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FORM – 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE
(Section 10, rule 13)
HIGH RESISTANCE AND LOW POWER LOSS FERRITE
DGP HINODAY INDUSTRIES LTD.,
of Bhosari Industrial Estate, Bhosari MIDC, Pune 411 026,
Maharashtra, India, an Indian Company
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES
THE NATURE OF THIS INVENTION AND THE MANNER
Original IN WHICH IT IS TO BE PERFORMED:-
4-1-2003 19 APR 2004
This invention relates to a method of making ferrite material having high resistance and low power loss and a ferrite material so produced.
In particular, this invention is concerned with the method of production of high resistance and low power loss Manganese -Zinc ferrite suitable for ferrite rods (impeder core) used in tube welding.
Ferrite rods for welding are also called as impeder cores. They are used in making pipes (tubes) by welding.
Figure 1 of the accompanyiiig drawings is a schematic illustration of a welding process in which the reference numerals indicate the following
1. Impeder core
2. Induction coil
3. Impeder case
4. Steel strip (pipe)
5. Cooling water
6. Roll
As shown in Fig.l of the accompanying drawings, the steel strip (sheet 1) 4 continuously passing from left to the right of the figure, is bent in approximately round shape of the pipe, by keeping a small gap at both of its ends, by means of several stepped rolls (not shown in the figure) situated in front of the induction coil 2.While this steel strip 4 passes through the induction coil 2, high frequency current is induced in the system consisting of steel strip 4 and the impeder core 1. Since the impedance/resistance of the impeder core is very high, mostst of the current passes along the steel strip maximising the heat generation. Under this condition the two ends^et welded
temperature retention process is kept below 1 % and the cooling after sintering is carried out in oxygen atmosphere in the range determined by the following formula.
log P02= a-2000/(T+273)
13.6
P02 : oxygen concentration (%), T: temperature (°C), a : constant
The problems this invention seeks to solve are as follows: In case of applications like ferrite rods (impeder core) used at high frequency for tube welding, ferrite rods with high resisistivity of more than 2.0 Q.m and low power loss are required. However, conventionally such ferrite rods with high resistivity and low power loss are not available.
Under such circumstances, the present inventors concentrated their attention on using suitable auxiliary material and aimed at obtaining a Manganese -Zinc ferrite with a high resistance and, low power loss at a frequency of more than 300 kHz, by selecting an optimum composition.
In accordance with a first aspect of the invention there is provided a high resistance and low power loss ferrite which has Fe203, Manganese Oxide and Zinc Oxide as the main components and contains 150 ~ 600 ppm of Calcium Oxide, 60 ~ 400 ppm Silicon dioxide, 20-100 ppm Ta205 100 ~ 500 ppm Nb2O5 and 200 ~ 1000 ppm of V205 as auxiliary material.
In accordance with a preferred embodiment of the invention the quantities are Fe203: 52.5 ~ 54.5 mol%, Manganese Oxide: 36 ~ 40 mol %, Zinc Oxide: 7 ~ 11 mol % and to obtain a high resistance and low power loss ferrite with
due to the roll 6 situated behind the induction coil 2 next to it and pipe 4 is formed.
Here the impeder core 1 acts like the yoke used for improving the efficiency of magnetic circuit. The impeder core 1 is cooled by cooling water 5 flowing through the impeder case 3. The impeder core 1 gets excited by high frequency of 400 kHz and the magnetic material which makes the impeder core 1, poses a problem of high power loss due to large amount of evolution of heat.
Manganese -Zinc ferrite is well known as a conventional low power loss ferrite for power transformers. In case of this ferrite, a high resistance layer is created at the crystalline grain-boundary by addition of Calcium Oxide and Silicon dioxide and this reduces power loss at high frequency. For example, in patent JP 7-297018[ no Indian equivalent available] , a low power loss ferrite for power transformer having Manganese Oxide and Zinc Oxide and Fe203 as the main components and 0.03 ~ 0.1 weight % Calcium Oxide, 0.005 ~ 0.05 weight % Silicon dioxide and 0.1 ~ 0.4 weight % Ti02, 0.005 ~ 0.06 weight % Nb2O5 as auxiliary material has been mentioned.
Patent JP 4-354304 [ no Indian equivalent available] discloses a method of production of a ferrite with very good insulating properties and having high surface resistance by heat-treating Manganese -Zinc ferrite sintered material having Manganese Oxide, Zinc Oxide and Fe2O3 as the main components, in oxidizing atmosphere.
In patent JP 5-217734, [ fio Indian equivalent available] method of production of a low power loss Manganese -Zinc ferrite is mentioned. In this, the oxygen concentration in temperature-rise process and beginning of the sintering
resistivity of more than 2.0 Q-m and power loss of less than 2000W/kg at 100°C and 400 kHz. This high resistance and low power loss ferrite is ideally suitable for making welding rods.
In accordance with a second aspect of the invention, there is provided a method of production of high resistance and low power loss ferrite having Fe203, Manganese Oxide and Zinc Oxide as the main components and containing 150 ~ 600 ppm of Calcium Oxide, 60 ~ 400 ppm Silicon dioxide, 20 ~ 100 ppm Ta205 100 ~ 500 ppm Nb205 and 200 ~ 1000 ppm of VZ05 as auxiliary material by sintering in which the oxygen concentration (P02 ) in sintering atmosphere during temperature-rise and temperature-retention is kept at 10 ~ 21% and the oxygen concentration during cooling process is controlled in the range given by the following formula :
Upper limit of oxygen concentration P02 (%) is
log P02 = 4.23 - 4500 / (T+273) and, Lower limit of oxygen concentration P02 (%) is
log P02 = 7.1 - 9400 / (T+273)
In this aspect of the invention, the temperature maintained during temperature-retention during sintering process was in the range 1240 ~ 1290°C. By controlling the oxygen concentration (P02) and in the sintering atmosphere in the temperature range of retention temperature in cooling process (during sintering) ~ 900°C, as mentioned above, it is possible to obtain the high resistance and low power loss ferrite
High resistance and low power loss ferrite of this invention has Fe203, Manganese Oxide and Zinc Oxide as the main components and it contains 150 ~ 600 ppm of Calcium Oxide, 60 ~ 400 ppm Silicon dioxide, 20 ~ 100 ppm Ta205 100 ~ 500 ppm Nb205 and 200 - 1000 ppm of V205 as auxiliary material.
This high resistance and low power loss ferrite is prepared as follows:
Starting material is taken so that the composition after sintering will be as mentioned above. It is dried and 1.0 weight % binder is added. It is then granulated, pressed and sintered in the retention-temperature range of 1240 ~ 1290°C in an atmosphere with oxygen concentration (P02) in the range 10-21 %. After this, the cooling is carried out by controlling the concentration of oxygen in the atmosphere in the range given by the following formula: Upper limit of oxygen concentration P02 (%) is
log P02 -4.23 - 4500 / (T+273) and, Lower limit of oxygen concentration P02 (%) is
log P02 = 7.1 - 9400 / (T+273)
The reason for composition range for various additives is as follows:
If Calcium Oxide is less than 150 ppm, the electrical resistance reduces and therefore power loss due to eddy currents at high frequency region becomes large. If Calcium Oxide is more than 600 ppm, the soft magnetic properties deteriorate. If Silicon dioxide is less than 60 ppm, electrical resistance reduces and if Silicon dioxide exceeds 400 ppm, abnormal (over) sintering takes place and power loss increases. If Nb205 and Ta205 are less than the range stated in this invention, the electrical resistance reduces and high frequency power loss
increases. If it is more than the range, abnormal sintering takes place and power loss increases. Further, V205 causes enhancement of growth of crystalline grains and it is added for achieving low power loss. If it is less than 200 ppm, the effect of its addition is not obtained. If, however, it is more than 1000 ppm, the loss increases. Out of the above additives, Calcium Oxide and Silicon dioxide form a high resistance layer on the boundary of the crystal grains and reduce power loss at high frequency. Manganese -Zinc ferrite for Impeder core material of tube welding is used under the conditions of high frequency of more than 300 kHz and a high applied excitation current. The resistance of the entire material does not increase sufficiently just by a high resistance layer on crystal boundary. Therefore large amount of heat evolution occurs due to eddy current loss and its durability may be affected for long time use. Thus in this invention, for increasing electrical resistance of not only the boundary of crystals but for increasing the electrical resistance of crystals themselves, a material of high electrical resistance was obtained by controlling the sintering retention-temperature, oxygen concentration of the atmosphere during sintering and oxygen concentration of the atmosphere in the subsequent cooling.
The reason for keeping limits for the range of various components as Fe203: 52.5 ~ 54.5 mol %, Manganese Oxide: 36 ~ 40 mol %, Zinc Oxide: 7 ~ 11 mol % is as follows. If Fe203 is less than 52.5 mol %, the loss near the working temperature becomes large when it is used as a material for Impeder core for tube welding. If, however, Fe203 is more than 54.5 mol %, the eddy current loss in high frequency region increases and power loss also becomes high. If Manganese Oxide is less than 36 mol %, high magnetic flux density cannot be obtained near the working temperature required for the use as Impeder core material. If, however, Manganese Oxide is more than 40 mol %, it becomes
difficult to get sufficient sintered density for giving sufficient material strength. If Zinc Oxide is less than 7 mol %, sintering of the material is difficult to proceed. If, however, it is more than 11 mol %, it becomes difficult to get high magnetic flux density near the working temperature.
It is already known that in case of Manganese -Zinc ferrite, not only the sintering atmosphere, but also control of oxygen concentration in the cooling atmosphere is also important. High resistance and high frequency ferrite of this invention is obtained by carrying out the sintering at a higher oxygen concentration-side than the conventional one while sintering and cooling, in such a way that oxygen concentration will be in a specific range. Further by controlling the cooling temperature in a precise manner, it was possible to make not only the surface of the material but also inside of the material to show high electrical resistance and low power loss at high frequency.
In the method of production of high resistance and low power loss ferrite of this invention, the reasons for the limits of ranges for sintering temperature, oxygen concentration in sintering atmosphere and oxygen concentration in the cooling atmosphere are as follows :
If the sintering temperature is less than 1240°C, sufficient soft magnetic properties cannot be obtained because of low sintered density and the loss is high. If the temperature exceeds 1290°C, the specific resistance lowers down. If oxygen concentration of the sintering atmosphere is less than 10 %, the resistivity becomes low. If the concentration exceeds 21 %, the loss increases. Further, if the oxygen concentration in the cooling atmosphere is more than the upper limit of the range stated above, the loss becomes high. If however, it is lower than the lower limit, of the range, the resistivity becomes low.
The invention will now be described with reference to the accompanying examples
Application example 1
Raw material consisting of Fe203 (53 mol %), Manganese Oxide (38 mol %) and Zinc Oxide: (9 mol %) was mixed in a ball mill and calcined at 900°C. Then CaC03 (in appropriate quantity to give 250 ppm of Calcium Oxide), 100 ppm of Silicon dioxide, 50 ppm Ta205, 150 ppm Nb205 and 500 ppm of V205 were added as the auxiliary materials and ground in a ball mill for 12 hours. In case of auxiliary material like Calcium Oxide or Silicon dioxide that may be already present in the raw material, proportionately lesser quantities of these materials were added after calcinations, so that the quantities as a whole were in agreement with those mentioned above, This ground material was dried and 1.0 weight % of binder was added and then granulation and pressing was carried out. This pressed material was sintered for 4 hours at sintering retention temperature of 1240 ~ 1290°C at oxygen concentration of 10 ~ 21 %. After this, cooling was carried out while controlling the oxygen concentration in the atmosphere, in the range mentioned below. Upper limit of oxygen concentration P02 (%) is
log P02 = 4.23 - 4500 / (T+273) and, Lower limit of oxygen concentration P02 (%) is
log P02 = 7.1 - 9400 / (T+273) The sintered material was ring-shaped, with outer diameter: 29 mm, inner diameter: 19 mm and height: 10 mm.
The invention will now be described with reference to the accompanying drawing in which:
Figure -1 is a Schematic diagram explaining tube welding by means of ferrite rod using high resistance and low power loss material of application example of this invention.
Then various samples were prepared by similar method of preparation, but by varying the quantities added. The results of property evaluation of these are given in Table 1. In Table 1, the pattern indications represent the following:
A (Upper limit): logP=4 23-4500/(T=273)
B (Intermediate): Concentration between A and C
C (Lower limit): logP=7.1 -9400(T+273)
D: Concentration exceeding A
E: Concentration below C
By controlling the quantity of above 5 types of additives, oxygen concentration in temperature increasing process, retention temperature, oxygen concentration in sintering, and oxygen concentration during cooling process, it was possible to get a high resistance and low power loss material.
A tube welding Impeder core was prepared in the form of a rod of sintered dimensions of 10 mm outer diameter and 20 mm length, by using the method similar to the one used for preparing the samples. The temperature rise by using the sample thus obtained as Impeder core material for tube welding is shown in Table 2. The Impeder core material corresponding to the sample of application example from Table 1 showed that the features like lower
temperature rise, high resistance and low power loss at high frequency have been realized.
By the method of this invention, it is possible to get an Manganese -Zinc ferrite having high resistance and low power loss even at high frequency of more than 300 kHz, by setting the values of quantities of additives like Calcium Oxide, Si02, Ta205 Nb205, V205 appropriately and controlling oxygen concentration of the atmosphere in sintering and cooling process. Thus it is possible to get a high resistance and low power loss material suitable for the use at high frequency such as for ferrite rods (impeder core) for tube welding.
Table -1 is a table of the property evaluation of the ferrite produced in accordance with this invention.
Table-2 presents the data corresponding to a temperature of variation due to power loss rise.
We Claim:
1] A high resistance and low power loss ferrite, having Fe203, Manganese Oxide and Zinc Oxide as the main components and it contains 150 ~ 600 ppm of Calcium Oxide, 600 ~ 400 ppm Silicon dioxide, 20-100 ppm Ta205 100 ~ 500 ppm Nb205 and 200 ~ 1000 ppm of V205 as auxiliary material.
2] A high resistance and low power loss ferrite as claimed in claim 1, in which the quantities are Fe203: 52.5 ~ 54.5 mol%, Manganese Oxide: 36 ~ 40 mol %, Zinc Oxide: 7—11 mol %.
3] A high resistance and low power loss ferrite as claimed in claim 1 or 2 having resistivity more than 2.0 fi.m and power loss at 100°C and 400 kHz is less than 2000W/kg.
4] A method of production of high resistance and low power loss ferrite as claimed in any one of claims 1 to 3, having Fe203, Manganese Oxide and Zinc Oxide as its main components and Calcium Oxide, Silicon dioxide, Ta205, Nb205 and V205 as auxiliary components by sintering in which the oxygen concentration (pressure) in the atmosphere, during temperature rise in sintering process and during temperature-retention in sintering process (P02) is kept at 10-21 % and oxygen concentration while cooling at the time of sintering process is maintained in the range mentioned below :
Upper limit of oxygen concentration P02 (%) is
log P02 = 4.23 - 4500 / (T+273) and, Lower limit of oxygen concentration P02 (%) is
log P02 = 7.1- 9400 / (T+273)
5] A method of production of high resistance and low power loss ferrite as claimed in claim 4, in which temperature maintained in the temperature retention during sintering process is in the range 1240 ~ 1290 °C and the oxygen concentration P02 in the atmosphere in cooling process during sintering is controlled as above, in the range of sintering retention temperature in cooling process ~ 900 °C.
6] A ferrite rod for tube welding, made from the high resistance and low power loss ferrite mentioned in claims 1-3.
Dated this 21st day of July, 2003
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