RU2235794C2 - Method and apparatus for thermal-power processing of axisymmetric elongated parts - Google Patents

Abstract

FIELD: mechanical engineering, in particular, method used in quenching, normalizing and tempering of elongated axisymmetric low-rigidity parts.

SUBSTANCE: method involves preliminary processing of blank; screwing spacer bushings onto blank; locating blank with bushings into multilayer fixture; fixing blank at its lower end; heating to thermal processing temperature with following holding at this temperature; compressing; tightening of alternating blank deformation zones with following cooling; providing equally distributed axial stresses. Apparatus has set of spacer bushings manufactured from material having linear expansion coefficient smaller than that of blank material and adapted for axial deformation of blank, multilayer fixture manufactured of the same material from which bushings are made and having filler providing for minimal transverse flexure under gravitational force, and required cooling rate, cover and spherical surface allowing blank to be fixed in axial direction.

EFFECT: increased strength and stability of geometric parameters of products, increased operating precision of ready parts by creating equally distributed sign-changing residual stresses over the entire length of blank.

8 cl, 5 dwg

Description

The invention relates to mechanical engineering technology, and in particular to methods of thermomechanical processing, and can be used in hardening, normalization and tempering of parts of any complex transverse shapes, mainly long, particularly low rigidity, with a ratio of length to diameter of more than 10.

A device is known for heat treatment of shafts of low rigidity, including a slipway made in the form of a pipe with through holes evenly located on its surface; the stationary capture of the part in the form of a split washer in contact with the end face of the slipway, and the capture of the part, made in the form of a split sleeve with an external thread, installed at the ends of the pipe (SU 1407969, С 21 D 1/62, 07.07.1988).

The closest analogue to the invention is a method of heat treatment of axisymmetric lengthy parts, including pre-processing of the part, fixing spacer sleeves on the part, installing the part with the sleeves in a multilayer stock, fixing the part by contact with the spherical surface of the stock of the stock, installing the stock with the part in the furnace, heating to a certain temperature, holding to achieve the required level of strain uniformity and cooling (SU 1708884 A1, MPK7 C 21 D 9/06, 01/30/1992) [1].

A device for heat treatment of shafts of low rigidity, containing a multilayer slipway, a set of spacer sleeves and a mechanism for fixing the part, rigidly connecting the part with the slipway [1].

A disadvantage of the known device is the inability to keep the product in tension when the temperature drops to 20 ° C, because the slipway is compressed - it is shortened faster than the product.

The technical result of the invention is to increase the accuracy and stability of geometric parameters, increase the operational accuracy of finished products by creating uniform alternating residual stresses along the entire length of the workpiece.

To achieve a technical result in the known method of thermo-force processing of axisymmetric long parts, including pre-processing of the part, fixing spacer sleeves on the part, installing the part with the sleeves in a multilayer stock, fixing the part by contact with a spherical surface, installing the stock with the part in the furnace, heating to a certain temperature, holding to achieve the required level of deformation uniformity and cooling, form alternating in length and uniform in length in the part cross-section residual stresses using spacer sleeves and a multilayer slipway made of a material with a coefficient of linear expansion less than the coefficient of linear expansion of the material of the part.

The detail is fixed at the lower and upper ends.

When machining threaded parts, spacer sleeves are screwed onto the part.

When processing stepped parts, spacers are placed on the part.

In the known thermoset processing device for axisymmetric lengthy parts containing a multilayer slipway, a set of spacer sleeves and a part fixing mechanism, rigidly connecting the detail to the slipway, a multilayer slipway and a set of spacer sleeves are made of the same material with a linear expansion coefficient less than the linear expansion coefficient of the material of the part.

Spacer sleeves are threaded.

Spacer sleeves are made overhead, consisting of two parts.

The invention is illustrated in the drawing, where figure 1 shows a device that implements the method, a section; figure 2 is a section bB.

The method is as follows.

In the process, the following order of technological operations takes place. Part 1 is pre-processed on a lathe using lunettes and form a working profile 2 of the following types:

a) threaded, while its step is determined by the tensile strength of the material and the cross-sectional value of the workpiece, as well as the depth of threading (its inner diameter) should not exceed the machining allowance;

b) stepwise, while the difference between the outer and inner diameters is also determined by the tensile strength of the material and the cross-sectional value of the workpiece and should not exceed the machining allowance.

для обеспечения жесткости сжимаемой части детали. Во втулках 3 изготовлены отверстия 9, причем их форма и расположение выполнены так, что при любом взаимном расположении двух соединений втулок обеспечивается проход охлаждающей жидкости.After that, spacer sleeves 3 are applied to the workpiece according to the principle of plain bearing shells (the sleeve consists of two parts), while processing threaded parts, the spacer sleeves 3 are screwed onto the part. When processing stepped parts spacer sleeves 3 impose on the part. The bushings are made of a material whose linear expansion coefficient α _is less than the linear expansion coefficient of the material of the part α _d . The length of the sleeves is calculated from the condition of equal strength of that part of the product on which the sleeve is installed, as well as from the condition of minimizing the deflection boom. Moreover, to ensure uniform compression along the axis of the part, we take the ratio of lengths l ₁ = l ₂ ,

to ensure rigidity of the compressible part of the part. Holes 9 are made in the sleeves 3, and their shape and arrangement are such that, for any mutual arrangement of the two joints of the sleeves, the passage of coolant is ensured.

The assembled part 1 with spacer sleeves 3, wherein the spacer sleeves are threaded, if the part has a thread and two-part overheads, if the part is stepped, insert with a pre-calculated thermal gap into the multilayer slipway 4 and fix on the lower and upper ends of the slipway , the latter is made of a material whose linear thermal expansion coefficient is equal to the linear thermal expansion coefficient of the material of the bushings (to avoid jamming due to temperature deformations), with filler 5, last Depending on the required cooling rate, the slipway may have a different coefficient of thermal conductivity (for example, river sand with mixed fine cast-iron shavings).

The part is fixed at two ends by means of two spheres 7, rigidly fixed with covers 6 at the lower and upper ends. With this method, the part is rigidly connected with the slipway along the axis.

Four eyes 8 are welded to the top of the slipway 4 for suspension of the entire structure. To avoid the deflection of part 1 under the action of stresses arising from heating - cooling the structure: the part - spacer sleeves - slipway, the gap between the spacer bushings 3 and slipway 4 should be minimal, ensuring the operation of the device without jamming. The assembled structure is lowered into the shaft furnace and heated according to the heat treatment technology to the temperature of quenching or tempering, etc., maintained at this temperature until the part is completely heated. When heated, the part lengthens more than the bushings and slipways, due to the difference in the coefficients of linear thermal expansion. Selecting the numerical values of the positive difference in the coefficients of linear thermal expansion of the part and the bushings, we obtain the amount of plastic deformation of the part that exceeds the limit of proportionality, that is, the limit of Hooke's law.

Axial plastic deformation beyond the limits of proportionality (Hooke's law) when heated eliminates technological heredity from previous operations. In addition, the action of axial loads is the strain hardening of the material of the part (hardening), smoothing of internal microcracks.

When cooling with axial loading, residual stresses are formed in the part, alternating in length and uniform in the cross section of the part, which eliminates warping of finished products during operation.

Figure 3 shows a comparison of the internal stresses in the part before and after the application of heat treatment. In addition, the strength characteristics of the part are increased. Using this method allows you to minimize the amount of deflection of the product and to stabilize the level of residual stresses along its length, which allows to improve the operational accuracy of finished products, such as long lengthy, stiff shafts, and to improve the quality of finished products.

Implementation example. The shaft is made of steel 10X17H13M2T, the bushings and the slipway are made of steel 08X13, the temperature extensions are calculated by the formula:

Δ l = α _det (T °) T ° L-α _W (T °) T ° L,

where Δ l is the difference between the elongations of the shaft and the sleeve;

α is the coefficient of linear expansion;

T ° - heating temperature;

L is the length of the sleeve and the shaft section.

The amount of plastic deformation:

At L = 200 mm, T ° = 1050 ° C; α _det = 18.5 · 10 ^-6 mm / mm · deg, α _W = 12.8 · 10 ^-6 mm / mm · deg: Δ l = 18.6 · 10 ^-6 · 1050 · 200-12.8 · 10 ^-6 · 1050 · 200 = 1.197 mm.

The amount of plastic deformation:

Calculation of the cooling time is carried out with the following parameters: shaft diameter 40 mm, the inner diameter of the slipway 160 mm, the outer 260 mm, the filler is sand mixed with cast iron chips, the cooling medium is oil with a temperature of 30 ° C.

The shaft cooling time is calculated by the formula:

where γ is the bulk density of the material;

λ is the thermal conductivity of the material;

- критерий Фурье, который определяется как функция относительных температур

и критерия Вi, последний равен:

- Fourier criterion, which is defined as a function of relative temperatures

and criterion Bi, the latter is:

where δ is the radius of a long product;

λ _equiv - equivalent thermal conductivity of the system: sleeve - slipway;

At ₀ is the coefficient of heat transfer from the environment to the surface of the body.

Based on the selection of the material of the bushings and the slipway to this material of the shaft, throughout the entire heat treatment cycle, we have a positive difference in the coefficients of thermal expansion α _det and α _W (figure 4)

Claims (8)

1. The method of thermoset processing of axisymmetric long parts, including pre-processing of the part, fixing spacer sleeves on the part, installing the part with the sleeves in a multilayer slipway, fixing the component by contact with a spherical surface, installing the slipway with the component in the furnace, heating to a certain temperature, holding to achieve the required level of deformation uniformity and cooling, characterized in that the parts form residual stresses alternating in length and uniform in cross section via spacers and multilayer pile made of a material having a coefficient of linear expansion smaller than the coefficient of linear expansion of the material items. 2. The method according to claim 1, characterized in that the part is fixed at the lower end. 3. The method according to claim 1, characterized in that the part is fixed at the lower and upper ends. 4. The method according to claim 1, characterized in that when machining threaded parts, spacer sleeves are screwed onto the part. 5. The method according to claim 1, characterized in that when processing stepped parts, spacer sleeves are applied to the part. 6. Thermal power device for axisymmetric lengthy parts containing a multilayer slipway, a set of spacer sleeves and a mechanism for fixing the part, rigidly connecting the detail to the slipway, characterized in that the multilayer slipway and a set of spacer sleeves are made of the same material with a linear expansion coefficient less than the linear expansion coefficient of the material the details. 7. The device according to claim 6, characterized in that the spacer sleeves are threaded. 8. The device according to claim 6, characterized in that the spacer sleeves are made overhead, consisting of two parts.

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