Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1994-12-09
1997-01-14
Hail, III, Joseph J.
Metal founding
Process
Shaping liquid metal against a forming surface
164332, 164120, B22D 1908, B22D 2709
Patent
active
055929850
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of applying hard material to cutting tool teeth, especially the teeth of saw blades, wherein a mold cavity is defined around a tooth and the molten material forms a spherical segment therein, due to its surface tension, and the spherical segment is flattened under pressure which is applied progressively in the direction of the tip of the tooth.
The invention also relates to an apparatus for carrying out such a method, comprising mold jaws adapted to be engaged with a tooth and a pressing tool for exerting pressure on the spherical segment formed of the molten material.
SUMMARY OF THE INVENTION
A method and an apparatus of this kind are known from EP 0 374 950 A2. In that case provision is made for the pressure which progresses in the direction towards the tip of the tooth to be applied to the spherical segment, for instance, by a ram which is lowered to the spherical segment with a component of movement towards the tip of the tooth. Alternatively, a gas or plasma jet having been used to melt the: hard material may be moved over the spherical segment in the direction of the tip of the tooth, or the molten material may be forced away by a gas jet directed along the back of the tooth towards the tip of the tooth. As a result of these measures the mold cavity will be filled completely with molten material, and no great excess of material is required which, later on, only would have to be removed by grinding.
It is the object of the invention to provide further improvement in the accuracy of shape and durability of the teeth made of molten and subsequently solidified hard material. Starting from a method of the kind specified initially, this object is met, in accordance with the invention, inasmuch as the method is concerned, by the fact that, prior to applying pressure on the spherical segment, the molten material is cooled and subsequently heated again until a state is reached which is at least approximately liquid.
The invention is based on the finding that it is particularly favorable for precision in shape and durability of teeth or tooth parts having been applied by melting on to a basic body of a cutting tool, especially a saw blade, if the molten hard material first is left alone, in other words, if it is accepted that it solidifies more or less completely with a free surface having the shape of a spherical segment. When, for example, Stellite is used, that is achieved by allowing the molten material to cool down from its melting point at approximately 1200.degree. to 1300.degree. C. to from about 800.degree. to 700.degree. C. That takes from about 3 to 5 seconds, depending on the size of Stellite formation. During the subsequent heating, the melting point need not be reached again. Preferably, however, the material applied is heated beyond a doughy state before applying the pressure to flatten the spherical segment.
Allowing the hard material applied to a cutting tool to cool and then heating it once more, above all, counteracts the tendency of the material to form voids. This unexpected effect, not yet fully explained so far, which was observed and confirmed in numerous tests brings about a marked improvement in cutting performance of tools treated in accordance with the invention. That is true in particular of saw blades with which the frequent occurrence up to now of voids may result in considerable weakening of the relatively narrow teeth which, therefore, tend to crumble.
The means used for reheating the material are not of critical importance; the energy required for renewed heating may be supplied just like the energy needed for the original melting, for instance, electroinductively or by a gas or plasma burner. It proved to be especially advantageous to use one and the same plasma burner for both purposes; it is switched off for the time interval mentioned of, for example, from 2 to 5 seconds, following the original melting, and then ignited once more.
In terms of the apparatus, the mechanical aspect of the above mentioned proble
REFERENCES:
patent: 5101879 (1992-04-01), Beck et al.
Hensinger Bruno
Reichenzer Werner
Browning Clifford W.
Hail III Joseph J.
Lin I.-H.
Vollmer Werke Machinenfabrik GmbH
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