Power tools equipped with fiber-reinforced phenolic resin gears

Abstract

This proposal proposes power tools with less deterioration over time and a longer service life by using a combination of metal gears with superior physical properties and resin gears in the gear configuration that serves as the power transmission mechanism for power tools such as polishers and sanders. This reduces the amount of wear particles generated by the meshing of gear teeth, resulting in a more efficient power tool. [Solution] An electric power tool equipped with a power transmission mechanism 1 having a gear configuration consisting of an output gear 4 attached to the output shaft 3 of an armature 2, a final gear 8 attached to a spindle 9 for mounting a turntable, and an intermediate gear assembly 5 connecting the output gear 4 and the final gear 8, wherein the output gear 4 is a metal gear, and at least some of the gears in the intermediate gear assembly 5 are made of aramid fiber reinforced resin.

Description

Technical Field

[0001] The present invention relates to electric tools such as polishers and sanders, and particularly to a gear configuration which is a power transmission mechanism.

Background Art

[0002] In electric tools such as polishers and sanders, the rotational output from a motor is transmitted as rotational power to a rotating disk to which a pad-sheet-like polishing member or grinding member such as a buff or sandpaper is attached, via a power transmission mechanism having a gear configuration, and the rotating disk is rotated to perform polishing and grinding operations. In these electric tools, due to wear caused by meshing of gear teeth over time, failures such as breakage of gear teeth occur. In this case, it is not only the wear action between the gear teeth alone, but also the fine powder of the gear material generated in this meshing acts as an abrasive at the meshing joint, promoting wear and increasing the frequency of failures. When the material of the gears constituting the power transmission mechanism is metal, the generation of wear fine powder is also large, and the wear promotion effect by the metal fine powder is also significant. Particularly, in the case of steel materials, rust occurs due to oxidation of the steel wear fine powder, and the rusted steel fine powder invades the gear joint, not only hindering sliding, but also oxidizing the grease and significantly inhibiting the lubrication action, causing great damage to the gears.

[0003] Therefore, in automotive power transmission mechanisms, a structure is sometimes implemented that circulates lubricant to collect and remove the generated wear particles in order to prevent deterioration over time. Furthermore, in this automotive mechanism, it is rare for the gears to be used to the point where the high-hardness machined parts on the gear surface are worn away, so reducing the wear of these high-hardness machined parts is meaningful. However, it is difficult to implement such a lubricant circulation structure in small power tools like those mentioned above, and it has been necessary to replace the lubricant, clean the tool, or replace the gears after a certain period of use, assuming deterioration over time. Moreover, it is not uncommon for users to continue using the tool even after the high-hardness machined parts of the gears have worn away, and to continue using it until the gears can no longer mesh. This is thought to be because, in automobiles, abnormal gear noises immediately evoke thoughts of danger to life, body, or property, whereas abnormal noises from a polisher do not evoke thoughts of danger to life, body, or property.

[0004] On the other hand, as a material for gears, resin gears are also used, which use resin materials instead of metal, from the viewpoint of weight reduction and noise reduction. Furthermore, 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 to use aramid fiber-reinforced phenolic resin molded considering the orientation of the reinforcing fibers (see Patent Document 2).

[0005] However, while metal gears, which are made of materials with excellent wear resistance and strength, are used as gears in the power transmission mechanism, a gear configuration that combines them with resin gears has not been considered in order to prevent the generation of fine metal powder as described above, thereby preventing malfunctions such as damage to the gear teeth and extending the service life of the power tool. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-240326 [Patent Document 2] Japanese Patent Publication No. 2013-256998 [Overview of the project] [Problems that the invention aims to solve]

[0007] The objective of this invention is to propose an electric power tool with less deterioration over time and a longer service life by reducing the amount of wear powder generated by the meshing of gear teeth, through a combination of metal gears with superior physical properties and resin gears in the gear configuration of the power transmission mechanism of electric power tools such as polishers and sanders. [Means for solving the problem]

[0008] The power tool of the present invention is 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 rotary disc, 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 in the intermediate gear assembly are made of aramid fiber reinforced resin.

[0009] Furthermore, it is preferable that at least the gears of the intermediate gear assembly that mesh with the output gear are gears made of aramid fiber-reinforced phenolic resin, and in the power transmission mechanism, it is preferable that the drive gear is a metal gear and the driven gear is a gear made of aramid fiber-reinforced resin. Moreover, it is preferable that the intermediate gear assembly consists of an intermediate large gear and an intermediate small gear that are connected by sharing a central axis, the intermediate large gear is an aramid fiber-reinforced phenolic resin gear that meshes directly with the output gear, and the intermediate small gear meshes directly with the final gear. Furthermore, the power tool is preferably used as a rotary polisher or rotary sander with an abrasive or grinding member attached to a rotating disc. [Effects of the Invention]

[0010] As described above, the power tool of the present invention reduces wear particles generated by the meshing of metal gear teeth by using aramid fiber-reinforced phenolic resin gears for part of the gear configuration constituting the power transmission mechanism. This reduces the deterioration of the power tool over time and results in a longer service life. Furthermore, by using two intermediate gears, a large intermediate gear and a small intermediate gear, connected with a shared central axis, and by using an aramid fiber-reinforced phenolic resin gear for the large intermediate gear, meshing the large intermediate gear with the output gear, and meshing the small intermediate gear with the final gear, an even more durable power tool with less deterioration over time and a longer service life can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] Perspective diagram illustrating a power transmission mechanism including gears made of aramid fiber-reinforced phenolic resin. [Modes for carrying out the invention]

[0012] The following describes in more detail the form of the power tool equipped with the aramid fiber-reinforced phenolic resin gear of the present invention.

[0013] Figure 1 is a perspective view illustrating the power transmission mechanism 1 in an example of the power tool of the present invention. The power transmission mechanism 1 performs the function of transmitting the rotational output from the armature 2 to the spindle 9 for mounting the turntable, and consists of an output gear 4 attached to the output shaft 3 of the armature 2, an intermediate gear assembly 5 consisting of an intermediate large gear 6 and an intermediate small gear 7, and a final gear 8 attached to the spindle 9. The turntable to which the polishing member is attached is mounted on the spindle 9 and can be rotated by the rotational output from the armature 2, allowing for polishing 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 of such a power transmission mechanism 1 uses metal gears manufactured from metal materials. Common metals include carbon steel, alloy steel, stainless steel, cast iron, brass, and aluminum alloys.

[0015] Such a power transmission mechanism 1, composed of gears, is preferably equipped in a rotary polisher that has abrasive members such as wool or cloth buffs made of woven or knitted fabrics such as canvas, denim, twill fabrics, or napped fabrics, or sponge buffs made of foamed materials such as rubber or resin, attached to a rotary disk, or in a rotary sander that has abrasive members such as grinding wheels, files, or sandpaper attached to a rotary disk.

[0016] However, as mentioned above, in the case of metal gears, where the material of each gear constituting the power transmission mechanism is metal, a large amount of wear powder is generated due to friction between the gear teeth, and the wear-accelerating effect of the generated metal powder is significant. Furthermore, in the case of steel, there are major problems such as interference with sliding due to rust from the wear powder and inhibition of lubrication due to oxidation of grease, which have led to the problem of deterioration of power tools over time. Moreover, resin gears, which had been considered as a replacement for metal gears from the standpoint of weight reduction and noise reduction, were not expected to improve the durability of power tools using resin gears because the durability of the resin material itself is lower than that of metal materials.

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

[0018] The gears constituting the power transmission mechanism 1 shown in Figure 1 mesh with each other, causing their tooth surfaces to contact and slide against each other. This transmits the rotational output from the armature 2 to the intermediate large gear 6 via the output gear 4, and then to the final gear 8 via the intermediate small gear 7, which shares a central axis with the intermediate large gear 6, thereby rotating the turntable attached to the spindle 9 for mounting the turntable. Preferably, the gears are configured with the following tooth counts: output gear 4: 5-10 teeth, intermediate large gear 6: 35-70 teeth, intermediate small gear 7: 13-28 teeth, and final gear: 30-65 teeth. Each gear can be either a spur gear (spool gear) or a helical gear, but the latter is often used because it has a higher meshing ratio between gears, lower vibration, and less noise. In this combination, the rotational speed of the armature 2 is typically around 10,000 rpm to 32,000 rpm, and the rotational speed of the spindle 9 for mounting the turntable (the same as the turntable's rotational speed) is often set to 500 rpm (no-load speed) to 6,000 rpm when operating the power tool.

[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 thin teeth, and rotates at several times the rotational speed of the intermediate large gear 6 with which it meshes, resulting in a large amount of contact sliding between the tooth surfaces and a large amount of wear. For this reason, as mentioned above, resin gears have lower durability than metal gears, and if the output gear 4 is made of resin, it is prone to damage due to aging deterioration, so the output gear 4 must be made of metal. For this reason, 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 that can be used in combination with a metal gear. In particular, since the intermediate large gear 6, which is part of the intermediate gear assembly 5, meshes directly with the output gear 4, the effect of making the intermediate large gear 6 a resin gear is significant and it is a preferred configuration. Furthermore, generally, the output gear 4 is manufactured integrally with the armature and cannot be separated, and considering that the armature is the most expensive part in many power tools, this is judged to be economically beneficial.

[0020] In the power transmission mechanism 1 shown in FIG. 1, the intermediate gear assembly 5 consists of an intermediate large gear 6 and an intermediate small gear 7 that are connected sharing a central axis. The intermediate large gear 6 meshes directly with the output gear 4 which is a driving gear, receives the rotational output from the amateur 2 as a driven gear, and rotates the intermediate small gear 7 that is connected sharing the central axis. This intermediate small gear 7 transmits the rotational output as a driving gear to the final gear 8 that meshes directly with it as a driven gear. In this case, the intermediate large gear 6 functions as a driven gear with respect to the output gear 4 and also functions as a reduction gear, appropriately reducing the rotational speed of the amateur 2 as described above and transmitting the rotational output to the spindle 9 for mounting the rotating disk. In this case, the intermediate gear assembly 5 is constituted by the combination of two gears of different sizes, but considering the balance between the rotational speed of the amateur and the rotational speed of the rotating disk, a combination of more gears can also be used. Furthermore, bevel gears (bevel gears) can also be used to change the mutual direction between the rotational axis of the amateur and the rotational axis of the spindle.

[0021] In each gear constituting the power transmission mechanism 1, it is a preferred embodiment to configure the driving gear as a metal gear and the driven gear as a resin gear.

[0022] Also, as the resin material of the resin gear combined with the metal gear as the gear constituting the power transmission mechanism 1, a fiber-reinforced phenolic resin excellent in heat resistance and wear resistance is preferable. And in general applications of fiber-reinforced phenolic resins, reinforcing fibers such as cotton fibers, aramid fibers, glass fibers, and carbon fibers are used. However, when used for the gears used in the power transmission mechanism and particularly combined with metal gears, it has been found that there are differences in the durability of the gears depending on the fibers used. Therefore, in order to find the preferable fibers among these fibers, prepregs are prepared by impregnating non-woven fabrics of these fibers with uncured phenolic resin, and the prepregs are compression-molded by heating to cure the uncured phenolic resin, and fiber-reinforced phenolic resin gears made of various fibers are prepared. As a result of conducting a polishing test using a polishing machine equipped with the power transmission mechanism 1 combined with these gears to confirm durability, it has been found that aramid fiber-reinforced phenolic resin is preferable.

[0023] The fiber-reinforced phenolic resin gears subjected to the polishing test for confirming durability were compression-molded by heating the prepregs obtained by impregnating each short fiber non-woven fabric with uncured phenolic resin. As the molding conditions for molding and curing, molding can be performed at a mold temperature of 160°C to 220°C and a molding pressure of 50 MPa to 100 MPa, but molding was performed at 70 MPa to 90 MPa where particularly good durability can be obtained.

[0024] The durability of the various fiber-reinforced phenolic resin intermediate large gears 6 created in this manner was confirmed by a 50-hour endurance load test using a polisher equipped with a power transmission mechanism 1 that incorporated these gears together with the other metal gears. The number of teeth on each gear in the power transmission mechanism 1 was set as follows: output gear 4 had 7 teeth, intermediate large gear 6 had 48 teeth, intermediate small gear 7 had 19 teeth, and final gear 8 had 44 teeth, forming a helical gear combination. Under no load, 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 turntable was set to 1,200 rpm. For maximum load, a load of 4.3 N·m was applied to the spindle 9 for mounting the turntable. Furthermore, a polisher equipped with this power transmission mechanism 1 was set on a test machine programmed to automatically start, change operating conditions, and stop. A durability load test was then conducted by repeating the following operation for one hour: "Initially, it rotates without load, then the current value is gradually increased from 10 seconds, reaching the maximum setting value at 17 seconds, which is maintained for 43 seconds, and then it returns to no load." After this cycle was repeated, the operation was stopped for 15 minutes. The total operating time for this durability load test was set to 50 hours, which is the standard in the power tool manufacturing industry.

[0025] After conducting the above durability load tests, the condition of the tooth surfaces of various fiber-reinforced phenolic resin intermediate large gears 6 and the output gear 4 paired with these gears was observed, and the results of comparing durability based on the type of fiber 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 output gear 4 it meshes with, but its strength was insufficient, resulting in tooth breakage and overall durability comparable to conventional gears. Gears made of glass fiber-reinforced phenolic resin and carbon fiber-reinforced resin have high physical properties and good durability themselves, but it was found that they caused wear and damage to the metal gears they mesh with, thus compromising their durability. Furthermore, it was found that these two types of gears, by damaging the gears they mesh with in this way, can ultimately cause damage to the gears they mesh with.

[0027] Based on the results of this durability test, 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 intermediate large gear 6, which is part of the intermediate gear assembly 5 used in combination with a metal gear.

[0028] Furthermore, in order to determine which of the gears constituting the power transmission mechanism 1 is preferable to replace with an aramid fiber-reinforced resin gear, each gear except for the output gear 4, which would break if made of resin, was individually replaced with an aramid fiber-reinforced resin gear. Using a polisher equipped with the power transmission mechanism 1, which was then combined with the other metal gears, durability was confirmed in the same manner as the polishing tests of the fiber-reinforced phenolic resin gears made of various fibers described above.

[0029] Table 2 shows the evaluation results of the effect on improving gear durability 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, some degree of effect was observed in all gears except the output gear 4, but it was found that making the intermediate large gear 6, which directly meshes with the output gear 4, out of aramid fiber-reinforced phenolic resin was the most effective. Furthermore, this change not only improved the durability of the output gear 4, which it directly meshes with, but also improved the durability of the intermediate small gear 7 and the final gear 8, which do not directly mesh with the output gear 4. In addition, the commutator 10, carbon brushes 11, and the bearings of the output shaft 3, which experience sliding friction in relation to the rotation of the armature 2, also showed improved durability. This is thought to be because changing the intermediate large gear 6 out of aramid fiber-reinforced phenolic resin reduces vibrations when it meshes with the output gear 4 and rotates, resulting in smoother rotation, which in turn affects the meshing rotation of all the gears constituting the power transmission mechanism 1, thereby reducing wear and damage.

[0031] By changing the intermediate small gear 7 and the final gear 8 to gears made of aramid fiber-reinforced phenolic resin, improvements in the durability of each component were confirmed. However, the effect on the commutator 10, carbon brushes 11, and the bearings of the output shaft 3 remained the same as before. This is likely because there is no direct meshing, and the prevention of vibrations and other issues has an indirect effect.

[0032] As described above, the gear configuration used in the power transmission mechanism 1, which combines metal gears with resin gears, prevents the generation of fine metal powder, prevents failures such as gear tooth breakage, improves durability, and extends the service life of the power tool. The resin gear used is made of aramid fiber-reinforced phenolic resin, and it has been found that it is preferable to make at least a part of the intermediate gear assembly 5, particularly the intermediate large gear 6, of the gears constituting the power transmission mechanism 1 of aramid fiber-reinforced phenolic resin.

[0033] Either meta-aramid fibers or para-aramid fibers can be used as aramid fibers, but para-aramid fibers are preferred. The aramid fibers can be chopped to a thickness of approximately 0.25 to 12 mm, impregnated with phenolic resin to form a prepreg, which can then be subjected to heat molding under pressure. Furthermore, the aramid fibers can be formed into woven fabrics, nonwoven fabrics, or pulp, impregnated with phenolic resin to form a prepreg, which can then be subjected to heat molding under pressure. Both resol-type and novolac-type uncured phenolic resins can be used for the prepreg.

[0034] Furthermore, although the power transmission mechanism 1 shown in Figure 1 is an example in which the output shaft 3 of the armature 2 of the drive motor and the rotation axis of the spindle 9 are connected in the same direction, the output shaft of the armature and the rotation axis of the spindle may be perpendicular to each other by introducing a bevel gear in between. [Explanation of Symbols]

[0035] 1. Power transmission mechanism 2. Amateur (armature) 3 Output shaft 4 Output gears 5. Intermediate Gear Assembly 6. Intermediate large gear 7. Intermediate small gear 8 Final gear 9. Spindle for mounting the rotating disc 10 commutator 11 Carbon Brushes

Claims

1. A rotary polisher or rotary sander is equipped with a power transmission mechanism comprising an output gear mounted on the output shaft of an armature, a final gear mounted on a spindle for mounting a rotary disc, and an intermediate gear assembly connecting the output gear and the final gear, wherein a polishing member is attached to the rotary disc, and the output gear is a metal gear, and the intermediate gear assembly consists of an intermediate large gear and an intermediate small gear that share a central axis and are connected, the intermediate large gear is an aramid fiber reinforced phenolic resin gear that meshes directly with the output gear, and the intermediate small gear meshes directly with the final gear.

2. The rotary polisher or rotary sander according to claim 1, characterized in that the power transmission mechanism has a metal gear and a driven gear made of aramid fiber reinforced resin.

Images