Grease & Bearings

8/3/2019 Grease & Bearings

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WORLDPUMPS November 2009Feature363636

www.worldpumps.com 0262 1762/09 2009 Elsevier Ltd. All rights reserved

Hydraulic drives and pumps are

hard at work in almost every

conceivable area o manuacturing,

oten in the most critical, demanding

applications, rom the oil and gas industry,

chemicals and pharmaceuticals, through

to water, sewerage, metals processing,

ood and beverage.

The components inside these hydraulic

drives and pumps need to be reliable,

energy ecient and able to withstand

oten very harsh operating environments.

A gear pump, or example, is used in

almost all industrial sectors, supplying

coolants and oodstufs or keeping

hydraulic systems in motion. They

are also ound in municipal vehicles,

mobile hydraulic equipment and

agricultural machinery.

Good plain bearings or high quality needleroller bearings help to ensure that the

gears perorm with almost zero losses.

The supply medium is oten used as the

lubricant or the bearings. For the supply

o uids with low lubrication characteris-

tics, needle roller bearings are increasingly

used rather than plain bearings in order

to maximise the lie o the gear pump. In

addition, higher speeds can be achieved i

less heat is generated rom the bearings.

Hydrostatic gearboxes transer continu-

ously variable driving orce in quad

bikes, sit-on lawnmowers, tractors and

of-road vehicles. As well as rolling bear-

ings and plain bearings, Schaeer ofers

its INA-branded precision parts, including

deep drawn hollow pistons, valves and

ne blanked components.

Dr Steve Lacey, engineering manager,

Schaeer UK said: The pump speed

and load oten determine whether ball

bearings, cylindrical roller bearings, radialspherical roller bearings or plain bearings

are selected or the application.

High torque motors are oten specied

or applications in which abrupt stops or

reverse motion occur, including agricul-

tural machinery, crushers, eed devices,

rolling mills, paper mills and bulk handling

machines. High torque motors are used

rather than conventional gearbox and

motors where there are extremely high

torques present (as high as 1,400,000 Nm)

and harsh operating conditions. As Dr

Lacey explains: High torque motors

typically ofer low start-up riction and

stick-slip ree motion at low speeds.

Ready-to-mount unctional units, bent

axis motors are used in hydraulic systems

to generate pressure. The stroke motion

o the axially oscillating pistons is gener-

ated by the main output axis, which is

bent towards the rotor axis.

We manuacture geometrically accu-

rate steel seals with split butt joints or

Lubricants and bearings

Hydraulic drives and pumps require precision bearings and seals

that are reliable, but more than 40% of all premature failures of

rolling bearings are caused by inadequate or incorrect selection

of lubricant. Choosing the most appropriate bearings, grease and

re-lubrication equipment for any application is vital.

Correct bearing andgrease selection

Figure 1. A barrel-type pump for power generation (photograph courtesy of KSB Frankenthal).


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WORLDPUMPS November 2009 Feature 37

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designs with either centred or eccentric

crowned outer diameters, as well as for other

contours, states Dr Lacey. Our product

range also includes high precision control

discs and other ne blanked parts with

consistently accurate contours and smooth,

perpendicular cut surfaces that can also be

made from metal composites.

Schaeers INA-branded DRG steel seals are

characterised by their low press-on force,

minimal leakage, low wear, high resist-

ance to abrasion, and their resistance to oil

and temperature.

Grease selection

More than 80% of all rolling bearings are

lubricated with grease. It is therefore critical

that engineers select the most appropriate

grease for the bearing and the application

it is operating in. Not only will correct selec-

Special lubricants

Schaeer works closely with lubricant

manufacturers to develop special greases

that are suitable for rolling bearings.

The Arcanol range of greases

includes 15 rolling bearing greases,

each graduated to cover all

application areas.

Multitop is a universal grease for

ball and rolling bearings that is

suitable for use in construction

machinery, automotive engineering,

rolling mills and grinding machine

spindles.

VIB3 is a mineral-based grease with

a polycarbamide thickener, suitable

for use in blade adjusters in rotors

for wind turbines, packaging

machinery and rail vehicles. The

grease is designed to resist high

temperatures, high loads and

oscillating motion.

Multi3 is formulated grease for

large electric motors, agricultural

machinery and fans. Food2 is a

white, oil-based grease for use with

ball and roller bearings in

applications where contact with

food occurs.

Figure 2. The cam curves of

a typical high torque motor.

The pump speed and load

often determine whether ball

bearings, cylindrical roller

bearings, radial spherical

roller bearings or plain

bearings are selected forthe application.


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WORLDPUMPS November 2009Feature383838

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tion prolong the lie o the bearing, enabling

it to operate at its ull capacity, but it also

ensures smoother running behaviour and

improved operational saety.

But selecting a suitable lubricant or a rolling

bearing can be a complex process. Grease is

basically a type o oil with a thickening agent

added to it, giving it a more viscous orm.

There are many diferent types o bearing

grease available, so engineers should take

the time to make more inormed selections

that ensure a long and trouble-ree lie orthe bearing.

Greases can be used efectively to lubricate

bearings over a very wide range o oper-

ating conditions. However, initial selection is

based on two critical parameters.

First, the P/C ratio, which is a measure o

the load P on the bearing in relation to

the dynamic capacity C, which is calculated

according to international standards and

quoted by all leading bearing manuacturers

in their technical literature. In general, i the

P/C ratio is greater than 0.15, the bearing

is regarded as heavily loaded, and speciallubricants with extreme pressure addi-

tives will be required to increase the load

carrying capacity o the bearing and to

prevent metal-to-metal contact, which leads

to high wear and premature bearing ailure.

Generally, a P/C o less than 0.15 or radially

loaded bearings using standard lithium soap

greases (normal operating conditions) is

400,000 min-1.mm.

It is also important to keep the P/C ratio

above 0.02, as in general, below this value,

the bearing will skid rather than roll, again

resulting in possible premature bearingailure due to high wear and an increase in

riction. To avoid slippage with caged ball

bearings, engineers should work on a P/C o

0.01 and or caged roller bearings, a P/C o

0.02 is advised.

Second, the ndm value which is calculated

rom the speed o the bearing n in rpm and

the bearing mean diameter dm in mm will

give an indication o the relative speed o

rotation to the physical size o the bearing. In

general i the ndm value is below 400,000

then standard general purpose bearing

greases can be efectively used to lubricate

the bearing. For ndm values in excess o

this, special greases are required, which have

relatively low base oil viscosities, in order to

reduce the amount o heat generated bythe bearing when rotating at higher speeds.

It is quite possible, with recent developments

in both bearings and grease lubricants, to

achieve ndm values o up to 2,000,000.

Whilst grease lubrication is inherently simple,

there are many bearing applications where

oil is the only choice available, since it has

the key attribute o being able to remove

the heat generated in the bearing due to

load and speed. It is quite possible that

ndm values up to 4,000,000 are achievable

or oil jet lubrication.

In harsh operating conditions or aggressiveenvironments, rolling bearings should be

re-lubricated requently via lubrication nipples.

While, Schaefer has its own product range

or this (see box), FAG metering devices are

also provided, enabling customers to supply

grease to rolling bearings in metered quanti-

ties, rom 10 cm3 up to 133 cm3. By using

a pneumatically driven, double-direction

piston pump, the lubricant is transerred rom

the grease drum (25 kg or 180 kg) via the

metering valve to the point o application.

Contactwww.schaeer.co.uk

Figure 5. Ready-to-mount functional units, bent axis motors are used i n

hydraulic systems to generate pressure.

Controlled re-lubrication

Controlled re-lubrication o bearings is

oten required in order to extend service

and maintenance intervals and minimiseplant downtime. Schaer ofers three

main products or this:

Motion Guard Compact is a single

point electro-chemical lubrication

system that comprises a housing

lled with 120 cm3 o grease,

controlled via an activation screw.

Motion Guard Champion is a single

point, battery-operated lubricator

that comprises either a 120 cm3 or

250 cm3 volume o grease, with drive

unit and adaptor.

Motion Guard Concept6 is an

electromechanical single pointlubrication system that can be

expanded to include up to six

lubrication points.

Figure 4. Motion Guard Concept 6 is an electromechanical

single point lubrication system that can be expanded to

include up to six lubrication points.

Figure 3. A typical gear pump. Good plain bearings or highquality needle roller bearings help to ensure that the gears

perform with almost zero losses.

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Grease & Bearings