This application is claiming priority based on European Patent Application No. 20211403.9 filed on Dec. 3, 2020, the disclosure of which is incorporated herein in its entirely by reference.
The present invention relates to an item obtained by multi-injection of ceramics and/or cermets. It relates more particularly to a horological component such as a bezel produced by injecting ceramics and/or cermets of different colours.
Horological components are commonly produced from injected plastics material with different colours. It is thus possible to obtain middles and bezels having distinct colours. With ceramics or cermets that are obtained by sintering, manufacturing components with different colours is much more complex. This is because significant shrinkage, which may amount to 30%, is observed during sintering. The amount of shrinkage will be dependent on several factors, which are among others the choice of the material and the volume of the material injected. In bi-injection methods or more generally multi-injection methods, differences in shrinking during sintering that will lead to a disconnection at the junction between the various materials may result. More specifically, in the case of injected bezels, a gap related to the difference in radial shrinkage between the materials is observed. This difference is all the more marked if the volumes of material injected are different for the two materials, which is typically the case if one of the materials occupies only a small arc of a circle compared with the other material
To overcome this drawback, it has been proposed in the document EP 2 746 243 to inject a single material and to impregnate a part of the unfired body before sintering with a solution comprising a metal acting as a pigment. This method has the disadvantage that it is difficult to obtain a uniform colour in the mass of the coloured part.
The object of the present invention is to overcome the aforementioned disadvantages by proposing a novel method for injecting multi-material limiting the differences in shrinkage between the distinct materials injected.
To this end, the present invention relates to a manufacturing method using, during the injection step, an insert having a structure in relief or hollow intended to impress on the first injected material an attachment surface for the second injected material. This attachment surface makes it possible to hold the second injected material, to reduce shrinkage during the sintering step and to prevent disconnection of the two materials during the machining step.
More precisely, the method for manufacturing the item according to the invention includes the following steps:
The method further comprises a machining step before and/or after the sintering step to size respectively the unfired body and/or the blank and to partially remove the second material so as to reveal the first material.
The present invention also relates to the item made from ceramic and/or cermet resulting from the manufacturing method. The item according to the invention includes at least two distinct materials differentiated by the colours thereof, or more generally by the aesthetic appearance thereof, and/or the mechanical properties thereof. According to the invention, the item includes a part where the two materials are interleaved. Preferably, the item includes a part where one of the materials fills hollows formed in the other material.
Other features and advantages of the present invention will emerge in the following description of a preferred embodiment, presented by way of non-limitative example with reference to the accompanying drawings.
The present invention relates to a method for manufacturing by injecting an item or article produced with at least two distinct materials that are either a cermet or a ceramic. Distinct materials means materials differentiated through their aesthetic appearance, in particular their colour, and/or through their mechanical properties. This is represented by differences in chemical composition. It may be a case of the same base material with different pigments for changing the colour or different base materials. By way of example, it may be the same base material based on zirconium oxide with on the one hand a black pigment for obtaining a black material and on the other hand alumina for obtaining the white colour. More generally, ceramics may be nitrides, carbides and/or oxides. Likewise, cermets may include a ceramic phase including carbides, nitrides and/or oxides and a phase of a metal binder selected for example from precious elements such as ruthenium, rhodium, palladium, osmium, iridium, platinum, gold and silver.
The item according to the invention may be a decorative item or article such as a constituent element of watches, jewelry, bracelets, etc. In the horological field, this item may be an external component such as a middle, a bottom, a bezel, a push-piece, a bracelet link, a dial, a hand, a dial index, etc. It may also be a movement component such as an oscillating mass, a disc, etc. By way of illustration, the item is a bezel 1 produced with two ceramics 2 and 3 of different colours, for example black and white, with one colour that occupies a quarter of the circle of the bezel and another colour that occupies the remaining three quarters of the circle, as shown in
The item is produced by injecting different materials to form an unfired body or green body and by sintering said unfired body. The manufacturing method is illustrated below for an item comprising two distinct materials but it could be a case of an item comprising 3, 4, etc different materials with the production of an attachment surface for each of the successive injected materials.
The manufacturing method includes the following steps with reference to
The method further includes a machining step preferably implemented on the unfired body before sintering so that the material is not too hard. During this machining step, the second material is at least partially removed in order to reveal the first material. The present invention does not exclude the machining step being implemented partly before the sintering and partly after the sintering.
The method may optionally include a step of debinding before the sintering step if the materials have been injected with a system of organic binders (paraffin, polyethylene, etc.).
In the example illustrated, the injection device includes a mould 5 with a fixed part 5a formed by two cavities 6 with a first cavity 6a intended for injecting the first material 2 and a second cavity 6b intended for injecting the second material 3 (
(1) Bezel
(2) First material, also referred to as ceramic
(3) Second material, also referred to as ceramic
(4) Part of the item
(5) Mould
(6) Cavity
(7) Insert, also referred to as portion of the cavity
(8) Unfired body
(9) Pocket
(10) Sprue of the unfired body
(11) Junction
(12) Index
Number | Date | Country | Kind |
---|---|---|---|
20211403.9 | Dec 2020 | EP | regional |