MXPA98009048A - Method to obtain inserts formed by roci - Google Patents

Abstract

A method for obtaining seat inserts by spraying mass material, this method comports the steps of: (a) preparing a mandrel having an outer dimension no greater than the desired inner dimension of the desired insert, this mandrel has resources to supply the separation of the mass material sprayed from the mandrel; (b) separated, thermally sprayed particles of one or more types of steels or nickel alloys, in the presence of a controlled atmosphere, to form a composite material in bulk on the mandrel , which has a density of at least 99%, and (c) after cooling the material in bulk, remove such material from the mandrel and slice the material in discrete configurations of the seat inset, for the implant in the fine product

Description

METHOD FOR OBTAINING INSERTS FORMED BY SPRAYING BACKGROUND OF THE INVENTION Technical Field This invention relates to the technology of mass or volume materials, formed by spraying, to create objects and, more particularly, to the manufacture of high performance inserts, without the chemical restrictions, with the use of spray formation techniques.

Discussion of the Prior Art Inserts have been used to increase the physical characteristics of certain parts of a component, particularly the components in an automobile engine. For example, steel alloy valve seat inserts are used extensively on aluminum motor heads and on some cast iron motor heads that use high performance or alternative fuels. The list of desired, high-performance, desired features in the seat is often quite long, which includes increased resistance to wear at room temperature and at high temperatures, greater resistance to drag, greater resistance to thermal fatigue (under the load of repeated impact of the valve), the best thermal conductivity, better resistance to corrosion, lower manufacturing costs, and the ability to be tribologically compatible with the valve materials that are attached to the insert. A common manufacturing approach, which tries to obtain these characteristics, is to manufacture the inserts by powder metallurgical processes, which involve several steps: the dosage and combination of the selected powder mixtures, the compaction and formation of the crude body in molds and dies; sintering and sometimes infiltration of copper into compact material respectively 1080 and 15002C; the controlled cooling, the heat treatment of tempering, after the sintering and finally the machining to the desired dimensions of the seat. This is obviously an involved process that adds a considerable cost. To achieve the desired physical characteristics, chemical additions are made to the powder mixture of carbon, chromium, molybdenum (for wear resistance), cobalt and nickel (for heat resistance) and other additions to obtain better thermal conductivity or better self-lubrication. In the ferrous-based powder mixtures, the resulting product may have its matrix consisting of perlite, bainite or tempered martensite, depending on the heat treatment used during compaction and sintering. The sintered insert will always have the same chemical components as the untreated raw material and its micro-structure will depend on the heat treatment used. To obtain optimum physical characteristics in inserts, very high concentrations of certain additions (ie, 15 to 25 wt.% Cobalt, up to 20 wt.% Pb) may be necessary, as well as the introduction of certain ingredients chemicals, such as rare earths, which, unfortunately, inhibit or prevent sintering by powder metallurgy techniques. Also, powder metallurgy does not allow the introduction of inexpensive oxides or ceramics during the process; ceramics are very useful in achieving certain physical characteristics. When an engine is operating with alternative fuels, such as natural gas or an alcohol, the metal valve seat inserts in powder for the internal combustion engine heads are often inadequate. These metal valve seat inserts, when used for inlet valve seats and reciprocating engines, often contain too little self-lubricating, such as lead, and thus lead prematurely to wear. severe. Lead is also inconvenient as an embedded self-lubricant, since it can foul the catalytic surfaces used in treating the emissions.

The prior art has not attempted to use thermal spraying techniques to obtain high performance inserts. The Osprey spray technique uses a refractory funnel to supply a stream of molten metal, which is atomized under an inert or vacuum atmosphere, to form bulk materials by spraying; however, difficult and exact procedures are necessary to control the molten bath and the current, thus limiting its use to obtaining inserts in a non-economic way.

SUMMARY OF THE INVENTION It is an object of this invention to provide a technique for manufacturing high performance inserts, which are not only more economical but also not limited in chemistry or not limited in the ability to incorporate ceramic materials. It is also an object of the process to provide for the obtaining of improved insert articles having a higher hardness and a higher thermal resistance, in order to meet the higher demands of alternative fuel engines. The method of this invention, which meets the above objectives is a method for obtaining seat inserts by thermally spraying bulk material, this method comprises the steps of: (i) preparing a mandrel having an external dimension equivalent to the internal dimension For the desired insert of the desired insert, this mandrel has elements for supplying the separation of the mass material sprayed from the mandrel, (ii) the thermal spraying of particles separated from one or more steels or nickel alloy, in the presence of a controlled oxidation medium. , to form a composite material in bulk on the mandrel, with a density of at least 99% e (iii), after cooling the bulk material, remove such material from the mandrel and slice it in discrete seating configurations to implant it in the Final product. Brief Description of the Drawings Figure 1 is a schematic block diagram of the method of the present invention; Figure 2a is a schematic illustration of a mode for carrying out the thermal spray passage of the apparatus of this invention and Figure 2b is an alternative mode; Figure 3 is an enlarged view of a cylindrical mass reservoir, made by this invention, the reservoir is sliced into individual seat inserts; Figure 4 is a perspective view of a seat inserts showing the engine head, in place in the intake and exhaust doors; Figure 5 is a fragmentary sectional elevational view of a portion of an internal combustion engine head assembly, showing the implanted valve seats, obtained by this function of the invention; and Figure 6 is a schematic illustration of a wear test apparatus used to determine the characteristic wear of the seat inserts produced by the method of the invention; Figures 7a and 7b are micrographs of the miscrostructure of an insert formed by spraying of the invention and a powder metallurgy insert, respectively; and Figures 8a and 8b are photomicrographs respectively of a sputter-shaped copper infiltrate insert of the invention and a copper-infused powder metal insert. Detailed Description and Best Mode The first step of this invention (as schematically illustrated in Figure 1) is that of preparing a mandrel 10 having an external dimension 11 not greater than the desired anterior dimension 12 of the insert designated to be manufactured. To obtain valve seat inserts for internal combustion engine heads, a hollow aluminum tapered tube 13 is used as the mandrel; the tube has a wall thickness 14 of about 5.35 to 12.7 mm and a surface finish of about 6-8 micras Ra. The mandrel is preferably rotated about its own central axis 15 at a speed in the range of 20 to 60 revolutions per second. This apparatus 16 is provided to pass air or cooling liquid through the interior of the tube at a flow rate of about 566 to 2831 liters / minute during the thermal spray passage, the aluminum alloy from which the tube is made , has a different characteristic of thermal expansion distinctly than the material sprayed in bulk, to facilitate the final release of the mandrel 10 from the bulk material. The taper 18 of the outer surface of the tube is preferably about 2-3, which serves to initiate the separation between the sprayed mass material and the mandrel upon cooling, the tube shrinks at a higher rate; as it cools down further, the delamination initiated, due to the taper, propagates through the entire axial length 19 of the bulk material to promote complete release. Other materials can be used for the mandrel, such as copper alloys or elemental iron, all of which have a higher coefficient of thermal expansion than the mass material deposited. An assembled mandrel that allows instantaneous release of the insert is also possible. The second step requires the thermal spraying of the bulk material on the rotary mandrel 10. This only creates or forms a sleeve of bulk material 17 composed of metal / oxide, as shown in Figures 2a and 2b. The thermal spray technique may be the wire arch, powder plasma, oxy-fuel, or any of the high-speed methods, such as the HVDF or the detonation gun. The thermal spray gun has a spray head 20 advantageously positioned about 15.24 to 30.48 cm from the target mandrel surface 21. As the mandrel rotates, the thermal spray gun emits a dew 22 of droplets of melt, which line the mandrel, at a rate of about 0.907 to 4.54 kg / hr. By repeatedly moving the gun back and forth through the length 19 of the mandrel (7.6 to 10.16 cm or more, typically), a coating thickness 32 of about 3.175 to 6.35 mm can accumulate in about 15 minutes. Alternatively, the mandrel can be moved through a spraying station in which several spray guns apply the coating to the workpiece. The selection of the chemistry for the supply of 23 wire or powder feed to the gun, to carry out the thermal spraying, is less inhibited than that for the powder metallurgy or the Osprey process. It is possible to produce novel self-lubricating composite structures by (a) by forming the steel 23 or nickel alloy feedstock 23 and (b) by protecting the hot melt droplets sprayed in a controlled atmosphere of air or oxygen 24, to produce certain self-lubricating oxides of steel or nickel, while the droplets are still in transit to the target or during the initial impact with the target. The details of how to achieve the creation of self-lubricating oxides is taught in U.S. Patent No. 5,592,927, the disclosure of which is incorporated herein by reference. It is advantageous if the material supply is selected from the group of (i) low carbon steel lubricant and FeO (2-15% by weight); (ii) lubricant of low carbon steel and high carbon steel and FeO (2-20% by weight); e (iü) high carbon steel and nickel alloy, plus iron or nickel oxides. The low carbon steel can be a 1010 steel (such as a single wire feed 40, as shown in Figure 2a), which has a composition by weight% of: 0.1 C, 0.6 Mn, 0.045 P, 0.04 S and the rest of iron. The resulting seat, formed by spraying, will consist of an iron alloy matrix, within which there are scattered Fe oxides. The content of the oxide will vary between 2-15% by weight, depending on the nature of the propellant gas (air or nitrogen) that is used during the spraying. The porosity of the material deposited 17 will be extremely low (2% or less); The inserts will have a hardness of 25-32 Rc and can be easily used in gasoline engines. The second material can be applied by the use of two different wires, which are fed in a two wire arc spray gun 20 (as shown in Figure 2b), the first wire 38 being steel 1010 and the second wire 39 being of high carbon steel, which has a composition of around 1.0 C, 1.6-1.0 Cr, 1.6-1.9 Mn and the rest iron. The gun can be operated under a power of 25-30 volts, 100-250 amps and an air pressure of 4.2 to 7 kg / cm2. The seat inserts formed in this sasso will have a hardness value ranging from 35-42 Rc (depending on the spray condition) with the oxide content being 2-20% by weight. The third selection uses a high carbon steel wire, as indicated above and a nickel-based alloy wire, which contains 58% nickel and 4% Nb, 10% Mo, 23% Cr and about 5%. % of iron; The wires are fed as separate charge materials in a two-wire arc system, with the gun operated at a voltage of approximately 30-33 volts, 200-330 amperes and 4.2 to 7 kg / cm2 of air or nitrogen pressure. The inserts produced with the third selection comprise several phases of nickel, iron, Fß3? 4, NiO, FeO and have hardness values ranging from 40-50 Rc. Copper can be introduced into the valve seat inserts formed by spraying, to increase the thermal conductivity and the ability to extract heat from the valve. The spray-formed inserts can have copper incorporated in the microstructure, using another flame spray gun 25 (as shown in Figure 2b) to co-deposit the copper together with the reservoir of the two-wire arc gun 26, as mentioned earlier; the additional flame spray gun 25, of course, uses a wire 27 of powdered copper feedstock. The amount of copper can be controlled precisely by adjusting the flame spray parameters. The last elementary step of the process is to cool the sprayed mass material 17 to separate it from the mandrel 10 and to slice the sleeve 28 into rings 29 (see FIG. 3), which are inserts to be implanted in the wall 30 of the gate. exhaust or intake 41 of an aluminum motor head 31, as shown in Figures 4 and 5. The ends or edges 32 of the ring inserts 29 have an approximate angle of 902 as a result of being sliced. These inserts are press fit or shrink fit within a slot or groove 33 machined complementary to the head wall; the implanted insert 29 and the wall are then machined together to provide an outline 42, which is configured to the curved wall of the intake or exhaust passage 43, as shown. Usually, the valve guide 34 immediately above the valve opening 35, with the seat insert, are machined simultaneously to be sure that the valve guide 34 and the valve seat 29 are in absolute alignment to allow the valve 44 work properly Other mandrel release mechanisms may be used in addition to those previously described. For example, the mandrel can be made of steel and coated with zinc or tin so that, in the spray, the initial deposit does not attach directly to the steel; Copper or zinc are melted in situ during the spraying process to ensure a release. The mandrel can also be made of steel and destroyed after the thermal spray passage has been completed, by the destructive machining of the mandrel outside the sprayed combination. Alternatively, the mandrel can be formed from a dissolvable salt, which, after spraying, can be removed by dissolution. As shown in Figure 6, several insert materials were evaluated using a block-on-ring tester 36. A counter-face ring 37, of hardened steel AISI 4620, is rotated at 100 rpm under an applied force of 40 newtons against a quantity of the deposited material 17, which has been sprayed onto a substrate. The wear resistance was determined by measuring the wear volume of the hardened steel ring after about 30 minutes of testing, using a three-dimensional profile meter. The results of this test showed that there is less recoil or wear of the seat therein with the powder metallurgy inserts or other equivalent insert of the prior art. Such a reduction in the backward movement of the seat is due to the increased wear resistance and self-lubrication of the seat insert, and thus there is less need for any impulse adjustment of the engine valve, after a predetermined period of use, avoiding thus the need for continuous maintenance of the valve train. The material applied by the technique of this invention was also tested in comparison with a standard production insert in a single cylinder engine. A 4-valve engine, cooled with air, capable of delivering 62 HP / liter, was equipped with two inserts (1 exhaust and 1 intake) made from the third material selected above. The other seat inserts were made of powder steel, characteristic of the prior art. The single cylinder engine was operated at 6200 rpm with the throttle valve open wide, for 99 hours. The wear results showed that the sprayed insert of this invention has a considerably smaller dimensional change than that for the other comparative inserts. The high alloy inserts manufactured for alternative fuel engines have a cost factor of approximately 6 times that of powder metallurgy steel. Using the method of this invention, the cost of producing a valve seat insert for the same application is less than _ of such costs.

Figures 7a and 7b compare the microstructures of a seat insert formed by spraying, according to this invention, with a powder metallurgy insert of the prior art (the micrographs are with a magnification of 200 times). The chemistry of the deposit in Figure 7a is 0.3-0.6% by weight of C, 10-15 of Cr, 0.8-1.2 of Mb, 25-30 of Ni, 0.5-1.5 of Nb, 2-5 of Mo, 10 -20 of Fe, 10-15 of Fe304 (magnetite) and 2-5 of FeO westita) and 5-10 of Cu; the chemistry of the powder metallurgy material in Figure 7b is 1-7% by weight of C, 0.8 of Mo, 6 of Cu, other 1-2, and the rest of Fe. Figures 8a and 8b compare the photomicrographs (200 times) of the spray tank according to this invention, which contains copper and a copper-infiltrated powder metallurgy insert. Such a comparison illustrates that effectively high levels of co-deposited copper can be produced by the spray-forming process. While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention, and attempts are made to cover all of these modifications and equivalent in the appended claims. find within the true spirit and scope of the invention.

Claims (11)

1. CLAIMS 1. A method for obtaining seat inserts by spraying bulk material, this method comprises the steps of: (a) preparing a mandrel having an outer dimension no greater than the desired inner dimension of the desired insert, this mandrel has resources for supplying the separation of the mass material sprayed from the mandrel; (b) separate, thermally sprayed particles of one or more types of steels or nickel alloys, in the presence of a controlled atmosphere, to form a composite material in bulk on the mandrel, which has a density of at least 99%; and (c) after cooling the bulk material, removing such material from the mandrel and slicing the material in discrete configurations of the seat insert, for implantation in the final product.
2. 2. The method according to claim 1, wherein the thermal spraying is carried out by a wire arc spraying, with a controlled air cover to promote the in situ formation of the FeO.
3. 3. The method according to claim 1, wherein the final product is a motor head made of aluminum alloy, the seat inserts form the valve seats for such head, the bulk material has a chemical combination selected from the following group : (a) low carbon steel and FeO lubricant (2-15% by weight); (b) low carbon steel and high carbon steel and FeO lubricant (2-20% by weight); and (c) high carbon steel and nickel alloy and iron or nickel oxides.
4. 4. The method according to claim 3, wherein the chemistry the bulk material is modified by the co-deposit of the copper.
5. 5. The method according to claim 1, wherein the mandrel is a cylindrical element that rotates in relation to the thermal spray to form the bulk material as a multiple coating on the mandrel.
6. 6. The method according to claim 5, wherein the mandrel is a hollow tube, through which the air passes to control the temperature of this mandrel and control the cooling of the deposited mass material.
7. 7. The method according to claim 5, in which the mandrel has an external diameter that tapers uniformly along the axis of the tube, this taper is in the range of 1-32, so that when cooling, the material in bulk and the mandrel are released, at least at one end, from the bulk material.
8. 8. The method according to claim 5, wherein the mandrel is made of aluminum.
9. 9. The method according to claim 1, wherein the mandrel is comprised of a material having a thermal expansion characteristic greater than the mass material that is sprayed, so that, upon cooling from the thermal spray temperatures, this material mass is released from the mandrel.
10. 10. The method according to claim 1, wherein the mandrel is formed of a dissolvable or melting material, which resists the temperature of the thermally sprayed tank, but which can be easily released from the bulk material tank.
11. 11. The method according to claim 10, wherein the material that can be dissolved or melted is zinc or tin.