Choosing Capping Equipment for Glass Bottles and Jars

Prepare a capping requirement by starting from the glass finish and the closure, not from the machine. The finish and closure decide how the closure has to be applied: turned on with torque, formed onto the neck with rollers, crimped over the lip, seated by vacuum or inserted into the bore. Once the method is clear, the remaining questions are how the closure is fed and held, how seal quality is checked, and what the line needs around the capper.

This guide covers six application methods, explains why application torque and removal torque are different measurements, and shows how to turn finish and closure data into a request a supplier can answer. It is a selection aid. Torque windows, vacuum levels and inspection frequencies depend on the closure maker’s specification and the product, and no figure here replaces them.

Start from the finish and closure data

A neck finish is more than a diameter. A designation such as 24-410 carries a nominal diameter and a thread style, and Propacks, a closure supplier, notes that a cap of one thread style may screw onto a finish of another far enough to feel secure although the geometry differs and the seal cannot be assumed. The closure’s material and liner matter as much as the diameter. Read the closure maker’s drawing and the glass maker’s finish drawing together; the guide to neck finishes and closure compatibility explains how.

For food jars, the same logic applies to the jar and lid pair; see glass jars for food for shapes, finishes and closures. Cornell University food scientists describe three general finish types for jars (lug, press-on/twist-off and continuous thread), each with its own closure design.

Gather the following before talking to capper suppliers:

Data item	Where it comes from	Why the capper supplier needs it
Finish designation and drawing	Glass supplier	Chuck, roller or head geometry, neck centering
Closure type, size and drawing	Closure supplier	Application method, feeding and sorting
Liner or gasket material	Closure supplier	Compression, torque and vacuum behavior
Application torque or head setting, and removal torque range	Closure supplier, then validated on the line	Clutch or head setting and acceptance limits
Product, fill temperature, headspace	Your process	Vacuum formation, purge, foaming
Vacuum or inert gas requirement	Product and closure	Steam or vacuum equipment, gas dosing
Tamper-evident or safety-button features	Closure design	Band forming, button check
Feed method	Closure supplier and capper supplier	Hopper, elevator, chute, orientation

Closure application methods

Screw capping

A pre-threaded screw cap is turned onto a matching thread, typically by a chuck that grips the cap and applies rotation until a set torque is reached. A ROPP machine supplier’s guide describes the pre-threaded screw cap as one where the threads are already formed and the machine applies tightening torque, so torque control is critical.

ROPP (roll-on pilfer-proof)

A ROPP closure is an aluminum shell with a liner and a perforated lower band. According to the same ROPP guide, the capping head applies top pressure to seat the liner, thread rollers press the aluminum into the glass thread, and pilfer rollers tuck the band under the neck bead. The guide lists cap height, thread detail, band position, opening torque and leak performance among the checks, and notes that ROPP needs a matching cap, bottle finish, roller setup and torque testing.

Crowning

A crown cap is a metal shell with a corrugated edge that is crimped around the bottle lip over a liner. The crown cork was patented by William Painter in 1892, and ASME describes the original as a thin steel cap with 24 pleats crimped under the bottle lip. A supplier guide describes 26 mm as the most common size and 29 mm for some larger or higher-pressure bottles, and notes that twist-off crown caps rely on shallow glass threads while pry-off caps do not. A crowner needs the crown size, the finish type and the liner type specified.

Lug capping with steam or vacuum

Lug closures are used widely for jars because they need only a partial turn, according to the Cornell paper. They are lined with plastisol to hold a vacuum, and the vacuum is central to the seal. Cornell lists the factors affecting vacuum formation as headspace, product sealing temperature, air in the product, and capper vacuum efficiency where cappers are used. Hot filling is one source of vacuum. A steam flush capper is another: a supplier page describes an automated steam capper injecting hot steam into the headspace of a cold-filled package. Equipment for steam or vacuum application should be matched to the product, the headspace and the closure, and suppliers should state which they provide.

Press-on and snap

Press-on twist-off closures are applied by pressing straight down rather than rotating; the seal commonly relies on vacuum, as with lug closures. This description is editorial and should be confirmed with the closure maker. Cornell identifies press-on/twist-off as one of the three general finish types, which means the finish and closure are a matched pair.

Cork insertion

AWRI describes a corker that compresses the closure between jaws, pushes it into the neck and, on some machines, extracts air from the neck during insertion. It lists insertion depth (a stopper should not protrude above the rim or be over-inserted by more than 1 mm), fill height and ullage, and recovery time upright after insertion among the things to control. Corks are a bore seal, so the finish bore dimensions, not the thread, are the critical data.

Application torque versus removal torque

Application torque is the rotational force used to put a cap on. Removal torque is the force needed to start opening it after it has settled. Propacks and Kanda Cork Closures both stress that the two are related but not interchangeable, and that a complete closure specification should define both.

The two are also tested differently. According to ebottles, a closure supplier, the torque a capping machine applies cannot be measured directly, so the packaging industry standard is to measure the removal torque of caps applied by capping machines, with a correlation worked out for each bottle and closure combination. Propacks says many packaging programs check removal torque shortly after capping and again after a defined hold period, with 24 hours common, because closures relax, and that the right hold time and acceptance range should be documented for the package. It also reports that many references use removal torque of about 40% to 60% of application torque, and calls that a screening guideline, not a substitute for a package-specific range.

Published torque charts are mostly written for plastic closures. For glass, validate your own bottle, closure and liner combination. Over-tightening can damage the closure or finish, and under-tightening can leave the closure loose or leaking; Kanda says high torque can crush the liner or distort a tamper-evident band.

Verification and inspection

Ask what is checked, how often and by whom. Examples from the sources:

Lug closures: Cornell reports that U.S. FDA canning regulations for shelf-stable hermetically sealed foods call for visual examination at intervals not above 30 minutes and destructive examination at intervals not above 4 hours. Visual checks look for defects, misapplication, lid concavity indicating vacuum, and pull-up. Destructive checks include vacuum, removal torque and security. Adequate pull-up and security values are specified by the closure manufacturer. These rules apply to those foods; check what applies to your product.
ROPP closures: cap height, thread detail, band position, opening torque and leak performance are checked before production sign-off, according to the ROPP guide.
Cork closures: insertion depth and protrusion are checked, along with extraction force as an indirect measure of performance.

Inline inspection of closure presence and position is covered in the bottle inspection systems guide.

Questions to send suppliers

Which application method do you propose for my finish and closure, and what closure drawings did you base it on?
How is the head setting or torque controlled and recorded, and how do you recommend I correlate it with removal torque for my package?
What closure feeding method is proposed, and what closure tolerances does it need?
For vacuum closures, how is vacuum produced (hot fill, steam flush, mechanical vacuum), and how is it checked?
What inline checks are included (closure present, height, cocked), and how are rejects handled?
What gas purging or dosing does the proposal include for my product?
What change parts and adjustments are needed for a second closure or finish?
How does the capper connect to the filler for synchronization and handling of stops?
What acceptance testing, documentation and spare parts are in scope?

The wine bottling equipment guide shows how these questions apply to cork and screwcap lines. The Bottling Lines section covers related stations.

Evidence and limitations

The methods above are described from public explanations by equipment and closure makers, a peer-reviewed food-protection paper, a wine research institute and a mechanical engineering society. Machines for the same method differ by maker. Torque windows, vacuum levels and inspection rules depend on the closure, the glass, the product, and regulations that apply to the product. Several sources are supplier-written, and some torque guidance is oriented to plastic closures. No torque figures are given here because none apply across closures. SG Containers Review analyzes sources and does not test machines.

New Aluminum Lug Closure Reduces Removal Torque while Ensuring Hermetic Seals in Glass Jars, Food Protection Trends (Cornell University authors): lug closures, vacuum formation, steam flush cappers, closure inspection.
ROPP Capping Guide, ropp.co.uk (UK supplier of ROPP capping machinery): ROPP anatomy, head sequence and comparison with other capping methods.
Applying cylindrical closures, Australian Wine Research Institute: corker operation, insertion depth, fill height and ullage.
Closure Torque Guide: Application, Removal, and Testing, Propacks: application versus removal torque, hold period and the 40% to 60% screening guideline.
Screw Cap Torque Guide for Leak-Proof Bottle Closures and Testing, Kanda Cork Closures: effects of too much or too little torque and what a closure specification should define.
Application and Removal Torque Guidelines, ebottles: why removal torque is the industry measure for machine-applied caps.
One Cap to Bottle Them All, ASME: history and construction of the crown cap.
Crown Bottle Caps: Pry-Off vs Twist-Off Caps Explained, nwbottlecaps.com (crown cap supplier): crown cap sizes, pry-off and twist-off types, liners.
Gold Metal Lug Caps with Safety Button, Berlin Packaging (supplier page): hot fill and steam capper vacuum generation for safety-button lug caps.