JPH04203383A - Screw rotor - Google Patents

Abstract

PURPOSE:To prevent any concentration of stress and improve an accuracy in size after molding operation by a method wherein a ratio between an outer diameter of resin material and an outer diameter of a metallic insert member is kept constant at each of locations and a rapid change in shape may not occur. CONSTITUTION:A male rotor (a female rotor) is a complex rotor in which a metallic insert 1 for the male rotor (a metallic insert 2 for the female rotor) is coated with a resin 3. Both rotors can be got by injection molding resin in a shape of teeth around the metallic insert. Shape of the metallic insert is machined in such a way as a ratio between an outer diameter r2 at the resin and an outer diameter r1 of the metallic insert is kept constant and made smooth at a location where severe irregular surfaces as found at a tooth crest of an F rotor. After injection molding, the resin is shrinked as the cooling is promoted. However, a residual stress may be produced due to a difference of liner expansion coefficient between the resin and the metallic insert. At this time, if a ratio of outer diameter were constant, a residual stress might also be kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to rotors for screw compressors and pumps.

[Conventional technology]

In conventional composite rotors in which metal inserts are coated with resin,
The insert shape was a tooth shape, and the resin wall thickness was thin and uniform. However, with thin walls, air bubbles do not remain inside the resin and it is possible to mold a dense resin, but the ratio of the outer diameter of the resin part to the outer diameter of the metal insert becomes small, making it difficult to Residual stress increases at the joints, making it easier for cracks to occur after molding. In the case of uniform wall thickness, since the outer diameter ratio is different, the residual stress at the joint becomes uneven, resulting in stress concentration.

The relationship between the outer diameter ratio and residual stress can be expressed as an approximate formula for maximum stress by applying the shrink fit formula for dissimilar materials: (1)
It becomes like the formula.

δθWAX: (α2-α1)(t□-tz)Ex(ni2
+1)/[ni2(1+ya,)+(1-92))
...(]) δθWAX: Maximum stress (circumferential direction of joint) α, fan expansion coefficient of two metals α2: Linear expansion coefficient of resin t□: Molding temperature t2: Room temperature E2: Elastic modulus of resin 乍2: Resin Poisson's ratio: 2: r2/rl r: Outer diameter of metal insert (joint part) = 2 - r2 + outer diameter of resin (1) As shown in equation (1), the maximum residual stress occurs at the joint part. If the tooth-shaped insert is formed with a thin and uniform wall thickness, the residual stress will be large because the outer diameter ratio is small, and the outer diameter ratio will be different at each joint, resulting in stress concentration.

As described in Japanese Patent Publication No. 1-301975, even when the insert shape is a cylinder and resin is molded around the outer circumference into a tooth shape, stress concentration occurs because the outer diameter ratio is different. Furthermore, since thermal contraction is non-uniform, it is difficult to improve dimensional accuracy.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, the shape of the metal insert with respect to residual stress in the joint portion is not considered. Therefore,
There were issues with stress concentration after molding and dimensional accuracy.

In order to make the residual stress and the amount of heat shrinkage uniform at the joint after molding, the present invention is designed to ensure that the ratio of the outer diameter of the resin part to the outer diameter of the metal insert is constant at each location, and that rapid shape changes are avoided. The purpose of the present invention is to provide a metal insert 1- which is free from scratches.

[Means to solve the problem]

One of the points to be considered in a composite rotor coated with a metal insert and a resin is the problem of residual stress that occurs at the joint between the metal insert and the resin after molding. The resin hardens at high temperatures during molding and shrinks as it cools, but because the amount of shrinkage is greater than that of metal inserts, residual stress may remain, which can lead to cracks.

As seen in equation (1), the maximum residual stress after forming is
One of the parameters is the ratio between the outer diameter of the metal insert and the outer diameter of the resin part. Therefore, by keeping this outer diameter ratio constant, the maximum residual stress generated at the joint between the metal insert and the resin can be made uniform at the joint. Furthermore, the amount of heat shrinkage becomes uniform and dimensional accuracy improves.

Furthermore, by increasing the outer diameter ratio (increasing the wall thickness of the resin), residual stress can be reduced and crack generation can be prevented.

[Effect]

By making the metal insert such that the ratio of the outer diameter of the resin to the outer diameter of the metal insert is constant and that there is no sudden change in shape, the residual stress will be uniform at the joint between the metal insert and the resin. No more stress concentration. Furthermore, since the amount of thermal contraction of the resin becomes uniform, the dimensional accuracy after molding can be improved. Furthermore, by increasing the outer diameter ratio, residual stress can be reduced and cracks can be prevented from occurring.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In FIG. 1, the male rotor (female rotor) is a composite rotor in which a metal insert 1 for male rotor (metal insert 2 for F40-tor) is coated with resin 3. Both rotors are obtained by injection molding resin into a tooth shape around a metal insert. As shown in Figure 2, the shape of the metal insert is such that the ratio of the outer diameter r2 of the resin part to the outer diameter r2 of the metal insert 1 is constant, and it is designed to be shaped in areas with severe irregularities such as the tips of the teeth of the F rotor. It is processed to be smooth.

14= After injection molding, the resin contracts as it cools, but residual stress is generated due to the difference in linear expansion coefficient with the metal insert. When using the shrink fit calculation formula as shown in formula (1),
The residual stress is maximum in the circumferential direction of the joint. At this time, if the outer diameter ratio is constant, the residual stress is also constant. Therefore, by using a metal insert like the one of the present invention, stress can be distributed almost uniformly at the joint, and stress concentration can be prevented. Furthermore, since the amount of thermal contraction becomes uniform, dimensional accuracy can be improved. Furthermore, by increasing the outer diameter ratio, residual stress after molding can be reduced and crack generation can be prevented.

〔Effect of the invention〕

According to the present invention, residual stress in the joint can be made uniform and stress concentration can be prevented. Further, the amount of heat shrinkage becomes uniform, and dimensional accuracy after molding can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a composite rotor made of metal inserts and resin according to an embodiment of the present invention, and FIG. 2 is a right side view of FIG. 1. 1...metal insert for female rotor, 2...metal insert for female rotor, 3...resin, r□...outer diameter of resin part.

Claims (1)

[Claims] 1. In a composite rotor in which a metal insert is coated with resin, the ratio of the outer diameter of the resin to the outer diameter of the metal insert is kept constant at each location and there is no sudden change in shape, so that the , a screw rotor characterized by uniforming residual stress and thermal contraction of the joint.