Every case erector brochure quotes a CPM number, and almost none of them deliver that number in production. The gap between rated speed and real throughput is where intermittent and continuous motion machines differ most. This article gives you the actual comparison our engineers use when sizing a machine: how the two kinematic concepts work, what speed they truly hold, and why a continuous motion design holds 60 CPM while an intermittent machine of the same frame size settles at 25–40 CPM.

If you are deciding between the two, read the analysis below before you compare price lists. The throughput difference is not a small advantage — it is usually 1.5x to 2x on real board, and it changes how many machines you need on the line.

The Kinematics Difference

Intermittent (start-stop) case erector. The blank moves through the machine in discrete steps: feed stops, pickup stops, folding stops, sealing stops. Each station parks the blank while the next operation happens. The machine is simpler, cheaper, and easier to maintain, but every cycle pays a kinematic tax: accelerating and decelerating the moving mass, then waiting for the drive to settle before the next operation.

Continuous motion case erector. The blank never stops moving. Rotary or cam-driven mechanisms carry it through feeding, erecting, folding, and sealing in a single continuous flow. The drive moves at constant speed, so there is no acceleration tax per cycle — output scales with rotational speed, not with how fast the machine can stop and restart.

The tax is real. An intermittent machine with a 4-second theoretical cycle (15 CPM) loses 0.5–1.0 second per cycle to acceleration, settling, and sensor confirmation. That alone drops real output to 11–13 CPM — a 13–27% loss off the sticker. A continuous motion machine at the same theoretical speed loses under 0.2 seconds per cycle to settle, because nothing has to stop.

Speed: Rated vs. Sustainable

Here is the speed table we use in machine sizing, measured on B-flute single-wall (2.5–3.0 mm, 250–350 gsm):

The sustainable speed matters more than the sticker. A line that needs 40 CPM will be short by a wide margin on an intermittent double-station machine that quotes 30 CPM, and it will never reach 40 on that hardware. On a continuous double-head machine quoting 60 CPM, the same line runs at 66% capacity with room for spikes — which matters when a case packer upstream hiccups and you need to catch up.

What Changes with Board Weight

Board weight moves both numbers down, but not equally:

• Intermittent machines lose speed proportionally on heavy board because each heavier blank takes longer to accelerate and settle. On BC double-wall (6–7 mm, 400–500 gsm), expect 20–30% less than rated speed.
• Continuous motion machines lose less, roughly 10–15%, because the heavier blank rides the same constant-speed path; the extra time is in the folding and sealing stations, not in acceleration.

For heavy logistics cases, this compounds the throughput gap. At 40 CPM required, an intermittent machine rated 50 CPM may only deliver 35–38 on BC board — and the line is short again. A continuous machine rated 60 CPM delivers 51–54 on the same board, with margin to spare.

Changeover: Where Intermittent Wins a Point

Continuous motion is not all upside. The start-stop machine has one honest advantage: simpler changeover geometry. Because each station handles the blank independently, size adjustment is more straightforward on an intermittent machine — typical changeover is 5–8 minutes with wrench and scale.

Continuous motion machines need coordinated adjustment across the feed, erecting, and sealing stations to preserve the phase relationship. On the ZRAY double-head former, servo-driven adjustment brings this down to 3–5 minutes, but a mechanically-cammed continuous machine from another builder can take 20–30 minutes if the cams need physical repositioning.

The rule we give customers:

• Fewer than 3 changeovers per shift → the continuous machine’s speed advantage dominates. Take the 3–5 minute changeover.
• More than 8 changeovers per shift (short runs, mixed SKUs) → consider the intermittent machine, or verify the continuous machine has full servo changeover. Do not buy a mechanically-cammed continuous machine for a short-run plant.

Total Cost per Formed Case

Speed and changeover only matter through cost per case. Using the sustainable speeds above, with 7,000 USD/month operator cost and 3,500 USD/month machine-hour overhead:

The continuous double-head machine produces 2.4x the cases per hour of the intermittent double-station at roughly the same floor space. Over a year at 250 days, that is 9.9 million extra cases of capacity — which either lets you skip buying a second line, or lets one line feed two downstream packers.

Technical Parameters (ZRAY Double-Head Continuous Motion)

PLC Alarms Specific to Continuous Motion

Continuous machines add their own alarm class — anything that breaks the phase relationship between stations:

Alarm 401 — Phase Deviation.
The cam master and the station follower drifted out of sync. This is the continuous-motion equivalent of a jam detection. Steps: stop the line, check for a blank stuck between stations, clear the photo eyes, then home the cam axis and restart. Typical recovery: under 5 minutes.

Alarm 402 — Servo Torque High.
A station is fighting the drive, usually because a double-wall blank did not fully feed. Steps: remove the blank, check the feed table gap against the board thickness (should be board thickness + 1–2 mm), and verify the blank is not catching on a worn guide.

Alarm 203 — Vacuum Low.
Same root causes as any erector: worn cups, kinked lines. On a continuous machine the symptom appears as intermittent skips rather than a hard stop, because the blank keeps moving. Check the cup set before chasing the PLC.

Alarm 101 — Air Pressure Low.
Supply below 0.5 MPa at the regulator. The continuous drive keeps spinning but folding quality degrades, producing cases that fail downstream checks. Fix the supply before it becomes a quality claim.

Maintenance Rhythm for Continuous Motion

The cam followers on a continuous machine run 40–80 cycles per minute for a full shift — that is 9,600–19,200 rolling contacts per hour. Weekly roller inspection is not optional on this machine class.

Board Specification Notes for Continuous Machines

Continuous feeding is more forgiving of board variance than start-stop feeding, but not immune:

• B-flute (2.5–3.0 mm): ideal. Feeds flat, folds without spring-back issues.
• E-flute (1.5–1.8 mm): watch static. Thin board clings and double-feeds; a static bar before the feed section is worth its cost.
• EB double-wall (4.5–5.5 mm): excellent balance of stiffness and feed behavior.
• BC double-wall (6–7 mm): feeds fine but expect the 10–15% speed reduction noted above. Deep scoring is mandatory.

If you process a mixed diet of E-flute and BC double-wall on the same line, the continuous machine holds up better because the feed system tolerates the stiffness range without the settle-time penalty of a stop-start design.

Which One Does ZRAY Recommend?

We build both concepts. For most high-volume plants the answer is clear:

• Demand above 30 CPM sustained, stable formats, 2+ shifts → continuous motion. The Double-Head High-Speed Case Former runs 40–80 CPM, and one machine replaces two intermittent units in the same footprint.
• Demand below 25 CPM, frequent short runs, tight budget → intermittent. The Single-Piece Case Erector keeps the simple kinematics that make 5-minute changeovers and easy maintenance realistic.
• Both cases → measure your real board, run the sustainable-speed calculation above, and compare the cost-per-case table. Then send us the numbers; we will confirm which ZRAY model matches, with a 45-day production lead time and FAT witnessed remotely on your own samples.

Send your target CPM, board spec, and changeover frequency to [email protected]. We will size the machine on sustainable speed, not sticker speed — and show you the cost-per-case math before you commit.

Email: [email protected]
WhatsApp: +86 13681839278
Request a quotation: Contact ZRAY — tell us your required sustainable CPM and board type, and we will confirm model, parameters, and delivery within 24 working hours.