Machinery Lubrication July August 2008

CONTAMINATION CONTROL
Copper Passivators
Copper (metal) passivators employ chemical treatment to
make the surface of metals less reactive or inactive to chemical
attacks. These compounds passify, prevent or counteract
catalytic effect of metals on oxidation. Typical passivators are
organic nitrogen- and sulfur-containing compounds such as
certain amines and sulfides.
Emulsifiers
Emulsifiers promote the emulsification of the free water.
Specifically, these are surface-active agents that reduce interfacial
tensions so oil can be finely dispersed in water.
Examples include soaps of fats and fatty acids, sulfonic acids
and naphthenic acids.
R&O oils are necessary for use in circulating oil systems.
Besides the necessity to lubricate roll necks, journals and
roller bearings, effective R&O oils also act to lubricate other
equipment such as drain pipes, bearing housings and reservoir
ceilings. Many major steel equipment manufacturers
(Morgan Construction, Danieli) and bearing manufacturers
(SKF, FAG) have established specifications and guidelines for
lubricant selection and performance.
The standard MORGOIL specification (for a new oil) by
Morgan Construction is an example of this. In recent years,
many specifications have been refined to differentiate lubricants,
particularly regarding their abilities to separate out
water quickly and efficiently under various conditions.
In the 1990s, Morgan Construction Company spearheaded
an industry-wide initiative for improved lubricant
performance in rolling mill bearings. The idea behind the
MORGOIL advanced lubricant standard was to establish
new specifications for oils that would shed water at normal
operating tank temperatures (for example, 125 to 130°F)
and retain the ability to shed water in service. This new specification
allows for the identification of better lubricants for
steel mill applications that are particularly prone to high
water ingress.
To differentiate the more stringent requirements of this
specification from the previous standard MORGOIL requirements,
lubricants meeting the criteria established by the
Advanced Lubricant Specification were dubbed “super
demulsibility” oils. The term super demulsibility describes
lubricants that efficiently separate from water at normal
operating temperatures upon return from the bearings (typically
125 to 130°F). In other words, these kinds of lubricants
have outstanding demulsibility characteristics.
Shell Morlina Oils are an example of an oil meeting the standard
MORGOIL specification. Shell Morlina SD (or super
demulsibility) oils meet the criteria established by the MORGOIL
Advanced Lubricant New Oil Specification. Shell Morlina T oils
are used in higher-speed mill roller bearings, especially in mills
that produce long bars and rods that should not undergo any
twisting in the finishing process. These are all heavy-viscosity
products, measuring 100 centistokes or greater.
Minimize the Effects of Water
Although the presence of water in steel mill operations is
both essential and unavoidable, there are many things the
operator can do to minimize its effect on the performance of
the lubricants. Perhaps the simplest means is allowing the
free water to settle out of the containment tank that holds
the circulating oil. The free water may then be drained out of
the bottom of the tank.
Heating the tank will certainly accelerate the settling out of
water, but the operator must be careful not to overheat the
oil, which could induce premature oxidation. If the plant
logistics allow it, a two-tank system may be used to get the
most life out of the lubricants. When one oil tank becomes
too saturated with water, the operator switches over to the
other oil tank and drains the water from the initial tank. The
process is repeated as needed.
Plant maintenance personnel may benefit from the use of
drop legs along the oil return lines to the tanks. As the tanks
supply circulating oil to the bearings in the mill and receive
the used lubricant back through return lines, many return
lines contain sections of pipe protruding from them called
drop legs. These drop legs accumulate water and oil as the
water ingresses (enters) at each roll bearing and can be
viewed to assess the condition of the lubricant.
As a rule of thumb, the maintenance department will not
typically allow more than two percent water in the lubrication
system at any time. It is common to use a simple
instrument such as the HydroScout test kit to quickly determine
water content at a sampling point (drop leg).
The HydroScout is a portable field test that quantifies
water concentration in oil in a variety of ranges and produces
instantaneous results of water content in the oil. Data generated
from the HydroScout, tank temperatures, tank levels,
system pressures and other parameters may be recorded
several times each week to ensure that the systems are
running efficiently and that the oil is performing as expected.
Methods such as these allow for instantaneous estimation of
the state of the lubricant and allow the operator to make
recommendations on switching tanks or increasing tank
temperatures immediately.
Processes such as centrifugation and the application of a
vacuum dehydrator are also useful to remove water from oil.
30 July - August 2008 machinerylubrication.com Machinery Lubrication