The gears must be made of extremely hard steel that will resist abrasion, corrosion and mechanical damage. The use of gears in various types of machines and devices requires selecting them in terms of technical parameters. In this text you will learn what a rack module is and how it is calculated.
Features of the gear
Gears are parts used in machinery and equipment to change torque, angular velocity and direction. These are the most important elements of transmissions working with a wheel, disk or modular rack. Each gear is distinguished by:
- number of teeth (z),
- pitch diameter (d),
- apical diameter (da),
- the diameter of the feet (df),
- base circle diameter (db),
- circumferential pitch (p),
- basic scale (pb),
- tooth height (h),
- tooth head height (ha),
- tooth foot height (hf),
- tooth height factor (y),
- correction factor (x),
- apex clearance (c),
- tooth module (m).
The modulus is a quantity that allows to determine the dimensions of teeth and gears resulting from the strength conditions. It is a parameter used when selecting the gears that are to cooperate with each other. Regardless of the size of the gears, their module must remain the same. The mismatch leads to improper meshing, which may result in rapid tooth wear.
Standardization and formula
The gear module is a size standardized by the Polish standard PN-ISO 54: 2001 General purpose and heavy industry helical gears - Modules. It is possible to use other module values than those given in the standard, but it involves the production of non-standard tools suitable for making gears with such modules. To calculate the rack module, use the formula:
m = ⌀ / (T + 2).
- m - rack module,
- ⌀ - rack diameter,
- T- number of teeth.
Gear modules have been standardized along with pitch parameters, tooth head height, foot height, and total tooth height. Tooth height factor is expressed in multiples of the module. In most cases, normal teeth y = 1 are used. Below this value are the low teeth used in curved bevel gears where the small gear has a number of teeth from 5 to 10, in worm gears, in spur gears and in involute spline connections. A value above 1 is used in gear pumps. In normal teeth, the height of the head is equal to the module and the height of the foot is 1,2 mm. When added, the total height of normal teeth can be obtained, i.e. 2,2 mm.
Conversion from the inch system
It is a bit different in countries that use the inch system. The module is known as the Diametral Pitch. This is a quantity that represents the number of teeth gear wheel on one english inch of the diameter of the pitch circle. The formula is as follows:
DP = z / d "
- DP - Diametral Pitch,
- z - number of teeth,
- d ”- wheel diameter expressed in inches.
D / m can be substituted for the number of teeth, i.e. the diameter of the pitch circle expressed in millimeters by the module. Conversely, convert the diameter of the pitch circle from inches to millimeters (1 English inch = 25,4 mm). Thus, we obtain the conversion formula DP = 25,4 / m.