Basics

Technical Background

STÜWE fricitional connections can be mounted easily and without any damages, different from thermally jointed or otherwise jointed frictional connections. The clearance-fit between shaft and "STÜWE disc" resp. shaft-hub and STÜWE disc ensures easy mounting.

All STÜWE frictional connections function by the same principal. Basically they consist of one inner ring and one outer ring, with corresponding conical surfaces By axially moving the outer ring against the inner ring – the movement can be done mechanically or hydraulically – the outer ring will be pushed outwards and the inner ring will be pushed inwards. The pressure between shaft and hub, created by this displacement, can be used to transmit a torque resp. an axial load, by using the friction between the two contact faces.

The transmittable load depends on the coefficient of friction between the partners involved, the clearance fit, the length of contact and the shaft´s diameter.

• Transmittable torque M_t
  The values for the transmittable torque in our catalogue are calculated for a specific shaft's diameter. The calculation bases on an assumed coefficient of friction, the maximum possible clearance fit and an axial load P_ax = 0.
  
  
• Coefficient of friction
  The coefficient of friction of dry and grease-free surfaces (steel/steel) ranges from 0.15 to 0.33. The transmittable torques of the external shrink discs are calculated using a coefficient of friction of μ_w = 0,15.
  The coefficient of friction can be increased by special surface treatment. Thus, the transmittable torque can be increased accordingly.
  
  
• Clearance fit
  The torque calculations are based on the maximum clearance and the design surface roughness. If the actual fit between shaft and hub is different, then the transmittable torque consequently is different, too.
  
  
• Shaft diameter
  The shaft diameter-range for each shrink disc is specified in the chart. The transmittable torque can be interpolated with sufficient accuracy for shaft diameters which range between two sizes given in the chart.
  
  

• Axial load "P_ax"
  The max. transmittable axial load (for M_t = 0) can be determined on the basis of the following equation:

  
  
  
  

• Transmission of torque combined with axial load
  If torsional and axial loads are to be transmitted simultaneously, following equation can be used:

  
  M^II_t is the reduced transmittable torque whenever an axial load P_ax is present.
  
  
• Surface finish
  The surface roughness (R_t) of shaft and hub should be below 16 μm (turning machining is sufficient).
  
  
• Lubricant
  Conical surfaces as well as bolts are greased with a MoS₂- lubricant. The following lubricants (coefficent of friction appr. 0.04) are examples of commercially available lubricants.
  
  

  Lubricant		Commercial size and packing/manufacturer
  Molykote D-321 R (anti-friction coating)		Spray Dow Corning
  Molykote G Rapid-plus		Paste Dow Corning
  Aemasol MO 19 P		Paste A.C. Matthes