JPH01186310A - Resin molded piece and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a resin molded piece having sufficient mechanical and electrical characteristics against heat by adhering resin ultrafine particles to inorganic fiber, and forming an intermediate layer having high inorganic fiber concentration on a resin/metal insert boundary. CONSTITUTION:When a metal insert 1 is masked except its molding face, heated to approx. 200 deg.C and resin-adhered glass short fiber 10 is sprayed by a spray gun 8 to the insert 1, since the temperature of the insert 1 is high, the resin on the fiber 10 is softened to be adhered. This is mounted in a metal mold 11, resin 2 is poured, and injection molded. When the resin 2 is invaded to the gaps among the fibers 10 to arrive at the surface of the insert 1 to be cured, an intermediate layer 5 having high metal insert short fiber concentration is formed near the insert 1 in bushing. The layer 5 has a thermal expansion coefficient intermediate between those of the insert 1 and the resin 2, being effective to reduce its thermal stress. Thus, a resin molded piece having excellent thermal, mechanical, electrical characteristics is obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a resin molded part for high voltage insulation having a metal insert, such as a resin insulator in heavy electrical equipment, and a method for manufacturing the same. is.

(Prior Art) As is well known, high-voltage insulating resin molded parts used in heavy electrical equipment are often molded with a built-in metal insert for the purpose of connection to a conductor or supporting side.

In addition, resin bushings, which are intended to electrically connect the inside and outside of the casing2, are composed of insulators that are insulated from the casing and have a built-in conductor to secure them. There is also.

FIG. 9 is a sectional view showing an example of such a resin bushing. The metal insert 1, which is a conductor, is molded with resin 2, which is an insulator, in order to fix it to the housing and insulate it. Fixing to the housing is carried out by providing a through hole or a filler metal in the 7 flange portion 3 and using bolts or the like.

Furthermore, for example, epoxy casting materials are excellent in moisture resistance, flame resistance, chemical resistance, two-dimensional stability, electrical properties, mechanical properties, etc., and are widely used as resins for resin bushings. Since this epoxy casting material also has good adhesion to metal, peeling or cracking at the metal insert/resin interface is usually not observed in the product immediately after casting.

However, due to the heat cycle caused by equipment shutdown, considerable stress is generated at the metal insert/resin interface.

In the case of molded parts such as resin bushings, which have a long conductor as a metal insert, the conductor at the outer connection part has a large cross-sectional area, while the inner shaft part has a large cross-sectional area, as shown in Figure 9. has a small cross section. Then,
As shown in FIG. 10, stress is particularly concentrated at parts of the conductor where the shape changes rapidly, and cracks 4 are likely to occur. Many of the resins used as structural materials for heavy electrical equipment, including epoxy casting materials, are highly brittle, so once a crank occurs, it quickly propagates through the resin 2 without stopping and breaks. leading to. Mechanical damage to resin bushings sometimes causes accidents such as ground faults.

(Problems to be Solved by the Invention) 1. One way to solve these drawbacks is to increase the strength of the resin. Since the strength of the resin itself is limited, the mechanical strength can be significantly improved by filling it with a fibrous material such as glass fiber. but,
When this fibrous material is added to a low-viscosity liquid epoxy resin and stirred, the viscosity becomes very high, reducing workability, and even under reduced pressure, the air contained in the mixture cannot be completely removed. First, small ids remain in the molded resin, resulting in inferior electrical properties compared to resin bushings using powder fillers.

Another method is to lower the coefficient of thermal expansion of the resin to bring it closer to that of metal, thereby minimizing the generation of thermal stress. The coefficient of thermal expansion of the resin is reduced by adding a large amount of an inorganic filler such as a wrinkle strength powder. However, as mentioned above, when a large amount of filler is added to the resin, the viscosity increases significantly and impairs fluidity, which interferes with the casting process, making it difficult to apply it to products with complex shapes in practice. is impossible.

Furthermore, a "two-stage casting method" is used in which only the vicinity of the metal insert is cast with a resin having a composition with a low coefficient of thermal expansion, and the complex-shaped parts outside of that are cast with a low-viscosity resin. but,
Since this method uses multiple resin materials, it results in the creation of new interfaces in the resin bushing, and the peeling of these areas degrades the mechanical and electrical properties of the component.
The reliability of the parts will be reduced.

Another method is to wrap glass fiber or glass cloth around a metal insert and cast it to provide a reinforcing layer against thermal stress. This method basically increases the strength and is effective in terms of mechanical strength. However, since the interface clearly exists and the elastic modulus increases, a long bushing (4
, the thermal stress becomes large, and the edges tend to peel off. Therefore, assuming such a case, it is sometimes possible to peel off the crimp end to loosen the restraint against thermal stress. However, if a bushing made of glass cloth wrapped around a metal insert and cast is used in SF6 gas, the SFS gas will decompose under corona discharge, and this decomposed gas will damage the peeled or peeled edges. Infiltrate inside from. This decomposed gas significantly corrodes the glass, attacks the glass fibers at the interface, and significantly reduces the strength.

As a result, peeling at the interface progresses and cracks occur.

Another method is to prepare a conductor wrapped with rubber or the like as a stress buffer layer, and then mold this.

The rubber used in this method is silicone rubber, which is chemically stable and shows little change in rigidity over a wide temperature range for electrical equipment. The occurrence of cranks can be prevented by using silicone rubber.

However, since it does not adhere to epoxy resin or the like, moisture, SF6 gas, etc. enter the epoxy resin/silicone interface and the properties deteriorate. On the other hand, molded parts using a flexible material as a stress buffer layer basically have a drawback of low mechanical strength.

As explained above, resin molded parts having metal inserts do not have sufficient countermeasures against thermal stress generated during heat cycles, and have the drawback of being susceptible to cracks and the like.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a resin molded component that suppresses peeling and cracking at the metal insert/resin interface due to thermal stress and has sufficient mechanical and electrical properties against heat.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides resin molded parts in which a metal insert is embedded in a resin molded body, in which ultrafine resin particles are attached to inorganic fibers, and the inorganic fibers are bonded to the surface of the metal insert. After adhering to the resin and then casting, an intermediate layer with a high concentration of inorganic fibers is formed at the resin/metal insert interface.

(Function) For example, as shown in Fig. 1, if a resin 2 (coefficient of thermal expansion α12 modulus of elasticity eE1) and a flat metal insert (α2, E2) of equal length and cross-sectional area are joined at a temperature of 0. do. However, it is assumed that α1 > α2 and that no stress is generated at the temperature To. Suppose now that the temperature rises from T0 to T1. When the two materials are not bonded, they are free to elongate due to heat, and △! for resin 2 metal insert 1. 1-α1 ・ (D1-To ) ・1- (
1) △β2-α2 ・(T1-To >4'-(2
). When both materials are completely bonded, they are constrained to each other, and the resin 2, which has a large coefficient of thermal expansion, is subjected to compressive loads,
The metal insert 1, which has a low coefficient of thermal expansion, is subjected to tensile loads. As a result, a negative part arises for both.

Equilibrium occurs when the elongation is equal. At this time, if the resin 2 is △diB and the metal insert 1 is 8 and 4, and they change due to mutual restraint, the load (stress) σ generated on both from the equilibrium condition is σ−△! 3 ・[1/! −△! 4 ・E2/1...(
3) Also, the elongation is △, 1 - △, 2 - △, 3 + △, 4... (4) (3)
, Eliminate △123 from equation (4) and △! 3-(1-△12 for △)・F2 / (El + E2)...(5) Substituting equations (1,) and (2) into equation (5), △13
−<al −a2)・(T1−To)・!・E2
/ (El +E2)... (6) Therefore, the load σ generated is σ-(α1-α2)・
(Bottom 1-To)・E-Ez/(E1+E2)・
...(7) Therefore, the larger the temperature change, the more
The larger the difference in thermal expansion coefficients, the higher the generated thermal stress. For example, a bisphenol-based epoxy casting material (α+
≠50X10-6 ・℃-', El":, L
200Kgf/mm2) and mild steel insert (A2'
:; 10x to-8-℃-1, E2 Mai 21,00
0Kgf/m2) (D combination: b cera. Assuming that no thermal stress occurs when the resin curing temperature is 120°C, To
= 120'C. This is the maximum temperature T1 = 20°C
Now, the stress generated at the time of cooling is calculated as 4. from equation (7).
, 5 Kg f /Inm 2. Cooling process T[,
Acts as a tensile load on the resin side. Furthermore, considering temperature gradients caused by rapid temperature changes, curing shrinkage of resin, etc.
The load will be high. The resin molded parts themselves are
Although the shape is quite complex, basically following the above idea, cracking and peeling are likely to occur due to a sudden temperature drop. 'In the present invention, as shown in FIG. 2, an intermediate layer 5 having a coefficient of thermal expansion between that of the metal insert 1 and the resin 2 is provided to reduce thermal stress by half.

The intermediate layer 5 is a resin layer filled with glass fibers at high density. Since the thermal expansion coefficient of glass fiber is as small as 5×10 −5 ·° C. −1, by filling the matrix resin with an appropriate amount of glass fiber, a thermal expansion coefficient intermediate between that of the insert 1 and the resin 2 can be provided.

Furthermore, as seen in GFljP (glass fiber reinforced plastic), glass fiber has a high tensile strength, so it acts as a mechanical reinforcing material, dramatically improving the mechanical strength of the intermediate layer itself. Therefore, it exhibits a sufficient effect against rough thermal stress.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 3 shows a resin bushing to which the present invention is applied, in which an intermediate layer 5 is formed between a metal insert 1 serving as a conductor and a resin 2.

Next, a method for manufacturing this resin bushing will be explained. Figure 4 shows ultrafine resin particles 6 (e.g., highly dispersible acrylic ultrafine powder M P-1000, manufactured by Soken Kagaku ■) with a diameter of 5 to 20 mm.
The state shown is that it is attached to the surface of a 1 tm short glass fiber 7 (for example, milled fiber REV-7 manufactured by Nippon Sheet Glass Co., Ltd.). This resin-attached short glass fiber can be easily obtained by mixing ultrafine resin particles 6 and short glass fiber 7.

FIG. 5 is an explanatory diagram of a method for attaching the resin-attached short glass fibers produced in this way to the metal insert 1. The area other than the casting surface of the metal insert 1 is masked with a suitable tape, etc., and heated to around 2'00°C. next,
Using a spray gun 8, pressurized air 9 is used to spray the resin-attached short glass fibers 1o onto the metal insert 1. Since the temperature of the metal insert 1 is high, the resin on the surface of the resin-attached short glass fibers 10 softens and adheres to the metal insert 1. There is no separation between the resin particles and the glass during the spraying process.

The metal insert 1 with the resin-attached short glass fibers -11=10 adhered to the casting surface in this manner is attached to the mold 11 as shown in Fig. 6, and the resin 2 (for example, epoxy resin) is injected and the casting is carried out. Do this. The resin 2 enters the gap between the resin-attached short glass fibers 10 by capillary action, reaches the surface of the metal insert 1, and acts as a matrix. When the resin 2 hardens, as shown in FIG. 3, an intermediate layer 5 with a high concentration of short crow fibers is formed in the vicinity of the metal insert 1 in the bushing.

This intermediate layer 5 has a coefficient of thermal expansion between that of the metal insert 1 and the resin 2, and is effective in reducing thermal stress. For example, FIG. 7 shows the relationship between the filling amount of an epoxy resin filled with short glass fibers having a diameter of 5 to 20 mm and a length of 10 # or less and the coefficient of thermal expansion. When short glass fibers are attached to a metal insert and casting is performed, the content of short glass fibers near the metal insert is 60 to 80 wt%. therefore,
The coefficient of thermal expansion is 20~30X10-6・°C-1,
From equation (7), the thermal stress generated during cooling can be calculated from 30 to 60
%. In addition, the short glass fibers decrease with a certain concentration gradient from the vicinity of the metal insert, and do not form an obvious interface in the resin, so they are difficult to peel off. If the fiber diameter is less than 5%, the filling amount will be more than 90wt%, the matrix resin will decrease, and the adhesive strength with the metal insert will decrease significantly, so it is inappropriate. This is not preferable because the gap between them becomes large and the amount of filling decreases.

On the other hand, the filling of short glass fibers improves the mechanical strength of the material. FIG. 8 shows the relationship between the filling amount and the tensile strength of the above-mentioned short glass fiber filled epoxy resin. The tensile strength of the resin near the metal insert is 20 to 25 KIJ'
f/mm2. Filling with a large amount of short glass fibers
In addition to lowering the coefficient of thermal expansion and reducing thermal stress, it is also effective in terms of mechanical strength. Since such a large amount of short glass fibers significantly increases the viscosity, it is impossible to uniformly mix and cast as a film-type resin, which is achieved by the present invention.

The intermediate layer produced in this manner exhibits sufficient strength against thermal or mechanical stress.

The resin bushings of the above-described examples and the resin bushings without an intermediate layer were subjected to a liquid phase cooling/heating cycle of O'C for 1 hour 10 times, and the presence or absence of cracks was checked. As a result, cracks reaching the surface were observed in the resin bushing without an intermediate layer after 5 cycles, but the resin bushing of the above example with an intermediate layer showed no cracks even after 10 cycles. No occurrence was confirmed,
Corona characteristics were also good.

Furthermore, the resin bushing of the above embodiment having an intermediate layer is
Compared to the resin bushing of the above example having an intermediate layer,
It was verified that it has sufficient strength against thermal stress.

Although the embodiments described above are directed to resin bushings, it goes without saying that the present invention can be applied to resin insulators and other resin molded parts.

[Effects of the Invention] As explained above, the present invention involves attaching inorganic fibers on the surface of which are coated with ultrafine resin particles to the surface of a metal insert to be incorporated, and incorporating this metal insert into a mold. By casting, an intermediate layer with a high concentration of inorganic fibers is formed near the metal insert, so it is possible to provide a resin molded part with excellent thermal, mechanical, and electrical properties.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram related to the present invention showing the occurrence of thermal stress when materials having different coefficients of thermal expansion and modulus of elasticity are joined, and FIG. 2 is an explanatory diagram showing the structure of the present invention in a cut state. , FIG. 3 is a sectional view showing the structure of a resin bushing according to an embodiment of the present invention, and FIG. 4 is an explanatory view showing a state in which ultrafine resin particles are attached to inorganic fibers in the manufacturing method of the present invention.
FIG. 5 is an explanatory diagram showing a state in which inorganic fibers with resin attached are attached to a metal insert in the manufacturing method of the present invention, and FIG. 6 is an explanatory diagram showing a state in which resin is cast into a metal insert in the manufacturing method of the present invention. 7 are related to the present invention and are diagrams showing the relationship between the filling rate and the coefficient of thermal expansion when epoxy resin is filled with short glass fibers. A diagram showing the relationship between tensile strength and filling rate when filled with fibers, Figure 9 is a cross-sectional view showing the structure of a conventional resin bushing, and Figure 10 is an explanatory diagram showing the occurrence of cracks in a conventional resin bushing. be. 1...Metal insert 2...Resin 5...Middle layer (8733) Agent: Patent attorney Yoshiaki Inomata (and others)
1 person) Figure 2 Figure 4 Figure 5 9 Figure 7 Figure 6 Figure 8

Claims (3)

[Claims] (1) A resin molded part in which a metal insert is embedded in a resin molded body, characterized in that an intermediate layer having a high concentration of inorganic fibers is formed in the vicinity of the metal insert. (2) A method for producing resin molded parts, which comprises adhering ultrafine resin particles to inorganic fibers, adhering the inorganic fibers to the surface of a metal insert, and then casting. (3) The method for manufacturing resin molded parts according to claim 2, wherein glass fibers having a diameter of 5 to 50 μm are used as the inorganic fibers.