EP1133580B1 - Process for producing a corrosion- and wear-resistant layer by thermal spraying - Google Patents

Abstract

The invention relates to a material for producing a corrosion- and wear-resistant layer on a substrate by thermal spraying. Said material consists of at least 20 wt.-% - preferably more than 30 wt.-% - magnetite (Fe3O4 and/or FeFe2O4). Preferably, the inventive material consists of pure magnetite or of magnetite and at least one other metallic material or at least one intermetallic compound.

Description

The invention relates to a method for producing a Corrosion and wear-resistant layer on one Substrate by spraying an iron oxide-based material.

Such a method is known from DE 30 48 691 A1, with which a piercing mandrel for a plug and stretching mill is coated; a protective layer is formed on the mandrel surface by spraying on a powder consisting largely of iron oxide in the molten state; Such a piercing mandrel is said to be inexpensive to manufacture and to have excellent durability and to offer better insulation and sliding properties. For this purpose, the compounds FeO, Fe ₃ O ₄ and Fe ₂ O ₃ or their mixtures are offered as iron oxides, which make up more than 50% by weight of the powder. Oxides of chromium, nickel, copper and manganese or metals from the group iron, chromium, nickel, cobalt, copper and manganese can also be used.

DE 34 35 748 A1 describes the use of a laser anemometer, whose measurement volume is relative to a hot one Gas jet is adjustable to determine particle speeds with thermal spraying. The particle current density is determined by a particle counter, the the number of each flying through the measuring volume Spray particles count. The mean particle trajectories and the melting state are digital in a facility Data processing calculated.

EP 0 443 730 A shows a process for producing magnetite-coated electrodes, in which a mixture is produced by mixing FeO and Fe ₂ O ₃ powder and polyvinyl alcohol solution, pressed into a green body and then sintered to form magnetite , The magnetite sinter is then pulverized to a particle size of 5 to 150 μm and the magnetite powder is applied to the electrodes by means of thermal spraying, for example by means of plasma spraying, plasma jets or water plasma. The plasma jet is not checked.

According to DE 23 35 995, the coating of a sliding body - for example a piston ring - is achieved by thermal spraying of a mixture of Fe ₃ O ₄ and Cr ₂ O ₃ (ratio 50:50), Fe ₃ O ₄ and Cr ₃ C ₂ (60 : 40) as well as Fe ₃ O ₄ and a self-flux alloy (70: 30).

EP 0 837 305 A describes a measuring method - with a device for measuring temperature, particle density and Particle size, current, carrier and plasma gas velocity, the amount of plasma gas - to determine the Data of the particles and the plasma jet during the Spritzens discussed. With another thermal device According to JP 08 269 672 A, this is done using a camera or image processing coupled to it.

Finally, US 5 180 921 A discloses a thermal Plasma coating device with sensors for monitoring the particle velocity of the sprayed particles by means of two photodetectors (two-color pyrometer), with which then the flow, the powder feed rate, the powder feed gas flow or the like. to be controlled.

Corrosion and wear protection layers are usually made from powder mixtures various types of surfaces to be protected in production or applied for maintenance. The main ones are thermal Spray processes or vapor deposition processes such as CVD (chemical vapor deposition) or PVD (plasma vapor deposition) is used. With the CVD and PVD processes can have thin layers of corrosion and wear protection Oxide or hard material base, especially applied in mass production become. Electrochemical or galvanic processes are also used.

Thermal spraying mainly turns layers into one Layer thickness of more than 0.1 mm created. In the case of thermal Sprayed corrosion and wear-resistant layers mostly around metallic or oxide layers in which to improve Hard materials are stored.

One of the biggest problems with thermal spraying is manufacturing of layers of constant properties and quality. For this The thermal spraying processes on substrates or parts were basically able with high quality requirements in series production only limited use Find.

Experiments with selection of the material regarding its chemical composition or its shape - for example the wire diameter of a cored wire or on the other hand the grain size distribution and the grain shape of wettable powder - did not lead to a sufficient increase in quality. Changes to the spraying systems also did not help to improve it Quality.

Attempts were made to protect against wear and corrosion by thermal means to create sprayed-on layers of iron oxide or magnetite. At all Experiments of this kind showed that the quality of the respective layer in With regard to the layer structure, only with great effort could be secured.

Knowing these facts, the inventor has set the goal that Creating a constant wear and corrosion resistant surface coating on the basis of oxide by means of thermal spraying.

The teachings of the independent claims lead to the solution of this problem; the subclaims indicate favorable further training.

Carbides, nitrides, silicides, borides and oxides have proven their worth as additives for hard materials. In the carbides, the carbide formers such as tungsten, chromium molybdenum, niobium, tantalum, titanium, vanadium or the like are suitable. The addition of the carbides should be limited to a maximum of 30% by weight, preferably 20% by weight. With borides and nitrides as additives at this level, improvements in properties are observed. Oxidic additions of chromium oxide (Cr ₂ O ₃ ) in the order of 1 to 40% by weight - preferably 5 to 30% by weight - also show good results.

To achieve high quality, the powdery spray materials a grain size of 0.05 to 150 µm - preferably 0.1 to 120 µm - have. When mixing different powdery materials it is recommended to avoid segregation and to improve the flow behavior to agglomerate or spray-dry them.

When using wire-shaped spray materials with a high magnetite content in the context of the invention from a metallic shell and magnetite powder a cored wire can be produced.

To apply the wear and / or corrosion layer are according to the invention all thermal spray processes such as autogenous flame spraying, high-speed flame spraying (HVOF spraying), plasma spraying under air (APS), Shroud plasma spraying (SPS), vacuum spraying (LPPS), high-performance plasma spraying (HPPS), the autogen Wire spraying or arc wire spraying can be used.

The online control and control takes place with a combination of different Procedures that allow the temperature of the particle or the Degree of melting, the particle size, the speed, the impact of the same on the substrate and the heating of the layer and the substrate to measure during the spraying process. The measurement signals are then the Computer fed to a control system for the spraying system and the flame parameters as well as the performance adjusted to the values.

The inventor has thus found that it is possible to use one of those mentioned above To meet coating requirements if an iron-based oxide is used as the material, which - depending on of the corrosion or wear problem to be solved - metals, Hard materials or intermetallic compounds added. The material must are produced by a certain manufacturing process; According to the invention, one is made from the powdery material mixture Spray drying produced powder grain with good flow properties proposed as well as from the powdery material mixture anti-segregation manufactured in an agglomeration process Powder grain.

The spraying system is equipped with an online control system Equipped to provide high quality and layers to be able to produce consistent properties by spraying.

For this purpose, an online control and control by means of a Spray jet directed ITG camera, an LDA detector with LDA laser as well as an HSP head proved to be cheap or an online control using an ITG camera directed at the spray jet and an HSP head one Measuring body.

The online control system is to be used for measurement conveniently the particle speed in the spray flame, for example by a laser doppler anemometer using one from a laser device emitted beam, which by means of a transmission optics in two partial beams is disassembled.

Another feature of the invention is through online control and controlling the particle temperature in the spray flame by means of a High speed pyrometers observed. This is done by means of Infrared thermography.

It also turned out to be. proven conveniently through online control and Control measure the amount of gas, such as a quantity of plasma gas.

Thanks to the online control and control, you are also able to evaluate the measured current-voltage characteristic or one of the Measure the amount of powder fed into the spray flame.

Fig. 1:

ein Online-Steuer- und Kontroll-System für eine Plasmaanlage;

Fig. 2:

eine Anlage zur Infrarot-Thermographie (ITG) und zur Hochgeschwindigkeits-Pyrometrie (HSP = High Speed Pyrometry) beim thermischen Spritzen;

Fig. 3:

ein Schema zur Infrarot-Thermographie (ITG);

Fig. 4, 5:

jeweils eine Anlage zur Hochgeschwindigkeits-Pyrometrie (HSP);

Fig. 6:

eine Ausgestaltung eines Laser-Doppler-Anemometer (LDA);

Fig. 7:

eine Skizze zur Partikelform-Messung im Fluge (PSI = Particle Shape Imaging);

Fig. 8:

eine Partikeltemperatur-Messung im Fluge (PTM = Particle Temperature Measurement);

Fig. 9:

eine Skizze zur Messung von Partikeltemperatur und -geschwindigkeit.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments and from the drawing; each shows schematically in

Fig. 1:

an online control and monitoring system for a plasma system;

Fig. 2:

a system for infrared thermography (ITG) and for high-speed pyrometry (HSP = High Speed Pyrometry) in thermal spraying;

Fig. 3:

a scheme for infrared thermography (ITG);

4, 5:

one system for high-speed pyrometry (HSP);

Fig. 6:

an embodiment of a laser Doppler anemometer (LDA);

Fig. 7:

a sketch for particle shape measurement in flight (PSI = Particle Shape Imaging);

Fig. 8:

a particle temperature measurement in flight (PTM = Particle Temperature Measurement);

Fig. 9:

a sketch for measuring particle temperature and speed.

All are required for the application of wear and / or corrosion layers thermal spraying processes - such as autogenous flame spraying, high-speed flame spraying (HVOF), plasma spraying under air (APS), the so-called Shroud plasma spraying (SPS), plasma spraying in a vacuum (LPPS), High-power plasma spraying (HPPS), autogenous or arc wire spraying - applicable. Online control and control is carried out using a Combination of different processes that allow the temperature of the particle or the degree of melting, the particle size, the speed, the impact of the same on the substrate and the heating of the Measure layer and substrate during the spraying process. The measurement signals are then the computer of the control part of the thermal Spraying system fed to the flame parameters and the performance to be able to adjust measured values.

An online control and monitoring system for the flame shown in FIG. 1 or the spray jet 10 of a spray gun or the like indicated at 12. Spraying device 12 with its burner nozzle 14 upstream powder feed 16 - has an ITG camera 18 - that is, an infrared thermography camera - via the spray jet 10 - and a laser Doppler anemometer (LDA - Detector) 20 for an LDA laser that can be seen below the spray jet 10 22 on; next to this is an HSP head 24 - HSP = high speed pyrometry - too recognize that is connected to a coil-like measuring body 26.

To measure substrate temperature T _s and coating temperature T _c by means of infrared thermography, according to FIG. 3 there is a substrate 30 - to be provided with a coating 32 - in the recording area of an ITG camera 18. A glass fiber cable 36 extends from the latter leads to a video PC card indicated at 42 - 500 kHz. A computer 46 with a monitor 48 is connected to this, to which a temperature recording device 50 is assigned.

4 is for measuring the cooling rate or the coating temperature Tc by means of high-speed pyrometry (HSP) of the coating 32 of the Substrate 30 of the HSP head 24 switched on via an AD converter 52 to a computer 46 having a storage element 44 and a monitor 48 connected. A high-speed pyrometer with HSP head 24, AD converter 52 and with a computer 46, the user menu 54, a Control menu 56 and graphics software 58 contains, can be seen in Fig. 5.

The process of so-called laser Doppler anemometry (LDA) can be used to optimize the spray parameters with little time and effort. In the preferred two-beam technique, the beam 60 of an argon ion laser (λ = 514.5 nm, P = 150 mW) indicated at 62 is broken down into two partial beams 60 _a , 60 _{b of the} same intensity by means of a transmission optics 64. Both partial beams 60 _a , 60 _b are focused in a fixed measuring volume 66. There they intersect at a defined angle so that a stripe-shaped intensity-modulated interference pattern is created. A particle of the spray jet 10 that flies through this stripe pattern generates a scattered light signal 68 that changes periodically over time for a receiving lens system with a photodetector 70. The modulation frequency of the scattered light signal 68 is proportional to the velocity component of the particle perpendicular to the interference fringe system. The frequency of the LDA scattered light signals is a measure of the local density of the particles in the plasma spray jet 10. By scanning the beam, a spatially resolved measurement of relevant particle parameters is possible. Results such as speed distribution, trajectories and dwell times of the particles can be obtained from this.

Since an individual determination of the size and shape of a spray particle with LDA cannot be carried out, particle-shape imaging (PSI) is used according to FIG. 7, an imaging method for the spatially resolved determination of size and shape of individual powder particles in plasma spray jets 10. The measuring principle is based on a telemicroscopic image of the shadow of the particles, the measuring method has the advantages of a high light intensity compared to scattered light methods and at the same time a reduction to the desired image information. Similar to laser Doppler anemometry, the beam 60 of an Nd-YAG continuous wave laser 60 _a (λ = 532nm, P = 100 mW) is split on a beam splitter 72 with mirrors 74 into two equally intense partial beams 60 _a , 60 _b , which are by means of the mirror 74 can be crossed in the object plane E of the long-range microscope objective of a long-range microscope 76. Its use allows a safety distance of 600 mm to be observed. With a 1:10 scale, an optical resolution of 2.7 µm is still achieved. The image recording system consists of a CCD camera 78 with an upstream micro-channel plate (MCP) image intensifier with a minimum exposure time of 5 ns.

The geometric dimensions of the 512 x 512 pixel CCD chip and the depth of field of the lens result in a measurement volume of 410 x 410 x 940 µm ³ .

In the event that a particle in the measurement volume is exactly in the object plane E _, partial rays are generated from both beams 64, 64 _a , which completely overlap when they are imaged on the CCD chip and thus form a full shadow. Proportional to the distance of the particles from the object plane E, the partial shadows move apart in the image plane and the full shadow area decreases. With this effect, the position of a particle relative to the object plane E can be determined. The area and contour of the silhouette provide information about the size and shape of the particle. The LDA interference fringe pattern, also shown, provides the size scale. With the minimum exposure time of the MCP-CCD camera of 5 ns, a value of 500m / s results as the maximum particle speed at which the motion blur does not exceed the optical resolution.

In the so-called in-flight particle diagnosis method - to which reference is made to FIG. 8 - up to 200 individual particles per second can be measured simultaneously in every point of a spray jet for their surface temperature, speed and size, regardless of the spraying method. A non-reproduced moving unit additionally enables a plane to be scanned perpendicular to the spray jet 10, so that the distribution of the particles in the spray jet 10 can be determined precisely. The temperature is determined using two-wavelength pyrometery at 995 ± 25 µm and 787 ± 25 µm. The particles are treated as gray emitters so that knowledge of the exact emissivity is not necessary for the temperature measurement. The system comprises imaging a two-slit mask 80 with 25 μm × 50 μm — on a measuring head 82 — at a focal point at a distance of approximately 90 mm with a high depth of field. This creates a measurement volume which, according to the graphic representation in FIG. 10, is characterized by two visible and one shadow region in between. The measuring volume is approximately 170 x 250 x 2000 µm ³ . The natural radiation of individual particles that fly through this measurement volume is recorded by two IR detectors with two different wavelengths. The two partial measurement volumes result in two temperature peaks in a row. The time interval between the two peaks is a measure of the speed of the particle. The principle corresponds to that of the light barrier.

This procedure enables the determination of particle surface temperatures between 1,350 ° C and 4000 ° C. The measurable particle size depends essentially on the temperature of the particles. It is down limited to about 10 microns and up to about 300 microns and is by the absolute energy radiated by the particle determines that proportional to the square of the diameter. The measurable speed range is 30m / s - 1500 m / s.

The illustration in FIG. 9 follows on from that in FIG. 1 and illustrates this Measuring the particle temperature and speed using an HSP head 24th

The procedure is further extended by some application examples discussed:

EXAMPLE 1

A casting mold for aluminum casting should be provided with a layer, which prevents caking and sticking in the mold.

Korngröße

> 5 µm
< 45 µm

bei einer Korngröße des Ausgangsmaterials > 1,5 µm.For the tests, a 0.2 to 0.5 mm thick coating of a material composition of 95.5% by weight Magnetite (Fe ₃ O ₄ ) 4.5% by weight Iron oxide (Fe ₂ O ₃ ) selected; this should prevent sticking and caking of aluminum and its alloys. Other properties of the wettable powder were

grain size

> 5 µm
<45 µm

with a grain size of the starting material> 1.5 µm.

The grain structure of the round grains was determined by agglomeration Spray drying manufactured.

The application was carried out by plasma spraying in air (APS) with one performance of 60 KW and argon / hydrogen plasma, which with an online control unit 1 was provided; the particle velocity and particle temperature are measured there during the flight to the plasma spray to control so that the necessary degree of melting of the particle is achieved.

The mold surface to be coated was forced-cooled with CO ₂ with the aim of keeping the oxidation on particle impact as low as possible.

The layer thus produced by thermal spraying was then ground and tested in an aluminum foundry. It was found that caking and sticking to the form is prevented as well as the complex Spraying the mold with a mold release agent can be omitted.

Example 2

An approximately 1.0 to 2.0 mm thick protective layer against wear and corrosion in aqueous solutions should be applied to the transport roller of a paper manufacturing machine. This protective layer must have a high density (at least 99% of the theoretical density) due to working in aqueous solution. A cored wire of the following composition was used as the spray material: filling Magnetite (Fe ₃ O ₄ ) coat NiCr 80/20 with about
30% by weight of the cored wire.

The grain size of the starting material for the filling was> 1.0 µm.

To spray the protective layer, an arc spraying system equipped with an online control and monitoring system was used for processing cored wire, and a control system was a combination of the two systems shown in FIGS. 1 and 3. The forced cooling is done with CO ₂ and air.

After coating, the 200 cm long roll was applied to a surface quality ground from Ra 0.4 µm. When checking the surface with a Binocular loupe with a magnification of x = 20 could not find any errors in the Layer can be determined.

After a test run of six months, it was in the paper machine used transport roller removed together with a chrome-plated roller, and the surfaces were examined. During this investigation found that on the coated for the test by plasma spraying Transport roller no errors or attacks due to corrosion or wear could be found. The chrome-plated comparison roller showed that for this Known attack duration.

Example 3

For the piston rings of internal combustion engines, improvements in the coatings are constantly required during development. After several considerations, tests with a pure magnetite coating should now be carried out. The problem with such a coating of pure magnetite (Fe ₃ O ₄ ) is the undesirable possibility that the magnetite could be oxidized to Fe ₂ O ₃ during the spraying process, which would lead to a loss of the desired good properties.

Pure magnetite was used as the spray material. The grain size of the wettable powder was:
<37 µm
> 5 µm,
the grain size of the starting material
<0.5 µm.

The spray powder of round grain shape was obtained by agglomeration during spray drying manufactured.

• Partikelgeschwindigkeit;
• Partikeltemperatur;
• Substrattemperatur;
• Aufschmelzen des Partikels.

A plasma system equipped with a gas shroud and an online control unit for plasma spraying under air (APS) with an output of 80 KW was used to apply the coating. The parameters to be kept constant for controlling the plasma system were:

• Particle velocity;
• Particle temperature;
• Substrate temperature;
• Melt the particle.

CO _{2 was} used as forced cooling for the substrate and the layer during the spraying process. The Shroud used to protect against oxidation was operated with pure starch.

The piston rings coated with pure magnetite using this process showed a high quality in the control and showed in the endurance test in Engines good results.

Example 4

An immersion device for a salt bath working at 500 ° C for heat treatment of smaller parts shows after about a week of operation a high level of corrosion.

An attempt should now be made to avoid wear and corrosion by applying a protective magnetite / carbide layer. A mixture of: 75% by weight magnetite, 25% by weight Chromium carbide.

The thermal spray process for applying the layer with a thickness of 80 µm was a high speed flame spray (HVOF) in which the Control took place online. After spraying, the layer was polished.

The service life of the layer applied in this way was under the same conditions two weeks.

Example 5

A hydraulic cylinder for underground mining with a length of 1000 mm and a diameter of 200 mm should be protected with a protective layer Corrosion and wear are provided. So far it was used as a protective layer an electroplated hard chrome layer was used, which has a service life due to the appearance of hairline cracks in the layer of at most two months.

Now a protective layer of the composition 70% by weight Fe ₃ O ₄ (magnetite), 30% by weight Cr ₂ O ₃ (chromium oxide) chosen, the grain size of the agglomerated spray material
> 5 µm,
<37 µm
scam.

For applying the protective layer with a layer thickness between 1.0 and 1.5 mm was an HPPS (High Power Plasma) system with an output of 200 KW used to maintain the exact spraying parameters or the Avoiding oxidation was provided with an online control.

The protective layer thus produced was removed after a period of two months checked, and it was found that the surface of the layer was none Attacks caused by corrosion or wear. The lifespan of the Shift was nine months.

Example 6

The piston of a vacuum pump with a diameter of 20 mm and a length of 500 mm should be provided with a wear and corrosion protection layer. An agglomerated wettable powder with the composition: 80% by weight Fe ₃ O ₄ 20% by weight Ni ₃ Al and one
grain size
> 5 µm
<45 µm
used.

An LPPS system with an output of 40 KW was used for coating, which was provided with an online control.

The coating produced in this way showed very good results in later use compared to normal pistons.

Claims (23)

1. Method of producing a corrosion-resistant and wear-resistant layer on a substrate by spraying on an iron oxide-based material, characterised in that the iron oxide-based material comprising at least 20 % by weight, preferably more than 30 % by weight magnetite (Fe₃O₄ and/or FeFe₂O₄) is applied by on-line controlled flame spraying, in particular high-speed flame spraying, or plasma spraying, in particular plasma spraying in air or in vacuo, high-power plasma spraying (HPPS) or shroud plasma spraying (SPS), or by on-line controlled wire flame spraying or electric-arc wire spraying and the properties of the layer consisting of the material are monitored and kept constant by an on-line monitoring and control system.
2. Method according to claim 1, characterised by on-line monitoring and control by means of an ITG camera directed on to the spraying jet (10), an LDA detector (20) with LDA lasers (22) and an HSP head (24).
3. Method according to claim 1 or claim 2, characterised by on-line monitoring and control by measuring the particle speed in the spraying flame.
4. Method according to claim 1 or claim 3, characterised by on-line monitoring and control by means of measuring the particle speed in the spraying flame by means of a laser Doppler anemometer by way of a beam (60) emitted by a laser instrument (62) and divided into two partial beams (60_a, 60_b) by means of a transmitting optical unit (64).
5. Method according to claim 1 or claim 3, characterised by on-line monitoring and control by measuring the particle temperature in the spraying flame by means of a high-speed pyrometer.
6. Method according to either of claims 1 or 5, characterised by on-line monitoring and control in which the particle temperature in the spraying flame is measured by means of infrared thermography.
7. Method according to claim 1, characterised by on-line monitoring and control in which the quantity of gas measured is analysed.
8. Method according to claim 1 or claim 7, characterised by on-line monitoring and control in which a quantity of plasma gas measured is analysed.
9. Method according to claim 1, characterised by on-line monitoring and control in which a current-voltage curve measured is evaluated or in which a quantity of powder supplied to the spraying flame is measured.
10. Method of producing a corrosion-resistant and wear-resistant layer according to one of claims 1 to 9, characterised by on-line controlled plasma spraying in which air is used as the plasma gas.
11. Method of producing a corrosion-resistant and wear-resistant layer according to one of claims 1 to 9, characterised in that on-line controlled water-stabilised plasma spraying is used as the coating method.
12. Method of producing a corrosion-resistant and wear-resistant layer according to one of claims 1 to 11, characterised in that a material comprising at least 20 % by weight, preferably more than 30 % by weight magnetite (Fe₃O₄ and/or FeFe₂O₄) is used.
13. Method according to claim 12, characterised in that the material consists of magnetite and at least one intermetallic compound.
14. Method according to claim 12, characterised by the addition of a mixture of metals, intermetallic compounds, carbides, nitrides, silicides, borides and/or oxides to the material.
15. Method according to claim 12, characterised by a material consisting of magnetite and carbides of W, Cr, Mo, Nb, Ta, Ti and V.
16. Method according to claim 15, characterised by a material consisting of magnetite with the addition of up to 30 % by weight, preferably up to 20 % by weight tungsten carbides and/or chromium carbides.
17. Method according to claim 12, characterised by a material consisting of magnetite and at least one further metallic material.
18. Method according to claim 17, characterised by magnetite and the addition of up to 50 % by weight, preferably up to 40 % by weight Cr, CrNi or a ferritic steel.
19. Method according to claim 12, characterised by a mixture of magnetite and chromium oxide as the material, with a chromium oxide content of between 1 and 40 % by weight, preferably between 5 and 30 % by weight.
20. Method according to one of claims 12 to 19, characterised by a particle size of the pulverulent spraying material of 0.05 to 150 µm, preferably 0.1 to 120 µm.
21. Method according to one of claims 12 to 20, characterised by the use of a filler wire as a wire-shaped spraying material, its filling consisting of magnetite and its covering consisting of an alloy.
22. Method according to one of claims 1 to 21, characterised by a powder grain with good flow properties produced from a pulverulent material mixture by spray drying.
23. Method according to one of claims 1 to 21, characterised by a separation-resistant powder grain produced from a pulverulent material mixture by means of an agglomerating process.

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