Vulcanizing Machine
Upper Ring Cylinder · Centre Mechanism

0.5 mm Off-Centre
at the Bead =
Vibration at 120 km/h

Deep inside the vulcanizing press — at the very centre of the mold — the centre mechanism grips the tire by its two bead wires and shapes it against the bladder before the mold closes. The upper ring cylinder drives the upper chuck of this mechanism: lowering it to grip the upper bead, holding it concentric during shaping and cure, then raising it to release the cured tire. If the upper bead is 0.5 mm off-centre, the tire has radial force variation — the steering wheel shimmy that sends a tire back for warranty.

384 KN

Max Thrust

50–140mm

Bore

≤1,000mm

Stroke

±0.5mm

Concentricity Target

The Centre Mechanism — The Mechanical Heart of the Tire Press

The previous vulcanizing cylinders (#28–#30) handle the mold — clamping it, opening it, flipping the finished tire. The upper ring cylinder is the first of two cylinders (#31, #32) that handle the tire itself — specifically, its bead wires. These cylinders are part of the centre mechanism, a vertical assembly mounted at the centre of the lower mold container.

The centre mechanism consists of a central post, the rubber bladder (which inflates inside the tire during cure), the upper bead chuck (driven by this cylinder), the lower bead chuck (driven by the lower ring cylinder #32), and the shaping air/steam supply lines. Together, these components grip the green tire by both beads, inflate the bladder to shape the tire against the mold cavity, and hold everything concentric during the 10–30 minute cure cycle. Korea Ever-Power manufactures the upper ring cylinder as part of the vulcanizing machine cylinder family.

Upper Ring Hydraulic Cylinder for Vulcanizing Machine

Technical Specifications

Parameter	Value
Product	Upper Ring Hydraulic Cylinder for Vulcanizing Machine
Function	Drive the upper bead chuck for tire loading and shaping
Bore Diameter	50 mm – 140 mm
Rod Diameter	28 mm – 100 mm
Stroke	≤ 1,000 mm
Maximum Thrust	384 KN (bore 140 mm / pressure 25 MPa)
Working Pressure	Up to 25 MPa
Certification	ISO 9001 · 100% hydrostatic tested

Why Bead Concentricity Determines Tire Uniformity

A tire's "uniformity" is how evenly it rolls — how consistent the force is at every point of the rotation. Perfect uniformity means the tire pushes the road with exactly the same force at every degree of rotation. Any variation is called "radial force variation" (RFV) — the primary cause of steering wheel vibration at highway speed.

RFV is largely determined during vulcanization — specifically by how concentrically the two bead wires are positioned in the mold. The beads are the structural anchors of the tire: the entire carcass (the internal structure of plies and belts) is stretched between the upper and lower beads. If one bead is off-centre by even 0.5 mm, the carcass tension is uneven — creating a thicker, stiffer zone on one side and a thinner, more flexible zone on the opposite side. This asymmetry produces RFV that cannot be corrected after curing.

The upper ring cylinder positions the upper bead chuck — and the concentricity of the upper bead is a direct function of the cylinder's rod alignment, the chuck's concentricity on the centre post, and the cylinder's ability to hold the chuck at the exact axial position during bladder inflation (which applies lateral forces on the chuck that try to shift it).

Upper Ring + Lower Ring — A Pair That Grips Both Beads

The tire has two bead wires — upper and lower. The centre mechanism uses two ring cylinders to grip both:

Upper Ring Cylinder (#31) — This Product

Drives the upper bead chuck. During loading: the cylinder lowers the upper chuck to meet the green tire's upper bead as it is placed into the press. The chuck clamps the bead wire from above. During cure: the cylinder holds the upper chuck at the set height — maintaining the bead-to-bead distance (which determines the tire section height). After cure: the cylinder raises the chuck, releasing the upper bead for tire removal. Stroke ≤1,000 mm — enough to lift the upper chuck fully clear of the tire.

Lower Ring Cylinder (#32) — Partner

Drives the lower bead chuck. The lower chuck positions the lower bead wire from below. During loading, it rises to meet the green tire's lower bead as the tire settles into the lower mold container. During cure, it holds the lower bead concentric with the mold centre axis. After cure, it lowers to release the lower bead. The two chucks work as a matched pair — gripping both beads at exactly the same distance from the mould centre axis.

The distance between the upper and lower chuck positions during cure sets the tire's section height — the vertical dimension of the tire. If the upper ring cylinder does not hold its position to the specified tolerance, every tire produced in that press has a different section height — failing the dimensional specification. Contact the hydraulic cylinder engineering team for centre mechanism cylinder specifications.

The Shaping Sequence — How the Upper Ring Cylinder Transforms a Flat Tube into a Tire Shape

The green tire arrives at the press as a roughly cylindrical shape — the beads are close together and the sidewalls are nearly vertical. During "shaping," the centre mechanism transforms this cylinder into the toroidal (doughnut) shape of a finished tire:

1. Beads gripped — chucks close

The upper ring cylinder lowers the upper chuck onto the upper bead. The lower chuck rises to grip the lower bead. Both beads are now clamped. The green tire hangs between the chucks like a drum.

2. Beads brought closer — cylinder retracts

The upper ring cylinder retracts partially — bringing the upper bead downward, closer to the lower bead. This reduces the bead-to-bead distance, which forces the sidewalls to bulge outward — starting the transformation from cylinder to torus.

3. Bladder inflates — tire takes shape

Low-pressure shaping air (1–3 bar) inflates the bladder inside the tire. The bladder pushes the sidewalls outward into the toroidal shape. The upper ring cylinder holds the upper chuck at the exact bead-to-bead distance — resisting the bladder's upward push on the upper bead.

4. Mold closes — full pressure — cure begins

The mold opening cylinder (#30) lowers the dome onto the shaped tire. The pressurized cylinder (#29) applies clamping force. The bladder pressure increases to 15–25 bar with steam/hot water. The upper ring cylinder holds position throughout the 10–30 minute cure — maintaining bead concentricity against the full bladder pressure.

Upper ring cylinder in tire shaping centre mechanism

Manufacturing — Precision for Concentricity

Korea Ever-Power upper ring cylinder precision manufacturing

The upper ring cylinder operates inside the centre mechanism — a thermally stressed, mechanically constrained space at the very centre of the mold. The rod must run concentric with the centre post to within tight tolerances — any rod misalignment translates directly into upper bead misalignment, which becomes tire RFV.

The bore is honed to Ra 0.2–0.4 µm. The rod concentricity to the bore axis is verified to ≤0.1 mm TIR (total indicated runout) — tighter than the standard for non-precision cylinders. FKM seals are standard (the centre mechanism is heated to 150–180 °C by the bladder steam). Chrome plating is 50–80 µm for thermal resistance and the inevitable contact with rubber fumes and cure by-products.

Every upper ring cylinder is hydrostatic tested at 1.5× working pressure and position-hold tested — verifying that the cylinder holds its set position (simulating the bead-to-bead distance hold) against a simulated bladder-pressure load without drift during a defined hold period.

OEM & ODM

What You Provide

Centre mechanism model, upper chuck travel range, bead-to-bead distance (shaping and cure positions), bladder pressure (for hold-force calculation), rod concentricity requirement, centre post diameter (for spatial fit), temperature at the cylinder mounting position, and the centre mechanism assembly drawing. Ideally ordered with the lower ring cylinder (#32) as a matched pair.

What the Factory Delivers

Engineering drawing with bore, rod (concentricity-verified), stroke, FKM seal specification, position-hold performance guarantee, and mounting dimensions for the centre mechanism housing. Hydrostatic + position-hold test certificate. Seal kits. Browse the complete vulcanizing machine cylinder family and the full hydraulic cylinder product range.

FAQ

What is the difference between the upper ring cylinder and the lower ring cylinder?

Both grip a bead wire, but from opposite directions. The upper ring cylinder moves downward to grip the upper bead and upward to release it. The lower ring cylinder (#32) moves upward to grip the lower bead and downward to release it. Their strokes differ (upper: ≤1,000 mm; lower: ≤2,000 mm) because the lower chuck must travel further to accommodate the bladder assembly and the centre post geometry. They are manufactured as a matched pair to ensure matched concentricity.

Does the upper ring cylinder hold position during the entire 10–30 minute cure?

Yes — the cylinder must maintain the upper bead chuck at the exact set height throughout the cure. The bladder pressure (15–25 bar) pushes upward on the upper chuck, trying to open the bead-to-bead distance. The cylinder's position-hold circuit (check valve or proportional valve) must resist this force without drift. Any drift changes the tire's section height — a dimensional defect.

How does bead concentricity affect the end customer?

Directly — through ride quality. Off-centre beads create radial force variation (RFV), which the driver feels as steering wheel vibration or a rhythmic pulse at highway speed. Premium tire manufacturers specify RFV limits of 50–80 N (first harmonic); exceeding the limit means the tire is either scrapped or "match-mounted" (paired with a specific wheel to compensate). Both outcomes cost the tire manufacturer money. The upper ring cylinder's concentricity performance directly affects the percentage of production that meets the RFV specification. Browse forklift cylinders and telescopic cylinders for other precision-positioning applications.