The Evolution of High Frequency Shakeout

Looking back over the years prior to 1975, the foundry industry used brute force type shakeouts. These units had several problems associated with their operation. The two major drawbacks were high horsepower and an inability to handle fragile castings. Then, in 1975, the first two-mass shakeout was put into service. Again, fragile castings were subject to damage, but from an energy point of view, the horsepower was reduced. From 1975 to 1982, many improvements were made to the twin-mass shakeout design.

Throughout this whole period, foundry requirements dictated greater flexibility in their shakeout applications. Greater emphasis was placed on the ability to handle fragile castings, as well as much heavier, bulkier castings. Both types of castings had to be capable of total separation of sand and casting without casting damage.

In 1982, the first high frequency, 1800 cycle units were placed in service. This tandem shakeout design provided total flexibility and achieved the above goals.

The key features of the high frequency shakeout are as follows:
1. Extremely low horsepower drives.
2. Easy maintenance of drive components, with extremely quick replaceability.
3. Easy change for angle of attack and amplitude.
4. Capability of handling heavy and fragile castings.
5. Maximum sand separating efficiency.

With the advent of high production molding machines, job shop foundries were finding that their shakeout requirements had expanded to encompass the ability to handle not only fragile castings (usually light sections), but also heavy castings on a continuous basis. Prior to 1975, the shakeouts available for sand and casting separation were of "brute force" design. This would include either double shafts geared together, or single shaft-type units (Figs. 1 and 2).

The limitations of such shakeouts were based on bearing design; these bearings were in the area of 180 mm which would limit the WR of the eccentric shaft and roller speed. The greater the diameter of shaft, the higher the roller speed. In order to protect the bearings, either oil cooled or water cooled drives were designed. Needless to say, making sure that the cooling systems were properly maintained was another problem for Maintenance.

Limitations on these units were:
1. Extremely high horsepower for starting.
2. The ability to change angle of attack (usually through gear re-alignment, which increased gear wear).
3. Change of amplitude of stroke (with fixed eccentric fixed stroke).
4. Dampening under extreme head loads.
5. Material impacts on decks transferred to rotating bearings.
6. Limitations on size of units due to bearing limitations.
7. Starting and stopping of units going through isolation frequency (erratic bouncing).
8. Maintenance difficulty on bearing replacement and alignment.

In 1975, the first twin-mass shakeout was providedand furnished to Galva Foundry, Galva, Illinois (Fig. 3). This shakeout was provided with a twin 5 HP drive; the motors were double extended shaft using ball bearings. If of the brute force design, this shakeout would have required a minimum of 30 H P The angle of attack on this shakeout was fixed; the frequency was fixed but the amplitude was variable. Its initial design was to eliminate the large horsepower, as well as the transmittal of shock forces back through the bearings caused by the impacts from the material on the deck. The
stroke was similar to the brute force design providing 3/8” to ½” of displacement at 900 cycles. Fragile castings again were subject to damage due to the high velocity of impacts imparted to the castings. Control of castings was erratic and violent bouncing would occur:

From 1975 to 1982, much work had been done to improve on the twin-mass design, and shakeouts were provided having shakeout decks in the neighborhood of 150,000 Ibs. vibrating weight. These shakeouts were driven with twin 7 ½”  horsepower motors, with the material loads on the deck exceeding 200,000 Ibs. Up to that point, shakeouts of this nature were normally brute force, and required in the neighborhood of 100 horsepower drives. Bearings would have to be cooled through external means; and again severe problems did occur through the tremendous impacts of materials on the deck, and then transmitted through the drive bearings.

Throughout this seven year period, foundry requirements dictated greater flexibility in their shakeout applications. Greater emphasis was placed on the ability to handle fragile castings, as well as the much heavier, bulkier castings. Both wanted the capability of total separation of sand and castings without casting damage. Tests with Waupaca Foundry, Inc. were performed using twin 1800 RPM heavy-duty shaker motors directly mounted to the shakeout frame. Limitations in these designs were that of the motor, which would dictate the size of the shakeout frame and with the impacts still being directed from the deck to the vibrating motor. However, the test did show that the high frequency provided a better action on reducing the unpoured molds, as well as the poured molds, and with infinite control (in both angle of attack and amplitude) the reduced amplitude eliminated the erratic casting bouncing on the shakeout deck.

The problems that were encountered in the design of such a unit were:
1. With high frequency, the structural design of the frame, and its members, would be increased to the square power of the frequency. There was no easy solution since the design of the structure had to be increased in strength, with minimum increase in weight.
2. The second problem that occurred was to develop a spring that could withstand the increased number of cycles and remain below the fatigue stress limits under a predesigned displacement. In order to incorporate complete design flexibility, a rotating device was designed to change the angle of attack, its amplitude, and displacement (Figure 4).

All of these were accomplished through the use of already designed heavy-duty, high frequency motors with "sealed for life" bearings. Periodic lubrication of motors was totally eliminated. By using the twin-mass design again, the impact forces to the shakeout frame were isolated through the reaction springs, and not transmitted to the motors. In developing a shakeout system with total flexibility, a tandem shakeout design was used. This tandem design allowed for the maximum separating efficiency of sand and castings, with the flexibility of making either shakeout feed at a different rate and/or amplitude. The stroke was less than that of brute force design, having a 1/8” inch stroke displacement at 1800 cycles. With the cushion of sand and castings on the first shakeout, the greatest separation could occur with the greatest feed rate. With the maximum percent of burden removed, the second shakeout is designed to feed at a lesser rate to accomplish core knockout and/or casting cleaning. Having successfully accomplished the design of a frame and drive for the new high frequency shakeouts, the deck designs were as critical as the shakeout frame. It was our recommendation that on each shakeout application a series of tests should be performed at the customer's facility in order that design criteria could be established.

In review, the features of the high frequency shakeout are as follows:
1. Extremely low horsepower drives.
2. Easy maintenance of drive components, with extremely quick replaceability.
3. Easy change for angle of attack and amplitude.
4. Capability of handling heavy and fragile castings.
5. Maximum sand separating efficiency.