Who is the turntable device designed for?
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I have always been unclear about which equipment the shaft turning device is used to turn, and under what circumstances it is necessary to use such a device. In multi-axis systems, where are the shaft turning devices installed – on the drive motors or turbines? Is it necessary to install shaft turning devices for the driven machines such as centrifuges, fans, or special types of machinery? For systems that consist of shafts, such as catalytic units or other systems that involve motor-gearbox-centrifuge configurations, if shaft turning is required, how many shaft turning devices should be installed, and where should they be placed?
Set one, place it near the drive end
Cranking the equipment at low speed allows 1. the lubricating oil to penetrate fully into the bearings and bearing shells； 2. Prevent the shaft from bending when it is at rest
Cranking the equipment at low speed allows 1. the lubricating oil to fully reach the bearings and bearing shells； 2. Prevent the shaft from bending when it is at rest
Inspect the turning gear before starting the equipment
Answer key: (1) Turning the engine before starting it facilitates startup, reduces the starting current, and allows an oil film to form on the moving parts； ⑵After major or medium repairs of the compressor, turning it over allows any debris present in the cylinders to be detected promptly ； ⑶When there is water in the cylinder, turning the crankshaft allows one to ensure that the machine will not be damaged due to collision with the cylinder during operation ； ⑷Regularly turning the standby unit also benefits the main shaft bearings, preventing the main shaft from bending ； ⑸Turning the crankshaft when the engine is shut down allows the temperature of each cylinder block to decrease evenly, preventing the pistons from stopping at the top and bottom dead centers.
Turning the equipment is necessary before it is started up, as well as during routine maintenance and inspections. However, not all rotating equipment requires a turning device; those that can be turned by manual effort or with simple tools do not need such a device. Therefore, turning devices are typically used in large, critical units. There are two types of turning devices: manual and automatic. A single unit only needs one turning device – it’s not possible to have one for the motor, one for the gearbox, and another for the centrifuge!
Put it this way: most rotating equipment requires barring. Only small rotating equipment, such as small centrifugal pumps, can be manually turned (that is, the coupling is turned manually before starting the machine). Large equipment such as reciprocating compressors requires significant force for turning, which is why a turning mechanism is installed. The main purpose of turning the machine is to check whether there is any jamming in the unit
The main purpose of turning large units is to prevent shaft bending
Slightly larger turbines require shaft turning; for example, a 400KW gas generator needs the oil pump to create pressure before startup, after which shaft turning is carried out to form an oil film in each bearing, thereby facilitating the startup of the unit. After the unit stops operating, due to prolonged operation, mechanical fatigue, and high temperatures, an abrupt stop of the main shaft can cause it to bend and deform. Therefore, shaft turning is necessary after shutdown, allowing the main shaft to rotate slowly, cooling down at the same time and returning to its normal shape, thus preventing bending and deformation that could lead to damage. Another purpose of turning the shaft after parking is to continue supplying oil to the bearing shells through the residual pressure in the oil system (large installations have separate oil pumps), thereby cooling the bearing shells and preventing them from sticking due to localized high temperatures. For small units, manual turning is usually sufficient, but large units exceed the capabilities of manual operation, so special turning devices are required. After a turbine shuts down due to an accident, and when all station power is lost, in order to protect the turbine’s main shaft and bearing shells, crane-driven shaft rotation as well as supply of oil from DC oil pumps are employed in special cases, since human intervention is completely ineffective. The gear turning device mainly consists of a motor and an acceleration gearbox, along with a gear engagement mechanism. Gear turning is required to activate this gear engagement mechanism; the output gear of the reduction gearbox meshes with the gear used for turning the device, and the motor, after reducing its speed to increase torque, drives the main device to start turning.
A barring gear is installed on the turbine to rotate the rotor at low speed during startup and shutdown, thereby preventing bearing damage