BILL OF MATERIAL

Sr. No. Component (All

dimensions in mm )

Material Quantity Cost

1 Base plate:

Area-270×270×5

M.S. 1 1500

2 Vertical shaft

Lenth-220, Dia.- 30

EN8 1 900

3 Bearing holder

OD-100, ID-55,

Thickness-10

Cast Iron

FG 200

2 2000

4 Ball Bearing holding

rectangular plate

Area-167×167×5

Cast Iron

FG 200

1 800

5 Working Table

OD-275,ID-

25,Thickness-15

Mild Steel

40C8

1 1000

6 Disc plate for

demonstration

OD-248,ID-28,

Thickness-3.5

Mild Steel

40C8

1 800

7 Worm and worm wheel

1/36/11/4

Mild

Steel,

1 2500

8 Square plate EN8 1 700

9 M16 Hexagonal Nuts

and bolt

Diameter- 16mm, e-

30mm

M.S. 4 100

Material Properties Application

Acetal /Nylon

Low Cost, low duty Toys, domestic appliances, instruments

Phos Bronze

Reasonable strength, low friction and good compatibility with steel

Normal material for worm gears with reasonable efficiency

Cast Iron Excellent machinability, medium friction.

Used infrequently in modern machinery

4.1.2 Selection of Material for Worm Gear

Plastic worm drives are often used on small battery-operated electric motors, to

provide an output with a lower angular velocity (fewer revolutions per minute)

than that of the motor, which operates best at a fairly high speed. This motor-

worm-gear

[3] The threads of worm are subjected to fluctuating stresses and the number

of stress cycles is fairly large. Therefore the surface endurance strength is an

important criterion in the selection of worm material.

The magnitude of contact stresses on worm wheel teeth is the same as that

on the worm threads. However the number of stress cycle is reduced by a factor

equal to the speed reduction. The worm wheel can’t be accurately generated in

Hobbing Process. The final profile and finish of the worm is the result of plastic

deformation during the initial stages of the service. Therefore, the worm wheel

material should be soft and conformable Phosphor Bronze, with a surface

hardness of 90-120 BHN. Phosphor Bronze worm wheels are sand-cast, sand-cast

and chilled, or centrifugally cast. Phosphor Bronze is costly and in case of worm

wheels with large dimensions, only the outer rim is made up of Phosphor Bronze.

It is then bolted to the CI wheel. There are two reasons for using dissimilar or

heterogeneous materials for worm and worm wheel:

1) The coefficient of friction is reduced.

2) The conformability of worm wheel with respect to worm is improved

drive system is often used in toys and other small electrical devices.

Gear Bushings

Materials for Worm Gearing - The Hamilton Gear & Machine Co. conducted an extensive series of test on a variety of materials that might be used for worm gears , to ascertain which material is the most suitable.

Gears Material

• Aluminum Gears

• Cast Iron Gears

• Plastic Gears

• Steel Gears

• Other Metal Gears • Brass Gears

• Copper Gears

• Powdered Metal Gears

• Wood Gears

Industries Served

• Defence

• Marine

• Aluminum

• Chemical

• Food Processing

• Grinding Mills

• Hot and Cold Rolling

• Lock and Dam Machinery

• Moveable Bridges

• Paper

• Petroleum

• Plastics

• Rubber

• Sugar

• Stamping Presses Steel

• Strip Processing

• Surface Mining

• Petrochemical

• Turbine Plant

• Rubber Plants

• Power Industry

• Fertilizer Industry

• Sponge Iron

• Material Handling

• Earth Moving Industry

Classifications of Gear Steels - Gear steels may be divided into two general classes - the plain carbon and the alloy steels. Alloy steels are used to some extent in tthe industrial fiels, but heat- treated plain carbon steels are far more common. the use of untreated alloy steels for gears is seldom, if ever, justified, and then, only when heat-treating facilities are lacking. The points to be considered in determinig whether to use heat-treated plain carbon steels or treated alloy steels are: Does the service conditionor design require the superior characterstics of the alloy steels or, if alloy steels are not required, will the advantages to be derived offeset the additional cost? For most applications, plain carbon steels, heat treated to obtain the best of their qualities for the service intended, are satisfactory and quite economical. The advantages obtained from using heat-treated alloy steels in place of heat-treated plain carbin steels are as follows:

Increased surface hardness and depth of hardness penetration for the same carbin content and quench.

Ability to obtain the same surface hardness with a less drastic quench and in the case of some of the alloys, a lower quenching temperatur, thus giving lesser distortion.

Increase toughness, as indicated by the higher values of yield point, elongation and reduction of area.

Finer grain size, with the resulting higher impact toughness and increased wear resistance.

In the case of some of the alloys, better macining qualitites or the possibility of machining at higher hardness.

Use of Casehardening Steels: Each of the two general classes of gear steels may be further subdivided as follows :

Case hardening Steels

Full-hardening steels

steels that are heat-treated and drawn to a hardness that will permit machining.

The first two rechangeable for some kinds of service, and the choice is often a matter of personal op- casehardening and full-hardening steels - are interchangeable for some kinds of service, and the choice is often a matter of personal opinions, Casehardening steels with their extremely hard, fine-grained (when properly treated) case and compartively soft and ductile core are generally used when resisitance to wear is desired. case hardening alloy steels have a fairly tough core, but not as tough as that of the full-hardening steels. In order to realize the greatest benefits from the core properties, casehardened steels should be doubled-quenced. This is particularly true of the alloy steels, because the benefits derived from their use seldom justify the additional expense, unless the core is refined and toughened by a second quench. The penality that must be paid for the additional refinement is increased distortion, which may be excessive if the shape or design doen not lend itself to the casehardening process.

Use of "Thru-Hardening Steels." - Thru-hardening steels are used when great strength, high endurance limit, toughnessand resistance to shock are required.The medium and high-carbon percentages require an oil quench, but a

water quench may be necessary for the lower carbin cintents, in order to obtain the highest physical properties and hardness. The distortion, however, will be greater with the the water quench.

Heat-Treatment that Permits Machining - When the grinding of gear teeth is not practicable and a high gdegree of accuracy is required, hardened steels may be drawn or tempered to a hardness that will permit the cuting of the teeth. This treatment gives highly refined structure, great toughness and, in spite of of the low hardeness, elimination of the increment loads due to the impacts which are caused by inaccuracies. when steels that have a low degree of hardness penetration from surface to core treated in this manner, the design cannot be based on the physical properties mined by the hardness. Since the physical properties are determined by the hardness, the drop in the hardness from surface to core will give lower physical properties at the root of the tooth, where the stress is greatest. The quenching medium may be either oil, water or brine, depending on the steel used and hardness penetration desired. The amount of distortion, of course, is immaterial, because the machining is done after heat-treating.

Making Pinion Harder than Gear to Equalize Wear - Beneficial results from a wear standpoint are obtained by making the pinion harder than the gear. The pinion, having a lesser number of teeth than the gear, naturally does more work per tooth, and the differential in hardeness between the pinion and the gear(the amount being dependent on the ratio)serves to equalize the rate of wear. The harder pinion teeth to burnish the teeth to some extent by the initial wear by the greater hardness due to the cold-working`of the surface. In application where the gear ratiois high and there is no severe shock loads, a casehardened pinion running after treating, is an excellent combination. Yhe piniion, being relatively small, is distorted but little, and the distortion in the gear is circumvented by cutting the teeth after treatment.

Forged and Rolled Carbon Steels for Gears - These compositions cover steel for gears in three groups, according to heat treatment as follows: a) case-hardened gears, b) unhardened gears, not heat treated after machining, and c) hardened and tempered gears.

Forged and Rolled Alloy Steels for Gears - These compositions cover alloy steel or gears in two classes according to heat treatment as follows: a) casehardened gears, b) hardened or tempered gears.

Effect of Alloying Metals on Gear Steels - The effect of the various alloying elements on steel will be summarized in order to assist engineers in deciding upon the particular kind of alloy steel to use for specific purposes. The characteristics apply only to heat-treated steels. when the effect of the addition of an alloying element is stated, it is understood that reference is made to alloy steels of a given carbon content , compared with a plain carbon steel of the same carbon content.

Nickel

Chromium

Manganese

Vanadium

Molybdenum

Chrome - Nickel

Bronze and Brass Gear Castings

Spur and Bevel Gears

Types of failure of worm gearing

Sliding can not be totally avoided and therefore the principal causes of worm gearing failure are surface damage, tooth wear and seizing. Fatigue pitting is observed mainly in gearing with a worm gear made of seizure-resistant bronze. Breakage can be found mainly after severe wear, and usually only the teeth of the worm gear are broken.

scuffing pitting wear

Principle of design of worm gearing

Failure form of exposed gears is, mostly, surface wear and tooth breaking of worm gear. So the assurance of beam fatigue strength of tooth is the principal of design. Failure form of enclosed gears is, mostly, seizing and fatigue pitting of the tooth surface. So the design is first done according to contact fatigue strength and then the beam fatigue strength of tooth root is checked.

Materials of worm gearing

In view of the types of failure observed and tooth damage, the selection of materials is based on the durability of the surface layers.

The first, basic requirements of materials

1 Worm

Characteristic of worm :slender and long，selection of materials is based on rigidity and intensity. Usually choose steel of proper heat treatment

2 Worm gear

Materials with excellent wearing capacity and gluing resistant to pair up worm. Usually choose aldary, aluminium alloy cast iron or nonferrous metal

The second , Common materials

1 Worm:

Usually: 45、35SiMn、40Cr、40CrNi;

Surface quencher HRC=45-50 High speed, heavy loads; 20Cr、15Cr、20CrMnTi;

Carburizing quencher HRC=56-62.Low speed and power or nonsignificant transmission: 45、40 hardening and tempering：HB=220~300

2 Worm gear

High speed transmission：ZCuSn10Pl、ZCuSnPb5Zn5

Low speed but heavy loads：ZCuAl10Fe3

Low speed and loads：HT150、HT200