CA1126465A - Optimum rubber mill roll cooling water temperature determination - Google Patents
Optimum rubber mill roll cooling water temperature determinationInfo
- Publication number
- CA1126465A CA1126465A CA312,108A CA312108A CA1126465A CA 1126465 A CA1126465 A CA 1126465A CA 312108 A CA312108 A CA 312108A CA 1126465 A CA1126465 A CA 1126465A
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- water
- stock
- mill
- cooling water
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000498 cooling water Substances 0.000 title claims abstract description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 54
- 238000000034 method Methods 0.000 claims description 8
- 230000007423 decrease Effects 0.000 claims description 4
- 238000003801 milling Methods 0.000 claims description 3
- 238000001816 cooling Methods 0.000 abstract description 8
- 238000013329 compounding Methods 0.000 abstract 1
- 239000004615 ingredient Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000005057 refrigeration Methods 0.000 description 2
- 206010037660 Pyrexia Diseases 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B7/00—Mixing; Kneading
- B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices
- B29B7/58—Component parts, details or accessories; Auxiliary operations
- B29B7/72—Measuring, controlling or regulating
- B29B7/724—Measuring, controlling or regulating for continuous roller mixers, e.g. calenders
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B7/00—Mixing; Kneading
- B29B7/80—Component parts, details or accessories; Auxiliary operations
- B29B7/82—Heating or cooling
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
- Confectionery (AREA)
Abstract
OPTIMUM RUBBER MILL ROLL
COOLING WATER TEMPERATURE DETERMINATION
Abstract of the Disclosure By varying the temperature and/or the flow rate of water passing through rubber mill rolls and measuring the stock temperature of the rubber being milled, the optimum flow rate and water temperature to be used in cooling the mill can be obtained. The desired stock temperature is predetermined by a compounding chemist and the optimum flow rate and water temperature is de-termined by the energy costs involved in running the mill.
COOLING WATER TEMPERATURE DETERMINATION
Abstract of the Disclosure By varying the temperature and/or the flow rate of water passing through rubber mill rolls and measuring the stock temperature of the rubber being milled, the optimum flow rate and water temperature to be used in cooling the mill can be obtained. The desired stock temperature is predetermined by a compounding chemist and the optimum flow rate and water temperature is de-termined by the energy costs involved in running the mill.
Description
~6~
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
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.
.
646~
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.
~?
~ 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.
( 8 ~
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.
.
646~
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.
~?
~ 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.
( 8 ~
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for milling uncured rubber stock on a mill having one or more internally water cooled mill rolls comprising:
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 85 F.
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 85 F.
2. The method of claim 1 wherein the water temperature is within 10 C
above the temperature of the cooling water which, on a plot of cooling water temperature against stock temperature corresponds to a minimum in the stock temperature.
above the temperature of the cooling water which, on a plot of cooling water temperature against stock temperature corresponds to a minimum in the stock temperature.
3. The method of claim 1 wherein the chosen water temperature is the maximum temperature +10°C in a temperature range wherein the stock tempera-ture decreases with an increase in water temperature at a constant water flow rate.
4. The method of claim 1 wherein the water temperature is in a temperature range wherein the stock temperature decreases with an increase in water temperature at a constant water flow rate.
5. The method of claim 1, 2 or 3 wherein the milling is performed at a stock temperature of the order of 200 F to 220°F.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US87129178A | 1978-01-23 | 1978-01-23 | |
| US871,291 | 1978-01-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1126465A true CA1126465A (en) | 1982-06-29 |
Family
ID=25357131
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA312,108A Expired CA1126465A (en) | 1978-01-23 | 1978-09-26 | Optimum rubber mill roll cooling water temperature determination |
Country Status (16)
| Country | Link |
|---|---|
| JP (1) | JPS54103484A (en) |
| AR (1) | AR224113A1 (en) |
| AU (1) | AU512638B2 (en) |
| CA (1) | CA1126465A (en) |
| CH (1) | CH639894A5 (en) |
| DE (1) | DE2849349C2 (en) |
| ES (1) | ES473717A1 (en) |
| FR (1) | FR2414989A1 (en) |
| GB (1) | GB2016019B (en) |
| IN (1) | IN148934B (en) |
| IT (1) | IT1099380B (en) |
| LU (1) | LU80812A1 (en) |
| PT (1) | PT68745A (en) |
| RO (1) | RO82403A (en) |
| SE (1) | SE440623B (en) |
| ZA (1) | ZA786170B (en) |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1850450A (en) * | 1929-04-05 | 1932-03-22 | Gen Tire & Rubber Co | Rubber mixing mill |
| NL32600C (en) * | 1931-09-14 | |||
| DE733436C (en) * | 1939-09-23 | 1943-03-26 | Hermann Carl Amme | Method and device for cooling the rolls of rolling mills for processing synthetic rubber or similar plastics |
| DE913697C (en) * | 1944-03-21 | 1954-06-18 | Hermann Berstorff Maschb Ansta | Roller for processing rubber, plastic or the like with helical guide channels for the heating or coolant provided inside |
| US2431473A (en) * | 1945-02-09 | 1947-11-25 | Seamless Rubber Co | Temperature control means for hollow rolls |
| DE1035890B (en) * | 1956-04-25 | 1958-08-07 | Wilhelm Ellermann | Kneading and mixing tools for plastic masses such as rubber and thermoplastics |
| BE637984A (en) * | 1962-10-09 | |||
| US3376601A (en) * | 1966-05-12 | 1968-04-09 | Adamson United Company | Mixing mill with independent drive means for each cooperating mill roll |
-
1978
- 1978-09-19 IN IN677/DEL/78A patent/IN148934B/en unknown
- 1978-09-26 CA CA312,108A patent/CA1126465A/en not_active Expired
- 1978-09-27 AU AU40234/78A patent/AU512638B2/en not_active Expired
- 1978-09-27 ES ES473717A patent/ES473717A1/en not_active Expired
- 1978-10-06 AR AR273997A patent/AR224113A1/en active
- 1978-10-11 IT IT28655/78A patent/IT1099380B/en active
- 1978-11-02 ZA ZA00786170A patent/ZA786170B/en unknown
- 1978-11-06 PT PT68745A patent/PT68745A/en unknown
- 1978-11-13 GB GB7844275A patent/GB2016019B/en not_active Expired
- 1978-11-14 DE DE2849349A patent/DE2849349C2/en not_active Expired
- 1978-11-22 JP JP14347778A patent/JPS54103484A/en active Granted
- 1978-12-29 RO RO7896127A patent/RO82403A/en unknown
-
1979
- 1979-01-16 SE SE7900390A patent/SE440623B/en not_active IP Right Cessation
- 1979-01-22 CH CH63279A patent/CH639894A5/en not_active IP Right Cessation
- 1979-01-22 LU LU80812A patent/LU80812A1/en unknown
- 1979-01-23 FR FR7901601A patent/FR2414989A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| AU4023478A (en) | 1980-04-03 |
| AU512638B2 (en) | 1980-10-23 |
| SE440623B (en) | 1985-08-12 |
| IT7828655A0 (en) | 1978-10-11 |
| DE2849349C2 (en) | 1983-04-07 |
| AR224113A1 (en) | 1981-10-30 |
| GB2016019A (en) | 1979-09-19 |
| ES473717A1 (en) | 1979-04-01 |
| FR2414989B1 (en) | 1982-05-07 |
| JPS54103484A (en) | 1979-08-14 |
| GB2016019B (en) | 1982-10-20 |
| CH639894A5 (en) | 1983-12-15 |
| DE2849349A1 (en) | 1979-07-26 |
| FR2414989A1 (en) | 1979-08-17 |
| IT1099380B (en) | 1985-09-18 |
| LU80812A1 (en) | 1979-09-07 |
| RO82403A (en) | 1983-11-01 |
| ZA786170B (en) | 1979-10-31 |
| JPS6218325B2 (en) | 1987-04-22 |
| SE7900390L (en) | 1979-07-24 |
| IN148934B (en) | 1981-07-25 |
| RO82403B (en) | 1983-09-30 |
| PT68745A (en) | 1978-12-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |