One of the most often used and cheapest methods to closed paper bags is to sew them closed. 

There are 2 types of paper bag sewers: portable and fixed head sewing systems.

Videos on bag sewers.

 

Fischbein Model F Portable Bag SewerPortable, or handheld, sewers are usually used in: an entry level bagging operations (<5 bags/minute), when there just a few bags to sew at a time, or where a fixed sewing head is not suitable (i.e. out in the field). A portable sewer typically uses a single thread, but for textile bags a dual thread is normally used. A spring loaded suspension unit can be used to reduce fatigue. As the bagging operation grows, a portable sewer can be mounted on a pedestal above a conveyor.   

More information about portable bag sewing closers

 

Fixed Head Bag Sewing SystemFixed sewing heads are mounted on pedestals above a horizontal bag closing conveyor. Fixed head sewers are manually fed and designed to run 24/7 and on higher volume (up to 20 bags/minute) bagging operations. Fixed head sewers use a dual thread stitch. They can be integrated into fully automated systems. Tape coders and tag placers are often added to label the bags 

There are 2 kinds bag sewers: plain sewer & tape sewer.

Sewing ThreadPlain sewers close paper bags with a single thread stitch (portables) or a dual thread stitch (fix heads). For fine powders where leakage may be an issue, a bag with a top that is folded over before sewing closed can be used.    

Tape sewers close paper bags with a crepe tape applied over the bag top before being sewn closed. The crepe paper produces a nice finished top and reduces product leaking. With real fine products where leaking is a Crepe Tapemajor issue, a filler cord can be added to “seal” the needle holes.

More information about fixed head bag sewing systems