter and needs extra room for the outer guide roller frames.
Why strip thickness and material strength change the choice
The strip is wound on edge and turns near the inner ring. At the same bending radius, thicker strip is strained more at its surfaces, and if the radius is too small the strip takes a permanent bend. So thicker strip needs a larger winding diameter. For high-strength strip, a larger diameter is also usually chosen in practice: the higher the strength, the greater the bending force and springback, and the heavier the load on the rollers and drive. Our engineers confirm this for each material. That is why selection usually starts by fixing the diameter from the maximum strip thickness and the material strength, and then checks strip width and storage length.
Bending also explains the two winding methods of the floor-type accumulator. In a variable accumulator, the strip makes a 180° U-turn with a small radius, where thicker strip would be bent severely and harder strip needs more bending force and springs back more, putting a heavier load on the rollers and drive, so variable accumulators are used for thinner strip, and thicker or harder strip generally goes to a fixed accumulator. In a fixed accumulator, the strip continues in its running direction into the inner ring without a U-turn reversal, so it suits all thicknesses.
Floor-type winding methods: fixed accumulator and variable accumulator
The choice between a fixed accumulator and a variable accumulator depends on strip thickness and material strength, and our engineers set the limit for each project. Note that the storage comparison below is theoretical; real strip shape makes the usable storage somewhat lower.
- Variable accumulator: the strip is stored in the outer loops, makes a 180° U-turn into the inner loops and is pulled out by the mill. The number of loops changes as the accumulator fills and empties, almost all of the stored strip can be used, and storage is large. Not suitable for thicker or harder strip.
- Fixed accumulator: after the first threading, the total number of loops stays the same, and the strip moves into the inner ring in its running direction before being pulled out. Usable storage is smaller than a variable accumulator of the same diameter, but it suits all strip thicknesses.
Four selection steps
Do not start by picking a diameter. Work through these steps in order:
- Step 1, type: from strip width, thickness, material strength and storage requirement, decide between horizontal and floor type; for floor type, also decide between a fixed accumulator and a variable accumulator.
- Step 2, diameter: set the diameter from the maximum strip thickness and the material strength.
- Step 3, width check: confirm that the chosen diameter takes the maximum strip width.
- Step 4, storage check: required storage length ≥ mill line speed × time for one complete coil change and joint × 1.2 to 1.5. Also check the refill: net refill speed = feeder speed − mill speed, and refilling must finish before the next coil change.
Plan the floor space early
On both designs, strip enters at the outer ring along a tangent and leaves near the center. As a result, the center line of the tube mill is usually offset sideways from the center line of the entry equipment. Include this offset when you plan the workshop width. The offset depends on the accumulator type, its diameter and how the exit line is arranged, and is shown on the project layout drawing.
The accumulator is also where the strip can change direction. Besides the usual straight, parallel layout, an L-shaped or U-shaped layout can be used when the workshop is not long enough. Our engineers prepare the layout drawing from your workshop conditions.
Foundation requirements differ between the two types. Build the foundation to the foundation drawing InGen MillTek provides; when the drawing is delivered is set in the contract.
What to include in your inquiry
Spiral accumulators are configured to order and quoted separately. To decide between horizontal and floor type and choose the diameter, please send as much of the following as you can:
- Strip width and thickness range (maximum and most common)
- Material grade, and yield and tensile strength
- Tube mill model, maximum and normal line speed
- Joining method (integrated shear and manual welder, semi-automatic or fully automatic shear and welder) and the approximate coil-change time
- Floor length and width available, and entry and exit directions
- Mill pass-line (center) height
- Local voltage and frequency
- New line, or an accumulator to add to or replace on an existing mill
Frequently asked questions
- Is a horizontal accumulator also divided into fixed and variable accumulators? No. A horizontal accumulator already works on the outside-in, U-turn principle. Fixed and variable accumulators are the two winding methods of the floor-type accumulator.
- Is there a width or thickness above which a floor-type accumulator is required? Strip wider or thicker than the range covered by the horizontal series in our catalogue (up to 6.5 m in diameter) generally goes to a floor-type unit. Within the range both types can cover, there is no fixed value for every project: strip width, thickness, material strength, line speed and storage length together decide the type, and our engineers state it in the proposal.
- Does a floor-type accumulator always store more strip than a horizontal one? Floor-type units cover larger diameters and suit large storage needs, but usable storage also depends on diameter, strip thickness and winding method. For example, a fixed accumulator stores less usable strip than a variable accumulator of the same diameter. Always check the storage length.
- Are the controls different? Both use VFD speed control for storage and feeding; a floor-type unit drives several groups of outer rollers at the same time. Motors and controls are configured for your local grid voltage and frequency.
About this article
Prepared by the InGen Engineering Team. This is a general technical guide, not a specification or performance guarantee for any project. The final type, diameter and parameters are set in the project's technical proposal and technical agreement.