Surfacing of marine diesel valves. Method for obtaining valve seats for cast-iron cylinder heads of internal combustion engines during their manufacture or restoration by electric arc welding Material for valve seats for internal combustion engines

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The article discusses the question of the necessity and expediency of using austenitic manganese cast iron for valve seats of internal combustion engines operating on gas motor fuel. Information is given on mass-produced valve seats for internal combustion engines of cars, the most common alloys for the manufacture of seat parts, their shortcomings, the imperfection of the alloys used in operation, and the reasons for the low life of parts of this type are described. As a solution to this problem, it is proposed to use austenitic manganese cast iron. Based on many years of research on the properties of manganese cast iron, it was proposed to use this alloy for the manufacture of valve seats for automobile engines with gas motor fuel. The main properties possessed by the proposed alloy are considered. The research results are positive, and the resource of new saddles is 2.5 ... 3.3 times longer than serial ones.

cylinder head

supply system

wear

parts resource

natural gas motor fuel

ICE car

1. Vinogradov V.N. Wear-resistant steels with unstable austenite for parts of gas-field equipment / V.N. Vinogradov, L.S. Livshits, S.N. Platonov // Vestnik mashinostroeniya. - 1982. - No. 1. - S. 26-29.

2. Litvinov V.S. Physical nature of hardening of manganese austenite / V.S. Litvinov, S.D. Karakishev // Heat treatment and physics of metals: interuniversity coll. - Sverdlovsk, UPI. - 1979. - No. 5. - S. 81-88.

3. Maslenkov S.B. Steels and alloys for high temperatures. Reference book: in 2 volumes / S.B. Maslenkov, E.A. Maslenkov. - M. : Metallurgy, 1991. - T. 1. - 328 p.

4. Stanchev D.I. Prospects for the use of special austenitic manganese cast iron for parts of friction units of forest machines / D.I. Stanchev, D.A. Popov // Actual problems of development of the forest complex: materials of the international scientific and technical conference of VSTU. - Vologda, 2007. - S. 109-111.

5. Engineering technology. Restoration of quality and assembly of machine parts / V.P. Smolentsev, G.A. Sukhochev, A.I. Boldyrev, E.V. Smolentsev, A.V. Bondar, V.Yu. Sklokin. - Voronezh: Publishing House of the Voronezh State. those. un-ta, 2008. - 303 p.

Introduction. The use of gas motor fuel as a fuel for internal combustion engines is associated with a number of technical issues, without which the efficient operation of vehicles on dual-fuel power systems is impossible. One of the most pressing issues technical operation vehicles running on gas motor fuel is a low resource of interface "seat-valve".

An analysis of the damage to the seat made it possible to establish the causes of their occurrence, namely: plastic deformation and gas erosion caused by the deterioration of the fit of the friction pair during operation. Figures 1 and 2 show the main characteristic damage to seats and valves when operating on gas fuel.

Traditionally, for gasoline engines, valve seats are made of gray cast iron grades SCH25, SCH15 according to GOST 1412-85 or carbon and alloy steels 30 HGS according to GOST 4543-71, which provide satisfactory operational reliability and durability of the interface throughout the guaranteed engine life. However, when switching to a dual-fuel power supply system for internal combustion engines, the interface resource is sharply reduced; according to various estimates, repair of the block head is required after 20,000-50,000 thousand kilometers. The reason for the decrease in the interface resource is the low combustion rate of the gas-air mixture in operating modes with a high crankshaft speed and, as a result, a significant heating of the seat metal, loss of its strength and further deformation from interaction with the valve.

Thus, to ensure a guaranteed service life of the seat-valve interface, when using gas motor fuel, materials require not only high anti-friction properties, but also increased heat resistance.

Purpose of the study. Research results. The purpose of the research is to substantiate the feasibility of using manganese austenitic cast iron for the manufacture of valve seats. It is known that steels and cast irons of the ferritic-pearlitic and pearlitic class do not differ in heat resistance and are not used for parts operating at temperatures above 700 ºС. For work in extreme conditions, at operating temperatures of about 900 ºС, in particular, heat-resistant austenitic cast irons with a minimum amount of free graphite in the structure are used. These alloys include austenitic manganese cast iron, the binding base of which is austenite containing carbide inclusions and fine lamellar graphite. Traditionally, such cast iron is used as antifriction cast iron under the AChS-5 brand and is used for plain bearings.

Long-term studies of manganese cast iron have revealed the valuable qualities of this material, achieved by improving the properties of the alloy by modifying it and improving the production technology. In the course of the work performed, the effect of manganese concentration in the alloy on the phase composition and operational properties austenitic cast iron. To do this, a series of melts was made, in which only the manganese content varied at four levels, the composition of the remaining components, the conditions and mode of melting were constant. The microstructure, phase composition and properties of the cast irons obtained are shown in Table 1.

Table 1 - Influence of manganese concentration on the structural composition and mechanical properties of manganese cast iron in the cast state

	microstructure (etched section)		Hardness	Microhardness, 10 ∙ MPa
				austenite	martensite
	Austenitic-martensitic mixture, martensite, carbides of medium and small sizes. Martensite predominates. Large lamellar graphite
	Austenite, austenite-martensite mixture, carbides, fine graphite. Predominance of austenite
	Austenite, a small amount of martensite, carbide network, fine graphite. Predominance of austenite
	austenite, significant the amount of large carbides, unevenly distributed, isolated fields of ledeburite

As a result of the study of the microstructure, it was noted that with an increase in the manganese content in cast iron, the ratio of phase components changes (Fig. 3): the ratio of the gamma phase to the alpha phase of iron increases, the amount of the carbide phase (Fe3C, Mn3C, Cr3C2) increases and the amount of graphite decreases .

As the results of X-ray studies have shown, with an increase in the manganese content, the ratio of the areas of integral intensities occupied by the gamma phase of austenite and the alpha phase of martensite (I111/I110), respectively, on the X-ray pattern of the surface of the section increases. With a manganese content of 4.5% I111/I110 = 0.7; at 8.2% I111/I110 = 8.5; at 10.5% I111/I110 = 17.5; at 12.3% I111/I110 = 21.

To establish the effect of manganese on the physical and mechanical properties of cast iron, tests were carried out, in particular, for wear resistance under conditions of dry friction and uncontrolled frictional heating. Comparative tests for wear of cast irons with different manganese content were carried out on the SMTs-2 machine according to the “block-roller” friction scheme at a specific pressure of 1.0 MPa and a sliding speed of 0.4 m/s. The test results are shown in Figure 4.

With an increase in the manganese content from 4.5 to 10.5% in cast iron, the amount of austenite contained in the structure increases. An increase in the proportion of austenite in the metal matrix of cast iron provides reliable retention of the carbide phase in the base. An increase in the manganese content above 12% did not lead to a significant increase in the wear resistance of cast iron. This circumstance is explained by the fact that the increment of the carbide phase (separate fields of ledeburite are observed) does not significantly affect the wear resistance of the material under these friction modes.

Based on the results obtained when testing experimental cast iron with different manganese content, cast iron containing 10.5% Mn has the highest wear resistance. This content of manganese ensures the creation of an optimal structure from the point of view of frictional contact, formed by a relatively plastic austenitic matrix uniformly reinforced with carbide inclusions.

At the same time, the alloy containing 10.5% Mn differed in the most optimal ratio of phase components, as well as their shape and arrangement. Its structure was predominantly austenite, reinforced with medium and small-sized heterogeneous carbides and finely dispersed graphite inclusions (Fig. 5). Relative wear tests in dry friction, carried out with samples of cast irons with different manganese concentrations, showed that manganese cast iron containing 10.5% Mn was 2.2 times superior in wear resistance to cast iron with 4.5% Mn.

An increase in manganese content above 10.5% led to a further increase in the amount of austenitic and carbide phases, but carbides were observed in the form of separate fields, and the wear resistance of cast iron did not increase. Based on this, the chemical composition of cast iron was chosen for further research and testing, %: 3.7 C; 2.8Si; 10.5 Mn; 0.8Cr; 0.35 Cu; 0.75Mo; 0.05B; 0.03S; 0.65p; 0.1Ca.

In order to study the influence heat treatment on the structural composition and properties of austenitic manganese cast iron of the proposed chemical composition, the samples (pads) were subjected to hardening. Volumetric hardening of the samples was carried out in running water from a heating temperature of 1030–1050 °C and a holding time during heating: 0.5, 1, 2, 3, 4 h.

Studies of the structure of samples after volumetric hardening showed that the heating temperature, the duration of exposure during heating and the cooling rate play a significant role in the formation of the structure of manganese cast iron. Hardening in the general case led to almost complete austenization, obtaining grains of medium and small size. Heating ensures the dissolution of carbides in austenite. The completeness of these transformations increases with an increase in the duration of exposure of the samples in the oven. The martensite present in the casting structure was completely dissolved in austenite during heating and did not precipitate during quenching. Carbides, depending on the duration of exposure during heating, having partially or completely dissolved in austenite, are released again upon cooling. After quenching, the amount of graphite in the cast iron structure becomes significantly less compared to the cast state. In hardened cast iron, the plates of graphite inclusions are thinner and shorter. Brinell hardness of quenched manganese cast iron is reduced, toughness is increased and machinability is improved.

In order to determine the hardening mode that provides the maximum wear resistance of the experimental manganese cast iron, samples with different holding times during hardening were subjected to wear. The study of wear resistance was carried out on a friction machine SMTs-2 at a specific pressure on the sample of 1.0 MPa and a sliding speed of 0.4 m/s.

As a result of the tests, it was found that increasing the holding time to 2∙3.6∙103 s at the quenching temperature causes an increase in the relative wear resistance of manganese cast iron, after which its wear resistance does not change. These tests confirm the assumption that the structural composition of manganese cast iron obtained by quenching after holding for 2∙3.6∙103 s is the most perfect and is capable of providing high performance in dry friction.

In addition, reducing the hardness to 160-170 HB of austenitic manganese cast iron during hardening is likely to have a positive effect on damage and wear of the counterbody (roller) simulating a locomotive wheel. In this regard, for subsequent laboratory and operational tests, austenitic manganese cast iron in the cast (ACHl) and quenched state, obtained after 2 hours of holding at the quenching temperature (ACHz), was used.

Based on the research and testing carried out, it was possible to develop special composition austenitic cast iron, obtained by modifying manganese, which is characterized by high wear resistance in dry friction conditions (brakes, friction clutches), characterized by high frictional heating up to 900 ºС (“Wear-resistant cast iron”, RF patent No. 2471882) . The results of testing this composition of cast iron under the conditions and loading modes of the “seat-valve” interface of the timing showed a high performance of the material, exceeding the resource of saddles made of gray cast iron SCH 25 according to GOST 1412-85 and 30 HGS according to GOST 4543-71 in 2.5-3, 3 times. This allows us to consider such cast iron promising for use in conditions of dry friction and high temperatures, in particular for valve seats, clutch pressure plates, brake drums of hoisting and transport machines, etc.

Findings. Thus, it can be concluded that the use of austenitic manganese cast iron for the manufacture of valve seats will significantly increase the service life of the cylinder head of engines converted to gas motor fuel and using a combined power supply system (gasoline-gas).

Reviewers:

Astanin V.K., Doctor of Technical Sciences, Professor, Head of the Department of Technical Service and Engineering Technologies, Voronezh State Agrarian University named after Emperor Peter I, Voronezh.

Sukhochev G.A., Doctor of Technical Sciences, Professor of the Department of Mechanical Engineering Technologies, Voronezh State Technical University”, Voronezh.

Bibliographic link

Popov D.A., Polyakov I.E., Tretyakov A.I. ON THE FEASIBILITY OF APPLICATION OF AUSTENITIC MANGANESE CAST IRON FOR ICE VALVE SEATS OPERATING ON GAS ENGINE FUEL // Contemporary Issues science and education. - 2014. - No. 2.;
URL: http://science-education.ru/ru/article/view?id=12291 (date of access: 01.02.2020). We bring to your attention the journals published by the publishing house "Academy of Natural History"

The invention can be used in the restoration or manufacture of valves for internal combustion engines (ICE). After cleaning the surface under the saddle and flaw detection, machining. The seat is made by arc welding of the valve surface under the seat. The nickel sublayer is deposited with a short arc with a current of direct polarity in a welding gas environment with forging of the deposited bead at a speed that does not allow the metal to cool. Carry out mechanical processing of the surface deposited with Nickel. The working layer of heat-resistant austenitic steel is welded with a consumable electrode with reverse polarity current with forging each bead at a speed that does not allow the metal to cool. The final machining of the working surface of the saddle is carried out. The method makes it possible to completely eliminate the possibility of seats falling out of the cylinder heads during operation of the internal combustion engine, to increase the thermal fatigue strength of the cylinder heads, and to increase the strength and wear resistance of the welded valve seats. 4 ill.

Drawings to the RF patent 2448825

SUBSTANCE: invention relates to internal combustion engines (ICE), namely to valve seats of ICE cylinder heads.

Modern transport internal combustion engines are characterized by high liter power. The increase in liter power is achieved mainly by increasing the average effective pressure by increasing the cyclic fuel supply. At the same time, there will inevitably be an increase thermal loads on the parts that form the combustion chamber, especially pistons, cylinder heads and valves, and it is their performance that limits further increase in power.

The cylinder head is the most complex in design and the most thermally loaded part of the engine. The complexity of the design leads to a large unevenness of thermal loads on its individual elements. The working conditions are also unfavorable, because the cylinder head does not have the possibility of free thermal expansion.

The most common operational defects in cylinder heads are valve seat failures: cracks in inner surface, catastrophic wear of the working surface, destruction and loss.

In modern domestic and foreign engines, valve seats are plug-in [p.249-250. Orlin, A.S. Design and strength calculation of reciprocating and combined engines. / A.S. Orlin, M.G. Kruglov, D.N. Vyrubov and others - M.: Mashinostroenie, 1984. - 384 p.]. Seats are either pressed into the seats of the cylinder heads with a relative interference fit, or inserted cooled. The method of pressing valve seats with an interference fit into the cylinder head is the most common. In this case, one significant drawback should be noted - the possibility of the seat falling out of the head socket.

If a valve seat falls out and is subsequently replaced during repair, it is necessary to install seats of a larger diameter to ensure the required interference, and for this it is necessary to bore the diameters of the inlet and outlet channels of the cylinder head to a larger diameter, which will lead to a decrease in the size of the intervalve jumper, which is the most loaded area of ​​the head cylinders.

It should also be noted that pressing due to significant stresses involves the manufacture of a massive seat.

On ship, locomotive and stationary diesel engines of large dimensions, cast-iron cylinder heads are used, in which valve holes are not equipped with plug-in seats [Voznitsky, I.V. Marine internal combustion engines. / I.V. Voznitsky, N.G. Chernyavskaya, E.G. Mikheev. - M.: Transport, 1979. - 413 p.], [Rzhepetsky, K.L. Marine internal combustion engines. / K.L. Rzhepetsky, E.A. Sudareva. - L .: Shipbuilding, 1984. - 168 p.]. Therefore, when the wear limit of the holes is reached, it is necessary either to send the head to scrap metal, or to bore the holes and press insert saddles into them. Both of these options are not optimal.

In the first case, a still fully functional cylinder head is lost and it becomes necessary to purchase a new expensive part.

In the second case, boring holes in the cylinder head for the installation of seats leads to a decrease in its cross sections in the most thermally and mechanically loaded areas on the bottom and thereby provokes the formation of thermal fatigue cracks along the intervalve webs and between the holes for valves and nozzles. In addition, it is impossible to exclude the possibility of falling out of the inserted seats during the operation of the diesel engine.

Thus, the objective of the present invention is to create a method for obtaining valve seats for cast-iron cylinder heads of internal combustion engines during their manufacture or restoration by electric arc welding. The proposed method of manufacturing or restoration will eliminate the above disadvantages that occur when valve seats are pressed into the cylinder head, and will optimally solve the problem of restoring the cylinder head to working capacity. In addition, when using the proposed method, the possibility of the seat falling out is completely excluded, and the thermal fatigue strength of the cylinder head is increased.

The task is achieved by the fact that in the manufacture or restoration of valve seats of cast-iron cylinder heads of internal combustion engines, the method of electric arc surfacing is used, which will provide new properties of the working surface of the seat by choosing different steel for surfacing. Also, the cylinder head becomes more maintainable in the future.

A method for producing valve seats for cast-iron cylinder heads of internal combustion engines during their manufacture or restoration, including cleaning of surfaces under the seat, flaw detection, its machining and manufacturing of the seat, is carried out by electric arc surfacing of the said surface with a short arc current of direct polarity with surfacing of a nickel sublayer, in a welding environment gas, with forging of the deposited bead-weld at a speed that does not allow the metal to cool down, mechanical treatment of the surface deposited with nickel, and then surfacing of the working layer with heat-resistant austenitic steel with a consumable electrode current of reverse polarity with forging each bead-weld at a speed that does not allow the metal to cool down, and final machining of the working surface of the saddle.

Figure 1, 2, 3, 4 shows a diagram for work to obtain the valve seat of the cast-iron cylinder heads of the internal combustion engine during their manufacture or restoration.

The method of obtaining valve seats of cast-iron cylinder heads of internal combustion engines during their manufacture or restoration consists of preparing the cylinder head 1 for surfacing by pressing out seats 2 (figure 1), cleaning, boring the seating surfaces 3 of valve seats for surfacing a nickel sublayer in accordance with figure 2 and cleaning the surfaces adjacent to the valve seats with a metal brush to a metallic sheen.

The poor technological weldability of gray cast iron leads to the following defect: bleaching, i.e. the appearance of areas with secretions of cementite in one form or another. The high hardness of the chilled areas practically makes it impossible to process cast irons with a cutting tool. Surfacing of the nickel sublayer eliminates the formation of these areas.

Surfacing of the sublayer is carried out with a short arc at a current of direct polarity in a welding gas environment with forging of each bead-seam at a speed that does not allow the metal to cool down, with light blows of a metal hammer. Expendable materials- PANCH welding wire, which includes: Cu - 2.3-3%, Mn - 5-6%, Fe - up to 2%, Ni - the rest. Impurities not more than: Si - 0.3%, C - 0.3%, welding gas (Ar 80%, CO 2 20%).

After surfacing, bore the seating surfaces 4 of the valve seats in accordance with Fig.3.

Next, the working surface of the valve seat is surfacing with heat-resistant austenitic steel, a consumable electrode (the choice of surfacing material is due to a unique combination of properties: high ductility, strength, corrosion resistance and the ability to work hard during operation under the influence of valve shocks when seated in the seat). Before welding, it is necessary to bake the electrodes at a temperature of 330-350°C for one hour. The surfacing of the working layer is carried out on a current of reverse polarity with the forging of each bead-seam at a speed that does not allow the metal to cool. After that, it is possible to perform the final machining of the seating surfaces 5 of the valve seats in accordance with Fig.4.

CLAIM

A method for producing a valve seat for cast-iron cylinder heads of internal combustion engines during their manufacture or restoration, including cleaning the surface under the seat, flaw detection, machining and manufacturing of the seat, characterized in that the seat is made by electric arc surfacing of the valve surface under the seat, while the sublayer of nickel is fused with a short arc current of direct polarity in a welding gas environment with forging of the deposited bead at a speed that does not allow the metal to cool down, machining of the nickel-deposited surface is carried out, then the working layer of heat-resistant austenitic steel is deposited with a consumable electrode current of reverse polarity with forging of each bead at a speed that does not allow the metal to cool down , and carry out the final machining of the working surface of the saddle.

Valve plates with welded chamfers. The technological process of restoring the valve disc.

Valves. The resource of the valves of autotractor engines is mainly limited by the wear of its chamfer, as a result of which, in the seat-chamfer connection of the valve, the depth of immersion of its plate relative to the surface of the cylinder head increases, which leads to a deterioration in the economic performance of the engine: a decrease in power, an increase in fuel consumption, oil, etc. The chamfer is usually restored by grinding. When worn to a size less than the nominal value, the valve must be replaced with a new one or restored.

The rapid wear of the chamfers of the valves is explained by the fact that during operation they are exposed to chemical and thermal effects, and 3-5 times more heat is removed through the chamfer than through the rod. Almost all valves of engines coming in for repair have wear along the chamfer of the plate.

In increasing the strength of the chamfers of newly manufactured valves, the compressed arc surfacing method has proven itself well. direct action on the U-151 installation, developed by the PWI. E. O. Paton. A cast ring is placed on the workpiece, which is then fused with a compressed arc. An attempt to transfer the experience of this method for surfacing worn valves did not give positive results. This is due to the fact that the height of the cylindrical belt of the valve disc decreases to 0.4-0.1 mm as a result of wear, and the surfacing of a thin chamfer edge due to uneven heating of the valve head and the applied filler ring is difficult: burning occurs.

An effective way to restore valves is the method of plasma surfacing with the supply of heat-resistant powder hard alloys to a worn chamfer. To do this, the Maloyaroslavets branch of the State Scientific and Technical Institute, TsOKTB and VSKHIZO on the basis of the U-151 machine according to the design of the PWI im. E. O. Paton developed the OKS-1192 installation. The installation consists of a semi-automatic surfacing machine complete with a ballast rheostat RB-300, a plasma torch designed by VSKHIZO.

Technical characteristics of the OKS-1192 installation

Types of welded valves (plate diameter), mm 30-70

Productivity, piece/h< 100

Gas consumption, l/min:

plasma-forming<3

protective and transporting<12

Cooling water consumption, l/min >4

Powder feeder capacity, m 3 0.005

Power, kW 6

Overall dimensions, mm:

installation 610X660X1980

control cabinet 780X450X770

In the absence of an industrial installation, if it is necessary to restore the valves, repair enterprises are able to assemble a plasma installation from separate ready-made units based on a lathe according to the scheme shown in Fig. 42. The valve is mounted on a water-cooled copper mold corresponding to the size of its plate, which is driven by a lathe spindle through a thrust bearing and a pair of bevel gears.

Rice. 42. Scheme of installation for plasma welding of valves:

1 - power supply; 2 - throttle; 3- tungsten electrode; 4 - inner nozzle; 5 - protective nozzle; 6 - valve; 7 - copper form; 8, 16 - bearings; 9 - installation body; 10 - water supply tube; 11, 12 - fittings; 13 - base; 14 - rack; 15, 17 - oil seals; 18 - locking screw; 19, 20 - bevel gears; 21 - cylinder

The principle of operation of the OKS-1192 installation and the installation assembled in the conditions of a repair enterprise is approximately the same and consists in the following. After cooling water (from the water supply network), plasma-forming argon gas (from a cylinder), electrical energy (from a power source) is supplied to the plasma torch, an indirect compressed arc (plasma jet) is excited between the tungsten electrode and the internal nozzle of the plasma torch using an oscillator. Then, powder is supplied from the powder feeder with the transport gas - argon through the protective nozzle of the burner to the chamfer of the rotating valve and at the same time current is supplied to the valve through the ballast rheostat. A compressed arc arises between the electrically conductive plasma jet and the valve chamfer, which simultaneously melts the valve chamfer and the welding powder, forming high-quality dense layers (Fig. 43).

Rice. 43. Welded valve discs

For surfacing of chamfers of valves of tractor engines having a large mass, in addition to those recommended, it is also possible to use iron-based powder hard alloys PG-S1, PG-US25 with the addition of 6% Al to the latter.

When choosing a material for surfacing valves, one should be guided by the fact that chromium-nickel alloys have higher heat resistance and wear resistance, but they are 8-10 times more expensive than iron-based hard alloys and are less processed.

Modes of plasma welding of chamfers of valves

Current strength, A 100-140

Voltage, V 20-30

Gas consumption (argon), l/min:

plasma-forming 1.5-2

transporting (protective) 5-7

Surfacing speed, cm/s 0.65-0.70

Distance from the plasma torch to the chamfer of the valve, mm 8-12

Layer width, mm 6-7

Layer height, mm 2-2.2

Penetration depth, mm 0.08-0.34

Hardness HRC of the deposited layer with an alloy:

PG-SR2, PG-SR3 34-46

PG-S1, PG-US25 46-54

Technological process restoration of the valve disc contains the following main operations: washing, flaw detection, cleaning the end face and chamfer from carbon deposits, plasma surfacing, machining, control. Machining of valves is performed in the following sequence: clean the end face of the valve disc; grind the valve disc along the outer diameter to the nominal size, pre-process the chamfer disc; grind the chamfer to the nominal size. The first three operations are performed on a lathe with cutters with carbide inserts. The use of the plasma surfacing method made it possible to increase the wear resistance of the working surface of the car valve disc by 1.7-2.0 times compared to the wear resistance of new ones.

It is installed in the holes of the cylinder head, designed to install valves and distill the air-fuel mixture and exhaust gases through them. The part is pressed into the cylinder head at the factory.

Performs the following functions:

• hole tightness;
• transfers excess heat to the cylinder head;
• provides the necessary air flow when the mechanism is open.

Replacement of the valve seat is required in the event that it is not possible to restore its tightness by mechanical processing (numerous processing in the past, burnout, heavy wear). You can do it yourself.

Parts are repaired when:

• plate burnout;
• after replacing the guide bushings;
• with a moderate degree of natural wear;
• in case of violation of the tightness of the connection of the ring with the plate.

Editing worn and damaged saddles at home is done using cutters. In addition, a welding machine or a powerful gas burner, a standard set of wrenches necessary for dismantling and disassembling the cylinder head, lapping paste, and a drill may be required.

Seat Replacement

The replacement procedure consists of two critical procedures: the removal of old parts and the installation of new ones.

Removing old planters

Valve seats are replaced on a dismantled cylinder head with a disassembled gas distribution mechanism. You can remove the old ring using a welding machine, if the material from which it is made allows this.

To perform the procedure, a valve seat puller is made - an old unnecessary valve is taken, the plate of which must be machined to the size of the inner diameter of the seat.

After that, the resulting tool is sunk into the seat, not reaching the edge of 2-3 mm and "tacked" by welding in 2-3 places. After the valve, together with a metal ring, is knocked out from the back with a hammer.

Important! A procedure using welding may result in some deformation of the seat. In this case, the standard saddles will have a weak fastening, which can lead to their spontaneous dismantling during the operation of the motor. Requires rings of increased diameter, which are not sold in stores, but are made to order.

A valve seat made of non-weldable metals can be removed by screwing a piece of pipe into it, which is used as a valve seat puller. To do this, a thread is cut on the inner surface of the ring. A similar thread is applied to the outer surface of a metal pipe of suitable diameter.

An old valve is taken, which is pre-welded to the end of the pipe in the reverse position. In this case, the valve stem is inserted into the hole intended for it, the pipe is screwed into the thread, after which the element is removed by tapping on the stem.

Installing new saddles

Before starting the installation procedure for new saddles, the seats for them are cleaned of dirt. After the cylinder head, it should be evenly heated to a temperature exceeding 100 ° C. In this case, the metal expands, allowing the ring to be pressed in.

The part to be mounted is cooled with liquid nitrogen. In its absence, you can use a combination of ice and acetone, which allows you to reduce the temperature of the metal to -70 ° C. The dimensions of the parts are selected so that the difference between the diameter of the seat and the ring is no more than 0.05-0.09 mm on cold parts.

The valve seat is pressed in using a special mandrel or a piece of pipe of suitable diameter. The part should fit into the seat with little effort. In this case, it is important that the ring stands up without skew.

After pressing and cooling the cylinder head, you should check if the element is hanging on the seat. If there is no gap, and the replaced element is tightly held in place, the replacement procedure can be considered completed. Next, cutting of the valve seats is required using cutters.

Important! With the standard procedure for replacing the plates of all valves, they are planted quite high. However, some experts recommend that the chamfers be machined so that the exhaust valves sit slightly deeper than the normal position. The inlet valve seat is left in its original position.

Saddle repair

Repair of valve seats is carried out with their natural wear and loose fit of the plate to its seat.

In order to restore the geometry of the rings, cutters for valve seats are used - a set of milling heads that allow you to make the necessary angles.

Cone cutters can be used in combination with special equipment. However, it is costly. Therefore, at home, a ratchet wrench with an extension cord is used. Correctly processed places have angles of 30˚, 60˚ and 45˚. The processing of valve seats to create each of them is carried out with an appropriate cutter.

Valve seat grinding does not require heating or other processing. The groove is made "dry". In the future, at the time of lapping, it is necessary to use a special lapping paste. For best results, lapping into new seats is recommended to be done by hand rather than with a drill.

Another type of repair is the groove of seats for repair inserts. To do this, according to the algorithm described above, the saddles are removed, after which, with a special cutting tool, the places under them are machined. The size of the repair site should be 0.01-0.02 cm smaller than the insert. Installation is carried out after heating the cylinder head and cooling the mounted elements.

You can try to properly bore yourself at your own peril and risk. However, given the complexity of the procedure and the required high accuracy of work, such manipulations are best done in a qualified car repair shop or car repair plant.

6.10.1 Plasma welding of valves .

The exhaust valves of medium-speed marine diesel engines (for example, "SULZERA 25") are made of steels 40X9C2 and 40X10C2M.

To ensure increased valve performance, the sealing belt of the plate is hardened by surfacing. To ensure optimal properties of the deposited metal, HAZ and base metal, a process of automatic plasma surfacing with self-fluxing powder PR-N77Kh15SZR2 has been developed. (Previously, manual argon-arc surfacing with stellite was used for this).

Plasma surfacing is carried out on the UPN-303 installation with the following mode parameters: direct polarity arc current 100-110A, arc voltage 35-37V, powder consumption 2kg/h, surfacing speed 7-8 m/h. The powder is blown into the plasma. Surfacing is performed with transverse oscillations of the plasma torch. Argon is used as a plasma-forming, protective and transporting gas. Before surfacing, the valve disc is heated with an acetylene-oxygen flame to a temperature of 200-250 0 C.

Edge preparation is performed according to Fig. 1. To ensure the horizontal position of the surface of the welded band, the valve stem in the manipulator of the welding installation is placed at an angle of 30 0 to the vertical. Surfacing is carried out in one layer.

After surfacing, annealing is performed at a temperature of 700 0 C.

The valves have the required hardness of the base metal HRC 24-25, the required increased hardness of the deposited HRC 38-41 and the acceptable hardness of the HAZ metal HRC 36-37.

6.10.2 Welding of valves with stellite.

The valves of powerful marine diesel engines are also surfacing with stellite.

Cobalt alloys with chromium and tungsten, the so-called stellites, are distinguished by remarkable performance properties: they are able to maintain hardness at high temperatures, resist corrosion and erosion, and also have excellent wear resistance in dry metal-to-metal friction. By itself, cobalt does not have high heat resistance, this property is given to alloys by additives of chromium (25-35%) and tungsten (3-30%). An important component is carbon, which forms special hard carbides with tungsten and chromium, which improve the resistance to abrasive wear.

Valves of internal combustion engines, sealing surfaces of steam fittings of ultra-high parameters, dies for pressing non-ferrous metals and alloys, etc. are deposited with cobalt alloys. When surfacing steels, it is necessary to strive for a minimum transition of iron from the base metal to the deposited metal, otherwise the properties of the latter deteriorate sharply. The deposited metal is prone to the formation of cold and crystallization cracks, therefore, welding is carried out with preliminary and often with concomitant heating of parts.

Ensuring the minimum proportion of the base metal and compliance with the necessary thermal conditions are the most important features of the technological process of surfacing cobalt alloys. Surfacing is carried out by gas flame or argon-arc welding with rods made of V2K and VZK alloys, as well as coated electrodes of the TsN-2 brand with a rod made of VZK rod.

Parts are heated to a temperature of 600-700 0 C. With such heating, the proportion of the base metal is large (up to 30%), therefore, to obtain a minimum iron content, surfacing has to be performed in three layers. This increases the consumption of a very expensive surfacing material and increases the complexity of the work.