Every case erecting machine belongs to one of two motion families, and the choice between them determines the achievable speed, the wear pattern, the fault profile and the maintenance skill the plant will need.

The distinction is straightforward but its consequences are not. An intermittent machine moves, stops, moves again. A continuous motion machine never stops the product path. Deciding which belongs on a given line is a question about the required case rate and about how much engineering the plant is prepared to support.

The Short Answer

Intermittent motion covers 10 to 30 CPM. Each station completes its motion, the case indexes, and the next station acts. Timing is easy to observe, faults are easy to isolate, and the mechanism is straightforward to maintain in-house.

Continuous motion covers 30 to 45 CPM and above. Stations act on the case while it is moving, and all motions are timed to the transport velocity. The mechanism is more complex, the tolerances are tighter, and the fault diagnosis requires understanding the timing relationship rather than a single station.

The crossover is real. Below roughly 25 CPM, building a continuous machine is engineering effort spent on a problem that does not exist. Above 35 CPM, an intermittent machine starts losing the advantage it had — not through breakdown but through the dynamics of accelerating and decelerating a case forty times a minute, which shakes glue lines, disturbs flap positions and consumes a disproportionate share of the cycle time in acceleration alone.

What Intermittent Motion Actually Does

An intermittent machine progresses the case in discrete steps. The magazine releases a blank, the picking head places it on the mandrel, the mandrel holds while the flaps fold, the compression section closes, and the formed case is ejected. Each step waits for the previous one.

The advantages are substantial and often undervalued by buyers chasing a speed figure.

Timing is visible. An operator can watch the machine and see which step is not completing. Fault-finding on an intermittent machine is a matter of observation, which means the plant can fix most faults without a specialist.

Tolerances are generous. Because each motion completes before the next begins, a small error in one station does not propagate. A slightly mis-set fold rail produces a slightly imperfect fold, not a jam.

Wear is concentrated and predictable. Components that move repeatedly wear at known intervals, and those intervals appear in the maintenance schedule as a specific part number.

Board tolerance is better. Thin or recycled board that varies in calliper is handled more forgivingly, because each station has a dwell in which the board can settle. This matters in plants running high recycled content, where calliper varies plus or minus 0.3 mm within a pallet.

The cost is the acceleration itself. Every stop-start cycle spends part of its time accelerating and decelerating the case and the transport mechanism, and that time is not available for forming. At 10 to 25 CPM the loss is acceptable. At 35 CPM it is not.

What Continuous Motion Actually Does

A continuous motion machine keeps the case moving at constant velocity through the forming sequence. Fold rails are angled so that the flaps fold progressively as the case advances. The glue applicator fires on the fly. The compression section is a belt or roller run of sufficient length that the dwell time is achieved by the case travelling through it rather than by stopping.

Three consequences follow.

Cycle time is fully used. There is no acceleration loss, which is why continuous machines reach 40 CPM with a mechanism that is often more compact than a 20 CPM intermittent machine.

Compression length is designed, not timed. Achieving a three-second glue dwell at 40 CPM means the case travels 40 metres per minute through the compression section, so the section must be 2 metres long. This is a physical length that appears in the machine footprint, and it is why high-speed machines are long machines.

Synchronisation determines quality. Every station must act at the right instant relative to the transport. This is what servo drives with electronic cam profiles exist for, and it is why continuous machines are overwhelmingly servo-driven rather than mechanically linked.

The Timing Relationship

The relationship between speed, dwell and section length is the design equation of a continuous machine.

Transport speed (m/min)     = cases per minute × case pitch (m)
Compression length (m)      = transport speed (m/min) ÷ 60 × dwell time (s)

At 40 CPM with a 500 mm case pitch, transport speed is 20 metres per minute. A glue dwell of 3 seconds requires a compression section of 1.0 metre. Increase the pitch to 800 mm and transport speed rises to 32 metres per minute, and the same dwell now requires 1.6 metres.

This is why case size drives machine architecture as much as case rate does. A plant running large cases at 40 CPM is asking for both a long compression section and a long glue-application window, and the machine grows accordingly. High-volume single-format work at that rate is where a Double-Head High-Speed Case Former belongs, because two forming heads share the transport and the compression run is amortised across both.

Comparing the Two Architectures

Choosing Between Them

The decision follows from four questions, and the answer is usually unambiguous.

What case rate is actually required in the peak hour? Not the average. A plant needing 1,200 cases in its busiest hour needs 20 CPM sustained, which an intermittent machine delivers comfortably. A plant needing 2,400 cases per hour needs 40 CPM, which points to continuous.

How many formats? Frequent changeover favours intermittent motion, because the mechanism is more tolerant of settings that are approximately right and because the changeover itself is simpler. A continuous machine run across eight formats per shift spends more time being re-synchronised. Where the format count is high and the formats include multi-piece constructions, the Three-Piece Carton Erector is the relevant reference for how the forming sequence changes when a body and lid are involved.

How stable is the board supply? Continuous motion tracks a case accurately only if the case is dimensionally consistent. Calliper variation within a pallet introduces tracking error that shows up as flap mis-folds at speed. Plants buying board on spot markets should weight this heavily.

What maintenance competence exists? An intermittent machine can be maintained by a competent mechanical fitter. A continuous machine needs someone who can read a servo parameter set and understand a cam profile. If that person does not exist and a service contract is not budgeted, the machine will underperform its specification.

Fault Profiles Differ

On an intermittent machine, E-41 Flap Detect Missing is usually a mechanical adjustment problem — a rail out of position or a sensor misaligned. On a continuous machine, the same alarm is more often a timing problem: the sensor is in the right place but fires at the wrong instant relative to the transport, so it samples the flap before it has fully folded. The first check is different even though the code is the same.

Maintenance Rhythm

Every shift — verify the current format’s settings against the sheet, inspect suction cups for glazing, and check glue or tape position on a sample case. On a continuous machine, additionally verify the transport belt tension, since tracking depends on it.

Every week — clean the vacuum filter, check fold rail alignment, and inspect feed belts. On a continuous machine, verify the synchronisation between the transport encoder and the forming axes by running a timing check.

Every month — verify squareness on five cases, inspect the glue nozzle for charring, and review alarm logs for repeat events. On a continuous machine, check the compression belt for wear and for tracking drift.

Every quarter — inspect cam followers and bearings, re-baseline glue consumption, and re-verify the timing relationship at both the minimum and maximum rated speed rather than at one operating point.

Annually — replace or assess suction cups against a wear standard, re-grease gearboxes and linear guides, replace transport belts showing surface cracking, and re-baseline squareness across the format range.

FAQ

Can a continuous machine run slowly?
Technically yes, but its advantage is at speed and its glue dwell depends on transport speed. Running a continuous machine far below its design speed shortens the effective compression dwell unless the belt speed and glue timing are both re-parameterised. It is not a machine to buy for occasional peak use.

Is an intermittent machine outdated?
No. It covers the majority of real production requirements, tolerates board variation better and is far easier to maintain. Most plants should be buying intermittent machines and spending the difference on reliability and tooling. The full product range spans both motion families for exactly this reason.

Which is better for multi-format work?
Intermittent, generally. A continuous machine can handle multiple formats with recipe control, but the timing relationships must be re-verified per format, which adds to changeover.

Does continuous motion improve squareness?
Not inherently. Squareness comes from the mandrel and the fold geometry in both families. What continuous motion improves is throughput consistency at high case rates, where an intermittent machine’s acceleration losses and shake begin to affect the fold.

Not sure which motion profile your case rate requires? Send your peak cases per hour, format count, board specification and case dimensions to [email protected] or WhatsApp +86 13681839278. Our engineers will recommend an architecture, size the compression section and return a specification sheet within 24 hours.