Flat band and buckle assemblies, also known as ties, have existed for sometime for use in bundling or securing objects together. Typically, a tie, comprising an elongate band having a free end and a buckle at the opposite end, is wrapped around a group of objects with the free end passed through the buckle. The buckle and overlapping band are secured in some fashion to thereby constrain the group of objects. Similarly, tools for tightening bands around objects, for securing or locking the free end of the band within a buckle or locking member and for cutting any excess portion of the band have existed for some time. Typically, these tools grasp the free end of the band after it has passed through the buckle and apply a force to the free end of the band while simultaneously maintaining the position of the buckle to tighten the band around the group of objects. Once an appropriate tension is applied to the band, the tool will create the desired locking geometry in the band and shear the portion of the free end of the band extending through the buckle. Typically, a pair of opposed knife-edges perform the shearing or cutting operation. One blade is stationary and is positioned beneath the free end of the band and the other knife reciprocates between a first and second position. Each knife-edge comprises a single linear blade or edge that simultaneously engage and simultaneously cut the entire width of the band at once.
Tools that perform the tightening, locking and cutting functions are primarily manual, pneumatic or electric in nature. In the case of pneumatic or electric tools for use in such purposes, the power generated results in these functions being accomplished with limited or reduced physical efforts required by the operator. Band tightening tools that are pneumatic or electric are usually semiautomatic in that the operator of such a tool is required to perform some, but not all, of the tasks or functions associated with providing a band clamp about an object. Manual tasks that remain can include locating the band or tie about the object and inserting or otherwise locating the band clamp relative to the tool so that a tool can perform one or more of its tightening, locking and cutting functions. In one such device, a desired tension can be set for the band clamp about the object. A pneumatic cylinder or similar component is activated to pull the band until the desired band tension is reached. Pneumatic control can also be involved with cutting the free end or band tail portion after the band clamp is tightened, and which can also involve forming a lock that prevents unwanted release of the band clamp.
Current band clamps, however, have significant drawbacks. For example, there is a need for improving loop tensile force (the force required to break the band or separate the lock) other than by simply increasing the physical size of the band. Also, there is a need for improving the percentage of retained force (the residual force in the band after forming the lock). Stated differently, there is a need to reduce or eliminate the force that is lost following formation of the lock and release of the band by the tool. For a number of reasons, including tolerances and imprecise metal forming techniques, once the tool cuts the free end of the band, a portion of the band slips back through the buckle expanding the circumference of the band, a portion of the retained tensile load is lost, and the percent retained force decreases. The lock may also relax or loosen over time, causing the band to expand, particularly if the outward force applied on the band by the constrained objects is large or if the band and buckle are subjected to external forces such as vibration or other motion causing relative motion of the band and buckle. Still further, there is a need in some applications to increase the clamping force (the maximum force reached just prior to the band tightening tool cutting off the excess end of the band). The clamping force is related to the retained force. Typically, the higher the clamping force, the higher the retained force. Unfortunately, there are upper limits to the clamping force in some applications, as the objects being clamped may be damaged if too large a clamping force is applied.
A prior art band clamp is shown in FIGS. 18-20. It consists of a band 10 and a buckle 12. The buckle is secured to a first end 14 of the band, between a retaining dimple 16 and a load dimple 18, generally preventing axial or lateral movement of the buckle relative to the length of the band. In the embodiment shown, the buckle comprises a box-like piece of metal having two side walls 20, a bottom 22, a top 24 and two open ends 26 which permit two layers of the band to pass through the buckle. The top of the buckle 24 has an opening 28 aligned with a similar opening 30 formed in the first end 14 of the band and another opening 32 formed in bottom 22 of the buckle.
A locked band clamp using a prior art tool is illustrated in FIG. 21. As used, the free end 34 of the band is wrapped around one or more objects and inserted into the buckle 12 above the first end of the band 14, thereby creating an overlapping band portion 36. Using a tool of the type generally known to those of skill in the art, the free end 34 of the band is grasped and pulled while the buckle 12 and first end of the band 14 are held stationary by abutting the buckle against a front surface of the tool and positioning the free end of the band clamp over an underlying cutter blade. A punch 38 having a conical shaped tip 40 is then driven through the upper opening 28 and forced into the free end 34 of the band 12 to form a locking dimple 42 in the free end 34 of the band. The locking dimple 42 extends through the opening 30 in the first end of band 14. The aperture 30 defines a two-dimensional area, bounded by surface 44, that defines where the locking dimple 42 may be formed. In general terms, the locking dimple 42 fixes and secures the circumference of the band by abutting the inside surface 44 of the opening 30. The constrained or banded objects place an outward force on the band which, in turn, causes the circumference of the band to expand until locking dimple 42 abuts the inside surface 44 of the aperture 30. The inside surface 44 of the aperture 30 may also be referred to as a load bearing surface.
Simultaneously, a knife 46, as shown in FIGS. 5 and 6, is lowered to cut the free end of the band in conjunction with the underlying cutter blade. The knife 46 includes a single linear blade or cutting edge 48 that extends across the width of the band. The knife-edge engages and cuts the entire band width at once. Therefore, a significant portion of the force driving the tool is applied to cutting the band rather than driving the punch to form the locking dimple. Once the band is cut, the tool no longer holds or constrains the band clamp. Also, there is no further downward travel of the punch, no further formation of the locking dimple and the tool releases its hold of the free end of the band.
The manner in which the locking dimple 42 is formed limits the retained tensile force of the band and contributes to loss of tensile force due to band slip-back. A punch 38 is attached to and extends out in front of the knife 46. Typically, the punch is oriented perpendicular to the band. As the knife 46 travels toward the band, the punch 38 begins formation of the locking dimple 42. When forced against the free end 34 of the band 12, a conical shaped locking dimple 42 is created, as shown in FIG. 21. Moreover, the process of cold forming the locking dimple in combination with the pointed conical tip 40 causes the walls 50 of the locking dimple to be thinner or non-uniform in thickness at the base 52. In addition, and primarily due to manufacturing tolerances, the location of the locking dimple 42 may vary laterally along the band. In particular, the locking dimple 42 may be formed anywhere within the area defined by the inside surface 44 of the opening 30. The lateral or axial distance between the inside surface 44 of the opening and the wall 50 of the locking dimple 42 is shown as Δx1 in FIG. 21. As a result, when the free end of the band is cut and the tool releases its grip of the band, the band 12 will laterally release or slip-back at least the distance Δx1, as shown by comparing FIG. 21 with FIG. 22. Moreover, additional slip-back may occur, immediately or over time, due to the conical shape of the locking dimple 42 and the relative freedom of movement that the band has in the “Z” direction (Δz as shown in FIGS. 21-23). In particular, the space 54 defined between the top 20 and bottom 22 of the buckle 12 is greater than the combined height of the overlapping bands. This space permits the free end 34 of the band to pass through the buckle. The additional height also permits the overlapping bands to move vertically within the interior space 54 of the buckle, as shown in FIG. 22. This additional degree of movement, combined with the sloped outer wall 50 of the locking dimple 42, also allows further slip-back of the band, as illustrated in FIG. 23 as Δx2. Thus, even if the locking dimple 42 were initially formed abutting the interior surface 44 of the opening 30 such that there was no Δx1, as shown in FIG. 21, lateral slip-back would still occur due to the freedom of movement allowed by the gap Δz in combination with the sloped surface 50 of the locking dimple, as shown in FIG. 23. This results in further loss of the retained tension force.
Often, end users specify a retained tensile force for their end use applications, for example, 600 pounds. If the tie being used has a fifty percent loss in retained tensile force following locking and cut off of the free end, then the tie, just prior to locking and cut off, must have a tensile load or clamping force applied to it in the amount of 1,200 pounds to accommodate the fifty percent loss of tensile force. In many situations, the applied or clamping force can exceed the tensile load of the band, causing it to fail. This is more often true when clamping objects having hard surfaces.
Yet the process of forming conical shape of the locking dimple 42 causes another problem. The conical shape of punch tip 40 causes the walls 50 of the locking dimple 42 to be thinned, even to the point that there is no material left in the wall of the dimple, as they are cold formed. The non-uniform or thin portion 52 creates a weak spot that is susceptible to the shear forces acting on the locking dimple 42 by the retained tensile load. The additional height (Δz) creates a freedom of movement inside the buckle and allows the sloped walls 50 to ride up the edge 60 of the inside surface 44, further opening the band and releasing retained tensile load. The thinned portion 52 will then abut the inside surface 44 of the aperture 30, as shown in FIG. 23. When the retained load is applied against the thinned portion 52 of the walls of the locking dimple, a failure may occur where the edge of the surface 44 shears off the locking dimple or causes the locking dimple to collapse. Thus, the locked band will fail and the bundled objects will be released.
In addition to the foregoing problems, other considerations are relevant in designing a band clamp. First, the clamp should have a high tensile strength to resist the outward tensile force exerted on the clamp by the constrained objects. Second, the clamp should be inexpensive to manufacture. Band clamps are used in a variety of applications where cost is a concern. Thus, simply increasing the physical size of the clamp does not address all of the design considerations. A physically larger band clamp will have a greater loop tensile force, but it will cost more. Also, the band clamp should be simple in design and easy to use.