CN112355451A - Welding method of mining round-link chain - Google Patents

Abstract

The invention relates to a welding method of a mining round-link chain, which comprises the following steps of a) preparing before flash welding: fixing the chain ring on a welding machine by using an electrode, and connecting an inert gas pipe beside the electrode to prepare for introducing inert gas around the interface in the welding process; b) flash preheating: after the inert gas is introduced for 5-7s, the welding machine applies pressure stress to the chain link through the electrode for multiple times of interruption, so that two end faces to be welded of the chain link are in intermittent contact, lintel blasting, namely intermittent flashing, is formed to realize preheating, and the electrode is pushed to promote the burning quantity of the butt welding end to reach a set value; c) upsetting: applying upsetting pressure on the welding end face to rapidly reduce the welding interface gap, extruding liquid metal or softened metal and oxide inclusions on the welding end face to reach a set upsetting allowance, and enabling the joint to generate plastic deformation to form a firm welded junction joint; d) upsetting and maintaining pressure: keeping the upsetting pressure for 5-7 s.

Description

Welding method of mining round-link chain

Technical Field

The invention discloses a method for controlling welding of a round-link chain for a mine.

Background

The mining high-strength round-link chain is main equipment for mechanized mining under a coal mine, namely a transmission chain on a scraper conveyer, a scraper reversed loader, a coal mining machine and a coal plough; with the updating and upgrading of coal mining equipment, the requirement of the high-strength mining circular chain in a coal mine is increased day by day, and the strength requirement is increased; the ring forming welding of the round-link chain adopts flash butt welding, and the basic principle of the flash butt welding is as follows: the weldment is assembled into a butt joint, the power supply is switched on, the end faces of the weldment are gradually moved close to achieve local contact, the contact points are heated by resistance heat (flash is generated), the end face metal is melted, and when the end portions reach a preset temperature within a certain depth range, upsetting force is rapidly applied to complete welding. The chaining and welding process is divided into three types: cold braid cold welding, hot braid cold welding, and hot braid hot welding. The hot-braided chain cold welding, namely the flash welding mode, is more selected for the high-strength circular chain.

Flash effect of flash welding: 1) the heat source mainly comes from the resistance heat of the liquid lintel and the heat brought by the ejection of part of the metal liquid drops on the opposite end surfaces during the lintel blasting. 2) Foreign matters and unevenness on the welding end face are burnt, so that the surface quality requirement of the end face before welding is reduced; 3) the metal steam generated during the liquid lintel blasting reduces the invasion of air to the gap of the opposite opening, and forms self-protection. 4) The liquid metal layer formed on the end face at the end of flash provides an advantage for removing oxides and overheated metal during upset forging.

Upsetting effect of flash welding: 1) and closing the gap between the two opposite openings and extruding the fire hole left by the lintel blasting. 2) And completely removing the liquid metal layer on the end face, so that no cast structure remains in the welding seam. 3) Eliminating the inclusion of overheated metal and oxide, resulting in a tight bond of clean metal. 4) The proper plastic deformation of the butt joint and the adjacent area is obtained, and the recrystallization process of the welding seam is promoted.

At present, the high-strength mining circular-ring chain steel flash welding process is still immature, the problem of welding quality is prominent, the requirement of the chain-ring flash welding process on the capacity of a welding machine is high, and the process adjusting window is narrow; the method is mainly characterized in that a cold bending test and a tensile test of the chain ring have cracking phenomena, the main cracking position of the cracking is a flash welding crater, and analysis shows that most of crack sources on the fracture are cracked on the gray spot defects.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a welding method of a mining round-link chain aiming at the prior art, and through increasing the inert gas protection near a welding opening in the flash welding process, the alloy elements in chain steel such as Al, Si, Mn and the like are prevented from being oxidized at high temperature to form gray spots, so that the quality of the welding opening is improved, and the cracking phenomenon is inhibited.

In addition, through controlling parameters such as proper flash preheating times, upsetting speed, upsetting allowance, upsetting pressure, pressure maintaining time and the like, the overfire metal near the welded junction is fully ejected, and the quality and the performance stability of the flash welded junction are ensured.

In addition, the technological parameters of the flash welding are optimized by a method for judging the residual stress of the flash welding crater of the round-link chain for mining, and the technological parameters include but are not limited to the upsetting pressure, the upsetting pressure-holding time, the preheating time and the like of the flash welding.

The technical scheme adopted by the invention for solving the problems is as follows: a welding method for a mining round-link chain comprises the following steps

a) Preparation before flash welding: placing the chain ring subjected to surface shot blasting in the middle of an electrode, fixing the chain ring on a welding machine by using the electrode, connecting an inert gas pipe beside the electrode, and preparing for introducing inert gas around an interface in the welding process; the clamping length of the electrode is directly related to the burning amount of flash welding, the clamping length is too long, the burning amount is too large, unnecessary large ring back shunt is easily caused, the hot zone temperature gradient is too small, the clamping length is too small, the burning amount is too small, the hot zone temperature gradient is too large, and therefore the clamping length is determined according to the burning amount.

b) Flash preheating: firstly, an inert gas switch is started, an electrode is electrified after ventilation is carried out for 5-7s, a welding machine applies pressure stress to a chain ring through multiple discontinuous electrodes, two end faces to be welded of the chain ring are in discontinuous contact, lintel blasting, namely discontinuous flash, preheating of the end faces and the vicinity of the end faces is achieved in the process of flashing, metal on a section is melted through preheating, in the process of discontinuous flash, the electrode is pushed to promote the burning amount of the end faces to reach a set value, the length of a bar corresponding to one chain ring is set in advance, and the length of a part of bar is included, namely the burning amount. The qualified chain link has the length requirement, and the length of the sintering amount is equal to the blanking length, the perimeter of the finished chain link and the upsetting allowance.

c) Upsetting: applying sufficient upset forging pressure on the welding end face to rapidly reduce the gap of a welding interface, stopping lintel blasting, rapidly extruding liquid metal or softened metal and oxide inclusions on the welding end face to reach a set upset forging allowance, and enabling the joint to generate plastic deformation to form a firm welded junction;

d) upsetting and maintaining pressure: and maintaining the upsetting pressure for 5-7s, so that the joint part is fully welded, and the welded junction is prevented from cracking or cracking due to the deformation and rebound tensile stress of high-temperature metal at the welded junction on the chain ring.

Preferably, in order to achieve the crater temperature and hot zone temperature gradient required by welding, the setting of the sintering amount and the sintering time is not easy to overlong, the overlong sintering amount and the overlong sintering time cause material waste, and meanwhile, the annular control is not good, so that a D-shaped ring is easy to appear; and in the step b), the sintering amount is 20 percent of the diameter of the section of the chain ring, so that the temperature gradient of the ring opening cannot meet the welding requirement, cold welding is easy to occur, and the quality of the welded opening is affected.

Preferably, in step b, the electrode is connected with a power system, and electrode propulsion means that the electrode propels at a certain speed, namely the propulsion speed of the whole power system. The speed is controlled by a computer, the signal is fed back to the computer by the change of parameters such as current between electrified electrodes, and the feeding speed is automatically adjusted by the computer; generally, the propulsion is carried out at a constant speed, and if a horn mouth ring appears, the current between electrodes is relatively large, and the propulsion is faster.

Preferably, in step c), the upset forging allowance is blanking length-finished chain ring perimeter-sintering amount; the upset allowance has certain relation with the ring mouth quality during ring weaving, and when the ring mouth is the horn mouth type, the burn volume can grow, and the upset allowance can reduce, and upset allowance and burn volume sum are unchangeable basically, and the computer can be according to crater temperature gradient, adjust. The setting of the upsetting allowance is generally larger than the sintering length, and preferably, the setting is 2-3 mm larger than the sintering amount; but also considering the influence of steel grade, the higher the steel grade is, the larger the upsetting allowance is, and the upsetting allowance is increased by 0.4-0.8mm for every 100MPa of increase of the strength of the chain ring steel.

Preferably, in step c), the upsetting speed refers to the electrode running speed and is also the power system instantaneous upsetting speed, that is, after the flash firing is finished, the relative moving speed of the electrodes on the two sides of the crater is applied to rapidly extrude the high-temperature molten metal. Because the welding interface is protected by inert gas, the upsetting speed has little influence on the welding interface quality, namely, the process window of the upsetting completion time is enlarged, in the actual operation process, the upsetting speed is not too fast, the too fast upsetting speed means that a welding machine is required to provide larger load, and the upsetting speed is preferably less than or equal to 60 mm/s.

Preferably, in the steps b-d, the aeration flow of the inert gas is 20-60L/min, so that the formation of gray spots caused by high-temperature oxidation of alloy elements such as Al, Si, Mn and the like in the base metal is avoided, and the quality of a welded junction is improved.

The upsetting pressure, the upsetting pressure maintaining time and the burning amount in the flash welding method are adjusted by adopting the following correction methods:

1) sampling: taking the chain ring which is just subjected to end upsetting welding, and removing burrs at the welding seam of the chain ring;

2) and (3) cooling: after the welding is finished, the chain ring with the burrs removed is placed in a dry environment for air cooling;

3) cutting a gap: cutting a seam along the cross section of the chain ring to be measured, which is cooled to room temperature, wherein the cutting mode is that a molybdenum wire is cut at room temperature, and the spacing distance between the cutting position and the welding seam is less than 5 mm;

4) and (3) gap measurement: measuring the width of the cutting slit of step 3) and comparing it with the theoretical cutting width directly caused by the cutting device used to cut the slit,

if the cutting gap is smaller than the theoretical cutting width and is even 0, the upsetting pressure of flash welding is too large, the upsetting pressure maintaining time is too long, or the preheating sintering amount is too long, the residual compressive stress of the chain ring is increased, and the smaller the cutting gap is, the larger the residual compressive stress is;

if the cutting gap is larger than the theoretical cutting width, the upsetting pressure of flash welding is too small, the upsetting pressure maintaining time is too short, or the preheating sintering amount is too short, the residual tensile stress of the chain ring is large, and the larger the cutting gap is, the larger the residual tensile stress is;

if the cutting gap is equal to the theoretical cutting width, the upsetting force, the pressure maintaining time and the preheating and burning amount are proper;

5) adjusting the technological parameters of the flash welding according to the measurement result of the step 4, wherein the technological parameters comprise one or more of upsetting pressure, upsetting pressure maintaining time and preheating sintering amount;

6) repeating steps 1-4 until the cutting gap is close to or equal to the theoretical cutting width.

Compared with the prior art, the invention has the advantages that:

1) by adding the inert gas protection process near the crater in the flash welding process, the alloy elements in the steel matrix metal such as Al, Si, Mn and the like are prevented from being oxidized at high temperature to form gray spots, the source of gray spot defects is eliminated from the source, and the crater quality is improved.

2) The invention can effectively reduce relevant parameters such as the upsetting capability of the welding machine, has wider process adjustment window, and can reduce the rigorous requirement on the capability of the flash welding butt welding machine particularly for high-strength chain steel after inert gas protection is adopted.

3) Parameters such as flash preheating times (to adjust preheating sintering amount), upsetting speed, upsetting allowance, upsetting pressure and pressure maintaining time are adjusted to be proper, so that overfire metal near a welding opening is fully ejected, and residual stress (residual tensile stress or residual compressive stress) of the welding opening is reduced to ensure the quality and the performance stability of the flash welding opening.

4) The method for correcting the welding process parameters has the advantages of simple equipment and convenient operation; the welding engineer can quickly judge the form of the residual stress according to the clearance: residual tensile stress or residual compressive stress, and parameter adjustment is properly carried out to assist in improving welding efficiency and crater quality.

Drawings

FIG. 1 is a schematic view of the springback force, i.e., the residual tensile stress, of a chain link crater after flash welding;

FIG. 2 is a view showing the chain ring sample after wire cutting.

Detailed Description

The present invention will be described in further detail below with reference to the attached drawings, which are illustrative and are not to be construed as limiting the invention. The description of the present embodiment is corresponding to the accompanying drawings, and the description related to the orientation is also based on the description of the accompanying drawings, and should not be construed as limiting the scope of the present invention.

The embodiment relates to a high-strength mining round-link chain which comprises the following chemical components in percentage by mass: c: 0.20 to 0.26; ti: 0.45 to 0.57; si: less than or equal to 0.25; mn: 1.10 to 1.50; p is less than or equal to 0.013; s is less than or equal to 0.010; cr: 0.40 to 0.60; ni: 0.90 to 1.10; 0.19 to 0.30 percent of Cu; mo: 0.50 to 0.60; the balance of Fe, and the specification of the mining chain bar material is phi 34 mm. The tensile strength grade is above 1300 MPa. Finally welding to form a chain ring with the size of phi 34mm x 126 mm; the manufacturing process of the mining round-link chain mainly comprises the following steps: firstly, blanking; induction heating; thirdly, thermally knitting rings; fourthly, shot blasting on the surface; flash welding; sixthly, deburring; seventhly, stretching for the first time; eighthly, medium-frequency induction quenching and medium-temperature tempering; ninthly, secondary stretching.

Firstly, optimizing parameters of a flash welding process:

1. according to the experience of welding engineers, a flash welding process specification is set approximately, and a middle value in a specification range is taken for testing.

2. Cooling the welded chain ring;

after the flash welding is finished, the chain ring with the burrs removed is placed on the dry ground for air cooling; water cooling or placement on a wet ground should be avoided to prevent excessive internal stresses in the tissue from developing as a result of cooling too quickly. And the steel plate is not easy to be placed in a heating furnace for heat preservation, so that tempering in the heating furnace is prevented, and further, partial high-temperature residual stress is eliminated. The chain ring is cooled by following the normal air cooling mode of the chain ring, so that the relation between the residual stress and the notch gap can be really reflected.

3. Cutting slit

As shown in fig. 2, a seam is cut along the cross section of the chain ring to be measured, which is cooled to room temperature, and the cutting position is within 5mm from the welding seam; wire cutting is adopted, and the diameter of the molybdenum wire for wire cutting is as follows: 0.12mm and the theoretical cutting width is 0.12 mm.

4. Gap measurement

Measuring the size of the gap by using a feeler gauge; for the chain ring with residual compressive stress, the cut gap is smaller than the diameter of the molybdenum wire, even the two cut surfaces are tightly attached, the size of the gap cannot be measured, and the residual stress is judged to be the residual compressive stress, which indicates that the upsetting pressure is too large or the pressure maintaining time is too long. For the chain ring with tensile stress, the slit is larger than the diameter of the molybdenum wire after cutting, the larger the opening slit is, the larger the residual stress is, the upsetting force is too small or the dwell time is too short, and if the upsetting force is just equal to the diameter of the molybdenum wire, the upsetting force and the dwell time are proper. And adjusting the upsetting pressure and/or the upsetting pressure maintaining time according to the comparison between the gap width and the theoretical cutting width.

5. And performing a welding test again by using the adjusted welding process, continuously measuring the deviation of the cutting gap relative to the theoretical cutting width, further adjusting the welding process until the deviation range is controlled to be 0-0.01mm, and taking the corresponding welding process parameter as a better process parameter of the mining circular-ring chain flash welding in the embodiment for batch welding.

Secondly, the flash welding step of the high-strength mining round-link chain of the embodiment is as follows:

1. and (4) preparing flash welding.

And placing the chain ring with the shot-blasted surface in the middle of the electrode, and fixing the chain ring on a welding machine by using the electrode. Meanwhile, an argon pipe is connected to the side of the electrode to prepare for introducing argon in the welding process. In order to prevent the problems of short circuit, high temperature influence on an argon pipeline and the like, a ceramic tube is selected for the area of the argon tube close to the electrode. The argon gas adopts 100 percent pure argon; the control of the clamping length also has great influence on flash welding, and the clamping length is too long, so that unnecessary excessive large ring back shunt is easily caused, and the temperature gradient of a hot zone is reduced. Too small a clamping length will cause too large a temperature gradient in the hot zone; in order to achieve the crater temperature and hot zone temperature gradient required for cold welding, the burn length and burn time are relatively long, resulting in a narrow hot zone that does not achieve the desired temperature gradient required for a good quality joint. Affecting the quality of the weld.

End face clearance of chain ring: (3-4) mm; clamping length: (30-40) mm;

2. flash preheating;

firstly, an argon pipe switch is started, in order to ensure that the periphery of a welding electrode is filled with argon, the electrode is electrified after 5-7 seconds of ventilation, a welding machine applies pressure stress to a chain link through the electrode for multiple times, the end face of the chain link to be welded is in intermittent contact, lintel blasting, namely intermittent flashing, the part near the end face to be welded is heated in the flashing process, and metal on the section is melted. The electrode is advanced uniformly until the burning amount reaches a set value. The principle of selecting the sintering amount is to ensure that the two heating surfaces of the weldment are uniformly heated, the chain ring has the optimal temperature distribution, and high-temperature plastic deformation-prone areas in a certain range exist on the two end surfaces, so that good upsetting conditions are created for upsetting.

Preheating related parameters: the argon gas ventilation flow is as follows: 30L/min; electrode advancing speed: (0.3-0.4) mm/s; the burning speed is as follows: (0.5-1.0) mm/s; reversing stroke: 2.5 mm; the flash frequency: (11-13) times; flash burn amount set value: 3 mm. Actual amount of firing: 3.1 mm. Secondary voltage: (10-12) V.

3. Upsetting;

and applying enough top pressure on the welded end face, rapidly reducing the interface clearance, stopping the lintel blasting, rapidly extruding out liquid metal or softened metal and oxide inclusions on the end face to reach the set upsetting amount, and finally generating certain plastic deformation on the joint to form a firm welded junction. The high-strength mining chain steel is high in high-temperature strength, so that a larger upsetting force needs to be loaded during upsetting to ensure that a welded junction is fully fused.

Relevant parameters of the upsetting process: and (3) setting of upsetting stroke: 4 mm-7 mm; actual upsetting stroke: 5.2 mm; setting upsetting speed: (50-80) mm/s; the actual upsetting speed is as follows: 52 mm/s. Upsetting pressure: 120bar (12 MPa).

4. Upsetting and maintaining pressure;

in the embodiment, cold welding is adopted, enough pressure maintaining time after upsetting is required to be ensured, when two end faces of a chain ring are gradually close to each other and are subjected to rapid upsetting, a clamp (an electrode) is rapidly opened, two sides of a welding ring generate resilience force diagram 1, high-temperature metals which are just fused together bear tensile stress, and a welded junction structure is loose; as the diameter of the bar increases, the upset pressure holding time needs to be gradually prolonged, but in order to improve the welding efficiency, the pressure holding time after upset forging needs to be controlled within a certain range.

Upsetting and pressure maintaining relevant parameters: and the upsetting oil cylinder continuously upsets for 5-7s, so that the joint part is fully welded, and the welded junction is prevented from cracking or microcracking caused by the deformation and rebound tensile stress of high-temperature metal at the welded junction on the chain ring.

In addition to the above embodiments, the present invention also includes other embodiments, and any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of the claims of the present invention.

Claims (7)

1. A welding method of a mining round-link chain is characterized by comprising the following steps: comprises the following steps

a) Preparation before flash welding: placing the chain ring subjected to surface shot blasting in the middle of an electrode, fixing the chain ring on a welding machine by using the electrode, connecting an inert gas pipe beside the electrode, and preparing for introducing inert gas around an interface in the welding process;

b) flash preheating: firstly, an inert gas switch is started, an electrode is electrified after ventilation is carried out for 5-7s, a welding machine applies pressure stress to a chain ring through multiple intermittent electrode application, two end faces to be welded of the chain ring are in intermittent contact, lintel blasting, namely intermittent flash, preheating of the end faces to be welded and the vicinity of the end faces to be welded is achieved in the process of flashing, metal on a section is melted through preheating, in the process of intermittent flash, electrode propulsion is carried out to promote the burning quantity of the end faces to be welded to reach a set value, the burning quantity refers to the length of the end to be welded of the chain ring, and the length of the burning quantity is equal to blanking length, finished chain ring perimeter and upsetting allowance;

c) upsetting: applying sufficient upset forging pressure on the welding end face to rapidly reduce the gap of a welding interface, stopping lintel blasting, rapidly extruding liquid metal or softened metal and oxide inclusions on the welding end face to reach a set upset forging allowance, and enabling the joint to generate plastic deformation to form a firm welded junction;

d) upsetting and maintaining pressure: and maintaining the upsetting pressure for 5-7s, so that the joint part is fully welded, and the welded junction is prevented from cracking or cracking due to the deformation and rebound tensile stress of high-temperature metal at the welded junction on the chain ring.

2. The welding method of the mining round link chain according to claim 1, characterized in that: in step b), the amount of burning is 20% of the diameter of the chain ring section.

3. The welding method of the mining round link chain according to claim 1, characterized in that: in the step c), the upsetting allowance is 2-3 mm more than the burning allowance in the step b).

4. The welding method of the mining round link chain according to claim 1, characterized in that: in the step c), because the welding interface is protected by argon, the upset forging speed has little influence on the welding interface quality, namely, a process window of the upset forging finishing time is enlarged, and the upset forging speed is less than or equal to 60 mm/s.

5. The welding method of the mining round link chain according to claim 1, characterized in that: in the steps b-d, the aeration flow of the argon is 20-60L/min.

6. The welding method of the mining round link chain according to claim 1, characterized in that: the upsetting pressure, the upsetting pressure-maintaining time and the burning amount in the welding method are adjusted by adopting the following correction method:

1) sampling: taking the chain ring which is just subjected to end upsetting welding, and removing burrs at the welding seam of the chain ring;

2) and (3) cooling: after the welding is finished, the chain ring with the burrs removed is placed in a dry environment for air cooling;

3) cutting a gap: cutting a seam along the cross section of the chain ring to be measured, which is cooled to room temperature, wherein the spacing distance between the cutting position and the seam is less than 5 mm;

4) and (3) gap measurement: measuring the width of the cutting slit of step 3) and comparing it with the theoretical cutting width directly caused by the cutting device used to cut the slit,

if the cutting gap is smaller than the theoretical cutting width and is even 0, the upsetting pressure of flash welding is too large, the upsetting pressure maintaining time is too long, or the preheating sintering amount is too long, the residual compressive stress of the chain ring is increased, and the smaller the cutting gap is, the larger the residual compressive stress is;

if the cutting gap is larger than the theoretical cutting width, the upsetting pressure of flash welding is too small, the upsetting pressure maintaining time is too short, or the preheating sintering amount is too short, the residual tensile stress of the chain ring is large, and the larger the cutting gap is, the larger the residual tensile stress is;

if the cutting gap is equal to the theoretical cutting width, the upsetting force, the pressure maintaining time and the preheating and burning amount are proper;

5) adjusting the technological parameters of the flash welding according to the measurement result of the step 4, wherein the technological parameters comprise one or more of upsetting pressure, upsetting pressure maintaining time and preheating sintering amount;

6) repeating steps 1-4 until the cutting gap is close to or equal to the theoretical cutting width.

7. The welding method of the mining round link chain according to claim 6, characterized in that: the cutting mode adopted in the step 2) is molybdenum wire cutting, and the cutting is carried out at room temperature.

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