JPS5848726B2 - gas turbine rotor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to gas turbine rotors, and more particularly to a wheel stacked gas turbine rotor suitable for use in high temperature gas turbines.

Some gas turbine rotors are made by cutting the entire length out of a single piece of material, while others are made by machining multiple disc-shaped wheels and joining them together with welding or bolts to form a rotor shape. .

Among the types of bolts that are connected, there are those that sequentially connect two adjacent wheels with relatively short bolts, forming all the wheels into a rotor shape, and those that use bolts that pass through all the wheels to connect the entire wheel at the same time. There are some that combine to form a rotor shape.

Among these, in the case where the entire wheel is simultaneously connected using bolts, the following considerations have been conventionally taken regarding the strength and loosening of the bolts.

That is, since the gas turbine rotor rotates at high speed due to high temperature, it tends to expand in the axial direction due to thermal expansion and also tends to contract in the axial direction due to centrifugal force.

For example, the coefficient of thermal expansion α is 1 3.5 X 1 0-617'
c. If the temperature of a rotor with a total length of 2000 mm increases by 300°C, the total length will increase by 8.1 mm.

In addition, the stress due to the centrifugal force of the wheel is 15 kg/cm in the circumferential direction.
7nn, and if 15kg/m4 is generated in the radial direction,
Poisson's ratio of wheel material is 0.3, Young's modulus is 1 9
It shrinks by about 0.95 mm as 0 0 0 kg/xi.

Therefore, if the coefficient of thermal expansion of the wheel material is smaller than the coefficient of thermal expansion of the bolt material, the tightening force of the bolt will decrease as the rotor temperature increases, and in the opposite case, the tightening force will increase and the tensile stress of the bolt will increase.

What has been explained above can be expressed by the following simple relationship.

However, the contraction of the wheel due to tightening the bolt can be ignored compared to the elongation of the bolt.

here σ: Tensile stress of bolt rotating at high temperature σ.

: Tensile stress Jσ of the bolt at rest at room temperature.

: Variation in the tensile stress of the bolt caused by the wheel shrinking in the axial direction due to centrifugal force Jσt : Variation in the tensile stress of the bolt caused by the difference in coefficient of thermal expansion between the wheel and the bolt Also, jσ.

, Aσ, is expressed as follows. where ν: Poisson's ratio σθ, σr of the wheel material: nominal stress in the circumferential and radial directions at the position corresponding to the bolt hole of the wheel AT: temperature rise of the rotor αw1αB: coefficient of thermal expansion EB of the wheel material and bolt material
: Young's modulus of bolt material In conventional gas turbine rotors, αB is α for bolt material.
Jσ using something slightly smaller than W.

Care was taken to ensure that jσ and jσ cancel each other out, reducing fluctuations in the tensile stress of the bolt.

For example, if the wheel material is Cr-Mo heat-resistant steel, α is 13.5 x 10 = 17' at around 300°C.
αB is about 12X' as a bolt material.
If 12Cr heat-resistant steel is used at around 17℃, σθ−σ
Aσ as r−1 skg/mi1 ν=0.3.

=-9kg/ma, JT=300℃, EB=
1 9 0 0 0k9/mt? t as lσ(=
8.5 5 kg/mi, and the tensile stress of the bolt hardly changes between when it is stopped and when it is running.

However, the above-mentioned conventional technology cannot cope with the case where the wheel material is made of a high heat resistant alloy such as A286.

The coefficient of thermal expansion of A286 is approximately 17xl at around 300℃.
O'i/'c is large, and for heat-resistant steels other than A286, it is at most 14X10''1/°C near 300'C, so JT = 300°C, EB = 1 9 0 0
If 0 kg/mvt, J σt = 1 7.
1 kg/mm, and Aσ.

From equation (1), where σ is the same as above, a = σ(,
+8. 1 (kg/m4) and the tensile stress acting on the bolt during movement becomes excessive.

On the other hand, if we try to suppress the tensile stress of the bolt during operation to an appropriate value, we have to reduce the tensile stress of the bolt when it is stopped, which may cause slippage between the wheels due to the torque when starting. .

This phenomenon occurs because the tensile stress acting on the bolt and the wheel tightening force are directly proportional.

The present invention has been made in an attempt to improve the above-mentioned drawbacks, and its purpose is to suppress the tensile stress acting on the bolts that connect the wheels to below a certain limit, and to prevent slippage between the wheels. It's about doing.

In FIG. 1, the horizontal axis represents the elapsed time after starting the gas turbine, and the vertical axis represents a dimensionless number obtained by dividing the tensile stress generated in the bolt by the yield strength of its material.

Now, the tensile stress σ allowed in the bolt.

is 0.5 times the proof stress, and the bolt tensile stress σl required to prevent slippage between the wheels is 0.35 times the proof stress.

・The marks and solid lines indicate that the bolt material is the same heat-resistant alloy A2 as the wheel.
86 (a heat-resistant alloy consisting of 25% by weight of Ni, 5% by weight of Crl, and the rest Fe) shows the relationship between the elapsed time after starting the gas turbine and the tightening stress (i.e., bolt tensile stress).

Since the bolt and the wheel are made of the same material, the tightening stress on the bolt does not change due to temperature changes, but as the rotational speed of the wheel increases, the wheel contracts in the axial direction due to centrifugal stress, so the tightening stress on the bolt decreases.

After reaching the rated rotational speed, the tightening stress becomes constant, but depending on the amount of axial contraction of the wheel, the tightening stress becomes less than σl.

On the other hand, the O mark and the broken line indicate changes in bolt tightening stress when the wheel material is A286 and the bolt material is Cr-Mo heat-resistant steel.

The dashed-dotted line shows the change in tightening stress assuming that the wheel temperature does not rise until the wheel rotational speed reaches the rated speed. However, in an actual gas turbine rotor, the wheel temperature increases with rotational speed, so bolt material The bolt tightening stress increases due to the difference in thermal expansion coefficient between the wheel material and the wheel material.
This changes as shown by the broken line due to the decrease in tightening stress due to centrifugal force.

As mentioned above, the coefficient of thermal expansion of A286 is significantly higher than that of other practical heat-resistant steels, so when the temperature of the wheel rises to the temperature of steady-state operation, the clamping stress becomes significantly large, easily causing σ.

It exceeds. Figure 2 is a reproduction of the same relationships as in Figure 1, and the solid lines are exactly the same as in Figure 1, but the thin dashed and dashed lines indicate that the wheel is tightened even when the wheel temperature reaches the steady operating temperature. The applied stress is σ.

Mark O, that is, the change when the tightening stress at rest at room temperature is lowered so as not to exceed .

In the change shown by the broken line, there is a risk that the bolt tightening stress is insufficient when the gas turbine is started, causing relative slippage between the wheels.

On the other hand, the thick dashed-dotted line shows the average bolt tightening when half of the bolts are made of A286, which is the same as the wheel material, and the other half are made of Cr-Mo heat-resistant steel with a coefficient of thermal expansion lower than that of A286. It shows the change in applied stress.

By using half of the two types of bolts made of different materials in this way, the following effects can be obtained.

First, the tightening stress generated in the bolt is σ for any bolt.

Since the strength of the bolt can be prevented from exceeding , the strength and reliability of the bolt can be increased.

On the other hand, with A286 bolts, C
In bolts made of r-Mo heat-resistant steel, the tightening stress becomes less than σ1 after reaching a steady operating state, which is favorable for the bolt itself in terms of strength.

The problem is that the tightening force (not the tightening stress) of the bolts that tighten each wheel is insufficient.

However, by combining two types of bolts as described above, the average tightening stress of the bolts can be maintained at σ1 or more throughout the entire period of gas turbine operation, as shown by the thick dashed line.

Having an average tightening stress of σl or more means that the required tightening force is secured, so there is no relative slippage between wheels that would be a concern if only one type of bolt was used. can be prevented.

Next, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 3, three wheels 1 are stacked in the axial direction, and shafts 2 are stacked on both ends thereof.

Each wheel 1 and shaft 2 is provided with a bolt hole that penetrates in the axial direction on the same radius, and a bolt 3 is inserted into this bolt hole.
a and 3b are inserted and tightened with a nut 4 to form a rotor shape.

As shown in FIG. 4, 16 bolts 3a and 3b are installed at the same intervals and so that the bolts 3a and 3b are arranged alternately.

In this embodiment, the material of the wheel 1 and bolt 3a is A2.
86. The material of the bolt 3b was Cr-Mo heat-resistant steel.

First, the bolt 3a has a tightening stress of σ when stopped at room temperature.
.

Tighten as much as possible without exceeding.

3b, the wheel temperature and wheel axial shrinkage due to centrifugal force under steady operating conditions are estimated, and even if the bolt tightening stress changes due to both, σ.

Tighten so that the tightening stress is as large as possible without exceeding.

When the gas turbine configured in this manner is started, the tightening stress of the bolt 3a decreases as the rotational speed increases, as shown by the solid line in FIG.

On the other hand, the tightening stress of the bolt 3b decreases once at the beginning of startup as shown by the broken line in FIG. 2, but increases as the temperature of the wheel 1 rises, and reaches just σ in the constant temperature operation state.

and will be retained as is.

The average tightening stress of the bolts 3a and 3b decreases once when the gas turbine is started, as shown by the thick dashed line in Fig. 2, but
σ1 increases again without falling below σ1, and maintains a constant value under steady operation conditions.

In this embodiment, bolts made of different materials are attached alternately one by one, but of course two or more bolts may be attached alternately.

According to the present invention, since changes in bolt tightening stress (tensile stress) and changes in wheel tightening force can be set separately, bolt tightening stress (tensile stress) can be kept below a certain limit. At the same time, it satisfies the contradictory conditions of keeping the wheel tightening force above a certain limit and has the effect of preventing slippage between the wheels.

[Brief explanation of drawings]

1 and 2 are diagrams explaining the operating principle of the present invention,
FIG. 3 is a longitudinal cross-sectional view of a gas turbine rotor showing an embodiment of the present invention, and FIG. 4 is a cross-sectional view along line AA in FIG. 3. 1...Wheel, 2...Shaft, 3
a, 3b... Bolt, 4... Nut.

Claims (1)

[Scope of Claims] 1 A plurality of wheels concentrically stacked, a shaft coupled to the wheels, a plurality of bolt holes passing through each of the wheels and the shaft in the axial direction, and bolts inserted into the bolt holes. In a gas turbine rotor formed into a rotor shape by passing through the bolt and tightening it with a nut, the bolt is made of a material having approximately the same coefficient of thermal expansion as the wheel, and a material having a coefficient of thermal expansion lower than that of the wheel. , a gas turbine rotor characterized in that bolts made of different materials are arranged alternately. 2 25% by weight of Ni and C on the wheel and one bolt material
2. The gas turbine according to claim 1, wherein the gas turbine is made of heat-resistant alloy steel comprising 5% by weight of rl and the balance being Fe.