Cap Liner Assembly Circular Conveyor System

Cap Liner Assembly Circular Conveyor System: Building Liner Insertion into a Multi-Station Closure Line

Author: ShanGong, Director of Engineering Department | Published: 15 October 2026 | Last updated: 15 October 2026 | Category: Packaging

Our 30-slide V50 loop, the platform used as the worked example in this guide.

A liner that is present is not always a liner that is seated. On a cap liner assembly circular conveyor system, as on any lining machine, a cap can pass a presence sensor with its liner resting on top of the retention undercut. That cap then leaks at the filler, or the liner drops out in the customer’s hand.

So where should liner insertion happen? One route is a dedicated lining machine; the other is a lining station on the same loop that carries the closure through its other steps. This guide helps you choose between them, then shows how to build the station so that liners go in centred, go in deep enough and stay there.

Throughout, we use one real platform as the worked example: our 30-slide V50 loop. Where we describe liner stations on it, they are proposed configurations, and we say so.

What Is Cap Liner Assembly — and Where Does a Circular Conveyor System Fit?

Cap liner assembly is the step that places a separate sealing disc into a moulded closure and retains it there. The disc may be called a liner, a wad or a gasket. Inserted liners differ from in-shell moulded liners, which are formed from compound inside the cap during moulding. In-shell liners belong to the moulding equipment and sit outside this guide.

You can insert liners in two ways. A dedicated lining machine, such as a star-wheel, rotary-die or multi-lane shuttle machine, does one job at high speed. Alternatively, a lining station sits on a cap liner assembly circular conveyor system, where located carriers take each cap past the liner station and the other assembly steps in turn.

The loop route makes sense in three cases:

• Lining is one of several located steps, for example liner, plug press and label seal on one closure.
• The cap is large, so dedicated machines run fewer heads and lose their speed advantage.
• Several liner variants run on one line, and you want to switch by recipe rather than by changeover.

For the broader platform choice between turrets, dials and loops, see our plastic cap circular conveyor selection guide. Unfamiliar terms are explained in our circular conveyor terminology glossary.

Cap Liner Types and What Each Asks of the Station

Every liner type is held in the cap by a retention method. That method, rather than the liner material, decides the station design. The table below maps common liners to what the insertion station has to deliver.

Common liner build-ups, from foam to two-piece induction.

Retention is where station design starts. An undercut or retention ribs need the liner pushed past them to a defined depth. Hot-melt retention needs a glue station and a short dwell. A friction fit depends on tight control of liner diameter against the cap bore.

Orientation is the second filter. A two-piece induction liner must keep its wax-bonded backing toward the cap top and its foil seal toward the container. Liner makers such as Tri-Seal publish their induction liner construction for each product family. Printed liners add rotational registration on top.

Variants raise the stakes further. On our 55 mm closure line, a foam liner and a silicone ring are two variants of the same cap, so the station must know which one each carrier holds. That is why the liner type comes first in any station design, and the feed method second.

Pre-Cut vs Roll-Fed Liner Insertion on a Loop

The pre-cut vs roll-fed cap liner insertion choice applies whether you line caps on a dedicated machine or on a loop. On a loop, however, space and reloading weigh more heavily.

With roll-fed insertion, the station die-cuts each disc from a coil. The punch then carries the disc straight into the cap. This leaves a scrap skeleton to wind up or extract, and cut edges shed liner dust. A coil change also stops the station.

With pre-cut insertion, liners arrive already cut and stacked in a magazine or tube. A pick-and-place head or plunger moves one liner at a time into the cap. There is no scrap at the station, but someone must refill the magazine.

The same located carrier under a roll-fed die (left) and a pre-cut magazine (right).

If you are asking how to insert liners into plastic caps on a loop, decide by liner type, print and volume first. Printed liners usually point to pre-cut, because registration is easier in a magazine. Dedicated machine builders publish both configurations; MACA, for example, lists published cutting-lining machine outputs for coil-fed and pre-stacked machines.

On a loop, the feed choice also sets how much inner space the layout must reserve. A coil feed with a scrap path can live inside the loop, while a magazine sits beside the straight, next to the station it serves.

Dedicated Lining Machine vs Cap Lining Station on a Circular Conveyor

When buyers compare a circular conveyor vs rotary lining machine for one plain liner on a standard cap at high volume, the dedicated machine wins. It is built for that one job, and it is faster.

The published figures make the point. MACA lists cutting-lining machines at 8,000–36,000 pcs/h, depending on punch count, and pre-stacked liner inserters at 6,000–12,000 pcs/h. The rates change with cap size, though. Aoqite’s published liner inserter specification runs 25–60 mm caps on six stations but only two stations for 90–120 mm caps. Its published output for the large caps is roughly a third of the small-cap figure.

A loop station wins on other grounds:

• Several located steps. Liner, press, seal and checks share one carrier path.
• Large closures. Nest size and pitch follow the tooling, not a fixed turret.
• Liner variants. Stations skip or switch by the recipe tagged to each carrier.
• Inspection between steps. A check can sit between lining and the next press.
• No transfers. Every machine-to-machine transfer is a chance for a loose liner to drop.

To estimate liner output on a loop, multiply indexes per minute by the caps each carrier holds. Then cap that figure at the slowest station; on a liner line this is often the magazine refill or coil change, not the punch. C Motion’s cycle time calculation guide shows the method in full, and our precision indexing circular conveyor page covers index motion.

Decide by the number of located steps, cap size and liner variants.

Designing the Liner Insertion Station in a Cap Liner Assembly Circular Conveyor System

A good liner insertion station answers four questions. How is the cap located? How deep does the liner go? Where does the liner feed sit? And how do you stop static from moving liners? These four cap liner insertion solutions connect in one chain. An unlocated cap gives an off-centre punch, and an off-centre punch gives a cocked liner.

The plan below uses our 30-slide V50 loop, introduced in the case reference later in this guide. Today it has one located place-and-pick-up station. The liner insert, check and reject stations are proposed additions for a liner configuration. Adding them means adding stations to the loop, not changing the loop.

Solid: the located station in the released model. Dashed: stations a liner configuration would add.

Locating the Cap Under the Punch

A cap lining station needs the carrier located, not just stopped. A chain-driven loop with a positioning mechanism holds each carrier to ±0.03 mm at the station. A belt-driven loop with positioning holds ±0.05 mm, and without positioning either drive is around ±0.5 mm. C Motion’s guide to station positioning accuracy explains how locators achieve this.

On the 30-slide loop, one AirTAC pneumatic positioning set works the station, combining a cylinder, a swing arm, a long shaft and bearing blocks. Each of the 30 slides is fitted with its own positioning accessory, which means the locator can fix any slide that stops in front of it. A proximity sensor confirms arrival before the locator acts.

Because the locators are pneumatic, the line needs compressed air. Carrier position is only half the job, however: the cap nest must also be concentric with the punch, or a perfectly located carrier still delivers an off-centre cap.

Insertion Depth, Retention and Press Reaction

Centring alone does not keep a liner in, because an undercut or a set of retention ribs holds the liner only after the liner has passed it.

For that reason, measure insertion depth from the carrier’s datum face instead of trusting the press stroke alone. A stroke-based setting drifts as tooling wears, whereas a datum-based depth tracks the cap itself. This is the practical answer to how to insert liners into plastic caps so that they stay put.

The insertion force should also be reacted by the locator and the frame below the carrier; the chain only moves the carrier and should never take the press load. If you use hot-melt instead of an undercut, add a glue station and allow for dwell and a temperature check.

A common error is to rely on a presence sensor at this point, since a shallow liner still registers as present.

In practice, set the target depth from the cap drawing, then confirm it on first articles by cutting sample caps in half. Once the depth is proven, a depth or force signal at the press can watch every cap. That signal belongs in the station’s reject logic, not only on a trend screen.

Where the Liner Feed Sits on the Loop

Liner feeds take space, and a loop gives you two kinds of it. Beside each straight there is room for stations in a row. Between the straights there is inner space for a coil, die and scrap path.

The 30-slide loop shows the scale. It has two 7,748 mm straight rails, S612 180° arcs and a 560 mm nominal slide pitch. That is enough straight length for a liner insert, a check and a reject station in sequence, with a pre-cut magazine at the station or a coil feed inside the loop.

The flat carrier plates at 560 mm pitch also leave room for a multi-cavity nest. One index could then line more than one cap. That is a design option to evaluate, not a delivered feature. Changeover between liner variants follows the same logic. A pre-cut line swaps magazines, and a coil line swaps coil and die, while the carrier recipe tells each station which variant to expect. Whatever the layout, keep clear access for coil changes and die removal. A custom circular conveyor layout fixes this space in the first drawing.

Static and Liner Dust

Foam liners and PP or PE caps pick up static charge, especially in dry rooms. Liners then cling to punches and guides, or lift after insertion. Static is therefore a placement fault, not just a cleanliness issue.

Ionising bars at the feed and the insertion point are the usual fix, and roll-fed dies need dust extraction. For cleanroom zones, see our notes on hygiene and cleanroom options, including felt lubrication instead of spray lubricant.

Inspecting Lined Caps Before They Leave the Loop

Even a well-built station needs checks, and the placement rule is simple: check straight after insertion, before the next press, and reject before unload. The table maps each liner defect to the check that catches it.

Each check sits where its defect first becomes visible.

A height probe is the simplest strong check, because it catches both missing and double liners in one measurement. Vision then covers what a probe cannot see: tilt, orientation and print position. On a loop, the recipe on each carrier also tells every station which liner variant to expect.

Order matters as much as the checks themselves. Place the probe and the camera before any later press, because a press can flatten a cocked liner into a shape that looks seated. Then give rejected caps their own located station before unload. On the 30-slide loop, the spare positions on the return straight suit that role.

Line checks do not replace container testing. For sampling, a standard such as ASTM’s vacuum leak test for rigid containers verifies that lined caps actually seal.

Why Cap Liners Fall Out — and How the Line Prevents It

Why do cap liners fall out? Detection tells you that a liner is wrong; this section deals with why. Usually the liner never passed the retention undercut, or liner diameter and cap bore do not match. Static, transfer shocks and moisture then make a marginal fit fail sooner.

Separate the causes into two groups, because different people fix them:

• Line causes: insertion depth, carrier location, machine-to-machine transfers and static.
• Design causes: undercut depth, moulding flash in the cap, liner diameter and liner material.

Moulding flash deserves a special mention. A thin ring of flash at the undercut can stop a liner short of its seat while every station setting looks correct. When fall-out appears suddenly on one cavity, check the mould before you adjust the line.

Most fall-out traces back to depth, fit or handling.

Once lined caps have shipped, a fall-out problem means sorting, relining or scrapping stock, which is far more disruptive than setting a correct depth reference at the station. When you send samples, include the retention drawing so both groups of causes can be checked together.

Induction Seal Liners for Pharmaceutical and Food Caps

An induction seal liner assembly line for pharmaceutical caps inserts the liner at the closure plant. The seal itself forms later, at the filler. That gap is the risk. Orientation and retention at insertion decide whether the seal works days later on another site.

An inverted induction liner gives no seal at all. Vision of the foil face, straight after insertion, is therefore the key check for these caps.

Retention matters too. During heating at the filler, the foil must stay flat against the container rim. A liner that has lifted or tilted in the cap can give a partial seal that is hard to see. For that reason, the depth check from the station design section applies to induction liners as much as to foam.

Regulated caps also bring documentation. For drug products, drug product containers and closures are covered by 21 CFR 211.94. The FDA container closure guidance, issued in 1999 and still listed by FDA, describes the packaging information expected in submissions. For food, 21 CFR 177.1210 covers closures with sealing gaskets for food containers. These rules apply to the closure and liner materials, not to the conveyor.

On the line side, options include stainless contact parts, H1 food-grade lubricant and cleanroom testing to ISO 14644-14. See our stainless steel circular conveyor, our vial filling and capping line article and our overview of pharmaceutical packaging lines.

The foil seal faces the container; the backing stays in the cap.

Case Reference: Planning a Cap Liner Assembly Circular Conveyor System on Our 30-Slide Loop

Our 30-slide V50 loop shows what a cap liner assembly circular conveyor system starts from. It carries 30 slides on a chain-driven oval with an 8.8 m frame and one located station. A Delta 2 kW servo (ECM-B3M-E21320RS1) drives it under EtherCAT motion control. Drive, reducer and controller details are in the hub guide’s full specification of the 30-slide loop.

The line is engineered, and its 3D model was released in August 2026. The released model contains the loop, the drive and the positioning system, but no liner tooling. The table below lists only the elements that matter for liners: what the platform already provides, and what a liner configuration would add.

Drive end: servo and reducer under the drive sprocket.

The key point is in the positioning row. Because every slide already carries a positioning accessory, each new located station needs a locator set, not new carriers. The loop is our chain drive oval platform.

Our 55 mm line takes the other approach: a dense loop of 80 carriers that handles foam-liner and silicone-ring variants of one cap on the same line as its plug press and label seal. Read the 55 mm closure line write-up for its geometry, coil handling and press reaction path.

For a liner project, the choice between the two is about carrier length. Short, dense carriers suit a cap that passes many steps; long carriers with room for a multi-cavity nest suit lining added as a single operation along the straights.

Cap Liner Assembly Circular Conveyor System Checklist: Liner Details for Your Quote Request

To size a configuration like this for your cap, we need liner details as well as cap details. Our quote form covers the general line inputs. For cap liner insertion solutions, add the following:

1. Liner samples for every variant you run
2. Liner type and supplier specification
3. Retention design: the undercut or rib drawing
4. Feed preference: coil-fed, pre-cut, or open
5. Print registration needs for printed liners
6. Checks you require: height, vision, depth or force
7. Cap sizes and the range you expect to add

A printable version of the liner input checklist.

Two items on that list change our proposal more than the rest. The retention drawing tells us how deep the liner must go and what the press must do. The liner samples tell us whether a pre-cut magazine will feed them cleanly, or whether a coil feed is the safer choice.

Cap liner assembly for small batch production does not need a large line. A pre-cut magazine and one located lining station on a short loop is a workable start, with straight length kept free for later stations. Our quotation comes with a layout drawing, which lets you confirm floor space and service access before you commit.

FAQ about Cap Liner Assembly Circular Conveyor System

Liners, Feeding and Fall-Out

What is cap liner assembly?

It is the step that places a separate liner, wad or gasket into a moulded closure and retains it, usually behind an undercut or ribs. It differs from in-shell moulded liners, which form inside the cap during moulding.

Should I use pre-cut or roll-fed liners?

Choose by liner type, print and volume. Roll-fed suits high-volume plain liners but brings scrap and dust to the station. Pre-cut suits printed and induction liners and frequent changeover, at the cost of magazine refills.

Why do cap liners fall out?

Start by checking one thing: whether fall-out is spread across all mould cavities or limited to one. One cavity points to the mould, such as flash at the undercut; all cavities point to insertion depth or liner diameter.

How do you detect a missing or double liner?

A height probe placed straight after insertion catches both, because a missing liner reads low and a double liner reads high. Vision covers tilt, inversion and print position.

Which liners suit pharmaceutical caps?

Induction seal liners are common, because they bond to the container rim and show tampering when removed. The station must keep the foil face toward the container, and the closure maker supplies material documentation for the liner.

Choosing and Quoting a Cap Liner Assembly Circular Conveyor System

Is a lining machine faster than a conveyor station?

For one plain liner on a standard cap, yes. The gap narrows on large caps: one published inserter drops from six stations to two above 90 mm, while a loop keeps its station count and simply uses a larger nest.

Can one line handle several liner types?

Yes, if each variant has a suitable nest and feed. Each carrier carries its recipe, so stations can skip or switch per cap. Send samples of every variant with your quote request.

Can a loop line large 89–120 mm closures?

Yes. The nest is sized to the cap and the carrier pitch is set by the tooling, so large closures do not cost station count the way they do on a fixed turret.

Is a liner station practical for small batches?

It can be. A pre-cut magazine and one located station on a short loop is a practical first configuration. Talk to an engineer about which stations to build first.

What should I send for a quote?

Liner and cap samples for every variant, the retention drawing, your feed preference and the checks you need. We reply with a layout drawing.

Conclusion

Choose a dedicated lining machine when lining stands alone, and a cap liner assembly circular conveyor system when it shares the carrier with other located steps, large caps or liner variants.

The single input that most changes our recommendation is your retention drawing, together with liner samples. Send both through the circular conveyor quote page, or talk to an engineer before you decide.