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1 large gear repairable large, heavy-duty gears are generally made of cast steel, the basic structure. The main cause of the scrapping of the large gear is the wear and gluing of the tooth surface and the tooth shape damage. Obviously, one of the methods of repairing the gear is to cut off the damaged part of the tooth working surface, that is, to turn the tooth top circle and then re-cut the new tooth shape, and then formulate the pinion gear according to the repaired gear parameters. However, after cutting, it is bound to cause the thickness of the inner edge of the repaired large gear to decrease. At this time, whether the value can satisfy the working strength of the gear becomes the key to whether it can be repaired. Through the actual measurement of several commonly used large gears, these gears have a design margin when designing, the value is generally 3035mm, and according to the design strength and design experience, the value is generally not less than 1520mm. The analysis and preliminary calculation of the overall gear wear situation shows that the value of the large gear after repair is reduced by about 15mm. Therefore, the value of the large gear after repair should meet the strength requirement. According to the actual situation of the large gear after repair, It also proves this.
2 Control of the outer diameter of the pinion gear According to the mechanical design manual, the meshing angle of the external meshing gear and the total displacement coefficient can be calculated according to the formula (1) and formula (2): cos=acos/a(1)X=(Z1 Z2 (inv-inv)/2tan(2) where: the required center distance after a displacement; the meshing angle; the center distance when a is not displaced; the indexing circle pressure angle; the X total displacement coefficient; Z1 pinion Number of teeth; Z2 large gear teeth.
In the above process of repairing the gear, if the installation center distance of the two meshing gears is to be kept constant, according to the formulas (1) and (2), the total gear displacement coefficient X of the two gears is unchanged. Since the diameter of the top circle is reduced after the large gear is repaired, the displacement coefficient is also reduced, thereby correspondingly increasing the displacement coefficient of the pinion, resulting in an increase in the outer diameter of the pinion (about 30 mm). The outer diameter of the pinion is limited by the gear cover during installation and cannot be increased too much, so the increase in the outer diameter of the small wheel must be controlled. Through the investigation of the installation site, the center distance of the gear can be adjusted by 20mm. Therefore, it is decided to reduce the total displacement coefficient X by changing the center distance to achieve the purpose of controlling the outer diameter of the pinion.
The compensation of the 3 tooth strength of the large gear is designed to adapt to the working environment and improve the contact strength. Generally, a large displacement (the displacement coefficient is about 3) is adopted. This plays a crucial role in improving the wear resistance and gluing resistance of the gear. However, the displacement coefficient of the large gear is reduced, which reduces the wear resistance and gluing resistance of the gear. In this regard, we use a short tooth system for the two gear tooth shapes (ie, the tooth top height coefficient h=08, radial backlash coefficient c=0.3), and the gear tooth portion of the short tooth gear has high working strength. The advantage of long life, which makes up for the reduction of wear resistance and anti-adhesive ability of the gear after repair, and guarantees the service life of the gear after repair. At the same time, the use of short-toothed gears to control the outer diameter of the small wheel can also have a certain effect.
4 Large gear outer diameter control The large gear should be turned to the outer diameter when repairing. After turning, it is necessary to ensure that the complete tooth shape can be cut when trimming, and the total cutting amount should be as small as possible to ensure the inner edge thickness value. Not less than 1520mm. Therefore, the outer diameter of the large gear should be controlled to reach or approach the optimum value. By analyzing the tooth profile wear condition, the complete tooth profile can be repaired as long as the tooth diameter of the outer gear of the gear after turning is equal to the tooth thickness of the tooth tip of the repaired gear. However, the round tooth thickness of the repaired gear can not be determined. Therefore, we use the top tooth thickness of the standard gear as a reference. When the gear is positively displaced, the top tooth thickness becomes smaller. After the big wheel is repaired, it is still a positive displacement gear. The top scallop thickness is smaller than the standard top scallop thickness, and the difference between the two is small. Therefore, as long as the tooth thickness of the large gear after turning is equal to the top scallop thickness Sa of the standard gear, the outer diameter of the large gear can be ensured. Close to the optimum value to ensure the quality of the gear after repair.
5 application examples have a pair of meshing gear parameters: m = 14mm, ha = 1, c = 0.25. The gear parameters are: number of teeth Z2 = 150, top circle diameter da2 = 2192mm, displacement coefficient X2 = 264. parameters of the pinion The number of teeth is Z1=21, and the diameter of the top circle is da1=330mm. The calculation process of gear repair is as follows.
1) Calculation of the standard gear top scallop thickness Sa Since we use Sa as the measurement standard for the outer diameter of the turning gear, we must first calculate the Sa:Sa=S-2ra(inva-inv) formula: S is the dividing circle Tooth thickness, S=m/2=21.98mm; ra is the radius of the top circle: ra=m(Z2 2ha)/2=10612mm (where the height coefficient of the tip is ha=0.8); r is the radius of the circle: r= mZ2/2=1050mm; a is the tooth top engagement angle: a=arccos(rb/ra)=216 (where rb is the base circle radius, rb=rcos).
So calculate: Sa = 13.7mm.
2) The meshing parameters of the original two gears are calculated to determine the variation coefficient of the tooth height y according to the diameter of the top circle of the large wheel da2=d2 2(ha X2-y)m=2192mm, which can be obtained as: y=0.3543mm, where d2 is the big wheel Index circle diameter.
(See the small wheel displacement coefficient X1 according to the small wheel top circle diameter da1=d1 2(ha X1-y)m=330mm; available: X1= 0.64, where d1 is the small wheel index circle diameter.) Seeking total change The bit coefficient XX=X1 X2=3.28 calculates the meshing angle from the formula (2): X=(Z1 Z2)(inv-inv)/2tan=3.28, which can be obtained:=24.7.
Calculate the actual center distance a by the formula acos=acos, where a is the standard center distance.
Can get a = 1238mm.
3) After the repair, the calculation of the gear parameters is to control the outer wheel of the small wheel. Now adjust the installation center distance a to a, = 1228mm.
Calculate the meshing angle, obtained by the formula a, cos, = acos, available, = 239'.
(Calculating the total displacement coefficient X, from the formula X, = (Z1 Z2) (inv, -inv)/2tan, can obtain X, = 2.41.) Calculate the variation coefficient y of the center distance, by the formula y, = (a, - a) / m, can get y = 2.21. Calculate the variation coefficient y of the tooth height, from the formula y, = X, - y, can get y, = 0.2. Calculate the large wheel displacement coefficient X, 2 if the standard gear The top scallop thickness is the outer diameter of the large wheel after standard turning by the formula dy, a2 = d2 2 (ha X, 2-y,) m = 2165 mm (where ha = 0.8); X, 2 = 1.72.
Calculate the small wheel displacement coefficient X,1 from the formula X, 1 = X, -X, 2, which can be obtained X, 1 = 0.69. The outer diameter of the small wheel is calculated by the formula d, a1=d1 2(ha X,1-y,)m=330.12mm (where ha=0.8), it can be seen that the size of the outer diameter of the small wheel is almost unchanged after the repair, which can meet the assembly. Claim.
The check of the value after the repair of the big wheel is known as: =(d, f2-d3)/2, where df2' is the diameter of the root circle after the repair of the big wheel, which can be obtained = 21.7mm. Obviously, the value after gear repair can be satisfied. Strength requirements.
6 The use effect and economic analysis practice prove that it is feasible to repair the gear by the above method, and its strength meets the work requirements. This not only reduces the waste of raw materials, but also saves a lot of money for the company. The above gear repair method is also applicable to the repair of other large failure gears.