Considerations on Yuken Cylinder Selection
(1) Models (JIS B 8367: 1999 Mounting dimensions for hydraulic cylinders)
®7HT: For 7 MPa (1 015 psi), Rectangular Cover, Tie-rod
©10HS: For 10 MPa (1 450 psi), Built-in Cylinder ©10HT: For 10 MPa (1 450 psi), Rectangular Cover, Tie-rod
©14HT: For 14 MPa (2 031 psi), Rectangular Cover, Tie-rod
©16HT: For 16 MPa (2 320 psi), Rectangular Cover, Tie-rod
©16HR: For 16 MPa (2 320 psi), Round Cover, Flange-Welding or Screw-In
©21HT: For 21 MPa (3 046 psi), Rectangular Cover, Tie-rod
®25HR: For 25 MPa (3 626 psi), Round Cover, Flange-Welding
(2) Cylinder Speed
Generally, a cylinder speed of 15 to 300 mm/s (.59~ 11.8 in/s) is recommended. An excessively high or low speed leads to rapid packing wear, causing fluid leakage from the rod seal or internal leakage. When the cylinder speed is too low, a stick-slip phenomenon may affect smooth cylinder operation. Special caution must be paid to the packing and the sliding parts when operating the cylinder beyond the recommended speed range.
(3) Cylinder Mounting
The cylinders can be mounted as shown in Table 10.1. They should be mounted so that the pressure is always applied in the moving direction with the minimum radial load, depending on the load characteristics and cylinder motion.
(4) Cylinder Bore and Rod Bore
Table 10.2 lists rod bores corresponding to cylinder bores. The rods are classified according to the area ratio between the head and rod sides.
(5) Rod Buckling
When a rod is subject to tensile stress, only its tensile strength need be considered. On the other hand, a long rod subject to a compression force may bend and easily break with a small stress. This phenomenon is called buckling, and the buckling strength of the rod must be determined, based on the load, rod bore, the rod-end coefficient (depending on the cylinder mounting type), and rod length. The buckling strength is an essential factor in determining the maximum stroke length. The safety factor is normally set at 4.
(6) Minimum Operating Pressure
The operating pressure is defined as follows: 0.5 MPa (72.5 psi) or less for U-packing, X-rings, O-rings (JIS B 2401), and combination seals (S), and 0.25 MPa (36.3 psi) or less for piston rings. Standard cylinders operate with 0.3 MPa (43.5 psi) of the working pressure.
(7) Cushion
The piston in a cylinder, which moves in the reciprocating motion, contacts the cover at the stroke end to produce shocks. To minimize the shocks, the cylinder should be provided with a cushion mechanism to reduce the piston speed at the stroke end. However, the cushion mechanism generates a higher internal pressure as inertial force increases.
(8) Packing Materials and Hydraulic Fluids i . Nitrile rubber (NBR):
Standard fluids and other than phosphate ester
ii. Hydrogenated rubber (HNBR):
High-temperature fluids
iii. Polytetrafluorethylene (PTFE):
High-temperature fluids
iv. Fluorinated rubber: Phosphate ester
Categories: Actuators | Leave a comment