FR2481165A1 - PROCESS FOR MANUFACTURING PRODUCTS FROM POWDERS OF FERROMAGNETIC MATERIALS, DEVICE FOR IMPLEMENTING SAME AND PRODUCTS OBTAINED BY SAID PROCESS - Google Patents

Abstract

A method comprises mixing the powder for homogenization of its granulometric composition, filling in a capsule (8) with the powder, vibrocompacting the powder, subsequent heating the capsule (8) up to the sintering point of the powder, sealing the capsule (8) and its pressing. The granulometrically homogenized powder before filling in the capsule (8) is magnetized to ensure the formation of particle conglomerates and to exclude its classification. A device for implementation of the method comprises a mixing reservoir (1) provided with a shutter (5) of the discharging window (4) of the mixing reservoir (1), and further comprising a heater (9) of the capsule (8) and a press (10). The device is provided with an electromagnet (11) mounted near the mixing reservoir (1), whereas the mixing reservoir (1) and its shutter (5) are made of a non-magnetic material.

Description

 The present invention relates to powder metallurgy and in particular relates to a method and a device for manufacturing products from powders of ferromagnetic materials.

The invention can be used with the greatest dryness for the manufacture of products from magnetizable metallic powders in metallurgy and in mechanical constructions.

 In powder metallurgy, a technical solution has so far not been found to be sufficiently cool to give a uniform structure and isotropic properties to the material constituting the products made from powders of non-homogeneous particle size composition.

 We contact a technique for manufacturing products from metal powders which consists in kneading the powder in order to homogenize it from a particle size point of view, filling a mold with it, closing the mold hermetically, heating and subjecting it to pressing (see, for example, the description of the invention annexed to the author's certificate of URUS NO 417246).

The mixing operation of the powder makes it possible to distribute the particles in a relatively regular manner in the mass of the powder, whether these particles are large or small. Despite the fact that the products thus obtained are characterized by a relatively homogeneous structure of the material which constitutes them, the use of the technique in question poses a certain number of problems. In particular, the friable mass of powder has a low thermal conductivity and requires, for its sintering, a heating operation of a relatively long duration. In addition, the technique described does not allow a rational use of the useful volume of the mold.

 Another technique is also known for manufacturing products from powders of ferromagnetic materials, which consists in kneading a powder to homogenize it from a particle size point of view, in filling a mold, in compacting the powder in the mold by vibration, bring the mold to the sintering temperature of the powder, close the mold hermetically and then subject it to pressing (see L.Kh.Strokovsky et atl. 'Proizvodstvo bystrorezhuschei stali metodom poroshkovoi metallurgii za rubezhom " , sbornik wProisvodstvo zheleznykh poroshkov ", series 28, vypusk 1, M., Chermetinformatsia", 1973, pp 1-11).

To implement this method, use is made of a device comprising a mixing capacity with a valve in its unloading window. The mixing capacity is a structural steel drum, which steel is a magnetizable material. Below the valve is a vibrator carrying a platform for supporting the mold. The device further comprises a mold heater and an extrusion press.

 The undeniable advantage of the technology and the device in question lies in the reduced heating time during which the sintering of the compacted powder takes place. However, during the filling of the mold and, above all, during the compacting operation by vibration, there is a segregation of the powder into fractions. As a result, the structure of the material constituting the manufactured product is not homogeneous and the properties of said material are not similar throughout its volume, which significantly deteriorates the mechanical characteristics of the product.

 The invention therefore relates to a process and a device for manufacturing products from powders of ferromagnetic materials, the technology and construction of which would make it possible to give the powder properties protecting it against any fractions aggregation during filling. of the mold and during compacting by vibration of said powder.

 This problem is solved in that in the process for manufacturing products from powders of ferromagnetic materials, of the type consisting in kneading a powder in order to make it particle size distribution, in filling a mold, in compacting said powder by vibration , to bring the mold to the sintering temperature of the powder, to close the mold hermetically and to subject it to pressing, according to the invention the powder made of particle size distribution is subjected, before being introduced into the mold , to a magnetization. During magnetization, we see conglomerates of small and large particles of the powder. Thanks to the effect of remanent magnetism, these conglomerates remain intact during filling of the mold as well as during compacting of the powder by vibration. This excludes the segregation into fractions of the powder, which ensures the conditions necessary for the formation of 'a homogeneous structure of the material constituting the product to be manufactured.

A preferred embodiment of the method provides that, during the magnetization operation, the powder is placed for 0.1-0.5 minutes in a permanent magnetic field whose intensity is 1.103-2.104 A / m. These regimes are the most economical and ensure a sufficiently high quality of the material constituting the product to be manufactured.

The problem posed is also solved in that in the device for the manufacture of products from powders of ferromagnetic materials, of the type comprising a kneading capacity having a valve placed in its unloading window, a vibrator with a platform for support a mold, and being below said valve, as well as a mold heater and a press, according to the invention said device is provided with an electromagnet installed in the vicinity of the mixing capacity, said mixing capacity and its valve being made from a non-magnetizable or non-magnetic material.

 The device thus designed makes it possible to magnetize the powder in the kneading capacity in no contact of said powder with the electromagnet. The residual magnetism of the powder particles is not opposed to the introduction of these into the mold because the kneading capacity and the valve are made of non-magnetizable material.

It is rational that the electromagnet is placed below the mixing capacity. In this case, the distance separating the electromagnet from the powder is minimum, which corresponds to minimum energy expenditure to magnetize the powder.

 In order to facilitate the loading and unloading operations of the mixing capacity, it is rational for the device to include a member for approaching and moving away the electromagnet. The presence of the member in question makes it possible to bring the electromagnet into contact with the mixing capacity, the efficiency of the magnetization operation then being maximum.

 Another embodiment of the device is also possible and is characterized in that the member for approaching and distancing the electromagnet is produced in the form of vertical guides carrying a carriage on which 11 electromagnet is located, said carriage being connected to a back-to-back movement command.

 It is also possible to make the device so that the member for approaching and moving the electromagnet away is produced in the form of an upright with a horizontal pivoting arrow at the end of which the electromagnet is fixed.

Other advantages and characteristics of the invention will be better understood on reading the description which follows of various embodiments illustrated by the accompanying drawings in which
- Figure 1 is a general view of the device for implementing the method of manufacturing products from powders of ferromagnetic materials according to the invention (with cutaway and partial sections);
- Figure 2 shows an embodiment of the device comprising a member for approaching and moving away the electromagnet according to the invention (with cutouts and partial cuts);
- Figure 3 shows an embodiment of the device comprising a member for approaching and moving away the electromagnet according to the invention (with cutouts and partial cuts);
- Figure 4 shows an embodiment of the device comprising a member for approaching and distancing the electromagnet according to the invention (with cutaway and partial cuts).

 To implement the claimed process for manufacturing products from powders of ferromagnetic materials, use is made of a device which comprises a mixing capacity 1 in the form of a drum connected to a rotation control 2 (FIG. 1). The mixing capacity 1 is provided with a loading window 3 and an unloading window 4. In the unloading window 4 is provided a valve 5 below which is a vibrator 6 with a platform 7 to support a mold 8. The mixing capacity 1 and its valve 5 are produced, according to the invention, from a non-magnetizable material (for example, from stainless steel). The mold 8 is made of structural steel.

 In the immediate vicinity of the platform 7 is arranged a heater 9 for the mold 8 and a press 10.

 According to the invention, the device is provided with an electromagnet 11 placed below the mixing capacity 1.

 FIGS. 2, 3, 4 of the appended drawings represent different embodiments of the device comprising a member 12 for approaching and moving away the electromagnet 11.

 FIG. 2 represents an embodiment of the device in which the member 12 for approaching and moving away the magnet 11 is produced, according to the invention, in the form of vertical guides 13 on which is mounted a carriage 14 supporting the magnet 11 Lechariot 14 is connected to a return travel control.

FIG. 3 represents an embodiment of the device in which the member 12 for approaching and moving away the magnet 11 is produced, according to the invention, in the form of an upright 16 with a horizontal pivoting arrow 17 at the end of which is fixed magnet 11.

 FIG. 4 represents an embodiment of the device in which the member 12 for approaching and moving away the magnet It is produced, according to the invention, in the form of horizontal guides 18 on which is mounted a carriage 19 supporting the magnet 11 The carriage 19 is connected to a return movement control.

 The process for manufacturing products from powders of ferromagnetic materials is carried out in the following manner.

The ferromagnetic material powder (for example: structural steel powder) is passed through a sieve to separate the particles whose dimensions exceed 800 km. The powder with particles of 800, k m and less is introduced, through the loading window 3, into the kneading capacity 1, which is put into rotation to knead the powder and make it particle size distribution. Then the powder, made granulometrically homogeneous, is subjected to a magnetization by being placed for 0.1-0.5 min in a magnetic field with an intensity of 1.103-2.104 A / m. To this end, use is made of the magnet II by bringing it to the mixing capacity 1 using the member 12 (FIGS. 2, 3 and 4).

Then the magnetized powder is poured through the window 4 (FIG. 1) of the mixing capacity into the mold 8 placed on the platform 7 of the vibrator 6. The magnetized powder introduced into the mold 8 is subjected to compacting by vibration frequency 50 Hz and amplitude 0.5 mm.

 Then the mold 8 containing the powder thus compacted is heated, using the heater 9, to the sintering temperature of the powder. During the heating operation, the powder is degassed, after which the mold 8 is closed hermetically.

 Then the mold 8 containing the agglomerated powder is subjected to extrusion using a press 10 to obtain, for example rods of predetermined dimensions.

The powder thus sintered and pressed or compressed (targeted product) is then released from the material constituting the deformed mold 8.

 The products manufactured in accordance with the technology described after having undergone a heat treatment (quenching, tempering), are subjected to a metallographic analysis and to physico-mechanical tests in order to determine the resistance of the material to bending, the Rockwell hardness and toughness to shock.

In order to determine the bending strength of the material, samples are prepared from the products obtained in the form of bars whose dimensions are 6 x 6 x 50 mm and which are subjected to a heat treatment (quenching , triple income). The samples are subjected to bending in a special device made in the form of two supports spaced from each other at a distance of 40 mm and a punch placed between them and connected to a hydraulic press. Said supports and the working part of the punch have rounds of 15 mm radius for the supports and 7.5 mm for the working part of the punch.

 The sample is placed on the supports and subjected to bending, using the punch, until destruction.

The speed of movement of the punch is 0.1 mm / s.

When the sample is destroyed, the bending force deployed is read on the indicator of the press.

The flexural strength of the products is determined by calculations according to the formula 6 xf = 3Pl
flex. - = bh2 where: rf is the bending moment, kg.mm;
W = bh is the moment of resistance, mm3;
6
P is the bending force at the time of destruction
tion of the sample, kg;
1 is the distance between the supports, mm;
b is the width of the sample after destruction,
mm;
h is the height of the sample after destruction,
mm.

 In order to determine the toughness of the material at impact, samples are prepared from the products obtained in the form of bars, the dimensions of which are 10 × 10 × 55 mm and which are subjected to heat treatment (quenching, triple tempering).

 Said samples are tested using an impact machine, the pendulum of which performs an impact work equal to 30 kgm.

The pendulum strikes the sample until it is destroyed, after which, at the place of destruction, the area of the cross section of the sample is measured, and using the indicator the work of the pendulum shock is determined at the time of the destruction of the sample.

The toughness at impact is determined by calculations according to the formula = 7A kgm / cm2 where: A is the shock work of the pendulum at the time of
destruction of the sample, kgm;
F is the cross-sectional area of the sample
at the place of destruction, cm2.

 In what follows, several concrete but nonlimiting examples of embodiment of the invention are described.

Example 1
The products according to the invention are produced from a structural steel powder, the composition of which is as follows,% by weight: carbon -1.3, silicon-0.4, manganese-0.4, chromium- 4.0, nickel-0.4, tungsten-11.5, molybdenum-3.0, vanadium-3.0, cobalt-10.0, sulfur-0.03, phosphorus-0.03, iron- the rest . To this end, the powder particles whose dimensions exceed 800 mm are separated using a sieve. Then the powder with grains of 800> m and less is subjected to a kneading for 30 min in the kneading capacity in order to distribute its particle size uniformly. Then, the powder whose particle size is uniformly distributed is subjected to a magnetization by being placed in a permanent magnetic field whose intensity is 1.104 A / m. The magnetization operation continues 0.25 min, after which the magnetized powder is poured into a structural steel mold with a carbon content of the order of 0.2S / o, The mold is a cylinder whose diameter is 300 mm and the height of 600 mm.

Introduced into the mold, the magnetized powder undergoes compacting by vibration of said mold at a frequency of 50 Hz and at an amplitude of 0.5 mm. Three minutes later, the compacting operation of the powder by vibration ends and a cover with a tube is welded to the open end of the mold. Then the tube is placed in communication with a vacuum pump to produce inside the mold a vacuum of 10 2 mm Hg. Simultaneously, the mold is brought to 11500C and maintained at said temperature for 8 hours, during which s '' perform sintering and degassing of the powder.

 The degassing of the powder being finished, the tube is strangled in order to hermetically close the mold, and the place of throttling is welded. Brought to the aforementioned temperature, the mold and the powder contained therein are subjected to an extrusion which results in cylindrical rods of 100 mm in diameter.

The core of each rod is powdered metal (target product), its envelope being the deformed mold. The rods obtained are annealed at the temperature of 8500C for 4 hours and then cooled at a speed of 200C / min to the temperature of 500C, the operation being continued in air until room temperature.

So we remove the envelopes from the rods by turning.

 Thus obtained, the products are subjected beforehand to a heat treatment (quenching, tempering) and, then, to a metallographic analysis and to physicomechanical tests, these in order to determine the resistance of the material to bending, the Rockwell hardness and toughness to shock.

The results obtained are collated below
flexural strength, kg / mm ............... 260
Rockwell hardness, HRC ......................... 69
impact toughness, kgm / cm2 .................... 1.8
Similarly, products are made from a similar powder but without resorting to the magnetization operation, and these products are subjected to the tests mentioned. The mechanical characteristics of the two kinds of products being compared, the conclusion drawn is that the specific resistance is increased by 20 to 25%, on average, and the toughness at impact, by 30%.

Metallographic analysis shows a better homogeneity of the particle size structure of the material constituting the products obtained according to the claimed technology.

Example 2
Products according to the invention are manufactured from a tool steel powder, the composition of which is as follows,% by weight: carbon-1,2, chromium-4,2 nickel-0,4, manganese-0 , 4, silicon-0.4, tungsten-12.0, molybdenum-3.0, vanadium-2.2, cobalt-8.2, sulfur-0.03, phosphorus-0.03, iron - the rest. To this end, the powder particles whose dimensions are greater than 800 m are separated using a sieve. Then the powder is subjected to particles of 8002Xm and less to a kneading for 30 min in the kneading capacity in order to uniformly distribute its particle size. Then the powder, the particle size of which is uniformly distributed, is subjected to magnetization by being placed in a permanent magnetic field whose intensity is 1.104 A / m. The magnetization operation continues 0.25 min, after which the magnetized powder is poured into a structural steel mold with a carbon content of the order of 0.2. The mold is a cylinder with a diameter of 300 mm and a height of 600 mm. Introduced into the mold, the magnetized powder undergoes compacting by vibration of said mold at a frequency of 50 Hz and an amplitude of 0.5 mm. Three minutes later, the compacting operation of the powder by vibration ends and a cover with a tube is welded to the open end of the mold. Then put the tube mentioned in communication with a vacuum pump to produce inside the mold a vacuum of 10 mIn of Hg.

Simultaneously, the mold is brought to 11500C and maintained at said temperature for 3 hours, during which the powder undergoes sintering and degassing.

 The degassing of the powder being finished, the tube is strangled in order to hermetically close the mold, and the place of throttling is welded. Brought to the aforementioned temperature, the mold and the powder contained therein are subjected to an extrusion which results in cylindrical rods of 100 mm in diameter.

 The core of each rod is the powdered metal (product), its envelope being the deformed mold. The rods obtained are annealed at the temperature of 8500C for 4 hours and then cooled at the speed of 200C / min to the temperature of 500C, the cooling then continuing in air to room temperature.

Then we remove the envelopes from the rods by turning.

The products thus obtained are subjected beforehand to a heat treatment (quenching, tempering) and then to a metallographic analysis and to physicomechanical tests, these in order to determine the resistance of the material to bending, the Rockwell hardness and the toughness. to shock.

The results obtained are collated below
flexural strength, kg / mm2 270
Rockwell hardness, HRC .................. HRC 68
impact toughness, kgm / cm2 1.5.

 The conclusion drawn is that the resistance of the products obtained according to the claimed technology is increased, compared to the products obtained by the prior art, by 25% on average, and its impact toughness, by 30%.

Example 3
Products according to the invention are produced from a tool steel powder, the composition of which is as follows,% by weight: carbon-1.0, manganese-0.4 silicon-0.4, chromium-3 , 9, tungsten-6.6, molybdenum-4.8 vanadium-1.7, cobalt-4.8, sulfur-0.03, phosphorus-0.03 iron - the rest. To this end, the powder particles whose dimensions are greater than 800 km are separated using a sieve. Then the powder is subjected to particles of 800 m and less to kneading for 30 min in the kneading capacity in order to uniformly distribute its particle size. Then the powder, the particle size of which is uniformly distributed, is subjected to magnetization by being placed under a permanent magnetic field whose intensity is 1.103 A / m. The magnetization operation continues for 0.25 min, after which the powder. magnetized is poured into a structural steel mold with a carbon content of 0.2%. The mold is a cylinder with a diameter of 300 mm and a height of 600 mm.

Introduced into the mold, the magnetized powder undergoes compacting by vibration of said mold at a frequency of 50 Hz and an amplitude of 0.5 mm. Three minutes later, the compacting operation of the powder by vibration ends - and a cover with a tube is welded to the open end of the mold. Then said tube is placed in communication with a vacuum pump to produce inside the mold a vacuum of 10 -2 mm Hg. Simultaneously, the mold is brought to 11300C and maintained at said temperature for 2 hours, during which the sintering and degassing of the powder take place.

The degassing of the powder being finished, the tube is strangled in order to hermetically close the mold, and the throttling place is welded. When brought to the aforementioned temperature, the mold and the powder contained therein are subjected to an extrusion which results in cylindrical rods 100 mm in diameter.

 The core of each rod is powdered metal (target product), its envelope being the deformed mold. The rods obtained are annealed at the temperature of 8500C for 4 hours and then cooled at a speed of 200C / min to 5000C, the cooling then continuing in air to room temperature. Then we remove the envelopes from the rods by turning.

The products thus obtained are subjected beforehand to a heat treatment (quenching, tempering) and then to a metallographic analysis and to physicomechanical tests, these in order to determine the resistance of the material to bending, the Rockwell hardness and the toughness. to shock.

The results obtained are collated below
flexural strength, kg / mm2 ............ 300
hardness, HRC ............................... 68
impact toughness, kgm / cm2. 1.8
The conclusion drawn is that the resistance of the products obtained according to the claimed technology is increased by 25% compared to the products obtained by the prior art, and its impact toughness, by 30%.

Example 4
The products according to the invention are produced from a tool steel powder, the composition of which is as follows,% by weight: carbon-1.0, silicon -'0.4 manganese-0.4, chromium- 3.2, nickel-0.4, tungsten-9.0 molybdenum-4.0, vanadium-2.3, cobalt-8.0, sulfur-0.03 phosphorus-0.3, iron - the rest. To this end, the powder particles whose dimensions exceed 800> t m are separated using a sieve. Then the powder is subjected to particles of 800 h m and less to a kneading for 30 mX in the kneading capacity in order to uniformly distribute its particle size. Then the powder whose particle size is uniformly distributed is subjected to a magnetization by being placed in a permanent magnetic field with an intensity of 2.104 A / m. The magnetization operation continues for 0.25 min, after which the magnetized powder is poured into a structural steel mold with a carbon content of 0.2%. The mold is a cylinder whose diameter is 300 mm, and the height g of 600 mm.

Introduced into the mold, the magnetized powder undergoes compacting by vibration of the mold at a frequency of 50 Hz and an amplitude of 0.5 mm. Three minutes later, the compacting operation of the powder by vibration ends and a cover with a tube is welded to the open end of the mold. Then said tube is placed in communication with a vacuum pump to produce inside the mold a vacuum of 10 2 mm Hg. Simultaneously, the mold is brought to the temperature of 11300C and maintained at said temperature for 2 hours, at during which the sintering and degassing of the powder are carried out. The degassing of the powder being finished, the tube is strangled in order to hermetically close the mold and the place of throttling is welded. Brought to the aforementioned temperature, the mold and the powder contained therein is subjected to an extrusion which results in cylindrical rods of 100 mm in diameter.

The core of each rod is powdered metal (target product), its envelope being the deformed mold. The rods obtained are annealed at the temperature of 8500C for 4 hours and, then, cooled at a speed of 2O0C / min to the temperature of 5000C, the cooling then continuing in air to room temperature.

 Then we remove the casing of the rods by turning.

 The products thus obtained are subjected beforehand to a heat treatment (quenching, -return) and then to a metallographic analysis and to physico-mechanical tests, these in order to determine the resistance of the material to bending, the Rockwell hardness. and toughness to shock.

The results obtained are collated below
flexural strength, kg / mm2. 320
hardness, HRC, 67
impact toughness, kgm / cm2 ......................... 1.8
The conclusion drawn is that the resistance of the products obtained according to the invention is increased by 25 compared to the products obtained by the prior technology, and its impact toughness, by 30%.

Example 5
Products according to the invention are produced from a tool steel powder, the composition of which is as follows,% by weight: carbon-1.0, manganese-0.4 silicon-0.4, chromium -3 , 9, tungsten-6.0, molybdenum-4.8, vanadium-1.7, cobalt-4.8, sulfur-0.03, phosphorus-O, 03 iron - the rest.

 To this end, the powder particles whose dimensions are greater than 800 m are separated using a sieve. Then the powder with particles of 8003 m and less is subjected to mixing for 30 min in the mixing capacity in order to uniformly distribute its particle size. Then the powder, the particle size of which is uniformly distributed, is subjected to magnetization by being placed in a permanent magnetic field whose intensity is 1.104 A / m. The magnetization operation continues for 0.1 min, after which the magnetized powder is poured into a structural steel mold with a carbon content of 0.2%. The mold is a cylinder with a diameter of 300 mm and a height of 600 mm. Introduced into the mold, the magnetized powder undergoes compacting by vibration of said mold at a frequency of 50 Hz and an amplitude of 0.5 mm. . Three minutes later, the powder compacting operation ends and a cover with a tube is welded to the open end of the mold. Then said tube is placed in communication with a vacuum pump to produce inside the mold a vacuum of 10 -2 mm Hg.

At the same time the mold is brought to the temperature of 71300C and maintained at said temperature for 2 hours, during which the sintering and degassing of the powder are carried out. The degassing of the powder being finished, the tube is strangled in order to hermetically close the mold, and the throttling place is welded.

 Brought to the aforementioned temperature, the mold and the powder contained therein is subjected to an extrusion which results in rods of 100 mm in diameter.

 The core of each rod is powdered metal (target product), its envelope being the deformed mold. The rods obtained are annealed at the temperature of 8500C for 4 hours and then cooled at a speed of 2O0C / min to the temperature of 5000C, the cooling operation then continuing in air to room temperature . The casing of the rods is removed by turning.

 The products thus obtained are subjected beforehand to a heat treatment (quenching, tempering) and then to a metallographic analysis and to physicomechanical tests, these in order to determine the resistance of the material to bending, the Rockwell hardness and the toughness. to shock.

The results obtained are collated below
flexural strength, kg / mm2 ........... 310
hardness, HRC ....., ......................... 68 impact toughness, kgm / cm2 ........ .......... 1 ,.

 In an analogous manner, products made up of the same powder are produced and tested, but without subjecting the latter to magnetization. The mechanical characteristics of the two types of products being compared, there is an average increase in strength of 20 to 25%, and in impact toughness of 709r .;

 Metallographic analysis shows a better homogeneity of the particle size structure of the material forming the products obtained according to the claimed technology.

Example 6
Products according to the invention are produced from a tool steel powder, the composition of which is as follows,% by weight: carbon-i, 0, manganese-0.4 silicon-O, 4, chromium-3 , 9, tungsten-6.0, molybdenum-4.8 vanaditm-1.7, cobalt-4.8, sulfur-0.03, phosphorus-0.03 iron - the rest.

 To this end, the powder particles whose dimensions are greater than 800 m are separated using a sieve. Then the powder with particles of 800 t m and less is subjected to kneading in the kneading capacity for 30 min in order to uniformly distribute its particle size. Then the powder, the particle size of which is uniformly distributed, is subjected to magnetization by being placed in a permanent magnetic field whose intensity is 1.104 A / m. The magnetization operation continues for 0.5 min, after which the magnetized powder is poured into a structural steel mold with a carbon content of 0.2%. The mold is a cylinder with a diameter of 300 mm, and the height, 600 mm. introduced into the mold, the magnetized powder undergoes compacting by vibration of said mold at a frequency of 50 Hz and an amplitude of 0.5 mm. Three minutes later, the compacting operation of the powder by vibration ends and a cover with a tube is welded to the open end of the mold.

Then said tube is placed in communication with a vacuum pump to produce a vacuum of 10 2 mm Hg inside the mold. At the same time the mold is brought to the temperature of 11300C and maintained at said temperature for 2 hours, during which the sintering and degassing of the powder are carried out.

 The degassing of the powder being finished, the tube is stored and stored in order to close the mold hermetically, and the place of throttling is welded. Brought to the aforementioned temperature, the mold and the powder contained therein are subjected to an extrusion which results in cylindrical rods of 100 mm in diameter.

The core of each rod is powdered metal (target product), its envelope being the deformed mold.

The rods obtained are annealed at the temperature of 8500C for 4 hours and then cooled at a speed of 200C / min to the temperature of 5000C, the cooling operation then continuing in air to room temperature. The casing of the rods is removed by turning.

 The products thus obtained are subjected beforehand to a heat treatment (quenching, tempering) and then to a metallographic analysis and to physicomechanical tests, these in order to determine the resistance of the material to bending, the Rockwell hardness and the toughness. to shock.

The results obtained are collated below
flexural strength, kg / mm2 320
hardness, HRC ............................... 68
impact toughness, kgm / cm2 ................. 2.0
The conclusion drawn is that the specific resistance of the products obtained according to the claimed technology is increased on average by 25% compared to the products obtained by the prior art, and their impact toughness, by 35%.

Example 7 (negative)
Products are obtained in a substantially identical manner to that described in Example 1 and from a similar material. However, during the magnetization operation, the value of the intensity of the permanent magnetic field constitutes 1.102 A / m, which is less than the minimum limit claimed.

The results obtained by testing the products thus obtained are collated below
flexural strength, kg / mm2 ........... 180
hardness HRC .................................. 69
impact toughness kgm / cm2 .................. 1.1.

The above results show a decrease in the quality of the products, due to a segregation of the particles of the powder into particle size fractions when it is molded. This phenomenon is the result of the low degree of magnetization of the powder by the above-mentioned permanent magnetic field of intensity.

Example 8 (negative)
Products are prepared in a manner substantially similar to that described in Example 4 and from an identical material. However, during the magnetization operation, the value of the intensity of the permanent magnetic field constitutes 5.104 A / m, which exceeds the maximum limit claimed.

The results obtained during the tests of the products thus produced are gathered below
flexural strength, kg / mm2 .............. 320
hardness, HRC ............ 67
impact toughness, kgm / cm2 9 1.8.

 The above results show that the intensity of the permanent magnetic field used does not improve the quality of the products compared to that obtained by the claimed technology, while the energy expenditure increases unjustifiably.

Example 9 (negative)
Products are obtained in a manner substantially identical to that described in Example 3 and from an identical material. However, the magnetization operation only lasts 0.04 min, which is less than the claimed minimum limit.

The results of the tests to which the products thus obtained are subjected are collected below
flexural strength, kg / mm2 ............. 230 hardness, HRC ......................... ........ 68
impact toughness, kgm / cm ................... 1.2
The aforementioned results show that the chosen duration of the magnetization operation does not give the powder the necessary degree of magnetization, which causes the powder particles to segregate into particle size fractions when it is molded and, therefore, a deterioration of the properties of the products obtained.

Example 10 (negative)
Products are obtained in a manner substantially identical to that described in Example 2 and from an identical material. However, the magnetization operation takes 1.0 min, which exceeds the claimed upper limit.

The results of the tests to which the products thus obtained are subjected are collected below:
flexural strength, kg / mm2 270
hardness, HRC ..................... 68
impact toughness, kgm / cm2 ...... 1.5
The aforementioned results show that the chosen duration of the magnetization operation does not make it possible to improve the quality of the products compared to that which characterizes products obtained by the claimed technology, while the energy expenditure increases in a way unjustified.

The present invention can be used in particular in metallurgy and in mechanical constructions for the manufacture of cylindrical or shaped blanks, from magnetic metallic powders, for example based on structural or tool steels. In addition, the invention can be used for the production of various bi-metallic blanks. Said blanks are used for the manufacture of highly resistant cutting and stamping or stamping tools.

 Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means described as well as their combinations if these are executed according to its spirit and implemented within the framework of protection as claimed.

Claims (8)

 1.- Process for manufacturing products from powders of ferromagnetic materials, of the type consisting in kneading a powder to make it homogeneous from a particle size point of view, in filling a mold, in compacting the powder by vibration, in carrying the mold at the powder sintering temperature, closing the mold in a hermetic manner and compressing it, characterized in that the powder made homogeneous from a particle size point of view is subjected to a magnetization before being introduced into the mold.  2.- Method according to claim 1, characterized in that, to be magnetized, the powder is placed for 0.1 to 0.5 min in a permanent magnetic field with an intensity of 1.105 to 2.104 A / m. 3.- Device for implementing the method according to one of claims 1 and 2, of the type comprising a mixing capacity provided with a valve placed in its unloading window, a vibrator with a platform for supporting a mold, said vibrator located below said valve, as well as a heater for the mold and a press, characterized in that it comprises an electromagnet disposed in the vicinity of the mixing capacity, said mixing capacity and its valve being made of non-magnetizable or non-magnetic material.  4.- Device according to claim 3, characterized in that the electromagnet is disposed audessous of the mixing capacity. 5.- Device according to one of claims 3 and 4, characterized in that it comprises a member for approaching and moving away the electromagnet. 6.- Device according to claim 5, characterized in that the member for approaching and distancing the electromagnet is produced in the form of vertical guides on which is mounted a carriage carrying the electromagnet and connected to a forward movement control -return. 7. Device according to claim 5 characterized in that the member for approaching and moving away the electromagnet is produced in the form of an upright with a horizontal pivoting arrow at the end of which is fixed the electromagnet. 8.- Products in powders of ferromagnetic materials, characterized in that they are obtained by the process which is the subject of one of claims 1 and 2.