by Suzie Fenton
TricorBraun - St. Louis, MO - August 20, 2013
Cap drag, what is it and how does it happen? Usually this issue comes to light when either the bottle thread dimensions (T & E) are too large or the closure thread dimensions (T & E) are too small. For many years Society of the Plastics Industry (SPI) has published the thread dimensions of numerous neck finishes used in the industry. These thread sizes are standards and they work with the closure thread dimensional sizes published by Closure & Container Manufacturers Association (folded into the International Society of Beverage Technologists in April 2013).
What we see happen many times is that a bottle or a closure supplier will for example have a 24mm finish, everyone assumes that all 24mm finishes are identical and will work with all 24mm closures. Sadly this is not the case. If the bottle and closure drawing finish details are not compared to the standards to ensure they follow them there is a chance that as a result cap drag could occur. This is why it is always a safe bet to have the drawings reviewed by technical personnel in your company to be sure the two components are compatible on paper before you have a warehouse full that are not usable.
What occurs in cap drag when a closure is too small is that the T and the E dimension of the closure rub against the T and E dimension of the bottle it is being applied to which creates friction. When this happens on a fill line this issue can potentially cause false application torque. As a result the risk of leakage increases because your closure may not have been applied all the way, thus not creating a seal.
Try to avoid cap drag by having your component drawing reviewed prior to the start of a project. Also be sure that your component suppliers are conducting regular QC checks during any production run to ensure that these parts are made to the drawing spec. you have requested. Sometimes everything is checked up to production and then parts are made out of spec. and functionality of your package can be compromised.