EP1040884A1

EP1040884A1 - Vibratory decoring machine

Info

Publication number: EP1040884A1
Application number: EP99830191A
Authority: EP
Inventors: Bartolomeo Tosco
Original assignee: Fata Group SpA
Current assignee: Fata Group SpA
Priority date: 1999-04-02
Filing date: 1999-04-02
Publication date: 2000-10-04
Also published as: BR0002327A; MXPA00003280A

Abstract

A machine (1) for shaking out foundry castings (G) comprises a structure (2) for supporting the castings (G) to be shaken out and vibrator means (8a, 8b) for selectively producing the vibration in the support structure (2). First and second vibrator means (8a, 8b) are provided and can be operated selectively (13, 21) in at least one first operating condition, in which the vibrator means (8a, 8b) operate in phase opposition so that the support structure (2) remains substantially stationary, and one second operating condition, in which the vibrator means (8a, 8b) operate in phase coincidence so that the support structure (2) is subjected to vibration.

Description

The present invention relates to vibration decoring (i.e. shaking-out) machines. Machines of this type, which are intended primarily for removing the residual cores from foundry castings produced by casting in sand moulds, are widely known in the art. In this connection and also for a general description of the purposes and criteria of use, reference may usefully be made to EP-A-0 111 461.
Specifically, the present invention relates to a machine according to the preamble to Claim 1 which, as well as being known from the document already cited, is also known from European patent application 98830686.6 which may form part of the prior art solely for the purposes of Art. 54(3) EPC.
Machines of the type specified above comprise, basically, at least one vibrating structure or frame with one or more associated vibration-generating units which, in the most usual embodiment, are constituted by masses rotated at high speed about an axis which is generally eccentric relative to the mass.
In the production of the machines in question, various factors have to be taken into account.
In the first place, the vibration-generating units (or, in short, vibrator units) mentioned are usually constituted by commercial devices designed and arranged with a view to substantially continuous operation (for example, for driving tumblers, etc.). The typical methods of use of a shaking-out machine, on the other hand, provide for the castings to be shaken out to be mounted on the vibrating frame in stationary conditions and then to be subjected (usually after an initial hammering operation) to a violent vibratory motion. This continues for a certain period of time, usually of the order of a few tens of seconds, and the frame is then brought back to stationary conditions for the discharge of the castings which have been shaken out.
In the methods used predominantly up to now, the vibrator units are intended to be used intermittently by being switched on at the start of the shaking-out operation and then switched off again upon its completion. This method of operation has been found very detrimental to the useful life of the support elements (typically bearings) associated with the eccentric masses. This results in a need to replace the bearings at intervals much shorter than the average life expected of the bearings in continuous operating conditions. Moreover, this problem becomes more evident the greater is the speed of rotation of the vibrator units.
More generally, the acceleration which the machine can apply to the castings subjected to shaking out can generally be expressed (as a number of Gs) by a relationship of the following type: No.G= ΣKg·mm Kgt ·rpm 2 K in which:

ΣKg·mm is a factor which represents, in general, the characteristics of eccentricity of the eccentric masses of the vibrator units,
Kgt represents the overall mass of the vibrating structure, including the vibrator units,
rpm represents the speed of rotation of the vibrating masses, which is raised to the power of two, and
K represents a proportionality constant.

The first two parameters cited above (ΣKg·mm and Kgt) are not actually independent of one another since, particularly if it is necessary to purchase commercially-available vibrator units, an increase in the eccentricity factor of the eccentric masses (ΣKg·mm) leads to an increase in the dimensions of the respective support structure and hence in its weight. The result is that even a significant increase of the factor ΣKg·mm often translates into an inadequate increase in the ratio ΣKg·mm/Kgt.
It will be appreciated that, in formula (I) given above, the numerator is composed substantially of the product of the rate of revolution rpm (squared) and the ratio (ΣKg·mm/Kgt) of the first two parameters given above.
The fact that the above-mentioned ratio can be increased thus enables the rate of rotation of the vibrator units to be reduced significantly (for a given value of the final acceleration - and of the amplitude of the vibrations imparted to the castings), correspondingly increasing the useful life of the bearings; this latter factor is one which, over and above the considerations already given above relating to intermittent operation, is adversely affected by the speed of rotation of the devices of the vibrator units.
On the other hand, the ability to increase the ratio ΣKg·mm/Kgt enables the final acceleration value achieved to be increased correspondingly - if other factors remain unchanged. By way of reference, in the shaking-out machines currently in use, it is possible to achieve acceleration values of the order of about 20 G, whereas an ability to reach much higher values, for example 35-40 G is desirable.
From another point of view, a possible reduction in the amplitude of the vibration movement, linked with optimization of the weights of the masses involved (the eccentric masses and the frame) and with an increase in the speed of rotation, facilitates the implementation of the solution of performing the hammering operation on the castings not as a stage preliminary to vibration (as usually takes place in machines currently in use) but as an operation performed simultaneously with the vibration.
It should also be stated that most shaking-out machines currently in production are at risk of further problems connected, for example, with the location of the masses of the vibrator units in positions in which they are exposed to sand falling from the castings being shaken out.
In view of the highly abrasive nature of sand, this falling phenomenon (which affects differently the edges of each of the masses disposed upstream and downstream in the direction of rotation) may give rise, with time, to an undesired phenomenon of loss of symmetry of the masses in question.
In addition, there is also a need to ensure acceptable conditions of leak tightness of all of the bearings associated with the shafts to which the eccentric masses are keyed, particularly to prevent undesirable migration of the lubricating oil or grease of these bearings towards the outside of the housings in which the respective driving gears are disposed.
The object of the present invention is to provide a shaking-out machine of the type specified above in which, on the one hand, the problems outlined above are eliminated and, on the other hand, the various hypotheses outlined above for optimizing the operating parameters can be implemented.
According to the present invention, this object is achieved by means of a shaking-out machine having the specific characteristics recited in the following claims.
The invention will now be described, purely by way of nonlimiting example with reference to the appended drawings, in which:
Figure 1 is a general front elevational view of a machine according to the invention, with some parts removed or shown cut away for greater clarity,
Figure 2 is a side elevational view of the machine shown in Figure 1,
Figure 3 is a general plan view of the machine shown in Figures 1 and 2, and
Figure 4 shows one of the components of the machine of Figures 1 to 3 in a cut-away and sectioned view.
In the drawings, a shaking-out machine, that is, a machine which can be used for shaking out foundry castings such as, for example, internal-combustion-engine heads or blocks, is generally indicated 1. Naturally, the reference to this possible field of use should not be interpreted as in any way limiting of the scope of the patent.
In Figure 1, the profiles of two castings of this type are shown schematically in broken outline and indicated G.
In particular, each casting is mounted on a vibrating structure (or frame) 2 - having the characteristics described further below - and is clamped as in a jaw between a central abutment element 3 (which is usually common to the two castings G) and a respective outer clamping portion 4.
The machine 1 shown in the appended drawing is arranged for operating on two castings G simultaneously and has a symmetrical structure. The following description is therefore given almost exclusively with reference to one of the two symmetrical portions of the structure, upon the understanding that the portion which is not described should be considered identical or substantially identical to that described.
Moreover, the selection to provide a machine which can operate simultaneously on two castings G, as well as the use of a symmetrical structure, clearly constitute selections which are preferable in some situations of use but which are certainly not essential for the purposes of the implementation of the invention. In particular, the invention may be implemented in the form of a machine which can operate on one or more castings simultaneously and with a structure other than a symmetrical structure.
Two percussion units, indicated 5, are constituted substantially by a plurality of percussion elements 6 (of known type) comparable to pneumatic hammers. These elements have heads 7 which, when the elements 6 are operated (by known means not shown) can perform a violent hammering action on the castings G so as to bring about an initial breaking-up of the sand cores which are contained in the castings G and are to be removed by the shaking-out action. In any case, although the solution according to the invention is intended greatly preferably for use in combination with the aforementioned percussion means, it is not per se restricted to the use of such means.
An important characteristic of the solution according to the invention is that, as well as being configured for supporting the castings G subjected to vibration, the frame 2 acts as a support which can house two vibrator units, indicated 8a and 8b.
According to a solution known per se, the two vibrator units in question are constituted by eccentric masses rotated by one (or preferably two) motors 9 and 10 by means of a kinematic chain described further below. Each vibrator unit 8a or 8b usually comprises eccentric masses arranged in pairs of contra-rotating elements disposed in a manner such that, during rotation, they remain in a symmetrically opposed condition relative to a theoretical plane passing between the two elements. The set of eccentric masses thus constantly remains in conditions of equilibrium in a direction perpendicular to the said plane, whilst the conditions of disequilibrium upon which the generation of the vibrations is based arise almost exclusively along this plane. In the solution illustrated, the plane of symmetry is oriented horizontally so that the vibration stress appears mainly along a horizontal axis.
The frame 2 is supported by means of resilient feet or bases 22 formed in a known manner such as to allow the frame 2 to vibrate along a substantially horizontal axis.
A first important characteristic of the solution according to the invention is that, instead of being located outside the frame 2, mounted on respective supports in a generally bracket-like arrangement (see, for example, the drawings of European application 98830686.6 cited in the introduction), the vibrator units 8a, 8b are located inside the frame 2 in positions generally concealed from the exterior.
The arrangement of the vibrator units 8a, 8b inside the frame 2 has been found advantageous for various reasons.
In the first place, it is no longer necessary to provide specific support structures for the eccentric masses. This translates (with reference to formula I reproduced in the introductory portion of the description) into an ability to reduce the factor Kgt for a given factor ΣKg·mm or, on the other hand, to increase the value of the latter parameter, whilst keeping the former substantially unchanged.
A second important advantage lies in the fact that it is no longer necessary to provide seals for preventing the lubricant applied/supplied to the support elements from leaking towards the exterior in the region of the bearings which support the shafts to which the eccentric masses are keyed. In the solution according to the invention, the vibrating frame 2 is in fact constituted by a type of box or casing which encloses the vibrator units 8a, 8b almost completely (the casing is not usually arranged to be completely closed at the bottom), preventing the dispersal of this lubricant to the exterior. In practice, it is necessary to provide sealing elements exclusively in the region in which the shafts for transmitting the driving force from the motors 9, 10 towards the vibrator units 8a, 8b extend through the wall of the frame 2. This is because the members for supporting the masses of the vibrator units 8a, 8b in motion are also located entirely inside the casing formed by the frame 2.
Finally, the vibrator units 8a, 8b are protected by the frame 2 against any falling sand which is removed from the castings G.
In the currently-preferred embodiment of the invention, the eccentric masses 8 are arranged in two vibrator units 8a, 8b, each comprising four eccentric masses rotated by a respective drive shaft 11a, 11b. Clearly, however, practically any number of eccentric masses may be included in the units 8a, 8b without prejudice to the general operating principle described below.
The masses included in each unit 8a, 8b are keyed to respective shafts (not shown specifically in the drawings) which are rotated by the shafts 11a and 11b, respectively, so as to give rise to conditions of rotation which are unbalanced horizontally but are constantly balanced vertically. This corresponds - in known manner - to the need to arrange for the vibratory motion induced by the rotation of the masses included in the units 8a, 8b to be developed substantially horizontally, as shown by the double arrow 12 visible in the lower portion of Figure 1.
The fact that there are two sets of eccentric masses 8a, 8b, driven by respective drive shafts 11a, 11b enables at least two different operating conditions to be implemented selectively, whilst the condition of rotation of both sets of masses 8a, 8b is maintained.
In particular, a first condition corresponds to the situation which can be defined as rotation "in phase" or "in phase coincidence".
In this operating situation, the relative phases of rotation of the shaft 11a and of the shaft 11b are regulated in a manner such that, for example, when all of the eccentric masses of the unit 8a are oriented towards the right (with reference to the viewpoint of Figure 1), all of the eccentric masses of the unit 8b are also oriented in the same direction and, similarly, when all of the eccentric masses of the unit 8a are facing towards the left, all of the masses of the unit 8b are also facing in the same direction. This latter situation is shown schematically in Figure 1 in continuous outline for the masses of the unit 8a and in broken outline for the masses of the unit 8b.
In these conditions, the vibration stress induced by the rotation of the masses of the unit 8a is superimposed additively on the analogous vibration stress induced by the masses of the unit 8b, being added thereto and thus achieving the condition of maximum vibration of the frame 2.
The second relative operating condition, on the other hand, may be defined as "in phase opposition".
In these conditions, the respective phases of rotation of the shafts 11a and 11b are adjusted in a manner such that (again with reference to the example given above), when all of the eccentric masses of the unit 8a are facing towards the right, all of the eccentric masses of the unit 8b are facing towards the left and, conversely, when all of the masses of the unit 8a are facing towards the left, all of the masses of the unit 8b are facing towards the right. This latter situation is shown in continuous outline in Figure 1.
In these conditions, although the masses of the units 8a, 8b continue to rotate in the same conditions of speed (rate of revolution) described above, the vibration stresses induced in the frame by the two units 8a, 8b are precisely in phase opposition and are superimposed subtractively, cancelling one another out. In these conditions, even though the frame is stressed (violently) alternately in compression and in tension in the direction of alignment of the two sets of masses 8a, 8b, the net result, for the purposes of the vibratory motion as a whole, is practically zero. In these conditions, the frame 2 is therefore brought to a practically stationary condition, whilst housing the sets of masses 8a, 8b which continue to rotate. In these conditions, it is possible to load and unload castings at the start and upon completion of the vibration operation. This can be done without the need to stop the rotation of the eccentric masses of the units 8a, 8b. The intermittent operating conditions which are so damaging to the bearings of the vibrator units are thus prevented. In particular, the fact that it is no longer necessary to set the vibrator units 8a, 8b in motion and then to stop them (which, in practice, translates into a gradual variation of the vibration frequency generated by the vibrator units in accordance with a general curve having an upward and downward slope), avoids causing the frame 2 to vibrate, at least momentarily, in resonance conditions at its own frequency.
To achieve the two different phase relationships between the shafts 11a, 11b corresponding to the two operating conditions of the frame described above (as described, without interrupting the conditions of rotation of the masses of the units 8a, 8b at constant velocity), the embodiment of the invention described herein provides for the use of a so-called synchronizer 13.
This is a mechanical device of known type the structure of which will now be described briefly with reference to the sectioned view of Figure 4.
The device 13 usually has at least one input drive shaft (in this embodiment, for reasons described further below, two input shafts 101 and 102 are provided) which rotate a first driven shaft 103 and a second driven shaft 104 by means of respective kinematic chains (usually constituted by gears).
In the embodiment shown, the input drive shaft 101 (driven by the motor 9) drives the first driven shaft 103 by means of a gear 105 and is also coupled to the second input shaft 102 by means of a gear 106, the function of which, naturally, is to connect the motors 9 and 10 kinematically. The shaft 102 is also coupled (by means of gearing not explicitly shown as a whole) to a gear 108 mounted so as to be freely rotatable on a shaft corresponding, directly or indirectly, to the second driven shaft 104. Two further gears 109, 110 (or equivalent kinematic elements) are keyed to the same shaft (for example, by means of a splined coupling) and can move in an opposed manner towards and away from the freely-rotatable gear 108. The freely-rotatable gear 108, on the one hand, and the above-mentioned two kinematic elements 109, 110, on the other hand, carry respective sets of complementary engagement elements 111, 112 (for example, a catch, a projecting element such as a drive tooth, etc.), such as to achieve, with respect to the freely-rotatable gear 108, two respective conditions of drive coupling corresponding, with regard to the conditions of rotation of the second driven shaft 104, to two coupling conditions with a phase difference relative to one another of 180° (in practice two conditions of rotation with a phase difference of one half turn).
The coupling of one or other of the kinematic elements 109, 110 with the freely-rotatable gear 108, thus enables the phase of rotation of the second driven shaft 104 to be brought selectively to two phase conditions, relative to the first driven shaft 103, corresponding, respectively, to an angle of 0° (identical or coinciding phase) and 180° (phase opposition).
The above-mentioned translational movement of the two kinematic elements may be brought about by known means such as, for example a lever, which may be driven, for example, by means of a linear actuator such as a jack 21.
In the appended drawings, the synchronizer, indicated 13, is mounted in a position generally beside the frame 2 of the machine so that the two output shafts 103 and 104 of the synchronizer 13 can be connected by means of kinematic couplings of known type (for example, by means of articulated shafts 15a, 15b) to the shafts 11a, 11b which rotate the two vibrator units 8a, 8b.
As already stated, the currently-preferred embodiment of the invention provides for the synchronizer 13 to have two input shafts 101 and 102 rotated by the motor 9 and by the motor 10, respectively, for example, by means of belt transmissions (visible in Figure 2).
This solution, which is preferred but not essential, has the advantage that the operating conditions of the drive unit can be optmized.
The actuator, indicated 21, (for example, a fluid jack) associated with the synchronizer 13 is controlled by a processing unit K (this may be, for example, a so-called PLC or programmable logic controller) which supervises the general operation of the machine 1.
This enables the synchronizer 13 to be operated selectively, in accordance with the general operating cycle of the machine 1, in the two different operating positions corresponding to the rotation of the two vibrator units 8a, 8b in phase and in phase opposition, respectively.
The normal operation of the machine according to the invention provides, basically, for the cyclic repetition of the operating sequence described below.
The castings G are placed on the frame 2 of the machine 1 whilst the control unit K which supervises the operation of the machine keeps the actuator 21 in the operating position such that the shafts 11a and 11b rotate the vibrator units 8a, 8b in phase opposition. In these conditions, the frame 2 is in a stationary condition, since its overall vibratory motion is zero.
When the castings G have been fixed in their mounting positions on the frame 2, the control device K brings about activation of the percussion elements 6 which are intended to perform a violent hammering action on the castings G with a consequent initial breaking-up of the sand cores to be removed.
When the hammering action has continued for a certain period of time (for example 10-15 seconds) - or, according to an advantageous possibility offered by the machine according to the invention, with the hammering action being started only at a subsequent time - the control device K acts on the actuator 21 in a manner such that the synchronizer 13 causes the shafts 11a and 11b to rotate in the condition which corresponds to in-phase rotation of the vibrator units 8a, 8b. The rotation of the units 8a, 8b in phase induces in the frame 2 the violent vibratory motion (with accelerations which, in dependence on the design parameters, may even reach values of 35-40 G) upon which the action to remove the sand (the shaking-out) from the castings G is based.
At the moment at which the vibration treatment - which may be supplemented by the hammering action started whilst the vibration is in progress - is considered complete (for example, after about 40 seconds), the device K acts on the actuator 21 again so as to return the synchronzer 13 to the operating condition such that the shafts 11a, 11b again rotate the vibrator units 8a, 8b in phase opposition. The overall vibratory motion of the frame 2 comes to an end so that it is possible to remove the castings G which have been subjected to shaking-out by the machine 1.
At this point, the machine 1 is ready to receive further castings G to be shaken out by repetition of the operating sequence described above.
It will be appreciated that the operations described above (and, in particular, the bringing of the frame 2 from the stationary condition to the vibration condition required to perform the shaking-out and then back to the stationary condition) are performed whilst the conditions of rotation - at constant speed - of the motors 9, 10 and of the entire kinematic chain which connects these motors 9, 10 to the eccentric masses of the units 8a, 8b, are kept unchanged. The vibrator units are also kept constantly rotating at constant speed. This is achieved exclusively by the operation of the synchronizer 13 so as to vary selectively the relative phases of rotation of the shafts 11a, 11b, causing the two units 8a, 8b to operate alternately in phase opposition or in phase coincidence according to the criteria described above.
Naturally, the principle of the invention remaining the same, the details of construction and forms of embodiment may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the invention, as defined by the following claims.

Claims

A machine (1) for shaking-out foundry castings (G), comprising:

a structure (2) for supporting the castings (G) to be shaken out, and

vibrator means (8a, 8b) associated with the support structure (2) in order to apply vibration stresses to the support structure (2),

characterized in that first and second vibrator means (8a, 8b) are provided and can be operated selectively (13, 21) in at least one first operating condition, in which the first and second vibrator means (8a, 8b) operate in phase opposition so that the respective vibration stresses applied to the support structure (2) are superimposed subtractively and the support structure (2) remains substantially stationary, and one second operating condition, in which the first and second vibrator means (8a, 8b) operate in phase coincidence, so that the respective vibration stresses applied to the support structure (2) are superimposed additively and the support structure (2) is subjected to vibration.
A machine according to Claim 1, characterized in that the vibrator means (8a, 8b) are mounted on the support structure (2) in positions inside the support structure (2).
A machine according to Claim 1, characterized in that each of the first vibrator means (8a) and the second vibrator means (8b) comprises a plurality of masses which are driven in eccentric rotation about respective rotation axes with the masses of each of the pluralities retaining conditions of symmetry about a given plane, so that the vibration stress induced by the vibrator means (8a, 8b) is directed substantially along the said plane (12).
A machine according to Claim 3, chracterized in that the eccentric masses are rotated in a manner such that the said plane is oriented substantially horizontally.
A machine according to any one of the preceding claims, characterized in that the first and second vibrator means (8a, 8b) are driven by respective shafts (11a, 11b), and in that drive means (9, 10) are provided and drive the respective shafts (11a, 11b) by synchronizer means (13) which can vary the conditions of rotation of the respective shafts (11a, 11b) selectively between at least one condition of phase opposition and one condition of phase coincidence of the first and second vibrator means (8a, 8b).
A machine according to Claim 2 or Claim 5, characterized in that the support structure (2) has a substantially closed box-like shape with at least one drive shaft (11a, 11b) of the first and second vibrator means (8a, 8b) extending through the structure (2).
A machine according to Claim 6, characterized in that the first and second vibrator means (8a, 8b) have associated members for supporting them in motion, the support members also being located entirely inside the support structure (2).
A machine according to any one of the preceding claims, characterized in that it comprises percussion means (5) which can be activated selectively in order to perform a hammering action on the castings.
A machine according to Claim 8, characterized in that it comprises control means (K) which can act (13, 21) both on the first and second vibrator means (8a, 8b), and on the percussion means (5), in order to activate the percussion means (5) when the first and second vibrator means (8a, 8b) are operating in phase coincidence.
A machine according to any one of the preceding claims, characterized in that the vibrator means (8a, 8b) are configured for applying to the support structure (2) vibration acceleration values greater than 20 G and preferably equal to 35-40 G.