The use of gears is reflected in two aspects: one is to transmit motion, and the other is to transmit power. At present, domestic plastic gears are mainly used to transmit motion, and Western countries are now using plastic gears more and more in the choice of transmitting power. . Due to the advantages of low transmission noise, shock absorption, self-lubrication, high production efficiency and simple process, plastic gears will become more and more widely used in the gear industry and become a worldwide trend.

How to view the parameters of the gear:

1. What is modulus?

The modulus indicates the size of the gear teeth.

In addition to the modulus, there are cp (circular pitch: circular pitch) and dp (diameter pitch). (Ps: tooth pitch is the length of the dividing arc between the equivalent points on two adjacent teeth.)

2. What is the diameter of the dividing circle?

The diameter of the dividing circle is the reference diameter of the gear.

The two major factors that determine the size of the gear are the module and the number of teeth, and the diameter of the dividing circle is equal to the product of the number of teeth and the module (end face). (Ps: The diameter of the dividing circle is called the reference pitch diameter. According to the iso standard, it is uniformly called the diameter of the dividing circle.)

3. What is the pressure angle?

The acute angle between the radial line at the intersection of the tooth shape and the dividing circle and the tangent to the tooth shape at this point is called the dividing circle pressure angle. Generally speaking, the pressure angle refers to the graduated round pressure angle.

The commonly used pressure angle is 20°, but there are also gears that use pressure angles of 14.5°, 15°, 17.5°, and 22.5°.

4. What is the difference between single-headed and double-headed worms?

The number of helical teeth of the worm is called the head number, which is equivalent to the number of gear teeth of the gear. The greater the number of heads, the greater the lead angle.

5. How to distinguish between r (right-handed) and l (left-handed)?

When the gear shaft is placed flat on the ground, the right-handed gear is inclined to the upper right, and the left-handed gear is inclined to the upper left.

6. What is the difference between m (modulus) and cp (week festival)?

cp (circular pitch: circular pitch) is the circumferential pitch on the dividing circle. The unit is the same as the modulus in millimeters.

　

cp is divided by pi (π) to get m (modulus).

　

The relationship between m (modulus) and cp is shown below:

　

m (modulus) = cp/π (pi)

　

Both are units that indicate the size of gear teeth. (The length of the dividing circumference =πd=zpd=z p/π p/π is called modulus)

　

7. What is backlash?

When a pair of gears mesh, the gap between the tooth surfaces. Backlash is a necessary parameter for smooth operation of gear meshing.

　

8. What is the difference between bending strength and tooth surface strength?

The strength of the gear should generally be considered from the two aspects of bending and tooth surface strength.

　

Bending strength is the strength with which the tooth that transmits power resists breaking at the root of the tooth due to the bending force.

　

The tooth surface strength is the anti-friction strength of the tooth surface during repeated contact.

　

9. Among the bending strength and tooth surface strength, what strength should be used as the basis for selecting the gear?

In general, it is necessary to discuss the bending and the strength of the tooth surface at the same time. However, when selecting gears with low frequency of use, hand gears, and low-speed meshing gears, there may be cases where only the bending strength is selected, which should be decided by the designer.

　

10. What is the spiral direction and thrust direction?

Thrust is generated on gears other than spur gears whose gear teeth are parallel to the axis.

　

11. What is the center distance?

The center distance refers to the distance between the shafts of a pair of gears.

　

The size of the center distance affects the backlash. The greater the center distance, the greater the backlash.

12. How much should the center distance of the spur gear be allowed?

Generally, the standard value is taken as a tolerance of ±0.

　

The relevant regulations are the Japanese Gear Industry Association standard jgma 1101-01 (2000).

13. What is the axis intersection angle?

The angle between the two shafts of the intersecting shaft gear (bevel gear) and the interlaced shaft gear (interlaced shaft helical gear and worm gear) is generally 90°.

　

The size of the shaft intersection angle is an important factor that has an important effect on the tooth contact and backlash.

14. What is the assembly distance?

The axial distance from the cone vertex of the bevel gear to the positioning surface (installation reference surface).

　

The installation distance is an important dimension that affects the contact and backlash of the gear teeth. (Ps: In English, the assembly distance is called locating distance (mounting distance).)

15. What is the tolerance of the assembly distance?

The axial distance from the cone vertex of the bevel gear to the positioning surface (installation reference surface).

　

It is recommended to use js7~js9 for the tolerance of the reference size (the tolerance is close to 0).

16. What is a zero-degree bevel gear?

Spiral bevel gear with a helix angle of 0°. The shape is similar to the spiral bevel gear of straight tooth bevel gear.

　

The advantages are as follows: the force acting on the gear is the same as that of the straight-tooth bevel gear, which has higher strength and lower noise than the straight-tooth bevel gear (in general). (Ps: The spiral angle of the spiral bevel gear is generally 35°)　

17. How to find the index circle diameter (dp8-15z) of dp (diameter pitch) spur gear?

Convert dp (diameter pitch) to modulus.

　

m (modulus) = 35.4/dp (diameter pitch) = 25.4/8 = 3.175 mm

Approximate indexing circle diameter.

da=m*z=3.175 ×15 = 47.625 mm (ps: 1 inch=25.4mm)

18. What is tooth shape modification?

In order to avoid tooth tip interference during gear meshing, the tooth shape is intentionally trimmed near the tooth tip.

　

The purpose of the tooth shape modification is the smooth meshing of the gear teeth, which is similar to the drum repair in the tooth shape direction.

19. What is the addendum chamfering process?

At the same time as machining the gear teeth, the chamfering of the tooth tip is performed.

　

Its advantages are: to prevent burrs generated during cutting of teeth, etc.; to prevent collision marks that are easy to occur during use and transportation. (Ps: addendum = intersection of tooth surface and addendum surface)

20. What is the drum repairing process?

The tooth shape is trimmed along the tooth width direction so that the tooth shape in the central part of the tooth width has an appropriate drum shape.

　

By repairing the drum shape, one-sided contact at the end of the tooth is prevented, and the tooth contact of the gear is concentrated near the center of the tooth. The larger the drum shape, the smaller the tooth contact area.

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