How To Get The Most From Your Edge Bead Reduction Equipment

The edge bead reduction mechanism is an important feature of today's extrusion coating dies, such as the Black Clawson Converting Machinery ROI Die. Although its proper use can significantly improve the productivity of your line, it does take some knowledge to fully realize its potential. This BC Tech Tip is intended to provide the die operator with the background and information necessary to get the most out of the edge bead feature.

What Is Edge Bead?

Edge bead is formed when the polymer in the melt curtain is drawn down and necks-in. The amount of neck-in affects the thickness of the edge bead - the greater the neck-in, the greater the edge bead.
Some common factors that affect edge bead are:

The shape of the neck-in affects the profile of the edge bead.
Low-viscosity and/or melt strength resins generally neck-in more and will have greater bead.
Longer air gap distances will cause more neck-in.
Excessively high melt temperatures can increase neck-in.
Slower line speeds affect the amount of edge bead.

Benefits to Reducing Edge Bead:

By reducing the edge bead, converters can realize:

Reduced polymer waste
Improved line yield
Money savings
Reduced or eliminated chill roll wrap-ups
Increased nip roll life

How Do You Reduce Edge Bead? There are three ways to reduce edge bead:

Reduce the air gap.
Increase line speed.
Thin the polymer at the die lip exit so that it has a uniform thickness after neck-in.

How To Thin The Edge Bead On A Bead Reduction Die:

Using the Bead Reduction Data Sheet and measuring gauge provided with your die, gather a sample and measure the thickness of the bead as shown on the data sheet.
If the very outermost portion of the bead is high in thickness, then increase the distance from the tip of the deckle rod to the leading edge of the lower deckle. If the area just inboard from the outermost poly edge is high in thickness, then increase the distance from the leading edge of the upper deckle to the leading edge of the lower deckle. Measure the edge trim and document the results on the data sheet to see the effects of the adjustment.
Repeat the above procedure until you have sufficiently reduced the edge bead to the point where the coating width can be reduced without causing a high edge on the winding roll.

If during the process of reducing the bead the poly edge becomes unstable or tears, then check the temperatures of the melt and die. Too low a temperature in either of these areas will limit the amount of possible bead reduction.

This is a general description of the process. Keep in mind that there are more variables that come into play than
discussed here.

Black Clawson Converting Machinery's Spare Parts and Service Team is available 24 hours a day, 365 days a year to provide you with spare parts and technical assistance. Call 1-800-338-3660 to speak with a representative.

Questions? Call Black Clawson Converting Machinery at 315-598-7121 or e-mail us at bc@bc-egan.com

BC Publications is a technical newsletter designed to provide operational and maintenance information to improve the performance of your Black Clawson Converting Machinery equipment.