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Assembly of sprockets and gears for mechanical design equipment

2021.08.16

When assembling the chain drive, you must first confirm that the chain pitch is the same as the meshing of the sprocket teeth.  Before assembly, use 400-600# emery cloth to polish the respective assembly shaft and sprocket holes.  Make sure that there are no big burrs and bumps, and finally clean it with kerosene, then apply butter or lubricating oil, and knock it in with a copper rod.

In the assembled chain drive mechanism:

The axes of the two sprockets must be parallel. You can use a wire and a ruler to test whether the two sprockets are on the same plane.

The axial offset between the two sprockets must be less than the allowable value.

After the sprocket is fixed on the shaft, its radial runout and end face runout must meet the specified requirements.

In order to reduce the falling off and vibration of the chain, for the horizontal or inclined chain drive within 45 degrees, the sag of the chain should be 0.02L. In the vertical drive, f should be greater than or equal to 0.02L.

(1) Gear transmission requirements for gear manufacturing accuracy

A. The accuracy of the transmission movement requires the gear to be within the rotation range, and the maximum rotation angle error should be limited within a certain range, so as to make the gear ratio change small and ensure the accuracy of the transmission movement.

B. Transmission stability requires small short-term gear ratio changes.

C. The uniformity of the tooth surface load requires that the gear is in good contact with the tooth surface in the transmission, and the load is even, so as to avoid the concentration of the load in the local area and cause the stress concentration, cause local wear and affect the service life.

D. Gear play backlash. The gear play is not working and requires a certain gap to store lubricating oil and compensate for gear manufacturing errors.  Assembly error, thermal expansion error, etc.

(2) Assembly requirements of cylindrical gear transmission mechanism:

A. The gear hole and the shaft must be properly matched, and there must be no eccentricity and skew.

B. The center distance and the tooth side clearance must be correct. If the clearance is too small, the gear transmission is not flexible, or even the teeth are jammed, which will aggravate the wear of the tooth surface. If the clearance is too large, the commutation loss will be large and impact will be generated.

C. The two tooth surfaces meshing with each other should have a certain contact area and correct contact.

D. The sliding gear should not be bitten or blocked.  The transformation mechanism should ensure accurate positioning.  The misalignment of the gears must not exceed the specified value.

E. The large gear with high speed must be dynamically balanced when assembled on the shaft to avoid excessive vibration during work.

(3) Measure the radial runout and end runout errors of the gears connected to the shaft.

When measuring the radial runout error, the gear shaft is supported on the V-shaped frame or on the two centers, so that the shaft is parallel to the inspection platform, and the standard measuring rod is placed between the gear and the gear, and then the probe of the dial indicator is pressed against it.  Take a reading on the standard measuring stick. Turn the gear shaft and repeat every count of teeth. In this way, the difference between the maximum and minimum readings of the dial indicator is the radial direction on the graduation circle after the gear has rotated for a full circle.  Circle runout error.

When measuring the end circle run-out error, put the shaft with the gear between the two centers, make the probe of the dial indicator abut on the end face of the gear, and rotate the gear shaft to measure the end face circle run-out error of the gear.

(4) Measure the backlash of meshing with the adjustable gear

The dial indicator probe is in contact with the tooth surface of one gear, the other gear is fixed, and then the gear contacting the dial indicator probe is meshed from one side to the other. The reading difference on the dial indicator  , Which is the backlash (note that the dial gauge is not available, because the range of the dial gauge is too small) Gear backlash can also be measured by the lead pressure method.  Place two lead wires in parallel along the two ends of the tooth width on the tooth surface. The diameter of the lead wire should not exceed 4 times the minimum backlash. Turn the gear and measure the thinnest size of the lead wire after being squeezed, which is the backlash.

(5) The reason and adjustment method of tooth tip contact and tooth root contact caused by spur gear transmission.  The reason for tooth tip contact: the center distance of the gear axis is large, the original tooth profile displacement error or the tip diameter of the gear is too small, etc., the adjustment method: adjust the axis if possible, reduce the center distance, otherwise it is necessary to trim the tooth surface  .

Saturation of gear transmission mechanism after assembly

If the transmission mechanism requires high gear contact accuracy and low noise, and in processing, due to the small batch size, when the contact accuracy requirements cannot be economically achieved, saturation must be performed after assembly.

There are two types of saturation methods: load saturation and electric spark saturation.  Load saturation is often used in assembly.  The specific method is to add a torque on the output shaft of the gear pair, install a pulley on the driving wheel shaft, select a certain power motor and reduction box for transmission according to the operating speed, add abrasives between the gears to make the gear contact surfaces run in with each other.  In order to increase the contact area of the gear, improve the quality of meshing.  After the saturation is qualified, the entire gearbox should be thoroughly cleaned to prevent abrasives and other impurities from remaining in the bearings.

Electric spark saturation is the pulse discharge in the contact area to remove the first part of the metal to make the contact area gradually increase to achieve the required contact accuracy.

Before assembling the gear, the burrs of the gear should be polished with sandpaper or a file.