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BACKGROU~D OF TEIE INVENTION
Field of the Invention The present invention is directed to a method of deter-mining the optimum flow rate and the optimum water temperature to be used in a rubber mill and the use o such optimum con-ditions in the operation of the mill.
DESCRIPTION OF THE PRIOR ART
In the manufacture of rubber products, the ingredients are first mixed in a Banbury*. The Banbury, until recently, was cooled by flowing cold water through it during the winter months and warm water during the summer. At the present time, the Banbury is cooled by passing warm water through the Banbury all year long. This has resulted in a higher through-put of the Banbury as compared to the previous cold water process.
After the ingredients are mixed in the Banbury, they are milled on a two-roll rubber mill. The mill rolls are cooled by passing cold water through them. The rubber being processed has a memory of its heat history. If the rubber is maintained at too high a temperature for too long a period (total heat history), it will scorch. When scorching problems were encountered, the solution at The General Tire & Rubber Company has historically been to use colder water in the mill rolls. The General Tire & Rubber Company has even gone so far as to install mechanical refrigeration units employing Freon*
refrigerant gas to cool the cooling water passing through the mills. It is not believed that our competitors have followed our lead in this regard.

* denotes Trademark

-2-~L~;26~65 The use of refrigerated water in our mill rolls has resulted i.n great expense and energy consumption in the opera-tion oE the refrigerating units. The extreme cooling has also increased the stiffness of the rubber being milled which has resulted in the mill motors working harder, thus, consuming more energy. In some instances where cold water from wells was plentiful and cheap, large quantities of cold water were used and discharged. Water treatment to prevent mill corrosion, however, in these instances was quite expensive.

1~ SUMMP.R~ OF THE INVENTI ON
It was unexpectedly discovered that by varying the temperature of the cooling water in the mill that stock temperatures could actually be decreased by increasing the cooling water temperature at a constant flow rate. It was also discovered that by increasing the Elow rate at constant temper-ature that stock temperatures could be significantly reduced.
These phenomenon of stock temperature reduction occur only in selected areas of the stock temperature vs. mill surface temperature graph and the stock temperature vs. flow rate graph.

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The invention provides a method for milling uncured rubber stock on a mill having one or more internally water cooled mill rolls comprisiny:
supplying cooling water to said water cooled roll or rolls at a temperature and a rate such that the rubber being milled is not scorched, the temperature of the cooling water supplied to the said roll or rolls being at least 85F.
What is desired is to obtain the minimum differential between the stock temperature and the mill surface temperature or to work in that part of the graph where the stock temperature decreases with an increase in mill surface temperature up to and slightly beyond the point where stock temperature increases with an increase in mill surface temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure la is a schematic diagram partially in cross-section of a two roll rubber mill in combination with a variable volume water pump and a variable temperature water supply. A
water recycle loop is also included to limit the total volume of water pumped through the system.
Figure lb is a top view of the apparatus of Figure la.
Figure 2 is a graph showing the variation of the stock temperature as the volume of cooling water through the mill is increased.
Figure 3 is a graph showing the variation of stock temperature as the cooling water temperature is gradually increased at a constant flow rate through the mill. The shape of the graph will vary with the rubber compound being milled.

, --4--1~26~65 DESCRIPTION OF THE PREFER~ED EMBODIMENTS
The apparatus of the present invention and its operation will now be described in conjunction with the drawings.
Figures la (side) and lb (top) are directed to a water cooled rubb~r mill; the mill has two rolls 3 and 5. The rolls are 27 inches in diameter and 84 inches long. On the rolls is positioned a mass of rubber in its uncured state 7. The mill is internally cooled by a water spray 9. The water is pumped into the mill through conduit 11 by variable volume pump 13. The water 15 collects in the bottom of the mill rolls and is returned to a cooling tower 18. A variable valve 20 is positioned so as to bypass cooling tower 18.
Figure 2 shows the effect of varying the cooling water flow rate while maintaining the cooling water at a constant temperature. The optimum flow rate is es-tablished at a constant water temperature. The water temperature is arbitrarily chosen for the first flow ra~e determination. In the presen~ case 30gpm provided the best cooling for the volume range studied.
As is shown in Figure 3, the temperature of the cooling water was varied by the operation of valve 20 which allows a partial recycle of hot water coming from the mill while the volume of wat~r pumped through the ( 5 ) l~'hl~65 mill was held constant by pump 13 to 30 gallons per minute. As is shown by the stock temperature graph of Figure 3, the stock temperature increased from 200 F to 222F as the water temperature increased from 70 F to 85 F. The stock is the rubber 7 being milled. As the water temperature increased from 85 F to 90 F, the stock temperature took a drop from 222F to 208 F, then stabili~ed with slight temperature increases when the water temperature was varied from 90 F to 100 F. The stock temperature was 208 F at a water temperature of 90F. The differential between the water temperature and the stock temperature was 118 F. This is the beginning of the minimum differen-tial range obtainable from the graph. As the water temperature increased to 100 F, the stock temperature increased to 211 F, a differential of 111 F.
The preferred stock temperature-cooling water temperature differential is ~lO C from the lowest stock temperature cooling water differential. A ~20 C
differential can be employed. Another preferred cooling water temperature is a temperature within the range wherein the stock temperature decreases with an increase in cooling water temperature.
The graph above the stock temperature graph is the heat graph which outlines the amount of heat being removed from the milled rubber. The amount of heat being removed also reaches a peak at a water temperature of about 90F. The temperature of the front and back mill rolls are also shown on the graph. It will be seen that the mill roll temperature at temperatures above the minimum differential between the stock temperature and the water temperature is increased.

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~ 5 The graphs (Figure 2 and Figure 3), represents the results one would obtain with a particular rubber stock. Other rubber stocks would produce graphs which would be expected to be difEerent, but similar in shape.
After the optimum cooling water flow rate and the optimum cooling water temperature have been obtained, the mill is then operated at that cooling water temp-erature and at that flow rate to yield the necessary energy savings. Optionally, the flow rate determination can be redetermined at the optimum temperature established~
optionally followed by a redetermination of the optimum temperature. ~-Since most of the water is recycled, there is also a significant savings in the quantity o water used in plants which previously used a once-through sys-~; tem. Energy is saved because while temperate water is used at a higher flow rate than would normall~ be the case. Energy is saved because when the prior art re-frigerated water was used, a large amount of energy was required for refrigeration and the rubber stock required more energy to mill.
The mills employed are preferably drilled~ i.e., cast as a solid roll and then water channels drilled into the roll. The rolls can also be cast around a sand core with or without machining the rough interior. The ( 7 ) ~ 5 mills are commercially available from Steward Bolling, and Farrel, among others. The mills except for the temperature and flow of cooling water, are operated in a conventional manner.
The variable volume pump used is a commercial centriugal pump.
The variable bypass valve used is also a commer-cial valve. The cooling tower is also a conventional water evaporative cooling tower. The cooling tower capa-city is dependent upon the volume of water used. The heated water coming from the mill can also be cooled by heat exchange with cold air or the cold water supply coming into the factory.
The manufacturing source of the above components is not critical. The components are normally selected by an engineer to suit particular mills or a particular plant. Variations such as the quantity and quality of the water source, water temperature, etc., are de-ciding factors in the selection of equipment.

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