Automated accurate rubber strip stacking--part 2.

(This article is continued from the March 2004 issue.)

The current situation

It is apparent that the use of and need for narrow rubber strips to supply feed material for rubber injection molding machines and extruders has increased dramatically over the past few years. This, in turn, has increased the demand for accurate (and dense) strip stacking.

Accurate strip stacking of narrow rubber strips has traditionally been a manual function, in order to lay strips into a basket or on a pallet, one or two laborers are required. Each laborer must fold the strip at the end of the pallet and start the strip back toward the opposite end. The labor is tedious and repetitive, and the speed of the mixing line is limited by the speed the operator can stack. A manual stack is shown in figure 7. Note that it is a very accurate and dense stack.

[FIGURE 7 OMITTED]

First generation accurate strip stacker

The accurate strip stacker, also known as an AccuStrip stacker, was developed to resolve the problems associated with manual stacking (i.e., labor intensive, slow, ergonomically questionable and costly). The intent of the first generation AccuStrip stacker was to meet the needs of a single strip compound with a fixed dimension strip and a fixed dimension pallet or basket. The machine proved to be very useful for tire manufacturers and other users who ran a single compound at a fixed width, but it did not meet the needs of custom compounders and smaller users who were constantly changing strip widths, thicknesses, compounds and even pallet sizes.

The multi high density stacker

Simultaneous with the development of the AccuStrip stacker was the development of the multi high density (MHD) stacker. The MHD stacker was designed to stack narrow rubber strips into baskets or boxes. But this machine is also capable of stacking wide strips and multiple narrow strips. Hold-down flap assemblies are included to guarantee the folds at each end of the basket. As the flaps fit into the basket, the basket size is predetermined at a fixed size. The MHD stacker includes a programmable oscillating inlet conveyor with a pinch roll at the top, a driven hugger-belt wigwag, flaps, lift, necessary frames and controls.

Together, the first generation AccuStrip stacker and MHD stacker (figure 8) solved the problems of stacking a dense stack of rubber strip on a pallet or in a box, but there were limitations, as described previously. A new design was required to fulfill the requirements of custom compounders and other producers of various rubber strips.

[FIGURE 8 OMITTED]

State-of-the-art accurate strip stacker

Automated accurate narrow strip stacking was made possible with the invention of the AccuStrip stacker and the MHD stacker, but with limitations as to pallet size and strip parameters. And the new accurate strip stacker does indeed solve these problems. Narrow strips from 1" to 6" wide and 3/16" to 5/8" thick can be automatically stacked by the machines. High degrees of control have been incorporated into the systems to allow automatic detection of strips, automatic feeding, speed control, automatic threading, automatic stacking on pallets, weight control, automatic cutoff on a signal that the pallet is full (based on weight or height of the stack) and automatic handling of empty and full pallets. Communication to overhead systems is available to define current stock identification, skid information and stacking information. Even multiple pallet sizes and stack dimensions, including rectangular patterned stacks, can be accommodated.

These state-of-the-art accurate strip stackers have been successfully installed in tire plants, automotive parts suppliers and custom compounders.

The custom compounder model

A custom compounder has a successful installation of a system of four AccuStrip stackers, as shown in figure 9. This system includes individual strip conveyors from the batch-off machine, 90[degrees] turns, automatic strip detection, strip speed control, automatic threading, accurate and automatic stacking, automatic cut-off upon full skid and skid handling.

[FIGURE 9 OMITTED]

Each of the four AccuStrip stackers removes narrow rubber strip from a cooling rack and automatically feeds it through the indexing head, which accurately lays the strip onto a pallet. After completing one or two layers of the strip on the pallet, the pallet is turned 90[degrees] and stacking continues. This creates a cross layering of the strip for increased stack stability and density. When the strip reaches the desired height, a hot knife automatically cuts it off. After the stack is complete, the lift table is lowered onto a skid conveyor, which removes the full pallet and brings an empty pallet into position for the next cycle. All of the parameters for the pallet size, strip overlap, strip length on the pallet, stacking pattern, etc., are programmed by an overhead control system or a touchscreen controller.

Prior to this system installation, the stacking of the four strips was done by hand. Four human stackers, plus one trucker, created a labor-intensive operation and lost mixing time. But now, this four-machine system requires only one operator to monitor it and load and unload pallets.

Extruder line

One manufacturer installed a single AccuStrip stacker system, as shown in figure 10. The rubber strip is led from an extruder through a RotoStrip cooler for coating, cooling and drying. Then it is conveyed through a metal detector and on to the AccuStrip stacker. Pallets are stored in a pallet magazine and fed automatically via a chain conveyor to the AccuStrip stacker. After the pallets are full, they are conveyed to the discharge end for removal by a fork truck as a new pallet is fed to the stacking position.

[FIGURE 10 OMITTED]

AccuStrip stacker (stand-alone unit)

The basic single stand-alone unit AccuStrip stacker, as shown in figure 11, includes loop control, stock detection, overhead transport conveyor, three-axes motion (including one turntable), driven pinch rollers, flaps and PLC system controls with an HMI, variable speed drives and linear transducers. This machine also includes transport wheels. The wheels allow the end user to move the AccuStrip stacker to a variety of different machines for accurate stacking of strips. Note that the speed of the left and right motion of the stacking mechanism allows varying the overlap of the strip layers from no overlap to total overlap. Overlapping the strips a small amount along with the 90[degrees] turn creates a denser and more stable stack with better release properties than when the layers are stacked flat without the turn.

[FIGURE 11 OMITTED]

Conclusions

* Spools are for low volume and/or fragile stock.

* Wind-up with liner is for no anti-tack.

* Manual stacking is for short runs and low volume.

* Notched sheet accurate wigwagged stacking is high volume, but multiple strips are on the same skid.

* Multiple high density stacking is for stacking in boxes or two strips on a pallet.

* AccuStrip stacking is for high volume and/or multiple stack and strip sizes.

* No one solution is ideal for all users, stock specifications or processes.