Capacity is the first number buyers ask about. It is also one of the most misunderstood figures.
Suppliers might say that a Plastic Bag Manufacturing Machine can produce 120 bags a minute. Buyers can add 480 minutes, with an estimated 57,600 bags per shift. But the first orders may take longer than expected. It is then unclear which number was wrong.
The main difference is rated speed and actual production. Bags size, film width, number of lanes, seal time and gear shift efficiency all affect actual production.
This paper introduces the calculation method of the production capacity of plastic bag forming machine. This helps buyers compare the machine's stated capacity to the number of bags actually produced at the time of shift change.
The real meaning of rated speed, driveway and "Bags per minute"
Machine suppliers use two different devices to improve speed. If buyers get them mixed up, they miscalculate capacity.
Some providers use minute-by-minute loops. This means the number of sealing and cutting cycles the machine completes per minute. Other suppliers use plastic bags every minute. This allows you to calculate the number of bags in all lanes of a multiline machine.
One-line T-shirt bags produce 60–120 cycles per minute and 60–120 cycles per minute. A multi-lane production line can produce several bags in a single cycle. For example, a Plastic Bag Manufacturing Machine with six lanes produces six bags per cycle. At 60–120 laps per minute, when all six lanes are running, it can produce 360–720 bags per minute.
The number of lanes matters, but more lanes doesn't mean free speed. Each lane needs its own membrane, sealing tools and stacking channels. All lanes still use the same frame and transmission.
Multi-lane machines are typically used in high-capacity bags, such as grocery T-shirt bags and thin retail bags. Compared to the width of the film, they work well when the bags are small.
For example, a 1,200mm wide machine can run four lanes with a 300mm bag. The same machine can only travel in two lanes with 600mm bags.
Therefore, at the same rate of circulation, capacity depends on the film width and the width of the bag. edge trim for each driveway must also be included.
How to cap bag size
The effect of cloth bag size on capacity is mainly reflected in two aspects: width and length. Each affects the machine in a different way.
Width is the limit of space. A 1,200mm wide spider web cannot be made into a 700mm bag on four lanes because 4x700mm is wider than a spider web. There must also be room for edge trim. A simple rule is to take the usable film width, subtract edge trim, and then divide the the bag's flat width by the the side-gusset space. Rounding off the result is the number of driveways. It depends the machine tooling. Changing it requires a machine reconfiguration, not just setting changes.
There is a time limit on length. Sealing and cutting each cycle takes a set amount of time. The servo also need to pull membranes for the next bag. Longer bags require more film to be pulled out in the same cycle. When the bag is short, the machine can run at maximum speed. When the bag is long, the circulation rate goes down.
For example, on a typical servo-driven line, a 300mm bag can run at rated cycling speed. A 1,000-millimeter bag may only run at only 60–70% speed because film takes more time to transport. That's why a specification table for a Plastic Bag Manufacturing Machine should show capacity of different bag lengths, rather than only a number.
Thick membranes add another time limit due to sealing dwell time. A 15 μm film requires only a short chin contact time. A 50-micron or laminated film may require 0.4–0.8 seconds of heat to pass through the material. If the stay exceeds the machine's cycle time, the seal becomes the limit. Even if the length of the cloth bag is short, it cannot be recycled at the rated rate.
Efficiency: the number between rating and reality
None of the machines operated at their rated speed at full speed. The actual production capacity of plastic bag making machines is the efficiency losses, not the figures in the brochure.
Production efficiency of a well-run cloth bag production line is usually between 75% to 90%. This means that at rated speeds, the actual number of good bags is 75% to 90% of theoretical production. The main losses come from several common sources:
On servo systems a servo line recipes stored recipes size or format change takes about 20–40 minutes. Old machinery can take 30–60 minutes. A plant that replaces four machines a day can lose about an hour of production a day.
Stop for about 5–10 minutes at a time. The time of roll changes depends on film roll weight, bag size and film thickness.
When the quality of the film changes in the process of starting up after replacement and during production, there will be a situation of return and installation obsolescence. Stable lines with closed-loop tension control can limit this loss to less than 1–2% of output. Unstable lines have higher scrap rate.
Timed parking, such as breaks, shifts and planned maintenance, will also reduce total shift production. These are not equipment losses in the OEE calculation, but they still reduce the number of production bags.
ISO 22400-2 uses usability, performance and quality to measure overall effectiveness of equipment. Pocket dusters with 75–85% OE generally perform well. For capacity planning, buyers should use efficiency-adjusted outputs. For a new Plastic Bag Manufacturing Machine, rated speed x 0.8 is a reasonable planning figure.
A working example: from Spec Sheet to shift output
For clarity, take this typical machine and product setup:
Whole machine: Servo-driven line, 800mm wide membrane, single wire, rated speed 100 rpm.
Products: Flat pack retail bag, 400 mm wide, 250 mm long, low density polyethylene 20 μm.
Lane count: 800mm web with 20mm trim, leaving 780mm usable width. 780 ÷ 400 = 1 lane. Two 400mm lanes need more than 800mm plus trimming, so one lane is the actual setting.
Cycle rate 250mm bag length: The machine can run at or near 100 cycles rated per minute.
Theoretical output: 100 bags per shift x 60 mins x 8 hours = 48,000 bags.
Efficiency output 80%: 48,000 × 80% = 38,400 bags per shift. One shift per day for 250 working days, which equates to 9.6 million bags per year.
Change one thing now. Using the same machine, the film is 1200 mm wide and runs two 400 mm bag lanes. Cycle speed stays at 100 laps per minute, but output doubles. Production efficiency is 80% per cent, with 76,800 bags per shift.
This explains why ability cannot be judged by speed alone. The width of the film, lane count, and the size of the bag all affect the actual production of a Plastic Bag Manufacturing Machine. The same rack can produce 5 million or 15 million bags a year, depending on configuration.
The same calculations can be used for requirements planning. For example, a buyer who needs 3 million T-shirt bags a month and works 26 business days needs about 115,000 bags a day. At 80 per cent efficiency and two shifts a day, the Plastic Bag Manufacturing Machine needs to produce about 9,000 bags per hour. This requirement helps determine the correct count of lanes and bike speeds. This is better than simply choosing a single line machine with a higher rated speed.
Frequently Asked Questions
Are the prices on each machine the same?
No. Some suppliers quote per minute for a lane. Others cited the total number of bags in all lanes. Both numbers. You can also ask about the bag-size rating used. When the bag is longer or the film is thicker, the Capacity usually drops.
How different is the actual output from rated speed?
For well-run lines, 75 to 90 per cent of the rated speed should be planned. Differences come from switching, roll changes, starting scrap, and planning downtime. OE under the ISO 22400-2 KPI system is used to measure these factors.
Can one machine run fast enough to produce more bags?
Only within the size of the cloth bag and the thickness of the film. If the machine is already at rated cycling speed, higher output usually requires a larger network with more lanes or a second machine.
For the same bag duster, it is often more effective to increase the dust removal efficiency than to increase the dust removal speed. Faster switching and faster scrolling can reduce downtime and allow the Plastic Bag Manufacturing Machine to run longer.
Source of information
- ISO 22400-2 - Automated systems and integration: key performance indicators for manufacturing operations (OEE, availability, performance, quality)
- ISO 9001:2015 - process control control and document Quality management
- ASTM F88/F88M - Standard test method for sealing strength of Flexible Barrier Materials
- IEC 60204-1 - Mechanical safety: mechanical and electrical equipment
- Machinery Directive 2006/42/EC - European Union Mechanical Safety Requirements
- Grand View Research and Hemp Bags Production market data
