Shrink wrap machine speed should be specified as accepted packages produced over a defined period and SKU mix. A maximum cycle figure is not the same as sustainable throughput. Product arrival, loading, film feed, sealing, tunnel residence, cooling, inspection, normal stops, changeovers and downstream capacity can each become the line constraint.
Build the requirement from shift demand, validate every stage at representative conditions, and compare suppliers on the same accepted-output definition.
Keep Four Rate Measures Separate
| Measure | Definition | Correct use |
|---|---|---|
| Machine cycle rate | Mechanical cycles in a short run | Equipment mechanism comparison |
| Instantaneous package rate | Packages observed while running | Short-condition check |
| Sustainable accepted rate | Accepted packs over an elapsed run window, including defined micro-stops | SKU performance requirement |
| Scheduled shift output | Accepted packs after planned and normal losses | Staffing and capacity planning |
A supplier quoting cycles per minute and a buyer measuring accepted packs per shift are not reporting the same result. State the product, film, package criteria, measurement period and included losses beside every rate.
Calculate the Required Accepted Rate
Start with the production obligation rather than a brochure number.
Net scheduled production time = shift duration − breaks − planned changeovers − warm-up − planned checks − other scheduled non-running time
Required accepted rate = required accepted packages ÷ net scheduled production time
Use consistent units. If demand and SKU mix vary by shift, calculate each planned scenario rather than relying on one average. Add a capacity margin only after naming the uncertainty it covers, such as demand variation or observed normal stops. Do not hide unidentified losses inside an arbitrary multiplier.
Build a Constraint Map
Measure the stable accepted rate of each stage under the same product and run conditions:
| Stage | Evidence to collect |
|---|---|
| Product supply | Correct orientation and gap delivered over time |
| Loading or metering | Stable pitch without repeated correction |
| Film feed | Tracking, replenishment and splice behavior |
| Sealing | Accepted seals at the required cycle |
| Tunnel | Required spacing and validated exposure |
| Cooling and inspection | Film set, product condition and reject handling |
| Downstream | Acceptance without blocking or damaging packs |
The lowest demonstrated stable rate is the current line constraint. Increasing a faster stage will not raise output until the limiting stage also changes.
The line-integration guide covers conveyor interfaces, sensors and control states. This article owns the rate calculation, not the control design.
Check Tunnel Occupancy, Not Only Sealer Cycles
Tunnel demand depends on product length in the running direction, required gap and conveyor speed. The proposed pitch must also preserve airflow and prevent packages from contacting one another. Raising belt speed changes residence time; reducing the gap changes loading and air access.
Use the tunnel supplier’s approved operating range and validate the combination physically with the intended film and product. A theoretical occupancy calculation screens a proposal, but it does not establish an acceptable shrink result.
Include Human Work Where It Actually Occurs
For semi-automatic equipment, time the complete repeated cycle: pick, orient, position, initiate, unload and inspect. Include normal corrections and film changes. Observe enough cycles and more than one trained operator when staffing decisions depend on the result.
For automatic equipment, record replenishment, monitoring, sampling, reject clearing, changeover and authorized fault response. Automation relocates work; it does not make every support task disappear.
Convert SKU Rates into a Shift Forecast
Create a worksheet with one row per SKU family:
- Planned accepted quantity.
- Validated sustainable accepted rate.
- Calculated run time.
- Number and duration of changeovers.
- Warm-up, first-piece approval and planned checks.
- Normal stops not already represented in the validated rate, based on measured evidence.
Run time for a SKU family = planned accepted quantity ÷ its validated sustainable accepted rate
Add all run time and planned non-running time. The plan fits only if the total stays within the available shift. This method exposes slow products and frequent changeovers that a simple average would conceal.
Keep reject rate visible. If a test reports input rate, convert it to accepted output using the observed accepted-pack count rather than assuming every input becomes a saleable package.
Use a Production-Like Performance Test
Test the minimum, typical, maximum and least stable products that materially affect the requirement. For every run, lock the film, orientation, approved appearance, seal criteria, target spacing and duration. Record:
- Total input and accepted packages.
- Rejects by reason.
- Run time and stop time by cause.
- Operator interventions.
- Film changes or splices.
- Upstream starvation and downstream blocking.
- Restart performance after a normal stop.
- One representative changeover when changeover time affects capacity.
Report both the stable-run result and the scheduled-output forecast. Do not blend them into one unexplained rate.
Make the Purchase Decision from the Constraint
Select the machine type that can support the package and operating model, then compare configurations at the required sustainable accepted rate. A faster claimed cycle has no value when the tunnel, operator, product presentation or downstream process remains the constraint.
The basic shrink wrapping process defines the stages included in the review. Send SelectPack the SKU rate worksheet, package criteria and test conditions when requesting a comparable proposal for shrink wrapping equipment.
