- May 01, 2001, William E. Hawkins, Film Handling Solutions Ltd.
Upgrade Can Add Years to Older Converting Machines
Many older converting machines, such as slitters, coaters, and laminators, depend on the operator to make manual adjustments to windup tension and contact roll pressure while the rewind roll is building up. The operator must do this to regulate the amount of boundary air that is being entrapped between the rewind roll wraps in order to produce good production rolls.
Some operators are very good at making these adjustments, but many are not so gifted. To remove the skill requirement for daily operation, most of these older machines can be successfully upgraded.
There are two good incentives for keeping the older machines producing. The first is that some machines have been part of a development process for specialty products. The machines fit the converter's production scheme and staffing. Usually the material handling process for these older machines has evolved through the years and is efficient for that site.
The second incentive to keep older machines producing is that the cost of upgrading an old machine can be much less than replacing it with a new one.
The key to a successful and low-cost upgrade is to have a competent engineering analysis done of all the critical machine interactions as they relate to web control and winding on that particular machine before the selections are made to modify and/or purchase new components for web control.
The most common winding problem I have seen on older machines is that of excluding the proper amount of boundary air, especially when specialty products that are coated with an adhesive are being produced. The operator usually has three variables that he or she must work with on these machines: contact roll pressure; web tension before laydown on rewind roll; and machine speed.
The converter's production problems become very vexing when there doesn't appear to be any combination of the three that satisfies the production demands.
There are two other machine variables that are not so apparent that may have to be changed in order to wind a certain type of product successfully: contact roll surface texture; and contact roll construction.
The contact roll surface can be textured when more boundary air is needed between the wraps to help lubricate slip between the web wraps in the contact roll nip. The amount and type of contact roll texturing required usually is a function of how much boundary air is needed for a specific product.
There are many ways to texture the contact roll surface. I have found that a fine-tooth knurl works well on many products. As a general rule, the depth of the knurled grooves should be between 0.007 and 0.010 in. All sharp edges must be removed from the knurled surface before the roll is used against the production roll.
The contact roll surface smoothness (RA) and construction must be examined when more boundary air must be excluded for high quality rolls than can be done with the standard equipment on the machine. I have found that a very smooth surface (roughness <50 micro in.), small diameter (diameter <2 in.) works very efficiently in removing boundary at high-speed winding (>1,000 fpm) on films with medium roughness (RA about 0.250 microns).
A very rigid backup roll must be used in conjunction with this type of contact roll construction. The requirement of a rigid backup roll when using a small-diameter control roll places severe limitations on the web thread path. Usually it is necessary for the contact roll to touch the winding roll many degrees after the former touchdown point of the web.
An observer may conclude the winding roll is not smooth and wrinkle-free when watching such a winding system. This means the observer is not looking at the winding wraps that have gone under the contact roll. The proof of any winding system is how good the rolls look after many days in lag storage.
William E. Hawkins has 30-plus years of process and equipment development in web handling, including experience on all types of converting equipment. He specializes in thin web applications. Contact him at 740/474-5840; fax: 740/474-3148; e-mail: email@example.com.