What is a flat die roll

What is a flat die roll

What is a flat die roll?

Flat die roll, the two square templates on the tooth rubbing machine are divided into two pieces, one long and one short, with tooth patterns on them, which are used to extrude the screws into threads.

Screw plate is a special tool for machining taps and bolts.
Screw plate is the most commonly used thread tool for processing screws and bolts in the standard fastener industry. The processing principle mainly adopts cold extrusion, which has the advantages of high production efficiency, low processing cost, high thread precision and strength, good surface quality and so on.

Structural form of screw plate

There are two structural forms of wire rubbing plate: movable wire rubbing plate and fixed wire rubbing plate.

Working characteristics of flat die roll

The flat die roll is generally formed by cold rolling. It is not processed after heat treatment. During operation, the tooth shall bear severe impact load and extrusion stress. After heat treatment, the hardness within 3 to 5mm below the tooth root is 58 to 61hrc, quenched martensite is less than grade 3, and there is no decarburization on the tooth surface.

Work requirements of flat die roll

The wire rubbing board shall have high hardness, wear resistance, sufficient strength, certain impact force and strong fatigue resistance.

Material selection requirements of flat die roll

GB / T 972 flat die roll stipulates that the flat die roll is made of 9SiCr and Cr12MoV steel, and the hardness of the working part is 59-62hrc. If it is > 62Hrc, it is easy to collapse and if it is < 59HRC, it is easy to wear; Quenched martensite < grade 3; The working surface shall be free of decarburization and low hardness; The surface of the flat die roll shall be free of cracks, nicks, rust, grinding burns and other defects affecting the service performance.
According to the working conditions of the flat die roll, the selected materials shall have the following properties:

• (1) Good hardenability, high matrix hardness and good wear resistance;
• (2) Good dimensional stability;
• (3) Good impact toughness and appropriate strength;
• (4) Good machinability and hot machinability.

Therefore, the common materials suitable for manufacturing are 9SiCr, Cr12 or Cr12MoV, but most factories use 9SiCr at present.

Processing technology of thread rolling board

The manufacturing route of thread take-up plate is: blanking – forging – spheroidizing annealing – machining – cold rolling thread – quenching + low temperature tempering – grinding
Forging of flat die roll:
This process is to repeatedly upsetting and lengthening the bar in order to make the carbide distribution uniform and change the internal streamline distribution of the steel.
Spheroidizing annealing of flat die roll:
The hardness of the blank is high and the composition is uneven. In order to reduce the hardness and facilitate cutting, it is also well prepared for the final heat treatment. The technical indicators are:

• ① 9SiCr Steel, hardness 197-241hb
• ② The depth of decarburization layer shall not exceed 1 / 2 of the machining allowance. Heat it to 790 ℃ for 2h, cool it to 710 ℃ for 7h, cool it to 500 ℃ for air cooling. Structure after spheroidizing annealing: spherical pearlite.

Cold rolling thread of thread take-up plate:
It is a key process in the manufacturing process. The thread is processed by needle roller, and its accuracy directly affects the quality of the processed external thread. Therefore, the technical requirements should be strictly implemented.
Heat treatment of flat die roll:

• ① Technical requirements: hardness 58-62hrc; Quenched martensite is less than grade 2.5 [in metallographic examination (500X)]; The tooth surface shall be free of oxidation, decarburization and pitting.
• ② Process flow: preheating – heating – cooling – Cleaning – tempering – hardness inspection – blackening – appearance inspection.

Tempering process of flat die roll:

• ① Due to the action of Si and Cr elements, the tempering stability of steel is improved, so it is tempered at 200-230 ° C. At this temperature, the hardness decreases little, and it still has high hardness after tempering.
• ② The microstructure after tempering is: m-back + granular carbide + a small amount of retained austenite.

Failure form of thread take-up plate:
The most common failure forms of flat die roll mainly include fatigue failure, wear, knife collapse, tooth stacking, tooth pattern peeling, etc.
The failure forms of flat die roll are mainly caused by cold working, hot working and improper use by users.
Cold working:

• (1) The screw thread is buckled disorderly, mainly because the helix is not straight, and the thread take-up plate has axial displacement during manufacturing.
• (2) Tooth profile peeling, dislocation during thread rolling, resulting in tooth profile jacket and double tooth tip, mainly because the rolling time is too long and repeated for many times, or the mechanism of tooth profile is unreasonable, such as too sharp tooth top, tooth root or right angle and poor machining, or grinding speed and feed rate are too large and poor lubrication and cooling, resulting in grinding paste and microcrack and other defects; The demagnetization of the wire rubbing plate before leaving the factory is not complete, and the fine iron powder is adsorbed on the teeth during service, resulting in the mutual grinding of the teeth, which will affect the service life.

Heat treatment:
(1) Oxidative decarburization – the final heat treatment after the thread rolling processing of the thread rolling plate. If heated in a non protective atmosphere furnace, it is easy to lead to oxidative decarburization. Decarburization of steel reduces the amount of carbon on the surface of steel materials due to oxidation. Decarburization occurs when the oxidation rate is lower than the diffusion rate of carbon (c) to the outer layer of the metal. On the contrary, oxidation occurs when the oxidation rate is higher than the diffusion rate of carbon to the outer layer of the metal, forming iron oxide scale peeling. The ferrite grain structure formed by decarburization has two forms: columnar grain decarburization and granular grain decarburization, which leads to the reduction of hardness, wear resistance and fatigue strength, and early failure such as tooth pile and whole tooth pattern peeling during service. Due to the chemical reaction between O2, CO2, H2O and iron (FE) in steel during heating:

• 2Fe+O2→2FeO
• Fe+CO2→FeO+CO
• H2[O]+H2+3Fe+4[O]→ Fe3O4
• 2Fe+3[O] →Fe2O3
• Fe2O3+mH2O→ Fe2O3·mH2O

Under the action of furnace gas, carbon (c) in steel reacts with furnace gas to decarburize the die. Chemical reaction formula:

• Fe(C)+1/2O→2Fe+CO
• Fe(C)+2H2O →Fe+CH4+O2
• 2Fe(C)+CO2→2Fe+2CO
• Fe(C)+H2O →Fe+H2+CO

Coarse austenite grain – the austenite grain grows significantly to Grade 5-6 (grade 10.5-11.0 is required) due to excessive quenching heating temperature and holding time, inaccurate instrument temperature control and improper preliminary heat treatment, and the original structure is not refined. The austenite grain of steel is determined as grade 13, with grade 1 being the coarsest and grade 13 being the finer. Grades 1-3 are coarse grains, grades 4-6 are medium coarse grains, grades 1-4 are superheated austenite grains with poor mechanical properties, grades 7-9 are fine grains, and grades 10-13 are ultra-fine grains. The finer the grain, the better the strength and toughness of the steel, the better the comprehensive mechanical properties, and the required cryptocrystalline martensite can be obtained by quenching; The coarser the grain, the worse the strength and toughness of the steel. The brittle coarse martensite structure is obtained by quenching, which is easy to lead to tooth spalling and edge collapse failure. However, it is not suitable to reduce the quenching heating temperature and hardness to obtain strength and toughness, because it will reduce the wear resistance of teeth. Distortion – although the steel is rolled, the eutectic carbides of Cr12 Steel are broken to a certain extent, but they are distributed in strips along the rolling direction, resulting in obvious directionality of properties and distortion. Therefore, it is necessary to modify the forging, smash the eutectic carbides to make them ≤ grade 3, and make the forged fiber fabric have no directional distribution, which can effectively reduce the distortion. Secondly, the tooth profile of the thread take-up plate is formed by rolling, and there is large internal stress on the surface. In the rolling process, due to uneven stress and inconsistent metal flow, it is easy to cause distortion of the parallelism between the tooth profile surface and the bottom plane. The process must be strictly controlled to control the distortion within the allowable range.
Corrosion – Cr12 Steel is a high carbon and high chromium ledeburite steel. There is (Fe · CR) 7C3 eutectic carbide in the structure, which has serious segregation, generally grade 3-7. After repeated double cross upsetting and drawing forging, it can be reduced by grade 2-3. The die requires eutectic carbide ≤ grade 3, preferably grade 1-2.
Improper use by users:
When the two dies are misaligned, the rubbing wire will move axially, so that the tooth pattern will be subjected to extrusion and shear stress; The hardness of the twisted thread blank is too high and uneven, or the twisted thread blank is mixed without tempering after quenching; The worn thread blank with oxide scale, grinding wheel particles, dirt and no lubricant will lead to tooth collapse and early wear failure. The research shows that gw30 alloy has higher hardness, wear resistance and small distortion than Cr12 Steel. It can also carry out cold and hot working, heat treatment strengthening and forging deformation, which fills the gap between cemented carbide and tool and die melting steel.

Heat treatment process of flat die roll

According to the processing object, select the appropriate wire rubbing plate material and carry out targeted heat treatment, so as to produce high-quality and long-life cutting tools. The following introduces the more applicable and stable heat treatment process according to the material of wire rubbing board for reference.
1. Heat treatment of 9SiCr Steel Wire rubbing plate
Thread rolling plate is a tool for rolling external thread. When working, the tooth is subjected to strong impact load and extrusion stress, which usually fails due to wear or fatigue. The hardness shall be 58-61hrc within 3-5mm below the tooth root after heat treatment; Quenched martensite < grade 3; Decarburization is not allowed on the tooth surface; The tooth surface deformation is within the tolerance range. Quenching is generally carried out in a fully deoxidized salt bath, and the heat treatment process is as follows.
(1) Binding
According to experience, bind the two workpieces back to back on the special quenching fixture.
(2) Quenching
860-870℃ × 0.4-0.5min/mm, ≤ M6 specification quench 170-180 ℃ nitrate, > M6 specification quench 60-90 ℃ oil, oil cooling to about 200 ℃, oil outlet air cooling.
(3) Tempering
210-230℃ × 2-3H nitrate tempering, hardness 59-62hrc after tempering.
2. Micro deformation quenching of Cr12MoV steel arc flat die roll
In the instrument industry, a large number of screws of several millimeters are required, and the deformation of these screws is strictly required, which is only allowed to be ≤ 0.01mm. This puts forward higher requirements for the arc wire rubbing plate: small deformation, high hardness and good wear resistance. Therefore, Cr12MoV steel is selected to manufacture the wire rubbing plate, and the heat treatment process is as follows.
(1) Preparation before quenching
Wrap the flat die roll with multi-layer newspapers (do not tie it with iron wire to prevent corrosion of the flat die roll during heating), so that the surface of the flat die roll is smooth and clean. Then put the wire rubbing plate into a small iron box, fill and compact it with fine charcoal particles around, seal it with yellow mud, make preparations according to the requirements of solid carburization, and finally heat it in a box furnace.
(2) Quenching heating
The flat die roll has no requirements for thermal hardness, but the wear resistance must be high. Therefore, the quenching heating temperature is selected to ensure high hardness, and the lower 980 ℃ is used for heating and quenching.
(3) Cooling
Take out the workpiece quickly after the furnace is discharged. During cooling, the upper and lower planes of the flat die roll are pressed and cooled with brass plate. At the same time, blow a small amount of compressed air on the outer working surface. When it is cooled to about 500 ℃, put it into oil cooling. Note that at this time, the brass plate clamp is still used for continuous cooling, and the thickness of the copper plate is generally 12-15mm.
(4) Tempering
170-180℃ × 2h × Twice tempering in oil. Nitrate tempering can also be used, but the oil must be removed before tempering.
After the above process, the hardness of the arc wire rubbing plate can reach 65hrc, and the toughness is very good, the deformation is ≤ 0.007mm, no crack and wear are found after more than 100000 times of wire rubbing, and the service life is more than 150000 times.
3. Salt bath quenching of Cr12MoV steel screw threading plate
Cr12MoV steel tool salt bath quenching generally consists of two processes: low quenching and low recovery (1020-1030 ℃ heating quenching and 180-200 ℃ tempering) and high quenching and high recovery (1100-1120 ℃ heating quenching and 500-520 ℃ tempering). This process is different from the first two. It adopts not high but not low quenching temperature and high temperature tempering. The operation procedure is as follows.
(1) Preheat
After drying at 400-500 ℃, it is preheated in a medium temperature furnace at 820-850 ℃, and the heating coefficient is 30-40s / mm.
(2) Heat
When heating in high-temperature furnace, the slag shall be fully deoxidized, 1040-1050 ℃ × 15-20s/mm。
(3) Cooling
When Cr12MoV steel is heated and quenched at about 500 ℃, there is a relatively stable area of austenite. If this area is maintained for a long time, austenite will not change. In view of this, graded isothermal quenching is adopted: grade in 580-620 ℃ neutral salt bath for 3-5min, and immediately transfer to 250-280 ℃ nitrate for isothermal 30-45min.
(4) Tempering
500-520℃ × 2h × Twice tempering in nitrate.
The wire rubbing plate treated by the above process has small deformation, hardness of 59-60hrc and long service life compared with conventional treatment.
4. Cr12MoV steel wire rubbing plate vacuum quenching
Cr12MoV steel M2.5 thread rubbing plate is used to rub bicycle web threads. It is quenched in salt bath for a long time, with low hardness, decarburization and easy deformation. The maximum service life is 120000 pieces. Vacuum quenching at 1030-1060 ℃ and 120-150 ℃ × After 5-6h vacuum tempering, the hardness is high, the distortion is small, and the average service life is 688500 pieces, which is more than 4 times longer than that of salt bath treatment.
5. Cr12 Steel flat die roll is rapidly heated and quenched at high temperature
Cr12 Steel tools are generally quenched by 960-980 ℃ salt bath heating. In order to improve the toughness of the matrix and refine the grain, high temperature salt bath rapid heating has been successfully used in the heat treatment of flat die roll. The test shows that the service life of the wire rubbing plate treated by the conventional process is generally 540000-550000 pieces, while that of the high-temperature rapid heating is 1450000-1540000 pieces, which is nearly three times longer. The heat treatment process is:
(1) Preheat
820-850 ℃ after drying at 400-500 ℃ × 2-3min preheating.
(2) Heat
1080℃ × 100-200s (depending on the specific product) heating.
(3) Cooling
Cool in hot oil at 50-80 ℃.
(4) Tempering
Remove oil stains at 230-240 ℃ × Tempering in nitrate for 2h.
Why can high temperature and rapid heating improve the service life of the wire rubbing plate? It is generally believed that due to the uneven dissolution of carbides, the reduction of average carbon content in austenite and the uneven composition of austenite during high-temperature and rapid heating, part of low-carbon martensite can be obtained after quenching. At the same time, carbon can not diffuse in a short time (100-200s) around the original carbide and at the austenite grain boundary to form austenite with high carbon content. After quenching, the retained austenite with high toughness is continuously distributed around the carbide and at the grain boundary, which is helpful to improve the strength and toughness.
6. Vanadizing composite treatment of Cr12 Steel flat die roll
At present, vanadium infiltration is one of the methods to obtain high surface hardness and high wear resistance in various chemical heat treatments. Physical vapor deposition has the advantages of low processing temperature and small workpiece deformation, but the equipment cost is expensive; The equipment used in CVD is also expensive and complex, and the treatment temperature is high and the workpiece deformation is large; Vanadium infiltration by molten salt method is to form a carbide coating of vanadium on the surface of the workpiece. Its advantages are simple equipment, convenient operation and pollution-free. The method of adding ferrovanadium powder into salt bath is usually used for vanadium infiltration, but the cost is high and the process is complex. The application of borax salt bath vanadizing process on Cr12 Steel flat die roll is introduced below.
Vanadization is carried out in a self-made salt bath furnace. The molten salt is anhydrous borax and the carburizing agent is V2O5 powder. After the salt is completely melted, add a small amount of aluminum powder, heat it to 950 ℃ after full melting, put the strengthened and toughened samples and workpieces into the furnace and heat them for 3.5H and 4.5H. In order to simplify the process, the test of vanadium infiltration into 950 ℃ salt bath after quenching at 1050 ℃ and tempering at 680 ℃ was carried out. After strengthening and toughening treatment and vanadium infiltration composite treatment, the mechanical properties of the matrix are shown in Table 1.
Table 1 Mechanical Properties of Cr12 Steel after different heat treatment processes

Heat treatment process	hardness /HRC	The bending strength Degree/MPa	The deflection /mm	Impact toughness /(J/cm2)
1050℃ oil quenching +680℃×2h tempering +950℃ quenching +220℃×2h tempering	61.5	2685	1.98	4.9
1050℃ oil quenching +680℃×2h tempering +950℃×3.5h vanadium infiltration	61.5	2853	2.74	4.8
1050℃ oil quenching +680℃×2h tempering +950℃×4.5h vanadium infiltration	62.5	3003	2.87	4.9

After surface strengthening, the grain is obviously refined and the mechanical properties are obviously improved. The surface after vanadium infiltration treatment is 7-12 μ M thick white bright layer is mainly composed of VC compounds. The main reason is that the carbon content of Cr12 Steel Matrix is high, so carbon can be fully supplied during vanadium infiltration, which is conducive to the formation of VC.
Cr12 Steel Wire rubbing plate can obtain high wear resistance after strengthening and toughening + vanadizing composite treatment. First, the surface hardness is high (2800-3000hv). In addition, the matrix strength and hardness are also high. The infiltration layer is firmly combined with the matrix. Under the actual wear conditions, the infiltration layer is not easy to fall off, so the wear resistance is significantly improved.
The practice shows that the service life of Cr12 Steel flat die roll treated by vanadium infiltration is 3-4 times longer than that of conventional treatment.
7. Heat treatment of T8 steel flat die roll
Railway thread spike (M24) × 195) by Φ 20mm Q235A steel is rolled on the wire rolling machine after cold heading and extrusion. The overall dimension of the thread take-up plate is 350mm × 100mm × 70mm, which bears high extrusion stress, certain impact force, bending force, strong friction and other mechanical effects. Therefore, the flat die roll shall have high deformation resistance, fracture resistance, fatigue resistance and wear resistance to prevent early and medium-term brittle fracture, soft collapse, fatigue tooth breakage and wear failure in the process of use. The required hardness is 58-62hrc.
The flat die roll is generally made of 9SiCr or Cr12 section steel, but many units use local materials and T8 steel. Because T8 steel is cheap, practical, low cost, wide source and good process performance. The following is a brief introduction to the step quenching process of T8 steel flat die roll with brine bluing solution.
(1) Original process
790℃ × 2H box furnace protection heating, water quenching and oil cooling, 180 ℃ × After tempering for 2h, the surface hardness can reach 55-62hrc, and the service life is only 2000-3000 pieces. The main failure forms are soft collapse, tooth collapse, fatigue fracture and medium-term wear. Therefore, technological reform must be carried out.
(2) Improved process
600℃ × After 2H preheating (the working face is coated with boric acid for protection), quickly transfer to another box furnace in thermal insulation state (≥ 900 ℃) for 830 ℃ × 35 min quenching and heating, and the total time into the furnace shall be controlled within 50 min. Quench 10% (mass fraction) NaC1 aqueous solution for 35S (calculated as 1s / 2mm). Take it out of the brine, wait for the surface of the thread rolling plate to be dried and the brine evaporates. When the temperature is 300-400 ℃, immediately put it into the boiling bluing solution at 140 ℃ for isothermal 30min. When it is air cooled to about 70 ℃ on the surface, conduct 160 ℃ again × 1h+240℃ × 2H tempering treatment.
The surface of the wire rubbing plate treated according to the above process is light brown, with a hardness of 59-61hrc. The hardness at 5mm below the tooth root is 59HRC, with uniform hardness and a service life of 10000-15000 pieces, which is 2-4 times higher than that of the original process.
8. Heat treatment of 6cr4w3mo2vnb (65Nb) steel dry wall nail rubbing plate
With the development of mechanical and electrical, construction, instrument and plastic industries, the demand for dry wall nails at home and abroad has increased sharply. However, the flat die roll for processing dry wall nails in China basically depends on imports. It not only consumes a lot of foreign exchange every year, but also has a long import cycle, which can not keep up with the changes of specifications and varieties of dry wall nails, which directly affects the normal production and development of manufacturers. At present, the tool has not been made in China. One of the reasons is that the shape of the wire rubbing plate is complex and the machining is difficult; On the other hand, the service life of Cr12MoV and 9SiCr wire rubbing plates designed and manufactured by China is low, while the dry wall nail wire rubbing plate made of 65Nb steel has been subjected to a variety of heat treatment and surface strengthening, so that the service life of wire rubbing plate completely reaches or even exceeds that of imported similar products.
Dry wall nail is a kind of self tapping nail with high forming difficulty and large plastic deformation. The thread and screw tip are formed by one-time extrusion and rubbing of the thread rubbing plate, which belongs to non cutting processing. The tooth shape of the feeding part of the thread take-up plate is sharp, where the knife plate is subject to wear impact and contact stress, and the early tooth collapse failure and normal wear failure occur in this part. The dry wall nail is formed instantaneously in the process of extrusion, kneading, friction and shear. In addition, the flat die roll works faster, and the tooth surface also bears the impact force. A large amount of plastic deformation of the nail blank and the heat generated by friction make the surface temperature of the flat die roll reach about 200 ℃. From the stress analysis, the thread rolling plate bears complex stress and impact in the service process, so it is required to have high hardness, high contact fatigue strength and wear resistance, sufficient toughness and certain tempering stability. Before formulating the heat treatment process, the chemical composition and metallographic structure of foreign flat die rolls such as Japan, South Korea and Italy are analyzed. Most of them are made of M2 and Cr12MoV steel, with a surface hardness of 61-63hrc and a service life of about 1 million pieces / pair. 65Nb steel is selected as the thread rolling plate, and the heat treatment process is shown in Table 2.
Table 2. Heat treatment process of 65Nb steel flat die roll

Heat treatment process	Hardness after heat treatment	Nitriding layer depth /μm	Impact toughness /(J/cm2)	Grain size	using Life/ten thousand times
Salt bath furnace 1120℃ heating quenching and tempering	61HRC	–	67	11	80
Vacuum furnace 1100℃ heating quenching and tempering	61.5 HRC	–	100	12	80 ~ 100
Vacuum furnace 1140℃ heating quenching and tempering	65HRC	–	75	10.5	100 ~ 120
Quenching + nitrocarburizing + protective atmosphere tempering	1050HV	60	86	10.5	100 ~ 150
Quenching + nitrocarburizing + salt bath tempering	888HV	70	81	10.5	100 ~ 140
Quenching + tempering + nitrocarburizing	1236HV	30	93	10.5	100 ~ 130
Quenching + tempering + electron beam surface hardening	918HV	60	–	–	–

Note: quenching temperature not indicated is 1140 ℃; The tempering process is 540 ℃ × 1.5h × Twice.
Based on the analysis that the above processes can improve the service life of 65Nb steel flat die roll, a preliminary conclusion is drawn:

• (1) Compared with salt bath furnace heating and quenching, the service life of wire rubbing plate is obviously improved. Because the vacuum heating is slow and uniform, and the high-pressure gas quenching, not only the deformation is small, but also there is no oxidation, a bright and clean surface can be obtained, which obviously changes the surface quality of the flat die roll. Lath martensite and twin martensite can be obtained when the final quenching temperature is fixed at 1140 ℃. After tempering at 540 ℃, fine dispersed carbides are precipitated, with good strength and toughness. The flat die roll is normally worn during use, without early edge collapse.
• (2) After quenching + oxycarburizing + tempering, the composite structure with high strength and toughness can be obtained, which reduces the surface friction factor, improves the wear resistance, improves the surface stress state and improves the contact fatigue strength, so it can improve the service life.
• (3) Electron beam heating quenching is a relatively new surface strengthening process, which is characterized by extremely fast heating and cooling speed and good treatment effect. However, due to the high cost of heat treatment, it is difficult to popularize it.

To sum up, the use of 65Nb steel to make wire rubbing plate can make it have a long service life, whether it is salt bath treatment, vacuum quenching or other surface strengthening.
9. Heat treatment process of gw30 steel bonded cemented carbide wire rubbing plate
The service life of the thread rolling plate made of gw30 steel bonded alloy is 7 times longer than that of the original Cr12 Steel thread rolling plate, and the surface roughness of the thread half angle of the processed workpiece is increased to RA = 1.6 μ m。 The flat die roll made of gw30 steel bonded cemented carbide is used to process spokes of JL650 rubber tyred vehicle. The spokes are made of Q235 steel. The heat treatment process is introduced as follows:
Through 500 ℃ × 2H air furnace stress relief, 960 ℃ × 4min / mm heating, quenching, 60-80 ℃ hot oil, 160-180 ℃ × 2H tempering. The hardness after heat treatment is 60-65hrc.
Operation essentials of heat treatment of flat die roll
(1) The salt bath furnace must be fully deoxidized to remove slag, and the barium oxide content of high-temperature furnace shall be ≤ 0.25%.

• (2) Before quenching, check the bending of the flat die roll one by one. If it exceeds the tolerance, it must be calibrated to the range required by the process, and apply 450-500 ℃ × 3-4h air furnace stress relief treatment.
• (3) Control the quenching medium temperature within the ideal range.
• (4) Quenching fixture is very important, it must be appropriate, and the deformation fixture should be repaired in time.
• (5) Adhere to the quenching first article inspection system, including hardness, metallography, deformation, etc.
• (6) The tempering can be cleaned only after cold penetration. The tempering temperature should be accurate. It is best to set a double temperature control device.

Factors affecting the service life of screw plate

The service life of flat die roll is affected by a series of factors, which can be summarized into the following four aspects.
(1) Materials
It includes two major aspects, namely, wire rubbing plate material and twisted material. Although the national standard only stipulates 9SiCr and Cr12MoV steel grades, the service life of wire rubbing plate made of 65Nb is very high. Wire rubbing plates made of HSS steel such as M2 are also used abroad to achieve high service life. Many materials are also suitable for making wire rubbing plates. People should be bold to test. The rubbed materials are also complex, and we should study them carefully.
(2) Heat treatment
Heat treatment is undoubtedly the most important factor affecting the service life of wire rubbing plate. The heat treatment process of wire rubbing plate with different materials and different purposes should be personalized.
(3) The machining dimensional accuracy has an obvious influence on the service life of the flat die roll.
(4) Service conditions
That is, it depends on the condition of the rolling equipment, the hardness of the rolling blank and the type of lubricating coolant. It also depends on the actual deviation of blank shape and size, especially whether the screw head is chamfered or not.

Source: China Pipe Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(Yaang Pipe Industry is a leading flange manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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