The present invention relates to a method for primarily extending the useful lifespan of ceramic tools of the kind with which at least certain parts thereof are brought to a high temperature in use.

Several reasons are to be found for working metallic materials, particularly steel, at elevated temperatures, such as high temperatures or medium high temperatures.

By high temperature is meant here temperatures which lie relatively close to the solidus temperature of the mate¬ rial being worked. In certain instances, particularly in mechanical cutting operations, local regions of high temperature are generated automatically as a result of the deformation that takes place.

Naturally, high demands are placed on machine tools which become heated to high or medium high temperatures when in use. For example, the tools must be capable of retaining their hardness and wear resistance at tempera¬ tures of these high magnitudes. Normal tool materials in this regard are steel and hardmetal alloys.

It is also possible to obtain particularly high degrees of hardness and wear resistance with ceramic materials. The use of ceramic materials in this context, however, has not met with any great success, due to the inability of the material to withstand the high stresses to which it is subjected when undergoing rapid changes in temper¬ ature, primarily when cooled. This inability of the a- terial to withstand temperature variations is due to the relatively poor toughness or ductility of the material.

The present invention provides a solution to problems associated with ceramic tools, and thus enables ceramic materials to be used in the manufacture of tools, ac¬ companied by the advantages of, inter alia, high hard- ness and wear strength that such materials imply.

Thus, the invention relates to a method which is in¬ tended primarily for extending the useful working life of ceramic tools that are intended, primarily, for working metallic materials and at least certain ceramic parts of which tools are heated automatically to high temperatures in use, and of which tools ceramic parts thereof form material-engaging tool parts.

The method is particularly characterized in that ceramic parts of the tool are heated by microwaves prior to and or at least periodically during the period of time in which the tool performs a working operation, either con¬ tinuously or intermittently; and in that the ceramic ma¬ terial is given a significant loss factor with regard to microwaves.

The invention also relates to an arrangement which is intended primarily for extending the useful lifespan of ceramic tools that are intended for working, primarily, metallic materials, such as steel, said tools, at least in respect of certain ceramic parts thereof, being heated automatically to high temperatures in use; and in that the ceramic parts of the tools form material-engaging parts.

The arrangement is particularly characterized in that means are provided for additionally heating ceramic tool parts with the aid of microwaves prior to and/or at least periodically during the time period over which

the tool operates, either continuously or intermittently, to work said material; and in that the ceramic material has a significant loss factor with regard to microwaves.

The invention will now be described in more detail with reference to a number of exemplifying embodiments there¬ of and to the accompanying drawings, in which

Figure 1 is a schematic, axial sectional view of a first preferred embodiment of an arrangement according to the invention, taken on the line A-A in Figure 2 and includ- ing a wire drawing die;

Figure 2 is a view of the arrangement in Figure 1 , seen from above in said Figure;

Figure 3 is a schematic sectional view of a second em¬ bodiment of an arrangement according to the invention, including a cutting bit for cutting work;

Figure 4 illustrates the arrangement of Figure 3, seen from above in said Figure;

Figure 5 is a schematic vertical sectional view of a third embodiment of an arrangement according to the invention, including two die halves;

Figure 6 is a schematic, vertical sectional view of a fourth embodiment of an arrangement according to the invention, taken at right angles to the axes of two mu¬ tually parallel rolls forming part of the arrangement;

Figure 7 illustrates schematically one of the rolls of Figure 6 at right angles to the roll axis, and further illustrates cavity forming parts of the arrangement; and

Figure 8 is a schematic axial sectional view of a fifth embodiment of an arrangement according to the invention, comprising an extrusion matrix or die.

Figures 1 and 2 illustrate a ceramic central part of a ceramic draw-die having provided therein, in a substan¬ tially known manner, a through-hole 2 which is intended primarily to reduce the cross-sectional dimensions of an elongated product, such as wire, or the like. The reference 3 identifies a lining provided on the ceramic part 1 , and the reference 4 identifies a microwave appli¬ cator which forms a microwave cavity 4 ' around the ceram¬ ic part 1. The reference 5 identifies a waveguide con¬ nected to the applicator.

Dies of this kind can be used to draw hot goods, semi-hot goods or cold goods of the aforesaid kind.

In this case, as with preferably all cases described hereinafter, the microwave heating devices are con¬ structed to heat the tool prior to using the same and/or at least periodically during the time the tool is being used, such use being either continuous or intermittent. Preferably, the devices are constructed to heat the tool so that those ceramic tool parts which automatically become heated to high temperatures when performing work are maintained at a temperature which is higher than the critical temperature level of the ceramic material when cooling, primarily with regard to cracking, such as a temperature of about 800°C.

In Figures 3 and 4 the reference 6 identifies a cutting bit intended for cutting work, such as lathe work. The cutting bit 6 is surrounded by metallic or like parts 7 which form a microwave cavity 7 ' to which a waveguide 8 is connected. These metallic parts suitably incorporate

cutting-bit attachment means, not shown. According to one preferred embodiment of the invention, parts of the microwave cavity 7 ' are formed by parts 9 of a metallic net structure which includes the cutting bit 6, as indi- cated in Figure 3. The cavity is constructed such that edge parts 6 ' of the cutting bit 6 will protrude there¬ from and therewith can be used to perform a cutting ac¬ tion.

Figure 5 illustrates a ceramic tool 10 tool half, for foundry work, such as forging work, the tool of this embodiment comprising two mutually opposing tool halves, 10, each of which is surrounded by a res¬ pective metallic support device 11 , these support devices together forming a microwave cavity 12 to which a wave- guide 12' is connected. It will be understood that the tool may have any desired cross-sectional shape and may vary in configuration at right angles to the illustrated section in an obvious fashion.

The embodiment illustrated in Figures 6 and 7 includes two tools 13, each of which comprises a roll for hot rolling purposes, so-called tepid-heat rolling or cold rolling. The peripheral surface 14 of the roll is covered with a ceramic layer 13' along at least part of the barrel 15 of the roll, this layer being heated by means of microwaves. To this end, each roll is provided with a microwave cavity 17 formed by means of metallic or like parts 16, to which at least one waveguide 18 is connected.

Figure 8 illustrates a further embodiment comprising a so-called extrusion container 19 and a so-called extrusion matrix or die through which metal or corresponding mate¬ rial is extruded in a known manner. The tool may be used

to extrude tubing or rod, for example. In this embodi¬ ment the die 20 is surrounded by metallic parts 21 which form a microwave cavity to which at least one waveguide (not shown) is connected. In accordance with preferred embodiments, at least with regard to tools which are substantially axially symmetrical, such as the tool il¬ lustrated in Figures 1 and 2, the cavity 4 ' required for microwave heating is constructed so that the tool-part 1 of the arrangement can be heated both when metallic ma- terial passes through the hole 2 in said tool-part and also when substantially no metallic medium is present in said tool-part, and such that a respective mutually dif¬ ferent oscillating mode can be applied in the presence and absence of metallic medium.

In this regard, the cavity has a substantially circular cross-sectional shape in a plane at right angles to the longitudinal axis of said tool-part 1, i.e. to the di¬ rection in which the through-hole extends when said tool-part is arranged in the cavity in the manner in- tended. The cavity is preferably constructed to oscil¬ late in a co-axial mode, a first mode, when metallic medium is present in said part, and in a second mode when substantially no metallic medium is present in said part. In this regard, the cavity is preferably constructed so that said second mode is a cylindrical mode, preferably a mode, such as TMO10, whose resonance frequency is in¬ dependent of the length of the cavity, while the diameter is determined by the resonance frequency. The length, or axial dimension, of the cavity preferably corresponds to substantially half the wavelength of the intended micro¬ waves. In certain preferred embodiments the diameter and axial extension of the two oscillating modes are thus each determined per se. In some cases TMO10 is written M _nιn instead.

The ceramic material suitable for use in tools intended for heating in accordance with the invention may have differing compositions . In those embodiments often pre¬ ferred, however, the ceramic material will comprise A1-0-. as the base material

0-20% Zr0 ₂

0-5% CaO

0-5% MgO

0-5% i0 ₂ , and comparitively small quantities of i0 ₂ , FeO, , etc. all percentages being percentages by weight.

The method according to the invention and the manner in which the arrangement according to the invention operates will be understood in all essentials from the aforegoing. By heating at least parts of the ceramic tool material with the aid of microwaves, it is possible to pre-heat the material to a high temperature level and to maintain said material at a high level of temperature. This will prevent the occurence of large temperature differences and therewith avoid high thermal stresses and associated cracking of the material, etc.

It will be understood from the aforegoing that the in¬ vention provides fresh possibilities of utilizing ceramic materials for tool manufacture, with the advantages as- sociated herewith.

In the aforegoing the invention has been described with reference to a number of mutually different embodiments. It will be understood, however, that other embodiments are conceivable and that minor modifications can be made without departing from the scope of the inventive concept.

For example, the configuration of the various tools il¬ lustrated may be changed to other configurations adapted

to the product desired or the desired mechanical working result.

It will also be understood that, although not shown, microwave generators are provided for generating icro- waves for application to the waveguides present. Al¬ though not specifically described, heating may also be effected via microwave antennae, i.e. in the absence of a so-called cavity.

In the embodiments of the kind illustrated in Figures 1 and 2, where a space is found between the die and the external casing, this space may be filled with a ceramic material. In this case the ceramic material used shall have a low loss factor with regard to microwaves.

Thus, the invention is not restricted to the aforede- scribed and illustrated embodiments, since modifications can be made within the scope of the following claims.