US2041295A - Fuse plug - Google Patents

Description

May 19, 1936. L, LUDWIG 2,041,295

FUSE PLUG Filed March 25, 1935 INVENTOR. 1 00.15 L ua/w/ BY gy A TTORNEYS.

Patented May 19, 1936 UNITED STATES PATENT OFFICE FUSE PLUG Louis Ludwig, Brooklyn, N. Y. Application March 23, 1935, Serial No. 12,661

1 Claim.

My invention relates to fuse plugs of the type having an opening covered with transparent material through which the interior of the plug may be observed. The invention has for its main objects to provide simple means within such a fuse plug, immediately below the transparent opening, which will positively indicate whether or not the fuse is blown. Another object is to provide positive means for assuring that the fusible link will always blow at a predetermined point. An additional object is to so construct these means that they will add but very slightly to the cost of the fuse plug.

These and various other objects and advantages will be readily understood from the following description and from the accompanying drawing, in which, however, various modifications may be made. In the drawing Fig. 1 is a top view of a fuse constructed in accordance with my invention,

Fig. 2 is a cross-sectional side View of Fig. 1,

Fig. 3 is another, but fragmental cross-sectional side view,

Fig. 4 is a disc used with the fuse,

Fig. 5 is a similar disc slightly modified,

Fig. 6 is a side View illustrating the manner in which either of the discs, shown in Figs. 4 and 5, are attached to the fusible link of the fuse.

Fig. '7 is another top view of the fuse with parts broken away to show certain details of construction, and

Fig. 8 a side View of Fig. '7.

I am aware that many indicating fuses have been invented in which a disc, or certain symbols imprinted on a disc, are caused to be destroyed or obliterated when the fuse is blown. In some cases this has been accomplished by using a fusible powder in combination with the disc and in others by discoloring or imprinting the disc with some fusible material which will be discolored by the blowing of the fuse.

In other cases the gases and other products of combustion given off by the blowing of the fusible link has been relied upon to so discolor the disc as to indicate that the fuse has blown.

Repeatedly the blowing of such a fuse will fail to discolor the disc, either because the gases from the blowing of the fuse escaped too rapidly, or because the fusible link did not burn out on top of the disc as expected to. The time element is too short and there is not sufficient air in the closed chamber to always discolor the disc.

The purpose of the present invention is to remedy these defects. With this in mind, reference is now had to all the views on the drawing on which the ordinary porcelain body of a fuse plug is shown at III, the threaded metal ferrule at II, the cap at I2, the opening in the cap through which the interior of the fuse may be observed at I3, the interior recess at I4, and the transparent mica disc which covers the opening at I5.

The invention consists in bringing the fusible metal strip I6 right up to or. in very close proximity to, the mica disc and to place an insulating disc I'I under the exposed part of the fusible strip in such a manner that the smallest possible air pocket is formed between this disc and the mica disc. This I accomplished by slitting the disc in such a manner that two tongues I8 and I9 are formed substantially in the centerof the disc so that, when the disc is bent, as shown in Fig. 6, these tongues may be placed on opposite sides of the exposed part of the fusible strip and closed under this strip when the disc is go again straightened out by being clamped between the body member and the mica disc. This construction forms very small air pockets 20 on opposite sides of the fusible strip, while it causes the rest of the disc to contact with the mica disc. When the fusible strip blows, the very close proximity to the mica of the point where it blows will cause the mica disc to become translucent, due to charring, and whatever gases are generated will discolor the indicating disc.

One end of the fusible metal is connected, in the usual manner, to the center contact 2| and the other end to the metal ferrule I I. The metal strip is weakened, at the exposed part, as shown at 22. The correct width of this weakened part is all important if assurance is to be had that the fusible strip will always blow at this point. Many prior fuses of this type have failed because the strip would often blow below the disc and not at the weakened part as anticipated.

I have discovered that to assure the certainty of the strip blowing at the weakened part, the width of this part must not be greater than .065 of one inch, (the gauge of the strip varying in thickness according to the load the fuse is to carry.) I have alsofound it advisable to make the weakened part comparatively long. In fact, I make it almost as long as the whole exposed part of the strip. With this construction, there is no danger, even with a slow overload on the fuse, that the strip will blow at any other place than within the pockets 20.

The disc Il may be made of any non-conduc ing material and I have found that ordinary stiff paper will serve very well. The disc may be made circular, as shown in Fig. 4 and of a size to fit within the cap I 2, but I prefer to make it square or rectangular so that the corners 23 will be clamped down between the cap I2 and the body part I0. Furthermore the square shape is cheaper to produce.

It will be noted that the two tongues form two shallow chambers one on each side of the exposed part of the fusible strip. If symbols, such as for example an O and a K, are imprinted, one on each of the tongues or in line with the tongues, it is evident that, when the fuse blows, the chambers formed by the tongues will direct the gases so that they will flow over these symbols and obliterate them.

What actually takes place is that the gases soot and partially scorch the underside of the mica disc and the upper side of the paper disc. As this sooting and scorching takes place over and in line with the tongues it is evident that the symbols are sure to be obscured. In other words, a sooted streak is formed across the mica disc which will show very plainly, even when the mica disc is quite dirty and dusty as it may be from long use. The gases finally escape into the interior of the fuse through the opening of the tongues.

Figs. 7 and 8 illustrate the manner in which the fuse is vented so that the gases may escape from it without any fire hazard. The upper face of the body member ID is scored with a number of grooves at right angles to each other so as to form a plurality of raised points with a plurality of tortuous channels between them, as shown at 24. After the gases enter the interior chamber M, they are free to escape through these tortuous channels, still, if the gases should be ignited, the flame will be extinguished before it can pass through the channels.

The paper discs may be made in various colors to indicate the capacity of the fuse or the capacity may be imprinted on the disc, as shown in Figs. 4 and 5.

From the foregoing it -will be seen that this construction contains the essential elements for assuring the correct operation of the fuse. The shallow pockets not only prevent too rapid dissipation of the gases, but effectively direct them over the parts which are to be obscured. The tongues prevent excessive pressure on the mica disc, the correct weakening of the fusible link assures it blowing out at the correct place, and the channels remove any danger of fire. Furthermore, the only addition to the ordinary fuse is the paper disc which can be manufactured at very low cost and inserted without altering the ordinary assembling processes of the fuse.

Having described my invention and its objects, what I claim as new and wish to protect by Letters Patent is:

The combination with a fuse plug of the type comprising a one-piece body member made of insulating material and having an interior recess covered with a transparent disc, a threaded metal shell secured on the outside and. a metal contact secured in the bottom; of a fusible metal strip under said strip to form shallow pockets on both sides thereof, said disc clamped between the end of the body member and the transparent disc, and the fusible strip having a weakened portion contained within said pockets.

LOUIS LUDWIG.

Images