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Working with Wine Screwcaps: Common Application Errors & Fixes

Whether you’re new to the screwcap game or just need a refresher, there are a handful of common application defects that can be easily avoided or fixed until you get the hang of it. Here we have a shortlist of proper application tips and techniques for your bottling line, and what to do if something goes awry.

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Screwcap Terminology 

Let’s start out with common terminology and nomenclature when working with and applying screwcaps: 

  • Top/Redraw 
  • Thread start 
  • Bridges 
  • Tuck under/Pilfer proofing  
  • Support bead 
  • Skirt 

Common Screwcap Application Defects & Fixes

Pull Off's: A pull off is when the whole cap and skirt of the cap come off when you open the bottle, yet the wine is preserved and the seal remains intact. Pull-off's are caused by a combination of factors:

  • D angle of the bottle is more than 15 degrees and/or A1 radius is more than .026”
  • Side press on the tuck under rollers is too low
  • Bridge break strength is too high

The Fix:

  • Increase side pressure on the tuck under rollers in small increments until bottles open properly. 
  • The increase in side pressure flexes the cap and weakens the bridges while also forming a deeper groove in the skirt. 

Spinners: A spinner is when the threads on the cap fail before the bridges break. This creates a cap that will not open but continues to spin. Because the threads are what holds the liner in compression, the seal is compromised. Spinners are caused when the capping machine height is too high or threading roller side press is too low:  

  • The threads will not be correctly formed and will be weak 
  • Reverse or strip torque testing along with a visual inspection will help avoid spinners 
  • Cap bridge strength is also a factor 
  • If the bridges are too strong, the cap will be more likely to become a spinner 

The Fix: 

  • Verify machine height 
  • Visually inspect quality of threading and correct issues 
  • Increase threading roller side pressure and re-test reverse torque

Broken Bridges: A broken bridge is caused by excessive side pressure on the tuck under rollers: 

  • The size of the bottle (A1 diameter) is a factor because the cap is being supported by the glass inside it 
  • Tilt in the top of the bottle cap also causes broken bridges 

The Fix: 

  • Reduce side pressure on the tuck under rollers in small increments until broken bridges are eliminated 
  • Too much reduction in pressure can cause pull-off’s

Cuts in the Tuck Under: If you notice cuts in the tuck under, this is typically caused by the cap material getting pinched between the rollers and the details of the bottle:  

  • Since both tuck under rollers make two full revolutions around the cap during application, one or both rollers being too high will cause cuts 

The Fix: 

  • The severity of the cut will dictate how much the rollers will need to be lowered 
  • If the cut is severe, the adjustment will be bigger 
  • A small or infrequent cut will require a small adjustment 

Quality Control & Torque Tests

Even the most practiced screwcap user needs to conduct QC checks to ensure the best possible user experience. When conducting a visual inspection of your applied screwcaps, it’s crucial to look for the following: 

  • Redraw 
  • Thread start 
  • Threads are well formed and complete 
  • No broken bridges 
  • Well formed tuck under without cuts 
  • Smooth support bead 
  • Bottom of skirt is supported by the bottle neck 

Torque tests are relatively straightforward and easy to conduct. You will want to test for: 

  1. Slip: the twisting effort to cause the cap to initially move
    1. This friction is caused by the compression of the liner against the sealing surface on the top of the bottle.
  2. Bridge break: the force required to break the bridges
    1. Use as a target for the reverse or strip torque and to troubleshoot pull-off and spinner issues.
  3. Reverse/strip torque: the twisting effort in the closing or tightening direction to cause the threads to strip out or fail
    1. Verify that the threads are significantly stronger than the bridges to a void spinners.
    2. Low side pressure on the threads will cause a low result and create weak threads.

Have additional screwcap questions? Check out our recorded webinar with Eric Graham from Amcor as he walks through the above tips and techniques.

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