JPS6249176B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for rolling plastic bolts, and more particularly to a method for threading a plastic material highly reinforced with reinforcing fibers by rolling. Prior Art Metal bolts have been known as bolts for a long time. This is manufactured by the rolling method, which has the fastest production speed for thread processing. Although metal bolts are manufactured with such high productivity, they have the fatal disadvantage of being heavy and prone to rust. On the other hand, plastic bolts that are lightweight and have excellent corrosion resistance are already in practical use. However, plastic materials to which rolling can be applied are limited to non-fiber reinforced plastic materials such as hard vinyl chloride resin. This is because fiber-reinforced plastic materials have high strength and therefore have poor plastic deformability, making it impossible to form threads by rolling, which requires plastic deformability. Even if this is forcibly rolled, the threads will not form a normal triangular shape, and the top of the triangle will become two threads, or cracks will occur in the threads. Therefore, it has low strength and cannot be used as a screw. Bolts obtained by rolling non-fiber reinforced plastic materials have poor strength. Since its tensile strength is at most 4 to 6 kg/mm ² , it cannot be used as a bolt that requires strong fastening force. OBJECTS OF THE INVENTION An object of the present invention is to provide a method for rolling plastic bolts that are lightweight, have corrosion resistance, chemical resistance, electrical insulation properties, and are highly reinforced with reinforcing fibers. Another object of the present invention is to provide a method for manufacturing high-strength plastic bolts by thread rolling, which is the most economical method for thread processing. Summary of the Invention The method for rolling a fiber-reinforced plastic bolt of the present invention includes forming threads using a rolling die in the surface layer of a cylindrical material, at least the surface layer of which is made of a thermoplastic resin in which reinforcing fibers are dispersed. Nisaishi,
The above-mentioned object is achieved by carrying out the rolling process while contacting the cylindrical material with a heat medium having a temperature higher than the transition temperature and lower than the melting point of the thermoplastic resin. Examples of reinforcing fibers include inorganic fibers such as glass fiber, carbon fiber, boron fiber, and silicon carbide fiber; and organic fibers such as aramid fiber. It is also possible to use a mixture of two or more of these fibers. There is no particular restriction on the length of the fibers, as long as they can be dispersed in the thermoplastic resin molded into a cylindrical material. These reinforcing fibers are melt-mixed with a thermoplastic resin using a kneading means such as an extruder, and are uniformly dispersed in the resin. This reinforcing fiber is 10~
40% by volume, preferably in the range of 15-35% by volume. If the fiber content is too low, high strength plastic bolts cannot be obtained. If the fiber content is too high, it will become brittle and the reinforcing effect will decrease. Examples of thermoplastic resins include polyamide,
Polyethylene terephthalate, polybutylene terephthalate, polyacetal, etc. are used.
Needless to say, there is no need to be limited to this. These resins may be mixed with various additives such as fillers, processing agents for improving adhesion to fibers, flame retardants, and antioxidants, if necessary. At least the surface layer of the cylindrical material used in the present invention is composed of a thermoplastic resin in which the above reinforcing fibers are dispersed, and the center portion has high strength even though it has the same composition as the surface layer. The core material may be made of a metal material such as iron, a fiber-reinforced thermosetting resin material, or the like. When a core material is used, the surface of the core material may be provided with irregularities or grooves to improve bondability with the thermoplastic resin. The heat medium used in the present invention includes, for example, heat-resistant, nonvolatile, high-boiling fluids such as silicone oil and glycerin. This is heated to a temperature above the transition temperature and below the melting point of the thermoplastic resin constituting the cylindrical material. When the thermoplastic resin is, for example, polyamide, the heat carrier is maintained at a temperature in the range of 85 to 260°C. If the heating medium is used at a temperature lower than the transition temperature of the resin, good threads cannot be formed because the deformation resistance of the resin to be threaded is still large. Above the melting point, the resin melts and threads cannot be formed. A heat medium in such a temperature range is poured onto the cylindrical material during the rolling process to heat only the resin surface layer. By doing so, the plastic deformability of only the surface layer is improved and thread processing becomes possible. It is important to heat the cylindrical material with a heating medium during the rolling process.Instead, heating the cylindrical material to the above heating medium temperature in advance and then subjecting it to the rolling process will cause the entire cylindrical material to heat up. This is not preferable because it tends to be elastically deformed. If the cylindrical material becomes easily elastically deformed, when the rolling die compresses the cylindrical material to form a thread, the entire cylindrical material or the entire surface layer will become excessively distorted, making it impossible to form a thread on only the surface layer. This is because it becomes impossible to form them. The rolling method used in the present invention does not need to be special, and rolling machines such as a round die rolling machine and a flat die rolling machine that are commonly used for thread forming of metal screws can be applied. In order to prevent the cylindrical material from being excessively heated during rolling, it is preferable that the temperature of the rolling die be equal to or lower than the transition temperature of the cylindrical material resin. FIG. 1 shows an example of a thread rolling method. The rolling machine 1 has a pair of rolling dies 11 and 12 that can rotate in the same direction. These dice are driven by a motor M. A heat medium 2 flows down from a heat medium supply pipe 20 above the dies to a cylindrical material placement section 13 between the dies. These dies 11 and 12 are maintained at a temperature below the transition temperature of the resin of the cylindrical material 13. As shown in FIG. 2, a cylindrical material 3 obtained by dispersing reinforcing fibers 30 is placed in the arrangement section 13 between the dies, and while rotating the dies 11 and 12, the cylindrical material 3 is
are brought close to each other so as to press them, and a thread is machined into the material 3. Since the dies 11 and 12 are maintained at a temperature below the transition temperature of the material resin, the material 13 is not heated excessively. When the surface layer of the material is threaded, the rolling dies 11 and 12
be separated from A desired plastic bolt 4, as shown in FIG. 3, for example, is formed in the arrangement part 13. Examples The present invention will be described below with reference to examples. Example 1 First, polyamide resin (Amiran Nylon 66 manufactured by Toray Industries, Inc.) and glass fiber with a diameter of 13 μm and a tip of 6 mm were dry blended at a volume ratio of 70:30, and this was molded into a round bar with a diameter of 9 mm using an extrusion molding machine. Molded. Next, this was cut into 10 cm lengths to obtain eight cylindrical materials. While pouring silicone oil at 250°C, thread forming was performed using a rolling machine equipped with a rolling die controlled at 20°C. The thread shape of the obtained 10 cm long M10 bolt was visually observed. At the same time, attach nuts to both ends of the bolt and tighten the JIS
A tensile test according to B1051 was conducted to measure the breaking strength. The average value of the five samples is shown in the table below. The breaking strength includes not only the maximum tensile load at which the bolt body is about to break, but also the maximum tensile load at which the thread is about to break and the bolt comes out from the nut. Example 2 Everything was the same as in Example 1 except that the temperature of the silicone oil was 150°C. Example 3 Everything was the same as in Example 1 except that the temperature of the silicone oil was 90°C. Example 4 Everything was the same as in Example 1 except that the temperature of the rolling die was controlled at 75°C. Comparative Example 1 Everything was the same as in Example 1 except that the temperature of the silicone oil was 75°C. Comparative Example 2 Everything was the same as in Example 1 except that the temperature of the silicone oil was 280°C. Comparative Example 3 The same as Example 1 except that silicone oil was not used. Comparative Example 4 Everything was the same as in Example 1 except that the temperature of the rolling die was controlled at 90°C. Comparative example 5 A cylindrical material was heated in advance for a long time at 150
Example 1 except that it was heated to ℃ and subjected to rolling processing without using silicone oil.
It is similar to

[Table] Effects of the Invention According to the present invention, it is extremely easy to form threads by rolling on a plastic material highly reinforced with reinforcing fibers. Since thread forming by rolling is highly productive, bolts can be produced economically. Moreover, the thread shape of the obtained plastic bolt is good, and the top of the thread does not form two threads or crack or break. Furthermore, the bolt has all the characteristics inherent to fiber-reinforced plastic materials, such as high strength, light weight, and excellent corrosion resistance.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional front view of an example of a rolling machine used to carry out the method of the present invention, FIG. 2 is a perspective view showing an example of a cylindrical material in the present invention, and FIG. 3 is a front view of a rolling machine used in the method of the present invention. FIG. 3 is a perspective view of an example of the resulting plastic bolt. 1... Rolling machine, 2... Heat medium, 3... Cylindrical material, 4... Plastic bolt, 11, 12...
Rolling die, 13...Material arrangement section.

Claims (1)

[Claims] 1. When forming a thread with a rolling die on the surface layer of a cylindrical material, at least the surface layer of which is composed of a thermoplastic resin in which reinforcing fibers are dispersed, the transfer of the thermoplastic resin A method for rolling a fiber-reinforced plastic bolt, which comprises rolling a cylindrical material while bringing it into contact with a heat medium at a temperature higher than the melting point and lower than the melting point. 2. The method according to claim 1, wherein the rolling die is controlled at a temperature below the transition temperature of the thermoplastic resin.