The present invention relates to a method for the production of a cylinder for a two-stroke engine as well as to a casting core for this method.
Such cylinders are generally cast from an aluminum alloy, in a gravity casting method, using sand cores. It is problematic, in this connection, that casting defects and inclusions form very easily. For this reason, it is aimed at to cast such cylinders in a die-casting method. However, sand cores cannot be used for this, because they do not withstand the pressure conditions that prevail during casting.
DE 33 31 664 A1 describes a cylinder having closed overflow channels for a two-stroke engine, which is produced using the die-casting method. Divided steel cores are used to form the overflow channels; these cores are connected with the central core slide for the cylinder chamber. Both the configuration of the multi-part cores and the removal of the divided steel cores for the overflow channels from the cast cylinder are very complicated and difficult.
It is furthermore known to use cores made of a wood fiber material (cf. DE 198 20 246 A1). However, such cores have not proven themselves for the die-casting method, because they are not sufficiently stable for it.
The task of the present invention consists in further developing a method of the stated type and a casting core of the stated type, in such a manner that the casting core can easily be removed from the cast cylinder, and is also suitable for a die-casting method.
The solution consists in that first, a casting core is produced, whereby a central core slide for the cylinder chamber and at least one salt core for an overflow channel are produced, and the at least one salt core is connected with the central core slide, that the casting core is subsequently introduced into a casting mold, and the cylinder is cast using a die-casting method, that subsequently, the central core slide is removed from the cylinder, whereby the at least one salt core is separated from the central core slide, and finally, the at least one salt core is flushed out of the cylinder.
The casting core according to the invention is characterized in that it has a central core slide for the cylinder chamber, to which at least one salt core for an overflow channel is connected.
It has turned out, in surprising manner for a person skilled in the art, that a salt core connected with a central core slide is so stable that it withstands the conditions, particularly the pressure conditions, of a die-casting method. The at least one salt core can be flushed out of the cast cylinder particularly easily, in known manner. The method according to the invention and the casting core according to the invention therefore make it possible to produce cylinders for two-stroke engines, which have at least one overflow channel, with little effort, using the die-casting method.
Advantageous further developments are evident from the dependent claims.
The at least one salt core can be produced in known manner, by means of pressing, injection-molding, or also by means of sintering. Sodium chloride and/or potassium chloride, for example, are suitable as main components. If necessary, at least one binder can be added, for example at least one alkali carbonate and/or at least one earth alkali carbonate.
The central core slide can be produced from various desired materials. Metallic materials, particularly steel materials, are preferred.
The at least one salt core is preferably connected with the central core slide with shape fit and without binders.
The method according to the invention and the casting core according to the invention are particularly suitable for the production of cylinders that are cast from an aluminum alloy, using a die-casting method.
Exemplary embodiments of the present invention will be explained in greater detail below, using the attached drawings. These show, in a schematic representation, not true to scale:
In the cylinder 10, a combustion chamber 15 is formed, which is delimited by the cylinder head 13, the piston crown 16 of the piston 12, and the cylinder wall 17 of the cylinder chamber 11. In the exemplary embodiment, an overflow channel 18 is shown, which connects the combustion chamber 15 with the crankcase 14. The cylinder chamber 11 furthermore has an outlet channel 21 for conducting away the combustion gases that occur, out of the combustion chamber 15. Below the opening of the overflow channel 18 into the combustion chamber 15, the cylinder chamber 11 furthermore has an inlet channel 22, by way of which a fuel/air mixture is introduced into the crankcase 14. The outlet channel 21, the inlet channel 22, and the opening of the overflow channel into the combustion chamber 15 are opened and closed by the piston 12, which is moving up and down, as a function of its stroke position.
In the position of the piston 12 shown in
The casting core 30 according to the invention used for this purpose has a central core slide 31 and a foot plate 32 provided on it. The core slide 31 serves for forming the cylinder chamber 11. The foot plate 32 essentially serves to close off the casting mold and to pull the core slide 31 out of the cast cylinder 10, in the direction of the arrows A, after casting. The core slide 31 and the foot plate 32 consist, in the exemplary embodiment, of the steel material X37CrMoV5-1 hardened to 48-52 HRC.
In the exemplary embodiment, two salt cores 33 are connected with the core slide 31; these serve to form two overflow channels 18, 19. The salt cores 33 consist, in the exemplary embodiment, of pressed sodium chloride or of pressed potassium chloride.
Connecting the salt cores 33 to the core slide takes place by means of a shape-fit connection.
The salt cores 33 support themselves on the foot plate 32 in the exemplary embodiment. The finished casting core 30 is laid into a casting mold. The cylinder 10 is cast from an aluminum material, using a die-casting method.
When the core slide 31 is pulled out after casting of the cylinder 10, the salt cores 33 are sheared off from the core slide 31 or separated from the foot plate 32. The salt cores 33 are not flushed out of the cylinder 10 in known manner, so that two overflow channels 18, 19 result. The support of the salt cores 33 on the foot plate 32 brings about the result that the overflow channels each have an opening 18a, 19a in the direction of the crankcase to be added later. After the crankcase is added, the overflow channels open into the crankcase.
Number | Date | Country | Kind |
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10 2010 026 597.7 | Jul 2010 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE2011/001408 | 7/5/2011 | WO | 00 | 6/17/2013 |