BACKGROUND
1. Field of Invention
This invention relates specifically to a retaining device for drill steels used on percussive rock drills.
2. Description of Prior Art
Every percussive rock drill includes certain basic features. A striking piston imparts impact energy to a drill steel and bit, a rotation mechanism causes the drill steel to rotate to give the bit a fresh rock surface to strike with each blow, and a drill steel retention mechanism allows removal of the drill steel and bit when the hole is completed.
Manufacturers of small drilling rigs, designed to drill holes in the range of 1¼ to 2 inch diameter, typically use hand-held drills that are modified for mounted use. Modifications may be as simple as removing handles and locking control valves in the “on” position. Hand-held drills have a variety of drill steel retainer designs, each with its own disadvantages. One type is too weak to resist the pulling force of a mounted arrangement. A second type can withstand a strong pulling force but sometimes cannot be opened if the drill steel becomes stuck in the drilled hole. A third type can withstand a strong pulling force but is difficult to open and expensive to manufacture.
SUMMARY
The object of the present invention is to provide a simple and positive drill steel retention method, capable of withstanding strong pulling forces while being easy to open.
DRAWING FIGURES
FIG. 1 is a perspective view of a rock drill that embodies the object of this invention.
FIG. 2 is a perspective view of a prior art steel retainer in the engaged position.
FIG. 3 is a perspective view of a prior art steel retainer in the disengaged position.
FIG. 4 is a front view of a prior art steel retainer in the engaged position.
FIG. 5 is a cross-section view of a prior art steel retainer in the engaged position.
FIG. 6 is a cross-section view of a prior art steel retainer in the disengaged position.
FIG. 7 is a perspective view of a second prior art steel retainer in the engaged position.
FIG. 8 is a perspective view of a second prior art steel retainer in the disengaged position.
FIG. 9 is a front view of a second prior art steel retainer in the engaged position.
FIG. 10 is a cross-section view of a second prior art steel retainer in the engaged position.
FIG. 11 is a cross-section view of a second prior art steel retainer in the disengaged position.
FIG. 12 is a perspective view of a third prior art steel retainer in the disengaged position.
FIG. 13 is a perspective view of a third prior art steel retainer in the engaged position.
FIG. 14 is a front view of a third prior art steel retainer in the engaged position.
FIG. 15 is a side view of a third prior art steel retainer.
FIG. 16 is a cross-section view of a third prior art steel retainer in the engaged position.
FIG. 17 is a cross-section view of a third prior art steel retainer in the engaged position.
FIG. 18 is a perspective view of the new steel retainer in the engaged position.
FIG. 19 is a perspective view of the new steel retainer in the disengaged position
FIG. 20 is a front view of the new steel retainer in the engaged position.
FIG. 21 is a front view of the new steel retainer in the disengaged position.
FIG. 22 is a cross-section view of the new steel retainer in the engaged position, and
FIG. 23 is a cross-section view of the new steel retainer in the disengaged position.
DESCRIPTION
Conventional drill steel retainers for hand-held drills may be placed into three general classifications with certain common characteristics. The most significant common characteristic is the lack of full circle contact between the retainer and the drill steel locating shoulder. This characteristic may be clearly seen by referring to FIGS. 2, 3, and 4. Shoulder 60 positively locates drill steel 50 during drilling and while retracting from a drilled hole. Opening 111 in retainer 102 is in the form of a circle with one side removed. When shoulder 60 is pulled against retainer 102 during retraction of drill steel 50 from a drilled hole, as in FIG. 2, the non-symmetrical loading between shoulder 60 and retainer 102 urges retainer 102 toward an open position as in FIG. 3. It is not uncommon for retainer 102 to open suddenly while trying to retract drill steel 50. The result is lost productivity, excessive wear on components, and possibly a lost drill steel. Examples of prior art drill steel retainers illustrate various methods of keeping a retainer closed during use. The subject invention shows a superior way of keeping the retainer closed during use while allowing ease of opening when desired.
The first type of drill steel retainer is frequently referred to as a “yoke” retainer. FIGS. 2 through 6 show a typical example, although there are many variations. Retainer 102 is attached to housing 101 by bolt 104, which has a flat surface 109. Retainer 102 is held in the closed position by a spring 106 and cam 110 acting against surface 109. Bolt 104 is constrained to rotate with retainer 102 about the centerline of bolt 104. When attempting to retract a drill bit and drill steel from a drilled hole, retainer 102 contacts shoulder 60 on drill steel 50 and transfers the retracting force to drill steel 50. FIGS. 3 and 6 show retainer 102 in an open position. With retainer 102 in the open position, shoulder 60 on drill steel 50 encounters no resistance and may be easily removed from housing 101. FIG. 6 clearly shows that the rotation of surface 109 has caused spring 106 to be compressed, creating a closing force on retainer 102. The primary disadvantage of the “yoke” retainer is that the force holding the retainer closed is small and is easily overpowered. When the steel and bit are being retracted from a drilled hole by an operator's lifting efforts, the “yoke” retainer is usually strong enough. In a mounted application, the drill feed mechanism is capable of pulling much harder. Stronger pulling force is an advantage if the drill steel and bit become stuck, but the “yoke” retainer frequently pops open when subjected to this higher force and is incapable of withdrawing the drill steel and bit. If the geometry of the spring and cam mechanism is changed to provide more resistance to opening during operation, this same resistance makes the “yoke” retainer more difficult to open when removing the drill steel.
The second type of drill steel retainer is frequently referred to as a “beavertail” retainer. FIGS. 7 through 11 show a typical example, although there are many variations. Retainer 202 is attached to housing 201 by bolt 204. In the closed position as shown in FIGS. 7, 9, and 10, any pulling force exerted by shoulder 60 of drill steel 50 causes retainer 202 to try to rotate around bolt 204. This rotational force is resisted by shoulder surface 205 on retainer 202 as it rests against surface 206 on housing 201. The “beavertail” retainer cannot be overpowered by a large pulling force because the pulling force urges the retainer toward a closed position. The primary disadvantage of the “beavertail” retainer is the possibility that it may become jammed in the closed position if drill steel 50 has been driven into the ground until drill steel shoulder 60 contacts retainer 202, and the drill bit becomes stuck. The pivoting action of the “beavertail” retainer around bolt 204 when being opened will move the drill steel backwards toward the drill. If the drill steel cannot move, the retainer cannot be opened. FIGS. 8 and 11 show retainer 202 rotated to the open position.
The third type of drill steel retainer may be referred to as a “sliding gate” retainer. FIGS. 12 through 17 show a typical example, although there are many variations. Retainer 302 is slidably mounted in housing 301. Retainer 302 contains an elongated slot consisting of two overlapping holes 303 and 304. Hole 303 is larger than the diameter of drill steel 50 but smaller than the diameter of drill steel shoulder 60. Hole 304 is larger than the diameter of drill steel shoulder 60. FIG. 12 shows retainer 302 in the open position wherein hole 304 is concentric with drill steel 50, and drill steel 50 may be retracted from housing 301. FIG. 13 shows retainer 302 in the closed position wherein hole 303 is concentric with drill steel 50, and drill steel 50 is retained in housing 301 by contact between drill steel shoulder 60 and retainer 302. When attempting to retract a drill bit and drill steel from a drilled hole, retainer 302 contacts shoulder 60 on drill steel 50 and transfers the retracting force to drill steel 50. FIG. 17 shows the mechanism by which retainer 302 is held in the open or closed position. Ball 306 is loaded by spring 305, and spring 305 is retained by plug 307. When retainer 302 is in the closed position ball 306 protrudes into depression 309, and retainer 302 can only be moved out of the closed position by overcoming the force exerted on ball 306 by spring 305. When retainer 302 is in the open position ball 306 protrudes into depression 308, and retainer 302 can only be moved out of the open position by overcoming the force exerted on ball 306 by spring 305. The force required to move retainer 302 out of the open or closed positions may be regulated by varying the force exerted by spring 305. The primary disadvantage of the “sliding gate” retainer is that the force holding the retainer closed is directly related to the force exerted by spring 305. If the geometry of the spring and cam mechanism is changed to provide more resistance to opening during operation, this same resistance makes the “sliding gate” retainer more difficult to open when removing the drill steel. In practice, it is frequently necessary to strike the end of retainer 302 with a heavy object in order to overcome the force exerted by spring 305 on ball 306. A further disadvantage of the “sliding gate” retainer is the manufacturing complexity involved in slidably mounting retainer 302 in housing 301.
A superior steel retainer mechanism, the object of this invention, is shown in FIGS. 18 through 23. Retainer 402 is attached to housing 401 by shouldered bolts 404 and 405. Retainer 402 is allowed to pivot around bolt 404, and slot 412 in retainer 402 engages bolt 405. Tensioning device 409, which may be a Belleville spring or other means, prevents retainer 402 from rattling or otherwise experiencing uncontrolled motion. Latch 403 is attached to housing 401 by shouldered bolt 407. Latch 403 is allowed to pivot around bolt 407 but is held against pin 413 by spring 406. Shoulder 411 on latch 403, by contact with shoulder 410 on retainer 402, prevents retainer 402 from being opened. The geometric relationship between shoulder 411 and the center of bolt 407 is such that any force exerted by retainer shoulder 410 on latch shoulder 411 causes latch 403 to rotate in a counterclockwise direction against stop pin 413. Latch 403 thereby provides a positive locking mechanism for retainer 402. When latch 403 is rotated clockwise slightly around bolt 407 against the small force of spring 406, shoulder 411 is no longer engaged against shoulder 410 and retainer 402 can be rotated around bolt 404. When retainer 402 has been rotated sufficiently to bring shoulder 414 in contact with shoulder 411, as in FIG. 21, retainer 402 is fully opened and drill steel 50 can be removed. It may readily be seen that the new steel retainer mechanism shown in these figures is superior to the “yoke” retainer and the “sliding gate” retainer because it provides a positive locking mechanism that is easily opened whenever desired. The new steel retainer mechanism is superior to the “beavertail” retainer because it does not depend on movement of the drill steel in order to be opened. Additional benefits may be seen by recognizing that retainer 402, being essentially a flat plate with a predetermined shape, is much simpler in its geometry than retainer 102, retainer 202, or retainer 302. The simpler geometry of retainer 402 permits a more compact assembly and also reduces manufacturing complexity and cost.
CONCLUSION RAMIFICATIONS, AND SCOPE
The reader will see that the drill steel retainer of the invention provides a positively locking device that will not open under load yet may be easily opened whenever desired. Furthermore, the subject drill steel retainer has additional advantages in that
- it can be opened easily with one hand, without the use of any tools; and
- it is simple in construction and thus easy to manufacture.
Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing an illustration of the preferred embodiment of this invention. For example, in the preferred embodiment the retainer pivots around an axis parallel to the axis of the drill steel. In an alternative embodiment the retainer might pivot around an axis perpendicular to or at some other angle to the axis of the drill steel. Likewise in the preferred embodiment the latch pivots around an axis parallel to the axis of the drill steel. In an alternative embodiment the latch might pivot around a different axis or might have a sliding motion rather than a pivoting motion. In the preferred embodiment the retainer and latch are attached to the housing with shouldered bolts. In an alternative embodiment the retainer and latch might be attached by some other means that allows a free pivoting action.
Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.
Patent Grant
7044479
