The short answer
On a cantilever hydraulic uncoiler, the mandrel is built from a hollow main shaft, a draw bar running through its center, wedge guide plates, sliding blocks and curved segments. A hydraulic cylinder at the rear moves the draw bar along the shaft axis. The sliding blocks travel along 1:3 wedges, so the segments move outward to grip the inside of the coil, or inward so the coil can be loaded and removed. On InGen MillTek hydraulic uncoilers the expanding cylinder has a 90 mm stroke, which gives a basic diameter change of about 60 mm (a reference value that depends on model and configuration and is confirmed in the technical proposal).
In normal production the uncoiler does not drive the strip. Pinch rolls or the accumulator feeder downstream pull the strip, the uncoiler pays off passively, and the brake system keeps back tension on the coil.
Main parts of the mandrel
Taking a 10 t class single-head hydraulic uncoiler as the example (other capacity classes work the same way; sizes and part counts vary with configuration):
- Housing and hollow main shaft: a welded housing carries the shaft on a double-row tapered roller bearing at each end. These bearings take the coil weight and the payoff loads.
- Draw bar: runs through the center of the hollow shaft and turns with it.
- Wedge guide plates and sliding blocks: guide plates with sloped dovetail slots are welded on four sides of the shaft nose, and the sliding blocks travel along these slopes.
- Segments: curved plates, usually four, mounted on the sliding blocks. Together they form the mandrel surface the coil sits on.
- Expanding cylinder: mounted at the rear. The cylinder body stays still while the draw bar rotates.
- Brake: a brake disc on the main shaft with disc brake calipers provides back tension during payoff.
The 1:3 wedge: where the 60 mm comes from
A 1:3 slope (about 18.43 degrees) means that every 3 mm of axial travel moves a segment 1 mm outward. Segments on opposite sides move at the same time, so the diameter change is ΔD ≈ 2 × s ÷ 3, where s is the cylinder stroke.
Worked example (for illustration only): with s = 90 mm, each segment moves 30 mm radially and the diameter changes by about 60 mm. This matches basic ranges commonly shown on InGen MillTek drawings, such as Φ460–520 mm or Φ470–530 mm. The range for your machine is set in the technical proposal.
Because the slope is shallow, the axial force from the cylinder becomes a larger radial force, about three times the axial force if friction is ignored. All segments move out together, so the inner wraps of the coil are gripped evenly.
Why no rotary cylinder is needed
The mandrel turns during payoff, but the expanding action is hydraulic. InGen MillTek uses a standard cylinder connected through bearings: the cylinder body is fixed to the frame and does not turn, and the piston rod is linked to the rotating draw bar through bearings inside the cylinder. The cylinder only pushes and pulls, the bearings take care of the rotation, and no purchased rotary cylinder is required.
Matching the coil inside diameter (ID)
The basic diameter change is only about 60 mm, so one mandrel covers a limited spread of coil IDs. Tell us every ID you actually receive before the machine is specified.
- The standard coil ID is 508 mm (20 in).
- If your coils come with both 500 mm and 508 mm IDs, the expanding range must cover both sizes.
- For 610 mm (24 in) coils, spacer blocks or extra guide plates are added to the basic range. Drawings often show this as a staged range, for example 460–520 mm, extended to 610 mm with spacers.
- Larger IDs, such as 750 mm, are non-standard and need a separate design.
Brake and drag: why the coil needs back tension
Because the uncoiler pays off passively, an unrestrained coil would keep turning when the line slows down, and the outer wraps would loosen. The brake system prevents this. The brake holds the mandrel while a coil is being loaded. During payoff the operator switches to drag, which has a strong and a weak setting and keeps steady back tension on the strip.
Most current InGen MillTek hydraulic uncoilers use horizontal pneumatic disc brakes acting on the brake disc of the main shaft. The brake type depends on configuration and is stated in the technical proposal.
Fixed guide rollers on box-housing single-head uncoilers
On the machine side, something must hold the end face of the coil so the wraps do not spread sideways. Older designs used a large four-arm plate fixed to the shaft that turned with the coil. Current InGen MillTek box-housing single-head hydraulic uncoilers of the 10 t class and above use four guide rollers fixed to the front panel of the housing, arranged in an X when seen from the end. They do not turn with the mandrel, which removes the hazard of a large plate spinning with the coil. The 5 t class single-head uncoiler also has a box housing. On smaller single-head machines and on double-head uncoilers, the coil guide arrangement (the number and layout of rollers, or a guide plate) depends on the model and the proposal.
Options: powered payoff, hold-down, support arm, side shift, coil car
- Powered payoff: a gear motor drives the shaft through a clutch and a chain. Engage the clutch and run the motor forward or reverse to find and thread the strip head; disengage it for normal passive payoff.
- Hold-down arm: presses on the outer wrap so the coil does not loosen. A powered hold-down roll can turn the coil slowly to bring the strip head out.
- Outboard support arm: supports the free end of the cantilever shaft; it is fitted for strip widths over 800 mm and coil weights in the 15 t class.
- Side-shift base: a hydraulic cylinder moves the whole uncoiler sideways to line the coil up with the line (option for single-head machines).
- Hydraulic coil car: loads coils onto a single-head uncoiler. A pit-type car is standard; a floor-mounted car can be built where the workshop floor cannot take a pit.
What to include in your inquiry
Uncoilers are configured to the coil weight, strip width and options you need, and are quoted individually. The more of the following you can share, the more accurate the proposal; mark anything not yet decided as open.
- Maximum coil weight
- Coil ID (every size you use) and maximum coil OD
- Strip width and thickness range
- Material grade with yield and tensile strength
- Single-head or double-head, and options such as powered payoff, hold-down, support arm and coil car
- For a replacement or an add-on: strip center height of the existing line and feed direction (left-hand or right-hand)
- Local supply voltage and frequency
Frequently asked questions
Prepared by the InGen Engineering Team. All values are reference values; they depend on model and configuration and are confirmed in the technical proposal and technical agreement.
- How much does the mandrel expand? About 60 mm on diameter as the basic range (a reference value that varies with model and configuration), for example Φ460–520 mm. Coils with a 610 mm ID need spacer blocks or extra guide plates.
- Does the uncoiler drive the strip? Not in normal production. The strip is pulled by downstream pinch rolls or the accumulator feeder. A powered payoff unit is available as an option for threading.
- Does the expanding cylinder rotate with the mandrel? No. The cylinder body is fixed, and bearings inside it connect the piston rod to the rotating draw bar.
- What is the difference between brake and drag? The brake holds the mandrel while a coil is loaded; strong or weak drag keeps back tension on the strip during payoff.
- Can I buy just an uncoiler for my existing line? Yes. Uncoilers can be supplied as single machines. Tell us the strip center height and feed direction of your line, and whether you need a hydraulic unit and controls.