Thick or thin? That is the question. The answer depends on how you use your flexo press.

Rising costs and tighter margins are forcing printers to look for every opportunity to improve productivity and profitability, especially in light of today’s tight economic climate.

A staple in the flexographic printing industry for many years, print sleeves continue to be an under-utilized source for lowering costs and improving manufacturing efficiencies for printers running gear-style presses using metal cylinders. For printers who have invested in a new gearless press, sleeves are not an option. However, understanding the implications of choices made relative to the number of bridge mandrels and the specific print sleeves used is important.

Fundamentally, print sleeves are used for mounting tapes and plates on print cylinders or bridge mandrels. The sleeves are the carriers for plates. They are available in thicknesses ranging from 0.005 to 3.000 inches or thicker. The thickness depends on the amount of space needed to build sufficient diameter to reach the desired print repeat.

Regardless of the press design, the place to begin when considering sleeves is to examine the business needs. The following questions should be addressed:

• Are there many jobs at the same repeat or few?

• Do repeats tend to be close together or far apart?

• Are there more short runs or long runs?

• Are there many jobs that repeat month after month or do they tend to run only once?

• Do many jobs remain mounted after running or are they typically demounted?

• Are build-up tapes used due to switching from a thicker plate to a thinner plate or are the proper size cylinders available for all repeats?

• Are build-up tapes used to reach larger repeats or are the required cylinders available for all repeats?

• Are bottlenecks experienced in the mounting room due to a lack of sufficient cylinders or sleeves at the required repeat or is there an ample supply of cylinders and sleeves for mounting?

For the printer with the geared press using multiple cylinders, a “Yes” response to the first part of these questions suggests the use of sleeves rather than cylinders alone. For the printer with the gearless press using a fixed diameter mandrel and bridges with sleeves to build repeats, a “Yes” response to the first part of the questions suggests using more bridges with thin sleeves rather than fewer bridges with thicker sleeves.

The answers to these questions can suggest the proper direction regarding sleeve, print cylinder and bridge mandrel decisions and, ultimately, lead to greater profitability. Capital investment is minimized by purchasing lower cost thin sleeves and being aware of the options for building repeats. Variable cost is reduced because keeping jobs mounted lowers sticky-back costs, plate damage and labor costs. Productivity is maximized by increasing press up-time because jobs are pre-mounted and ready to go. Future flexibility is maximized by having more cylinders or bridges at strategic diameters that allow repeat ranges to easily grow through the use of thin sleeves that can be quickly produced.

Decisions about using sleeves on a gearless press versus a geared press are actually quite similar. In both cases, sleeves can be mounted on a supporting print cylinder or bridge mandrel. In the case of a gearless sleeve press, a fixed mandrel exists on the press on which the bridges are mounted. If the bridge is treated like a metal print cylinder used in a traditional geared press and both are simply referred to as the base cylinder, then the two subjects can be addressed simultaneously.

The simple realities are that base cylinders cost more than thick sleeves and thick sleeves cost more than thin sleeves. As printers look to fill their repeat needs, they have to determine the mix of base cylinders and sleeve thicknesses to accomplish their print requirements. While this typically results in a mix of thin and thick sleeves, it is useful to explore the relative costs of each approach in the extreme case of all thin sleeves or all thick sleeves to highlight the differences between the two options. Exploring some generic examples will help illustrate the point.

Consider a printer who has a base cylinder of a certain diameter. Suppose this printer needs to reach a repeat, which is about six inches larger than their current capability. Should the printer buy thick sleeves to go over the existing base cylinders or should a set of larger base cylinders be purchased and thinner sleeves used instead? The answer depends on how many sets of sleeves the printer wants at this new repeat. Figure 1 illustrates the financial implications of the two approaches.

The X-axis, titled “Number of Sleeve Sets,” is the number of sleeve sets desired for a given print repeat. For a 10-color press, one sleeve set would be a quantity of 10 and two sleeve sets would be a quantity of 20. The cost of the base cylinders is shown in blue and is a fixed amount, regardless of the number of sleeve sets purchased because only one set is required. The red line shows the combined cost of purchasing a new set of base cylinders and mounting thin sleeves over the new bases.

As Figure 1 indicates, the cost is lower for thick sleeves mounted on existing base cylinders when only one set of sleeves is required. As the number of sleeve sets increases, a point is reached where it is less expensive to purchase the new base cylinders and use thin sleeves.

Figure 2 helps to focus on the two distinct approaches. The break-even point, where the two lines cross, depends on a number of factors, including product size and supplier. However, it is not uncommon to find that this occurs somewhere between two and three sets of sleeves. To the left of that point, it is better to use thick sleeves. To the right of that point, it is better to use a new base cylinder and thin sleeves.



Two specific examples further illustrate the difference in the two approaches. The first examines the relative cost of each approach as a function of the number of sleeve sets at a given repeat. Table 1 shows four different repeats. In the extreme case, these can be reached by either purchasing four sets of base cylinders, one at each repeat and using thin, 0.040-inch sleeves, or by using an existing set of base cylinders and adding increasingly thicker sleeves to reach the larger repeat sizes.

Table 2 shows the average of the cost differences between the two approaches based on the number of sleeve sets purchased at each repeat. It reveals that, at one sleeve set, it is best to go with the thick sleeve approach because the cost of the base cylinders at each repeat far outweighs the cost of the thick sleeves. At two sleeve sets per repeat, the cost is about the same, but the savings begin at three sets and grow from there. In fact, if two sets are required at each repeat, it is still worth going with the thin sleeve approach because future thin sleeves are as much as 75% less than thick sleeves, depending on quantity, thickness and supplier.

The second example considers the repeat requirements shown in Table 3. In this instance, the repeats are close together and the option of buying a new set of base cylinders that meet the full repeat range using thin sleeves versus using an existing set of base cylinders that will require using thick sleeves to do the same is examined. Table 4 shows that the savings can be substantial, even if only one set of sleeves is required at each repeat and reaching as much as 50% if four sets are required. Figure 3 shows graphically how the savings change with the number of repeats being considered, as well as the number of sleeve sets per repeat.

In these examples it should be noted that the base cylinder is considered to be a standard metal print cylinder or a standard bridge mandrel, rather than a carbon composite bridge mandrel. Carbon composite bridge mandrels, especially those designed for high axial stiffness for improved deflection and reduced bounce, are three to five times more expensive than standard cylinders and bridges. Therefore, the economics change dramatically when presses are wide enough to require these types of bridges.

When considering the options between more base cylinders and thin sleeves versus thick sleeves alone, the ultimate cost will depend upon a number of factors including the specific supplier. However, two rules of thumb often apply when seeking the break-even point; the place where the cost is nearly the same. The first is when two sets of sleeves are required at a given repeat. The second is when there are two repeats that are close to each other and only one set of sleeves is required at each repeat. These rules of thumb apply when the thick sleeves under consideration are about ¾-inch thick or thicker.

This article has focused on the cost savings associated with thin sleeves, yet it remains true that both thin sleeve and thick sleeve approaches are viable options. Consequently, a mix of the two is often used. The key is for printers to assess which approach is best for their individual businesses. Elements of this assessment should include:

• The current needs of the business.

• How the business might change and which approach offers the greatest flexibility to respond to these future changes.

• The opportunities within the product mix (print jobs) to cut cost and maximize profit.

• The break-even point and the potential savings with each approach.

Mike Smoot, business manager for Xymid Print Sleeves (www.xymidllc.com/printsleeves), has more than 25 years combined experience in process and product development, composite design, manufacturing, sales and marketing. He holds several patents and has led multiple product introductions including composite air shafts, print cylinders, vacuum drums, print sleeves and bridge mandrels.