机械类文献翻译带传动设计

机械专业中英文文献翻译

英文译文

tape transport

Among the methods of material conveying quantity, belt conveyors play a very important part in the reliable carrying of material over long distances at competitive cost. Conveyor systems have become larger and more complex and drive systems have a l so been going through a process of evolution and will continue to do so. Nowadays, bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuang Mine). The ability to control drive acceleration torque is critical to belt conveyors' performance. A efficient drive system should be able to provide smooth, soft starts while maintaining belt tensions within the specified safe limits. For load sharing on multiple drives. torque and speed control are also considerations in the drive system's design. Due to the advances in conveyor drive control technology, at present many more reliable. Cost-effective and performance- driven conveyor drive systems covering a wide range of power are available for customers' choices[1].

1 tape transport on conveyor drive technologies 1. 1 The belt transmission mode

Full-voltage starters. With a full-voltage starter design, the conveyor head shaft is direct-coupled to the motor through the gear drive. Direct

full-voltage starters are adequate for relatively low-power, simple- Profile conveyors. With direct full-voltage starters. no control is provided for various conveyor loads and. depending on the ratio between full- and no-load power requirements, empty starting times can be three or four times faster than full load. The maintenance-free starting system is simple, low-cost and very reliable. However, they cannot control starting torque and maximum stall torque; therefore. they are limited to the low-power, simple-profile conveyor belt drives.

Reduced-voltage starters.

As conveyor power requirements

increase,controlling the applied motor torque during the acceleration period becomes

机械专业中英文文献翻译

increasingly important. Because motor torque is a function of voltage, motor voltage must be controlled. This can be achieved through reduced-voltage starters by employing a silicon controlled rectifier (SCR). A common starting method with SCR reduced-voltage starters is to apply low voltage initially to take up conveyor belt slack. and then to apply a timed linear ramp up to full voltage and belt speed. However, this starting method will not produce constant conveyor belt acceleration. When acceleration is complete. the SCRs, which control the applied voltage to the electric motor. are locked in full conduction, providing full-line voltage to the motor. Motors with higher torque and pull -vp torque, can provide better starting torque when combined with the SCR starters, which are available in sizes up to 750 KW.

Wound rotor induction motors. Wound rotor induction motors are

connected directly to the drive system reducer and are a modified configuration of a standard AC induction motor. By inserting resistance in series with the motor's rotor windings. the modified motor control System controls motor torque. For conveyor starting, resistance is placed in series with the rotor for low initial torque. As the conveyor accelerates,the resistance is reduced slowly to maintain a constant acceleration torque. On multiple-drive systems. an external slip resistor may be left in series with the rotor windings to aid in load sharing .the motor systems have a relatively simple a design.However,the control systems for these can be highly complex, because they are based on computer control of the resistance switching. Today, the majority of control systems are custom designed to meet a conveyor system's particular specifications. Wound rotor motors are appropriate for systems requiring more than 400KW.

DC motor. DC motors. available from a fraction of thousands of KW，are

designed to deliver constant torque below base speed and constant KW above base speed to the maximum allowable revolutions per minute (r/min). with the majority of conveyor drives, a .DC shunt wound motor is used. Wherein the motor's rotating armature is connected externally. The most common technology for controlling DC drives is a SCR device. which allows for continual variable-speed operation. The DC drive system is mechanically simple, but can include complex custom-designed

机械专业中英文文献翻译

electronics to monitor and control the complete system. this system option is expensive in comparison to other soft-start systems. but it is a reliable, cost-effective drive in applications in which torque,load sharing and variable speed are primary considerations. DC motors generally are used with higher-power conveyors, including complex profile conveyors with multiple-drive systems, booster tripper systems needing belt tension control and conveyors requiring a wide variable-speed range.

1. 2 Hydrokinetic coupling

Hydrokinetic couplings, commonly referred to as fluid couplings. are composed

of three basic elements; the driven impeller, which acts as a

centrifugal pump; the driving hydraulic turbine known as the runner and

a casing that encloses the two power components. Hydraulic fluid is pumped from the driven impeller to the driving runner, producing torque at the driven shaft. Because circulating hydraulic fluid produces the torque and speed, no mechanical connection is required between the driving and driver shafts.The power produced by this coupling is based on the circulated fluid's amount and density and the torque in proportion to input speed. Because the pumping action within the fluid coupling depends on centrifugal forces. the output speed is less than the input speed. Referred to as slip. this normally is between 1% and 3%. Basic hydrokinetic couplings are available in configurations from fractional to several thousand KW.

Fixed-fill fluid couplings. Fixed-fill fluid couplings are the most

commonly used soft-start devices for conveyors with simpler belt profiles and

limited

convex/concave

sections.

They

are

relatively

simple,low-cost,reliable,maintenance free devices that provide excellent soft starting results to the majority of belt conveyors in use today.

Variable-fill drain couplings. Drainable-fluid couplings work on the same

principle as fixed-fill couplings. The coupling's impellers are mounted on the AC motor and the runners on the driven reducer high-speed shaft. Housing mounted to the drive base encloses the working circuit. The coupling's rotating casing contains bleed-off orifices that continually allow fluid to exit the working circuit into a

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