SU1759551A1 - Method of isostatic pressing of powder shaped articles - Google Patents

Description

The invention relates to powder metallurgy, in particular, to isostotic pressing methods for predominantly refractory products made from powdered mass.

The known method allows the simultaneous production of several products from a powder mass with a hard-fitting part, which consists in filling the mold with mass, vibrating it, sealing the mold, removing air from the mold by evacuating the mass and pressing first with unilateral overpressure. , 6–0.8 atm (0.06–0.08 MPa) on the fitting, and then with a comprehensive static pressure on the whole mass.

This method allows to improve the quality of the shaped part of the product.

The disadvantage of this method is that the evacuation is made difficult by the resistance of the upper mass layer filling the mold and its drains, whose irregularities (projections or sinuses) prevent air from escaping.

The indefiniteness of the shape resistance eliminates the guarantee of the reliability of the vacuuming process, the likelihood of pressing air in the mass and obtaining a defect in the form of otkopoz or cracks of the shaped part after pressing, which limits the ability of the method, i.e. laziness products with a shaped head in the form of a sphere or a cone, facilitating the removal of air.

A known method of manufacturing shaped articles from a powder mass by cold isostatic pressing,

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This includes filling the elastic mold with powder and applying pressure of the working medium (material with open pores) to the pressure on its iron surface. Before carrying out isostatic pressing, the vacuum acting on the outer form is removed, and the internal cavity of the elastic form is connected to the eac / world system.

This method allows the manufacture of any shaped articles. However, the mass is evacuated through the entire volume of the product in height, for the GI vacuum area is ruined by the size of the hole of the vacuum wire with its direct contact with the mass; no complete sealing of the mold is also provided. As a result, in the process of pressing, it is possible that the shell encapsulates not only air from the mold, but also a powdery mass, which breaks the vacuum system, which complicates the vacuuming process and leads to an increase in the waste of products.

The closest to the proposed method is the manufacture of products from powder by isostatic pressing, including filling the mold with mass, compacting, sealing the mold, evacuating and applying pressure of the working medium.

The disadvantage of this process is that the evacuation process is complicated by the resistance of a thick mass layer that fills the mold and depends on the size and configuration of its cavity. At the same time, the likelihood of pressing in air — the mass increases with the size or number of simultaneously acoustically shaped forms and the presence of n), 1x irregularities, protrusions, or sleeves. This leads to an increase in the production of products for the reject fraction of spalls and cracks in complex shapes: due to the destruction of the raw material compressed in the mass (with air when the pressure of the working fluid is released).

The aim of the invention is to reduce the waste of products.

To do this, in the method of isostatic pressing of shaped articles from powders, mainly refractory, including filling the cavity of the elastic shell with powder, evacuating the cavity and applying an isostatic working pressure to its surface, applying pressure equal to 0.15-17% of the working pressure before its evacuation. and reset

The application and release of pressure is carried out repeatedly by the value of 0.15-10% of

operating pressure and with a frequency of application and discharge of 0.2-2 times per second with simultaneous evacuation.

The proposed process of manufacturing products by isostatic pressing ensures at the initial stage of pressing the formation of a free gap between the elastic walls of the mold and the mass molded in it, which allows you to freely remove air from the mold by evacuating it regardless of size and configuration over the entire area. surface of the product. Experimentally determined values and mode of application of low pressure at the initial stage of pressing ensure the stability of the formed mass, reducing the waste rate of products.

The drawing shows a mold with a powder mass in it, a slit. The half of the diagram on the left of the axis depicts the pressing process, the right is the process of evacuation. The solid arrows to the left of the axis show the application of pressure of the working medium at the initial stage of pressing. The dashed arrows to the right of the axis show the removal of air from the mold.

A mold for carrying out the proposed method consists of a perforated matrix 1, an elastic sheath 2, hermetically clamped bottom 3 at the bottom and top of the flanges 4, forming the mouth of the mold for filling the powder mass. The flange is made with a channel in which the valve 5 is integrated, connected to the vacuum line 8. The mold is also provided with a cap 7 with an elastic membrane 8 and a flexible plug 9 that ensures the formation of the head part of the product.

The proposed method for the manufacture of articles from powdered mass by isostatic pressing is carried out as follows.

First, the powdered mass 10 is poured into the mold through its neck. At the same time, the elastic elements of the mold copy the outlines of the product. This is achieved by using either a profiled shell 2, for example of polyurethane, or by creating a vacuum from the outer surface of the rubber shell 2, stretching it until the walls of the matrix 1 are completely enclosed in a vacuum chamber.

The mass poured into the mold is vibrated, subjecting the mold to an HS dibration stand (not shown). Then a movable elastic stopper 9 is installed in the throat and hermetically sealed.

cover 7. On this process weed, and the mold to the PP-RSGM nm. About ochkapchchsZ - ate.

Then successively r.-yuecrtiqioi isostatic light pressing. .L, 1,1, this pros -sbep iv placed about. a rep-ie .i, j by closing, kschmeyn & p or izostat chamber, where the mass per l / g ps- / | с - “Whose goal is the all-pervading oij tich. By imposing an overpressure of the working medium (liquid or air), the process was carried out by means of pressure in the range of 0.15-17% of the pressure of the press. Under the action of the pressure of the working medium, obolik 2, membranes 8 and i RPO. 9 are mixed to the center of the press of the farm, a powdered mass slmmo contained in it. The supply of the well-maintained tire was performed at a constant pressure. However, the air mass, air,; cb / et ng elggichnuke casing, cork i D / af, agmu, displaced and from the molded mass. In this part of the guzdu / s allocates, hz mchsgy and ZAFOLNYART free space between the elastic Gress-Fogm and the sun mass The formation of the mass occurs due to the presence of non-absorbing moisture. Dalg-karapgorloviny molds are connected with in kumunomay- and play 6, open 5 and remove the air from the PS-form. When this happens, the mass is evacuated almost simultaneously along its entire surface through the entire volume of the transverse chaprepeak at the least resistance of air through the porous wall of the seal to the right of the axis) vacuum in the line, due to the resulting free gap, corresponds to the vacuum in the cavity of the mold, as a result, the process is controlled and the mass is evacuated. Due to soto, air flow suction occurs immediately over the entire volume of the molded mass through its porous walls, the surface area of which is larger than the cross-sectional area, i-accuracy of the vacuum process increases, and the vacuum time decreases On the other hand, the porosity of the compacted MdCCb is less therefore, the amount of air in the pores is much less, since part of it after compression of the mass is released into the gap between the shell and the formed mass and is almost instantly removed through valve manifold due to the relative smallness of the gap equal to the shrinkage of the powder in the initial pressing stage small excess pressure.

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.as1-- rnn rozatip at the stage of press soyenpee to the working pressure. If it is more than 17% of its work, the likelihood of rezuch RZ increases due to the formation of a spiked icibi-iorc heading and increased the amount of splitting and greshgchem head part, because of the strength from the pressure of the compression unit. on the working environment of the L-soastat. The optimal value of pressure in the initial stage of pressing is about 0.15-17% of

5 the worker provides the stability of the molded mass and its strength, when comparing with the bottom contour ps, the strength allowing the removal of not air without destroying the end mass.

0When the mass is compressed by a small crush

- working environment such as compressed air,

The optimum wellness of excess dvleig can be from the working

pressure with a frequency prleshchenich and discharge

5 pressure 0.2-2 times per second. The preferred combination of pressure and frequency of its application is lower pressure and greater frequency. With less pressure reduction and a lower frequency of application

0 pressure mass in the mold is sprayed (not molded) and the reliability of the vacuum vacuum process is reduced. Poi pressure reduction, greater than 10% of the worker, vozzht- kgk1t the difficulty of creating a pulsating

5 modes in the isostat chamber and the complexity of incorporation into the vacuum mastrel The upper limit of the frequency is limited by the inertia of the system, in particular, the epastmic shell wall and the lid of the cover.

It is advisable to carry out the evacuation of mass P in the mode of pulsating reduction, for example, with the help of a three-way valve with an actuator. At the same time, the isostat chamber, where the molds are installed, is alternately connected to a pressure source, for example compressed, and then to the vacuum line of the IMS they discharge excess pressure to the atmosphere. In this case, clath1; the neck of the press-foo vu-1 tselesobrl

Into the position of connection of the cavity of the mold with the vacuum main for all the time of action of the pulsating dachlenshage of annealing.

Consequently, with a frequency of pulsating pressure, the mass is periodically subjected first to isostatic compression by the elastic elements of the mold, and then, when the excess pressure is removed, the elastic elements are resilient by force and air pressure in the mass to the initial state. vacuum outside the mold. Due to the compaction of the compacted mass, as well as the knitting of the binder in it, it does not scatter during the pulsating mode of pressing and forms a stable shape, copying the relief of the inner surface of the matrix 1, during periods of excessive pressure of the press between the elastic elements of the mold and the formed a mass forms a free space-gap, which ensures the free removal of air from the mold. Thus, in the pulsating mode of compression, the air is mainly removed from the mold in pauses during the release of pressure, when the resistance to evacuation is minimal,

After pre-compression with a low pressure (single or multiple) and vacuuming, the pressure in the isostat is increased to a value that provides the product with the required density. At the same time, the elastic shell 2 and the plug 9 under the action of uniform pressure are pressed against the surface of the molded mass, without disturbing its shape, compressing the mass by the workers of the medium 1, making it further compacted to the finished product. After the overpressure has been released, the mold is degenerated, the cover is removed, and the compressed products are removed.

PRI me R. At the Bogdanovichsky refractory plant, pilot testing of corundum-graphite complex-shaped products was carried out using the proposed method.

Monoblock stoppers and submersible glasses for tundish machines for continuous casting of steel billets were pressed, the Corundograficite mixture contained finely ground fractions of corundum, silicon, clay, and also graphite and other components. Technical lignosulfonate was used as a binder. The humidity of the finished powder mass is 1.5-3%.

Hollow monoblock-stoppers with a height of 1150 mm, an outer diameter of 130 mm, a wall thickness of 42-45 mm and a 35 mm MgSoy with a contoured shaped cone-shaped part were made in three- and four-shaped cassettes.

Submerged empty glasses with a height of 700 mm, with a variable thickness of the stack from 15 to 40 mm, weight of kg with a shaped annular ledge in the middle part of 12-15 mm, a diameter of 170 mm and a width of 120 mm, with a shaped head part with a diameter of 130 mm Four and four cassettes. In addition, molds for the manufacture of immersed glasses contained inserts for the formation of cavity-holes, an opening 5 mm in diameter was made at the neck of each form of the cassette, which was blocked by a valve 5 to connect the form with a vacuum / smart main line

A cassette with molds was placed in a vacuum chamber mounted on a stand. A vacuum was created in the vacuum chamber by connecting it to a vacuum line, the remaining air pressure in which was not more than 0.01 MPa, while the elastic shells. molds pressed against the walls of the matrix 1, a copy of the shape of the cavities of the forms. After this, the molds were loaded with a powdery mixture. Then, for 30–35 s, the vibrostand was turned on and the mass was vibratedly compressed from the molds. Shake table turned off. Elastic plugs 9 were installed in the throats of the molds to form the head shaped parts of the products. Then the molds were hermetically sealed with a lid and 1 with elastic membranes 8 and the cassette with molds was placed in a hydrostat container, where successive pressing was performed.

At the initial stage of pressing, the excess pressure of the liquid in the hydrostat container was raised to 6 MP (b% of the operating pressure of the press pump 100 MP) until the evening. After that, the overpressure was removed, the container sealing cap was opened, the vacuum line was connected to the valve fittings of the molds and, opening the valves, the masses were evacuated to a residual pressure of 0.05 MPs for 40- 60 seconds (less time for single and three-shaped cassettes). Then the valves 5 were closed, the vacuum line was turned off, the hydrostat container was closed, and the final compression was carried out mass, the pressure of the fluid in the container was increased to 100 MPa, corresponding to these factors.

After pressing, the mold cassette was removed from the hydrostat container. The molds were unsealed, removed the crumbs 7. Elastic plugs 9 were removed, and then the pressed products were removed from the molds. Chips of the head of the parts were absent, the surface quality of the raw material and its dimensions corresponded to the current requirements. After the necessary machining of the raw material, the products were dried to a residual moisture content of 1%, glazed and burned. The quality of the finished products corresponded to the mechanical conditions according to TU 1-1-8-371-81 Monoplock stoppers, refractory corundum graphite for continuous casting machines and TU 14-8-578-89 Products of medium refractoriness. Immersion cups hers-phytosteric for steel casting.

The vacuum time of the molds for the production of monoblock stoppers according to the current technological instruction was 5-8 minutes to a residual pressure of 0.15 MPa. At the same time, the failure rate for the head part spalling was 3-5%. The evacuation time of press molds for the production of poguezha glasses for single molds is 1B 20 min, and the four-mold cassette is up to 40-50 min. At the same time, the damage rate for the head part was split by 30% due to the complexity of the forms. Thus, together with the elimination of defects in the splitting off of the head part, an additional effect was achieved - reduction of the evacuation time. Taking into account the time of the additional operation - pre-reduction of the mass, the gain in reducing the production cycle in the manufacture of monoblock stoppers was 10-20% and immersed cups 4-5 times with the guarantee of obtaining suitable products.

A significantly greater reduction in the production cycle was achieved during the first stage of pressing in the pulsed mode of applying an overpressure.

For this cavity, the lids of the molds loaded with the charge and fixed in the vacuum chamber were connected to the cavity of the vacuum chamber, which is connected through a three-way valve to the compressed air line, discharged into the atmosphere and the vacuum main with a residual vacuum of 0.01 MPa. The valves of the molds at the same time for all the time of pulsating reduction were connected to the vacuum line with a residual pressure of 0.015 MPa. By turning the knob

alternately applied air overpressure of 0.2 - 0.25 MPa (0.2-0.25% or working pressure) to the mass through the shell 2. membrane 8 and npoGkv, g - overpressure release into the atmosphere and vacuum chamber in the chamber with Frequency 0, 3 times about a second in those “90 seconds. After the CLSG / us, 5 molds were closed and the GH was disconnected from

the vacuum line, and the cavities of the lids were disconnected from the vacuum chamber, Kassztus was removed by the press molds and a vacuum chamber was placed in the hydrostatic container, where the second stage of pressing was carried out

operating pressure 100 MPa. The dimensions of the pressed products met the technical requirements. Marriage on the head part was absent, and the time of the technological cycle of production of products was reduced and coincided with the time.

application of pulsating crimp. With

In this process, vacuuming is practically

did not depend on the configuration of the molds.

The proposed method for the manufacture of products from a powdery mass by isostatic pressing makes it possible to reduce the scrap of products due to the fact that evacuation of the mold produces an equal amount of compression of the mass by repeated or

by the repeated application of a small overpressure (fraction of the working pressure of the extrusion), when free mass is formed in the mold for the shrinkage of the mass, allowing unhindered

air removal and charging all over the mass. This is facilitated by the optimal value and mode of initial static reduction, ensuring the stability of the molded mass,

Claims (2)

1. The method of isostatic pressing of shaped articles from powders, mainly refractory, including filling the cavity with elastic powder, evacuating the cavity and applying isostatic working pressure to the surface of the elastic shell, due to the fact that, in order to reduce the defectiveness of products, before evacuating The OLT exerts an application of pressure equal to 0.15-17% of the worker and its discharge. 2. Method of pop, 1, characterized in that the application and discharge of pressure is carried out repeatedly by a value of 0.15% to 10% of the working pressure and with a frequency of application and discharge of 0.2-2 times per second with simultaneous evacuation.