Balancing of big rotors, processing of frames

Balancing of shaft • vertical rotors – hydro („lens“ or lentils design)• horizontal rotors – AC generators, synchronous

rotors (rulers design)• principle:

– static balancing– dynamic balancing

• typical dimensions of rotors:– Hydrogen: up to 6 meters height, diameter 6-10 meters– Synchronous gen.: 10-12 meters length!, diameter 1

meter (limited with the solidity of used steel)

Note: some parts of rotor have nearly supersonic velocity!

Balancing of shaft Rotor „DANA“ is more than 60 m long (Nuclear power plant)

Vibrations are limited and measured in 8 parallel plains (both static and dynamic balancing)

Balancing of shaft • Centrifuge forces/moments, impact on life-time,

• Caused:• by unbalanced mass (most often)• oval bearings• another reason

• Solution: add/remove the same mass from opposite site (weight/plumb). Typical material – „modeling clay“

• Balancing:• static• dynamic (can be discovered just during rotation)• mixed (both principles)

• Critical runs: unbalanced mass is on the opposite site

Special (long) rotors, turbo-rotors

• Auxiliary „bed“ (lunettes) • Bending – unwanted, undesirable• Issue of long rotors (10 m)• Low-speed synchronous drivers

– Accurate placing of poles

– a lot of poles

– RPM = 50 Hz / number of double-poles

• Poles – fixed by „dovetail“ lock

Turbo-rotors: groves: 9-12 mm width

• number: 16-40 (divisible by 4)

• critical solidness: perimeter speed (circumferential speed) very high (100 m/sec), near to supersonic speed

• wedge: groves are fixed by bronze wedge

Machining of frames (AC drivers)

• „hard“ requirements– solidity– Parallelism of frontal surfaces– Perpendicularity (somewhere)– coaxially – aligned surfaces– deformation / not allowed

• Clamping– Important accuracy (< 0.1 mm)– Mechanical clamps– Electromagnetic clamps– Clamping of tools /induction heating/

Processing of frames

• Ageing – important for solidity, often are frames stored outside – climatic stress

• 1st. Basic issue – not rotating parts – difficult to machine• 2nd. Basic issue – accuracy of clamping (fixing)

minimizing of clamps:– Piece production:

• big work pieces – special tools and machines necessary

– Serial production:• often used machining centers with many tools and ONE clamp!

Processing of frames• machining center

• horizontal and vertical tools

• one clamping table moving in 2 axis (X, Y)

• processing of frames must be discussed according:

length x diameter!!!!

(next slide)

1) Frames with length ~ diameter (L~D):

• Clamping from “inside”(frame – hatching part)

2) Frames with wide-body: D > L

• Clamping from front-side1st. step: turning outside parts2nd. step: turning inside parts3rd. step – 4th. step: fixing and finishing

rotor stack

Cutting of metal sheets/plates• used in many procedures – rotor stacks, stator stacks,

transformers, coils etc.• Cutting machine – scissors/clippers• Crowbar clip. (manually driven)• Panel/board clip. (hydraulic, big stress)• Disc/wheel clip. (sheets for transform.)

Drivers: for cutting: manual, hydro/pneumatic, eccentric principle

Forces: up to 85% of tensile strength

Very important: space (gap) between cutting edge (tool) and fixed form (shape)

Technology issues of cutting