DK149307B - PROCEDURE FOR THE CREATION OF A GLASS BRAIN ON AN ORIENTED SILICONE-CONTAINING STEEL BAND - Google Patents

Description

149307

The invention relates to a method for forming a magnesium oxide-silica glass membrane on an oriented silicon-containing steel band, where the band is first cooled at 700-900 ° C, then an aqueous slurry of MgO is applied as a separator on the surface of the band and the band is wound up; is dried and annealed at a high temperature to form the magnesium oxide-silica glass membrane.

To form electrically insulating glass membranes, a cold-rolled silicon-containing steel strip with a desired final thickness is continuously heated at a temperature of 700-900 ° C for several minutes. This is done in an H2-H2O atmosphere to simultaneously obtain a decay and formation of a silica membrane on the steel band surfaces by oxidation of silicon in the steel. Then, the charred steel strip is applied to a glow separator containing magnesium oxide (MgO) as the main component. The rewinding and final annealing is then carried out at a high temperature, whereby the aforementioned silica and magnesium oxide react to form a glass-like insulating film on the surfaces of the silicon-containing steel strips.

2 149307

It is well known that magnesium oxide visibly affects the glass membrane formed during the last annealing. This has therefore been studied extensively.

5 Although the properties of magnesium oxide as a separator have been extensively investigated, the glass membranes made on an industrial scale are nonetheless sometimes damaged as to dissimilar appearance in longitudinal and transverse directions. These disparities weaken the glass membranes locally in terms of insulating properties and adhesion to the steel strips. First, the damage is due to the insulating glass membranes being formed by the reaction of magnesium oxide applied as a separator with the oxide layer containing silica formed on the steel surfaces between the windings. This reaction is greatly influenced by the ambient atmosphere, ie. of the atmosphere between the spo-15 layers. However, it is impossible to make the spaces between the coil layers uniform in the commercially cold rolled and wound coil. Therefore, the gas permeability varies locally, so that the atmosphere between the coil layers locally becomes uneven. Such atmospheric variations affect the growth of the vitreous. Consequently, the steel strip becomes uneven in longitudinal and transverse directions.

From US Patent No. 3,653,984, it is known to secure gaps between the coil layers and provide an atmosphere consisting essentially of hydrogen. A coil of silicon steel strip coated with 10-30 25 g / m magnesium oxide is mounted on a base plate which is provided with a large number of small holes for supplying gas, which evaporate the absorbing amount of water of the aforementioned hydroxide and produce gaps between the coil layers are forced or pressed into the gaps through the small holes. However, the installation costs associated with this process are relatively high and it is always necessary to keep the base plate flat for the base plate contact with the end side of the coil, which is why it is difficult to perform this process on an industrial scale. In addition, in order to make the passage of atmospheric gas efficient, it is necessary to apply 10-30 g / m 35 of magnesium hydroxide as a result of which the costs increase.

The object of the invention is to provide a method of avoiding damage due to poor adhesion of the insulating glass membrane and non-uniformity of the same without the use of expensive installations.

The inventors have produced magnesium oxide with various properties and made samples for forming insulating glass membranes. It has been found that an insulating glass membrane that is uniform in appearance and has a fixed adhesion in longitudinal and transverse directions on both sides of the coil by simply adjusting the size of the magnesium oxide particles to be used as a separator, to be within a suitable range and by using MgO of a certain purity and degree of hydration. The process according to the invention is thus characterized by the characterizing part of claim 1.

10

From U.S. Patent No. 2,906,645, U.S. Patent No. 3,186,867, and the specification to Japanese Patent Application No. 14,162 / 70, particle sizes for the magnesium oxide to be used as a separator are known. U.S. Patent No. 2,906,645 discloses that particle size travel is preferably determined by 98% of all particles passing through a 325 mesh screen which causes the mean particle size to be 5µ to 15µ. U.S. Patent No. 3,186,867 discloses that the crystallite size of the magnesium oxide powder is preferably 170 to 208 Å. The Japanese patent application states that mag = 20 nesium oxide is preferred, with at least 70% of the particles being less than 3 µ. The particle size mentioned in U.S. Patent No. 2,906,645 and in the Japanese patent application does not account for the size of the primary particles, but for the size of the secondary particles measured by sieving or deposition methods. The crystallite size of U.S. Patent No. 3,186,867, on the other hand, accounts for the size of the primary particles. This size is determined from the width of the X-ray diffraction tips. U.S. Patent No. 3,186,867 does not disclose the size of the secondary particles. However, to obtain a primary particle size of about 200 Å, the starting material in the form of magnesium = 30 hydroxide or magnesium carbonate must be calcined at a very low temperature (lower than 800 ° C). At such a low temperature, the sintering rate of the common primary particles is very low, so that the particle size of the secondary particles is also very low. As mentioned before, the size of the secondary particles of the magnesium = 35 oxide used so far as the annealing separator is smaller than that of a 325 mesh screen (44 μ) and preferably less than 15 μ, taking into account first and foremost the ability to be applied to the steel tape. The application is done as follows. A slurry of magnesium oxide in water is applied to the steel belt, the amount applied being adjusted by means of a pressure roller. The free amount of water is removed in a drying oven, after which the tape is rinsed. The relatively large magnesium oxide particles have a relatively low adhesion to the steel band. These magnesium oxide particles therefore rapidly fall off upon contact with an idle roller or as a result of bending at the winding. If there are still magnesium oxide particles of a relatively large particle size remaining on the belt, these particles could cause the coil layers to slide on each other, thereby causing the coil to contract and even the end of the coil to become irregular.

10 For the above reasons, large particle size magnesium oxide has been avoided.

Furthermore, from US Patent No. 3,627,594, it is known to apply magnesium oxide particles with a fineness which corresponds to the particles being able to pass through a 325 mesh screen. The respective tape is then wound into a coil and final annealed. However, in connection with this final annealing, a uniform atmosphere between the layers cannot be maintained.

The inventors have studied the effect of particle size on the formation of: insulating glass membranes on the surface of oriented silicon-containing steel bands. They have found that very uniform glass membranes are obtained when the magnesium oxide particle size has such a distribution that 1-20% of the particles pass through a 100 mesh screen but not through a 325 mesh screen. The reason for the very uniform glass membranes is apparent that the magnesium oxide particles thereby form spacers between wound coil layers and maintain the distance and atmosphere between the layers below the close glow.

So far, the glass membranes varied considerably both longitudinally and transversely, depending on the magnesium oxide type. This variation occurred although the same type of magnesium oxide was used. The disparity also depended on the production volume. In order to clarify the causes of the disparity, the inventors have investigated the effects of impurities, particle size and hydration of the magnesium oxide.

With regard to the impurities and hydrogenation, it has been found that if the impurities in the magnesium oxide are less than 1.0% CaO, less than 0.6% SC> 3, less than 0.04% Cl, less than 0.2 % B and less than 0.04% of an alkali metal - which are the impurities found in commercially available magnesium oxide - and the hydrogenation rate is less than 40% during the hydration test at 20 ° C for 30 minutes, then no 5 149307 has been determined correlation between the formation of the uniform glass membrane and the impurities and hydrogenation. On the other hand, there is a certain correlation between the impurities in the formed glass membrane and the distribution of the particle size. The method of measuring the size distribution of the secondary particles is known as the aiming method, the photo-deposition method, the deposition-balance method and Coulter's counting method. However, measurements on the same sample made using these four methods do not produce the same result. This is probably due to the difference in agglomeration rate due to the difference in sample slurry dispersion and the measurement limit for each of the measurement methods.

The inventors have studied the measurement results at the aforementioned different particle sizes in relation to the properties of the resulting glass membranes formed using a large number of magnesium oxide types 15 prepared from different starting materials and at different calcinations and sieves. Significant similarities have been found between the amount of magnesium oxide particles (greater than 44 · μ) that do not pass through a 325 mesh screen during the sieve test, and the uniformity of the glass membrane. From the experimental results, it appears that a uniform glass membrane can be obtained using magnesium oxide particles, of which 1-20%, preferably 3-15%, pass through a 100 mesh screen but not through a 325 mesh screen. When the magnesium oxide used contains less than 1% by weight of particles passing through a 100 mesh screen but not through a 325 mesh screen, the uniformity of the coating cannot be improved. When the magnesium oxide contains more than 20%, the loss of applied oxide increases during coating and flushing as previously mentioned.

Such a quantity is therefore not economical. A content of 3-15% is the most appropriate.

The magnesium oxide is prepared by calcining synthesized magnesium = hydroxide or basic magnesium carbonate at a high temperature in an oven, for example a rotary kiln. An externally heated rotary furnace can continuously provide homogeneous magnesium oxide. However, the calcination temperature can only be increased to 1000 ° C. In addition, it is difficult to obtain a sintering of the magnesium oxide particles and magnesium oxide particles with a larger particle size cannot be obtained. Using a muffle furnace, the starting material is stacked on the refractory furnace substrate at a thickness of several centimeters and heated by direct fire from a burner or electric heater so that a fairly large temperature difference is obtained by changing the amount of starting material. At the portion having a temperature of about 1300 ° C, the particle growth and the sintering and coarse particle formation can take place. At the part where the temperature is around 800 ° C, only fine particles can be formed. The calcined magnesium oxide is then powdered and classified. Once the classification has been done using a 100 mesh screen, all 5 particles passed through the screen are less than 150 µ. The amount of particles passing through the 100 mesh screen but not through the 325 mesh screen can be adjusted to 1-20% by selecting the stacking thickness depending on the calcination, burner temperature and powder conditions properly.

10 On the other hand, when the classification is done by means of an air classification unit, it is possible to classify any particle-size magnesium oxide by selecting the angle of a blade, the width of a gap and the rotor's rotational number. However, when the particles (44-150 y) passing through the 100 mesh screen but not through the 325 mesh screen make up 1-20%, it cannot be avoided that the particles (larger than 150 y) which do not pass through The 100 mesh screen is mixed to a certain degree. However, experiments showed that if the particles (larger than 150 y) that did not pass the 100 mesh screen formed less than a few percent, then they had no effect on the formation of the glass membrane. Even in the case that the content of such coarse-grained particles was greater than 10%, the glass membrane became uniform as the particles settled in the 2q application station slurry tank and, moreover, the particles quickly fell off after coating and drying and could not be used effectively, so such particles are not commercially advantageous.

Magnesium oxide with good hydrogenation properties obtained by calcining 25 basic magnesium carbonate in a rotary kiln is often used as a separator at the last annealing of the oriented silicon-containing steel strip. In magnesium oxide produced in this way, the size of the primary particles is 400-700 Å. Furthermore, the calcination temperature is so low that the secondary particles are small. The particles (greater than 44 µ) which did not fit the 325 mesh screen made up less than 0.1%. An insulating glass membrane provided by such a magnesium oxide and after a final annealing is poor. · As regards uniformity in the longitudinal and transverse directions, impurity patterns are often formed. However, if such a magnesium oxide is mixed with an appropriate amount of coarse-grained magnesium oxide produced by calcination in a furnace at a high temperature, a glass membrane of better uniformity is obtained. Even in this case, the distribution of the particle size of the resulting mixed magnesium oxide must be chosen in such a way that the particles which are 7-130 microns in size are 1 to 20%. For a mixture consisting of 70% of magnesium oxide produced in a rotary kiln and 30% of magnesium oxide produced in a muffle furnace, the coarse-grained particles produced in the muffle furnace are 44-5 150 µ large, constitute more than 3%.

When the particles (44 to 150 y) passing the 100 mesh screen but not the 325 mesh screen are present in an amount of 1 to 20%, the distribution of the particle size of particles less than 44 y does not matter. When the particle size is measured by the photo-deposition method, the weight of particles less than 3 y can be about 30% in the magnesium oxide calcined in a muffle furnace, while the weight amount can be about 85% of the magnesium oxide calcined in a rotary kiln .

The reason why coarse-grained magnesium particles have hitherto been avoided as an annealing separator is that the coated and dry steel strips after winding slip due to the coarse-grained particles and that the end surface of the coil assumes an irregularly compacted shape. However, the problems of irregular winding have been solved by the development of a centering apparatus which displaces the winding from the coil axis position to the edge of the coil and increases the winding voltage. If the tension is increased after the winding is displaced from the coil axis, a deformation in the form of a bend may appear as shown in FIG. 1. If, on the other hand, the voltage is low, the winding deforms to become flat 25 - see fig. 2. The bent part does not fit a non-coiling winding, while the flat-shaped winding is difficult to handle in connection with transfer to an annealing oven. However, it has been found that there is a correlation between the particle size of the separator and the bending or flattening deformation. When the particle size is small, a high winding voltage can cause bending. In addition, the voltage may affect the uniformity of the glass membrane. However, it has been found that a bend can be prevented and the glass membrane can be made uniform by using a large particle size separator and by applying a suitable winding voltage.

35 The reason that coarse-grained particles (44-150 y) have a great influence on the uniformity of the insulating glass membrane is likely that such coarse-grained particles act as spacers between the coil layers to maintain the interstices between the layers, resulting in 40 the uniformity of the atmosphere in the longitudinal and transverse directions on both sides is improved.

8 149307 When the coarse-grained particles (44 to 150 y) are suspended in water, they deposit faster than the fine particles. In connection with the embodiment of FIG. 3, a stirrer 2 must be arranged since the coarse-grained particles are deposited on the bottom of the slurry container 5 1. In this figure, the steel belt has the reference number 3 and the drying oven to the reference number 4. When high hydration particles are present in large quantities, however, the slurry container 1 is too large. A spray apparatus as shown in FIG. 3 is therefore preferable. In FIG. 4 has a spray nozzle reference numeral 5 and a collection unit reference numeral 6. In connection with this, a pump P. A drying furnace is designated 7, while the steel belt is designated 8. The coarse-grained particles (44 to 150 y) have a low hydration and adhesion to the steel band after slurry application and drying is low. However, if the content of the particles in the bounded size range is less than 20%, it is easy to maintain the adhesion by providing an adhesive such as methyl cellulose or active magnesium oxide which has good hydration properties in the slurry.

When the content of the coarse-grained particles exceeds 20%, the particles fall off upon contact with the transport rollers, even using the aforementioned agents, thereby improving adhesion. Accordingly, it is useless that the aforementioned particles be present in an amount greater than 20%. Thus, the upper gram for the presence of coarse-grained particles is 20%.

According to the invention, the amount applied is not limited in any particular way. Namely, the coarse-grained particles (44 to 150 µ) serve as spacers between the coil layers, thereby achieving the purpose to a lesser extent if only the magnesium oxide needed to form the insulating glass membrane is secured. Experiments showed that even at a magnesium oxide amount of 3 g / m on each side, a uniform 30 insulating glass membrane is obtained. However, the preferred range is 4 to 10 g / m when taking into account the safety of various handling and finances.

The starting materials for magnesium oxide may be magnesium hydroxide and basic magnesium carbonate, although magnesium hydroxide is preferred.

There have been several proposals concerning the particle size and purity of magnesium hydroxide to produce magnesium oxide to form a good insulating glass membrane. For example, the disclosure of Japanese Patent Application No. 14162/70 discloses that magnesium hydroxide having an impurity content of less than 0.2% and a particle size of less than 0.1 µ is preferred. These are the necessary requirements for the production of fine-grained magnesium oxide. According to the invention, no special requirements are made for the purity and particle size of the magnesium hydroxide, except the magnesium oxide mentioned in claim 1 can be obtained from this. Table 1 shows the content of the impurity in the magnesium oxide obtained by calcining magnesium hydroxide prepared from seawater or acidic or basic magnesium carbonate at a temperature of 1200 ° C in an oven.

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Magnesium oxide prepared from either magnesium hydroxide or basic magnesium carbonate contains a relatively large amount of impurities. According to the invention, good insulating glass membranes are obtained from these starting materials, containing the impurities, only in the amounts mentioned in claim 15.

The invention will be explained in more detail below with reference to the drawing, in which 1 is a sectional view of a coil with a bend, FIG. 2 shows a flat-shaped coil; FIG. 3 shows an apparatus for applying a soft annealing separator; and FIG. 4 shows an apparatus for spraying the separator.

The following examples serve to illustrate the invention.

Example 1

A 3.3% silicon-containing steel strip, with a thickness of 0.3 mm, a width of 970 mm and a length of about 250 m, was continuously soaked at 820 ° C for 5 minutes in an atmosphere consisting of hydrogen for 40%. s 25 and the remainder nitrogen at a dew point of 60 ° C. Magnesium oxide produced as the final annealing separator was prepared by the process, which will be discussed below in connection with Powder Nos. 1 to 6. In all cases, the degree of hydration of MgO was <8%. The tape was wound into a coil having an internal diameter of 508 mm. The resulting coil was placed in a muffle furnace at the coil winding axis perpendicular to the bottom of the furnace. The coil was then subjected to a final annealing at 1200 ° C for 20 hours in a hydrogen atmosphere to obtain the results shown in Table 2.

Powder No. ♦ 1.

Dried magnesium hydroxide was divided into grains, which were packed in an oven about 30 cm thick and shaken in air by a petroleum burner at 1300 ° C. The temperature at the surface was 1200 ° C and at the bottom about 850 ° C. The toasted sample was pulverized and classified by means of a classifier in the form of a so-called "micron separator", at a rotational speed of the rotor of 500 rpm. In the resulting magnesium oxide, the particles larger than 44 µ made up 0.2%.

Powder # 2.

Magnesium hydroxide was shaken in the same manner as previously described and powdered. The resulting particles were classified using a 100 mesh screen. In the resulting magnesium oxide, the particles larger than 44 µ, which did not pass the 325 mesh screen, accounted for 8%, and the particles larger than 150 µ, which could not pass the 100 mesh screen, 0.5 %. Thus, the size distribution of this sample is within the range of the invention.

Powder # 3.

15

Magnesium hydroxide was shaken in the same manner as previously mentioned and powdered. The resulting particles were classified by the micron separator at a rotor speed of the 85 rpm rotor. In the resulting magnesium oxide particles, the particles larger than 44 μ and which could not pass the 325 mesh screen ° 9, the Par_ 20 particles larger than 150 μ, and which could not pass the 100 mesh screen, 9%.

Powder # 4.

25 Basic magnesium carbonate particles were shaken in the same manner as previously described and powdered. The resulting particles were classified by the micron separator at a rotor speed of the 190 rpm rotor. In the resulting magnesium oxide, the particles that could not pass the 325 mesh screen were 6% and the particles that could not pass the 100 mesh screen were 0.5%. Thus, the size distribution of this sample is also within the range of the invention.

Powder # 5.

Basic magnesium carbonate particles were shaken by a rotary kiln at 700 ° C and pulverized. The particles that could not pass the 325 mesh screen made up 0.1%.

35 13 149307

Powder # 6.

Magnesium oxide in powder # 5 prepared from magnesium carbonate and magnesium oxide in powder # 3 made from magnesium hydroxide were mixed in a ratio of 9: 1. In this sample, the particles that could pass the 325 mesh screen were 2.5%, and the particles that could not pass the 100 mesh screen were 0.5%. Thus, the size distribution of this sample is also within the range of the invention.

The properties of the Insulating Glass Obstacles are shown in Table 2.

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