CN103182621B - Reverse flow method for shrinkage fitting of large sleeve type part - Google Patents

Abstract

The invention discloses a countercurrent method for hot-packing large-scale sleeve parts. The steps include: step 1, before hot-packing, determine the air volume of the air source of the counter-current method; step 2, heat and keep warm the sleeve parts according to the process requirements, Take out the sleeve parts from the heating furnace and place them on the bracket; step 3, insert the shaft into the sleeve parts from top to bottom to ensure that there is no gap at the shoulder of the shaft; step 4, blow air according to the air volume value determined in step 1, and force The air flows from top to bottom along the jacket parts to generate countercurrent, and the jacket parts are cooled until they are at normal temperature. The method of the present invention forces the air to generate a counterflow from top to bottom around the sleeve parts, so that the upper part of the sleeve parts is first held tightly to form a position, realizing zero clearance at the shaft shoulder, and improving the installation accuracy of the sleeve parts.

Description

Counterflow Method of Shrink Packing for Large Sleeve Parts

technical field

The invention belongs to the technical field of mechanical assembly, and relates to a countercurrent method for hot packing of large sleeve parts.

Background technique

Accurate positioning and fixing of parts on the shaft is the key to ensure their normal operation. Shrink fitting is a common choice for interference fit of shaft sleeve parts. In the hot-packing of large-scale sleeve parts mechanical products, as shown in Figure 1, the interference fit assembly situation, after the sleeve parts are heated, due to the influence of the natural convection of the surrounding air, the lower part of the sleeve parts cools first, so the sleeve parts The lower part of the shaft should be tightly held first, and the thermal strain in the h direction (longitudinal direction) of sleeve parts becomes the main source of the clearance at the shaft shoulder. The larger the dimension h, the larger the clearance of the shaft shoulder.

In order to eliminate and reduce the gap at the shaft shoulder, the method of applying pressure from the upper part of the press is mainly used at present. Due to the complex stress of the parts during the cooling process, it cannot be accurately measured, and the pressure of the press cannot completely balance the force in the axial direction, resulting in the problem that the clearance at the shaft shoulder exceeds the standard. Moreover, when large-scale sleeve parts are assisted by a press, it is often difficult to equip a suitable press due to the limitation of the external dimensions of the parts.

Contents of the invention

The object of the present invention is to provide a counterflow method for thermal charging of large-scale sleeve parts, which solves the problems in the prior art that there is a large gap at the shaft shoulder during thermal charging and it is difficult to equip a suitable press for pressure application.

The technical solution adopted in the present invention is a countercurrent method for thermal charging of large sleeve parts, which is implemented in accordance with the following steps:

Step 1. Before hot loading, determine the air volume of the counterflow air source

First determine the surface heat transfer coefficient α of the sleeve parts in the natural convection state of the surrounding air, obtain the heat dissipation Q _S of the sleeve parts under the natural convection condition, and then obtain the required air volume q of the air source;

Step 2. After heating and keeping warm the sleeve parts according to the process requirements, take the sleeve parts out of the heating furnace and place them on the bracket;

Step 3. Insert the supporting shaft into the sleeve parts from top to bottom to ensure that there is no gap at the shoulder of the sleeve parts;

Step 4. Blow air according to the air volume value determined in step 1, so that the air flows from top to bottom around the jacket parts to generate countercurrent, and cool the jacket parts until they are at normal temperature.

The beneficial effects of the present invention are:

1) The method of assembling and hot charging by countercurrent method is simple. The traditional shrink-fitting method requires the cooperation of a large-tonnage press, which has strict restrictions on the shape of the part, and has high strength requirements for the bracket supporting the lower part. Since the countercurrent method does not require a press to apply pressure, it saves equipment, and there is no special strength requirement for the lower foundation and support.

2) The cooling characteristics of sleeve parts remain unchanged. Because the heat taken away by the wind is just close to the heat emitted by the parts in the natural state, the cooling rate is basically unchanged, ensuring that the strength and toughness characteristics of the material are basically consistent with those in the traditional method of thermal charging.

Description of drawings

Fig. 1 is the structural schematic diagram of the installation position of existing assembly method;

Fig. 2 is a schematic diagram of the installation position of the method embodiment of the present invention.

In the figure, 1. bracket, 2. sleeve parts, 3. shaft, 4. deflector.

Detailed ways

Referring to Fig. 1, the existing large sleeve parts are assembled by interference fit. Due to the natural convection of the air around the sleeve parts 2, the flow of air around the large sleeve parts 2 after heating is from bottom to top.

With reference to Fig. 2, it is the counterflow method of hot-packing of large sleeve parts of the present invention. The counterflow to the bottom makes the upper part of the sleeve parts tightly hugged to form a position, so that the thermal strain in the h direction will not affect the shaft shoulders of large sleeve parts, and zero clearance at the shaft shoulders can be realized. To improve the installation accuracy of sleeve parts, this method is called the counterflow method of heat-fitting according to the working principle, which fully meets the heat-fit assembly of shaft sleeve parts under various installation conditions of vertical, horizontal and inclined.

When the shaft sleeve parts are not placed vertically but placed horizontally for assembly, the counterflow method of the present invention can also be applied. By setting an adjustable wind source above the shaft shoulder end of the shaft sleeve parts, the speed of the shaft shoulder end is accelerated. The cooling speed is high, so that the shaft shoulder is tightly held first, so as to realize the installation and positioning of the sleeve part 2.

In actual operation, according to the characteristics of different large-scale sleeve parts 2, the air volume is calculated and determined to eliminate the gap at the shaft shoulder and improve the installation accuracy; and to make the sleeve parts 2 achieve the effect of natural cooling in the air and improve the heat dissipation. Install quality.

For irregular sleeve parts, in order to better form counterflow on the side of sleeve parts 2, as shown in Figure 2, a deflector 4 with an inverted bell mouth structure can be added to the air source channel to make the air fully flow to the sleeve parts 2 sides.

The concrete implementation steps of the inventive method are:

Step 1. Before hot loading, determine the air volume value of the counterflow air source

First determine the surface heat transfer coefficient α of the sleeve parts in the natural convection state of the surrounding air, and obtain the heat dissipation Q _S of the sleeve parts under the natural convection condition, and then obtain the required air source air volume q according to the formula (2) the size of the value;

As the temperature of sleeve parts decreases, the heat dissipation decreases accordingly, and the required air volume also decreases accordingly. According to formulas (1) and (2), different levels are calculated, and in actual operation, the air volume is divided into several gradients and gradually reduced. , the more the gradient is divided, the better the effect of the countercurrent hot charging method. The existing AC frequency conversion technology can effectively adjust the air volume and realize the air volume gradient division.

The surface heat transfer coefficient α is obtained according to the existing relevant information, or the Nusselt number is obtained according to the natural convection criterion equation, and then calculated according to the characteristic size. The calculation formula for the heat dissipation Q _S of the sleeve parts is:

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&alpha;S</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, S—the heat dissipation area of the set of parts;

α—surface heat transfer coefficient;

t ₁ - the temperature of the set of parts;

t ₀ —ambient temperature,

The formula for calculating the air volume q of the air source is:

$q=\frac{Q_{\mathrm{the\; s}}}{\mathrm{\&rho;}{c}_f({\mathrm{\&theta;}}_{1f}-{\mathrm{\&theta;}}_0){\mathrm{\&eta;}}_f}$ (unit is m ³ /s), (2)

Among them, C _f - air ratio constant pressure heat capacity, the preferred value is C _f ≈ 1004J/(kg °C),

η _f —the utilization coefficient of blowing, the preferred value is η _f ≈ 0.8,

θ1 _f - the temperature of the exhaust air after blowing through the sleeve parts, θ1 _f = θ ₀ + (3 ~ 6) ° C,

ρ—Dry air density.

Step 2. After heating and keeping warm the sleeve part 2 according to the process requirements, take the sleeve part 2 out of the heating furnace and place it on the bracket 1, which is convenient for installing the shaft;

Step 3. Insert the matching shaft 3 into the sleeve part 2 from top to bottom to ensure that there is no installation gap at the shaft shoulder of the sleeve part 2;

Step 4. Perform blowing according to the air volume value determined in step 1. Use the auxiliary deflector 4 as needed to force the air to flow from top to bottom along the jacket parts 2 to generate a countercurrent, which is used to cool the jacket parts 2 until they are at normal temperature, that is, become.

The sleeve parts 2 are hot-installed, and the installation quality of the sleeve parts is checked according to the process requirements.

Claims (4)

1. a counter-current for large-scale cover parts hot charging, is characterized in that, specifically implement according to following steps:

Before step 1, hot charging, determine the air force of adverse current wind regime:

First determine the surface coefficient of heat transfer α of cover parts around under natural convection air state, try to achieve the heat dissipation capacity Q of the cover parts under free convection operating mode _s, then obtain the size of required wind regime air quantity q;

Step 2, according to technological requirement to cover parts (2) heating, insulation after, cover parts (2) is taken out from heating furnace, is placed on support (1);

Step 3, supporting axle (3) is from up to down inserted in cover parts (2), ensure that the shaft shoulder place of cover parts (2) is very close to each other;

Step 4, the airflow value determined according to step 1 blow, and make air produce adverse current along cover parts (2) from up to down flowing around, cooling cover parts (2) until normal temperature state.

2. the counter-current of large-scale cover parts hot charging according to claim 1, it is characterized in that: in described step 1, the deterministic process of wind regime air quantity q is: calculate different air quantity grades according to formula (1), (2), and divide several gradient successively to reduce air quantity in practical operation, realize air quantity gradient to divide

Surface coefficient of heat transfer α obtains according to related data, or according to free convection criteria equation, draws nusselt number, then calculates according to characteristic size, the heat dissipation capacity Q of cover parts (2) _scomputing formula is:

Q _S＝αS(t ₁-t ₀)， (1)

Wherein, S-cover parts area of dissipation;

α-surface coefficient of heat transfer;

T ₁the temperature of-cover parts;

T ₀-environment temperature,

The computing formula of wind regime air quantity q is:

$q=\frac{Q_s}{\mathrm{\&rho;}{c}_f({\mathrm{\&theta;}}_{1f}-{\mathrm{\&theta;}}_0){\mathrm{\&eta;}}_f},---\left(2\right)$

Wherein, the unit of wind regime air quantity q is m ³/ s,

C _f-air specific heat capacity at constant pressure,

η _fthe usage factor of-blowing,

θ 1 _fthe temperature that-wind is discharged after blowing over cover parts,

θ ₀expression wind blows over the temperature before cover parts;

ρ-dry air density.

3. the counter-current of large-scale cover parts hot charging according to claim 2, is characterized in that: in described formula (2), parameter value selects C _f≈ 1004J/ (kg DEG C), η _f≈ 0.8, θ 1 _f=θ ₀+ (3 ~ 6) DEG C.

4. the counter-current of large-scale cover parts hot charging according to claim 1, is characterized in that: the passage at described adverse current wind regime place is provided with deflector (4).