Course design for machine parts "Cylindrical single-stage gearbox"

Contents

Contents

Selection of lubricating oil and lubricating device

To reduce friction power losses, reduce the intensity of wear of friction surfaces, their cooling and cleaning from wear products, as well as to protect against jamming, gouging, corrosion, reliable lubrication of surfaces must be provided.

In mechanical engineering, the so-called crankcase system is widely used for lubricating gears, that is, the immersion of a moving wheel in an oil bath with liquid lubricant according to GOST 2079975. The lubricant must be liquid so that it is sprayed in the body and an oil mist is formed there, which is necessary for continuous lubrication of all friction parts of the mechanical transmission .

The choice of lubricant is based on the experience of the machines .

Oil grade assignment principle: the higher the wheel circumferential speed, the lower the oil viscosity and the higher the engagement contact stresses, the greater the oil viscosity. Therefore, the required viscosity of the oil is determined depending on the contact stress and the circumferential speed of the wheels [1, p. 179].

At a circumferential speed of up to 2 m/s and contact voltages αH = 6001000 MPa, the recommended kinematic viscosity of oil is 60 mm ²/s. For reducer we accept oil I-G-A-46 as per GOST 2079975 .

Bearings in the considered design version of shafts supports of cylindrical reduction gears are lubricated with plastic lubricant put (during assembly of the unit) into the internal cavity of the bearing sleeve. This is due to the fact that in this case, the value of the circumferential speed of the wheels (V < 3 m/s) does not allow to reliably lubricate these bearings with condensate of oil mist formed when oil is sprayed from the oil bath of the crankcase, the wheels of the reduction gear are immersed in it. Plastic (ointment-like) lubricants are liquid oils thickened with special thickeners with the inclusion of various additives.

The main plastic lubricants used in the bearing assemblies of the general purpose gearboxes are currently:

Litol-24 TU 2115075 (for operation in the temperature range - 40... + 130 ° С);

TSIATIM-201 GOST 626774 (-60... + 90 ° С).

Applicable in our case Litol-24 TU 2115075.

Gearbox assembly

Prior to assembly, inner cavity of reducer housing is thoroughly cleaned and covered with oil-resistant paint. Assembly is carried out in accordance with the general view drawing of the reduction gear box, starting from the shaft assemblies:

oil protection washers are put on the drive shaft on both sides and ball bearings No. 305 are installed, pre-heated in oil to t = 80... 100oC, then, from the side of the outlet end, the bushing (transition fit) is pressed until stop against the bearing, a spacer ring and a through cut-in bearing cover with a cuff previously packed in it are put on;

a key 18x11x60 is put into the driven shaft and the gear wheel is pressed to rest against the collar, a spacer ring is installed on the side of the output end, oil protection washers are put on at both ends and ball bearings No. 305 are installed, then the thrust ring is pre-heated in oil from the side of the output end of the shaft, and the remote bushing and the through-through bearing cover are fitted with it.

Blind cut-in covers are installed in body base, and assembled shafts with parts dressed on them are laid in body base.

Bearing sockets are filled in the required amount with plastic lubricant and put on the cover of the housing, covering the surfaces of the housing-cover joint with sealing lubricant of "Sealant" type.

For alignment, the cover is installed on the housing with the help of two conical pins, screws are tightened, which attach the cover to the housing.

Check a provorachivaniye of shafts lack of jamming of bearings (shafts have to be turned by hand). Then plug of oil discharge hole is screwed in and round oil indicator is installed on gasket. Oil is poured into the housing in the required amount, of the corresponding grade and the viewing window is closed with a cover - a sapun with gaskets; the cover is fixed with screws.

The assembled gearbox is rolled and tested on the bench according to the program set by the specifications.

12.1 Selection of gearbox main parts fits

The selection of mounts on the shaft of the inner rings of the rolling bearings is made, in accordance with GOST 3325 − 85, depending on the accuracy class of the bearings, their operating modes and the type of loading of the bearing rings.

Bearings operate in low load mode (moderate push operation) or medium loads under conditions of frequent re-installation. When the shaft is rotated, the inner race of the rolling bearing (when the outer bearing is stationary) is subjected to circulation loading. In this case, it is installed with interference on the shaft, since when the circulating loaded ring is installed with a gap, such a ring inevitably slips along the shaft, which leads to soaking and wear of the contacting surfaces. Depending on the mode of operation and the accuracy class of the bearing, we select the fit on the shaft of the internal rings of the rolling bearings k6.

Depending on the accepted degree of accuracy of the gear wheel manufacture, the accuracy quota (GOST 24643 − 81) for the manufacture of shaft seats will be 6.

At moderate loading (tcr ≤ 15 MPa) and non-revertive operation, fits are used: H6/k5; H7 / k6; H8 / k7.

Landing of the gear wheel on the cantilever of the slow-moving shaft is possible according to H7/k6.

The tolerance field for the width "b" of the key slot in the shaft intended for the prismatic key is selected according to GOST 23360-78 depending on the nature of the key connection and the type of load transmitted to it. For fixed connection of key with shaft at constant loading field of tolerance for width of shaft slot is assigned according to N9.

Bearing covers of high-speed and slow-speed assembly are installed as per fit H7

Literature

1. A.E. Sheinblit/Course design of machine parts/M. "Higher School," 1991.

2. S.A. Chernavsky/Course design of machine parts/M. "Mechanical Engineering," 2005

3. A.V. Kuzmin et al ./ Course design of machine parts. Reference manual in 2 parts/Mn., "The Highest School," 1982

4. P.F. Dunaev, O.P. Lelikov, L.P. Varlamova/Tolerances and landings. Justification of Choice/M. "Higher School, 1984.