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

Abstract

The invention discloses a reverse flow method for shrinkage fitting of a large sleeve type part. The reverse flow method comprises the steps as follows: step one, before the shrinkage fitting, the wind source air volume of the reverse flow method is confirmed; step two, after the sleeve type part is heated and subjected to thermal insulation according to processing requirements, the sleeve type part is taken out of a heating furnace and placed on a bracket; step three, a shaft is inserted into a sleeve type part from top to bottom, and no clearance is reserved in the shaft shoulder position; and step four, the air blowing is performed according to an air volume value confirmed in the step one, the air is forced to flow from top to bottom along the sleeve type part, so that a reverse flow is generated, the sleeve type part is cooled to be in a normal temperature state, and then the method is completed. According to the method disclosed by the invention, the air is forced to generate the reverse flow from top to bottom around the sleeve type part, so that the upper part of the sleeve type part is held firstly to form positioning, the zero clearance reserved in the shaft shoulder position is achieved, and the mounting accuracy of the sleeve type part is improved.

Description

The counter-current of large-scale cover parts hot charging

Technical field

The invention belongs to mechanical assembly technique field, relate to a kind of counter-current of large-scale cover parts hot charging.

Background technology

The accurate location of part on axle and be fixedly the key ensureing its normal work, during Model For The Bush-axle Type Parts interference fit, hot charging is common selection.In the hot charging of large-scale cover parts engineering goods, interference fit situation as shown in Figure 1, due to the impact of the free convection of surrounding air after cover parts heating, cover parts bottom first cools, thus the bottom of cover parts is first held tightly, on cover parts h direction, the thermal strain of (longitudinal direction) has just become the main source in gap, shaft shoulder place, and size h is larger, and pivot clearance is larger.

In order to eliminate and reduce gap, shaft shoulder place, the main method adopting forcing press to exert pressure from top at present.Because part is in temperature-fall period, stress is complicated, cannot accurately calculate, and the pressure of forcing press cannot complete equipilibrium power axially, causes the problem of shaft shoulder place gap overroof.And large-scale cover parts is when using forcing press to assist hot charging, be often difficult to be equipped with suitable forcing press by the appearance and size restriction of part.

Summary of the invention

The object of this invention is to provide a kind of counter-current of large-scale cover parts hot charging, large, the difficult problem being equipped with suitable forcing press and carrying out exerting pressure in gap, shaft shoulder place when solving hot charging in prior art.

The technical solution adopted in the present invention is, a kind of counter-current of large-scale cover parts hot charging, specifically implements 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 heating, insulation after, cover parts is taken out from heating furnace, is placed on support;

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

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

The invention has the beneficial effects as follows:

1) adopt counter-current assembling hot-assembling method simple.Tradition hot-assembling method needs large-tonnage forcing press to coordinate, and is subject to strict restriction, and has very high requirement of strength to the support of lower support part to the profile of part.Counter-current hot charging, owing to exerting pressure without the need to forcing press, is saved equipment, and is not also had specific intensity requirement to bottom ground and support.

2) cooling characteristics of cover parts is constant.Because the heat that wind is taken away is just close to the heat distributed of part under nature, so cooling velocity is substantially constant, ensure that the intensity of material, tenacity properties and this characteristic when traditional method hot charging are consistent substantially.

Accompanying drawing explanation

Fig. 1 is the installation site structural representation of existing assembly method;

Fig. 2 is the installation site schematic diagram of the inventive method embodiment.

In figure, 1. support, 2. cover parts, 3. axle, 4. deflector.

Detailed description of the invention

With reference to Fig. 1, existing large-scale cover parts adopts interference fit, and due to the free convection of cover parts 2 surrounding air, after heating, the flow direction of large-scale cover parts 2 surrounding air is from bottom to top.

With reference to Fig. 2, it is the counter-current of large-scale cover parts hot charging of the present invention, its operation principle is, the wind regime of an adjustable wind speed is added above large-scale cover parts 2, force air around cover parts, produce adverse current from top to bottom, the upper part of cover parts is first held tightly and forms location, thermal strain on such h direction would not have an impact to the shaft shoulder place of large-scale cover parts, also zero clearance, shaft shoulder place can just be realized, improve the installation accuracy of cover parts, this method is called the counter-current of hot charging according to operation principle, meet vertically completely, level, the various installation operating mode Lower shaft sleeve class part hot charging assemblings of tilting.

When Model For The Bush-axle Type Parts is not vertical placement but horizontal direction placement is assembled, counter-current of the present invention also can be applied, by arranging the wind regime of an adjustable wind speed above Model For The Bush-axle Type Parts shaft shoulder one end, accelerate the cooling velocity of shaft shoulder one end, shaft shoulder place is first held tightly, thus realizes the installation location of cover parts 2.

For the feature of the large-scale cover parts 2 of difference in practical operation, determining air quantity through calculating, reaching the gap of eliminating shaft shoulder place, improve the requirement of installation accuracy; And make cover parts 2 reach effect close to cooling naturally in air, improve hot charging quality.

For irregular cover parts, in order to the better side at cover parts 2 forms adverse current, as Fig. 2, the deflector 4 of bell-mouth structure of air can be increased on wind regime passage, make air fully flow to the side of cover parts 2.

The concrete implementation step of the inventive method is:

Step 1, before hot charging, determine adverse current wind regime airflow value

First determine the surface coefficient of heat transfer α of cover parts around under natural convection air state, draw the heat dissipation capacity Q of the cover parts under free convection operating mode _s, then the size of wanted wind regime air quantity q value is tried to achieve according to formula (2);

Along with the temperature of cover parts reduces, heat radiation reduces thereupon, the air quantity also corresponding reduction required, calculate different grades according to formula (1), (2), in practical operation, divide several gradient successively to reduce air quantity, gradient is got more, the effect of adverse current hot-assembling method is better, utilize existing alternating frequency conversion technique effectively can regulate air quantity, realize air quantity gradient and divide

Surface coefficient of heat transfer α obtains according to existing 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 _scomputing formula is:

$Q_S=\mathrm{\αS}(t_1-t_0),---\left(1\right)$

Wherein, S-cover parts area of dissipation;

α-surface coefficient of heat transfer;

T ₁the temperature of-cover parts;

T ₀-environment temperature,

The air quantity q computing formula of wind regime is:

$q=\frac{Q_s}{\mathrm{\ρ}{c}_f({\mathrm{\θ}}_{1f}-{\mathrm{\θ}}_0){\mathrm{\η}}_f}$ (unit is m ³/ s), (2)

Wherein, C _f-air specific heat capacity at constant pressure, preferred value is C _f≈ 1004J/ (kg ° of C),

η _fthe usage factor of-blowing, preferred value is η _f≈ 0.8,

θ 1 _f-blow over cover parts after discharge the temperature of air-flow, θ 1 _f=θ ₀+ (3 ~ 6) ° C,

ρ-dry air density.

Step 2, according to technological requirement, cover parts 2 heated, be incubated after, taken out from heating furnace by cover parts 2, be placed on support 1, support plays the effect being convenient to installation shaft;

Step 3, supporting axle 3 from up to down to be inserted in cover parts 2, ensure that the shaft shoulder place of cover parts 2 does not have assemblage gap;

Step 4, the airflow value determined according to step 1 blow, and adopt auxiliary deflector 4 as required, force air from up to down flow generation adverse current along cover parts 2, for cooling cover parts 2, until normal temperature state.

Cover parts 2 hot charging is complete, checks the installation quality of cover parts in addition according to technological requirement.

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:

$q=\frac{Q_s}{\mathrm{\ρ}{c}_f({\mathrm{\θ}}_{1f}-{\mathrm{\θ}}_0){\mathrm{\η}}_f},---\left(2\right)$

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).