US2246922A - Rotary frequency reducer for electromagnetic hammers - Google Patents

Description

June 24, 1941, P. A. MACCHIONI ROTARY FREQUENCY REDUCER FOR ELECTROMAGNETIC HAMMERS Filed Oct. 4. 1938 Imuam 'ur Pie hrg Aurel o Much-Ma Patented June 24, 1941 ROTARY FREQUENCY REDUCER FOR ELECTROMAGNETIC HAMlVIERS Pietro Aurelio Macchioni, Turin, Italy, assignor to Soc. An. S. I. M. B. I., Turin, Italy Application October 4, 1938, Serial No. 233,152 In Italy November 8, 1937 2 Claims. (Cuzco-s) In electromagnetic hammers, as now in use, the blow striking rate corresponds to th alternations of the current and as the commonly available frequencies range between 50-60 periods, the speed of the hammer lblows is very high; for instance, with a 50 period current, the blow striking rate is 6000 blows per minute.

Under these conditions, in order to obtain a reliable and constant operation it is necessary to maintain the travel and weight of the ram within small limits to prevent the setting up of inertia forces such as may cause the ram to go out of synchrcnism, arresting operation of the hammer.

Reduction in the travel and weight of the ram imposes a serious limitation on the capacity of electromagnetic hammers of which the use is for this reason precluded in many industrial branches Where a capacity exceeding the possibilities of hammers of this type is required.

Moreover, its efliciency is comparatively small on account of the residual magnetism.

An object of this invention is to eliminate the above mentioned drawback by providing a, mechanical frequency reducer by which it is possible to considerably lower the speed of blow, for instance, down to 1500 blows per minute with an alternating 50 period current, and at the same time to increase both travel and weight of the ram. It is thus possible to manufacture electromagnetic hammers meeting any practical requirements.

The frequency reducer according to this invention is essentially constituted by a pair of contacts connected into the A. C. energising circuit of the hammer and controlled by a cam driven by a synchronous motor fed by the same A. C. source. This cam is of a shape such that it opens the energizing circuit of the hammer for a period of time corresponding to one or more periods that are thus suppressed, so that current impulses are sent to the hammer solenoid representing periods spaced by one or more other periods.

It is clear that under these conditions the travel and weight of the ram may be increased in accordance with the interval between the individual current impulses, as any interference between the kinetic energy of the ram and alternations of the current is liminated and the frequency of impulses may easily be tuned on the natural frequency of the opposing spring.

The accompanying drawing shows by way of example a construction of the frequency reducer according to this invention.

Figure 1 is a front view.

Figure 2 is a cross section and Figure 3 shows in elevation, partly in section, an electromagnetic hammer that may be utilised by using in connection therewith the device shown in Figures 1 and 2.

Referring to the drawing, I denotes a synchronous motor, for instance a four-pole 1500 R. P. M. motor, having keyed on its shaft a cam 2 acting through an antifriction roller 3 upon a spring leaf 4 carrying an electric contact 5 connected through the leaf 6 to the terminal I. The movable contact 5 cooperates with a stationary contact 8 carried by a leaf spring 9 arranged parallel to the leaf spring 4 and connected by the leaf [0 to the terminal II.

The leaves 4 and 9 are fixed on a rim l2 of insulating material secured to the motor I by bolts l3; on assembly the leaves are slightly curved towards the cam so as to prevent them from curving in opposite directions under the action of changes in temperature, which might objectionably affect operation of the device.

In the construction shown the cam 2 is shaped in such manner as to open the contacts 5 and 8 during a period of time corresponding to a period of the alternating current so that on connecting to the terminals 1 and II the energizing circuit of an electromagnetic hammer, the latter is imparted current impulses with a frequency of twelve periods and the hammer strikes 1500 blows per minute, that is a quarter of the number of blows that would be struck if no A. C. periods had been suppressed.

Obviously, the number of blows may be further reduced by alternatively suppressing a larger number of periods, so as to increase the interval between each impulse.

By this suppression of periods of the A. C. it is possible to increase the travel and Weight of the ram, as shown in Figure 3 which shows a hammer that may be coupled with the device shown in Figures 1 and 2. The various members of this hammer are shown on the correct scale, so as to clearly show the relative proportions of said members. As will be seen, the core I4 forming the ram is of a considerably larger diameter than the core of ordinary electromagnetic hammers, its travel also being increased as shown by its distance from the armature IS.

The core is brought to its initial operative position by the sucking action of the solenoid Is as the latter is energized, and it strikes the blow under the action of an opposing spring as soon as the solenoid is disenergised. It is of course possible to adopt a reverse arrangement, that is, the core may be returned to its initial working position by the spring and the blow may be struck under the action of the current impulse.

The impulses of reduced frequency and in the form of a full wave offer the important advantage of eliminating from the magnetic circuitv the residual magnetism tending to remain at the end of the pole pieces, thereby considerably increasing the efficiency and capacity of the hammer.

I wish it to be understood that I do not desire 1 to be limited to the exact details of' construction shown and described, for obvious modifications will occur to a person skilled in the art.

What I claim is:

l. A periodic switch comprising an annular support of electrically insulating material, a pair of leaf springs diametrically arranged on saidsupport; the-free ends of said springs being rigidly fixed to said support, contacts facing each other annular support, the free ends of said springs being secured to said support so as to be resiliently curved in the same direction,-contacts facand fixed to the central portion of said springs, said contacts being connected to a source of alternatingcurrent and normally kept spaced by said springs in their inoperative position, and a vc'amjacting on the central portion of one of said springsso as to cause said contacts to engage at predetermined periods of time.

t PIETR;O AUREL'IO MACCI-IIONI.

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