Web Lines | How To Create an MD Running Fold in a Wide Web

Web handling expert Tim Walker offers three options for this folding process.

Q: I'm looking to fold a 10-in. (250-mm) web in half. How much space or span length is required for this process?

A: There are three approaches to create a machine direction running fold in a wide web (and I expect there are additional options). The first two I call the long fold; the third is the compact “box” fold.

The first two options are based on web twisting. You can do a lot of twisting without inducing great tension variations (loose edges or center), but you need long spans to twist 90–180 degrees. The stiffer your web, the longer spans you will need. Both twist methods could create wrinkles in thinner webs if too aggressive (too short of spans).

 

1. The long fold “UP”

The fold UP is essentially twisting each half of the web 90 degrees. This will take less length than a full 180 fold OVER. I'd recommend starting with 10x for 90 degrees. Since we are twist each half 90 degrees, my first estimate for span length is half web width x 10 or 50 in. (1.2m).

 

2. The long fold “OVER”

The long fold OVER requires half the web to turn 180 degrees, so I recommend 20x half web width or 100 in. (2.5m).

 

3. The 2:2:1 triangle box fold

This is the most common and stable approach. The 2:2:1 geometry formed by the entry roller, turn bar triangle, and creasing nip means nearly zero crossweb tension variations. Each lane of material travels the same path length from entering to exiting the folding “box.” This method is used in the newspaper industry.

 

If you go for the “long” fold options, I'd recommend 50 in. for the fold “up” option and 100 in. for the fold “over” option. The 2:2:1 folder can fit in a 12x12x6 box.

I do not know of commercial suppliers of this equipment. The 2:2:1 triangle box fold is common in newsprint and other industries. I expect you would also find this design in the envelope and food packaging industry.

Web handling expert Tim Walker, president of TJWalker+Assoc., has 25 years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; This email address is being protected from spambots. You need JavaScript enabled to view it.; www.webhandling.com.

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