阅读说明：本技术 一种坯料的热处理方法及装置 (Heat treatment method and device for blank ) 是由 高新亮 陈凡海 卢言路 于 2021-07-30 设计创作，主要内容包括：本发明涉及一种坯料的热处理方法及装置,该装置包括坯料、平台、上位机、脉冲电源、脉冲电流电极、喷火加热组件、控制台、红外测温组件和丝杠传动组件,丝杠传动组件包括固定安装在平台上的滑轨,滑轨的第一端焊接有第一定滑块,滑轨的第二端设置有可移动的第一动滑块,第一定滑块与第一动滑块顶端分别镶嵌有脉冲电流电极且二者间穿设有第一丝杠并与第一电机连接。本发明利用脉冲电流的焦耳热效应对坯料温差进行调整,保证坯料各点温度趋于一致,以提高坯料塑性变形能力,减少材料变形抗力,从而在后续坯料穿孔成型时,避免横向裂纹缺陷的发生,降低废品率,减少成型功耗,提高生产质量,从而能够大幅度提升生产效益。(The invention relates to a heat treatment method and a heat treatment device for a blank, wherein the heat treatment device comprises the blank, a platform, an upper computer, a pulse power supply, a pulse current electrode, a flame-throwing heating assembly, a control console, an infrared temperature measurement assembly and a lead screw transmission assembly, the lead screw transmission assembly comprises a slide rail fixedly arranged on the platform, a first fixed slide block is welded at the first end of the slide rail, a movable first movable slide block is arranged at the second end of the slide rail, the pulse current electrode is respectively embedded at the top ends of the first fixed slide block and the first movable slide block, a first lead screw penetrates between the first fixed slide block and the first movable slide block, and the first fixed slide block and the first movable slide block are connected with a first motor. The method utilizes the joule heating effect of the pulse current to adjust the temperature difference of the blank, ensures that the temperatures of all points of the blank tend to be consistent, improves the plastic deformation capacity of the blank, and reduces the deformation resistance of the material, thereby avoiding the occurrence of transverse crack defects during the subsequent punching forming of the blank, reducing the rejection rate, reducing the forming power consumption, improving the production quality and greatly improving the production benefit.)

1. A method for heat treatment of a billet, characterized by: which comprises the following steps:

s1, setting initial parameters: determining heating environment i and heating precision requirement K_iThe temperature T required by the blank perforation heat treatment, the maximum limit temperature difference delta T of each point of the blank after the pulse current heating is finished and the temperature measuring thermocouple temperature measuring time interval T, wherein when i is 1,2 and 3, when i is 1, the blank is heated in a heating furnace, when i is 2, the blank is heated by a flame spraying mode, and when i is 3, the blank is heated in an environment with the pulse current applied; k_iComprising K₁、K₂And K₃The precision requirement after the heating in the heating furnace is K₁The temperature precision requirement after the flaming heating is K₂The precision requirement after the heating by applying the pulse current is K₃；

S2, heating the blank by a heating furnace, which comprises the following steps:

s21, putting the blank into a heating furnace for heating, utilizing a temperature measuring device to detect the temperature of each point on the outer surface of the blank in the heating furnace in real time and transmitting the real-time temperature data to an upper computer, wherein the upper computer determines the maximum value of the temperature by comparing the temperatures of each point on the outer surface of the blank in the heating furnace, and the calculation formula is as follows:

T_1max＝max{T₁’，T₁”，T₁”’，...，T₁ ⁽ⁿ⁾then calculating the actual accuracy of the heating process in the furnace

S22 actual accuracy K in heating process in heating furnace₁' with accuracy requirement K after completion of heating in heating furnace₁And (3) comparison: if K₁’＜K₁Then, the steps S21-S22 are repeated until K₁’≥K₁(ii) a If K₁’≥K₁Then the step S3 is entered for next heating;

s3, carrying out flame spraying heating on the blank, which specifically comprises the following substeps:

s31, moving out of the heating furnace, carrying out flame spraying on the blank, stopping flame spraying after t time, inserting a temperature thermocouple into the blank to detect the temperature of the core part of the blank, transmitting real-time temperature data of each point on the inner surface of the blank to an upper computer in real time by the temperature thermocouple, comparing the temperature of each point on the inner surface of the blank in flame spraying heating by the upper computer, and determining the maximum value of the temperature, wherein the calculation formula is as follows:

T_2max＝max{T₂’，T₂”，T₂”’，...，T₂ ⁽ⁿ⁾calculating the actual accuracy in the flaming heating process

S32 actual precision K in heating process in flaming mode₂' with accuracy requirement K after completion of heating in flaming mode₂And (3) comparison: if K₂’＜K₂Repeating the steps S31-S32 until K₂’≥K₂(ii) a If K₂’≥K₂Then, the process goes to step S4 to perform the next heating process;

s4, heating the blank by pulse current, which comprises the following steps:

s41, stopping flaming heating, heating the blank in an environment with pulse current, increasing the temperature of the blank by using the joule heat of the pulse current, inserting a temperature thermocouple into the blank to detect the temperature of each point on the inner surface of the blank in the environment with the pulse current in real time, detecting the temperature of each point on the outer surface of the blank in the environment with the pulse current in real time by using an infrared thermometer, and transmitting the detected temperature data of the inner surface and the outer surface of the blank to an upper computer in real time; after the upper computer receives the temperature data, the temperature of each point on the inner surface and the outer surface of the blank in the environment of applying the pulse current is compared to obtain the maximum temperature value and the minimum temperature value, and the calculation formula of the maximum temperature value is T_3max＝max{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾The calculation formula of the minimum value of the temperature is T_3min＝min{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾}；

S42, calculating the maximum temperature difference delta T' between the inner surface and the outer surface of the blank under the environment of the pulse current application according to the maximum temperature value and the minimum temperature value and the actual precision in the heating process in the environment of the pulse current application

S43 actual accuracy K in heating process in environment of pulse current application₃' with accuracy requirement K after completion of heating in an environment where a pulse current is applied₃Comparing, and simultaneously comparing the maximum temperature difference delta T' of the blank with the maximum limit temperature difference delta T of the blank:

if K₃’＜K₃If yes, repeating the steps S41-S43; if K₃’≥K₃If delta T' is greater than delta T, stopping applying the pulse current, and ensuring that the temperature of each point on the blank tends to be consistent through a heat conduction mode;

if K₃’≥K₃Delta T' is less than or equal to delta T and T_3minIf T is less than T, the heating is continued in the environment of pulse current, and Joule of the pulse current is utilizedThe temperature of the lowest point of the blank is raised by heat;

if K₃’≥K₃Δ T' is less than or equal to Δ T, and T_3minAnd if the temperature is more than or equal to T, stopping pulse heating, and taking out the blank to perform a subsequent punching process.

2. The heat treatment method for a billet according to claim 1, characterized in that: in step S41, the infrared thermometer reciprocates by means of the slide rail, thereby measuring the temperature of each point on the outer surface of the billet.

3. A heat treatment apparatus for use in the heat treatment method of a billet claimed in claim 1, characterized in that: the lead screw transmission device comprises a workbench, an upper computer, a pulse power supply, a flaming heating assembly, a thermocouple temperature measuring assembly, a control console and a lead screw transmission assembly arranged on the workbench, wherein the lead screw transmission assembly comprises a first slide rail, a first fixed slide block, a first movable slide block and a first lead screw which are fixedly arranged on the workbench, the first end of the first slide rail is fixedly connected with the first fixed slide block, the second end of the first slide rail is provided with a first movable slide block capable of moving, the first lead screw is arranged between the first fixed slide block and the first movable slide block in a penetrating manner, the first lead screw and the first movable slide block are further connected with a first motor after being connected through a connecting piece so as to realize the reciprocating motion of the first movable slide block on the first slide rail, and the top ends of the first fixed slide block and the first movable slide block are respectively embedded with a pulse current anode and a pulse current cathode, the side surface of the workbench is symmetrically provided with infrared temperature measurement components;

the flame-throwing heating assembly comprises a second slide rail, a second fixed slide block, a second movable slide block and a second lead screw, the second fixed slide block is arranged on the second slide rail, the second lead screw is arranged between the second fixed slide block and the second movable slide block, the second lead screw is connected with a second motor, a first hydraulic cylinder is fixed on the second movable slide block, the first hydraulic cylinder is connected with a first hydraulic pump assembly, the other end of the first hydraulic cylinder is fixedly connected with an air inlet pipe bracket, and a spark plug ignition device is fixed on the air inlet pipe bracket;

the infrared temperature measurement assembly comprises a first infrared temperature measurement assembly and a second temperature measurement assembly, the first infrared temperature measurement assembly comprises a third slide rail, a third fixed slide block, a third movable slide block and a third lead screw, the third fixed slide block is fixed on one side of the third slide rail, the third lead screw penetrates through the third movable slide block and is connected with a third motor, a first supporting rod is fixed on the third movable slide block, a first infrared thermometer is connected onto the first supporting rod, and the second infrared temperature measurement assembly and the first infrared temperature measurement assembly are symmetrically distributed on the side face of the workbench;

the thermocouple temperature measurement component comprises a fourth slide rail, a fourth fixed slide block, a fourth movable slide block and a fourth lead screw, the fourth fixed slide block is fixed on the fourth slide rail, the fourth lead screw is arranged on the fourth slide rail, the fourth movable slide block is arranged on the fourth lead screw and connected with a fourth motor, a second hydraulic cylinder is fixed on the fourth movable slide block and connected with a second hydraulic pump component fixed on a second oil tank, the other end of the second hydraulic cylinder is fixedly connected with a thermocouple support, and a temperature measurement thermocouple is arranged on the thermocouple support.

4. The thermal processing apparatus of claim 3, wherein: the air inlet hard pipe is erected on the air inlet pipe support, fire spouts which are evenly distributed at 90 degrees along the circumferential direction are formed in the front end of the air inlet hard pipe, and the rear end of the air inlet hard pipe is connected with the oxygen gas tank and the natural gas tank through the oxygen air inlet hose and the natural gas air inlet hose respectively.

5. The thermal processing apparatus of claim 3, wherein: the top ends of the first fixed sliding block and the first movable sliding block are provided with inclined planes which are symmetrically distributed, so that blanks with different diameters can be supported.

6. The thermal processing apparatus of claim 3, wherein: the air inlet hard pipe front end of the flame spraying assembly is divided into a plurality of sections, a thread pair is arranged on the air inlet hard pipe, the air inlet hard pipe fixed connection of the plurality of sections is realized through the thread pair, so that flame spraying treatment on blanks with different lengths is realized, the hydraulic cylinder below the air inlet pipe support can be extended and contracted under the driving of the hydraulic pump, and therefore the height of the air inlet pipe support is adjusted to realize flame spraying treatment on blanks with different diameters.

7. The thermal processing apparatus of claim 6, wherein: the natural gas hard tube is internally provided with a conical gas inlet for preventing backfire, and the spark plug ignition device comprises a spark plug and an ignition coil.

8. The thermal processing apparatus of claim 3, wherein: when the blank is heated by the heating furnace, the position of the first movable slide block is adjusted by the console according to the length and the diameter of the blank, so that the sum of the distances between the first movable slide block and the first fixed slide block is close to the total length of the stainless steel tube blank, and the length of the air inlet hard tube and the height of the air inlet tube support are adjusted at the same time.

9. The thermal processing apparatus of claim 2, wherein: the other end of the first hydraulic cylinder is connected with the air inlet pipe bracket and the first support rod is connected with the first infrared thermometer by connecting pieces.

10. The thermal processing apparatus of claim 3, wherein: the first infrared thermometer and the second infrared thermometer synchronously reciprocate on the slide rail so as to realize real-time detection of the temperature of each point on the surface of the blank in the environment of applying pulse current.

Technical Field

The invention relates to the technical field of blank heat treatment, in particular to a blank heat treatment method and a blank heat treatment device.

Background

The seamless steel pipe is one of the important raw materials for national economic construction, and the large-caliber stainless steel seamless steel pipe is mainly applied to energy departments such as petroleum cracking, nuclear power and the like, and the requirements on the quality of used pipe fittings in the fields are quite high. In the process of actually producing the large-caliber stainless steel seamless steel tube, the situation that the tube blank is perforated after being heated, transverse cracks with irregular fish scales and saw teeth are often formed on the surface of the perforated tubular billet, the cracking degree is serious, the cracks are difficult to eliminate in the subsequent drawing and cold rolling processes, the problem of serious quality defects can be formed on the surface of the steel tube, and the production quality is seriously influenced.

In the prior art, the heating time and the heat preservation time are usually prolonged to eliminate defects, although the measures are convenient to implement, the production efficiency is seriously influenced, the energy consumption is very high, and meanwhile, the thickness of a decarburized layer and the number of oxidized round points are increased due to the overlong heating and heat preservation time, the development of micro cracks cannot be inhibited, and the defects of cracks are avoided.

Disclosure of Invention

In order to solve the defects of the prior art, the invention provides a blank heat treatment method and a blank heat treatment device, which can heat a tube blank by using the Joule effect of pulse current during treatment, so that the temperature of each point on the blank tends to be consistent, the plastic deformation capacity of the blank is improved, the plastic flow of a material is promoted to be continuous and uniform, and the material deformation resistance of the blank is reduced, so that the transverse crack defect is avoided during the subsequent blank perforation forming, the rejection rate is reduced, the forming power consumption is reduced, the production quality is improved, and the production benefit can be greatly improved.

In order to solve the technical problems, the invention provides the following technical scheme:

specifically, the invention provides a heat treatment method of a blank, which comprises the following steps:

s1, setting initial parameters: determining a heating environment i (i is 1,2,3) and a heating precision requirement K_iThe temperature T required by the blank perforation heat treatment, the maximum limit temperature difference delta T of each point of the blank after the pulse current heating is finished and the temperature measuring time interval T of the temperature measuring thermocouple, wherein when i is 1, the temperature represents the blankHeating in a heating furnace, wherein when i is 2, the blank is heated by means of flaming, and when i is 3, the blank is heated in an environment of applying pulse current; the precision requirement after the heating in the heating furnace is K₁The temperature precision requirement after the flaming heating is K₂The precision requirement after the heating by applying the pulse current is K₃；

S2, heating the blank by a heating furnace, which comprises the following steps:

s21, heating the blank in a heating furnace, detecting the temperature of each point on the blank in the heating furnace in real time by using a temperature measuring device, transmitting the real-time temperature data to an upper computer, determining the maximum value of the temperature by the upper computer by comparing the temperature of each point on the outer surface of the blank in the heating furnace, and calculating the following formula:

T_1max＝max{T₁’，T₁”，T₁”’，...，T₁ ⁽ⁿ⁾then calculating the real of the heating process in the heating furnace

S22 actual accuracy K in heating process in heating furnace₁' with accuracy requirement K after completion of heating in heating furnace₁And (3) comparison: if K₁’＜K₁Then, the steps S21-S22 are repeated until K₁’≥K₁(ii) a If K₁’≥K₁Then the step S3 is entered for next heating;

s3, carrying out flame spraying heating on the blank, which specifically comprises the following substeps:

s31, moving out of the heating furnace, carrying out flame spraying on the blank, stopping flame spraying after t time, inserting a temperature thermocouple into the blank to detect the temperature of the core part of the blank, transmitting real-time temperature data of each point on the inner surface of the blank to an upper computer in real time by the temperature thermocouple, comparing the temperature of each point on the inner surface of the blank in flame spraying heating by the upper computer, and determining the maximum value of the temperature, wherein the calculation formula is as follows:

T_2max＝max{T₂’，T₂”，T₂”’，...，T₂ ⁽ⁿ⁾calculating the actual accuracy in the flaming heating process

S32 actual precision K in heating process in flaming mode₂' with accuracy requirement K after completion of heating in flaming mode₂And (3) comparison: if K₂’＜K₂Repeating the steps S31-S32 until K₂’≥K₂(ii) a If K₂’≥K₂Then, the process goes to step S4 to perform the next heating process;

s4, heating the blank by pulse current, which comprises the following steps:

s41, stopping flaming heating, heating the blank in an environment with pulse current, increasing the temperature of the blank by using the joule heat of the pulse current, inserting a temperature thermocouple into the blank to detect the temperature of each point of the core part of the blank in the environment with the pulse current in real time, detecting the temperature of each point of the outer surface of the blank in the environment with the pulse current in real time by using an infrared thermometer, and transmitting the detected temperature data of the inner surface and the outer surface of the blank to an upper computer in real time; after the upper computer receives the temperature data, the temperature of each point on the inner surface and the outer surface of the blank in the environment of applying the pulse current is compared to obtain the maximum temperature value and the minimum temperature value, and the calculation formula of the maximum temperature value is T_3max＝max{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾The calculation formula of the minimum value of the temperature is T_3min＝min{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾}；

S42, calculating the maximum temperature difference delta T' between the inner surface and the outer surface of the blank under the environment of the pulse current application according to the maximum temperature value and the minimum temperature value and the actual precision in the heating process in the environment of the pulse current application

S43 actual accuracy K in heating process in environment of pulse current application₃' with accuracy requirement K after completion of heating in an environment where a pulse current is applied₃Comparing, and simultaneously comparing the maximum temperature difference delta T' of the blank with the maximum limit temperature difference delta T of the blank:

if K₃’＜K₃If yes, repeating the steps S41-S43; if K₃’≥K₃If delta T' is greater than delta T, stopping applying the pulse current, and ensuring that the temperature of each point on the blank tends to be consistent through a heat conduction mode;

if K₃’≥K₃Delta T' is less than or equal to delta T and T_3minIf the temperature is less than T, the heating is continuously carried out in the environment of pulse current, and the temperature of the lowest point of the blank is raised by using the joule heat of the pulse current;

if K₃’≥K₃Δ T' is less than or equal to Δ T, and T_3minAnd if the temperature is more than or equal to T, stopping pulse heating, and taking out the blank to perform a subsequent punching process.

In step S41, the infrared thermometer reciprocates by means of the slide rail, thereby measuring the temperature of each point on the outer surface of the billet.

Preferably, the invention further provides a blank heat treatment device, which comprises a workbench, an upper computer, a pulse power supply, a flaming heating assembly, a thermocouple temperature measuring assembly, a control console and a lead screw transmission assembly arranged on the workbench, wherein the lead screw transmission assembly comprises a first slide rail, a first fixed slide block, a first movable slide block and a first lead screw which are fixedly arranged on the workbench, the first end of the first slide rail is fixedly connected with the first fixed slide block, the second end of the first slide rail is provided with the first movable slide block which can move, the first lead screw penetrates through the space between the first fixed slide block and the first movable slide block, the first lead screw and the first movable slide block are connected through a connecting piece and then further connected with a first motor so as to realize the reciprocating motion of the first movable slide block on the first slide rail, the top ends of the first fixed slide block and the first movable slide block are respectively embedded with a pulse current anode and a pulse current cathode, the side surface of the workbench is symmetrically provided with infrared temperature measurement components;

the flame-throwing heating assembly comprises a second slide rail, a second fixed slide block, a second movable slide block and a second lead screw, the second fixed slide block is arranged on the second slide rail, the second lead screw is arranged between the second fixed slide block and the second movable slide block, the second lead screw is connected with a second motor, a first hydraulic cylinder is fixed on the second movable slide block, the first hydraulic cylinder is connected with a first hydraulic pump assembly, the other end of the first hydraulic cylinder is fixedly connected with an air inlet pipe bracket, and a spark plug ignition device is fixed on the air inlet pipe bracket;

the infrared temperature measurement assembly comprises a first infrared temperature measurement assembly and a second temperature measurement assembly, the first infrared temperature measurement assembly comprises a third slide rail, a third fixed slide block, a third movable slide block and a third lead screw, the third fixed slide block is fixed on one side of the third slide rail, the third lead screw penetrates through the third movable slide block and is connected with a third motor, a first supporting rod is fixed on the third movable slide block, a first infrared thermometer is connected onto the first supporting rod, and the second infrared temperature measurement assembly and the first infrared temperature measurement assembly are symmetrically distributed on the side face of the workbench;

the thermocouple temperature measurement component comprises a fourth slide rail, a fourth fixed slide block, a fourth movable slide block and a fourth lead screw, the fourth fixed slide block is fixed on the fourth slide rail, the fourth lead screw is arranged on the fourth slide rail, the fourth movable slide block is arranged on the fourth lead screw and connected with a fourth motor, a second hydraulic cylinder is fixed on the fourth movable slide block and connected with a second hydraulic pump component fixed on a second oil tank, the other end of the second hydraulic cylinder is fixedly connected with a thermocouple support, and a temperature measurement thermocouple is arranged on the thermocouple support.

Preferably, the hard pipe that admits air sets up on the intake pipe support, the hard pipe front end of admitting air is seted up and is 90 bocca that distribute along circumference, the hard pipe rear end of admitting air is admitted air the hose and is admitted air the hose through oxygen and natural gas and link to each other with oxygen gas pitcher and natural gas pitcher respectively.

Preferably, the top ends of the first fixed sliding block and the first movable sliding block are provided with inclined planes which are symmetrically distributed, so that blanks with different diameters can be supported.

Preferably, the front end of the air inlet hard pipe of the flame spraying assembly is divided into a plurality of sections, the air inlet hard pipe is provided with a thread pair, the air inlet hard pipes of the plurality of sections are fixedly connected through the thread pair, so that flame spraying treatment on blanks with different lengths is realized, the hydraulic cylinder below the air inlet pipe support can be driven by the hydraulic pump to extend and contract, and therefore the height of the air inlet pipe support is adjusted, so that flame spraying treatment on blanks with different diameters is realized.

Preferably, a taper air inlet for preventing backfire is arranged in the natural gas inlet hard pipe, and the spark plug ignition device comprises a spark plug and an ignition coil.

Preferably, when the blank is heated by the heating furnace, the position of the first movable slide block is adjusted by the console according to the length and the diameter of the blank, so that the sum of the distance between the first movable slide block and the first fixed slide block is close to the total length of the stainless steel tube blank, and the length of the air inlet hard tube and the height of the air inlet tube bracket are adjusted at the same time.

Preferably, the other end of the first hydraulic cylinder is connected with the air inlet pipe bracket and the first support rod is connected with the first infrared thermometer by means of connecting pieces.

Preferably, the other end of the first hydraulic cylinder is connected with the air inlet pipe support through a bolt, and the first support rod is connected with the first infrared thermometer through a cylindrical pin.

Compared with the prior art, the invention has the following beneficial effects:

(1) the blank after primary heating in the heating furnace is subjected to heat treatment in a pulse current auxiliary flame spraying mode, and during working, the blank is firstly placed in the heating furnace to be heated to a certain temperature, at the moment, the temperature difference between the inner surface and the outer surface of the blank is large, so that the temperature of the core part of the blank is rapidly increased in a flame spraying mode inside the blank, the temperature difference between the inner part and the outer part of the blank can be reduced, then pulse current is applied for heating, the temperature difference of the blank in different directions is reduced by utilizing the joule heat effect of the pulse current, the temperature of each point on the surface of the blank tends to be uniform, and the transverse crack defect generated during the punching process can be reduced.

(2) The invention adopts pulse current for heating, the pulse current is used as transient energy, which can provide motive power for diffusion migration of atoms in the blank, when the pulse current passes through the blank, the atoms on crack surfaces at two sides can be promoted to form bond combination again, the original long cracks are converted into short microcracks, holes are further formed, then, under the action of the pulse current, the dislocation and the atoms in the blank can move and fill the holes, finally, under the combined action of pressing and filling mechanisms, the sizes and the number of the holes are gradually reduced, the microcracks on the blank are finally healed, and the quality of the blank is improved.

(3) The pulse current can improve the heating efficiency, reduce the heat preservation time and the oxidation in the heating process, improve the plastic deformation capacity of the tube blank, promote the continuous and uniform plastic flow of the material, and reduce the deformation resistance of the material of the tube blank, thereby avoiding the occurrence of transverse crack defects, reducing the rejection rate of seamless steel tubes, reducing the forming power consumption, improving the production quality and greatly improving the production benefit during the subsequent perforation forming of the tube blank.

Drawings

The invention is further described below with reference to the accompanying drawings;

FIG. 1 is a schematic view of the general structure of the apparatus of the present invention;

FIG. 2 is a schematic diagram of the electrode and slider structure of the apparatus of the present invention;

FIG. 3 is a schematic view of the flame heating assembly of the apparatus of the invention;

FIG. 4 is a schematic view of the spark plug ignition device of the apparatus of the present invention;

FIG. 5 is a sectional view of the anti-backfire structure of the natural gas inlet hard tube of the device of the present invention;

fig. 6 is a flow chart of the operation of the heat treatment process of the blank of the present invention.

Some of the reference numerals in the figures are as follows,

1-a first hydraulic pump component, 101-a first oil tank, 102-a first hydraulic pump, 103-a hydraulic motor, 2-a natural gas inlet hose, 3-a natural gas tank, 4-a natural gas tank seat, 5-a second slide rail, 6-a second motor, 7-a second lead screw, 8-an oxygen tank seat, 9-an oxygen tank, 10-an oxygen inlet hose, 11-a flaming heating component, 111-an inlet hard pipe, 1111-a natural gas inlet hard pipe, 1112-an oxygen inlet hard pipe, 112-a spark plug ignition device, 113-a flaming port, 114-an inlet pipe bracket, 12-a pulse current cathode, 13-a first fixed slide block, 14-a blank, 15-a first lead screw, 16-a first slide rail, 17-a second infrared temperature measuring component, 18-a first movable slide block, 19-a pulse current anode, 20-a first motor, 21-a fourth slide rail, 22-a temperature thermocouple, 23-a thermocouple support, 24-a second hydraulic cylinder, 25-a fourth motor, 26-a fourth movable slide block, 27-a second hydraulic pump component, 28-a fourth lead screw, 29-an upper computer, 30-a fourth fixed slide block, 31-a control console, 32-a pulse power supply, 33-a third motor, 34-a workbench, 35-a third movable slide block, 36-a first support rod, 37-a first infrared thermometer, 38-a third slide rail, 39-a third lead screw, 40-a third fixed slide block, 41-a second fixed slide block, 42-a second movable slide block and 43-a first hydraulic cylinder.

Detailed Description

Exemplary embodiments, features and aspects of the present invention will be described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers can indicate functionally identical or similar elements. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

Specifically, the present invention provides a heat treatment method of a billet, as shown in fig. 6, which includes the steps of:

s1, setting initial parameters: determining a heating environment i (i is 1,2,3) and a heating precision requirement K_iThe temperature T required by the blank perforation heat treatment, the maximum limit temperature difference delta T of each point of the blank after the pulse current heating is finished and the temperature measuring thermocouple temperature measuring time interval T, wherein when i is 1, the blank is heated in a heating furnace, when i is 2, the blank is heated by a flame spraying mode, and when i is 3, the blank is heated in an environment where the pulse current is applied; the precision requirement after the heating in the heating furnace is K₁Spraying ofThe temperature precision requirement after the fire heating is K₂The precision requirement after the heating by applying the pulse current is K₃。

S2, heating the blank by a heating furnace, which comprises the following steps:

s21, heating the blank in a heating furnace, detecting the temperature of each point on the blank in the heating furnace in real time by using a temperature measuring device, transmitting the real-time temperature data to an upper computer, determining the maximum value of the temperature by the upper computer by comparing the temperature of each point on the outer surface of the blank in the heating furnace, and calculating the following formula:

T_1max＝max{T₁’，T₁”，T₁”’，...，T₁ ⁽ⁿ⁾then calculating the real of the heating process in the heating furnace

S22 actual accuracy K in heating process in heating furnace₁' with accuracy requirement K after completion of heating in heating furnace₁And (3) comparison: if K₁’＜K₁Then, the steps S21-S22 are repeated until K₁’≥K₁(ii) a If K₁’≥K₁Then the process proceeds to step S3 for the next heating.

S3, carrying out flame spraying heating on the blank, which specifically comprises the following substeps:

s31, moving out of the heating furnace, carrying out flame spraying on the blank, stopping flame spraying after t time, inserting a temperature thermocouple into the blank to detect the temperature of the core part of the blank, transmitting real-time temperature data of each point on the inner surface of the blank to an upper computer in real time by the temperature thermocouple, comparing the temperature of each point on the inner surface of the blank in flame spraying heating by the upper computer, and determining the maximum value of the temperature, wherein the calculation formula is as follows: t is_2max＝max{T₂’，T₂”，T₂”’，...，T₂ ⁽ⁿ⁾Calculating the actual accuracy in the flaming heating process

S32 actual precision K in heating process in flaming mode₂' with accuracy requirement K after completion of heating in flaming mode₂And (3) comparison: if K₂’＜K₂Repeating the steps S31-S32 until K₂’≥K₂(ii) a If K₂’≥K₂Then, the process proceeds to step S4 to perform the next heating process.

S4, heating the blank by pulse current, which comprises the following steps:

s41, stopping flaming heating, heating the blank in an environment with pulse current, increasing the temperature of the blank by using the joule heat of the pulse current, inserting a temperature thermocouple into the blank to detect the temperature of each point of the core part of the blank in the environment with the pulse current in real time, detecting the temperature of each point of the outer surface of the blank in the environment with the pulse current in real time by using an infrared thermometer, and transmitting the detected temperature data of the inner surface and the outer surface of the blank to an upper computer in real time; after the upper computer receives the temperature data, the temperature of each point on the inner surface and the outer surface of the blank in the environment of applying the pulse current is compared to obtain the maximum temperature value and the minimum temperature value, and the calculation formula of the maximum temperature value is T_3max＝max{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾The calculation formula of the minimum value of the temperature is T_3min＝min{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾}；

S42, calculating the maximum temperature difference delta T' between the inner surface and the outer surface of the blank under the environment of the pulse current application according to the maximum temperature value and the minimum temperature value and the actual precision in the heating process in the environment of the pulse current application

S43 actual accuracy K in heating process in environment of pulse current application₃' with accuracy requirement K after completion of heating in an environment where a pulse current is applied₃Comparing, and simultaneously comparing the maximum temperature difference delta T 'of the blanks'Comparing with the maximum limit temperature difference delta T of the blank:

if K₃’＜K₃If yes, repeating the steps S41-S43; if K₃’≥K₃If delta T' is greater than delta T, stopping applying the pulse current, and enabling the temperature of each point on the blank to be consistent in a heat conduction mode;

if K₃’≥K₃Delta T' is less than or equal to delta T and T_3minIf the temperature is less than T, the heating is continuously carried out in the environment of pulse current, and the temperature of the lowest point of the blank is raised by using the joule heat of the pulse current;

if K₃’≥K₃Δ T' is less than or equal to Δ T, and T_3minAnd if the temperature is more than or equal to T, stopping pulse heating, and taking out the blank to perform a subsequent punching process.

As shown in figure 1, the invention provides a heat treatment device for a stainless steel pipe blank, which comprises a blank 14 (a stainless steel pipe blank), a workbench 34, an upper computer 29, a pulse power supply 32, a pulse current electrode, a flaming heating assembly 11, a thermocouple temperature measuring assembly, a control console 31, infrared temperature measuring assemblies and a lead screw transmission assembly, wherein the two infrared temperature measuring assemblies are transversely and symmetrically fixedly arranged on two sides of the workbench 34, the lead screw transmission assembly is fixed between the two infrared temperature measuring assemblies, the flaming heating assembly 34 is arranged on one side of the stainless steel pipe blank 14, the pulse power supply 32 and the control console 31 are arranged on the other side of the stainless steel pipe blank 14, and the upper computer 29 is arranged in front of the control console 31. The host computer 29 is a computer or a central control machine or other controller in the embodiment.

The screw drive assembly comprises a first slide rail 16 transversely fixedly mounted on the workbench 34, a first movable slide block 18, a first fixed slide block 13 and a first screw 15, a first fixed slide block 13 is fixedly welded at the first end of the first slide rail 16, a first movable slide block 18 capable of moving is arranged at the second end of the first slide rail 16, a first screw 15 is arranged between the first fixed slide block 13 and the first movable slide block 18 in a penetrating mode, and the first screw 15 and the first movable slide block 18 are connected through bolts and a first motor 20 to achieve movement of the first movable slide block 18 on the first slide rail 16.

The flaming heating assembly comprises a second slide rail 5 arranged on the side face of a first fixed slide block 13, a second movable slide block 42, a second fixed slide block 41 and a second lead screw, a second lead screw 7 is arranged between the second fixed slide block 41 and the second movable slide block 42 which can move and welded on the second slide rail 5 in a penetrating manner, the second lead screw 7 is connected with a second motor 6, a first hydraulic cylinder 43 is fixed on the second movable slide block 42, the first hydraulic cylinder 43 is connected with a first hydraulic pump assembly 1, the first hydraulic pump assembly 1 comprises a first oil tank 101, a first hydraulic pump 102 and a motor 103, one end of the first hydraulic cylinder 43 is connected with a first hydraulic pump 102 fixed on the first oil tank 101, and the first hydraulic pump 102 is provided with a hydraulic motor 103. The other end of the first hydraulic cylinder 43 is fixedly connected with the air inlet pipe support 114 through a bolt or other connecting pieces, the air inlet hard pipe 111 comprises an oxygen air inlet hard pipe 1112 and a natural gas air inlet hard pipe 1111, the air inlet hard pipe 111 is erected on the air inlet pipe support 114, the air inlet pipe support 114 is fixed with a spark plug ignition device 112, the first end of the air inlet hard pipe 111 is provided with a flame jet 113 which is distributed at 90 degrees along the circumferential direction, and the second ends of the oxygen air inlet hard pipe 1112 and the natural gas air inlet hard pipe 1111 are respectively connected with the oxygen gas tank 9 and the natural gas tank 3 through an oxygen air inlet hose 10 and a natural gas inlet hose 2. The natural gas tank 3 is mounted by means of a natural gas tank mount 4. The oxygen tank 9 is fixed by means of an oxygen tank mount 8.

The infrared temperature measurement assembly comprises a first infrared temperature measurement assembly and a second infrared temperature measurement assembly, the first infrared temperature measurement assembly comprises a third sliding rail 38 fixed on the workbench, a third fixed sliding block 40, a third movable sliding block 35 and a third lead screw 39, the third fixed sliding block 40 is welded on one side of the third sliding rail 38, the third lead screw 39 penetrates through the third movable sliding block 35 and then is connected with a third motor 33, a first supporting rod 36 is fixed on the third movable sliding block 35, a first infrared thermometer 37 fixed by a taper pin or other connecting pieces is arranged on the first supporting rod 36, and the second infrared temperature measurement assembly 17 and the first infrared temperature measurement assembly are symmetrically distributed on the side face of the workbench 34.

The thermocouple temperature measurement component comprises a fourth slide rail 21 arranged on the side face of the first motor, a fourth lead screw 28, a fourth movable slide block 26 and a fourth fixed slide block 30, the fourth fixed slide block 30 is welded on the fourth slide rail 21, the fourth lead screw 28 is arranged between the fourth fixed slide block 30 and the fourth movable slide block 26 in a penetrating mode, the fourth lead screw 28 is connected with a fourth motor 25, a second hydraulic cylinder 24 is fixed on the fourth movable slide block 26, the first end of the second hydraulic cylinder 24 is connected with a second hydraulic pump component 27, the second end of the second hydraulic cylinder 24 is fixedly connected with a thermocouple support 23, and a temperature thermocouple 22 is arranged on the thermocouple support 23. The specific components of the second hydraulic pump assembly 27 are the same as those of the first hydraulic pump assembly 1, and will not be described herein.

As shown in fig. 2, the top ends of the first fixed sliding block 13 and the first movable sliding block 18 are provided with inclined planes which are symmetrically distributed to support stainless steel pipe blanks 14 with different diameters, meanwhile, the inclined planes at the top ends of the first fixed sliding block 13 and the first movable sliding block 18 are respectively embedded with a pulse current anode 19 and a pulse current cathode 12, and the material of the inclined planes at the top ends is selected to have excellent insulation and high temperature resistance, in a specific embodiment, the material of the pulse current electrodes embedded on the inclined planes at the top ends of the first fixed sliding block 13 and the first movable sliding block 18 is selected to be copper with very small resistance, and in the specific embodiment, the material of the inclined planes at the top ends is selected to be Hp5 mica plates with excellent insulation and high temperature resistance.

As shown in fig. 3, the front end of the air inlet hard pipe 111 of the flame-throwing heating assembly 11 is divided into a plurality of sections, and the sections are fixedly connected through thread pairs thereon to realize flame-throwing treatment of stainless steel pipe blanks 14 with different lengths, and the first hydraulic cylinder 43 below the air inlet pipe bracket 114 can be extended and contracted under the driving of the first hydraulic pump 1, so that the height of the air inlet pipe bracket 114 can be conveniently adjusted to realize flame-throwing treatment of stainless steel pipe blanks with different diameters.

As shown in fig. 4, the spark plug ignition device 112 includes an ignition coil 1121 and a spark plug 1122.

As shown in fig. 5, a conical air inlet is arranged in the natural gas inlet hard pipe 1111, and the conical air inlet can play a role in preventing backfire.

The working process and working principle of the present invention are further described below with reference to the following embodiments:

the following examples the parameters of the blanks to be heat treated and of the pulse current used are specified in the following table:

1. the billet parameters are as follows:

2. the pulse current parameters are given in the following table:

3. the temperature thermocouple temperature measurement time interval t parameter is shown in the following table:

specific example 1:

in this embodiment, the following table data is selected for the initial parameters:

the method specifically comprises the following steps:

step 1, setting initial parameters: determining a heating environment i (i is 1,2 and 3), wherein when i is 1, the stainless steel pipe blank 14 is heated in a heating furnace, when i is 2, the stainless steel pipe blank 14 is heated by means of flaming, and when i is 3, the stainless steel pipe blank 14 is heated in an environment where pulse current is applied; heating accuracy requirement K_iWherein the precision requirement after the heating in the heating furnace is K₁The temperature precision requirement after the flaming heating is K₂The precision requirement after the heating by applying the pulse current is K₃(ii) a The temperature T required by the piercing heat treatment of the stainless steel tube blank 14; after the pulse current heating is finished, the maximum limiting temperature difference delta T of each point of the stainless steel pipe blank 14 is achieved; measuring the temperature interval t by the temperature thermocouple;

step 2, adjusting the position of the first movable slide block 18 through the control console 31 according to the length and the diameter of the stainless steel tube blank 14, enabling the sum of the distances between the first movable slide block 18 and the first fixed slide block 13 to be close to the total length of the stainless steel tube blank 14, and adjusting the length of the air inlet hard tube 111 and the height of the air inlet tube bracket 114;

step 3, the stainless steel pipe blank 14 is placed in a heating furnace to be heated, i is equal to 1, the temperature of each point on the stainless steel pipe blank 14 in the heating furnace is detected in real time through a temperature measuring device in the heating furnace, temperature data are transmitted to an upper computer 29 in real time, and the upper computer 29 determines the maximum value T of the temperature of each point on the stainless steel pipe blank 14 in the heating furnace through comparison_1max＝max{T₁’，T₁”，T₁”’，...，T₁ ⁽ⁿ⁾After the minimum value of the temperature of each point in the heating furnace is determined, the upper computer 29 starts to calculate the heating in the heating furnace

Step 4, actual precision K in the heating process in the heating furnace₁' with accuracy requirement K after completion of heating in heating furnace₁And (3) comparison:

(1) if K₁' < 0.7, repeating the step 3-4;

(2) if K₁' > 0.7 or more, and carrying out the next heating process;

step 5, the stainless steel pipe blank 14 is placed in an i-2 mode, namely, heating is carried out in a flaming mode, after T time, flaming stops, the second motor 6 works to bring the flaming assembly 11 out of the stainless steel pipe blank 14, the fourth motor 25 works to insert the temperature thermocouple 22 into the stainless steel pipe blank 14 to detect the temperature of the core of the stainless steel pipe blank 14, the temperature thermocouple 22 transmits temperature data of all points on the inner surface of the stainless steel pipe blank 14 to the upper computer 29 in real time, and the upper computer 29 determines the maximum value T of the temperature of all points on the inner surface of the stainless steel pipe blank 14 in the flaming mode through comparison_2max＝max{T₂’，T₂”，T₂”’，...，T₂ ⁽ⁿ⁾After the maximum value of the temperature of each point in the flaming mode is determined, the upper computer 29 starts to calculate the actual precision in the heating process in the flaming mode

Step 6, actual precision K in the heating process in the flame spraying mode₂' with accuracy requirement K after completion of heating in flaming mode₂And (3) comparison:

(1) if K₂' < 0.92, repeating steps 5-6;

(2) if K₂' > 0.92 or more, and carrying out the next heating process;

step 7, stopping flaming heating, enabling the second motor 6 to work to bring the flaming assembly 11 out of the stainless steel pipe blank 14, enabling the fourth motor 25 to work to insert the temperature thermocouple 22 into the stainless steel pipe blank 14 to detect the temperature of the core part of the stainless steel pipe blank 14 in real time, enabling the two infrared thermometers to synchronously reciprocate on the sliding rails, so as to realize real-time detection of the temperature of each point on the surface of the stainless steel pipe blank 14 in the environment of applying the pulse current, the temperature data of the inner surface and the outer surface are transmitted to an upper computer 29 in real time, then the stainless steel tube blank 14 is placed in an environment where i is 3, namely, pulse current is applied for heating, the temperature of the blank is increased by using joule heat of the pulse current, after the upper computer 29 receives the temperature data, the maximum value T of the temperature at each point on the inner and outer surfaces of the stainless steel pipe blank 14 in the environment where the pulse current is applied is determined by comparison._3max＝max{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾And a minimum value T_3min＝min{T₃’，T₃”，T₃”’，...，T₃ ⁽ⁿ⁾After the maximum value of the temperature of each point in the environment of applying the pulse current is determined, the upper computer 29 starts to calculate the maximum temperature difference delta T' of the inner surface and the outer surface of the stainless steel pipe blank 14 in the environment of applying the pulse current and the actual precision in the heating process in the environment of applying the pulse current

Step 8, actual precision K in the heating process in the environment of pulse current application₃' with accuracy requirement K after completion of heating in an environment where a pulse current is applied₃The comparison is made by simultaneously comparing the maximum temperature difference Δ T' of the stainless steel blank 14 with that of the stainless steel blankThe maximum limit temperature difference Δ T of the steel pipe blank 14 is compared:

(1) if K₃' < 1, repeating the step 7-8;

(2) if K₃'is more than or equal to 1, and Delta T' is more than 30 ℃, the application of pulse current is stopped, and the temperature of each point on the stainless steel tube blank 14 tends to be consistent through a heat conduction mode of the stainless steel tube blank 14;

(3) if K₃'is not less than 1, Delta T' is not more than 30 ℃, and T_3minIf the temperature is less than 1210 ℃, the stainless steel tube blank is continuously heated in the environment of pulse current, and the temperature of the lowest point of the stainless steel tube blank 14 is raised by using the joule heat of the pulse current;

(4) if K₃'is not less than 1, Delta T' is not more than 30 ℃, and T_3minStopping pulse heating when the temperature is more than or equal to 1210 ℃, and taking out the stainless steel tube blank 14 to perform a subsequent perforation process;

specific example 2:

a TP316 stainless steel pipe blank with the initial temperature of 26 ℃ and the diameter of 329mm multiplied by 3000mm is taken to be heated to the temperature 1210 ℃ required by the perforation heat treatment, and the method comprises the following steps:

step 1, adjusting the position of the first movable slide block 18 through the control console 31 according to the length and the diameter of the stainless steel tube blank 14, enabling the sum of the distance between the first movable slide block 18 and the first fixed slide block 13 to be close to 3000mm, and adjusting the length of the air inlet hard tube 111 and the height of the air inlet tube support 114 to enable the height of the axes of the air inlet hard tube flame-throwing port, the stainless steel tube blank and the like.

Step 2, placing the stainless steel pipe blank 14 in a heating furnace for heating, detecting the temperature of each point on the stainless steel pipe blank 14 in real time through a temperature measuring device in the heating furnace, transmitting the real-time temperature data to an upper computer 29 in real time, and determining the maximum value T of the temperature of each point on the stainless steel pipe blank 14 in the heating furnace by the upper computer 29 through comparing the temperature of each point_1maxWhen the temperature is 860 ℃, the upper computer 29 starts to calculate the actual precision K in the heating process in the heating furnace according to a calculation formula₁’≈0.71。

Step 3, by comparing K₁' > 0.7, and therefore the next heating step is carried out.

Step 4, taking out the stainless steel pipe blank 14 and placingIs placed on the first fixed slide block 13 and the first movable slide block 18 and is subsequently heated by means of flame spraying, since at this time, the delta T₂1110-_2maxWhen the actual accuracy K in the heating process in the flaming mode starts to be calculated by the upper computer 29 at 1030 DEG C₂’≈0.85。

Step 5, by comparing K₂' < 0.92, so the heating is carried out by flame spraying, since the Delta T is in this case₂1110-_2maxWhen the actual accuracy K in the heating process in the flaming mode begins to be calculated by the upper computer 29 at 1130 DEG C₂’≈0.93。

Step 6, by comparing K₂If the temperature is higher than '0.92', the flaming heating is stopped, the second motor 6 works to bring the flaming component 11 out of the stainless steel tube blank 14, the fourth motor works to insert the temperature thermocouple 22 into the stainless steel tube blank 14 to detect the temperature of the core part of the stainless steel tube blank 14 in real time, the two infrared thermometers synchronously reciprocate on the slide rail to realize the real-time detection of the temperature of each point on the outer surface of the stainless steel tube blank 14 in the environment of applying the pulse current, the temperature data of the inner surface and the outer surface are transmitted to the upper computer 29 in real time, then the stainless steel tube blank 14 is placed in the environment of applying the pulse current to be heated, and the pulse current is utilized to carry out the heatingThe joule heat of the current increases the temperature of the billet, and the upper computer 29, after receiving the temperature data, determines the maximum value T of the temperature at each point on the inner and outer surfaces of the stainless steel pipe billet 14 in the environment where the pulse current is applied by comparison_3max1230 ℃ and minimum T_3min1160 ℃, the maximum temperature difference delta T' of the inner surface and the outer surface of the stainless steel pipe blank 14 is 70 ℃, and the actual heating precision K₃’≈1.02。

Step 7, by comparing K₃'is more than or equal to 1, and Delta T' is more than 30 ℃, the application of the pulse current is stopped, so that the temperature of each point on the stainless steel tube blank 14 tends to be consistent through the stainless steel tube blank 14 in a heat conduction mode, the temperature thermocouple and the infrared thermometer continuously carry out real-time detection on the temperature of each point on the inner surface and the outer surface of the stainless steel tube blank 14, and after a period of heat conduction, the maximum value T of the temperature of each point on the inner surface and the outer surface of the stainless steel tube blank 14 is_3max1220 ℃ and minimum value T_3min1190 deg.C, maximum temperature difference delta T' between inner surface and outer surface of stainless steel tube blank 14 equals 30 deg.C, and actual heating precision K₃’≈1.01。

Step 8, comparing the above values to find K₃'is not less than 1, Delta T' is not more than 30 ℃, and T_3minThe temperature is less than 1210 ℃, so the heating is continuously carried out in the environment of pulse current, the temperature of the lowest point of the stainless steel tube blank 14 is improved by using the joule heat of the pulse current, the temperature measuring thermocouple and the infrared thermometer continuously carry out real-time detection on the temperature of each point on the inner surface and the outer surface of the stainless steel tube blank 14, and after the pulse current is heated for a period of time, the maximum value T of the temperature of each point on the inner surface and the outer surface of the stainless steel tube blank 14_3max1230 ℃ and minimum T_3min1210 deg.C, 20 deg.C of maximum temp. difference delta T' between internal and external surfaces of stainless steel tube blank 14, and actual heating precision K₃’≈1.02。

Step 9, by comparing K₃'is not less than 1, Delta T' is not more than 30 ℃, and T_3minAnd stopping pulse heating at 1210 ℃, and taking out the stainless steel tube blank 14 for a subsequent punching process.

According to researches, the TP316 stainless steel pipe blank with the initial temperature of 26 ℃, the diameter of 300mm multiplied by 3000mm needs to be heated for 8 hours when the initial temperature is up to the process temperature of 1210 ℃, and the heat is preserved for 3 hours, which is 11 hours in total. The final inspection showed a rejection rate of 10.3% due to cracking, while the heating of the stainless steel tube blank using the apparatus and process proposed by the present invention was carried out for a total of 7.55 hours, and the final inspection showed a rejection rate of 5.2% due to cracking.

Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.