LUBRICATION OF GEARS and CAMS

Methods of Lubrication

There are three lubrication methods in general use:

1.Grease lubrication.
2.Splash lubrication (oil bath method).
3.Forced oil circulation lubrication.

There is no single best lubricant and method. Choice depends upon tangential speed (m/s) and rotating speed (rpm). At low speed, grease lubrication is a good choice. For medium and high speeds, splash lubrication and forced circulation lubrication are more appropriate, but there are exceptions. Sometimes, for maintenance reasons, a grease lubricant is used even with high speed.

Table 1 presents lubricants, methods and their applicable ranges of speed.

The following is a brief discussion of the three lubrication methods.

Grease Lubrication

Grease lubrication is suitable for any gear or cam system that is open or enclosed. It is usually applied to low speed, or when the cam or gears are exposed to the product, pack, or packaging running on a machine. There are three major points regarding grease:

1.Choosing a lubricant with suitable viscosity. A lubricant with good fluidity is especially effective in an enclosed system.
2.Not suitable for use under high load and continuous operation. The cooling effect of grease is not as good as lubricating oil. So it may become a problem with temperature rise under high load and continuous operating conditions.
3.Proper quantity of grease. There must be sufficient grease to do the job. However, too much grease can be harmful, particularly in an enclosed system. Excess grease will cause agitation, viscous drag, a temperature rise and result in power loss.

Splash Lubrication

Splash lubrication is used with an enclosed system. The rotating gears splash lubricant onto the gear system and bearings. It needs at least 3 m/s tangential speed to be effective. However, splash lubrication has several problems, two of them being oil level and temperature limitation.

1.Oil level.

There will be excessive agitation loss if the oil level is too high. On the other hand, there will not be effective lubrication or ability to cool the gears if the level is too low. Table 2 shows guide lines for proper oil level. Also, the oil level during operation must be monitored, as contrasted with the static level, in that the oil level will drop when the gears are in motion. This problem may be countered by raising the static level of lubricant or installing an oil pan.

2.Temperature limitation.

The temperature of an enclosed cam system may rise because of friction loss due to any gears, bearings and lubricant agitation. Rising temperature may cause one or more of the following problems:

Lower viscosity of lubricant.
Accelerated degradation of lubricant.
Deformation of housing, gears and shafts.
Decreased backlash.

New high-performance lubricants can withstand up to 80 to 90°C. This temperature can be regarded as the limit. If the lubricants temperature is expected to exceed this limit, cooling fins should be added to the gear box, or a cooling fan incorporated into the system.

Forced-Circulation Lubrication

Forced-circulation lubrication applies lubricant to the contact portion of the teeth by means of an oil pump. There are drop, spray and oil mist methods of application.

1.Drop method:

An oil pump is used to suck-up the lubricant and then directly drop it on the contact portion of the gears via a delivery pipe.

2.Spray method:

An oil pump is used to spray the lubricant directly on the contact area of the gears.

3.Oil mist method:
Lubricant is mixed with compressed air to form an oil mist that is sprayed against the contact region of the gears. It is especially suitable for high-speed gearing.
Oil tank, pump, filter, piping and other devices are needed in the forced-lubrication system. Therefore, it is used only for special high-speed or large gear box applications. By filtering and cooling the circulating lubricant, the right viscosity and cleanliness can be maintained. This is considered to be the best way to lubricate gears.

Cam Lubricants

An oil film must be formed at the contact surface between the cam and roller to minimize friction and to prevent dry metal-to-metal contact. The lubricant should have the properties listed in Table 3.

Also, the Lubricating Oil Viscosity is dependent on the ambient temperature and the operating speed of the dam.

Typically, a Cam indexing mechanism would have the following viscosity grades [CAMDEX drives precision indexing drives]

Input shaft speed [RPM]

0-20

20-100

100-200

200-300

300-400

>400

Lubricant Viscosity [cSt @40C

>680

680-460

460-320

320-220

220-150

15-=68

Heinz-Automation Cams recommend Klübersynth GH 6-460 'Synthetic gear and high temperature oils'.

Viscosity of Lubricant

The correct viscosity is the most important consideration in choosing a proper lubricant. The viscosity grade of industrial lubricant is regulated in JIS K 2001. Table 4 expresses ISO viscosity grade of industrial lubricants.

JIS K 2219 regulates the gear oil for industrial and automobile use. Table 5 shows the classes and viscosities for industrial gear oils.
JIS K 2220 regulates the specification of grease which is based on NLGI viscosity ranges. These are shown in Table 6.
Besides JIS viscosity classifications, Table 7 contains AGMA viscosity grades and their equivalent ISO viscosity grades.

Selection of Lubricant

It is practical to select a lubricant by following the catalog or technical manual of the manufacturer. Table 8 is the application guide from AGMA 250.03 "Lubrication of Industrial Enclosed Gear Drives".

Table 9 is the application guide chart for worm gears from AGMA 250.03.

Table 10 expresses the reference value of viscosity of lubricant used in the equations for the strength of worm gears in AGMA 405-01.

[Heinz-Automation Cams recommend Klübersynth GH 6-460 'Synthetic gear and high temperature oils'.


Table 1: Range of Typical Speed (m/s) for Spur and Bevel Gears

 

No

 

Lubrication Type

Range of Tangential Speeds [m/s]

0

5

10

15

20

25

1

Grease






2

Splash





3

Forced Circulation

Applies to 'Oil Mist', Circulating Oil, 'Oil Jets'.




Table 2: Oil Levels for different Gear Types

Oil Level

Table 3: The Properties that Lubricant Should Possess

No.

Properties

Description

1

Correct and

Proper Viscosity

Lubricant should maintain a proper viscosity to form a stable oil film at the specified temperature and speed of operation.

2

Anti-scoring Property

Lubricant should have the property to prevent the scoring failure of tooth surface while under high-pressure of load.

3

Oxidization and Heat Stability

A Good lubricant should not oxidized easily and must perform in moist and high-temperature environment for long duration.

4

Water Anti-affinity Property

Moisture tends to condense due to temperature change, when the gears are stopped. The lubricant should have the property of isolating moisture and water from lubricant.

5

Anti-foam

Property

If the lubricant foams under agitation, it will not provide a good oil film. Anti-foam property is a vital requirement.

6

Anti-corrosion Property

Lubrication should be neutral and stable to prevent corrosion from rust that may mix into the oil.


Table 4: ISO Viscosity Grade of Industrial Lubricant (JIS K 2001)

The correct viscosity is the most important consideration in choosing a proper lubricant. The viscosity grade of industrial lubricant is regulated in JIS K 2001.

ISO

Viscosity Grade

Kinematic Viscosity Center Value

10-6m²/s (cSt) (40ºC)

Kinematic Viscosity Range

10-6m²/s (cSt) (40ºC)

More Than

Less than

ISO VG

2

2.2

1.98

2.42

ISO VG

3

3.2

2.88

3.52

ISO VG

5

4.6

4.14

5.06

ISO VG

7

6.8

6.12

7.48

ISO VG

10

10

9

11.0

ISO VG

15

15

13.5

16.5

ISO VG

22

22

19.8

24.2

ISO VG

32

32

28.8

35.2

ISO VG

46

46

41.4

50.6

ISO VG

68

68

61.2

74.8

ISO VG

100

100

90

110

ISO VG

150

150

135

165

ISO VG

220

220

198

242

ISO VG

320

320

288

352

ISO VG

460

460

414

506

ISO VG

680

680

612

748

ISO VG

1000

1000

900

1100

ISO VG

1500

1500

1350

1650

Table 5: Industrial Gear Oil

Types of Industrial Gear Oil

Usage

Class One

ISO VG  32

ISO VG  46

ISO VG  68

ISO VG   100

ISO VG   150

ISO VG   220

ISO VG   320

ISO VG   460

Mainly used in a general and lightly loaded enclosed gear system

Class Two

ISO VG    68

ISO VG   100

ISO VG   150

ISO VG   220

ISO VG   320

ISO VG   460

ISO VG   680

Mainly used in a general medium to heavily loaded enclosed gear system

Table 6: NLGl Viscosity Grades

NLGI No.

Viscosity Range

State

Application

 

No 000

445...475

Semi-Liquid

For Central Lubrication Systems


No  00

400...430

Semi-Liquid


No   0

335...385

Very Soft Paste

Automotive Chassis


No   1

310...340

Soft Paste

 

No   2

265...295

Medium Firm Paster

Ball and Roller Bearing General Use

 

No   3

220...250

Semi-hard Paste

Automobile Wheel Bearing

No   4

175...205

Hard Paste

Sleeve Bearing (Pillow Block)

No   5

130...165

Very Hard Paste

No   6

85....115

Very Hard Paste


Table 7: AGMA Viscosity Grades

AGMA No. of Gear Oil

ISO Viscosity Grades

R & O Type

EP Type

 1

 2

 3

 4

 5

 6

7 comp

 8 comp

     8A comp

 9

 

2 EP

3 EP

4 EP

5 EP

6 EP

7 EP

8 EP

 

9EP

 VG 46

 VG 68

 VG 100

 VG 150

 VG 220

 VG 320

 VG 460

 VG 680

 VG 1000

 VG 1500

Table 8 Recommended Lubricants by AGMA

It is practical to select a lubricant by following the catalog or technical manual of the manufacture. This table is the application guide from AGMA 250.03 "Lubrication of Industrial Enclosed Gear Drives".

Gear Type

Size of Gear Equipment (mm)

Ambient temperature ºC

-10 ... 16

10 ... 52

AGMA No.

Parallel Shaft System

Single Stage Reduction

Center Distance (Output Side)

Less than 200

200 ... 500

more than 500

2 to 3

2 to 3

3 to 4

3 to 4

4 to 5

4 to 5

Double Stage Reduction

Less than 200

200 ... 500

More than 500

2 to 3

3 to 4

3 to 4

3 to 4

4 to 5

4 to 5

Triple Stage Reduction

Less than 200

200 ... 500

More than 500

2 to 3

3 to 4

4 to 5

3 to 4

4 to 5

5 to 6

Planetary Gear System

Outside Diameter of Gear Casing

Less than 400

More than 400

2 to 3

3 to 4

3 to 4

4 to 5

Straight and Spiral Bevel Gearing

Cone Distance

Less than 300

More than 300

2 to 3

3 to 4

4 to 5

5 to 6

Gear-motor

2 to 3

4 to 5

High Speed Gear Equipment

1

2

Table 9 Recommended Lubricants for Worm Gears by AGMA

Types of Worm

Center Distance mm

Rotating Speed of Worm rpm

Ambient Temperature, ºC

Rotating Speed of Worm rpm

Ambient Temperature, ºC

-10 ... 6

10 ... 52

-10 ... 16

10 ... 52

Cylindrical Type

<150

150 ... 300

300 ... 460

460 ... 600

600<

700<

450<

300<

250<

200<

7 Comp

8 Comp

700<

450<

300<

250<

200<

 

8 Comp

7 Comp


Throated Type

<150

150 ... 300

300 ... 460

460 ... 600

600<

700<

450<

300<

250<

200<

8 Comp

8A Comp

700<

450<

300<

250<

200<

8 Comp



Quick, subjective but important tests of the lubricant

There are several simple tests that can be performed on-site and at low cost to check for contamination or oxidation of the lubricant. The tests should be performed by the same person each time, because the tests require experience to accurately judge the results.

The tests can be run as often as necessary, but they should be done every time samples are taken for laboratory analysis.

Appearance Test: The simplest test is visual appearance. Often, this test will disclose problems such as gross contamination or oxidation. Look at the lubricant in a clean, glass bottle. A narrow, tall vessel is best. Compare the sample with a sample of new, unused lubricant. The oil should look clear and bright. If the sample looks hazy and cloudy, or has a milky appearance, there may be water present. The color should be similar to that of the new oil sample. A darkened color may indicate oxidation or contamination with fme wear particles. Tilt the bottle and observe whether the used oil appears more or less viscous than the new oil. A change in viscosity may indicate oxidation or contamination. Look for sediment at the bottom of the bottle. If any is present, .run the sedimentation test.

Sniff Test: Carefully sniff the oil sample. Compare the smell of the used oil sample with that of new oil.b, The used oil should smell the same as new oil; that is, it should have a bland, oily odor. Oils that have oxidized have a "burnt" odor, or smell acrid, sour, or pungent.

Sedimentation Test: If any sediment is visible during the appearance test, a simple test for contamination can be performed on site as follows: place a sample of oil in a clean, white, plastic cup and allow it to stand for 2 days. Carefully pour off all but a few milliliters of oil. If any particles are visible at the bottom of the cup, contaminants are present.

Resolution of the unaided eye is about 40μm. If particles respond to a magnet under the cup, iron or magnetite wear fragments are present; if they don't respond to the magnet, and the solids feel gritty between the fingers, they are probably sand. If another liquid phase is visible, or the oil appears milky, water is probably present.

Crackle Test: If you suspect there may be water present in an oil sample, you should perform a simple test for water contamination that can be performed on site as follows: drop a small drop of oil onto a hot plate at 135°C (275°F). If the sample bubbles, water is above 0.05%. If the sample bubbles and crackles, water is above 0.1 %

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