The invention concerns a method for the cold agglomeration of powders to be sintered and a mould suitable for implementing said method.
In particular, the method and the mould subject of the invention concern the agglomeration of abrasive powders on the edge of a disc-shaped metal core before the sintering process.
It is known that the sintering process consists in the cold compression of mixtures of very fine metallic and non-metallic powders into moulds with predefined shape and in their sintering inside furnaces at high temperatures; the non-metallic powders may contain even diamond powder.
The compression of the powders at high temperature is more properly called sintering and it is carried out at temperatures that usually correspond to 2/3 of the melting point of the most refractory material present in the powders, while the cold compression of the powders inside the moulds is called agglomeration.
Various types of mechanical components that are used for different purposes in various industrial sectors are produced through sintering processes.
In particular, sintering is used for the construction of abrasive discs that are obtained by sintering a mixture of metallic and non-metallic powders - the latter may even contain diamond powder - on the peripheral edge of a disc-shaped metal core.
Document US 2 686 439 discloses a method and an apparatus for making gears in which the teeth are pressed in a die.
According to the known manufacturing techniques, in the processing phases the metal core must first of all be positioned in a mould and the powders to be sintered must be distributed circumferentially on the perimetral edge of the core and contained in an annular chamber properly obtained in the mould.
After being uniformly distributed, the powders are cold-agglomerated by positioning the mould under a press provided with an apposite, property shaped pressing element that compresses them and makes them adhere to the core.
The mould, complete with the pressing element, is then introduced in a furnace, brought to the sintering temperature and left in the furnace for a pre-established time.
Successively the mould is extracted from the furnace and positioned under a press, so that the annular edge, which by then stably adheres to the core, is subjected to a further hot-pressing action before cooling down.
Once it has cooled down, the mould is opened and the metal core is extracted together with the sintered annular edge stably fixed on to it.
The abrasive disc has thus been obtained.
However, the production method described above has some drawbacks.
A first drawback is represented by the fact that this method requires repeated handling of the cores and moulds, and therefore considerable labour and rather long execution times.
A further drawback is constituted by the fact that the manufacturer must have a high number of moulds, since one mould contains only one core for the whole sintering cycle, from the distribution and agglomeration of the powders to the extraction of the sintered item.
The aim of the present invention is to eliminate all the drawbacks described above.
In particular, one of the aims of the invention is the implementation of a method for the cold agglomeration of powders to be sintered that makes it possible to reduce the manual operations necessary to move the pieces and the moulds.
Another aim of the invention is that the method subject of the invention should make it possible to use a single mould for the agglomeration of the powders on more than one core.
A further aim of the invention is the implementation of a method that for the agglomeration of the powders requires the use of a single mould, in fixed position and operating only at cold temperatures.
The goals described above have been achieved through the implementation of a method for the cold agglomeration of mixtures of metallic and non-metallic powders on to the outer perimetral edge of a support core, said method being according to the steps present in claim 1. manufactured in such a way as to house disc-shaped cores made of metal plate.
Advantageously, the method subject pf the invention and the mould suitable for implementing it according to claim 2 ensure high productivity in comparison with the known methods and moulds.
Furthermore, the use of a single mould for the agglomeration of the powders on the edges of all the cores that are subsequently sintered makes it possible to reduce the necessary equipment and to maintain a high quality standard for all the abrasive discs that are manufactured.
Another advantage is represented by the fact that the method subject of the invention and the relevant mould can obviously be employed to obtain the agglomeration of powders on the edges of any core, independently of its shape.
The aims and advantages described above will be highlighted in greater detail in the description of one among many possible applications of the invention in question, illustrated in the attached drawings, wherein:
With reference to the figures mentioned above, the method subject of the invention can be implemented by means of a mould, which is also subject of the invention, is indicated as a whole by 1 and, as shown in the enclosed figures, comprises an upper plate 2 and a lower plate 2'; said plates are spaced and opposite each other, can be coupled to the reciprocally movable elements of a press not represented in the figure, and are joined through guide means, indicated as a whole by 3, suitable for keeping them parallel to each other during their reciprocal shifting. Said guide means 3 comprise at least one column 4 fixed to the lower plate 2' and slidingly coupled to a sleeve 5 fixed to the upper plate 2.
The upper plate 2 is also provided with an upper body 6 that supports first core-pressing means constituted by an upper core-pressing means 7 and analogously the lower plate 2' is provided with a lower body 6' that supports second core-pressing means constituted by a lower core-pressing means 7'.
The core A is positioned between the lower core-pressing means 7' and the upper core-pressing means 7 and abrasive powder P is agglomerated on the peripheral edge B of the core according to the procedure described below.
An upper intermediate body 8 is interposed between the upper body 6 and the upper core-pressing means 7, housed in the upper body 6 and fixed to the upper core-pressing means 7. A piston 9 belonging to the upper intermediate body 8 is inserted into an upper chamber 10 obtained in the upper body 6, within which the piston can slide in the direction defined by the longitudinal axis X of the mould, the upper intermediate body 8 being guided by pins 11.
Helical springs 12 cooperating with respective spring guides 13 make the movement of the piston 9 and of the relevant core-pressing means 7 elastic.
A lower intermediate body 8' is interposed between the lower body 6' and the lower core-pressing means 7'; together with the lower core-pressing means 7' it defines a first lower chamber 7'' and with the lower body 6' it defines a second lower chamber 6''.
The lower core-pressing means 7' slides axially with respect to the lower body 6' and is guided by one or more pins 14 passing through the lower intermediate body 8' and having one end fixed to the lower plate 2'. Helical springs 15 coupled to respective spring guides 16 make the movement of the core-pressing means 7' elastic with respect to the lower intermediate body 8' and the movement of both of them elastic with respect to the lower body 6'.
The lower body 6' is fixed to the lower plate 2' by means of a bearing 17 with the vertical axis positioned so that the lower body 6', together with the lower intermediate body 8' and with the lower core-pressing means 7', can rotate on the vertical axis X of the mould. For this purpose, a fifth wheel 18 is provided outside the lower body 6' and engages with a pinion 19 coupled to an actuator 20, preferably constituted by a fluid-operated motor, for example an air motor.
An annular body 21 is positioned between the lower core-pressing means 7' and the lower body 6' and is fixed to the lower intermediate body 8', thus defining - between the lower core-pressing means 7' and the lower body 6' - an annular chamber 22 that contains the powder P to be agglomerated.
A powder-pressing ring 23 is fixed to the upper body 6, in correspondence with its outer perimetral edge, said ring 23 being provided with an annular protrusion 24 whose profile is conjugated to the concave part defined by the annular chamber 22 and is therefore suitable for fitting inside it.
Operatively, the powder agglomeration cycle begins when the mould is positioned open as indicated in Figure 1. The core A is positioned inside the mould, resting on the lower core-pressing means 7' and centered with respect to the longitudinal axis X of the mould by means of a central reference pin 25 that fits into a corresponding central hole F made in the core A.
The vertical, downward shifting according to the direction z indicated in Figure 2 generated by the movement of the upper plane of the press results in the shifting - in the same direction - of the upper plate 2 fixed to it, until the upper core-pressing means 7 is compressed against the core A.
After the clamping of the core-pressing means the motor 20, through the kinematic chain constituted by the pinion 19 and the fifth wheel 18, sets the lower body 6' of the mould rotating on the axis X, together with the lower intermediate body 8', the lower core-pressing means 7' and the core A positioned on it. At the same time, an appropriate powder-distributing device, not represented in the figure, introduces the powder P to be sintered into the annular chamber 22, as shown in Figure 2. This powder is a mixture of metallic and non-metallic powders and the latter may even contain diamond powder.
The further lowering of the upper plate of the mould results, as shown in Figure 3, in the compression of the powder P on the edge B of the core A and inside the annular chamber 22, due to the action of the powder-pressing ring 23, whose protruding edge 24 gets into the chamber itself and thus compresses the powder present inside it. During this movement, the piston 9 is housed inside the chamber 10 due to the elastic yield of the helical spring. 12.
During the compression of the powder P the lower core-pressing means 7' lowers and strikes against the lower intermediate body 8' due to the disappearance of the first lower chamber 7''. The lower intermediate body 8', therefore, constitutes the opposing element that reacts to the thrust of the press and contributes to the generation of the compressive action on the powder P in correspondence with the edge B of the core A.
After the powder compression phase, a pressurized fluid, preferably air, is introduced in the lower chamber 6'', as shown in Figure 4, and causes the lifting of the lower intermediate body 8' in the direction V together with the core-pressing means 7 and 7', the upper intermediate body 8 and the core A included between them. The core is then lifted and positioned at the distance D from the upper edge of the lower body 6'.
The upper plane of the press keeps moving upwards in the direction V, lifting first of all the powder-pressing ring 23, as shown in Figure 5, and then the upper core-pressing means 7, as shown in Figure 6, with respect to the core A, thus creating the clearance L that makes it possible to extract the core with the powder agglomerated on its edge B.
If the compressed air present inside the second lower chamber 6'' is bleeded, the lower intermediate body 8' and the lower core-pressing means 7' lower down and return to the position shown in Figure 1, in which the mould is ready for a new agglomeration cycle.
According to the above description, the method subject of the invention and the mould suitable for implementing said method achieve all the fixed goals.