ASME HST-4 pdf download

ASME HST-4 pdf download Performance Standard for Overhead Electric Wire Rope Hoists
SECTION 4-1.1 GENERAL All equipment selected in accordance with this Standard is designed to perform satisfactorily when installed, inspected, tested, operated, and maintained in accordance with Chapters 16-1 through 16-4 of ASME B30.16 and used within the rated load and hoist duty service classification. All equipment shall provide speeds, lifts, and headroom in accordance with the man- ufacturer’s specifications, or to specifications agreed upon by the manufacturer and user. SECTION
4-1.2 HOIST DUTY SERVICE CLASSIFICATION
4-1.2.1 General Considerations Service conditions have an important influence on the performance of wearing parts of a hoist such as gears, bearings, rope, sheaves, electrical equipment, brake lin- ings, 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 regardinghoistselection, the hoistsuppliershould 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 the hoist must perform. The factors thatinfluence the performance ofanyhoist include the following:
(a) Load Distribution. The actual distribution or pro- portion 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 totalrun- ning time of the hoist per hour or per work period.
(c) 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 6 components such as motors, brakes, and controls. For example, a hoist motor designed to operate 15 min out of each hour of an 8-hr shift cannot handle 2 hr of steady run and 6 hr of idle time even though either condition only requires 2 hr of operational time per 8-hr shift.
(d) Number ofStarts and Stops. This directly affects all electromechanical devices, such as motors, contactors, brakes, and solenoids.
(e) Repetitive Long Lowering Operations. Such opera- tions generate heat in control braking means.
(f) Environmental Conditions. Such conditions include ambient temperature and the presence ofdust, 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 other- wise specified.
4-1.2.2 Hazardous Locations When hoists are used in hazardous locations as defined by ANSI/NFPA 70 or other special codes, modi- fications or additional precautions not covered by this Standard may be required. In these locations, only hoists designed ina mannersuitablefor the conditions encoun- tered shall be used.
4-1.2.3 Duty Classification While all the factors listed in para.
4-1.2.1 must be considered in selecting the proper class of hoist, most industrial applications, having randomly distributed loads or uniform loads up to 65% of rated load handled periodicallythroughouttheworkperiod,canbegeneral- ized according to the type of workshop or area of appli- cation. Listed in Col. 1 of Table 4-1.2.3-1 are the five duty classes that have been established for electric wire rope hoists. In Col. 2 are listed typical areas of application where each class can normally be applied. The majority of hoist applications fall into one of the three categories H1, H2, or H3, and the use of the generalized descriptions in Col. 2 of Table 4-1.2.3-1 for selec- tion of the hoist will be adequate.
(a) Operational Time Ratings. If in doubt as to the required duty classification for an application, refer to the data in Cols. 3 through 6 of Table 4-1.2.3-1, which show the operational time ratings for each class. (1) Uniformly Distributed Work Periods