Procedure for strenghtening edges of work members of tillers

FIELD: machine building.

SUBSTANCE: surface of back side of edge is heated with electric arc of reverse polarity by means of carbon electrode and successively cooled. Also, the electrode is transferred along a curvilinear trajectory formed with linear transfer along a sharp edge and with a rotation around vertical axis. Angular speed of electrode rotation is determined from the ratio: 3 V/R < w < 9 V/R, where w is angular rate of electrode rotation, rad/s; V is velocity of linear transfer, m/s, R is radius of electrode rotation, m. Arcing is carried out under a pulse mode. Duration and amplitude of current pulses per one revolution of the electrode is increased at moving away from the sharp edge and is decreased at approach to it.

EFFECT: obtaining strengthened layer with alternate cross section facilitating edge self-sharpening.

8 dwg

 

The invention relates to agricultural machinery, in particular to the manufacture of operating tillage machinery.

There is a method of hardening metal surfaces by RF patent 2025509, MKI SS 8/22, publ. 30.12.94, bull. No. 24, in which the surface temperature of the electric arc reverse the polarity of the carbon electrode to the melting temperature and subsequent cooling to temperatures of phase transformations, in which the plastic deformation of the surface of a cooled tool. To increase the hardness to HRA78-80 (HRC 52-58) the product is subjected to cold treatment.

The disadvantage of this method is that when the hardening of the blades of the working bodies of tillage machinery plastic deformation produced after melting and cooling to the temperature of phase transformations, violates the geometry of the bimetal blade, which leads to violation of the terms of samosatene, which is ensured by the presence of unilateral hard wear-resistant layer in conjunction with soft base of the working body. Another disadvantage is that the cold treatment requires additional refrigeration units, which leads to additional costs and increase the value of tillage machinery.

The closest in technical essence and the achieved is the result (the hardness of the hardened layer HRC 58-60 in conjunction with soft base HB 140-160) is the method according to A.S. 1171538, MKI C21D 5/00, publ. 07.08.85, bull. No. 29, Varan for the prototype, in which the reinforcement is subjected to a surface of the back side of the blade of the plow blade by heating with an electric arc reverse polarity of the current 180-200A using a nonconsumable carbon electrode with a diameter of 8-10 mm and subsequent cooling speeds of 400-500°C/s, for example, flowing water.

The disadvantage of this method is the low degree of stabilization of the profile of the blade wear due to the impossibility of obtaining on the edge of a blade of solid layer thickness, provided the conditions samosatene, as with a uniform burning electric arc melting the edge of the blade is much more intense than the melting of the thickened part, which leads to the cross-melting metal and the disappearance of the soft layer on the tip of the blade.

It is known that the main conditions of samosatene bi-metal blades are the following dependencies (Wear and increase durability of parts of agricultural machinery. Tkachev VLADIMIR. "Engineering". M. 1971. Str).

The thickness of the soft layer is determined by dependence

where δ - the thickness of the soft layer,

δm is the thickness of the solid layer,

km is the coefficient of strength of solid layer of 1.0 to 1.8.

The hardness of the hard layer is determined by dependence

where Hm is the hardness of the hard layer,

Nm - hardness of the soft layer,

k=3-5 - coefficient depending on the abrasive properties of the soil.

From the above it follows that if the condition Hm=3-5 Nm in a known way, the condition δ=1-1,8 δm, fails because with a uniform distribution of energy of the electric arc on the treated surface or at the edge of the blade is missing soft layer, or thickened portion of the blade thickness of the soft layer is more desired. Thus, stabilization of the blade wear is disturbed, which leads to a sharp increase in traction resistance and villablino tillage tools.

The technical effect is to increase the degree of stabilization of the profile of the blade working bodies tillage machinery in wear by creating a solid layer having a cross section providing conditions samosatene.

This technical effect is achieved by the fact that in the proposed method, including heating the underside of the blade arc reverse polarity using carbon electrodes and subsequent cooling, according to the invention the hardening produces a pulse current, a moving electrode is produced along a curved path formed by the line p is ramieniem parallel to the edge with a speed V (m/s) and rotation around the vertical axis with radius R (m) and angular frequency w (rad/s), the value of the corner frequency is within the range determined from the ratio of 3V/R < w <9V/R, and the duration and amplitude of the current pulses for one revolution of the electrode increases with distance from the edge of the blade and decreases when approaching him.

Comparative analysis of the prototype allows us to conclude that the claimed method differs in that the movement of the electrode over the surface of the blade is produced along a curved path formed by the linear movement parallel to the edge of the blade and the rotation around the vertical axis with an angular frequency, determined from the ratio of 3V/R < w < 9V/R, and that hardening is produced by a pulsed current, with variable duration and amplitude of pulses during one revolution of the electrode, the magnitude of which increases with distance from the edge of the blade, and decreases when approaching him.

Thus, the claimed technical solution to meet the criteria of the invention of "novelty."

To verify the conformity of the invention the term "inventive step", the applicant conducted an additional search of the known solutions to identify signs that match the distinctive features of the prototypes of the features of the proposed method and device. The search results showed that the claimed invention does not follow for professionals explicitly known ur is VNA equipment, namely, declared essential features are a new property - enhancing stabilization of the profile of the blade throughout the entire process of wear, due to the receipt of a hard layer, having a cross section providing maximum conditions samosatene according to the formula(1), (2).

Thus, the claimed technical solution meets the criterion of "inventive step".

The invention is illustrated by diagrams and drawings.

Figure 1 presents the location of the electrode over the hardened surface and cross section of the blade, providing conditions samosatene where:

δ1 - the thickness of the soft layer at the edge of the blade;

δ2 - the thickness of the soft layer in a thickened portion of the blade;

δm1 - the thickness of the solid layer at the edge of the blade;

δm2 is the thickness of the solid layer in the thickened portion of the blade;

Hm - hardness hard coating;

Nm - hardness of the soft layer;

R is the radius of rotation of the electrode.

Figure 2 presents a pie chart of the distribution of current pulses per revolution of the electrode, not the shaded part corresponds to the arc at the minimum current J1, point 0(2π) corresponds to the position of the electrode on the tip of the blade, the point π corresponds to the position of the electrode above the thickened part of the blade. T1, T2, T3 - duration current pulse.

On IG presents a detailed diagram of distribution of current pulses per revolution of the electrode. J2, J3 - amplitude pulses of electric current.

Figs.4, 5, 6, 7, 8 shows the trajectory of the axis of the electrode defined in parametric form, with X-coordinate corresponds to the linear movement of the electrode and is determined by dependencewhere t is time (s), and the Y coordinate corresponds to the transverse movement of the electrode and is determined by the dependence Y=R cos (wt). The X-axis corresponds to the line on which lie the centers of rotation of the electrode, and the maximum coordinate value +and-correspond to the radius of rotation of the electrode.

4 shows the trajectory with parameters w=3V/R.

Figure 5 presents the trajectory with parameters w=4,5V/R.

Figure 6 presents the trajectory with parameters w=6V/R.

Figure 7 presents the trajectory with parameters w=7,5V/R.

On Fig presents the trajectory with parameters w=9V/R.

The method is as follows.

Carbon electrode set on the edge of the blade and excite an electric arc at a minimum current J1, after the formation of the molten bath and the onset of stable arc start rotation of the electrode and pulse change of the electric current. After the formation of the molten bath across the width of the blades start rotating movement of the electrode parallel to the sharp edge of the blade.

Change the thickness of the firmly what about the layer (reduction at the tip of the blade and increase with distance from it) in this way reach the uneven distribution of energy of the electric arc in cross-section machined blade so most stands out on thickness portion of the blade, and lower on the tip of the blade due to the asymmetric trajectory of the electrode and of different duration and amplitude of the pulses arc, the trajectory of the electrode according to the invention allows uniform saturation of carbon in the molten metal due to repeated exposure to the arc on the same spot of the surface of the blade.

The graph in figure 4 clearly shows that the trajectory of the axis of the electrode represents asymmetric with respect to the X-axis curve. This is because above the X-axis translational and rotational motion occurs in the same direction, and below the X-axis these movements occur in the opposite direction.

The described movement of the electrode leads to the unbalanced distribution of energy of the electric arc in cross-section of the molten weld pool and, consequently, to different depths of fusion hardened surface that allows changing the parameters of the trajectory change and the degree of heat to harden the surface.

The range of parameters of the trajectory is limited by the fact that when the angular frequency (w), equal to and less than 3V/R (figure 4), uneven saturation of carbon in the molten bath, as mixing tubs practically does not occur is it that is, when the angular frequency (w), equal to and less than 3V/R, a solid education in the parcel layer with low hardness, which violates the condition of samozatachivanie (2).

With increasing angular frequency higher than 3V/R, but less than 9V/R (figure 5, 6, 7), there is an increase in the uniformity of the carbon saturation, because the arc is in the process of moving affects the same place hardened surface repeatedly, while reducing the effect of uneven distribution of energy of the electric arc in cross-section of the molten bath, the conditions of samosatene according to the formulas (1), (2) are performed.

With increasing angular frequency (w) to a value equal to or more 9V/R (Fig), the effect of uneven distribution of energy in almost disappears, which leads to the cross-penetration of a thin section of the blade.

The above trajectory parameters allow you to create the uneven distribution of energy in the range of 20-40%, therefore, to increase the effect of the uneven distribution of energy and increase the control range, the melting of the hardened surface is performed with pulse current (2, 3) with varying duration and amplitude of the pulse arc during one revolution of the electrode, which increases when you delete an arc from the edge of the blade and decreases when approaching not the at. In the intervals between the pulses of the electric arc burns at the minimum current (J1), which provides a stable arc and the desired depth of penetration of the thin part of the blade.

Change the current value for one rotation of the electrode leads to a change in the amount of carbon derived from carbon electrodes in the molten bath, however, the rotation of the electrode allows to increase the uniformity of saturation by repeated exposure to the same place hardened surface that provides at least 3% of carbon over the whole cross section of the solid layer.

Thus, modifying the trajectory of the electrode, the magnitude of the current pulses of the electric arc, as well as the number and duration of pulses, you can change the depth of penetration of the hardened surface and create a hard layer, having a cross section with variable thickness varying from a minimum at the tip of the blade to the maximum in the thickened portion of the blade that provides conditions samosatene.

The value of the minimum voltage, current and pulse duration, number of pulses per revolution of the electrode will depend on the characteristics of the power source of the electric arc, the radius of rotation of the electrode rotation speed and the moving electrode, geometric shapes hardened blades, sizes and weight ed the lia, as well as the conditions of heat removal from the hardened surface, so the choice of these values is empirically for each specific product.

For example, for the blade of the working body tillage tools with the following dimensions: the thickness of the thin part of the blade is 2 mm, the maximum thickening - 6 mm, length 16 mm, material - steel 20, HB 140-180 (HRC12-15), weight - 1.2 kg, copper heat sink plate, the hardening was carried out in the following modes:

the speed of linear movement - V=0.01 m/s;

angular frequency of rotation of the electrode - w=7,5 rad/s;

the radius of rotation of the electrode, R=0,004 m;

the electrode diameter is 8 mm;

minimum current - Jmin=150A;

maximum current - Jmax=230V;

the number of pulses per revolution of the electrode 3.

Synchronous rotation of the electrode and the change in the arc current was produced using a stepper motor. The synchronization of the number of steps of the motor and the number, duration and amplitude of the pulse arc current during one rotation of the electrode was performed with the help of electronic unit assembled on standard digital modules (counters, timers).

In the melting back of the blade and further cooling the flowing water resulting layer with a hardness of HRC 58-60, width of 20 mm and a depth of penetration: at the edge of the blade from 0.8 to 1 mm and 2.5 to 3 mm above the thickened part of that is otvetstvuet conditions samosatene according to the formulas (1), (2), that is, the thickness of the soft layer, as at the edge of the blade (δ1), and in the thickened part (δ2), is in the range from 1 to 1.6 thickness of the solid layer (δm1), (δm2), and the hardness of the hard layer (Hm) is in the range from 3.2 to 5 hardness soft layer (Nm).

The use of the present invention provides stabilization of the profile of the blade throughout the entire process of wear, which is 1.5-2 times increases structural durability of the working bodies of tillage tools and their turnaround time of service.

The method of hardening the blades of the working bodies of tillage machinery, including heating the underside of the blade arc reverse polarity using carbon electrodes and subsequent cooling, wherein the heating is carried out by a pulsed current, a moving electrode is produced along a curved path formed by the linear movement parallel to the sharp edge of the blade and the rotation around the vertical axis with angular frequency determined from the relation:
3 V/R<w<9 V/R,
where w is the angular frequency of rotation of the electrode, rad/s;
V - speed of linear movement of the electrode, m/s;
R is the radius of rotation of the electrode, m,
duration and amplitude of the current pulses for one revolution of the electrode increases with the distance from the sharp edges of the blade and reduce when is lizanie to him.



 

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