Method and apparatus for lubricating metal strip with an oil-water emulsion

When rolling metal strip, an emulsion of rolling oil and water is applied to opposite surfaces of the strip. A measured flow of rolling oil is introduced into a measured flow of water to cause at least partial mixing and then it is subjected to turbulence to produce emulsion immediately prior to it being applied to the strip.

This invention relates to the cold rolling of metal strip and, in 
particular, to the application of liquid lubricant to the upper and lower 
surfaces of the strip immediately prior to rolling in a rolling mill. 
It is known to spray a mixture of oil and water on to the upper and lower 
surfaces of steel strip just before it enters the gap between a pair of 
rolls to reduce the thickness of the strip. The oil and water mixture, in 
the form of an emulsion, serves to lower the friction between the strip 
surfaces and the surface of the roll barrels. Heretofore it has been the 
practice to supply substantially the same amount of lubricant to each 
surface of the strip at several of the stands in a multistand cold rolling 
mill and also the mixture supplied at each stand has consisted of the same 
proportions of oil and water. It has been found that this is not an 
efficient practice and that both the quantity of emulsion supplied and the 
proportions of water and oil in the emulsion need to be different for 
various rolling conditions. 
It is known from US-A-4315421 for an oil-in-water emulsion to be pumped 
from an emulsion mixing tank to upper and lower manifolds where it is 
sprayed on to opposite surfaces of the strip being rolled. The oil and the 
water are supplied separately to the mixing tank where they are mixed 
together to form the emulsion. 
According to a first aspect of the present invention, in a method of 
lubricating metal strip being rolled in a rolling mill, rolling oil 
flowing at a predetermined rate and water flowing at a predetermined rate 
enter into an emulsifier to be subjected to turbulence to produce an 
emulsion which is applied to the opposite surfaces of the strip prior to 
the strip being rolled; characterised in that the flow of rolling oil is 
introduced into the flow of water to cause at least partial mixing thereof 
prior to the oil and water entering the emulsifier. 
According to a second aspect of the invention, apparatus for lubricating 
metal strip being rolled in a rolling mill comprises means for supplying 
rolling oil flowing at a predetermined rate and water flowing at a 
predetermined rate to an emulsifier where they are emulsified; and spray 
headers for applying the emulsion to the opposite faces of the strip 
immediately prior to the strip being rolled, characterised in the 
provision of means for introducing the flow of rolling oil into the flow 
of water to cause at least partial mixing thereof before entering the 
emulsifier. 
When the mill comprises a multistand cold rolling mill, some or all of the 
stands have provision for supplying an emulsion of rolling oil and water 
to the upper and lower surfaces of the strip material immediately prior to 
it entering the stand and, at each of these stands, the quantity of oil 
and the quantity of water are individually controlled prior to the oil and 
water being mixed together and subsequently applied to the strip material. 
The quantity of oil and the quantity of water may be determined in advance 
of rolling and then these quantities remain fixed during rolling or the 
quantities may be varied during rolling if the rolling parameters, such as 
strip speed and mill load, change during rolling. By varying the ratio of 
water and oil at one or more of the stands of a multistand rolling mill 
the rolling load pattern of the mill can be changed. These changes may be 
brought about manually by a mill operator or they may be under computer 
control. 
As a result of this invention, at each stand where emulsion is supplied, 
the quantity of emulsion supplied to the strip material can be varied to 
give optimum results and, furthermore, the proportions of water and oil 
making up the emulsion can be changed to give the required lubricity. This 
results in satisfactory surface properties of the rolled strip and avoids 
wasting expensive lubricating oil. 
In order that the invention may be more readily understood, it will now be 
described, by way of example only, with reference to the accompanying 
drawings, in which: 
FIG. 1 shows diagrammatically an arrangement for mixing the oil and water 
to form an emulsion which is applied to the strip at one stand of a 
multistand cold rolling mill; and 
FIG. 2 is a cross-section of a mixing tube shown in FIG. 1.

Referring to FIG. 1, a pair of headers 1, 2 are located immediately 
upstream of one of the stands of a cold rolling mill. Each header has a 
plurality of nozzles 3 spaced apart across the length of the mill rolls 
and the nozzles on header 1 direct liquid lubricant on to the upper 
surface of strip material S entering the mill stand and the nozzles on 
header 2 direct the lubricant on to the underside of the strip material. 
The lubricant is an emulsion of neat rolling oil, such as palm oil, and hot 
water. The neat oil is pumped along a line 4 and the rate of flow of the 
oil is controlled by a valve 5. The valve can be adjusted by a controller 
6 to vary the flow rate to required values. The flow rate is measured by a 
flowmeter 7. A valve 8A serves to divert the oil back to a storage tank 
(not shown), if necessary, but normally the oil is passed to the inlet oil 
pipe 9 of a mixing tube 10. 
In a similar manner, the hot water is controlled. The water is pumped along 
a line 11 and the flow rate is controlled to a required level by a valve 
12 adjusted by a controller 13. The flow rate is measured by a flowmeter 
14 and a valve 15A serves to divert the hot water to tank, if necessary, 
through a valve 15B, otherwise the water enters the water inlet pipe 16 of 
the mixing tube 10. 
As shown in FIG. 2, the mixing tube 10 has the water inlet tube 16 coaxial 
therewith at one end and an outlet tube 21 at the other end. The oil inlet 
tube 9 projects into the tube 10 at an angle of between 20-40 degrees, 
conveniently 30.degree., to the longitudinal axis of the tube 10 and 
extends into the tube 10 so that the longitudinal axis of the outlet end 
of the tube is substantially coincident with the axis of the tube 10. The 
cross-section of the tube 10 is greater than that of tube 9 so that there 
is space around the end of tube 9. 
In use, the flow of oil entering the tube 10 from the tube 9 is drawn in 
and enters freely into the flow of water passing through the tube 10 even 
though the flow rate is considerably greater than that of the oil. From 
the mixing tube 10, the at least partially mixed water and oil passes into 
an emulsifier 22 where the mixture is subjected to turbulence to bring 
about thorough emulsification. The emulsion then passes to the headers 1, 
2. 
The mixed flow rate of emulsion per stand may be from 5-25 litres per 
minute, with the oil having a minimum flow rate of 0.23 lpm and a maximum 
flow rate of 12.5 lpm and the water a minimum flow rate of 2.5 lpm and a 
maximum flow rate of 23 lpm. 
The supply of the lubricant to the strip material may be controlled 
manually by an operator but, preferably, it is under computer control. 
A flow control computer 25 receives signals indicating such parameters as 
type of material being rolled, the speed of the strip material, the load 
on the rolling mill stand and the power of the driving motor. From this 
information, the computer controls a flow control regulator 26. The flow 
of oil from the valve 5 is measured by the flowmeter 7 and the regulator 
receives this information and adjusts the controller 6 to ensure that a 
measured flow of oil at the required rate enters the pipe 9. Similarly, 
the flow of water from the valve 12 is measured by the flowmeter 14 and 
the regulator receives this information and adjusts the controller 13 to 
ensure that a measured flow of water at the required rate enters the pipe 
10. It will be appreciated that the regulator 26 can adjust the total 
quantity of oil and water supplied to the tubes 9, 10 and also the 
proportions of oil and water supplied to the tubes. 
The computer 25 is programmed to control the flow rate of lubricant 
supplied to the strip material and also the ratio of oil and water in the 
emulsion. The correct computer control of the emulsion brings about a 
reduction in the consumption of rolling oil, a reduction in the rolling 
load on the mill stand with a resultant saving of energy and a reduction 
in the slippage in the roll bite. 
An on-off flushing valve 30 controlled by the computer may be provided in a 
connecting pipe between the flow control valves 5 and 12. This permits hot 
water from line 11 to be used to flush out the system on completion of a 
rolling sequence. 
Lubricant may be supplied to the strip material at a single stand mill or 
to each stand of a multistand mill or at only some of the stands. 
It is essential that the measured flow of rolling oil enters into the pipe 
10, otherwise the quantity of emulsion and the proportion of oil and water 
in the emulsion will be incorrect. The flow of the greater quantity of 
water around the outlet end of the oil feed tube 9 ensures that the oil is 
drawn into the water flow and at least partially mixes with it. The 
mixture from the mixing tube is thoroughly mixed to produce the emulsion 
in the emulsifier 22.