DE901104C - Composite casting and process for its manufacture - Google Patents

Description

Composite casting and method for making the same. The invention refers to pistons for internal combustion engines made of light metal.

So far it has been suggested the wear property of aluminum pistons to be improved by inserting a band near the piston crown, into which the piston ring grooves are screwed. Steel and cast iron were used for such belts because of the lower wear of these metals compared to aluminum and aluminum alloys suggested. Because of the widely differing thermal expansion coefficients of cast iron and steel on the one hand and aluminum and aluminum alloys on the other it has also been proposed that iron and steel be an alloy metal such as Nickel, which gives it a coefficient of thermal expansion that closer to that of aluminum or the aluminum alloy that makes up the piston body. However, even in this case the mismatch in thermal expansion leaves between the inserted band and the piston body made of aluminum, the aluminum during the Heating process against the reticent effect of the iron or steel strip grow. This results in: a very low compression of the aluminum, so that when it Cooling down the tape is no longer as tight as it was originally. Further heating processes increase this state until the ring band is loosely at the end in the aluminum piston: will. Although inlays made of high-nickel cast iron with a high coefficient of thermal expansion in aluminum pistons are useful and desirable, this does not add to the problem completely resolved.

According to the invention are made of aluminum and aluminum alloys manufactured pistons in which wear-reducing ring bands are inserted, produced by a casting process in which the ring-shaped insert is molecularly with the aluminum is bonded to the piston under such conditions that there is a difference in the coefficient of thermal expansion between the aluminum and the ferrous metal sufficient to generate tension on cooling after casting, which increases the strength the connection exceeds. As a result, the piston will also operate afterwards not destroyed by large temperature fluctuations. The ring ligament stays as it is through hard operation in actual use has been proven firmly in the piston.

According to the invention, the iron rings and the aluminum in the pistons for internal combustion engines are connected by a thin film of a few hundredths of a millimeter of an iron and aluminum alloy. In addition, the ring must be made of an iron of high strength and a modulus of elasticity below about 1.12 X los kg / cm2. The modulus of elasticity of the iron ring should preferably be between about 0.77 X los kg / cm2 and about i, o5i X los kg / cm2. Gray cast iron with a low modulus of elasticity is particularly suitable. that the iron ring made of gray cast iron with a low modulus of elasticity is first coated with a thin film of molten aluminum of a few hundredths of a millimeter.

During the aluminum-coated ring, at least the melting temperature in which the aluminum or aluminum alloy used for the piston body is poured, and the aluminum film on the tape is liquid or plastic, becomes the metal of the aluminum body in a known manner, preferably in a permanent casting mold poured around the insert. When the flask has cooled down and removed from the mold the ring is made of an iron-aluminum alloy by means of the intermediate layer, which due to its brittle nature is measured to a few hundredths of a millimeter, extremely firmly connected to the aluminum.

The manufacturing method according to the invention results in a firmly jointed one and composite cast iron resistant to wear: lben. He owns the low one Weight of the aluminum and where the greatest wear occurs, the strength of cast iron or steel. The invention is illustrated below. Schematic drawings explained on an exemplary embodiment.

Fig. I is a cross-section through an illustrative of the invention Composite cast piston; Figure 2 is an enlarged cross-section through the piston liner (Piston ring) of Fig. I.

In the drawings, with io, is a ring-shaped insert made of cast iron or steel referred to in a piston m made of cast aluminum or aluminum alloy is inserted. This insert io is preferably made of a full ring without the piston ring grooves i2 formed, which are only screwed in after the composite piston has been completed. In addition, the insert preferably eats larger in outer diameter than the piston, so that it can be arranged in a recess of the permanent mold in which the aluminum or aluminum alloy is cast.

Before it is placed in the mold, the insert is made of cast iron or steel heated to the temperature at which aluminum is alloyed with cast iron or steel, which is preferably done in that the deposit is melted io in a bath Aluminum or an aluminum alloy is immersed long enough to this To reach temperature and alloy formation in the desired thin layer between the surface of the metal of the inserts and the molten aluminum or aluminum alloy takes place.

The coated inlay is then as long as the surface film is off Aluminum is still liquid or plastic, introduced into the permanent casting mold and the molten aluminum b: betw. Aluminum alloy of the piston body i i around the Inlay poured around. As a result of the fusion between the liquid or plastic aluminum film on the insert io, and the cast aluminum or the cast aluminum alloy are the piston body @i; i and the iron ring io: homogeneously with each other via the iron-aluminum alloy 13 verb: un @ As known, are the thermal and mechanical stresses or impact and wear loads, to which the piston is subjected in operation, considerably. It is therefore in the first place Line wanted to keep this down to a minimum. That is why, in order to the disparity the expansion coefficient between the material of the ring i0 and the material of the piston body i i to reduce the ring insert io made of an iron or steel of high strength and a modulus of elasticity below about 16 X ioB. Suitable is z. B. a cast iron with high nickel content, @ d'as contains about i2.5 ° / a nickel. This difference in thermal expansion can be further reduced by that the material for the piston body i i is an aluminum alloy with alloy components, which reduce the thermal expansion of the aluminum is used. Such alloy is z. B. an aluminum, the UNO, silicon, 2.5% nickel, r, 2% magnesium and o, 8% Contains copper. If a cast iron ring is ok with the aforementioned high nickel content and an aluminum alloy with a low expansion coefficient for the piston body i i is used, then the piston according to the invention withstands the toughest operation without damage other than normal wear and tear.

Gray cast iron with a low modulus of elasticity can also be used as the material for the insert with good results. The modulus of elasticity must, however, be less than about 1.12 X 10 kg / cm2 and preferably between 0.717 X IOß and 1.051 X 10 kg / cm2.

The strength of the joint 13 of the piston of this invention provides one. such a safety factor that the connection i'3 can easily be expanded axially so far that, if desired, the next adjacent piston ring groove 12 'can also be accommodated in the insert io, although usually the top one or two rings are the strongest Suffering wear and tear and therefore the iron insert is primarily required for this.

Claims (2)

PATEN TANSPRÜGIIE: i. Pistons for internal combustion engines with a cylindrical body made of light metal of relatively low strength, in particular aluminum and its alloys, and a substantially ring-shaped part made of iron of high strength embedded therein, characterized in that both parts are covered by a thin film of a few hundredths of a millimeter an iron-aluminum alloy are connected and the iron part is made of an iron of high strength and a modulus of elasticity below about i, r2 x 10 kg / cm2, preferably between about 0.77 x 10 kg / cm2 and about 1.05 X ioss kg / em2. 2. Piston according to claim i, characterized in that the ring body consists of There is gray cast iron with a low modulus of elasticity.