JP4879129B2 - Screw rotor - Google Patents

Description

  The present invention relates to a screw rotor in which a resin rotor is formed around a metal shaft.

  In a screw rotor in which a resin rotor is formed around a metal shaft, Patent Document 1 describes that a spiral groove is formed in the shaft in order to firmly fix the shaft and the rotor. Yes. However, forming a groove in the shaft has a problem that a step is formed on the inner surface of the rotor, stress is concentrated on the corner portion, and a crack is generated.

  Therefore, Patent Document 2 describes a screw rotor in which a groove having an arc-shaped cross section is formed on a shaft and adjacent grooves are connected by a smooth mountain-shaped curve having no corners.

  The shaft shape of Patent Document 2 can alleviate stress concentration on the inner surface of the rotor, but such a cornerless groove cannot be formed by a normal machine tool such as a threading machine or a composite lathe. There is a problem in that it requires time and cost to finish by hand.

  Moreover, since the shaft shape of patent document 2 requires the escape place of a tool when processing a spiral groove, the diameter of the both sides of the part which formed the spiral groove becomes thin. For this reason, a step is formed in the rotor at a portion where the diameter of the shaft becomes thin, and the rotor may be cracked due to axial stress during the formation of the rotor or during operation.

Furthermore, although it is described that the depth of the spiral groove in the shaft shape of Patent Document 2 should be about 1% of the shaft diameter, for example, in a shaft having a diameter of 40 to 80 mm, the depth of the groove is small. It is shallow as 0.4 to 0.8 mm, and the spiral groove wears out quickly due to rotational torque during operation, weight in the thrust direction and radial direction, and shear stress due to the difference in thermal expansion coefficient between the shaft and rotor. There's a problem.
JP-A-6-123292 Japanese Patent No. 3707378

In view of the above-described problems, an object of the present invention is to provide a screw rotor that can be formed by a general machine tool without cracking a resin rotor formed around a metal shaft.

In order to solve the above problems, according to the present invention, in a screw rotor in which a resin rotor is formed around a metal shaft, the shaft has a chamfered surface formed by cutting a surface flat. It is assumed that

  According to this configuration, since the chamfered portion functions as a key, the fixing force between the shaft and the rotor can be increased, and it is possible to resist stress acting during formation, processing, and operation. Further, since the shaft is only chamfered, there is no step or unevenness on the inner surface of the rotor, and stress concentration is small, so that cracks and breaks are unlikely to occur. Further, such chamfering can be easily processed by a general machine tool.

  Moreover, the screw rotor of this invention WHEREIN: The said shaft may carry out the sandblasting process on the surface.

  According to this structure, the adhesiveness with respect to the resin of a shaft can be improved, and durability of a screw rotor can be improved.

  In the screw rotor of the present invention, the rotor may be molded after a resin is applied to the surface of the shaft in advance.

  According to this configuration, the adhesive strength of the rotor can be increased and the durability of the screw rotor can be improved by applying the resin having good adhesion to the metal.

  In the screw rotor of the present invention, the chamfering may be performed directly below the tooth bottom portion of the rotor.

  According to this configuration, since the thickness of the rotor at the tooth bottom where the rotor is thinnest is increased, the durability of the screw rotor can be improved. In addition, since the cross-sectional shape is constant, the efficiency of design and manufacturing is high, which contributes to the improvement of product quality.

  In the screw rotor of the present invention, when the rotor is formed, a tensile load may be applied to the shaft in the axial direction, and the tensile load may be removed after the rotor is cured.

  According to this configuration, compressive residual stress can be applied to the rotor by contraction of the shaft by removing the tensile load, and concentration of the tensile stress of the rotor can be reduced, so that the durability of the screw rotor can be improved.

  In the screw rotor of the present invention, when the rotor is formed, the shaft may be set to a temperature higher than that of the resin, and the shaft may be returned to room temperature after the rotor is cured.

  According to this configuration, after the formation of the rotor, the shaft can be contracted to apply compressive residual stress to the rotor, and the concentration of the tensile stress of the rotor can be reduced, so that the durability of the screw rotor can be improved.

  According to the present invention, since the shaft is chamfered in a spiral shape, it is possible to provide a screw rotor with high durability while being easy to process.

  Embodiments of the present invention will now be described with reference to the drawings.

  In FIG. 1, the cross section of the screw rotor for compressors of one Embodiment of this invention is shown. The screw rotor according to the present embodiment includes a male rotor 1a and a female rotor 1b that form a pair of males and females, and are formed by molding resin-made rotors 3a and 3b around shafts 2a and 2b made of stainless steel SUS420F2. .

  The rotors 3a and 3b are formed by placing the shafts 2a and 2b in a mold (mold), injecting, for example, an epoxy resin into the mold, and heating the mold to, for example, 150 ° C. to cure the resin. . Since this resin requires high strength, elastic modulus, and dimensional stability, the resin to be applied is a resin containing a reinforcing material such as silica particles or glass fiber (for example, epoxy resin or urethane resin). preferable.

  The shaft 2a of the male rotor 1a of this embodiment has a diameter of 76 mm, and the rotor 3a has five teeth with an outer diameter of 154.4 mm, a length of 248.6 mm, and a left-handed twist. On the other hand, the shaft 2b of the female rotor 1b has a diameter of 54 mm, and the rotor 3b has six teeth with an outer diameter of 132.2 mm, a length of 243.6 mm, and a right twist.

  Furthermore, as shown in FIGS. 2 and 3, the shafts 2a and 2b are chamfered with chamfers 4a and 4b so as to extend directly below the tooth bottoms of the rotors 3a and 3b, respectively. As shown in the female rotor 1b shown in detail in FIG. 4, the chamfers 4a and 4b have the shafts 2a and 2b flattened to a depth of 1.5 mm (2% and 1.1% of the shaft diameter), respectively. Cut out. Five chamfers 4a are formed according to the number of teeth of the rotor 3a, and six chamfers 4b are formed.

  Such chamfers 4a and 4b can be easily formed by, for example, cutting a flat mill so as to be orthogonal to the shafts 2a and 2b in a composite lathe.

  In the male rotor 1a and the female rotor 1b formed in this way, the chamfers 4a and 4b serve as keys, so that the fixing force between the shafts 2a and 2b and the rotors 3a and 3b is high and can withstand high torque.

  Further, the angle formed between the chamfers 4a and 4b and the outer peripheral surfaces of the shafts 2a and 2b is very dull, and no stress is concentrated on the inner surfaces of the rotors 3a and 3b without forming a step. Yes, it is difficult to cause cracks in the rotors 3a and 3b.

  Further, after the surface of the shafts 2a and 2b of the present embodiment is subjected to sandblasting, the rotors 3a and 3b are formed in the same manner, thereby further increasing the fixing force between the shafts 2a and 2b and the rotors 3a and 3b. Can do.

  In addition, a resin having good adhesion to metal is applied to the surfaces of the shafts 2a and 2b of the present embodiment, and then the rotors 3a and 3b are placed in a mold, and the resin is injected and then cured by heating. It is preferable to form 3a and 3b. As a result, the resin having good adhesion to the metal applied to the surfaces of the shafts 2a and 2b is also cured, and the fixing force between the shafts 2a and 2b and the rotors 3a and 3b is increased. It becomes difficult to peel from 2b.

  There is an epoxy resin as a resin having good adhesiveness to metal. Particularly preferable epoxy resins include bisphenol A epoxy resin, urethane modified epoxy resin, rubber modified epoxy resin, and the like. Moreover, as those curing agents, polyamide polyamine, alicyclic polyamine, aliphatic polyamine, aromatic polyamine, acid anhydride, and Examples thereof include modified products and mixtures thereof.

  The rotors 3a and 3b may be molded with a urethane resin or the like that is inferior to the metal compared to the epoxy resin. In that case, the surface of the shafts 2a and 2b has good adhesion to the metal in advance. It is more effective to mold the rotors 3a and 3b after applying the resin.

  In addition, in a state where tensile stress is applied to the shafts 2a and 2b of the present embodiment, the rotors 3a and 3b are resin-molded around the shafts, and after the rotors 3a and 3b are cured, the tensile stress of the shafts 2a and 2b is removed. Thus, compressive stress can be applied to the rotors 3a and 3b in the normal state by contraction of the shafts 2a and 2b.

  During the operation of the screw rotor, tensile stress acts on the inner side of the rotors 3a and 3b to promote the generation of cracks. However, if the compressive stress is applied to the rotors 3a and 3b in advance, it acts substantially. The tensile stress can be relaxed and the occurrence of cracks can be suppressed.

  Further, such compressive stress is disposed in the mold in a state where the shafts 2a and 2b are heated and thermally expanded, and the rotors 3a and 3b are molded by filling resin around the shafts. It can also be applied by cooling the shafts 2a, 2b after curing.

  Based on the above embodiment, the following screw rotors were produced as experimental examples and comparative examples, and their strengths were tested.

(Experimental example 1)
The male rotor 1a and the female rotor 1b were manufactured as Experimental Example 1.

(Experimental example 2)
Experimental Example 2 was obtained by subjecting the surfaces of the shafts 2a and 2b to sand blasting and then molding the rotors 3a and 3b.

(Experimental example 3)
Experiment 3 was obtained by applying a resin having good adhesion to metal to the surfaces of the shafts 2a and 2b and then molding the rotors 3a and 3b. The resin used here is a mixture of Araldide AW106, HV953U and (epoxy resin and curing agent manufactured by Nagase Chemtech Co., Ltd.) at a weight ratio of 100: 60.

(Experimental example 4)
Experimental Example 4 was obtained by molding the rotors 3a and 3b in a state where a tensile load of about 10 kgf / mm ² was applied to the shafts 2a and 2b.

(Experimental example 5)
The shafts 2a and 2b were heated to 300 ° C. and placed in the mold, and the rotors 3a and 3b were molded as Experimental Example 5. The time required for curing the rotors 3a, 3b was about 1 hour, and the temperature of the shafts 2a, 2b when the resin of the rotors 3a, 3b was cured was about 200 ° C.

(Comparative Example 1)
Further, Comparative Example 1 was obtained by forming a spiral groove as described in Patent Document 1 on the shaft having the same diameter as the shafts 2 a and 2 b and molding the rotors 3 a and 3 b around the shaft.

(Comparative Example 2)
Comparative Example 2 in which a spiral groove having a smooth cross section as described in Patent Document 2 is formed on a shaft having the same diameter as the shafts 2a and 2b, and the rotors 3a and 3b are molded around the spiral grooves. It was.

  Although the above experimental examples and comparative examples were respectively produced, in Comparative Example 1, cracks were generated on the surfaces of the rotors 3a and 3b as soon as the rotors 3a and 3b were cured.

  With respect to the remaining experimental examples 1 to 5 and comparative example 2, when the external appearance was confirmed again after being installed in the compressor and operated for one month, the rotors 3a and 3b of comparative example 2 had the clearance of the cutting blades at both ends. For this reason, there was a crack at the top of the step.

  In Experimental Examples 1 to 5, since no damage was confirmed, it was re-installed in the compressor and operated for a total of 6 months. However, even after that, no damage was confirmed, and a decrease in the performance of the compressor was also observed. I couldn't.

Thus, in Experimental Examples 1 to 5, a large torque until breaking was applied and the breaking torque was measured, and the following results were obtained.

  Usually, the torque applied to the screw rotors 1a and 1b is about 100 kgf · m at the maximum, so the breaking torque indicates that each experimental example has sufficient proof stress.

  Further, in Experimental Examples 2 to 5, the breaking torque was improved as compared with Experimental Example 1, and it was confirmed that the production procedure added to Experimental Example 1 contributed to the improvement in the proof stress of the screw rotors 1a and 1b, respectively. .

Sectional drawing of the screw rotor of one Embodiment of this invention. The top view of the shaft of the male rotor of FIG. The top view of the shaft of the female rotor of FIG. FIG. 4 is a partially enlarged cross-sectional view of a shaft of the female rotor in FIG. 3.

Explanation of symbols

1a Male rotor 1b Female rotor 2a, 2b Shaft 3a, 3b Rotor 4a, 4b Chamfer

Claims (6)

In a screw rotor in which a resin rotor is formed around a metal shaft,
A screw rotor, wherein the shaft has a chamfer formed by cutting a surface flat .   The screw rotor according to claim 1, wherein a surface of the shaft is sandblasted.   The screw rotor according to claim 1 or 2, wherein the rotor is molded after a resin is applied to the surface of the shaft in advance.   The screw rotor according to any one of claims 1 to 3, wherein the chamfering is provided directly below a tooth bottom portion of the rotor.   5. The method according to claim 1, wherein when forming the rotor, a tensile load is applied to the shaft in an axial direction, and the tensile load is removed after the rotor is cured. Screw rotor. The screw according to any one of claims 1 to 4 , wherein when the rotor is formed, the shaft is heated to a temperature higher than that of the resin, and the shaft is returned to room temperature after the rotor is cured. Rotor.

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