GB2275218A - Vibratory finishing machines - Google Patents

Abstract

A method for finishing workpieces comprises vibrating the workpieces in contact with abrasive particles, the vibratory movement is varied from time to time, as by changing the movement of the vessel means containing the particles from time to time. Apparatus for finishing workpieces by the method comprises vessel means 10 adapted to contain the workpieces and abrasive particles, the vessel means being mounted to permit vibratory movement thereof, and means for imparting vibratory movement to the vessel means and means for varying the vibratory movement from time to time, the means for imparting vibratory movement preferably comprising a motor 26 attached to the vessel having a shaft 28 carrying an out-of-balance weight 18, 20, the weight being rotatably mounted on the shaft so as to be able to move around the shaft between locations separated by less than 360 DEG on change in direction of rotation of the shaft. The out-of-balance weight is preferably carried on a carrier arm which is rotatably mounted on the shaft. The vessel means is supported by pneumatic bags 14 the air pressure in which can be varied. <IMAGE>

Description

VIBRATORY MACHINES The present invention relates to vibratory finishing machines used for deburring workpieces and polishing or brightening them. The workpieces are typically cast pieces which have flashings on them and surface imperfections which need removal. The removal is done by abrasion of the surface by a mass of abrasive particles of sizes chosen to be appropriate to the size of the workpieces. Thus an appropriate mixture of workpieces and abrasive is vibrated in three dimensions for a suitable period of time and then the abrasive particles which are usually smaller than workpieces are filtered out by falling through a mesh screen and the workpieces conveyed, often by a vibratory conveyor, to an exit station from the machine.

Typically the vibrational movement of the vessel and thus the workpieces and abrasive particles or chips contained therein is achieved by rotation of an out-ofbalance weight or weights mounted on the drive shaft of one or more motors which rotates in a constant direction.

The motor is attached to the vessel in which the workpieces and abrasive are shaken together. In conventional arrangements, the weights are rigidly secured to the shaft and the motor rotates the weights in a single direction without varying the speed throughout the finishing cycle which typically may be of several hours duration. Provision has been made in the prior art for adjustment of the vibratory activity by changing the position of the weights on the shaft but during the process of the prior art procedure the abrasive particles and the components tend to reach the same speed and thus their relative speed is near to zero. This has the disadvantage that on occasion little or no abrasion of the workpieces may occur either in certain parts of these workpieces or in certain regions of the vessel, i.e. socalled "dead spots".The grinding impact accordingly reduces and the efficiency of the finishing process diminishes.

Typical constructions of devices used for finishing workpieces already known from the prior art employ fixed resilience spring means. During the finishing cycle, a coupling of the spring frequency to the vibration frequency of the vibrator, known as resonance, can occur.

This resonance effect leads to increases in noise produced by the machine and reduction in the efficiency of abrasion. Additionally these constructions suffer from large movements of the vessel which can be thought of as shuddering movements, with attendant noise and even possible spillage of the contents of the vessel, during the start-up and stopping of the vibrator.

In the present invention, the vessel which is preferably a toroidal trough or a straight or curved trough is mounted on spring means, which may be fluid bag supports and are desirably pneumatic bag or balloon spring means although conventional metal springs could be used or other spring means such as rubber bushes.

We have devised apparatus in which the conventional system of spring mounting of the vessel in which the abrasion occurs and to which the motor carrying the outof-balance weights is mounted are replaced by pneumatic devices located between the tank or vessel and the mounting for the vessel.

The pneumatic bag spring means are preferably provided with controllable air or gas supply means so that the pressure in the bags can be adjusted to suit the weight of the load being finished.

We have found that higher pressures are beneficial for heavier loads. Such adjustments, of the spring means to the load, have a number of advantages over the use of fixed resilience spring means. Thus, in the present invention, coupling of the spring frequency to the vibration frequency of the vibrator, known as resonance, occurs much less frequently. Additionally, during startup and stopping of the vibrator large movements of the vessel, as are encountered in the prior art, also occur less frequently.

The present invention provides a technique by which the three-dimensional movement can in effect be caused to change from time-to-time thus breaking down the homogeneity of the relative speed of the abrasive particles and the components and thus increasing the abrasive action making it more rapid and the process more economical. Whilst we prefer to achieve this by changing the direction of movement, in its broadest sense, the system does not require the direction to be actually reversed but merely to change from time-to-time so that it causes the workpieces and abrasive particles to impact with greater severity than when the three-dimensional movement remains constant. The vibration impacting mechanism utilises out-of-balance weights mounted on the shaft of the motor preferably in a freely removable manner.When removably mounted the out-of-balance weight selected can be easily changed between finishing cycles by merely slipping the previous weight off the shaft and slipping a new weight on. The finishing of the components is related to the frequency and amplitude of the vibration. Variation of the frequency of the input to the motor only changes the speed of rotation of the motor.

The motor is arranged to rotate the shaft in either direction; this is most conveniently achieved by using a reversible motor. We have devised control mechanisms whereby the frequency and period of the changes in direction of the vibratory movement can be pre-set and can automatically be controlled during operation of the process. If the motor is an AC motor the change in motor direction can be achieved by merely changing the phase of the AC supply.

In order to be able to change the direction of the three-dimensional movement of the weight in a controlled manner it is not sufficient merely to change the rotation of the motor as the resulting movement is uncontrolled and chaotic. This shuddering is avoided or diminished if the weight can change its angular position relative to the shaft when the direction of rotation of the shaft changes.

Preferably the weights are mounted on a carrier arm, which is free to rotate around the shaft of the motor.

The weights are mounted on the arm so that they can slide in a direction along the shaft of the motor. The vibrator mechanism also has stop means such as to allow the carrier arm to rotate through only a limited angular extent rather than through 3600 relative to the shaft.

The stop means may be constituted by stop arms extending out radially from the shaft or relative to the shaft.

The stop means may thus be carried on the shaft and consist of a collar secured to the shaft with the arms extending out therefrom carrying stops adapted to be engaged by the weights or the carrier arm so as to limit angular movement of the weights relative to the shaft.

The stops preferably permit the weights to move through less than 3600, e.g. 90 to 2700 and we have found 1800 to be satisfactory.

The frequency of the vibration can also be controlled by a frequency convertor which is part of the control circuity which we have devised.

The invention provides a number of advantages. For example under similar conditions of workpiece, abrasive particles and load, production can be increased by up to 40 percent with corresponding savings in energy. The separation of the vibration from the mounting environment can be improved very substantially and resonance effects can be avoided thus reducing the noise impact of the process on the environment.

In one preferred embodiment there is provided a vibratory finishing machine comprising a toroidal trough mounted on pneumatic bags which are mounted on the baseplate of the machine which is secured to the floor.

The vibratory mechanism preferably comprises an electric motor, with out-of-balance weights attached to the shaft of the motor. The motor is preferably mounted on the vessel with its shaft disposed vertically or nearly so.

The out-of-balance weights may be carried on a carrier arm which is preferably slidable on the shaft and which may be rotated through a limited angular extent less than 360 , preferably less than 2700, e.g. about 1800, relative to the shaft.

The weights are preferably slidable onto the carrier arm along or parallel to the motor axis. The carrier arm is desirably provided with a key configuration so that whilst the weights can slide longitudinally up and down the carrier arm and thus be readily removed between finishing cycles and replaced by larger or smaller weights to vary the amplitude of the vibration, the weights remain under gravity on the carrier arm during rotation thereof.

The shaft preferably also carries a stop mechanism consisting of a collar and outwardly extending arms, which may form a platform, carrying at their ends stops which are positioned so as to engage the weights.

When the motor is started rotating, for example in a clockwise direction, the inertia of the carrier arm and the weights will cause it to rotate anti-clockwise relative to the shaft until it engages with the anticlockwise positioned stop. This occurs almost immediately on commencement of the rotation. The weight thus continues to occupy a position bearing against the anti-clockwise stop so long as the shaft rotates in the clockwise direction, despite the vibrations induced by the fact that the weights are unbalanced relative to the shaft axis. When the direction of rotation of the motor is changed, preferably by changing the phase of the AC supply to the motor, the shaft slows down, stops and then changes direction and then picks up again. Again the inertia of the weight on the carrier arm causes it to move this time in a clockwise direction.The weight then bears against the clockwise stop for the rest of the period during which the shaft rotates in an anticlockwise direction.

This changing of direction occurs over a short period of time but is done smoothly so as to avoid significant impact shocks to the stop mechanism. The direction is changed a number of times, e.g. from 5 to 250, e.g. 5 to 100 or 10 to 70 times during the cycle, each period preferably being the same, e.g. 1 or 20 minutes for each period, preferably in the range 4 to 10 minutes, for example at intervals of 5 minutes.

The invention may be put into practice in various ways and one specific embodiment will be described to illustrate the invention with reference to the accompanying drawings in which: Figure 1 is a vertical section through a particular form of a vibratory finishing machine in accordance with this invention; Figure 2 is a vertical section showing in more detail the upper out-of-balance weight assembly; Figure 3 is a plan view showing the upper out-ofbalance weight assembly; Figure 4 is a plan view showing the rotation positions of the carrier arm of the upper out-of-balance weight with reference to the direction of rotation of the motor; Figure 5 is a vertical section showing the lower out-of-balance weight assembly in more detail; Figure 6 is a plan view showing the lower out-ofbalance weight assembly.

Figure 7 is a plan view of one of the out-of-balance slidable weights; Figure 8 is a block diagram of an electric control circuit for the operation of this embodiment of the invention.

Figure 1 shows a vertical section through a particular form of a vibratory finishing machine in accordance with this invention. A vessel 10 is mounted on pneumatic bags 14 which are secured to a base 12.

This enables the vessel to vibrate relative to the base 12. The base 12 is secured to a chassis 22. This is firmly secured to the floor by mounting blocks 24. The point of attachment for the pneumatic bags 14 to the chassis 22 is a substantially horizontal shelf element 23 attached to the side walls of the chassis 22. The air pressure inside the pneumatic bags 14 is controlled by an air springs regulator 16.

The vessel 10 also has a motor 26 attached to it with a drive shaft 28. In the particular embodiment shown here, the drive shaft 28 is extended upwards into the interior of the vessel 10 and also downwards into the interior of the chassis 22. At the upper end of the drive shaft 28 there is attached an upper out-of-balance weight 18 which is rotatable about the axis of the drive shaft 28. At the lower end of the drive shaft 28 there is attached a lower out-of-balance weight 20. The two weights 18 and 20 being 180 out of phase with respect to each other, but disposed at equal radial distances from the axis of the shaft. The vibrations caused by the action of the motor 26, with the weights 18 and 20 attached, is transmitted to the vessel 10 through the base plate 12.The workpieces requiring finishing in this apparatus are placed into the trough 11 with appropriate abrasive material, e.g. abrasive chips. The direction of motion of the workpieces in the trough 11 is indicated approximately by the arrow 30.

Figure 2 shows in more detail the upper out-ofbalance weight 18. This element comprises a stop platform 44 securely fixed to the drive shaft 28 of the motor 26. Mounted on this platform are two carrier arm stops 46 and 47, which act to restrict the rotation of the freely rotatable carrier arm 40 which carries the out-of-balance weight or weights 42. The carrier arm is kept in place on the drive shaft 28 by means of a fastening element 48, which is preferably a nut, and a washer 50.

Figure 3 shows a plan view of the upper out-of balance weight assembly 18 described in Figure 2. With the motor 26 rotating the drive shaft 28 in one direction, indicated as direction "I" as shown in Figure 3, the carrier arm 40 is engaged by a carrier arm stop 46 as shown by the solid line. Conversely when the motor 26 is rotating the drive shaft 28 in the opposition direction "D", the carrier arm 40 is engaged by the carrier arm stop 47 as indicated by the dotted line. The carrier arm stops 46 and 47 are composed of a block 33 secured to the stop platform 44 by fastening means 35 and 36, and a buffer 32 which engages the carrier arm 40.

The fastening means 35 and 36 are preferably nut and bolt assemblies.

Figure 4 shows the rotation positions of the carrier arm of the upper out-of-balance weight 18 with reference to the direction of rotation of the motor 26. Rotation position "I" 62 of the carrier arm is shown, as in Figure 3, by a solid line and rotation position "D" 60 of the carrier arm is shown by a dotted line.

The reference numeral 63 indicates the movement of the workpieces in the vessel when the shaft is rotating in the direction "I" and 61 when in the direction "D".

Figure 5 shows the lower out-of-balance weight assembly 20 in more detail. This element comprises a carrier arm 64 a fixed out-of-balance weight 68 and optional removable out-of-balance weights 66. This feature is attached to the drive shaft by fastening means 70 and 71 which are preferably nut and bolt assemblies.

It will be noted that the carrier arm 64 is not free to rotate around the shaft 28. In addition the upper element 18 should desirably have an out-of-balance weight 42 located on it SD as to match the fixed out-of-balance weight 68 on the bottom element 20. The fixed weight 68 is necessary to provide a platform on which removable weights can rest when the mass of the out-of-balance weights is to be increased by addition of extra removable weights top and bottom.

Conveniently the removable weights 66 and 42 are of the same size, weight and shape.

Figure 6 shows a plan view of the lower counterweight assembly 20 comprising the elements as described in Figure 5.

As can be seen from Figures 3, 6 and 7 the removable weights 42 and 66 are provided with a keyway 67 having a hemispherical head 69. This shape of keyway is not essential but is preferred.

The carrier arms 40 and 64 have at their outer ends keying shafts 73 and 72 of the same cross-section as the keyway 67 but which are of slightly smaller dimensions than the keyway, so that the weights are removably slidable onto and off the said shafts.

Figure 8 shows a block diagram of an electric control circuit for the operation of this embodiment of the invention. The points of connection 80, 81, 82 are to the power supply and points 92, 93, 94 are the connections to the motor vibrator shown as 'M'.

Connected in series with the main circuit at points 83 and 84 is the switch 87 for operating the motor in the "reverse" direction. Connected in parallel to this switch 87 is the switch 86 for operating the motor in the "forward" direction. Also connected in series to the main circuit is the control element 91. This is preferably a variable rheostat and is connected through points 88, 89, 90, which allows the speed of the motor to be varied.

In general the faster the speed of rotation the smaller is the amplitude of the vibration. In addition the larger is the mass of the weights 42 and 66 the greater is the amplitude of the vibration.

Adjustment of these variables enables the vibration conditions to be suited to the particular load which is being finished. If a heavy load is being finished heavier weights will be used. If a very smooth finish (taking longer time) is desired the amplitude will be kept small.

Clearly variations in the geometry of the device can be made. For example the carrier arms could be made longer or shorter than shown, different keyway shapes and shapes of the weights could be used. Also the invention could be applied to longitudinal troughs or bowl vessels instead of toroidal vessels.

Thus the precise shape and arrangement of the vessel or vessels in which the finishing occurs is not critical and the invention is not to be limited to vibration of any particular form or array of vessel or vessels.

A single out-of-balance element could be used at one end of the shaft only or when two out-of-balance elements are used they need not be 1800 out-of-phase and could in fact be in-phase.

Equally the motor could be disposed with its shaft not vertically, e.g. horizontally or at an angle to the horizontal.

Out-of-balance weights could again be keyed to the shaft but here gravity could not be relied upon so certainly to hold the weights in place during operation and locking mechanisms for locking the weights to the shaft would be desirable if not essential.

According to a further aspect of the present invention apparatus for finishing workpieces comprises vessel means adapted to contain the said workpieces and abrasive particles, the vessel means being mounted to permit vibratory movement thereof and means for imparting a vibratory movement to the said vessel means is characterised in that the vessel means comprises two or more separate vessels. The vessels are preferably toroidal and one vessel is placed outside the other so that the diameter of its median line is greater than the diameter of the median line of the other vessel. The cross-section of the vessels may be the same or different. The vessels may be placed in the same plane and preferably perpendicular to the axis of the vibratory means or may be located in different planes.

This aspect of the invention also extends to a method in which the apparatus is used with the same workpieces in each vessel but abrasive chips or particles of different sizes in the two different vessels. This enables workpieces to be finished to differing degrees of surface smoothness in a single finishing cycle.

Figure 9 shows one preferred embodiment of this double concentric annular trough version of the invention.

Claims (15)

1. A method for finishing workpieces comprising vibrating the said workpieces in contact with abrasive particles characterised in that the vibratory movement is varied from time to time.

2. A method as claimed in Claim 1 characterised in that the vibration is imparted to the workpieces and abrasive particles by placing them in vessel means and vibrating the vessel means and in that the movement of the vessel means is changed from time to time.

3. A method as claimed in Claim 2 characterised in that the vessel is vibrated by means of a motor carrying an out-of-balance weight and the rotation of the said out-of-balance weight is varied from time to time.

4. A method as claimed in Claim 3 characterised in that the direction of rotation of the out-of-balance weight is changed at least once during the finishing of the workpieces.

5. A method as claimed in Claim 4 characterised in that the direction of rotation is changed from 5 to 250 times in the finishing cycle.

6. A method as claimed in Claim 4 or Claim 5 characterised in that the rotation in each direction is carried out for from 1 to 20 minutes before the direction of rotation is changed.

7. A method for finishing workpieces comprising placing said workpieces in vessel means with abrasive particles, the vessel means being mounted on fluid bag supports, the pressure in which is adjustable, and imparting vibratory movement to the said vessel means, and adjusting the pressure in the said fluid bag supports in accordance with the load to reduce large movements of the vessel means on initiation and cessation of the vibratory motion.

8. A method as claimed in Claim 1 substantially as specifically described herein.

9. Apparatus for finishing workpieces comprising vessel means adapted to contain the said workpieces and abrasive particles, the vessel means being mounted to permit vibratory movement thereof, and means for imparting vibratory movement to the said vessel means and means for varying the said vibratory movement from time to time.

10. Apparatus as claimed in Claim 10 characterised in that the means for imparting vibratory movement comprises a motor attached to the said vessel having a shaft carrying an out-of-balance weight, the weight being rotatably mounted on the shaft so as to be able to move around the shaft between locations separated by less than 360O on change in direction of rotation of the said shaft.

11. Apparatus as claimed in Claim 10 characterised in that the out-of-balance weight is carried on a carrier arm which is rotatably mounted on the shaft.

12. Apparatus as claimed in Claim 10 or Claim 11 characterised in that the locations are defined by stop means carried on the said shaft.

13. Apparatus as claimed in Claim 10 or Claim 11 characterised in that the out-of-balance weight is afforded by one or more weights carried on a carrier arm, at least one of the weights being adapted to be removably secured to the said carrier arm.

14. Apparatus as claimed in any one of Claims 10 to 13 characterised in that the motor is affixed to the base plate of the vessel and rotates a substantially vertical drive shaft, out-of-balance weights being secured by gravity to each end of the shaft.

15. Workpieces whenever finished by a method as claimed in any one of Claims 1 to 8.