How to Get The Most From Your Spreader Roll

Almost all web processing systems require web spreading before critical components to remove wrinkles or for slit web separations.  Unfortunately, many of these spreaders are misapplied or not properly adjusted.  In this Tech Tip, we will review the different types of spreading systems which are commonly used, review their application and adjustment.

Description:

A conventional roll, normally an idler but may be driven, that has a diameter at the ends slightly larger than the diameter in the center of the roll.  Since the roll has a constant rpm, the surface speed is greater at the ends than the center.  The surface speed difference causes an ingoing web tension distribution that is shaped similar to the speed profile.  The rolls spreading action is a function of its’ crown and roll deflection.

Application:

• Wrinkle removal
• Most effective on extensible materials
• Web wrap should be greater than 90º
• Poor man’s reverse crown roll is tape on ends of roll at edges of web

Pros:	Cons:
Simplest to operate and adjust, and least expensive web spreader Easily retrofit	Very product dependent as the amount of reverse crown depends on extensibility of web No control on amount of spread flexibility

Description:

A straight roller that has a special grooving cut into a soft outer cover.  The grooving is undercut at an angle so that the web tension deflects the lands outward, carrying the web with it to accomplish the spreading action.  The amount of spreading is a function of rubber hardness and web tension.

Application:

• Wrinkle removal
• Prewind web spreading with no slitting
• Preslit web spreading with slitting
• Most effective on non-extensible materials
• Web wrap should be greater than 90º

Pros:	Cons:
Relatively low cost, easily retrofit, easily operated Self compensate for tight or loose areas across web for more uniform cross machine web tension Grooving eliminates slippage due to air entrapment	Needs web tension to provide spreading action Limited control of spread flexibility

Description:

A curved roll with a stationary axle on which segmented metal rotating sleeves are mounted on numerous bearing sets.  The metal sleeves are typically covered with a flexible piece tube of a soft, synthetic rubber.  Under high wear conditions, the outer rubber tube can be eliminated and the metal sleeves are traction coated.  Variable bow rolls have a split stationary axle where an applied force can change the amount of bow.

Application:

• Slit web separation
• Wrinkle removal
• Can be used on both extensible and non-extensible materials
• Cover or steel sleeve grooving reduces slippage from air entrainment
• Lead-in and lead-out geometry are critical for effective spreading
• Spreading action function of amount of wrap, bow and web tension

Pros:	Cons:
Web path length the same at center and ends  No upstream or downstream spreading action  Excellent control of spreading action  Can be adjusted to tighten center or edges of web by slight bow direction	More complex and costly than other spreaders  Needs to be driven on light tension applications  Bearings difficult to lubricate and replace, and may be difficult to thread  Bow position and amount of bow of variable rollers can be misadjusted by operators

Description:

Two bowed rolls that can be fixed or variable so that the lead-in and lead-out webs are parallel with the bows pointing 90 degrees to the lead-in and lead-out web paths as shown.  The spreading action takes place between the two bowed roll with no spreading effect upstream or downstream.  Additional spreading flexibility can be provided by a rotatable table to vary the amount of wrap.

Application:

• Slit web separation for slitting and spreading multiple rolls (usually 5 or more)
• Can be used for a wide range of material and slitting variations 
• Roll may be fixed or variable bow.
• Parallel lead-in and lead-out web leads and sufficient distance between rollers for web separation are critical.
• 1st and 2nd rolls will most likely have different amounts of bow due to deflection from tension vector.
• Spreading action function of amount of wrap, bow and web tension

Pros:	Cons:
Web path length the same at center and ends No upstream or downstream spreading action Excellent control of spreading action Can be adjusted to tighten center or edges of web by slight bow direction	More complex and costly than other spreaders Needs to be driven on light tension applications Bearings difficult to lubricate and replace, and may be difficult to thread Bow position and amount of bow of variable rollers can be misadjusted by operators

Bowed Rolls Maintenance Tip

If operators find that they must rotate the bow directly into the web in order to get spreading or proper web separation, then there is slippage between the web and the roll.  The rotating spreader has become a stationary spreader device such as a bent pipe or D-bar type spreader.  Most likely one or more bearings have failed.  Check to ensure the covering rotates freely.  If it does, then the covering needs to be roughed-up or vent-air grooved to restore traction.

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 equipment. 

Davis-Standard, LLC | Site Map | Contact Webmaster | Designed by MG Lomb Advertising