The invention relates to a method for producing hollow gas exchange valves for reciprocating engines as known, for example, from German Offenlegungsschrift 2,361,712.
In the printed publication mentioned, the application on the head side of the drilled hole seal is already mentioned as a previously known measure and also sketched in a drawing and critically assessed. The actual recommendation given in the above printed publication for sealing the cavity of cooled gas exchange valves takes an entirely different direction. During the above-mentioned sealing of the cavity at the head side, a true-to-size circular blank of a thickness corresponding to the wall thickness of the sealing plug is inserted into the drilled hole and welded into it by means of miniature welding. An aspect of the known procedure which may be criticized in connection with the present invention is that the sealing plugs, which in general consist of a high-grade alloyed material, can only be produced with high material losses in the form of machining or stamping losses In addition, the methods for producing these sealing plugs are expensive, in particular because the high-grade and tough material requires high tool costs for processing. A precise, localizable weld for seal welding the sealing plug requires a high precision positioning device, with the result that only a very expensive welding fixture can be used for this purpose, which likewise adds to the costs of the method. In addition, the welding methods preferred in this context, such as laser or electron beam welding, require a relatively involved and expensive testing technology for process and quality assurance. This involved testing also adds to the costs of the known method.
In addition to welding a sealing plug inserted true-to-size into the drilled hole by miniature welding, it is also known to seal cooled gas exchange valves from the head side, a sealing plug of high-grade material being placed and welded into a precentering portion of the open drilled hole end by butt-seam resistance welding. In principle, the same points of criticism apply to this method too, such as high material consumption due to machining or stamping losses, separate production of a sealing plug, and relatively high costs for process and quality assurance. In this method too, these points have the effect of increasing costs.
It is the object of the invention, starting from the generic method taken as a basis, to develop this method further such that the gas exchange valves can be produced more economically with the same reliability.
This object is achieved according to the invention. By virtue of the introduction of the material of the sealing plug by surfacing, the separate operation of producing the sealing plug is eliminated, with the result that not only are the costs for this operation saved but that machining waste or punchings for a very expensive material are also avoided. Moreover, the surfacings can be performed by means of conventional, easily manageable welding methods and using relatively cheap machines. Initial tests justify the expectation that a reliability check as regards tightness can be omitted. Defective welds can be detected externally by a simple-to-perform visual check. It is expected that outwardly satisfactory welds will also be reliably tight overall. The thin-walled circular blank for holding the welding melt, which also is produced with material losses, can be produced from a cheap and easily worked material, reducing the material waste without significantly effecting costs. Due to the thin wall thickness and the low strength of this material, a long service life can be expected of the tools used, keeping costs low.