Ringfeder RfN 7015.0 Locking Assembly, 100-800 mm

Self-centring precision assembly for bending moments and the highest torques

The RfN 7015.0 is RINGFEDER’s self-centring precision locking assembly for shafts of 100 to 800 mm. The product paper says it can transfer the greatest bending moments as well as maximum torque and axial force, with special concentricity demands on the clamped parts. Long, flat cones carry the load; during installation the assembly, shaft and hub stay in position relative to each other, and shaft and hub are only compression-loaded, which RINGFEDER cites as added safety compared with three-piece versions.

A centring ridge and the relatively wide body give the assembly excellent centring ability. Typical uses are large rotors, drive drums, sheaves and flywheels on shafts where run-out matters and bending acts together with torque.

Technical specifications

Selected sizes from the tech paper

The table has 41 sizes:

Series installation, bending and hub dimensions

If one assembly is not enough, two RfN 7015.0 assemblies can be positioned one behind the other and their torque and axial values are added. For combined bending and radial loads RINGFEDER asks you to contact its technical department. Values are valid for assemblies installed in oiled condition; a reduced tightening torque lowers the transmission values and should be agreed with RINGFEDER. Shaft h8 and hub H8 tolerances apply, with Ra 3.2 um.

The minimum hub outside diameter DN depends on the hub yield strength. For the 200 x 260 size it is —, 461 or 394 mm at 200, 300 or 400 N/mm2, and Tmax is 110,026 Nm against 93,522 Nm rated. The largest size, 800 x 910, transmits 2,427,520 Nm and 6,069 kN with 42 screws of M27 x 160 tightened to 1,600 Nm.

Confirm before ordering: the bending moment acting on the joint, hub material and outside diameter, torque and shock factors, and whether two assemblies in series are needed.

Like the other locking assemblies in the programme, the joint acts as a mild overload device: once the set frictional force is exceeded the assembly slips and protects valuable machine parts, although RINGFEDER states it is not suitable as a sliding clutch. Because shaft and hub are ungrooved, fatigue strength under constant reverse torsion stays high, and no maintenance is needed.

Key features of the RfN 7015.0

• Self-centring design with a centring ridge, so the hub runs true without a separate pilot fit.
• Long, flat cones that spread the clamping load and give high torque and bending moment capacity.
• Shaft and hub remain stationary relative to each other while the screws are tightened, so the axial position set during assembly is kept.
• Shaft and hub carry compression load only, with no keyway to weaken the shaft section.
• Wide size range from 100 mm to 800 mm shaft diameter in 41 sizes, using standard metric socket head screws.
• Easy removal by loosening the locking screws, which simplifies maintenance and repositioning of heavy components.

Keyless locking compared with keyed joints

A keyway concentrates stress at its corners, and under alternating torque or rotating bending this is a common starting point for fatigue cracks. A keyed fit also needs some clearance, which allows fretting and wear when the load reverses. A friction locking assembly removes both problems: the clamping pressure grips the full circumference, there is no backlash, and the shaft section stays intact. For heavy rotating parts that see start-stop cycles or reversing loads, such as drive drums or flywheels, this generally leads to a longer service life of the shaft-hub connection.

Selection guidance

1. Determine the maximum torque and axial force, including start-up peaks and shock factors for the driven machine.
2. Calculate the bending moment acting at the joint from the overhung or radial loads.
3. Choose the size from the shaft diameter and check that T and Fax exceed the design values with an adequate margin.
4. Check the hub outside diameter against the minimum DN for the hub material yield strength given in the tech paper.
5. Where one assembly is not enough, consider two in series, and refer combined bending and radial cases to the manufacturer.

Installation and removal

• Clean the shaft and hub bore, check the h8 and H8 tolerances and the Ra 3.2 µm surface finish.
• Lightly oil the contact surfaces and screws with a mineral oil without molybdenum disulfide or other friction-reducing additives, since the published values are based on an oiled condition.
• Slide the assembly into place, then tighten the screws in several passes in a diametrically opposite or circumferential sequence until all reach the specified tightening torque.
• Use a calibrated torque wrench; undertightening reduces the transmissible values, and the tightening torque should not be exceeded.
• For removal, loosen the screws in steps; use the forcing threads described in the installation instructions if the cones do not release on their own.

Applications in Oman and the GCC

Large locking assemblies are found on conveyor drive and tail pulleys at quarries, cement plants and ports, on sheaves and drums of hoisting equipment, on fan and blower rotors in power and desalination plants, and on mixers and crushers in mining. Coastal humidity and dust promote corrosion on exposed steel, so cover the screw heads or apply a protective coating after installation, and include a periodic visual check of the joint in the maintenance plan of the machine.

What to include in an RFQ

• Series RfN 7015.0 with shaft diameter d and hub bore D, as in the ordering example.
• Torque, axial force and bending moment at the joint, with service factors.
• Hub material, yield strength and outside diameter.
• Quantity and whether two assemblies in series are planned.
• Any requirement for corrosion-protected or special-material versions.

Documents and quotation

The PDF is the RINGFEDER tech paper for the RfN 7015.0 (05.2024). The related RfN 7015.1 is covered in the product paper. For a quotation send the shaft diameter, loads and hub details; drive items are listed under Electric Motors and Gear Units.