These are found in impulse turbines to create the requisiste number of
stages. They locate with a fixed row of blades and are sealed against
the rotor shaft by a gland arrangement which must remian effective
throughout the working range the diaphragm operates in.
They have a large surface area and so must have sufficient stregth to resist pressure drop across them without being excessively wide which would increase rotor length. Allowance must be made for rapid temperature fluctuations found during manouevring.
Teh take the form of a disc with a row of blades at the circumference and a hole at the centre for the rotor. A horizontal split allows for disassembly, rotation is prevent by a locking plate at the horizontal casing joint.
Steam pressure holds the diaphragm plate hard against the downstream face.
Diaphragm is a loose fit in the slot in the casing to allow for expansion.
The
nozzle is assembled in batches by pushing the tenon of the blade
throught the channel hole and riveting. A spacer is fitted and the whole
tack welded. The blade batch is caulked into the casing. A small
allowance is made for expansion.
Some sections on the first stages may be blanked where partial admission used.
Modern turbine designs have a curtis wheel first stage which absorbs a large portion of the energy in the steam. The exahust from this stage has a relatively high volume therefore all further stages are full admission.
Modern diaphragms are all welded.Nozzle plates or guide vanves fit into
slots in the inner and outer rim. The whole is welded to the centre body
and perpipheral guide ring. Expansion is allowed for in the casing
groove. The Nozzle blades or guide vanes are commonly made from
stainless iron. The centre body from Chrome Molybdenum steel in higher
temperature regions, mild steel for the lower.
They have a large surface area and so must have sufficient stregth to resist pressure drop across them without being excessively wide which would increase rotor length. Allowance must be made for rapid temperature fluctuations found during manouevring.
Teh take the form of a disc with a row of blades at the circumference and a hole at the centre for the rotor. A horizontal split allows for disassembly, rotation is prevent by a locking plate at the horizontal casing joint.
Methods of Diaphragm fixing
Alternate arrangement
Steam pressure holds the diaphragm plate hard against the downstream face.
Rotor Sealing
Loading on diaphragm = 207 to 280 NM/m2, deflection is approximately 2mm
Diaphragm material
In the high temperature regions typically Molybdenum-vanadium steel all parts. More generally a low carbon steel for the nozzle division plates and spacer bands, mild steel for rest. In the low temperature region cast iron diaphragms may be used. Alternatelychromium or Nickel alloy steel may be usedConstruction of Diaphragm Nozzles (all riveted attachment)
Diaphragm is a loose fit in the slot in the casing to allow for expansion.
Construction of Diaphragm Nozzles (partial welded attachment)
The
nozzle is assembled in batches by pushing the tenon of the blade
throught the channel hole and riveting. A spacer is fitted and the whole
tack welded. The blade batch is caulked into the casing. A small
allowance is made for expansion. Some sections on the first stages may be blanked where partial admission used.
Modern turbine designs have a curtis wheel first stage which absorbs a large portion of the energy in the steam. The exahust from this stage has a relatively high volume therefore all further stages are full admission.
Construction of Diaphragm Nozzles (welded attachment)
Modern diaphragms are all welded.Nozzle plates or guide vanves fit into
slots in the inner and outer rim. The whole is welded to the centre body
and perpipheral guide ring. Expansion is allowed for in the casing
groove. The Nozzle blades or guide vanes are commonly made from
stainless iron. The centre body from Chrome Molybdenum steel in higher
temperature regions, mild steel for the lower.Archaic design
Included for general interest .
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