JP2622684B2 - Manufacturing method of compound screw rotor for compressor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for manufacturing a composite screw rotor for a compressor, and more particularly to a screw rotor for an oil-free screw compressor which supplies a compressed gas containing no oil. About.

[Conventional technology]

In a conventional screw rotor for an oil-free screw compressor, a pair of screw-shaped rotors of a male 1 and a female 2 are used as shown in a plan view of FIG. By rotating these at high speed, gas such as air is compressed and exhausted. The rotor comprises a tooth 3, a shaft 4 and a joint boundary 5, as shown in FIG.

In this compressor, gas such as air is compressed and exhausted without containing oil, so that oil for lubrication or cooling is not supplied into the compression chamber. For this reason, a pair of male and female rotors engage with a certain gap, rotate in a non-contact state, and compress gas such as air. The screw rotor is heated by heat generated when a gas such as air is compressed, and is heated to about 100 ° C. to 250 ° C. during a steady operation. As a result, the screw rotor thermally expands to reduce the gap between the rotors, and finally the male and female rotors come into contact with each other, resulting in a seizure lock accident. Therefore, in order to properly maintain the gap between the rotors during the compression in the steady operation, it is necessary to set the gap between the rotors wider by the amount of the thermal expansion when assembling at room temperature. However, the temperature distribution inside the rotor during the actual steady operation is not uniform and is not accurately grasped.

Conventional screw rotor materials such as carbon steel and chromium molybdenum steel are used.However, since these materials have a high coefficient of thermal expansion of about 12 × 10 ⁻⁶ / ° C. at 20 ° C. to 250 ° C., the rotor is required for assembly at room temperature. The gap between the rotors must be large, and more rotor gaps are considered because the temperature distribution is not clear. However, setting such a large gap has the disadvantage that the compression efficiency during operation is greatly reduced. On the other hand, if the gap is reduced, there is a risk of a seizure lock accident.

In order to solve the above problems, there is a conventional example in which the compression efficiency is improved as a composite screw rotor in which the rotor tooth profile has low thermal expansion and high Ni ductile cast iron and the shaft portion is steel (Japanese Patent Laid-Open No. 61-169689). ).

In this conventional example, for example, Fe-39% Ni
Using a 2.4% C-2% Si-1% Mn ductile cast iron, insert a consumable electrode made of S45C steel forming a shaft into the hollow space of the cylindrical ingot and fill by electroslag remelting to form a composite. Manufactures screw rotors.

An apparatus for manufacturing a composite screw rotor by the electroslag remelting method is shown in FIG. 4 and will be described in further detail.

A water-cooling mold 7 for a shaft portion and a shell 8 forming a tooth portion are arranged on a water-cooling platen 6, and a consumable electrode 9 is inserted into the space. The surface plate 6 is rotatable, and a plurality of current collecting brushes 10 are mounted around the surface. One end of a cable 11 is connected to the current collecting brush 10, and the other end of the cable 11 is connected to a power supply 12.

Electroslag remelting is started with such an apparatus. The consumable electrode 9 has one end immersed in a slag bath 13 and the other end connected to a power supply 12 via a cable 14. Negative electrode 9
Is melted by Joule heat to form a molten metal, and solidifies to form the shaft portion 5.

[Problems to be solved by the invention]

However, in the above-mentioned conventional screen rotor, there is a problem that a hot crack is easily generated in the heat-affected zone of the ductile cast iron of the tooth profile as shown in FIG. Fig. 5 (A)
Is a micrograph showing the structure near the joint boundary 5 between the tooth profile portion 3 and the shaft portion 4, and FIG. 5 (B) is an enlarged micrograph of the structure in which a hot crack 6 has occurred near the boundary.

When such hot cracking occurs, the strength is lost and the usefulness as a rotor is lost.

To prevent oil from entering the compression chamber from the bearing that supports the rotor, insert a carbon ring, etc., between the rotors of the oil-free screw compressor, and contact the rotating surface without lubrication to stop the oil. However, when the shaft is made of steel, there is a problem that corrosion occurs depending on the use environment. If this portion is corroded, troubles such as malfunction of the rotor and penetration of oil into the compression chamber will be caused.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a composite screw rotor for a compressor free from hot cracking and corrosion in order to solve such problems.

[Means for solving the problem]

Before describing the means for solving the problems, a description will be given of the mistakes that led to the completion of the present invention.

The present inventors have proposed Fe-Ni-C-Si to achieve the above object.
Various studies were conducted on the weldability of high-Ni cast iron composed of -Mn system. As a result, it was found that the hot cracks generated in the heat-affected zone were cracks caused by liquefaction of the grain boundaries, and the crack susceptibility increased with the increase of Si. That, NiSi-NiSi ₂ of Si enriched in austenite grain boundaries low melting, NiSi-Ni
₃ Si ₂ such precipitation phases of the region which is heated in the electro-slag remelting, i.e. dissolved in the heat-affected zone, the thermal stress is found that the crack acts occurring there.

On the other hand, high Ni cast iron is required to have excellent machinability because the rotor tooth profile is cut by a hob, and graphite is crystallized in the matrix. However, in the heat-affected zone, graphite melts and causes a decrease in strength, so it has been found that reducing the amount of graphite to a level that does not cause a problem in hob workability is effective in suppressing cracking.

The present invention has been made based on such findings. That is, the present invention relates to a method for manufacturing a composite screw rotor for a compressor, which is used for a compressor and comprises a tooth portion and a shaft portion forming an axis of the tooth portion and projecting from both ends. Is composed of, by weight ratio, C; 0.5 to 1.2%, Si; 0.3% or less, Mn; 0.5 to 2.0%, Ni; 36 to 42%, the balance being Fe and unavoidable impurities. It is composed of low thermal expansion high Ni cast iron having an average thermal expansion coefficient of 20 to 250 ° C., determined to satisfy the following equation and not more than 6 × 10 ⁻⁶ / ° C., K = 6.447 + 0.914C% + 1.254Si% + 0.828Mn% -0.108Ni% (Temperature, K6) The weight of the shaft portion is C: 0.25% or less, Ci: 10 to 30%, Ni
The first water-cooled cast type, in which the material at one end of the shaft is cast on a water-cooled surface plate, made of stainless steel alloy with excellent corrosion resistance consisting of 6-15% balance Fe and unavoidable impurities, high Ni
A cylindrical material of a tooth profile portion made of cast iron and a second water-cooled mold for casting a material at the other end of the shaft portion are sequentially stacked with their axes aligned, and the first water-cooled mold and the material of the tooth profile portion are arranged. And placing the consumable electrode of the stainless steel alloy through the axial space of each of the second water-cooled molds, further adding a solvent to the first water-cooled mold, and then between the upper end of the consumable electrode and the first water-cooled mold. Electricity is applied to melt the solvent to produce a molten slag, and the consumable electrode is electroslag redissolved while rotating the water-cooled platen. A manufacturing method characterized by forming a material on the end side.

[Action]

In the present invention, the reason for limiting the composition in the tooth profile will be described.

C is added in order to crystallize graphite in the matrix and impart machinability, but if it is less than 0.5%, the amount of graphite is small, and hob workability is deteriorated. It is not preferable because it promotes cracking and increases the coefficient of thermal expansion. Si is added as a deoxidizing agent and a graphite spheroidizing agent, but if it exceeds 0.3%, hot cracking occurs. Mn acts as a deoxidizing agent, but if it is less than 0.5%, the molten metal is insufficiently deoxidized, which tends to cause casting defects (bleaching).
Exceeding this is not preferred because it increases the coefficient of thermal expansion and worsens the machinability. Ni content is 3 to make the average coefficient of thermal expansion at 20 ° C to 250 ° C less than 6 × 10 ^-6 / ° C.
It needs to be 6-42%.

Further, this composition needs to be determined so that the following K satisfies the following formula (1) in the above composition range.

K = 6.447 + 0.914C% + 1.254Si% + 0.828Mn% -0.108Ni
% (1) If K6K is not within the above range, the average coefficient of thermal expansion at 20 to 250 ° C. may be larger than 6 × 1.0 ⁻⁶ / ° C.
If the average coefficient of thermal expansion at 20 to 250 ° C. is more than 6 × 10 ⁻⁶ / ° C., there is a possibility that seizure lock may occur in the tooth profile. The above equation (1) is an empirical equation obtained as a result of examining the relationship between the composition of each element and the average coefficient of thermal expansion.

Next, the reason for limiting the composition of the shaft portion will be described.

If C exceeds 0.25%, the hardness of the shaft increases during electroslag remelting, resulting in poor workability. If the Cr content is less than 10%, the workability deteriorates, and if it exceeds 30%, the corrosion resistance decreases. If the Ni content is less than 6%, the corrosion resistance decreases, and if the Ni content exceeds 15%, the workability deteriorates and the strength decreases. The shaft portion is made of a stainless steel alloy having such a composition, and corrosion of the shaft portion can be prevented.

On the other hand, when the shaft portion is formed of steel, the melt-mixed portion of the tooth member and the shaft member has a martensitic structure due to the transfer of Ni from the tooth member, so that it is difficult to process cooling holes provided in the rotor shaft center. However, in the case of the present invention, since the amount of carbon is small, an austenite structure is formed. Therefore, workability is also improved.

〔Example〕

 Next, examples of the present invention will be described.

It consists of Fe-0.7% C-0.25% Si-1.8% Mn-39% Ni20
Inner diameter with an average thermal expansion coefficient of 4.56 × 10 ^-6 / ° C between ~ 250 ° C
26φ, outer diameter 68φ, height of 120mm shell, SUS303
A consumable electrode having a diameter of 11φ was inserted, and electroslag was redissolved using the apparatus shown in FIG. CaF ₂
A slag composed of —Cao—Al ₂ O ₃ —SiO ₂ —MnO was used. The remelting was started by a cold start method with a voltage of 30 V and a current of 300 A. The ingot produced in this manner was longitudinally examined to check the bonding state. As a result, as shown in FIG. 1, no crack occurred in the heat-affected zone, and it was found that the joint was good.

In FIG. 1, (A) is a micrograph near the joint, and (B) is an enlarged micrograph of (A).

Next, change the composition and redissolve the electroslag,
The average coefficient of thermal expansion and the presence or absence of hot cracks were examined. Table 1 shows the composition of each sample. Table 2 shows the value of the average thermal expansion of each sample and the presence or absence of a hot crack.

As can be seen from Table 2, in samples Nos. 4 to 6, 10, and Nos. 13 and 14, high-temperature cracking occurs when the Si content exceeds 0.3%. On the other hand, the other samples did not undergo hot cracking, and had the above-mentioned formula (1).
Since it is 6, the average thermal expansion coefficient at 20 to 250 ° C. is 6 × 10 ⁻⁶ / ° C. or less. Therefore, it is understood that the material is effective as a material for the tooth profile of the screw rotor.

Next, the Fe-0.7% C-0.25% Si-1.8% Mn-39% Mi
The ingot obtained from the above was hobbed to produce a rotor. The specifications of the rotor are 5 male rotor teeth, 63 mm outer diameter, 6 female rotor teeth, 53 mm outer diameter, and 97.5 mm rotor length. A performance comparison test was conducted of a conventional S45C integrated screw rotor having the same specifications as this rotor, and a composite consisting of Fe-2.4% C-2% Si-1% Mn-39% Ni ductile cast iron with a tooth profile and S45C with a shaft. . The gap between the male rotor and the female rotor is 50 μ in the rotor according to the embodiment, and 100 μ in the conventional integrated rotor.
μ.

As a result of comparison, discharge pressure 7 kg f / cm ² , suction flow 1000 m ³ / h
The compression efficiency of the screw rotor according to the present embodiment is 65% while the compression efficiency of the integrated screw rotor is 65%.
And improved. On the other hand, as a result of the shaft corrosion resistance test performed by the salt spray test method (spraying of 5% salt water for 96 hours), the conventional integral and composite screw rotors showed remarkable rust and corrosion, whereas the composite screw rotor of the present invention Rust and corrosion were hardly observed, and the tooth profile was slightly smaller than that of the conventional composite screw rotor.

〔The invention's effect〕

As described above, according to the present invention, when forming a shaft portion that penetrates the screw rotor tooth portion by the electro-remelting method, the screw rotor tooth portion does not generate hot cracks, and has a temperature of 20 ° C to 250 ° C. Average thermal expansion coefficient is 6 × 10 ^-6 / ℃
Composed of the following low-thermal-expansion high-Ni cast iron, and by using a composite screw rotor composed of a stainless steel alloy with excellent corrosion resistance, cracks that occur in the heat-affected zone of the tooth profile are prevented. The corrosion resistance of the part is improved, and the reliability of the product can be improved. As a result of preventing high temperature cracking of the tooth profile portion and corrosion of the shaft portion, it is possible to prevent oil from being mixed into the compressed gas, and it is possible to always supply a clean compressed gas.

[Brief description of the drawings]

FIG. 1 is a micrograph showing the metal structure of a longitudinal section of the composite screw rotor material according to the present invention, and FIG.
Plan view showing the structure of the screw portion of the screw compressor,
FIG. 2 (B) is a longitudinal sectional view, FIG. 3 is a transverse sectional view of a composite screw rotor, FIG. 4 is a configuration diagram of an apparatus for performing an electroslag remelting method, and FIG. It is a microscope picture which shows the metal structure of the longitudinal section of a rotor material. 1 ... male screw rotor, 2 ... female screw rotor, 3 ... tooth profile, 4 ... shaft, 5 ... joining boundary, 6 ... water-cooled surface plate, 7 ... water-cooled mold for shaft, 8 Shell, 9 Consumable electrode, 12 Power supply.

Claims (1)

(57) [Claims] 1. A method for manufacturing a compound screw rotor for a compressor, comprising: a tooth portion and a shaft portion that forms an axis of the tooth portion and protrudes from both ends. , By weight, C; 0.5-1.2%, Si; 0.3% or less, M
n; 0.5 to 2.0%, Ni; 36 to 42%, the balance being Fe and unavoidable impurities, and in the composition range, the following K is determined so as to satisfy the notation formula. Made of low thermal expansion high Ni cast iron with an expansion coefficient of 6 × 10 ^-6 / ° C or less, K = 6.447 + 0.914C% + 1.254Si% + 0.828MN% -0.108Ni
% (C, K ≦ 6) The shaft portion is, by weight ratio, C: 0.25% or less, Cr: 10 to 30%, Ni; 6
A first water-cooled mold for casting a material at one end of the shaft portion on a water-cooled platen so as to be composed of a stainless steel alloy having excellent corrosion resistance consisting of about 15%, the balance being Fe and unavoidable impurities. A cylindrical material having a tooth profile portion made of Ni cast iron, and a second water-cooled mold for casting a material at the other end of the shaft portion,
Each of the first water-cooled mold, the material of the tooth profile portion and the second water-cooled mold are arranged through the axial space of each of the first water-cooled molds, and the consumable electrodes to be the stainless steel alloy steel are arranged. After the solvent is put into the first water-cooled mold, a current is applied between the first water-cooled mold from the upper end of the consumable electrode to melt the solvent to generate a molten slag, and the consumable electrode is rotated while rotating the water-cooled platen. Manufacturing a composite screw rotor for a compressor, wherein a material on one end side of the shaft portion, a core portion of the tooth profile portion and a material on the other end side of the shaft portion are formed by electroslag re-melting. Law.