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Appraisal of the ISO classification of lubricants for machine tools
Appraisal of the ISO classification of lubricants for machine tools M. Radhakrishnan*
The current ISO standard on machine tool lubricants stipulates thirty three 'rationalised' lubricants, effectively defeating the very purpose of variety reduction and providing cause for confusion in lubrication management. This paper points out that many lubricants specified in ISO classifications are either redundant or unrelated to common machine tool practice. An alternate proposal, modified by CMTI, with a reduced number of lubricants is given Keywords: Lubricating oils, grease, International standard, classification systems Growing global trade has underlined the importance of International Standards to promote interchangeability and to ease communication between equipment builder, seller and buyer. Faced with hundreds of major lubricant manufacturers and thousands of brand names for a wide range of lubricants, machine tool builders and users had to grapple unaided with the problems of the correct choice of lubricants for many years. It was appropriate, therefore, that ISO gave the classification of machine tool lubricants a high priority. The earliest standard on machine tool lubricants was prepared by ASLE 1 but was not sufficiently comprehensive. Next came the British Standard 2 BS 5063:74 and in 1974 ISO took up the classification of machine tool lubricants. The final ISO classification has now been released a . To a great extent it does not fulfil the expectations. The standard stipulates thirty three varieties of rationalised lubricants which defeats one of the purposes of standardisation, namely variety reduction. This paper suggests that many of the lubricants specified in the ISO standard are either redundant or not in line with the common machine tool application.
Objective of the standard The 1SO standard describes its scope and field of application as: • to establish a rationalised range of internationally available lubricants from which machine tool manufacturers should make recommendations. • to avoid unnecessary restrictions on specifications or product descrip**Central Machine Tool Institute, Tumkur Road, Bangalore - 560 022, India
TRIBOLOGY international
tions which would inhibit future development. It is also mentioned that 'special' requirements are not covered in the standard. The cruxofthe problem is the dividing line between "rationalisation" and "unnecessary restriction". There is no yardstick to measure the correct level of rationalisation. Nevertheless, by any standard of measurement ISO's rationalised classification of thirty three lubricants is not in line with the basic objective of standardisation (see Table 1 (overleaf)).
Discussion The information required by the designer to achieve the desired performance, namely the type and viscosity of the lubricant, are very well covered in the standard. But the standard does not fulfil the requirement of plant engineers to facilitate easy lubrication management. Let us consider each type of lubricant and the various grades of lubricants given in the standard for their applicability.
Gear oils The load and speed encountered in machine too! gears are generally light to moderate, unlike many other indus.trial gears. Thus the hydraulic oils used in machine tools are generally adequate for lubrication of the gears, except perhaps for worm gears where there might be a requirement for a gear oil with mild ep properties. Even here, Summers-Smith s disputes the advantage of mild ep oils over straight mineral oils for worm gear lubrication. Under the circumstances it is not justifiable to have two classes of gear oils (CB and CC). This means that the three grades of CB class gear oils become redundant.
Spindle oils
Spindle bearingsare at the most only moderately loaded and the prime purpose of the spindle oil is heat removal. Hence the requirement for antiwear performance in spindle oils is questionable and, therefore, spindle oil FD class is unnecessary. Past experience suggests that VG22 grade (ISO Viscosity Grade) oil for spindle lubrication is not necessary; it is more common to find spindle bearings lubricated with VG32 grade oil. However, it is admitted that inclusion of VG22 oil could be a matter of opinion. Slideways
There is no need for G32 and G68 oils since these two grades are covered in hydraulic-cum-slideway oils (HG32 & HG68). Hence G32 and G68 oils are redundant.
Hydraulic system This writer is yet to come across the usage of HV class and VG15 grade oil in machine tool hydraulic system. Even taking for granted that it is being used, it can come only under the category of "special requirement" and therefore these oils can be deleted in the standard. In fact two classes of hydraulic oils (HM and HL) could be merged into one but for the reactive nature of ZDDP additive present in the HM class oil s . If all the lubricant manufacturers agreed to include in their range an ashless type hydraulic oil6,7 which would be non reactive and offer better performance than the zinc based oil, HL class hydraulic oil could be deleted.
Greases NLGI Grade I grease is generally used only in centralised grease lubrication systems which are not common in machine tools, except in transfer lines. Since Grades 2 and 3 greases are used in most applications, XM 1 grease could well be dispensed with. CMTI proposal Based on the points raised above Central Machine Tool Institute (CMTI) has modified the ISO classification as
0301-679X/83/020109-04 $03.00© 1983 Butterworth & Co (Publishers)Ltd
109
t~3
Z o
< o
2
~>
(3
Gears
Spindles, bearings and associated clutches
C
F
Slideways
Total loss systems
A
G
Subdivision in families according to application fields
First code letter
Enclosed gears
Subdivision in categories accordingto particular application fields
Refined mineral oils with very good anti-corrosion and antioxidation properties
Spindles, bearings and associated clutches Refined mineral oils with good lubricity and tackiness properties preventing stick-slip
Refined mineral oils with very good anti-oxidation, anticorrosion and anti-wear properties
Refined oils with good antioxidation properties (straight or inhibited mineral oils) and with good load carrying ability
Heavily .loaded gears
Spindles and bearings
Refined mineral oils with good anti oxidation properties (straight or inhibited)
Refined mineral oils
Subdivision in categories according to particular properties
Moderately loaded gears
More particular subdivision
Table 1. Clmification of lubricants for machine tools ISO 3498-1979(E)
G 32 G88 G 150 G 220
FC2 FC 10 FC 22
FD2 FD5 FD 10 FD 22
CC 150 CC 320 CC 460
CB 32 CB 68 CB 150
AN 68
Symbol and viscosity grade ISO.L
Lubrication of plain bearing slideways. They should be particularly useful at low traverse speeds to minimise discontinuous or intermittent sliding of the table (stick-slip)
Pressure, bath and oil mist (aerosol) lubrication of plain or rolling bearings and associated clutches
Pressure, bath and oil mist (aerosol) lubrication of plain or rolling bearings
Pressure and bath lubrication of enclosed gears of any type (except hypoid gears) and allied bearings when loads are high, provided that the operating temperature is not above 70°C
Pressure, bath and oil mist (aerosol) lubrication of enclosed gears and allied bearings of headstocks, feed-boxes, carriages, etc., when loads are moderate
Total loss general lubrication of lightly loaded parts
Detailed application
They can be used for the lubrication of all sliding parts such as lead and feed screws, cams, ratchets and lightly loaded worm gears with intermittent service
They are required for lubrication of systems including clutches which involve the use of oils which do not contain anti-wear additives
They can also be used for applications requiring particularly low viscosity oils, such as fine mechanisms, hydraulic or hydro-pneumatic mechanisms, electromagnetic clutches, air-line lubricators and hydrostatic bearings
They can also be used for manual or centralised lubricat.ion of lead and feed screws and highly loaded slideways
CB 32 and CB 68 can also be used for flood lubricated, mechanically controlled clutches. CB 68 may replace AN 68.
Remarks
3.
E-
3
I
(3
=o
0
O r" 0 .<
X
Applications requiring grease
Table I ( c o n t i n u e d ) H Hydraulic systems
~=
=
E
.~"
..~
i-i p~
=
~ . ~
XM 1 XM 2 XM 3
Greases with very good antioxidation and anti-corrosion properties
Multipurpose greases
~=,
HG 32 HG 68
Refined mineral oils of HM type with anti-stick-slip properties
Hydraulic and slideways systems
.
HV 32 HV 46
Refined mineral oils with good viscosity/temperature properties
~.
HM HM HM HM
Refined mineral oils with very good anti-corrosion, antioxidation and anti-wear properties
. . . . .
~.{,,,'~'
15 32 46 68
HL 15 HL 32 H L 46 HL 68
Refined mineral oils with very good anti-corrosion and antioxidation properties
Hydrostatic systems
=-=~
~
o o-
~
=. ,..o=
,_+~
E (~
= ~ = ,
=.~
o_*
(~
~
'
= .= E?= = ~ "
=.~
= ~-~*
Grease XM 1 is used in centralised systems while greases XM 2 and XM 3 are dispensed preferably by cup or hand gun. The equipment manufacturer should identify the grease used for the initial filling of each item to ensure that the grease subsequently introduced is compatible with it
Plain rolling bearings, open gears and general greasing of miscellaneous parts
~ ~ ~ = =-~
They can also be used for lubrication of separate slideways, when an oil of this viscosity is required HG 32 and HG 68 may replace respectively G 32 and G 68
Specific application to machines with combined hydraulic and plain bearing slideways lubrication systems where discontinuous or intermittent sliding (stick-slip) at low speed is to be minimised
= ~=
In some cases, HV oils may replace HM oils
They are also suitable for the lubrication of plain or rolling bearings, and all types of gears normally loaded (worm and hypoid gears excepted) HM 32 and HL 32, HM 68 and HL 68 may replace respectively CB 32 and CB 68
Application in computers
Operation of general hydraulic systems which include highly loaded components
Operation of general hydraulic systems. Lubrication of plain or anti-friction bearings and gears (hypoid types excepted)
=.
~"
Radhakrishnan/Cookson - Machine tool lubricants
Table 2 Modified CMTI propo=al Code
Type of Lubricant
Code & Viscosity Grade*
Application
P
Highly refined plain mineral oil
P 68
Normally used for total loss general lubrication of lightly loaded parts which do not call for any special requirements. Also used for bath lubrication of lightly loaded spur and helical gears, plain and rolling bearings
Highly refined oil with superior anticorrosion anti-oxidation properties
S2 S 10
Pressure, bath and mist lubrication of fluid film and rolling bearings used in spindles. Also used for lubrication of clutches, hydro-pneumatic mechanisms, etc
H
Highly refined mineral oil with anti-rust, anti-foam anti-oxidation properties with high viscosity index
H 32 H 46 H 68
Generally used as hydraulic fluid. Can also be used for pressure and bath lubrication of gears, rolling and plain bearings and slide-ways
HA
S~me as class H oil but with anti-wear performance
HA 32 HA 46 HA 68
For hydraulic systems. Preferred oils for high pressure systems and vane pump application
G
Highly refined mineral oil with improved load carrying capacity (with mild ep property)
G 150 G 320 G 460
Pressure and bath lubrication of heavily loaded gears and worm gears. Can also be used for lead screws and heavily loaded slideways
W
Mineral oil with improved boundary lubricating property to prevent stick-slip
W 100 W 220
For plain guideways. Also suitable for lead screws and heavily loaded worm gears. For lower viscosity requirements use HW oils
HW
Same as class H oil but high boundary lubricating property to prevent stick-slip
HW 32 HW 68
For combined hydraulic and slideway system. Can also be used for slideways only. Normally the bulk temperature of the oil is limited to 50°C, unlike H or HA oils
Gr
Multipurpose premium quality grease with anti-oxidation and anti-corrosion properties
Gr.2 Gr.3
For bearings and general greasing of miscellaneous parts. Gr.2 preferable for horizontal and high speed application. Gr.3 preferable for vertical and pre-packed applications
*I.
Viscosity grade corresponds to midpoint.value o f kinematic viscosity in cSt, at 40 ° C as p e r / S O with a tolerance o f ± 10%.
2. Gr.2 and Gr.3 grease refer to N L G I consistency numbers 2 & 3 respectively. 3. The classification does n o t cover the lubrication o f h y p o i d gears.
112
April 1983 Vol 16 No 2
The current ISO standard on machine tool lubricants stipulates thirty three 'rationalised' lubricants, effectively defeating the very purpose of variety reduction and providing cause for confusion in lubrication management. This paper points out that many lubricants specified in ISO classifications are either redundant or unrelated to common machine tool practice. An alternate proposal, modified by CMTI, with a reduced number of lubricants is given Keywords: Lubricating oils, grease, International standard, classification systems Growing global trade has underlined the importance of International Standards to promote interchangeability and to ease communication between equipment builder, seller and buyer. Faced with hundreds of major lubricant manufacturers and thousands of brand names for a wide range of lubricants, machine tool builders and users had to grapple unaided with the problems of the correct choice of lubricants for many years. It was appropriate, therefore, that ISO gave the classification of machine tool lubricants a high priority. The earliest standard on machine tool lubricants was prepared by ASLE 1 but was not sufficiently comprehensive. Next came the British Standard 2 BS 5063:74 and in 1974 ISO took up the classification of machine tool lubricants. The final ISO classification has now been released a . To a great extent it does not fulfil the expectations. The standard stipulates thirty three varieties of rationalised lubricants which defeats one of the purposes of standardisation, namely variety reduction. This paper suggests that many of the lubricants specified in the ISO standard are either redundant or not in line with the common machine tool application.
Objective of the standard The 1SO standard describes its scope and field of application as: • to establish a rationalised range of internationally available lubricants from which machine tool manufacturers should make recommendations. • to avoid unnecessary restrictions on specifications or product descrip**Central Machine Tool Institute, Tumkur Road, Bangalore - 560 022, India
TRIBOLOGY international
tions which would inhibit future development. It is also mentioned that 'special' requirements are not covered in the standard. The cruxofthe problem is the dividing line between "rationalisation" and "unnecessary restriction". There is no yardstick to measure the correct level of rationalisation. Nevertheless, by any standard of measurement ISO's rationalised classification of thirty three lubricants is not in line with the basic objective of standardisation (see Table 1 (overleaf)).
Discussion The information required by the designer to achieve the desired performance, namely the type and viscosity of the lubricant, are very well covered in the standard. But the standard does not fulfil the requirement of plant engineers to facilitate easy lubrication management. Let us consider each type of lubricant and the various grades of lubricants given in the standard for their applicability.
Gear oils The load and speed encountered in machine too! gears are generally light to moderate, unlike many other indus.trial gears. Thus the hydraulic oils used in machine tools are generally adequate for lubrication of the gears, except perhaps for worm gears where there might be a requirement for a gear oil with mild ep properties. Even here, Summers-Smith s disputes the advantage of mild ep oils over straight mineral oils for worm gear lubrication. Under the circumstances it is not justifiable to have two classes of gear oils (CB and CC). This means that the three grades of CB class gear oils become redundant.
Spindle oils
Spindle bearingsare at the most only moderately loaded and the prime purpose of the spindle oil is heat removal. Hence the requirement for antiwear performance in spindle oils is questionable and, therefore, spindle oil FD class is unnecessary. Past experience suggests that VG22 grade (ISO Viscosity Grade) oil for spindle lubrication is not necessary; it is more common to find spindle bearings lubricated with VG32 grade oil. However, it is admitted that inclusion of VG22 oil could be a matter of opinion. Slideways
There is no need for G32 and G68 oils since these two grades are covered in hydraulic-cum-slideway oils (HG32 & HG68). Hence G32 and G68 oils are redundant.
Hydraulic system This writer is yet to come across the usage of HV class and VG15 grade oil in machine tool hydraulic system. Even taking for granted that it is being used, it can come only under the category of "special requirement" and therefore these oils can be deleted in the standard. In fact two classes of hydraulic oils (HM and HL) could be merged into one but for the reactive nature of ZDDP additive present in the HM class oil s . If all the lubricant manufacturers agreed to include in their range an ashless type hydraulic oil6,7 which would be non reactive and offer better performance than the zinc based oil, HL class hydraulic oil could be deleted.
Greases NLGI Grade I grease is generally used only in centralised grease lubrication systems which are not common in machine tools, except in transfer lines. Since Grades 2 and 3 greases are used in most applications, XM 1 grease could well be dispensed with. CMTI proposal Based on the points raised above Central Machine Tool Institute (CMTI) has modified the ISO classification as
0301-679X/83/020109-04 $03.00© 1983 Butterworth & Co (Publishers)Ltd
109
t~3
Z o
< o
2
~>
(3
Gears
Spindles, bearings and associated clutches
C
F
Slideways
Total loss systems
A
G
Subdivision in families according to application fields
First code letter
Enclosed gears
Subdivision in categories accordingto particular application fields
Refined mineral oils with very good anti-corrosion and antioxidation properties
Spindles, bearings and associated clutches Refined mineral oils with good lubricity and tackiness properties preventing stick-slip
Refined mineral oils with very good anti-oxidation, anticorrosion and anti-wear properties
Refined oils with good antioxidation properties (straight or inhibited mineral oils) and with good load carrying ability
Heavily .loaded gears
Spindles and bearings
Refined mineral oils with good anti oxidation properties (straight or inhibited)
Refined mineral oils
Subdivision in categories according to particular properties
Moderately loaded gears
More particular subdivision
Table 1. Clmification of lubricants for machine tools ISO 3498-1979(E)
G 32 G88 G 150 G 220
FC2 FC 10 FC 22
FD2 FD5 FD 10 FD 22
CC 150 CC 320 CC 460
CB 32 CB 68 CB 150
AN 68
Symbol and viscosity grade ISO.L
Lubrication of plain bearing slideways. They should be particularly useful at low traverse speeds to minimise discontinuous or intermittent sliding of the table (stick-slip)
Pressure, bath and oil mist (aerosol) lubrication of plain or rolling bearings and associated clutches
Pressure, bath and oil mist (aerosol) lubrication of plain or rolling bearings
Pressure and bath lubrication of enclosed gears of any type (except hypoid gears) and allied bearings when loads are high, provided that the operating temperature is not above 70°C
Pressure, bath and oil mist (aerosol) lubrication of enclosed gears and allied bearings of headstocks, feed-boxes, carriages, etc., when loads are moderate
Total loss general lubrication of lightly loaded parts
Detailed application
They can be used for the lubrication of all sliding parts such as lead and feed screws, cams, ratchets and lightly loaded worm gears with intermittent service
They are required for lubrication of systems including clutches which involve the use of oils which do not contain anti-wear additives
They can also be used for applications requiring particularly low viscosity oils, such as fine mechanisms, hydraulic or hydro-pneumatic mechanisms, electromagnetic clutches, air-line lubricators and hydrostatic bearings
They can also be used for manual or centralised lubricat.ion of lead and feed screws and highly loaded slideways
CB 32 and CB 68 can also be used for flood lubricated, mechanically controlled clutches. CB 68 may replace AN 68.
Remarks
3.
E-
3
I
(3
=o
0
O r" 0 .<
X
Applications requiring grease
Table I ( c o n t i n u e d ) H Hydraulic systems
~=
=
E
.~"
..~
i-i p~
=
~ . ~
XM 1 XM 2 XM 3
Greases with very good antioxidation and anti-corrosion properties
Multipurpose greases
~=,
HG 32 HG 68
Refined mineral oils of HM type with anti-stick-slip properties
Hydraulic and slideways systems
.
HV 32 HV 46
Refined mineral oils with good viscosity/temperature properties
~.
HM HM HM HM
Refined mineral oils with very good anti-corrosion, antioxidation and anti-wear properties
. . . . .
~.{,,,'~'
15 32 46 68
HL 15 HL 32 H L 46 HL 68
Refined mineral oils with very good anti-corrosion and antioxidation properties
Hydrostatic systems
=-=~
~
o o-
~
=. ,..o=
,_+~
E (~
= ~ = ,
=.~
o_*
(~
~
'
= .= E?= = ~ "
=.~
= ~-~*
Grease XM 1 is used in centralised systems while greases XM 2 and XM 3 are dispensed preferably by cup or hand gun. The equipment manufacturer should identify the grease used for the initial filling of each item to ensure that the grease subsequently introduced is compatible with it
Plain rolling bearings, open gears and general greasing of miscellaneous parts
~ ~ ~ = =-~
They can also be used for lubrication of separate slideways, when an oil of this viscosity is required HG 32 and HG 68 may replace respectively G 32 and G 68
Specific application to machines with combined hydraulic and plain bearing slideways lubrication systems where discontinuous or intermittent sliding (stick-slip) at low speed is to be minimised
= ~=
In some cases, HV oils may replace HM oils
They are also suitable for the lubrication of plain or rolling bearings, and all types of gears normally loaded (worm and hypoid gears excepted) HM 32 and HL 32, HM 68 and HL 68 may replace respectively CB 32 and CB 68
Application in computers
Operation of general hydraulic systems which include highly loaded components
Operation of general hydraulic systems. Lubrication of plain or anti-friction bearings and gears (hypoid types excepted)
=.
~"
Radhakrishnan/Cookson - Machine tool lubricants
Table 2 Modified CMTI propo=al Code
Type of Lubricant
Code & Viscosity Grade*
Application
P
Highly refined plain mineral oil
P 68
Normally used for total loss general lubrication of lightly loaded parts which do not call for any special requirements. Also used for bath lubrication of lightly loaded spur and helical gears, plain and rolling bearings
Highly refined oil with superior anticorrosion anti-oxidation properties
S2 S 10
Pressure, bath and mist lubrication of fluid film and rolling bearings used in spindles. Also used for lubrication of clutches, hydro-pneumatic mechanisms, etc
H
Highly refined mineral oil with anti-rust, anti-foam anti-oxidation properties with high viscosity index
H 32 H 46 H 68
Generally used as hydraulic fluid. Can also be used for pressure and bath lubrication of gears, rolling and plain bearings and slide-ways
HA
S~me as class H oil but with anti-wear performance
HA 32 HA 46 HA 68
For hydraulic systems. Preferred oils for high pressure systems and vane pump application
G
Highly refined mineral oil with improved load carrying capacity (with mild ep property)
G 150 G 320 G 460
Pressure and bath lubrication of heavily loaded gears and worm gears. Can also be used for lead screws and heavily loaded slideways
W
Mineral oil with improved boundary lubricating property to prevent stick-slip
W 100 W 220
For plain guideways. Also suitable for lead screws and heavily loaded worm gears. For lower viscosity requirements use HW oils
HW
Same as class H oil but high boundary lubricating property to prevent stick-slip
HW 32 HW 68
For combined hydraulic and slideway system. Can also be used for slideways only. Normally the bulk temperature of the oil is limited to 50°C, unlike H or HA oils
Gr
Multipurpose premium quality grease with anti-oxidation and anti-corrosion properties
Gr.2 Gr.3
For bearings and general greasing of miscellaneous parts. Gr.2 preferable for horizontal and high speed application. Gr.3 preferable for vertical and pre-packed applications
*I.
Viscosity grade corresponds to midpoint.value o f kinematic viscosity in cSt, at 40 ° C as p e r / S O with a tolerance o f ± 10%.
2. Gr.2 and Gr.3 grease refer to N L G I consistency numbers 2 & 3 respectively. 3. The classification does n o t cover the lubrication o f h y p o i d gears.
112
April 1983 Vol 16 No 2