Strap welding system and method

Package making – Methods – Applying a partial cover

Reexamination Certificate

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Details

C053S438000, C053S529000, C053S590000, C100S002000, C100S003000, C100S0330PB, C156S073500

Reexamination Certificate

active

06487833

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to an apparatus for automatically strapping bales of cotton or other fibers or stacks of lumber or bricks or other items that are suitable for strapping. This invention relates more particularly to a system and method for welding the ends of thermoplastic straps together so as to form bales of cotton or so as to bind together any other desired material or items.
BACKGROUND OF THE INVENTION
In the cotton or fiber industry, the normal method of banding or tying cotton bales has been to have workmen direct a tie, such as a band or wire, around a pressed cotton bale and then secure the ends of the ties appropriately, depending on the design of the tie. In the cotton or fiber industry, there are generally three ways to secure a bale after the bale has been pressed. Pertinent securing means include pre-formed steel wires that have interlocking ends pre-formed to define loops which engage one another during a tying operation, flat ribbon-steel bands which have their ends inserted into a crimp by which they are secured, and flat thermoplastic strapping material, typically formed of polypropylene or polyester, which has its ends welded together.
The steel pre-formed wires have a loop manufactured into each end thereof. The ends are interlocked around to form a square knot. When the pressure is released from the bale, the knot formed by the interlocking loops pulls tight and retains the bale against further expansion. In a conventional bale-tying operation, two workmen (one on each side of the baling press) manually bend the wires around the bale and secure the ends of the wires together in a wire tie guide assembly. The wires are normally tied together sequentially, one at a time.
Alternatively, the wires might be tied in a hydraulically operated wire tying device mounted on a baling press. The hydraulically operated wire tying device ties a plurality of wires having pre-formed interlocking ends around a bale formed in the press. Pivotally mounted wire bending assemblies take the place of workmen on each side of the baling press. The pivotally mounted wire bending assemblies bend the tie wires around the bale by inserting the ends of the tie wires into a wire tie guide assembly. However, workmen are still required to individually load each of a plurality of tie wires into the wire bend assemblies.
Although an improvement over the manual bale tying operation, the hydraulically operated wire tying device still exhibits certain problems which slow the baling process. Exact timing is required for the sequence of events which make up the wire tying operation. If a wire does not follow the correct path at the correct time, several factors can combine to prevent the interlocking ends of the wire from engaging to form a knot.
In particular, the interlocking ends of the wires are conventionally oriented such that the loops are disposed in a generally horizontal plane. This geometric orientation forces the wire closers to be constructed with relatively wide cavities, in order to accommodate the wide aspect ratios of the loops. This, in turn, allows the wires a greater degree of freedom of movement within the cavities. Consequently, there is a greater probability of one wire merely sliding past another, without their loops engaging in a knot.
In addition, press wear, both alone or in combination with component manufacturing tolerances, can cause a follow block to vary its position or orientation both vertically or from side to side. Consequently, the wire bend assemblies may not be in alignment with the wire tie guide assemblies. All of the above-described cases result in mis-ties, with a consequent undesirable loss of time and possible damage to the press.
Bale tying using flat steel straps is hindered primarily by. the cost of the strapping material, the complexity of the machinery used, and the speed at which the machinery is able to operate. In addition, both the weight of steel strap tie material and its substantially sharp edges make it cumbersome and particularly dangerous to handle.
Further, once it is removed from a bale, steel strapping material is not easily recycled by an end user. Removal is difficult, and once removed, a large volume of sharp material must be colleted and crushed together to form the material into a package that can be more easily handled.
Additionally, steel strap tie material is further disadvantageous in that its weakest point (the joint) is located in the highest stress position on the bale. This is true because the forming machinery is only able to apply a joint, i.e., a crimp, on the side of the bale (the position of the bale with the highest degree of lateral pressure or stress). This non-optional position of the crimp results in significant tie breakage with a consequent loss of bale integrity.
Conversely, plastic or non-ferrous strapping is an ideal material for strapping bales of cotton or other fibers. Indeed, such plastic strapping may be used to strap a wide variety of different items, such as lumber or bricks, as well as many other materials which are suitable for such strapping. As those skilled in the art will appreciate, plastic is relatively light in weight and can be formed into a variety of widths and thicknesses. Plastic also has comparatively soft or non-sharp edges which allows for easy handling. Its reduced weight lowers shipping costs. This plastic or non-ferrous strapping material is very competitive with both wire ties and metal strapping, on a cost per bale basis. Further, plastic strapping is easily adaptable to fully automatic welding machinery. Plastic strapping material is readily recyclable by the end user and is considered substantially safer than steel strapping material, particularly in instances of strap breakage wherein the sharp edges of the steel strapping frequently move violently and dangerously in response to breakage.
Because of the particular orientation of conventional plastic strap automatic tying machinery, certain disadvantages arise when one adapts strapping and joint forming apparatus to the structure of a baling press. Typically, automated thermoplastic strapping machinery, including a material feeder, tensioner, cutting shear and joint former, are so large that they are precluded from being able to be placed anywhere except on the side of the bale. As was the case with steel strapping material discussed above, thermoplastic strapping joint formation therefore takes place in the region of the bale that exhibits the highest degree of tensile stress.
In this regard, conventional thermoplastic strapping machinery must typically wait until a baling press has completed operation and has reached “shut height” before it begins the strapping operation. The strapping head pulls strapping material off of a spool and directs it around the bale through a series of shoots, until the front edge of the strapping material has completed its circuit of the bale and is directed back to the region of the strapping head. The strap is then pulled tight around the bale to a pre-determined tension and the strap is then cut with a shear. The two ends are then joined by a friction weld, hot knife weld, or other similar joint forming operation, and maintained together until the joint is cool, in which time the strap is released and allowed to carry the tensile load of the bale.
Referring now to
FIGS. 1
a
,
1
b
and
1
c
, there is shown a semi-schematic view of cotton, or other fibers, being pressed into a bale
14
between the platens
24
and
25
of a hydraulic press
16
,
23
in accord with the prior art. Typically, fiber is pressed by a large hydraulic cylinder out of a box that measures approximately 30 inches wide by 54 inches long and 144 inches deep. Such a box is typically filled with approximately 500 pounds of cotton lint which is subsequently pressed into a 20 inch by 54 inch bale
14
measuring approximately 20 to 22 inches tall (in accordance with the illustration of
FIG. 1
a
). The box from which the bale
14
is pressed has been omitted for the sake of illustration

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