JPH0330014B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is used as a suspension spring for automobiles.
Regarding FRP leaf springs and their manufacturing method. When using longitudinal continuous fibers as reinforcing fibers in FRP (fiber-reinforced synthetic resin), the reinforcing fibers are fed out from a roving bundle, passed through a resin bath containing resin, guided into a mold, and heated and molded. This is a common molding method. For example, in the well-known filament winding method, the winding speed is generally 20 to 60 m/min, and the viscosity of the resin in the resin bath is 5 to 20 poise. However, at the above molding speed and resin viscosity, air is easily trapped, resulting in a large amount of air bubbles in FRP.
In some cases, the void ratio may be 5 to 10%. This causes a problem in that the bending strength deteriorates and the durability performance deteriorates. However, in the past, FRP has rarely been applied to parts that require strength, such as leaf springs for vehicles, and therefore, even if the voidage is large, it cannot be used unless the appearance is impaired or the static strength is significantly reduced. It is provided. However, in recent years, there has been a strong desire to use FRP for suspension springs, especially in order to reduce the weight of vehicles.
Development of FRP leaf springs is progressing. For example, in U.S. Patent No. 3530212, it has a performance that can withstand practical use as a suspension spring for automobiles.
As an example of a method for manufacturing FRP leaf springs, an epoxy resin and an amine curing agent are used to bring it to B stage (semi-hardened state) and then molded and hardened.
We are trying to reduce the void ratio. According to this manufacturing method, the ultimate strength is 140 Kgf/mm ² (20 x 10 ⁴ _psi or more), the void ratio can be kept below 3%, and the fatigue resistance of 63 Kgf/mm ² (9 x 10 4 _psi ) is achieved. The company says it has been able to produce leaf springs that can withstand 500,000 cycles in tests. However, the amine curing agent used in the above method is toxic and poses problems in terms of the working environment, and it also cures too quickly and therefore has a short pot life (time for replacing the resin). For this reason, in the above-mentioned known example using an amine curing agent, an extra step is required, such as once bringing the material to a semi-cured B stage and then molding and curing it. Moreover, although the ultimate strength is quite high at 140Kgf/mm ² or more, the fatigue strength is relatively low at 500,000 cycles at a maximum stress of 63Kgf/mm ² . The present invention has been made based on the above circumstances, and its purpose is to be able to demonstrate sufficient fatigue strength for practical use as an FRP leaf spring for automobiles even if the bending strength is relatively low, and to provide an amine-cured FRP leaf spring. FRP that can be manufactured without using agents
An object of the present invention is to provide a leaf spring and a method for manufacturing the same. The FRP leaf spring of the present invention consists of a matrix resin whose main component is a resin composition in which an epoxy resin and an acid anhydride curing agent or a vinyl ester resin and an organic peroxide are mixed and a filler is added; It is composed of reinforcing fibers that are contained so that the volume ratio of fibers is 46 to 59% and is continuous in the longitudinal direction of the leaf spring, and the bending strength is 120Kgf/mm ² or less and 95Kgf/
mm ² or more, and the void ratio of air bubbles mixed in the resin is 2% or less. In order to obtain the above FRP leaf spring, a pre-cured resin whose main component is a mixture of an epoxy resin and an acid anhydride curing agent, or a vinyl ester resin and an organic peroxide, and a filler is added. , the reinforcing fibers are heated so that the viscosity is 1 poise or less and placed in a resin bath, and the reinforcing fibers are passed through the resin bath so that they are immersed in the resin for at least 5 seconds. By heat forming with a resin content of 59%, the bending strength is 95 kg.
f/mm ² to 120Kgf/mm ² and cavity ratio 2
% or less. An embodiment of the present invention will be described below. FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. In the figure, 1 is a resin tank. , a resin 2 containing a mixture of an acid anhydride curing agent such as tetrahydrophthalic anhydride as a curing agent, and 2-ethyl-4-methyl-imidazole as a curing accelerator. The resin tank 1 is configured such that the resin 2 therein can be heated by a heating means (not shown). Moreover, 3 is a roving bundle, and is adapted to pay out reinforcing fibers 3a made by bundling known continuous fibers such as glass fibers, carbon fibers, or organic fibers. This reinforcing fiber 3a is
The material is impregnated with resin by passing through the material, is wound up into a mold 4, and is heated and hardened. The mold 4 may be a mandrel used in a well-known filament winding method, a mold used in a pull-forming method, or another mold. To manufacture the FRP leaf spring of the present invention using the above-described apparatus, the temperature of the resin 2 is increased by heating the resin bath 1, and the viscosity thereof is adjusted to be 1 poise or less. The reinforcing fibers 3a passing through this resin tank 1 are immersed in the resin 2 for 5 seconds or more, and the length L of the resin tank 1 is set in advance in relation to the winding speed. In order to ensure the resin impregnation time for 5 seconds or more, it is preferable to make the resin tank longer than the conventional resin tank. Preferably, it passes through the resin bath 1 within 15 seconds. As described above, after soaking in resin 2 with a resin viscosity of 1 poise or less for 5 seconds or more, the volume ratio of the fibers is 46~
Remove excess resin to 59%. and type 4
By winding it up and heating and curing it, an FRP board with a void ratio of 2% or less and a bending strength of 120 kgf/mm ² can be obtained. The samples shown in Table 1 are the same resins as those in the above examples.

[Table] As shown above, FRP leaf springs with a bending strength of 120 Kgf/mm ² or less and a void ratio of 2% or less are those described in the above-mentioned U.S. Patent No. 3530212 ( 140Kgf/mm ² ), but in terms of fatigue strength, this known example has a resistance of 63Kgf/mm ² (500,000 cycles), while the product of the present invention can withstand more than 500,000 cycles of 65Kgf/mm ² without breaking. , exhibiting excellent performance as automotive springs. In addition, in the above manufacturing method, if the resin viscosity is 2 poise or more, or if the soaking time is 5
If the time is less than 2 seconds, the void ratio will be 3% or more in all cases, resulting in a significant decrease in fatigue strength. For this reason, it is necessary that the viscosity of the resin in the resin tank 1 be 1 poise or less, and that the resin be immersed in the resin for at least 5 seconds. According to the above manufacturing method,
Not only can FRP leaf springs be obtained, but since there is no need to use a special amine-based curing agent, handling is easy, and the working environment will not be degraded. Moreover, since the acid anhydride curing agent is used, the pot life (time during which the resin can be handled) can be extended, and the extra step of B stage, which is required when using an amine curing agent, can be omitted. In carrying out the present invention, a vinyl ester resin and an organic peroxide are mixed as a resin other than the above-mentioned examples, and fillers such as an extender such as calcium carbonate, an anti-shrinkage agent such as polyethylene, etc. You may also use one in which . In this case as well, as in the above example, the resin in the resin bath is heated to a pressure of 1 poise or less, immersed in the resin for 5 seconds or more, and molded so that the volume ratio of the reinforcing fibers is 46 to 59%. Therefore, a leaf spring with a bending strength of 120 Kgf/mm ² or less and a void ratio of 2% or less can be obtained, and can exhibit excellent fatigue strength as a spring for vehicle suspension. In each of these examples, if the volume ratio of reinforcing fibers is less than 46%, the specified bending strength cannot be satisfied, and if it exceeds 59%, the strength decreases due to poor adhesion between fibers, etc. It is necessary to limit the volume fraction of the reinforcing fibers to the above range. In addition, the volume ratio of reinforcing fibers is set in the above range of 46 to 59%.
Accordingly, the lower limit of the bending strength of the leaf spring is limited to 95 Kgf/mm ² for the following reasons. For example, when glass fiber is used, the elastic modulus of commercially available glass fiber is 7500 Kgf/mm ² and the elastic modulus of resin.
300Kgf/mm ² , the elastic modulus E of the entire leaf spring when the fiber volume ratio is 46% is expressed as E=7500×0.46+300×0.54=3612Kgf/mm ² . Moreover, when the volume ratio of fibers is 59%, E=7500×0.59+300×0.41=4548 Kgf/mm ² . Between the elastic modulus E, stress σ, and strain ε,
Since there is a relationship σ=E·ε, the strain ε is expressed by the following formula: ε=σ/E. The usable strain ε range of this leaf spring (upper limit of bending stress: 120Kgf/mm ² ) is when the fiber volume ratio is 46
%, according to the above formula, ε=120/3612=0.0332. When the fiber volume ratio is 59%, ε=120/4548=0.0264. That is, ε
= Usable in the range of 0.0264 to 0.0332. Therefore, the lower limit of bending strength that does not fall below both the lower limit of elastic modulus, 3612 Kgf/mm ² , and the lower limit of strain, 0.0264, is: σ _nio = E _nio ×ε _nio = 3612 × 0.0264 = 95 Kgf / ^mm2 . On the other hand, when carbon is used for the fiber, the elastic modulus of commercially available carbon fiber is 23500 Kgf/mm ² ,
The elastic modulus of the resin is 300Kgf/mm ² , so the volume ratio of the fiber is
The elastic modulus E of the entire leaf spring in the case of 46% is E=23500×0.46+300×0.54=10972Kgf/mm ² . Moreover, when the volume ratio of fiber is 59%, E=25300×0.56+300×0.41=13988Kgf/mm ² . When the volume ratio of fibers is 46%, ε=120/10972=0.011 When the volume ratio of fibers is 59%, ε=120/13988=0.0086. That is, ε
= Usable in the range of 0.011 to 0.0086. Therefore, the lower limit of the elastic modulus is 10972Kgf/mm ² ,
The lower limit of the bending strength so that the strain does not fall below the lower limit of 0.0086 is σ _nio = 10972 x 0.0086 = 94.4 Kgf/mm ² . When organic fibers (e.g. aramid fibers) are used, the elastic modulus of the fibers is 13,000 Kgf/mm ² and the elastic modulus of the resin is 300 Kgf/mm ² , and if the volume ratio of the fibers is 46%, E = 13,000 x 0.46+300×0.54=6142Kgf/ ^mm2 . Moreover, when the volume ratio of fiber is 59%, E=13000×0.59+300×0.41=7793Kgf/mm ² . The strain ε when the fiber volume ratio is 46% is calculated by the following formula: ε=120/6142=0.0195 The strain ε when the fiber volume ratio is 59% is ε=120/7793=0.0154. Therefore, the lower limit of bending strength is σ _nio = 6142 x 0.0154 = 95Kgf/mm ² . As mentioned above, regardless of the type of fiber, it is sufficient to adhere to the lower limit of 95 Kgf/mm ² in order to withstand use as a spring. As explained above, according to the present invention, by keeping the bending strength to 120 Kgf/mm ² or less and the cavity ratio to 2% or less, it is possible to form a vehicle suspension spring even with a relatively low bending strength. can withstand practical use as
We can provide FRP leaf springs. Moreover, as mentioned above, since the bending strength is relatively low, FRP leaf springs can be manufactured in a simple process using a less toxic ordinary hardening agent without using a highly toxic amine hardening agent.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the method of the present invention. 1... Resin tank, 2... Resin, 3... Roving bundle, 3
a... Reinforced fiber, 4... type.

Claims (1)

[Scope of Claims] 1. A matrix resin whose main component is a resin composition in which an epoxy resin and an acid anhydride curing agent or a vinyl ester resin and an organic peroxide are mixed and a filler is added, and a fiber in this resin. The volume ratio is 46 to 59
% and continuous reinforcing fibers in the longitudinal direction of the leaf spring, and also has high bending strength.
An FRP leaf spring characterized in that it is 120 Kgf/mm ² or less and 95 Kgf/mm ² or more, and the void ratio of air bubbles mixed in the resin is 2% or less. 2. A pre-cured resin whose main component is a resin composition obtained by mixing an epoxy resin and an acid anhydride curing agent, or a vinyl ester resin and an organic peroxide, and further adding a filler, has a viscosity of 1 poise or less. The resin-containing resin is placed in a resin bath in a heated state such that the reinforcing fibers are immersed in the resin for at least 5 seconds, and then passed through the resin bath so that the reinforcing fibers have a volume ratio of 46 to 59%. Manufacture of an FRP leaf spring characterized by obtaining an FRP leaf spring having a bending strength in the range of 95Kgf/ ^mm2 to 120Kgf/ ^mm2 and a void ratio of 2% or less by heat forming in a quantity. Method.