Electric Furnace · Cover Rotating Cylinder

Lift — Then Swing.
The Two-Step Door.

The cover lifting cylinder raises the furnace roof. But a raised cover still blocks the furnace opening from above — the charging bucket cannot swing in with the cover hovering overhead. The cover rotating cylinder solves this: it swings the elevated cover horizontally on a pivot arm, rotating it 90–120° clear of the furnace opening. The bucket charges, the cover swings back, and the cover lowers. Two cylinders, two motions, one seamless door sequence.

484 KN

Thrust

210mm

Bore

125mm

Rod (59.5%)

90–120°

Swing Arc

The Two-Step Cover Opening Sequence

The EAF cover cannot simply swing aside from its seated position — it must first be lifted clear of the furnace rim, then rotated. Two cylinders from the electric furnace cylinder family coordinate this two-step motion:

Lift — Cover Lifting Cylinder (#14)

The 580 mm bore cover lifting cylinder raises the cover 200–500 mm vertically — enough to clear the furnace rim seal and any scrap that protrudes above the rim. The cover is now elevated but still directly above the furnace opening. Duration: 10–20 seconds.

Swing — Cover Rotating Cylinder (#17)

This cylinder extends, rotating the elevated cover on its pivot arm 90–120° to the side. The furnace opening is now completely clear — the charging bucket can swing in from above and dump scrap directly into the furnace shell. Duration: 15–30 seconds.

The return sequence reverses: the rotating cylinder retracts (swinging the cover back over the furnace), then the lifting cylinder lowers the cover onto the furnace rim. The total open-charge-close cycle takes 60–90 seconds — every second of which the furnace is losing heat through the open top. Fast, reliable cover handling directly reduces energy cost per heat.

Electric Furnace Cover Rotating Cylinder

Technical Specifications

Parameter	Value
Product	Electric Furnace Cover Rotating Cylinder
Function	Swing the elevated cover horizontally aside
Bore Diameter	210 mm
Rod Diameter	125 mm
Working Pressure	14 MPa
Maximum Thrust	484 KN
Rotation Arc	90–120° (depends on pivot arm geometry)
Certification	ISO 9001 · 100% hydrostatic tested

59.5% Rod/Bore Ratio — Why This Cylinder Is Different from #14 and #16

Cover rotating cylinder standard rod ratio

The cover lifting cylinder (#14) has a rod that fills 96.6% of its bore. The tipping cylinder (#16) has 93.8%. Both needed massive rods to serve as structural columns — holding the furnace cover or the furnace body against gravity. The cover rotating cylinder's rod is just 59.5% of the bore — a standard hydraulic ratio.

The reason is simple: this cylinder does not carry the cover's weight. The cover lifting cylinder holds the weight — the cover rotating cylinder only swings the already-elevated, already-supported cover sideways. The horizontal swinging force is much lower than the vertical holding force: the cover's weight acts downward (carried by #14); the rotating cylinder only overcomes the inertia and friction of the horizontal swing motion.

This means the cover rotating cylinder is a conventional hydraulic cylinder — standard bore-to-rod proportions, standard double-acting operation, standard seal configuration. It does not need the structural-column rod design of its EAF neighbours. The engineering is still demanding (heat, scale, fume), but the mechanical duty is less extreme than the weight-bearing cylinders.

It Is Not Just a Cover — Everything Connected to It Swings Too

The furnace cover is not an isolated lid. It is an integrated assembly carrying several heavy, connected systems — all of which must swing with the cover when the rotating cylinder operates.

Graphite electrodes (3 per furnace)

Each electrode is 300–750 mm in diameter, 3–6 metres long, and weighs 1–5 tonnes. They pass through holes in the cover and are supported by electrode arms mounted above the cover. When the cover swings, the electrodes, electrode arms, and electrode clamps all swing with it — adding significant mass and inertia to the rotating system.

Water-cooled power cables

The high-current cables (carrying 30,000–80,000 amps) connect the electrodes to the transformer. These cables are heavy, stiff, and must flex through the swing arc without kinking or disconnecting. The cable routing must accommodate 90–120° of cover rotation — typically through a cable festoon or a slack loop that unfurls as the cover swings.

Fume extraction duct

The fourth hole in the cover connects to the fume extraction system. When the cover swings, the duct must disconnect (via a slip joint or break-away flange) and reconnect when the cover returns. The rotating cylinder's final positioning accuracy determines whether the duct re-seats properly — a misaligned cover leaks fume into the melt shop.

Refractory-lined cover (20–80 tonnes)

The cover itself weighs 20–80 tonnes including refractory bricks on its underside. This mass, combined with the electrode assembly mass, creates a large rotating inertia. The cylinder must accelerate this mass at the start of the swing and decelerate it at the end — cushioning the stop to prevent the cover from overshooting the parked position.

Engineering Challenge — The Cover Must Return to Exactly the Same Position

Opening the cover is straightforward — swing it aside, any angular overshoot can be corrected before charging begins. Closing the cover is the precision challenge: the cover must return to its original position within ±5 mm so that the electrode holes align with the electrodes, the fume duct re-seats, and the cover sits flush on the furnace rim seal.

Electrode hole alignment

The electrode holes in the cover have a clearance of 50–100 mm around each electrode. If the cover returns more than this clearance off-position, the electrode strikes the cover rim during lowering — damaging both the electrode and the refractory lining. The rotating cylinder must bring the cover back to within ±20 mm of the original position for safe electrode clearance.

Rim seal contact

The cover's lower rim must sit flush on the furnace shell rim — a continuous metal-to-metal seal that contains the furnace atmosphere. Angular misalignment causes a gap on one side, allowing air ingress (which oxidises the melt) and fume escape (which degrades melt shop air quality). The rotating cylinder's return accuracy determines the seal quality.

Korea Ever-Power engineers the cover rotating cylinder with end-of-stroke cushioning on both sides and a mechanical stop (adjustable) at the closed position — ensuring repeatable return positioning within the required tolerance after every swing cycle. Contact the hydraulic cylinder engineering team for cover rotation positioning specifications.

Cover rotating cylinder installed on EAF pivot arm

Manufacturing

The cover rotating cylinder uses conventional bore-to-rod proportions (210 mm bore, 125 mm rod), but it is built to the same environmental protection standards as all EAF cylinders: FKM seals for sustained high temperatures, heavy-duty rod wipers to exclude scale particles, and chrome plating thickness of 50–80 µm for fume and splash resistance. The bore is honed to Ra 0.2–0.4 µm for smooth, consistent motion at the low speeds used during the deceleration and precision-positioning phases of the swing.

The end-of-stroke cushion is calibrated for the specific cover mass and swing speed — heavier covers at faster swing speeds require more aggressive cushioning to prevent impact at the mechanical stop. Korea Ever-Power adjusts the cushion needle valve setting during factory functional testing to match the customer's specified cover weight and target swing speed.

Every cover rotating cylinder is hydrostatic tested at 1.5× working pressure (21 MPa) and functionally tested for full-stroke extension and retraction, including cushion deceleration verification at both ends of the stroke.

OEM & ODM

What You Provide

Cover weight (tonnes including refractory and electrode assembly), pivot arm length, required swing angle (90°, 120°, or other), target swing time, return positioning accuracy requirement, mounting pin diameter, distance from cylinder to furnace shell (for thermal assessment), and the cover support structure drawing showing the pivot arm and cylinder mounting points.

What the Factory Delivers

Engineering drawing with bore, rod, stroke (calculated from pivot arm geometry and swing angle), cushion specification (calibrated for cover mass and swing speed), seal and thermal protection specification, and mechanical stop provisions. Hydrostatic + functional test with cushion verification. Seal kits. Browse the complete electric furnace cylinder family.

FAQ

Can the cover be rotated while it is still being lifted?

On some furnace designs, the lift and rotation are sequential (lift completes, then rotation begins). On others, the rotation starts partway through the lift — the cover lifts and swings simultaneously to reduce the total opening time. Simultaneous operation requires the rotating cylinder and the cover lifting cylinder to operate from independent hydraulic circuits that do not interfere with each other.

How does the linear cylinder produce 90–120° of rotation?

The same lever arm principle as the manipulator tilt cylinder (#5): the cylinder rod connects to the cover pivot arm at a distance from the pivot axis. As the cylinder extends, it pushes the attachment point in an arc around the pivot, rotating the cover. The lever arm length and the cylinder stroke determine the rotation angle. A longer lever arm requires less cylinder force but more stroke; a shorter arm requires more force but less stroke. Korea Ever-Power calculates the optimal geometry for each furnace.

What if the cover does not return to the correct position?

The cover lifting cylinder will not lower the cover until a position sensor confirms the cover is within the alignment tolerance. If the rotating cylinder undershoots or overshoots, the control system commands a correction stroke before lowering proceeds. This interlock prevents the electrodes from striking the cover rim — the most common damage scenario from a misaligned return. The principle parallels the interlock logic between the lock and tipping cylinders (#15 and #16) — no downstream action until the upstream cylinder confirms position. Similar interlocking applies in forklift mast sequencing and telescopic stage extension.