3. Gate Hoist

Article 25. Safety Factor of Gate Hoist

The safety factor of a gate hoist calculated from the rated torque of the prime mover shall be more than those listed in Table 2.25-1, and the stress calculated from the maximum torque shall be less than 9O°7o of the yield point of the material used. Materials not specified in Table 2.25-1 shall be corresponding to this Table.

Table 2.25-1 Safety Factor of Material Used

Type	Safety factor
	Tension	Com­pression	Shearing
Rolled steel for general structures & welded structures (SS, SM)	5	5	8.7
Carbon steel forgings for general use (SF)	5	5	8.7
Carbon steel for machine structural use (S-C)	5	5	8.7
Stainless steel bars (SUS)	5	5	8.7
Carbon steel castings (SC)	5	5	8.7
Gray iron castings (FC)	10	3.5	10
Bronze castings (BC)	8	8	10
Wirerope	8 (For static operating loads)
Plate link chains	6.5 (For static operating loads)

Description:

A force less than the rated torque acts on the gate hoist under normal use conditions, however the operating force can become extremely large due to rust, sediments and debris.

If a hydraulic gate is jammed during operation, the maximum torque of the prime mover (motor or internal combustion engine) may act on the gate hoist. Such maximum torque may be as high as twice the rated torque of the motor. Thus the stress for maximum torque has been speci­fied in such a way that the hoist will not be broken under these condi­tions. A check for maximum torque conditions is not necessary, provided that an overload prevention device, thoroughly reliable and properly con­trolled and inspectable, has been installed and that its functioning has long been confirmed to be satisfactory.

When the load at the maximum torque acts on a wirerope, the load should not exceed 90% of the load at the yield point. The load at.the yield point is generally about 65% of the breaking load.

The buckling strength of a spindle rod should basically be obtained from the following Euler’s formula. It is common to consider n = 2 since one * end is usually fixed and the other end is usually movable. In such a case, it is assumed that the spindle rod does not buckle with, a load at maxi­mum torque or a load set by a reliable overload prevention device.

rt7T²E/

^Pk~ P

’ where P_K: Buckling load (kgf)

n: Coefficient of fixity of a spindle

E: Modulus of elasticity (kgf/cm²)