Power tool equipped with fiber-reinforced phenolic resin gear

Abstract

To propose a power tool with little deterioration over time and a long service life, which combines a metal gear with excellent physical properties and a resin gear in a gear configuration that is a power transmission mechanism of a power tool such as a polisher or a sander, to reduce an amount of wear powder generated by wear due to meshing of gear teeth.SOLUTION: A power tool is equipped with: a power transmission mechanism 1 having a gear configuration consisting of an output gear 4 attached to an output shaft 3 of an armature 2, a final gear 8 attached to a spindle 9 for mounting a rotating disc, and an intermediate gear assembly 5 connecting the output gear 4 and the final gear 8, where the output gear 4 is a metal gear, and at least some of the gears of the intermediate gear assembly 5 are made of aramid fiber-reinforced resin.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to power tools such as polishers and sanders, and more particularly to a gear configuration that serves as a power transmission mechanism. [Background technology]

[0002] In power tools such as polishers and sanders, the rotational output from the motor is transmitted as rotational power to a rotating disk equipped with abrasive or grinding pads or sheets such as buffs or sandpaper, through a power transmission mechanism with a gear configuration, and the rotating disk is rotated to perform polishing and grinding work. In these power tools, wear caused by the meshing of the gear teeth over time can cause malfunctions such as damage to the gear teeth. In this case, it is not just the wear between the gear teeth, but also the fine powder of the gear material generated during this meshing acts as an abrasive at the meshing joint, accelerating wear and increasing the frequency of malfunctions. When the material of the gears constituting the power transmission mechanism is metal, a lot of wear powder is generated, and the wear-accelerating effect of the metal fine powder is also large. In particular, in the case of steel, the oxidation of the wear powder of the steel causes rust, and the rusty steel fine powder penetrates the gear joint and not only hinders sliding, but also oxidizes the grease, significantly hindering the lubricating action, causing great damage to the gears.

[0003] Therefore, in order to prevent deterioration over time in the power transmission mechanism of an automobile, a structure is also used in which a lubricant is circulated and the generated wear fine powder is collected and removed. Furthermore, in many cases, this mechanism of an automobile is rarely used to the extent that the high hardness processed part of the gear surface is worn away, so it is meaningful to reduce the wear of the high hardness processed part. However, it is difficult to structure such a lubricant circulating in the above-mentioned small electric tools, and it was necessary to replace the lubricant and clean it or replace the gear after a certain amount of use, assuming deterioration over time. Furthermore, it is not uncommon for some users to continue using the tool even after the high hardness processed part of the gear has worn away, and to continue using it until the gears no longer mesh. This is thought to be because, while the abnormal sound of the gear in an automobile immediately suggests a danger to life, the abnormal sound of the polisher does not suggest a danger to life, body, or objects.

[0004] Meanwhile, as for the material of gears, resin gears using resin materials instead of metals are also used from the viewpoints of weight reduction, prevention of noise generation, etc. Also, in order to ensure the wear resistance of the resin material, it has been proposed to use aramid fiber reinforced phenolic resin (see Patent Document 1) or aramid fiber reinforced phenolic resin molded in consideration of the orientation state of the reinforcing fibers (see Patent Document 2).

[0005] However, no consideration had been given to the possibility of preventing the generation of metal powder as described above, preventing malfunctions such as breakage of gear teeth, and extending the service life of power tools by using metal gears, which are materials with excellent wear resistance and strength, as the gears that make up the power transmission mechanism, in combination with resin gears. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-240326 [Patent Document 2] JP 2013-256998 A Summary of the Invention [Problem to be solved by the invention]

[0007] The objective of the present invention is to propose an electric tool that has a long service life and is less susceptible to deterioration over time, by combining metal gears with excellent physical properties and resin gears in the gear configuration that forms the power transmission mechanism of electric tools such as polishers and sanders, thereby reducing the amount of fine wear powder generated by wear caused by the meshing of gear teeth. [Means for solving the problem]

[0008] The electric power tool of the present invention is an electric power tool equipped with a power transmission mechanism having a gear configuration consisting of an output gear attached to the output shaft of an armature, a final gear attached to a spindle for mounting a rotating disk, and an intermediate gear assembly connecting the output gear and the final gear, characterized in that the output gear is a metal gear and at least some of the gears of the intermediate gear assembly are gears made of aramid fiber reinforced resin.

[0009] At least the gear of the intermediate gear assembly that meshes with the output gear is preferably an aramid fiber reinforced phenolic resin gear, and in the power transmission mechanism, the drive gear is preferably a metal gear and the driven gear is preferably an aramid fiber reinforced resin gear. Furthermore, the intermediate gear assembly is composed of a large intermediate gear and a small intermediate gear that are connected to each other and share a central axis, and it is preferable that the large intermediate gear is an aramid fiber reinforced phenolic resin gear and directly meshes with the output gear, and the small intermediate gear directly meshes with the final gear. The electric tool is preferably used as a rotary polisher or rotary sander with a polishing member or grinding member attached to a rotating disk. Effect of the Invention

[0010] As described above, the power tool of the present invention has a power transmission mechanism in which a part of the gear structure is made of aramid fiber-reinforced phenolic resin gears, thereby reducing the amount of wear powder generated by wear caused by meshing of the metal gear teeth, and thus has less deterioration over time and a longer service life.The intermediate gear is made of two gears, a large intermediate gear and a small intermediate gear, one large and one small, which are connected to each other by sharing a central axis, and the large intermediate gear is made of aramid fiber-reinforced phenolic resin gear, and the large intermediate gear is meshed with the output gear and the small intermediate gear is meshed with the final gear, thereby providing a power tool with even less deterioration over time and a longer service life. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a perspective view of a power transmission mechanism including an aramid fiber reinforced phenolic resin gear. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiment of the power tool equipped with the aramid fiber reinforced phenolic resin gear of the present invention will be described in more detail.

[0013] Fig. 1 is a perspective explanatory diagram of a power transmission mechanism 1 in an example of a power tool of the present invention. The power transmission mechanism 1 functions to transmit the rotational output from an armature 2 to a spindle 9 for mounting a rotating disk, and is composed of an output gear 4 attached to an output shaft 3 of the armature 2, an intermediate gear assembly 5 consisting of a large intermediate gear 6 and a small intermediate gear 7, and a final gear 8 attached to the spindle 9. The rotating disk on which the grinding members are attached is attached to the spindle 9 and can be rotated by the rotational output from the armature 2, thereby enabling grinding operations. In this figure, the gears in the power transmission mechanism 1 are shown as a combination of helical gears.

[0014] Typically, the gear configuration constituting such a power transmission mechanism 1 uses metal gears manufactured from metal materials, and various types of steel such as carbon steel, alloy steel, and stainless steel are commonly used as metals, as well as cast iron, brass, and aluminum alloys.

[0015] The power transmission mechanism 1 composed of such gears is preferably equipped in a rotary polisher having abrasive members such as wool or cloth buffs made of woven or knitted fabrics such as canvas, denim, twill fabric, or pile woven or knitted fabric which is a raised fabric, or sponge buffs made of foam such as rubber or resin, attached to the rotary plate, or in a rotary sander having grinding members such as whetstones, files, and sandpaper attached to the rotary plate.

[0016] However, as mentioned above, in the case of metal gears, in which each gear constituting the power transmission mechanism is made of metal, friction between the gear teeth generates a lot of wear powder, which also has a large effect of promoting wear, and in the case of steel materials, there are major problems such as the wear powder rusting the friction powder and inhibiting the lubricating effect due to oxidation of grease, which causes problems with deterioration of the power tool over time. Furthermore, in the case of plastic gears, which have been considered as a replacement for metal gears from the standpoint of weight reduction and noise prevention, the durability of the plastic material itself is lower than that of metal materials, so there was no hope of improving the durability of power tools using plastic gears.

[0017] The inventors focused on the generation of this metal powder and investigated the combination of metal gears and resin gears made of reinforced resin with various fibers in order to prevent the generation of metal powder by combining metal gears and resin gears and to improve the durability of power tools through a combined gear configuration, which led to the present invention.

[0018] The gears constituting the power transmission mechanism 1 shown in Fig. 1 mesh with each other and make their tooth surfaces contact and slide with each other to transmit the rotation output from the armature 2 to the large intermediate gear 6 through the output gear 4, and then to the final gear 8 through the small intermediate gear 7 connected to the large intermediate gear 6 and sharing a central axis, thereby rotating the rotating disk attached to the spindle 9 for mounting the rotating disk. The number of teeth of each gear is preferably configured as follows: the output gear 4 has 5 to 10 teeth, the large intermediate gear 6 has 35 to 70 teeth, the small intermediate gear 7 has 13 to 28 teeth, and the final gear has about 30 to 65 teeth. Each gear may be a spur gear (spur gear) or a helical gear (helical gear), but the latter gear is often used because it has a high meshing ratio between the gears, low vibration, and low noise. With this combination, the power tool is often operated with the rotation speed of the armature 2 being approximately 10,000 rpm to 32,000 rpm, and the rotation speed of the spindle 9 for mounting the turntable (the same as the rotation speed of the turntable) being 500 rpm (no-load rotation speed) to 6,000 rpm.

[0019] In the power tool of the present invention, the output gear 4 attached to the output shaft of the armature 2 has a small pitch circle diameter and a thin tooth thickness, and rotates at a speed several times faster than the meshing large intermediate gear 6, resulting in a large amount of contact sliding of the tooth surface and a large amount of wear. For this reason, as described above, in the case of a resin gear, the durability of the resin material itself is lower than that of a metal material, and if the output gear 4 is made of a resin gear, it is easy to cause damage due to aging deterioration, so it is necessary to use a metal gear for the output gear 4. Therefore, among the gears constituting the power transmission mechanism 1, it is preferable to combine a part of the intermediate gear assembly 5 or the final gear 8 as a resin gear as a resin gear that can be used in combination with a metal gear. In particular, since the large intermediate gear 6, which is a part of the intermediate gear assembly 5, directly meshes with the output gear 4, the effect of making the large intermediate gear 6 a resin gear is large and is a preferred form. Furthermore, the output gear 4 is generally manufactured integrally with the armature so as not to be separated from it, and considering that the armature is the most expensive part in many power tools, it is also considered to be economically advantageous.

[0020] In the power transmission mechanism 1 shown in FIG. 1, the intermediate gear assembly 5 is composed of a large intermediate gear 6 and a small intermediate gear 7, which are connected to each other while sharing a central axis. The large intermediate gear 6 directly meshes with the output gear 4, which is the driving gear, and receives the rotational output from the armature 2 as a driven gear, and rotates the small intermediate gear 7, which is connected to each other while sharing a central axis. This small intermediate gear 7 acts as a driving gear and transmits the rotational output to the final gear 8, which directly meshes with it, as a driven gear. In this case, the large intermediate gear 6 functions as a driven gear with respect to the output gear 4, and also functions as a reduction gear, and as described above, it appropriately reduces the rotational speed of the armature 2 and transmits the rotational output to the spindle 9 for mounting the rotating disk. In this case, the intermediate gear assembly 5 is composed of a combination of two gears, one large and one small, but more gear combinations can be used depending on the balance between the rotational speed of the armature and the rotational speed of the rotating disk. Furthermore, a bevel gear can also be used, and the relative directions of the rotation axis of the armature and the rotation axis of the spindle can be changed.

[0021] In a preferred embodiment, the driving gears constituting the power transmission mechanism 1 are made of metal and the driven gears are made of resin.

[0022] In addition, as the resin material of the resin gear to be combined with the metal gear as the gear constituting the power transmission mechanism 1, fiber-reinforced phenolic resin, which has excellent heat resistance and wear resistance, is preferable. In general applications of fiber-reinforced phenolic resin, cotton fiber, aramid fiber, glass fiber, carbon fiber, etc. are used as reinforcing fibers. However, when used in gears for power transmission mechanisms, particularly when combined with metal gears, it has been found that the durability of the gears varies depending on the fibers used. Therefore, in order to find a preferable fiber among these fibers, a nonwoven fabric of these fibers was impregnated with uncured phenolic resin to create a prepreg, which was then heated and compressed to heat cure the uncured phenolic resin, to create a fiber-reinforced phenolic resin gear using various fibers, and a polishing test was performed using a polisher equipped with the power transmission mechanism 1 combined with this gear to confirm its durability, and it was found that aramid fiber-reinforced phenolic resin was preferable.

[0023] The fiber-reinforced phenolic resin gears used in the polishing test to confirm durability were made by hot compression molding prepregs in which each short fiber nonwoven fabric was impregnated with uncured phenolic resin. The molding conditions for thermosetting were a mold temperature of 160°C to 220°C and a molding pressure of 50MPa to 100MPa, but molding was performed at 70MPa to 90MPa, which provides particularly good durability.

[0024] The various fiber-reinforced phenolic resin large intermediate gears 4 thus created were combined with other metal gears to form a power transmission mechanism 1, and a polisher was used to confirm their durability through a 50-hour endurance load test. The number of teeth of each gear in the power transmission mechanism 1 was set to 7 for the output gear 4, 48 for the large intermediate gear 6, 19 for the small intermediate gear 7, and 44 for the final gear 8, forming a helical gear combination. When no load was applied, the rotation speed of the armature output shaft 3 was set to 20,000 rpm, and the rotation speed of the spindle 9 for mounting the rotating disk was set to 1,200 rpm, and a load of 4.3 N·m was applied to the spindle 9 for mounting the rotating disk as the maximum load setting. Then, the polisher equipped with this power transmission mechanism 1 was set in a testing machine programmed to automatically start, change the operating conditions, and stop, and a durability load test was conducted in which the operation was continued for one hour, after which the operation was stopped for 15 minutes, with the cycle of "one minute, starting with no load, rotating at first, gradually increasing the current value after 10 seconds, reaching the maximum setting value after 17 seconds, continuing for 43 seconds, and then returning to no load" was repeated. The total operation time for this durability load test was set to 50 hours, which is the standard in the power tool manufacturing industry.

[0025] After carrying out the above-mentioned durability load tests, the condition of the tooth surfaces of the intermediate large gears 4 made of various fiber-reinforced phenolic resins and the output gear 4 combined with these gears were observed, and the durability of the various fiber types was compared. The results are shown in Table 1. [Table 1]

[0026] As shown in Table 1, the cotton fiber reinforced phenolic resin gear was effective in improving the durability of the mating output gear 4, but the strength was insufficient, and teeth were damaged, resulting in durability at the same level as conventional gears. Gears made of glass fiber reinforced phenolic resin and carbon fiber reinforced resin have high physical properties and are durable, but they wear and damage the mating metal gear, impairing its durability. Furthermore, it was found that these two gears, by damaging the mating gear in this way, can ultimately cause damage to the gear itself that meshes with the damaged gear.

[0027] From the results of this durability check, it was found that in the power tool of the present invention, it is preferable to use an aramid fiber reinforced resin gear for the large intermediate gear 6, which is part of the intermediate gear assembly 5 used in combination with a metal gear.

[0028] Furthermore, in order to confirm which of the gears constituting the power transmission mechanism 1 should preferably be changed to aramid fiber reinforced resin gears, each gear other than the output gear 4, which would be damaged if made of resin, was individually changed to an aramid fiber reinforced resin gear, and durability was confirmed using a polisher equipped with the power transmission mechanism 1 in combination with the other metal gears, in the same manner as in the polishing test of the fiber reinforced phenolic resin gears using various fibers described above.

[0029] Table 2 shows the evaluation results of the effect of improving the durability of gears when some of the gears constituting the power transmission mechanism 1 are changed to gears made of aramid fiber reinforced phenolic resin. [Table 2]

[0030] As shown in Table 2, a certain degree of effect was seen for all gears other than the output gear 4, but it was found that the most effective was to make the large intermediate gear 6, which directly meshes with the output gear 4, from aramid fiber reinforced phenolic resin. This change not only improved the durability of the output gear 4, which directly meshes with it, but also improved the durability of the small intermediate gear 7 and the final gear 8, which do not directly mesh with it. Furthermore, an improved durability effect was seen not only for the gears, but also for the commutator 10, carbon brushes 11, and bearings of the output shaft 3, which are subject to sliding friction in relation to the rotation of the armature 2. This is thought to be because the change to making the large intermediate gear 6 from aramid fiber reinforced phenolic resin reduces vibrations when it rotates in mesh with the output gear 4, resulting in smoother rotation, which also affects the meshing rotation of the entire gears that make up the power transmission mechanism 1 and reduces wear and tear.

[0031] By changing the small intermediate gear 7 and the final gear 8 to gears made of aramid fiber reinforced phenolic resin, it was confirmed that the durability of each gear was improved, but the effect on the commutator 10, carbon brushes 11, and bearings of the output shaft 3 was the same as before. This is thought to be because there is no direct meshing, and the prevention of vibrations, etc. is an indirect effect.

[0032] As described above, by using metal gears as the gears that make up the power transmission mechanism 1 and combining them with resin gears, it is possible to prevent the generation of metal powder, prevent malfunctions such as breakage of gear teeth, improve durability, and extend the useful life of the power tool.The resin gears used are aramid fiber reinforced phenolic resin gears, and it has been found that it is preferable to use aramid fiber reinforced phenolic resin gears for at least a part of the gears that make up the power transmission mechanism 1, particularly the large intermediate gear 6.

[0033] As the aramid fiber, either meta-type or para-type aramid fiber can be used, but para-type aramid fiber is preferred. The aramid fiber can be impregnated with phenol resin into chopped fibers of about 0.25 to 12 mm to form a prepreg, which can be subjected to pressurized and heated molding. Furthermore, the aramid fiber can be made into a woven or nonwoven fabric, or made into a pulp shape, impregnated with phenol resin to form a prepreg, which can be subjected to pressurized and heated molding. As the uncured phenol resin to be used for the prepreg, either resol type or novolac type can be used.

[0034] In addition, the power transmission mechanism 1 shown in Figure 1 shows an example in which the output shaft 3 of the armature 2 of the drive motor and the rotating shaft of the spindle 9 are connected in the same direction, but by introducing a bevel gear in between, the output shaft of the armature and the rotating shaft of the spindle may be perpendicular to each other. [Explanation of symbols]

[0035] 1 Power transmission mechanism 2 Armature 3 Output shaft 4 Output Gear 5 Intermediate gear assembly 6 Intermediate large gear 7 Intermediate small gear 8 Final Gear 9 Spindle for mounting the turntable 10 commutator 11 Carbon Brush

Claims

1. An electric tool equipped with a power transmission mechanism having a gear configuration consisting of an output gear attached to an output shaft of an armature, a final gear attached to a spindle for mounting a rotating disk, and an intermediate gear assembly connecting the output gear and the final gear, wherein the output gear is a metal gear, and at least some of the gears of the intermediate gear assembly are made of aramid fiber reinforced resin.

2. 2. The power tool according to claim 1, wherein at least a gear of the intermediate gear assembly that meshes with the output gear is made of an aramid fiber reinforced phenolic resin gear.

3. 3. The power tool according to claim 1, wherein in the power transmission mechanism, the drive gear is a metal gear, and the driven gear is an aramid fiber reinforced resin gear.

4. The electric power tool according to any one of claims 1 to 3, characterized in that the intermediate gear assembly comprises a large intermediate gear and a small intermediate gear connected to each other and sharing a central axis, the large intermediate gear being a gear made of aramid fiber reinforced phenolic resin and directly meshing with the output gear, and the small intermediate gear directly meshing with the final gear.

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