ES2541004T3 - Procedure for blasting and vibrating gear finishing - Google Patents

Abstract

A method of processing a metal gear 20, 201 comprising providing a gear 20, 201, directing first blasting means to the metal gear 20, 201, thereby exposing a plurality of surfaces on the metal gear 20, 201 to the first blasting means, whereby the wear and strength properties of the bases of the gear teeth are improved, wash the gear 20, 201, and rinse the gear 20, 201 with corrosion inhibitor characterized by, before washing and rinse: directing a second shot blasting means to the metal gear 20, 201, thereby exposing a plurality of surfaces on the metal gear 20, 201 to the second shot blasting means, whereby the surface compressive tension of the gear surface 20, 201, provide a vibratory fine finish container (200), place a fine finishing medium (212) comprising means Ceramics in a slightly acidic solution in the vibratory fine finish container, place the gear 20, 201 with the fine finishing medium in the vibratory fine finishing container (200), couple vibrations to the vibratory fine finishing container to make the medium vibrate of fine finish (212) with the gear 20, 201, and remove the gear 20, 201 from the vibratory fine finish container (200) after achieving a fine finish of the gear 20, 201 of between 5 and 25 Ra.

Description

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DESCRIPTION

Procedure for blasting and vibrating gear finishing

5 BACKGROUND OF THE INVENTION

[0001] This invention generally relates to a process for the treatment by blasting of media and shot blasting of a metal gear according to the preamble of claim 1. Such a procedure is disclosed, for example, in EP 0 995 530. The power supply clamping device of the

10 US 5 272 897 can be used for the shot blasting steps of the present description.

[0002] The blasting or blasting of means is used to increase the fatigue resistance of a gear, part or part. Gears, such as those used in car transmissions, are sanded with means in order to increase their surface durability and ensure that they are suitable for the performance of

15 its intended functions. US 6 612 909 discloses a method for blasting gear means. US 3 073 022 refers to a two-step shot blasting process, in which first shot blasting means and subsequently a second shot blasting means are directed to the part.

[0003] A piece such as a gear is placed in a closed chamber, the system of

20 blasting, whereby the media is mixed with air and, after mixing the media with an air stream, the air / media mixture is directed against the part. This procedure is known as shot blasting.

OBJECTS AND SUMMARY OF THE INVENTION

[0004] An object of the present invention is to reinforce the radius of the base and face of the gear tooth by blasting the gears and subsequent vibratory finishing. The blasting steps harden the gears and provide roughness to the surfaces of the gears. The finish after blasting softens the surfaces of the gears and leaves holes or indentations. The holes or indentations help maintain oil retention on the surfaces of the gears. The vibratory procedure after blasting is intended to take the

30 Ra superficial to a smaller Ra (5-25 Ra) that is economical for medium and higher volume parts. Superfinishing procedures or the like to bring the surface Ra up to 1 Ra or less are cost prohibitive. «Ra» is an international standard of roughness. See, for example, ISO (International Standardization Organization) 4287.

[0005] An object of the present invention is to disclose a process for processing a metal gear consisting of subjecting the gear to media blasting by directing first means (eg, wire segments) against the surfaces exposed of the gear in order to increase the resistance of the gear base, stop the first blasting and subject the gear to a second blasting of media with a few second means (e.g., glass, ceramic or FINE STEEL ™ spheres) against surfaces

40 exposed of the gear to achieve a high compressive surface tension (KSI) on the face and base of the tooth, provide a container (eg, a bowl), place a thin finishing medium comprising ceramic means in a solution slightly acid in the container with the gear, couple vibrations to the container in order to vibrate the fine finishing medium with the gear, remove the gear from the container, wash the gear, and rinse the gear with corrosion inhibitor, as a result of all which improves the properties of

45 gear wear. The blasting of gear means according to the present invention achieves an important object, increasing the resistance of the radius of the base and the surface of the gears. In the present specification, the toughness is described in terms of "KSI" (kilo-pounds [-force] per square inch) or 1000 psi (corresponding SI units: 11 Pa or kPa). KSIs are often used in the field of materials science, civil engineering and mechanics to specify Tension and Young's modulus.

[0006] The foregoing objects are achieved by the method according to claim 1. Preferred embodiments are detailed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0008] Figure 1 is a front elevational view of a media blasting apparatus for treating a gear according to the invention;

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[0009] Figure 2 is a right side elevational view of the media blasting apparatus for treating a gear according to the invention;

[0010] Figure 3 is a top plan view of the blasting apparatus for treating a gear according to the invention;

[0011] Figure 4 is an enlarged, partial fragmentary side elevation view of a blasting station of the media blasting apparatus for the treatment of a gear according to the invention;

[0012] Figure 5 is a cross-sectional view of a container or bowl for immersing the gear in the superfinishing means for treating the gear according to the invention;

[0013] Figure 6 is a top plan view of a part of a bowl 200 with ceramic means and gears before closing the bowl for the vibration passage;

[0014] Figure 7 is a top view of a container or bowl for coupling vibration to a gear while the gear is submerged in super-finished means for the treatment of the gear according to the invention;

[0015] Figure 8 is a side view of a bowl or container according to the invention;

[0016] Figure 9 is a top view of three bowls in a production facility; Y

[0017] Figure 10 is a side view of three bowls in a production facility.

25 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0018] Referring now to the drawings, Figure 1 shows a front view of a media blasting apparatus, generally indicated by the number 10. As illustrated, the media blasting apparatus 10 includes a cabinet or chamber. blasting 15, in which a stream of media is directed against a piece 20. Such means may comprise, for example, wire segments, glass spheres, ceramic spheres or refined steel spheres. The cabinet 15 is connected to a media hopper of the cabinet 25 for collecting the falling media after colliding with the piece 20. The fallen media includes broken pieces of media that have been recycled, as well as virgin or unbroken pieces. A conduit 30 connects the media hopper of the cabinet 25 to a

35 media recovery system, generally indicated by the number 35. As best illustrated in Figure 2, the media hopper of the cabinet 25 is also connected to the air supply means 40. The air supply means 40 provides an air flow to the media hopper of the cabinet 25, to force the rise of the fallen media collected through the conduit 30 to the media recovery system 35.

[0019] As illustrated in Figures 1 and 2, the media recovery system 35 includes a conduit 45 for transporting the collected media to the separation means 50. The separation means 50 is a two platform system comprising an upper sieve 55 and a lower sieve 60. In a preferred embodiment of the present invention, the upper sieve has a mesh size between 20 and 40 and the lower sieve has a mesh size between 170 and 200 The separation means 50 generally separates the fallen media into media without

45 break or in broken media of a size large enough to be recycled for use in the blasting operation and fines or dust that cannot be reused. The separating screens 55 and 60 are constantly vibrating to increase the separation efficiency.

[0020] The media recovery system 35 also includes a conduit 65. The conduit 65 is connected to

50 a filter system 70 and a blower motor system 75. In the preferred embodiment, the blower motor system 75 includes a blower silencer 77 for noise reduction. The blower motor system 75 draws air from the duct 65, creating an upward flow in the duct 45 that extracts the non-reusable fines / media from the separation means 50 by the duct 45 to the duct 65 and to the filter system 70 The filter system 70 is connected to a dust collector 80 for collecting the fines and broken media. These

55 are collected in a drum 85 which is removed and emptied periodically. In a preferred embodiment, the drum 85 is adapted to be removed and emptied. For example, drum 85 may be coupled to a rolling platform.

[0021] As illustrated in Figure 1, the separation means 50 is connected to a double pressure chamber 90 through a conduit 95. Between the media hopper of the cabinet 25 and the pressure chamber 90 a path is created of 60 media. In a preferred embodiment, the double pressure chamber is maintained between 482.63 and 551.58 kPa (70 and 80 psi). Duct 95 provides the reclaimed media claimed to the double pressure chamber 90, where the media

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Recovered and reusable are mixed with virgin media. In a preferred embodiment, the recovered media is of mesh greater than 100 meshes and the virgin media is of a mesh size of between 60 to 100 and preferably between 60 and 80. As previously stated, in the present invention, the media They can comprise glass, ceramics or fine steel spheres. Virgin media is supplied to the pressure chamber

5 double 90 through a plurality of media supply valves 97. The double pressure chamber 90 is also coupled to a monitor of the media sensor 100 to automatically control the supply of the virgin media. The virgin media supply is controlled to ensure proper shot blasting of the piece. Specifically, the supply of the virgin means is controlled to ensure that an appropriate compression stress is applied to the piece 20 so that a sufficiently high fatigue resistance is obtained.

[0022] Advantageously, the double pressure chamber 90 also includes a metering valve for automatic on / off means 105. This valve 105 regulates the supply of the virgin / recycled media mixture to an air mixing point / media, where media is suspended in the air. An automatic air valve 110 is coupled to the double pressure chamber 90 to suspend the media in the air at the mixing point of

15 air / media and then transmit the suspended media to the blasting cabinet 15 through blasting hoses 115.

[0023] The automatic on / off media metering valve 105 of the present invention allows better control of the media flow, since the media supply and air supply can be controlled 20 separately. The presence of the automatic on / off means metering valve 105 of the present invention is made possible by the use of a pressure blasting system, instead of a suction type system, to supply the means. In a suction type system, the suction force is based on the entrainment of media from a media supply through a media supply hose to the suction gun. The presence of a metering valve 105 in a suction system, however, would reduce the fall

25 of the media supply hose causing a reduction in suction force. The reduced suction force, in turn, would interfere with the delivery of the media. The present system, on the other hand, is a pressure-driven system so that the positive pressure can depend on the thrust of the means through the media dosing valve 105 to the point of mixing the media.

[0024] An additional advantage of the pressurized system is that it helps ensure that an adequate media speed is obtained. As mentioned earlier, the speed of the means is an important control parameter to ensure that a sufficient compressive tension is provided to a part 20. The pressurized system helps ensure adequate media speed by controlling the flow rate and through the positioning of the air / media mixing point. The media flow rate is controlled through the metering valve of

35 means 105. The air / media mixing point is far enough away from the blasting hose so that the means have time to develop a desired or adequate speed.

[0025] We will now describe a blasting station 120 inside the blasting cabinet 15. As illustrated in FIG. 4, the part 20 to be processed, that is, drilled with means, is mounted on a 40-piece support 125. Preferably, the part support 125 has been tempered. The piece 20 is maintained in a predetermined position by means of an actuated part retention apparatus 130. This apparatus 130 provides a variable, compensated and damped fastener to keep the piece 20 in the predetermined position during media blasting. The device is very important to facilitate the processing of parts in high volume quantities. This is especially important for parts such as gears that tend to rotate when

45 shot blasting, as the clamping device prevents the free rotation of the pieces. The retention device also rotates the parts in a controlled manner at a desired speed. The rotation of the actuated retention apparatus 130 is provided through a rotating shaft 135.

[0026] Hardened rods 140, preferably of steel, provide a support system for a set

50 of gun-frame 145. The gun-frame assembly 145 has a nozzle holder 150. A blasting nozzle 155, to which the blasting hoses 115 are connected, is coupled to the nozzle holder 150. The blasting nozzle 155 directs a stream of media, suspended in the air, against the surface of the piece 20. Preferably, the blasting nozzle is placed between approximately 10.16 and 20.32 cm (four to eight inches) away from the part 20. Although only one blasting nozzle is illustrated in Figure 4, the experts

55 in the art they should understand that various nozzles 155 could be used. In a preferred embodiment of the present invention, those four blasting nozzles 155 are located in the blasting cabinet 15, as shown in the figure. 3. The blasting cabinet 15, which contains the part retention apparatus 130 and the blasting apparatus is also provided with a door 160 for the installation of a new part 20.

[0027] The operation of the present media blasting device is described below. After placing a gear 20 in the part retention apparatus 130, the door 160 is closed. A stream of media

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Suspended in the air, it is then directed against the gear 20 by the blasting nozzle 155. While the means are dripping, the actuated part retention apparatus 130 rotates the gear in a controlled manner. This controlled rotation ensures the uniform blasting of the surface of the gear 20 and avoids the use of a high directional current of the means, thus avoiding the need to use water-supported means.

[0028] The driven part retention apparatus preferably rotates between 8-12 rpm. However, it has been observed that a rotation speed of 10-12 rpm is particularly effective for the treatment of gears. The speed of rotation can be related to the degree of blasting required and the uniformity of the formation of holes in the resulting surface. A slow controlled turn allows for uniform shot blasting with uniform formation

10 of small holes and prevents the flow of media from hitting the surface unevenly, which would result in grooves that could act as breakage precursors. The controlled rotation ensures that the means, for example, wire segments, ceramic grains, fine steel grains or glass spheres, are directed towards the base and face of the gear during the course of rotation. By ensuring uniform shot blasting, the operational characteristics of the gear 20 are improved.

[0029] In one embodiment, a smaller media mass flow rate is run at a faster rate and for longer than in the prior art procedures. The preferred flow depends on the type and size of material used, as well as the particular application in question. For the treatment of gears, we have found that a media flow rate of approximately 0.68-1.36 kg / minute (1.5-3 pounds / minute) is effective. By

Of course, other flows could be used, depending on the desired results. It was found that this flow rate was effective with glass, ceramic and fine steel media of mesh size of the 50-100 range. In a preferred embodiment of the present invention, however, 60-100 mesh glass media are used. When 60-100 mesh glass means were used to treat certain gears, including those obtained using 8620 steel, a marked improvement in the operational characteristics of such gears was observed. The choice of means to

25 use depends on the application and relative profitability. Ceramic and steel media last longer than glass; However, they are more expensive.

[0030] After the media collides with the gear 20, they fall into the media hopper of the cabinet 25 and then transported to the recovery system 35. The reusable media is separated from the fines and dust and

30 return to the blasting station 120 after mixing with the virgin media. Said mixture reduces waste of media. The reuse of partially broken media also improves the polishing effect on the gear 20.

[0031] It has been observed that satisfactory results can be achieved using glass media to treat

35 by blasting certain gears, including those made of certain metals such as 8620 steel; gears made of other materials such as 5130 m steel have not shown desirable results when using glass media. In general, it has been found that the blasting treatment with ceramic media of the invention is effective with a wide variety of types of gears made of a variety of metals. In the process, a series of oxide ceramics can be used, such as, for example, ZrO2, Al2O3, SiO2, MgO, etc. Preferred media

40 includes a crystalline zirconia evenly enclosed in a vitreous phase of silica. Such media are sold under the trade name ZIRBLAST ™ and ZIRSHOT ™ by SEPR Co of Paris le Defense, France.

[0032] Surprisingly, it has been found that blasting treatment using ceramic media produces significantly better results than blasting treatment using glass for certain metal gears, for example, in obtaining a better resistance to pitting corrosion of surfaces of the gear teeth, as well as a better resistance in the radius of the base of the gear tooth with respect to the above procedures. For such gear applications, it has been found that ceramic media between 40 to 100 virgin mesh, a flow rate between 0.45 to 11.34 kg / minute (1 to 25 pounds per minute), a cycle time between 15 and 180 seconds, a pressure between 241.32 and 620.53 kPa (35 and 50 90 psi), a gear rotation speed between approximately 5-25 rpm and an Almen intensity between 15 and 28 n They are effective in the treatment of gears. Superior results have been observed in such gears under preferred processing conditions that include a small mass flow rate between 0.45 and 1.36 kg (1 to 3 pounds per minute), a pressure between 482.63 and 551.58 kPa (70 and 80 psi), a cycle time between 15 seconds and 120 seconds, a gear rotation speed between approximately 8-12 rpm, a media diameter between approximately 0.210 mm and approximately 0.150 mm of mesh. Preferably, since the ceramic means are relatively expensive, they are collected after the blasting of the gear and recycled by adding them to virgin means such that, after the initial start-up of the system, a mixture of media including recycled media is used. and virgins In this preferred procedure, a 170-200 mesh screen is used as the bottom screen in the separation media of the media recovery system

60 to exclude fragments of small media from the mix of recycled media.

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[0033] In a further embodiment of the invention, a method of treating a metal gear with a jet stream of fine metal means using the apparatus described above is illustrated. The preferred method includes a flow of media between 0.45 and 1.81 kg / minute (1 and 4 pounds / minute) approximately, a diameter of the media between approximately 150 and 200 microns, a

5 pressure between 482.63 and 551.58 kPa (70 and 80 psi), an Almen interval of between 18 and 26 N approximately. Preferably, the refined steel means will be collected after the blasting of the gear for recycling.

[0034] Since steel ball media have a significantly longer duration than ceramic or glass media, it is only necessary to add very few virgin media to the apparatus. This translates into a significant reduction in the monitoring and maintenance requirements, as well as in the amount of means used for the successful mass treatment of gears. Metal gears treated in this manner usually have fewer holes and less defined in their surface structure than those treated by blasting of media described herein using glass or ceramic media. On the other hand, gears treated in this way show a lower fatigue resistance than those treated with glass and ceramic media described herein. However, in dynamometer tests, stainless steel media exceeded 70 hours of continuous use before failing, which significantly exceeds the result of 40 hours before expected failure in coated gears. Due to the lower maintenance, supervision and media costs, the stainless steel process described here is a low-cost procedure that offers superior results to conventional gear blasting. Shot blasting with stainless steel media is enough for many

20 gears that show good surface resistance to pitting corrosion. When a much greater degree of pitting corrosion is observed during the gear dynamometer test, blast treatment with ceramic media is preferred.

[0035] Using the ceramic blasting treatment apparatus described herein, it is

25 produce gears with a double blasting process step as follows. The gears are blasted by directing the first means (for example, cutting wire) against the exposed surfaces of the gear. The passage of media jet (shot blasting) with the first medium makes the base of the teeth more resistant. After blasting with the first medium, the gear is dripped with a second medium (glass, ceramic or stainless steel spheres) against the exposed surfaces of the gear. The media jet passage (shot blasting) with the second medium

30 makes the gear surface more resistant and leaves the surface somewhat rough. The rough surface has holes or indentations resulting from blasting with, for example, means between about 150 and 200 microns. This blasting causes holes or crevices smaller than 150 microns and typically less than 75 microns. These small grooves provide high compressive tension and facilitate the retention of oil on the surface of the gear during its use. Subsequent finishing reduces the size of the holes or

35 grooves but retains the advantages of high compressive tension and oil retention on the gear surface.

[0036] After double blasting the gear 201 is transferred to a bowl 200 containing a fine finishing medium 212. The bowl 200 is shown in Figure 5 (the gears 201 are present in the medium of fine finishing 212 but the Gears 201 are not shown in Figure 5). The bowl 200 has an outlet 202, an inlet 204, sides 206, an upper part 208 and a lower part 210. A wet acid finishing medium 212 is provided in sufficient quantity to moisten the gears 201 and the ceramic means 212. Figure 6 is a photo of a portion of a bowl 200 with ceramic means 212 and the gears 201 before closing the bowl 200 for the vibration passage. The relative size of the gear 201 and the ceramic means 212 shown are only an example of a gear 201 and ceramic means 212. Typically the ceramic means are smaller than what is shown in Figure 6. That is, the size Relative of the ceramic means 212 and the gears 201 is such that the means 212 are small enough to fit in the space between the gear teeth during the fine finish (vibration) and apply a fine finish to the gear surfaces. The vibration of the bowl 200 is coupled to the bowl 200 through vibration coupler 214. The thin finishing medium 212 is composed of a mixture of ceramic media with a slightly acidic solution. Figure 7 shows a section of the production facility with three 200 covered bowls. Figures 8-10 are drawings of the bowls in a production plant. Each bowl is supported by three springs (more or less springs can be used). As seen in Figure 7, the three bowls 200 are covered to reduce noise, etc. The bowl 200 is typically made of steel and has a polyurethane lining that couples the vibrations to the medium. 55 As can be seen in, for example, Figure 6, the inside of the bowl 200 has a channel 250 that extends around the entire inner periphery of the bowl 200. The central portion of the bowl is shaped like a cylinder (see the outer wall of the cylinder at 300 in Figure 6) with the outer peripheral wall 400 separated from the wall of the cylinder 300 by a channel 250. An opening is provided with a removable cover on the side of the bowl 200 to allow the contents to be removed. The inside of the channel 250 has a cant shape so that when the vibrations are coupled to the bowl, the content moves along the channel in a circular flow. Other channel shapes can be applied to the channel wall or floor to move the contents in a circular manner. This movement improves the

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mixing of the content whereby all surfaces of gears 201 are exposed and subject to the smoothing action of means 212 in channel 250 with gears 201.

[0037] The gear is moistened with the fine finishing medium in the bowl and the vibrations are coupled to the

5 cup for the super finishing medium to vibrate with the gear moistened in it. The vibration continues for a sufficient time to achieve a gear with a 5-25 Ra finish. During vibration (fine finishing), additional water and / or fine finishing medium can be added through one or more inlets 204. Excess fine finishing medium, water, etc., can be removed by outlet 202. The Fine finish continues to smooth the surfaces of the gear (piece) leaving enough holes, crevices, etc., to improve oil retention

10 on the surface of the gear. It is not desirable to obtain a zero Ra finish because it leaves a completely smooth finish without holes, indentations, etc. surface that improve oil retention. It is believed that the holes provide places where the oil can accumulate and retain during gear operation so that an amount of lubrication is combined with the smoothness of the gears to extend the life of the gear. It has been found that the fine finish at a desired range of 5-25 Ra after double

The blasting set forth above significantly lengthens the life of the gears. After applying the fine finish, the gear is removed from the bowl, washed and rinsed. The gear is treated with a rust inhibitor in a final stage to obtain a gear with improved wear properties.

[0038] In an embodiment not according to the invention, the gears receive a fine finish in a bowl

20 without the addition of liquid medium (that is, with fine dry finishing medium). The gears receive a fine finish while they are dry and in the presence of wear material that smoothes the surface of the gear, but the wear material is not in liquid form. By coupling the vibrations to the bowl in order to vibrate the fine finishing medium with the gear, the size of the grooves on the gear surfaces is reduced making it possible to preserve the advantages of compressive tension and oil retention on the surface from

25 gear The resulting surface after finishing has smoothness as discussed above with indentations resulting from blasting and that have been reduced, but not completely disappearing after finishing.

[0039] The blasting steps with means produce a gear with a residual compressive tension in the

30 gear base radius of at least 551.58 MPa (80 KSI) and at the gear surface of at least 551.58 MPa (80 KSI). At depths of 12.7, 25.4 and 50.8 microns (0.0005, 0.001 and 0.002 inches) the residual compressive stresses will typically be at least 689.48 MPa (100 KSI). Using the procedure parameters set forth above, the gears are produced with a residual compressive tension in the gear base radius of at least 689.48 MPa (100 KSI) with typical values of at least 896.32 MPa

35 (130 KSI) at a depth of 0 cm (0.000 inches) (surface), 1.21 kPa at 12.7 microns (175 KSI at 0.0005 inches), 1,379 kPa at 25.4 microns (200 KSI at 0.001 inches) and 1.55 kPa at 0.51 mm (225 KSI at 0.020 inches).

[0040] For gears treated by the preferred method set forth above with two media blasting steps followed by a fine finish, the final tests confirm that the gears treated with this

40 shape exhibit superior performance in relation to gears not treated with this three step procedure. It has been found that gears treated with this preferred method exhibit superior fatigue resistance if properly performed with little evidence of wear for hundreds of hours in the tests. In contrast, gears treated by conventional procedures can be expected to fail in just 20 hours on dynamometer tests.

[0041] While the method of treating media blasting for gears here is set forth with respect to a clamping apparatus, it is contemplated that other conventional part holders and blasting apparatus can also be used with the steps described in this document. The procedure described above recognizes that in most cases the gears need steel blasting at the base of the

50 gear to prevent bending fatigue in the base radius.

Claims (6)

1. A method of processing a metal gear 20, 201 comprising 5 provide a gear 20, 201, directing a first shot blasting means to the metal gear 20, 201, thereby exposing a plurality of surfaces on the metal gear 20, 201 to the first shot blasting means, whereby the wear and strength properties of the bases are improved of gear teeth, 10 wash the gear 20, 201, and rinse gear 20, 201 with corrosion inhibitor 15 characterized by, before washing and rinsing: directing a second shot blasting means to the metal gear 20, 201, thereby exposing a plurality of surfaces on the metal gear 20, 201 to the second shot blasting means, whereby the surface compressive tension of the gear surface is improved 20, 201, 20 provide a vibratory fine finish vessel (200), placing a fine finishing medium (212) comprising ceramic means in a slightly acidic solution in the vibratory fine finishing container, 25 place the gear 20, 201 with the fine finishing medium in the vibratory fine finishing container (200), coupling vibrations to the vibratory fine finish vessel to vibrate the fine finishing medium (212) with the gear 20, 201, and 30 remove the gear 20, 201 from the vibratory fine finish vessel (200) after achieving a fine finish of the gear 20, 201 of between 5 and 25 Ra. 2. A method according to claim 1, wherein the container is a steel bowl coated with polyurethane (200). 3. A method according to claim 1, wherein the first shot blasting means comprises wire segments. The method according to claim 1, wherein the second shot blasting means comprises one of glass spheres, ceramic spheres and refined steel spheres. 5. The method according to claim 4, wherein the shot blasting means have a diameter of less than 250 µm. Four. Five 6. A method according to claim 1 wherein the first blasting means comprises ceramic means which are directed towards the metal gear 20, 201 at a pressure between 172.37 kPa (25 psi) and 620.53 kPa ( 90 psi) and in which the ceramic media have a diameter between 0.210 mm and 0.155 mm when added as virgin media. fifty 7. The method according to any one of the preceding claims, wherein the second shot blasting media has a size between 150 to 200 µm. 8