Getting A Better Glue Pattern, part 3

In Part One and Part Two of our series on Getting A Better Glue Pattern, we discussed how to keep mechanical parts set and operating in the proper ways. Following these basic mechanical settings, checking for bearing wear, and abiding by the proper air and cold water pressures allows the system operate with ease. While we do not assert a specific glue formula, we do offer glue recommendations on what formulas run best with our Gartech Glue System.


Regardless of what pattern size you’re gluing with a Gartech Glue Shoe and Gartech Glue Wheel, these settings function the same.


We want to switch gears now, and work out of some common problems that gentlemen such as our service techs–including Ed Erich, the late Ed Berkemeier, the late Kenny Hampton, Paul Duncan, Mike Frosh, Jim Garrett and a few others–have encountered over the years throughout various plants. Our thanks to them, of course, for their feedback, photos, and solutions to overcoming these issues.

Getting A Better Glue Pattern, Part 3

The above photographs show how a glue pattern should look, when set at .002” recommended gap. It’s easy to see that these aren’t taken from “brand new” equipment. We wanted these pics to reflect that a good pattern can be achieved and maintained on equipment that’s well-past the point of being broken in. Notice the “shiny” sides on the glue wheel.


Correct Adhesive Application

The following photographs show what a correct adhesive pattern on the tab should look like when the Gartech Glue Shoes are correctly set to a .002” glue gap and the nip adjustment between the two Gartech Glue Wheels is set correctly according to the board thickness.


Blockage

Gartech recommends that during an eight hour shift the glue unit is washed regularly. After four hours of production–or if an order set-up occurs near this time–it is recommended that an automatic wash cycle is performed. Four hours later, another automatic wash cycle should be performed and the shoe removed and wiped out.

If operators fail to complete this procedure, the performance of the mechanical glue unit and the adhesive will start to deteriorate. The glue will set inside the shoe and access to new glue will be limited due to blockage of the supply lines.

The most common course of action to improve this effect would be:

  1. Clean the shoes and perform Wash Cycles as recommended by Gartech.
  2. If the blockage has set too long, consider replacing necessary hoses.
  3. Blockage due to lack of cleaning can also affect performance of the Glue Manifold.

Gumballs

The effects of “gumballs” can start as small strands of adhesive building under the shoe, mainly along the glue shoe’s metering plate. General opinion suggests that the shearing action of the metering plate on the adhesive often causes this effect. A thicker adhesive is more susceptible to producing gumballs, also.

The problem is more serious when using the upper glue wheel, as the build-up progresses with time. These large masses of glue eventually drip adhesive onto the lower glue wheel and contaminate the lower wheel and box with adhesive. In this scenario, adhesive can be applied to the wrong side of the glue tab, causing the box to be glued inside.

The most common courses of action to improve this effect would be:

  1. Check that the metering plate is correctly adjusted (as shown in Fig. GA-01 below). A metering plate that extends from the glue shoe surface exaggerates this problem and wears down parts.
  2. Check that the metering plate edge is smooth with no grooves in the surface. Badly grooved or worn metering plate surfaces encourage the adhesive to strand and speeds up the gumball mass. If your Gartech Glue Shoe is worn, contact Gartech about sending it in for a precision redress. We can also redress the Gartech Glue Wheel.
  3. Check that the shoe is correctly adjusted to the glue wheel. Glue shoes that touch at the top but have a small gap at the bottom will encourage the adhesive to drip more readily and produce a very heavy glue pattern.
  4. Another problem is that the adhesive is too thick. Consider a slightly thinner adhesive.


Misting

This problem often manifests as a fine adhesive mist that’s created as the board leaves the glue wheel. The adhesive appears to break at the board and glue wheel at the exact same time launching a very small adhesive droplet into the atmosphere. The effect appears much worse when the lower glue wheel is being used. The information Gartech has gathered suggests that speed and thin adhesive worsen the effect.

The most common courses of action to improve this effect would be:

  1. Check that the glue metering plate is not set too far away from the glue wheel. Experience has proven that a glue thickness pattern of .002” is perfect for virtually all orders run. Not sure how to set this? A piece of .002″ shim stock is all you need. Not sure where to find that? Ask us. We’ll help you out.
  2. Check that the glue shoe is clean on the mating surfaces so the shoe sits close to the glue wheel. Dried glue on the shoes mating surface stops the shoe from reaching the correct position.
  3. Check that there is no small dripping of water going into the glue supply in the Glue Manifold, check the seat on the Skinner valve.
  4. The adhesive formula is too thin. Verify a thinning agent hasn’t been added. If not, consider changing to a slightly thicker adhesive.
  5. Ensure your adhesive formula is rated for the speed of the flexo and that it is sheer stable.

Double Bonding

Double bonding occurs when adhesive is applied across both sides of the glue tab. This often occurs due to transfer of adhesive from wheel to wheel. This also occurs with a heavy glue pattern and when the nip adjustment is set wrong, limiting the gap between the glue wheels.

On the lower glue wheel, excess adhesive is slung onto the upper glue wheel, creating a contaminated wheel. On the upper glue wheel, adhesive drips from the shoe due to the gumball effect (discussed above). This drip then lands upon the lower glue wheel and then transfers onto the box.

Here’s how we undo this problem:

  1. Check that the glue shoes are set correctly to the glue wheel with a .002” glue gap pattern. A heavy glue pattern produces excessive glue on the wheel, smears on the tab, and creates dripping.
  2. Check that the nip adjustment, as covered in this blog entry, is correct for the board thickness. A nip set too tight will squeeze adhesive out to the edges of the glue pattern, further increasing the glue pattern thickness then centrifugal force will throw or sling the adhesive from the wheel.
  3. If the nip adjustment setting creates too much gap between the wheels, the glued tab will appear light, uneven and spotty, especially when gluing from the upper wheel. See the photo below.


Under-to-No Adhesive Application

An under application of glue occurs when an insufficient amount of adhesive fails to create a strong bond; letting the glued box come apart or dry before making contact. If left unaddressed, this will cause the boxes to fail on the glue joint.

Here’s where to begin correcting the problem:

  1. Check that the glue shoe is correctly adjusted with a .002” glue gap at the metering plate. If it’s set too close, the glue isn’t given a chance to get from the wheel to the box. Also, as the glue shoe wears down, the metering plate gets closer to the wheel and cuts back the adhesive. This is another reason why we recommend consistent Wash Cycles.
  2. Check the nip adjustment that sets the gap between the glue wheels. A nip gap that is too wide will not apply the adhesive onto the board varying from no adhesive pattern to a light adhesive pattern.

Many of these problems share common causes:

  1. Incorrect setting of the Gartech glue shoe metering plate.
  2. Improper glue formula.
  3. Ignoring the recommended Wash Cycle.
  4. Failing to redress Gartech Glue Shoes and Glue Wheels.