SU1719161A1 - Method of applying powdered coating on inner surfaces process for parts and apparatus for realizing the method - Google Patents

Abstract

The invention relates to powder metallurgy. The goal is to increase the productivity of the process and reduce energy consumption. The powder material is loaded into the part cavity, rotated around its own axis, heated from the outer surface of the part to the temperature of the beginning of sintering the powder material, and then heated from the inner surface of the part, and the mass of powder to be poured is calculated according to the proposed dependence. The device contains a clamping device, a rotation unit, an inductor connected to the HDTV generator through a switch and a switch with its power control unit, which contains two sections for heating the product from the outside and inside, and a mechanism for feeding the part to the Inductor. The heating power control unit may be connected to an inductor section serving to heat the part from the inside. 2 sec. and 1 z. p. f-ly, 3 ill., 1 tab. f Ј

Description

The invention relates to powder metallurgy. A method of applying powder coatings on the inner surfaces of parts is known, including loading the material into the cavity of a part, rotating it around its own axis, and heating HFC from the inside surface of the part. The device with which this method is carried out comprises a heat source, a rotational drive with a spindle and a clamping device. These method and apparatus allow to obtain powder coatings on the inner surfaces of the parts. However, they do not solve the problem of obtaining coatings from powders of ferromagnetic materials in connection with the fact that these powders, possessing ferromagnetic properties, in the process of heating as a result of the action of an electromagnetic field are attracted to the internal high frequency inductor and stick to it. In addition, in the coating process, the internal HDTV inductor is constantly in the heat-affected zone, which leads to its erosion and collapse.

The closest to the proposed method to the technical essence and the achieved result is a method of applying powder coatings on the inner surfaces of the parts, including loading

H

you sc

powder material into the cavity of the part, rotating it around its own axis, heating by high-frequency currents from the outer surface and isometric exposure. The device with which this method is carried out contains a heat source (external inductor) connected to an HDTV generator, a rotation unit with a drive and a clamping fixture. The data of the process and the device allow to obtain coatings from metal powders of ferromagnetic materials on the inner surfaces of the cylindrical parts in the sintering mode. However, the main disadvantage is the low productivity of the process, due to the fact that during the process a large amount of time is spent on heating the part, and the powder material of the coating is already heated from it. In addition, heating the part during the entire process requires additional energy consumption, which is also a significant disadvantage.

The purpose of the invention is to increase the productivity of the process and reduce energy consumption.

This is achieved by the fact that in the method of applying powder coatings on the inner surfaces of parts mainly from ferromagnetic materials, including loading the powder material into the part cavity, rotating it around its own axis and heating by high-frequency currents on its outer surface and isothermal exposure, heating by high-frequency currents from the outer surface of the part is carried out until the temperature of the beginning of sintering the powder material, and then heated by high-frequency currents from the inner the part surface, and the required weight dose mn of the powder material to be placed in the cavity is selected from the condition

mn 503 - rp I at (1 - 1.5 P0)

I

 . J2R-503X y - (1 -1, 5Po) (1 -Po),

J.0) ..

where I is the length of the part;

RP specific gravity of the powder material;

y is the specific conductivity of the powder material;

The initial porosity of the powder layer formed as a result of the rotation of the part before heating starts from the external surface of the part;

f is the frequency of high frequency currents when heated from the inner surface of the part;

fi is the magnetic permeability of the powder layer with porosity P0;

R is the radius of the inner surface of the part.

The formation of a coating on the surface of the parts, involving sintering and compaction by the centrifugal forces of the powder material, is most efficiently achieved with induction

heating directly - powder layer. This type of heating, considered by analogy with the transmission of electric current through the powder layer during electrical contact sintering of powder coatings, has the following advantages: high productivity and low power consumption of the process, the minimum heat-affected zone of the current on the part due to its induction

in the powder layer, etc.

It is especially important for induction heating and sintering of the powder directly, that its particles in the initial state are not strongly oxidized and have metal contacts in the form of adhesions or bridges between them before sintering, which creates conditions for the induction of high frequency currents in the powder layer. To fulfill the condition, i.e. It is proposed to introduce a preliminary indirect heating of the coating material in order to provide a metallic bond between the particles of the powder from ferromagnetic materials. For this, it is not the powder itself that is heated, but the part on the side of its outer surface, since during induction heating of the part on the side of the applied coating (inner surface) due to the influence of high-frequency electromagnetic fields

attraction and adhesion of the HDTV inductor of non-interconnected powder particles occurs. Therefore, heating of an HDF from the outer surface of a part with a ferromagnetic powder is carried out under the conditions of shielding the powder from the influence of the magnetic field of an HDTV by a metallic medium, which is the part itself.

In the future, upon completion of the preheating, the powder layer can be

irrespective of the part, sinter with its direct induction heating (subsequent heating).

The productivity of the process is increased by reducing additional

loss of time for heating to the sintering temperature of the compact part of the part (workpiece) powder and maintaining this temperature throughout the entire coating process.

Heating by high-frequency currents from the outer surface of the part is carried out to a low temperature — the temperature of the beginning of sintering the powder, after which the PMC is already heated directly from the inner surface to the temperature of its full sintering (0.7-0.9 TPL).

By the start of sintering, it is necessary to understand the minimum heating temperature at which electrical contacts between powder particles form in the form of adhesions or bridges. In addition, the powder layer must have the necessary mechanical strength. This temperature is determined experimentally, based on the specific properties of the sintered powder, for which the component with the ferromagnetic powder is rotated and heated by high-frequency currents on the outer surface side to a certain predetermined temperature. The fulfillment of the conditions for providing electrical and mechanical coupling between the powder particles is then determined. In this case, heating and rotation are stopped, the part is removed from the rotation unit, and the state of joint of the particles of the pre-sintered coating is evaluated, i.e. Whether the powder under test is poured out or forms a relatively strong porous carcass, after which the heating temperature is changed.

In the proposed method, the reduction of energy consumption is due to the fact that the compact part of the part (billet) is heated to the lowest possible temperature corresponding to the temperature of the start of sintering (preheating), and the cost of sintering the powder layer when it is directly heated by high frequency currents (subsequent heating) is determined by the necessary costs for sintering the used powder of the coating without energy loss for the forced heating of the workpiece.

Providing the minimum energy consumption associated with induction heating of the coating alone, regardless of the part, presupposes the determination of the optimal initial thickness h0 of the powder layer and the calculation of the corresponding weight dose of the powder mn. Since the induction of high frequency currents should occur directly in the powder layer, the thickness h0 of the layer by the time of the beginning of the induction subsequent heating should not be less than the thickness Sn of the skin layer

h0 Sn

(2)

It was established experimentally that the compaction of the powder layer during preheating practically does not occur, and the thickness of the powder layer n0 remains unchanged, the corresponding porosity does not change either.

The depth of the skin layer in heated HDTV porous powder materials is determined. For compact materials, the skin depth S is calculated using the formula

5,503

 I y df

(3)

where / l is the magnetic permeability of the heated HDTV material;

f- frequency HDTV;

y is the specific conductivity of the heated HDTV material.

The specific electrical conductivity of sintered powder materials upn depends on their relative density V or porosity L and is determined, for example, by the formula of V.I. Odolevsky

Up. y (1 -1.5P),

(four)

where P is the porosity of the metallic powder material.

To heat the pre-sintered powder layer with a thickness h0 and porosity. By the depth of the skin layer, Sn is determined after substituting formula (4) in formula (3) instead of y value. Then get

Sn 503

Have

one

(five)

 , y (1 -1.5 Po) - -f

Using condition (2) and expression (5), the required weight dose mn of the filling of the metallic powder material is determined.

The volume V0 occupied by the powder on the inner surface of the cylindrical part during its rotation can be represented as

V0 7T I h0 (2R-h0)

(6)

where I and R are respectively the length of the part of the radius of its inner surface.

Taking into account the porosity of the powder layer P0 and the specific gravity pn of the powder material, the weight dose of powder filling with thickness L0 is determined

mn - p I RP; h о (2R - ho) (1 - П0) (7)

In accordance with condition (2) and after substitution in (7) instead of the parameters of formula (5), to determine the depth of the skin layer Sn, an expression is obtained for choosing the required weight dose of powder

Cn 5: 503 7G / On I y (1 - 1.5 P0)

  / 2R -503 - (1 - (8) I 1

, -1.5 Po) 2} (1 -Po),

The proposed powder method is carried out as follows.

A weight dose of metal powder, calculated and selected using the condition (8), is poured into the cavity of the cylindrical hollow part. The part is mounted in the rotation assembly of the centrifugal induction installation and secured. Rotation of the part and its heating by high-frequency currents from the outer surface of the part by the external HDTV inductor up to the temperature of the beginning of sintering the powder material are turned on. During the rotation, the heating temperature of the part is monitored with an optical pyrometer. Upon reaching the desired temperature, the heating is stopped.

Not interrupting the rotation of the part after the heating is turned off by the external HDTV inductor, high-frequency currents are heated from the internal surface of the part by the internal inductor of the powder layer directly to the sintering temperature of the powder material.

At the end of the sintering and sintering of the powder layer, the heating by the internal inductor is stopped. The coating process ends after turning off the rotation and cooling the part.

The invention allows pre-sintering the powder layer by heating the part with the outer section of the inductor, and then finally sintering and sintering the powder with the inner section. To do this, use the switch to turn on the switch. The inductor section starts to work outside the part, then the whole part is heated, for which the sections are switched with an additional switch and switch and switched on

sections for heating the part inside. In this case, the subsequent sintering of the powder layer itself is performed only by the section for heating the part inside.

To transfer the part from the position of heating by the section of the inductor located outside the part to the position of heating by the section inside the part, the device has a mechanism for supplying the part to the inductor with

switches that are part position switches relative to each of the sections.

The device is provided with the possibility of adjusting the heating power, respectively, in each of the inductor section, for which an additional section can be connected to the control unit of the heating power.

Figure 1 shows the device, a general view; On fng.2 and 3 - schemes for implementing the method.

The device comprises a frame 1 on which a plate 2 is fixed, comprising

a guide bushing 3. In the latter, a housing 4 is mounted for movement, in which a shaft of a rotation assembly, made of coaxial sleeves, is located on bearings 5 and 6

7 and stem 8. A cup 9 is installed on the rod 8. The workpiece 10 is placed in it, in which a volume dose of ferromagnetic powder 11 is placed. To prevent the powder 11 from welding, asbestos pads 12 and 13 are placed on the upper and lower ends of the part 10 during heating.

A rotational drive pulley 14 (not shown) is fixed to the sleeve 7. In the lower part

the sleeve 7 is screwed with one end of the nut

15, which is elastically connected to the other end with the rod 8. Between the nut 15 and the rod 8, the elastic connection is made by the element

16 compensating for thermal expansion of the part during heating 10. Inductor

for heating consists of sections 17 and 18, which serve respectively for heating outside and inside the part. Their location relative to each other is coaxial. Each

from sections 17 and 18 are connected to an HDTV generator through switches, which are electrically controlled high-frequency contactors 19 and 20, which are connected to their respective part location switches 21 and 22. Limit switches are used as switches 21,22 in the device. They are mounted on the axis 23, which in turn is attached to the frame 1.

For the movement of the workpiece 10 from the inductor section 17 to the section 18, a feed mechanism is provided comprising a bar 24 fixed to the housing 4 with the possibility of joint movement. Lever 26 is attached to plate 24 by means of earrings 25, which, in turn, is fixed on frame 1. On plate 24, flag 27 is set, which, when axially moving upwards together with plate 24, alternately interacts with switches 21 and 22 to turn contactors on and off 19 and 20.

The device contains a heating power control unit 28 connected to an inductor section 17 and connected to an additional section 18.

At the top of the case. 4 is provided with a cover 29 in which a hollow abutment 31 is rotatably mounted in the bearing 30. An automaton 32 is provided for supplying power to the network.

The device works as follows.

Item 10 is installed in the cup 9. At the same time, the asbestos pads 12 and 13 are placed on the upper and lower ends of the part 10, a dose of metal powder 11 is poured into the cavity of the part 10.

Next, the rotational drive pulley 14 is not locked (not shown) and, using a screw gear, rotates the nut 15 and moves the rod 8 upward in the axial direction until the part 10 with the powder 11 is moved to the dock with stop 31 and it will not clamp (eat. Figure 2).

The circuit breaker 32 is turned on. The lever 26 attaches the bar 24 with the flag 27 to a position at which the contactor 19 connected to the outer section of the inductor is turned on by means of the switch 21 and the part rotation drive (not shown) is also turned on. The part is rotated and heated by the inductor section 17 to heat the part outside to the sintering temperature of the powder material.

 Upon reaching the required temperature, without interrupting the rotation, the upward movement of the device body 4 is carried out using the feeder. The contactor 19 is then disconnected. When moving upward, the part 10 leaves the inductor section 17 and is positioned relative to the section 18 (see FIG. 3). At the same time, the strip 24 with the flag 27 occupies a position where the contactor 20 is turned on by means of the switch 22. The heating of the pre-sintered

powder currents of high frequency sections 18 of the inductor for heating inside the part.

After the formation of the coating is completed, the automaton 32 is turned off, and thereby the heating by the HD section of the inductor 18, as well as the rotation of the component 10, is stopped. Using the lever 26, the device body 4 is moved to the initial position. The rotational pulley 14 (not shown) is locked. The screw nut 15 is unscrewed by part 10. The part is removed from cup 9 and cooled.

Example. The coating was applied to a sleeve with a length of I 32 mm, outer He and inner DBH 2, the diameters of which were respectively 60 and 50 mm.

The self-fluxing iron-based powder PR-X4G2R4S2F (TU-14-22-14-88), which is produced by NPO Tulachermet, was used as the applied powder material. The specific gravity of this powder was 7.8 103 kg / m3.

For induction heating of the sleeves, an LPCH lamp generator of the LPZ type 2-67 M, with a power of 60 kW and a frequency of f 63 kHz was used.

The heating was made by a two-section inductor consisting of a single-turn section for heating the part outside and two-stage heating inside. The heating temperature of the bushing was controlled using the APIR-C optical measuring complex.

The required weight dose mn of the applied powder material was determined according to expression (8).

The data for calculation are the following: pn p PR-X4G2R4S2F - 7.8–103 kg / m3; at PR-X4G2R4S2F 4 106 Ohm V1, At - 0.4;

  503 L: rp I y (1 - 1, 5П0 / i - f Г17 х {2R-503 у -. (1-1,5 Po)

1-1 / 2

-3.

v2

(1-n0) 503 3.14 7.8- 3.2-1010 -10e (1 -1.5-0.4) -163- 103 x (1-0.4) x {2 5 -ten

-2

-503 1

10 (1-1.5-0.4)

63} 7.2 kg

Taking into account the allowance for the subsequent machining after obtaining the coating, the initial thickness of the powder layer h0 was set equal to 2 mm. The weight of the powder was found from the expression (7), which in this case amounted to mn 0, kg. Verification of the calculation results was performed using formula (5) to determine the depth of the skin layer Sn with the same initial data and compared with a given thickness h0.

Sn-503 (1-1,5no) -f 2

v3

10 3m.

-1,584 h0 2

The selected weight dose mn - 0.92 kg of powder was poured into the cavity of the hardened sleeve and secured in the fixture of the rotating unit of the proposed device.

The part was heated by high-frequency currents by a section for heating the part from the outside to the temperature of the beginning of sintering of the PR-X4G2R4S2F powder, which was previously determined and was 600 ° C.

Then they were heated by the section for heating the part inside to a temperature determined on the basis of 0.7-0.9 Tpl.pr-X4G2P4S2F. At a specific value, the temperature was 1100 ° C with an isothermal holding time of 10 minutes. The choice of the heating temperature of the applied coating, for example, when heating the high-frequency powder directly with the powder layer (internal inductor) is determined primarily by the sintering and melting temperature of the powder coating (0.7-0.9 Mp.powder). Hence the choice, which is a compromise between the sintering temperature and the lowest possible isothermal exposure. This takes into account the quality of the coatings produced.

At the end of the coating process, the powder layer on the inner surface had a thickness h of 1.3-10 m.

Similar studies on the implementation of the proposed method were carried out on powders, for example, ПЖРВ2 or ЖГрЗ. The results on the effectiveness of the method differed little from the powder material given in this example. The ferroalloy powder PR-X4G2R4S2F, possessing the highest physicomechanical properties as a reinforcing material, can find wider application in the national economy. .

The results achieved in the research process are presented in the table.

Invention Formula

Claims (3)

1. A method of applying powder coatings on the inner surfaces of parts mainly from ferromagnetic powder materials, including loading the powder material into the part cavity, rotating it around its own axis, heating with high frequency currents from the outer surface of the part and isothermal exposure, which , in order to increase the productivity of the process and reduce energy consumption, heating from the outside the surface of the part is brought to the temperature of the start of sintering of the powder material, after which the high-frequency currents are heated from the inner surface of the part, moreover, the material to be filled is selected from the condition tp 2: 503 k -rp I y (1 - 1.5 P0)  -.2P-503X |; y (1 -1, 5П0) (1-Po), where I is the length of the part, m; RP - ud. weight of powder material, kg / cm3; y is the specific conductivity of the powder material, m 1; Porosity of the powder layer, resulting from the rotation of the part before the start of heating; f is the frequency of currents when heated from the inner surface of the part, kHz; ft is the magnetic permeability of the powder layer with porosity P0; R is the radius of the inner surface of the part, m 2. Device for powder coating on internal surfaces parts mainly of ferromagnetic powder materials, comprising a clamping device ;, a rotation unit, an inductor for heating the part outside, connected to a high frequency current generator through a switch and a switch, with a unit for adjusting its power, and a mechanism for supplying the part to the inductor, characterized in that in order to increase productivity and reduce energy consumption, it is equipped with an additional switch and a switch, and the inductor is made with an additional section for heating the part inside, connected constant generator to a high frequency current through the additional switch and additional switch. 3. The device according to claim 2, characterized in that the heating power control unit is connected to an additional section of the inductor. (jit / S.I 32 Network " gg l L is long; , item but J / 30 I Kpereklyucha- lgslo poses. Zz 2