Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
  • C22C9/04—Alloys based on copper with zinc as the next major constituent
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L3/00—Lift-valve, i.e. cut-off apparatus with closure members having at least a component of their opening and closing motion perpendicular to the closing faces; Parts or accessories thereof
  • F01L3/02—Selecting particular materials for valve-members or valve-seats; Valve-members or valve-seats composed of two or more materials
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L3/00—Lift-valve, i.e. cut-off apparatus with closure members having at least a component of their opening and closing motion perpendicular to the closing faces; Parts or accessories thereof
  • F01L3/08—Valves guides; Sealing of valve stem, e.g. sealing by lubricant

Definitions

• the invention relates to a use of a copper-zinc alloy according to claim 1.
• Copper-zinc alloys or sintered steel alloys are used for a valve guide in an internal combustion engine.
• such a copper-zinc alloy is known.
• the properties of the Cu-Zn alloys no longer meet the requirements that are placed on such a valve guide that is to be used in the new FSI engines.
• the working temperature of the valve guides can reach and exceed 300 ° C.
• the currently used copper-zinc alloys soften at these temperatures.
• a comparable, disadvantageous effect is also observed with sintered steel alloys.
• Sintered steel alloys also soften at temperatures above 300 ° C, and the hardness also varies greatly. Incidentally, the manufacturing outlay for sintered steel alloys is high as a result of the powder-metallurgical manufacturing process.
• the present invention is therefore based on the problem of providing a copper-zinc alloy for use as a valve guide, the copper-zinc alloy satisfying the requirements for materials for valve guides, particularly at elevated temperatures and being easy to manufacture.
• the ones from the DE 29 19 478 C2 known alloy contains an Al content of 4-6% by weight and an Mn content of 6-8% by weight.
• the DE 759 865 discloses a cold rolled brass alloy for the manufacture of plain bearings.
• the alloy optionally contains Ni, Mn, Fe, Pb, Th and Al.
• DE 764 372 A1 discloses a copper-zinc alloy with a content of at least 0.1% by weight of cobalt.
• the DE 2 145 710 discloses a copper-based alloy with an Al content of 5-12% by weight.
• the specified copper-zinc alloy has a surprisingly high heat resistance which, in combination with its good wear resistance, makes it possible to use it as a valve guide in the first place.
• This surprising combination of material properties offers the possibility of using the known alloy in a new way as a valve guide.
• the use as a valve guide in modern engines requires a combination of high temperature resistance above 300 ° C with good wear resistance, which is necessary as a result of transverse forces acting on the valve tappets.
• the high coefficient of friction is negligible.
• the invention thus defies a prejudice that has hitherto been widespread among experts.
• valve guides can be manufactured in rod form by semi-continuous or fully continuous continuous casting, extrusion and drawing, i.e. by hot and cold forming.
• a copper-zinc alloy not according to the invention for use as a valve guide comprises 70 to 73% copper, 6 to 8% manganese, 4 to 6% aluminum, 1 to 4% silicon, 1 to 3% iron, 0.5 to 1 , 5% lead, 0 to 0.2% nickel, 0 to 0.2% tin, the remainder zinc and unavoidable impurities.
• the structure of the DE 29 19 478 C2 The manufactured alloy consists of an alpha and beta mixed crystal matrix with up to 60 to 85% alpha phase, the body-centered cubic beta phase being the basic matrix in which the face-centered cubic alpha phase is predominantly finely dispersed.
• the structure can also contain hard intermetallic compounds, for example iron-manganese silicides.
• the alpha phase determines the resistance of the alloy.
• Valve guides made from this alloy have a surprisingly high wear resistance, which is even significantly higher than that of sintered steel.
• the dry friction wear of valve guides made of said alloy enables use in engines that require "cleaner" fuels, i.e. those that are lead- or sulfur-free, as the absence of these additives means that there is no additional wear-reducing effect. This is particularly advantageous at temperatures around 300 ° C, the working temperature of the valve guides in FSI engines.
• Another advantage of using this alloy as a valve guide is that a stable hardness level is achieved in the desired working range above 300 ° C, since the alloy only softens above 430 ° C, whereas the copper-zinc used so far has softened -Alloys starts at 150 ° C.
• the associated drop in hardness occurs from 150 ° C as well as the hardness drop in sintered steel alloys from 300 ° C.
• the alloy comprises 69.5 to 71.5% copper, 6.5 to 8% manganese, 4.5 to 6% aluminum, 1 to 2.5% silicon, 1 up to 2.5% iron, 0.5 to 1% lead, 0 to 0.2% nickel, 0 to 0.2% tin, the remainder zinc and unavoidable impurities.
• the structure of the alloy produced in the usual way has an ⁇ - and ⁇ -mixed crystal matrix with up to 80% finely dispersed alpha phase.
• it can contain hard intermetallic compounds, for example Fe-Mn silicides.
• valve guide is particularly advantageous because it has a hot tensile strength that is twice as high as that of conventional copper-zinc alloys that have hitherto been used as valve guides. Further advantageous properties are a high softening temperature, high strength and high wear resistance.
• a copper-zinc alloy is then used for valve guides, the alloy being 60 to 61.5% copper, 3 to 4% manganese, 2 to 3% aluminum, 0.3 to 1% silicon, 0.2 to 1% iron , 0 to 0.5% lead, 0.3 to 1% nickel, 0 to 0.2% tin, the remainder zinc and unavoidable impurities.
• the structure of said and correspondingly produced alloy has a basic mass of ⁇ mixed crystals in which needle-shaped and ribbon-shaped ⁇ precipitates are embedded.
• the structure can also contain randomly dispersed manganese-iron silicides.
• Valve guides made from this alloy have a high level of wear resistance, which is even significantly higher than that of sintered steel.
• the dry friction wear of valve guides made of said alloy enables use in engines that require "cleaner" fuels, i.e. those that are lead- or sulfur-free, as the absence of these additives means that there is no additional wear-reducing effect. This is particularly advantageous at temperatures around 300 ° C, the working temperature of the valve guides in FSI engines.
• a copper-zinc alloy is used for valve guides, which additionally comprises at least one of the following elements with a concentration ⁇ 0.05% chromium, ⁇ 0.05% titanium, ⁇ 0.05% zirconium.
• Sintered steel and copper-zinc alloys with approximately the following composition are currently used as material for valve guides that are not subject to high temperatures: 56 to 60% copper, 0.3 to 1% lead, 0.2 to 1.2% iron, 0 to 0.2 % Tin, 0.74 to 2% aluminum, 1 to 2.5% manganese, 0.4 to 1% silicon and the remainder zinc along with unavoidable impurities.
• Such an alloy is referred to below as a standard alloy.
• Alloy 1 is an example of the alloy of the present invention.
• Alloy 2 is another comparative alloy.
• the softening behavior of the various materials has been investigated up to a temperature of 500 ° C. It has been shown that the standard alloy for valve guides shows a clear and continuous decrease in hardness from 195 HV50 to only 150 HV50 from a temperature of 100 ° C. In the case of sintered steel, there is a drastic decrease in hardness from 195 to a low 130 HV50 in the relevant temperature range from 300 ° C, with the hardness fluctuating upwards and downwards with increasing temperature. In contrast, alloy 2 has a hardness of around 10% higher (224 HV50), which only decreases from 350 ° C to around 170 HV50. The hardness values of sintered steel at room temperature are only reached from 450 ° C.
• alloy 1 shows a clear increase in hardness from 224 to 280 HV50 with increasing temperature up to 350 ° C.
• alloy 1 has a hardness of 140 HV50 higher than sintered steel. Alloy 1 thus has its maximum hardness at the temperatures that correspond to the working temperature of valve guides in FS1 engines.
• the higher hardness of alloy 1 and 2 compared to the conventionally used materials is due on the one hand to the higher initial hardness and on the other hand to hardening effects.
• the electrical conductivity can be used as a measure of the thermal conductivity, with a high value standing for good thermal conductivity.
• the electrical conductivity of the standard alloy is 11 m / ⁇ mm 2 .
• Alloy 2 has a good electrical conductivity of 7.5 m / ⁇ mm 2 , which is only about a quarter lower than that of the standard alloy.
• the electrical conductivity of alloy 1 is 4.6 m / ⁇ mm 2 .
• the heat dissipation of alloys 1 and 2 is significantly improved.
• the wear behavior was investigated with and without a lubricant.
• sintered steel has the highest wear resistance (2500 km / g).
• Alloy 1 also has an excellent wear resistance of 1470 km / g, which is more than a factor of 10 higher than the wear resistance of the standard alloy of 126 km / g.
• the wear resistance of alloy 2 with lubricant (94 km / g) is in this range.
• alloys 1 and 2 have clear advantages over sintered steel and the standard alloy.
• Sintered steel has a wear of 312 km / g, which roughly corresponds to the wear behavior of the standard alloy with 357 km / g.
• the dry wear behavior of alloy 2, at 417 km / g, is significantly better than that of standard alloy and sintered steel. In other words, there is much less wear and tear.
• Alloy 1, at 625 km / g has twice as much wear resistance as sintered steel.
• the low dry friction wear makes alloys 1 and 2 particularly interesting, because the increasing purity of the fuels due to the engine, i.e. the absence of lead or sulfur, the wear-reducing effect of the so-called "blow by", the lubrication by the fuel itself in the additives will not be available in the future.
• the hot tensile strength was determined using tensile tests at 350 ° C.
• the hot tensile strength of the standard alloy is 180 N / mm 2 .
• Alloy 1 has an amount twice as high (384 N / mm 2 ).
• alloy 2 has an approx. 35% higher hot tensile strength, which is 243 N / mm 2 .
• Alloy 1 and alloy 2 can preferably be produced by semicontinuous or fully continuous casting, extrusion, drawing and straightening.
• Alloy 2 and in particular alloy 1 have clear advantages over the previous standard alloy used as a valve guide alloy and compared to sintered steel. These advantages relate to the hot tensile strength, the softening temperature, the strength and the wear resistance. In addition, the conductivity is sufficient, which is why alloys 1 and 2 represent a considerable improvement in terms of use as valve guides, since these alloys meet the requirements for the material at the increased operating temperatures in the new engines.
• Table 1 shows the material properties of a Cu-Zn standard alloy, a sintered steel alloy, alloy 1 and alloy 2 in comparison.
• property Standard alloy Alloy 1 Alloy 2 electr.
• Conductivity (m / ⁇ mm 2 ) 11 4.6 7.5 Hardness (HV50) cold worked (10%) 197 224 224 Dry wear (km / g) 357 625 417 Lubricated wear (km / g) 126 1470 94

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