Dual Strip Feeders
niche markets have always existed
and companies trying to fulfill them often develop interesting machinery to meet customer requirements. The dual strip feeder is just one of the many strange breeds of feeding equipment found in today’s stamping rooms.
My first encounter with a dual strip machine was when a customer inquired about building such a machine for the manufacture of hose clamps. The machine was such a success that they to this day they insist that it doesn’t exist. Since then several other successful applications have been undertaken.
Feeding Two strips is not without its complications.
· Many times the customer also wants to run one strip that spans the width of the whole feeder.
· Spacing between strips varies widely
· Payoff and straightening equipment may need to be modified
· Tooling will need to be redesigned for dual strip operation.
Increased Profit is the point.
Without a pay back the whole exercise would be fun but really a waste of time. Aside from the design challenge associated with dual strip feeding it can be an effective means to increase production with a modest investment.
The key to obtaining proper dual strip performance is getting the proper grip on each strip. If you attempted to run two strips for instance through a set of pinch rolls and one strip was thicker than the other then it would tend to lift the roll off the other strip. In the world we live in one strip is always thicker than the other, Different amounts of slitter induced crossbow, camber, and gauge variations, insure that no two strips are exactly the same thickness. This fact led to the development of the Twin top roll series of feeders.
The easiest way (for the feed builder) to build a dual strip system is to use two separate feeders. Stampers using this method also get the ability to run two different feed progressions for completely different parts. This method is suited to applications where the physical dimensions of the feeders allow them to be mounted close enough together to accommodate the strip spacing dictated by the tooling constraints.
Independent Suspension
Just as independent suspension help keep your car level in a turn the twin top roll method of dual strip feeding allows the upper roll on each strip to remain parallel to the bottom roll making strip guiding much easier
Two types of Twin top roll feeders are the cantilevered and Supported.
Supported systems (see Figure 2) have shafts and bearing blocks on each roll
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end while cantilevered types feature outboard support with an un supported section (the driveling section) The driving section is backed up to provide a method of minimizing deflection.
allow two strips to be as close together as the edge guide design will allow.
Uncoilers
Due to differences in material thickness and differences in initial coil diameters a dual uncoiler system must be used. Fully independent control of each coil must be maintained to insure proper loop control operation. Operating with two different diameters on a common spindle results in one strip uncoiling at a different rate from the other and results in one loop gaining material faster than the other. Soon one loop is so much larger than the other that loop control failure results.
Since feeding with roll feeds requires that the material be payed off in a straight line the uncoilers should be arranged in a staggered formation (see Figure 1) and should be placed for proper strip spacing. When feeding with a roll feed alignment is everything. Bad habits at the start of a line usually end up as strip damage and misfeeds at the end. Take the time to properly align your equipment because not to do so can only result in problems.
Loop controls
Certainly one of my favorite subjects bad loop controls and non-regenerative payoff drives can often be the limiting factor in achieving maximum line performance. Since we are using a servo driven roll feed we should also have a high performance straightening and payoff drive system.
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NEW We also have a new design with inside-out inner shafts that allow .5 inches inner roll edge separation with full support. |
Straightners
Experience with two strips through one straightner although limited shows that reliable results cannot be achieved due to similar drawbacks encountered in using a standard roll feed for dual strip feeding. One strip is thicker than the other causing slippage of the thinner strip. Proper loop control is difficult and may be erratic which can be the same thing as non existent.
The standard thing to do when a strip is slipping is to increase the roll pressure, in dual strip applications this almost always results in a bending of the straightening rolls and induces all kinds of deformation of the strip. Not to mention the additional load placed on the straightner.
Offsetting two straightners (see Figure 1) at the proper strip spacing will insure consistent straightening and allow for positive and accurate loop control operation.
Typical applications include:
Most high volume narrow strip parts
Hose clamps
Shelving parts
left and right matching parts