ASME HST-4:2021 pdf free download

ASME HST-4:2021 pdf free download.Performance Standard for Overhead Electric Wire Rope Hoists.
SECTION 4-1.2: HOIST DUTY SERVICE CLASSIFICATION
4-1.2.1 GeneraL Considerations
Service conditions influence the performance of weanng parts of a hoist such as gears, bearings, rope, sheaves, electrical equipment, brake linings, load- and lift-limit devices, and wheels. Careful consideration of the hoist duty service classifications described in this Section will enable the user to evaluate the application and to obtain a hoist designed for optimum performance and minimum maintenance. If doubt exists regarding hoist selection, the hoist supplier should be consulted. Many factors enter into the selection of the proper hoist to perform a given function. Hoisting equipment consists of both mechanical and electrical components, and both must be considered when analyzing the service that the hoist must perform.
The factors that influence the performance of any hoist include the following:
(a) Load Distribution. The actual distribution or proportion of full and partial loads to be handled by the equipment, including lifting devices, has an important effect on the life of power transmission components. For example, ball bearing life generally varies inversely according to the cube of the load. A 2-ton (1 814.4-kg) hoist, operated at a mean effective load of 1 ton (907.2 kg), will have a ball bearing life eight times that of the same hoist used steadily at Its rated load.
(b) Operational Time. Operational time is the total running time of the hoist per hour or work period.
(ç) Work DIstribution. This is determined by whether the operational time is uniformly distributed over the work period or concentrated in a short time span. Work distribution generally does not appreciably affect mechanical wear but does materially affect the electrical components such as motors, brakes, and controls. For example, a hoist motor designed to operate 15 mm out of each hour of an 8-hr shift cannot handle 2 hr of steady run and 6 hr of idle time even though both conditions require 2 hr of operational time per 8-hr shift.
(d) Number of Starts and Stops. This directly affects all electromechanical devices, such as motors, contactors, brakes, and solenoids.
(e) Repetitive Long Lowering Operations. Such operations generate heat In control braking means.
(f) Environmental Conditions. Such conditions include ambient temperature and the presence of dust, moisture, corrosive fumes, etc. Hoist equipment is designed to operate in ambient temperatures between 0°F and 104°F (— 18°C and 40°C) and In atmospheres reasonably free from dust, moisture, and corrosive fumes unless otherwise specified.