Module - Variable-Speed Power Transmission Devices Flashcards
Why is it necessary to lock out prime movers before working on attached (coupled) variable-speed drives?
To prevent them from starting up while personnel are in direct working contact with couplings, shafts and guards
Explain the process of applying lockout scissors.
Apply the scissors through the breaker handle in the off position and then apply up to six locks on the lock end of the scissors. Tags for each lock should also be applied.
Why are there six sets of holes in most lockout scissors?
To provide space for more than one maintenance person to lock out the same breaker
Where do you find the MCC located, and what is its purpose?
The motor control centre is usually located at the main incoming power feed location where the electricity is distributed throughout a production facility.
What is the purpose of confirming correct lockout?
Confirming correct lockout is done by trying to start a unit at the local command station. If the unit does not start, it must be locked out. The reason for lockout is for ensuring the machine immobilized.
Which hand do you use to pull the starter disconnect handle to the OFF position?
The left hand always because an electrical arc explosion will blow the breaker door open. The breaker doors are hinged on the left side and as a result will not swing directly into your face or chest.
Why are guards placed near or around moving equipment?
Guards prevent entanglement of personnel who may come in contact with the running unit. The guards also contain broken coupling parts if failure occurs.
What is a pinch zone or area?
A pinch zone is any location or area that is mechanically reduced in size. If a body or parts of a body enters one of these zones an injury or fatality can occur.
To adjust the speed on a wide belt drive the unit must be:
a) stopped.
b) running.
b) running.
As drive pulley faces move apart, belt speed:
a) increases.
b) decreases.
b) decreases.
Wide V-belt drives are energized to perform best at:
a) 1:1 ratio.
b) 2:1 ratio.
c) 6:1 ratio.
d) 8:1 ratio.
a) 1:1 ratio.
Which type of V-belt gives the best crosswise rigidity?
a) classical series
b) wide belt series
b) wide belt series
You are repairing a wide V-belt drive and find the following numbers on the backside of the belt: 2322V721. Explain what the numbers mean.
23 means 23/16” wide or 1 - 7/16” wide
22 means belt side angle 22°
V721 means 72.1” in length
Why do V-belt drives have notches moulded into them on the narrow side?
so they can bend around smaller radius pulleys
What is a woodblock belt?
A special variable-speed belt that is constructed by mounting woodblocks or synthetic blocks 90° to the belt travel. The blocks are cut at an angle on the ends to match the pulley angle.
How do manufacturers of variable-speed V-belt drives prevent fretting corrosion?
by applying special coatings to the pulleys
Mounting belt drives on a solid flat metal surface is important. Explain why.
Belt drive cases are precision-machined transmissions that may be distorted when mounted on uneven surfaces. The distortion of the internal working parts causes early wear and failure due to a soft foot condition.
Base plates should be constructed of material that is:
a) as thick as the drive base.
b) as thick as the pulley shaft diameter base.
c) as thick as the base bolt hole size.
d) equal to the mounting bolt diameter.
d) equal to the mounting bolt diameter.
Within a variable V-belt drive the driven pulleys constantly and automatically set what characteristic?
correct belt tension
A variable-speed belt drive motor is mounted on a motor position adjuster. When mounting the pulleys on the shafts the fixed sheave is mounted on the:
a) driver shaft.
b) driven shaft.
b) driven shaft.
Metal chain drives that are variable in nature are:
a) roller chain design.
b) leaf chain design.
b) leaf chain design.
Metal chain drives __________________ (do, do not) provide overload protection.
do not
Another name for a metal chain variable-speed drive is PIV. What do these initials stand for?
Positive Infinitely Variable
The convex sides of PIV pulleys are:
a) smooth.
b) machined to have male and female tooth profiles.
b) machined to have male and female tooth profiles.
Hydraulic variable-speed drives are________________________ (hydrodynamic, hydrostatic) in design.
b) hydrostatic
In a closed loop, variable-speed hydraulic drive, the motor return oil goes directly to the reservoir.
a) true
b) false
b) false
Leakage oil in a closed loop, variable-speed hydraulic drive is replaced by what device?
a charge pump
Maintenance on variable-speed, closed loop hydraulic drives basically consists of servicing. Briefly explain how to service one of these units.
Change out oil and filters at regular recommended intervals.
Overhaul of variable-speed, closed loop systems should be carried out according to the OEM overhaul manual.
a) true
b) false
a) true
How many elements does a basic torque converter employ?
three
What is the purpose of a stator found within a torque converter?
to redirect and speed up recirculated oil
Variable fill hydraulic drives use what device to remove oil from the unit while it is running?
a scoop tube
Why would you clean the heat exchanger on a variable fill hydraulic drive?
Variable fill drives generate a lot of heat because they are designed to have fluid slippage. A clean exchange removes this heat effectively.
Damaged or worn bearings within a variable fill hydraulic unit should be replaced with OEM parts.
a) true
b) false
a) true
Internal linkage pivot pins and bushings found on control levers of variable fill fluid drives should be replaced during overhauls.
a) true
b) false
a) true
Variable-speed wet disc drives are designed to reduce output speed by allowing slippage.
a) true
b) false
a) true
How is pressure applied to the discs within a wet disc drive?
Through a hydraulic control circuit that directs oil to a piston that applies pressure to the plates.
During overhaul of a wet disc hydraulic drive the discs must be match marked and positioned in their relative locations to prevent what problem when reassembled and placed on-line?
to prevent a condition of dynamic unbalance
How can fire-polished discs be cross-dressed?
Use #600 wet and dry paper to manually scuff the disc surfaces in a cross-hatch type pattern.
What is a programmable logic controller?
It is a small computer and keypad mounted on or near a motor. The unit functions as a control device for the motor. The control logic is entered into the unit by the user.
What is an electric motor corona?
It is the force field around current-carrying insulated wires.
What does soft start mean?
Soft start means to start a rotating shaft slowly and then bring it up to speed over a longer period of time. This reduces current spikes and lessens the mechanical stresses and shocks experienced at start-up.
How should you program a variable frequency drive?
by entering values and codes into the keypad
What is the procedure for overhauling a variable frequency drive controller?
Package it up and send it to an authorized dealer for repair.
