DE1209477B - Process for the pretreatment of powders, which are processed by pressing and sintering into molded bodies, in particular into magnetic cores - Google Patents

Description

Process for the pretreatment of powders by pressing and sintering to be processed into molded bodies, in particular into magnetic cores. The invention relates focus on the use of lubricants and binders for the manufacture of Molded bodies by pressing powders, in particular made of ferromagnetic material, such as powders made of iron, alloys, oxides, metal salts or ceramic or metal powders.

It is already known in powder metallurgy and in manufacture Ceramic products use substances that are used in the manufacture of molded articles serve as a lubricant and binder by pressing. These substances are subsequently more or less completely removed by a suitable heat treatment before the final sintering or heating is carried out.

It is known that the ohmic resistance of bodies made of ferromagnetic Material, from powders of alloys or powders of metallic oxides, for example of ferrites, the manufacture of which is an important part of powder metallurgy is of great importance. It has been found that most of the currently known Lubricants and binders cannot be used here because they are residues that are left behind chemically at high temperatures with the ferromagnetic material can react, whereby the magnetic properties are adversely affected.

According to the present invention, it is proposed that powders made of iron, alloys, oxides or metal salts, which are intended for pressing magnetic cores and, in general, metallic, ceramic or other powders from which moldings are made by pressing, hexylene glycol or 2- Methylpentanediol-2,4 CH ;, - C (OHCH3) - CH, - CHOH - CH, to be used as a binder in a mixture with a plastic material. Polyvinyl acetate, polyvinyl alcohol or nitrocellulose can be used as the plastic material. The mixture of hexylene glycol and one of these substances, optionally with the addition of a suitable solvent, acts both as a lubricant and as a binder. The additive leaves practically no residue after a suitable heat treatment which is sufficiently deep that no reaction with the powder material occurs, which is particularly important when it comes to magnetic material.

The addition of these substances by mixing facilitates the production of pressed bodies of complicated shape, such as. B. of L-shape, U-shape, of pot cores or other forms: in particular of cores, which have a different cross-section to have. This results in bodies in which the required angles are well maintained and the breaking strength of the pressed parts is much greater.

When using the substance mixtures mentioned, the process step omitted, in which the walls of the mold are previously covered with a lubricant had to make it possible to use an automatic press to produce parts from complex shape to be pressed in quick succession. The wear of the die will is decreased and the shape is kept in good condition.

In addition, through the use of mixtures of the substances mentioned With the help of a suitable solvent, the powder in the form of granules which is very suitable for pressing, especially if with a automatic press with several molds and several pressing operations pressed and the mold or molds are filled with a given volume, a process in which the powders must be in granulated form. The powder grains must have a diameter that is as uniform as possible to avoid the deviations. to keep the degree of filling low. They are also not allowed to clump together before pressing and must be sufficiently plastic, so that in the case of press pressures in the order of magnitude of 5 t per square centimeter or a little more a good connection between the individual Particle results in one another, so that after sintering homogeneous Body are preserved.

The solid residue of a syrupy liquid, consisting of 6010 polyvinyl acetate, polyvinyl alcohol and 9% hexylene glycol, dissolved in a mixture of acetone and methyl alcohol, is less than 0.30% after 4 hours of heating in air at 600 ° C.

The solid residue of a syrupy liquid composed of 5.5% nitrocellulose with about 13% nitrogen, 8% hexylene glycol and the addition of a volatile one Solvent like ethyl acetate, acetone, dimethoxymethane etc. is after 15 hours Heating in air to 220 ° C also less than 0.30 ° / o.

It is therefore possible to add this mixture in quantities to magnetic powders up to 60% of the weight of the powder can be added without affecting the magnetic properties change the finished product as described in Example 3 later and can be found in the associated table. In particular, the reduction in Permeability less than 16%.

Also, the cost of these substances is not very high, they also do not pose a physiological hazard and are not flammable, in the case of Solutions of mixtures of hexylene glycol with polyvinyl acetate or polyvinyl alcohol only very little.

These substances can advantageously be dissolved in the various solvents, such as. B. in water, acetone, methyl alcohol, etc., if it is a mixture of polyvinyl alcohol and hexylene glycol, in ethyl acetate, methyl alcohol, etc., if it is polyvinyl acetate and hexylene glycol, and in ethyl acetate, acetone and dimethoxymethane if it is Nitrocellulose and hexylene glycol. These solvents facilitate the addition of the substances to the powder by means of a mixer and, if necessary, also the granulation, in which the mixture is pressed through two sieves with different mesh sizes and the entire fine powder is returned to the mixer. in which Rp the alternating current loss resistance in the magnetic core of an induction coil in ohms, L the induction of this coil Henry, f the frequency in Hertz, N the number of turns of the coil winding, I the effective value of the current in the winding in amperes and lnm the average length of the magnetic lines of force in centimeters means.

The specified magnetic values refer to toroidal cores with the following dimensions: Inner diameter ............... 29.0 mm outer diameter. . . . . . . . . . . . . . 15.9 mm height ............................ 5.2 mm ie the core has a cross-section of about 0.33 cm2. The coefficient of the eddy current losses F., the hysteresis losses h and the after-effects losses t with respect to a closed magnetic circuit, for example a toroidal core, were measured under the following conditions: The coefficient of the eddy current losses Fn, expressed in ohms per henry for a frequency f = 800 Hz, was measured between 100 and 200 kHz at a field of 2 millioersted and a temperature of about 20 ° C. Example 1 A mixture of metal oxides (iron oxide, manganese oxide and zinc oxide) is ground in an iron ball mill with steel balls for 24 hours. The composition of the mixture before grinding in mol percent is as follows: 52.5 Fe2O3, 28.3 MnOl, a3, 19.2 ZnO.

0.10 /, calcium in the form of calcium carbonate is added to the mixture, that is 0.2 mole percent Ca0.

A mixture of hexylene glycol is added to samples of this powder mixture and polyvinyl alcohol with a mixed solvent of water and methyl alcohol added. The amount of hexylene glycol is 3 percent by weight of the powder mixture, and the amount of polyvinyl alcohol for the various samples is 1 and 2, respectively or 3 percent by weight of the powder mixture. All of these samples and one sample without Additives for comparison are pressed into rings and kept at 500 ° C. for about 15 hours heated and held at this temperature for a further 15 hours, all in one Furnace that is not closed off from the surrounding air. Then be the samples in the same oven at a temperature of 1235 ° C in a nitrogen atmosphere annealed with a small percentage of oxygen.

The results are shown in Table I. The permeability and the losses are defined as described below.

The permeability A is understood to mean the permeability that a field of 2 millioersted was measured, d. H. the "initial permeability" for a frequency of 800 Hz at 20 ° C.

The coefficients of losses used apply to a frequency of 800 Hz, a field of one ampere turn per centimeter and an induction of 1 henry at 20 ° C according to the following equation: 45 The coefficient of hysteresis losses h, expressed in ohms per henry for a field of and for a frequency f = 800 Hz, measurements were made between fields of 2 and 22 millioersted at a frequency of 800 Hz and a temperature of 20 ° C.

The coefficient of after-effects losses t, expressed in ohms per henry for a frequency f = 800 Hz, was derived from the ordinate of the curve in the origin for the field zero at a temperature of about 20 ° C.

The coefficients with which the quality of the material can be assessed, were additionally introduced and do not depend on the air gap of the magnetic circuit under consideration. The after-effects losses t are very low and could not be measured in practice.

Example 2 The toroidal cores were produced in the same way as this is described in Example 1, but the addition to the powdered and with 3% hexylene glycol mixed metal oxides consisted of polyvinyl acetate with a Melting point of 150 ° C and corresponded to an amount of 1 or 3%. As a solvent a mixture of acetone and methyl alcohol was used. The toroidal cores were heated to 400'C.

The results obtained are summarized in Table II. The after-effects losses t are very low and could not be measured in practice.

Example 3 The toroidal cores were prepared in the same manner as in Is described by way of example, but a mixture of Equal parts of nitrocellulose with 13% nitrogen and hexylene glycol in one Amounts of 1 or 3 or 6% of the mixture, based on the weight of the powder, are added. Acetone was used as the solvent. The toroidal cores were on for a few hours 140 ° C, then heated to 250 ° C.

The values obtained are given in Table III. The after-effects losses t were very low and could not be measured in practice.

Claims (1)

Claims: 1. Process for the production of moldings by Pressing and sintering a corresponding powder with the addition of lubricants and binders, in particular for the production of magnetic cores, characterized in that the powder a mixture of hexylene glycol and an organic plasticizer before pressing is added as a binder. 2. The method according to claim 1, characterized know draws that as powder metal oxides or metal salts, which are used for the production of ferromagnetic cores are used, 3. The method according to claim 1 and 2, characterized in that the powder is a mixture of iron oxide, manganese oxide and zinc oxide is used. 4. The method according to one or more of the preceding Claims, characterized in that the mixture contains a solvent for the additives is added. 5. The method according to claim 1 to 4, characterized in that polyvinyl acetate is used as the plastic material. 6. The method according to claim 1 to 4, characterized in that polyvinyl alcohol is used as the plastic material will. 7. The method according to claim 1 to 4, characterized in that as plastic Material nitrocellulose is used. B. Method according to one or more of the preceding claims, characterized in that the addition of hexylene glycol 3 percent by weight of the powder mixture. 9. Procedure according to one or more of the preceding claims, characterized in that the powder mixture is 3 percent by weight to be added to plastic material. Publications considered: German U.S. Patent No. 874,269; British Patent Nos. 675195, 729 538, 673 720; U.S. Patent Nos. 2,582,993, 2,886,530.