Quick answer: On an 80-piece order, mold amortization is a third of the piece cost. Powder at 4.8 kg and 9.6 CNY per kilo is 46, machine time of 22 minutes adds 79, finishing 17.5, and a 6,200 CNY aluminum tool spread over 80 pieces is 77.5. That lands at 220 CNY, and only the mold line moves with volume.
Table of contents
- Four Cost Blocks Behind a Rotomolded Quote
- Wall From 3 to 6 mm and Powder Weight
- Tooling and Lot Size, 50 Against 200
- Five Lines Missing From the Quote
- FAQ
1. Four Cost Blocks Behind a Rotomolded Quote
A run of 80 cases, 600 x 400 x 260 mm, 4.5 mm wall, reinforced corners, two gasket grooves, two latches and a handle fitted at the end. Three quotes from a rotomolded plastic case manufacturer came back between 186 and 243 CNY, the spread sitting in four lines.
| Cost block | Calculation | CNY per piece |
|---|---|---|
| Powder | 4.8 kg at 9.6 per kg | 46.1 |
| Machine time | 22 minutes at 3.6 per minute | 79.2 |
| Finishing | Drilling, latches, labels, trimming | 17.5 |
| Mold amortization | 6,200 divided by 80 pieces | 77.5 |
| Total | 220.3 |
A rotomolded plastic case manufacturer prices by kilogram and by minute, not by shot. Change the powder grade and the number moves; hold the oven longer and the rate climbs.
A 186 CNY offer is not good news on its own. The missing 34 CNY is usually a hidden tool charge, or a wall quietly dropped from 4.5 mm to 3.2 mm.
2. Wall From 3 to 6 mm and Powder Weight
For a rotomolded plastic case manufacturer, wall is set by how much powder goes in, not by the cavity. On a 600 x 400 x 260 mm body, 3.0 mm takes about 3.2 kg, 4.5 mm takes 4.8 kg, and 6.0 mm takes 6.4 kg. The relationship is close to linear.
Powder price is only the visible half. A thicker wall needs longer heating and cooling, pushing the cycle from 32 minutes to 41. At two pieces per cycle over eleven effective hours, output falls from 40 pieces to 32.
The biaxial speed ratio is the parameter buyers rarely ask about. A main arm at 9 rpm against a secondary at 2.2 rpm, roughly four to one, is what distributes powder evenly across the mold wall. Get the ratio wrong and the base runs thick while the rim stays thin, with measured variation up to 1.2 mm. Under impact, the thin side always opens first.
A rotomolded plastic case manufacturer quoting one wall figure without a tolerance is giving a reference, not a specification. Write 4.5 mm plus or minus 0.5 mm and mark six measuring points.
3. Tooling and Lot Size, 50 Against 200
Rotomolded tools are thin shells, rolled and welded from steel or aluminum plate 3 to 6 mm thick, costing far less than injection molds and lasting fewer cycles.
- Aluminum plate, 6 mm, 6,200 CNY per tool, suited to runs under 200, fast heat transfer
- Steel plate, 3 mm, 12,800 CNY per tool, good past 800 pieces, tougher but slower to heat
Lot size then reshapes the piece cost. On the same tool, the gap between 50 and 200 pieces is neither powder nor labor but amortization.
| Lot size | Mold per piece (CNY) | Total per piece (CNY) | Against 50 |
|---|---|---|---|
| 50 | 124.0 | 266.8 | baseline |
| 80 | 77.5 | 220.3 | down 17% |
| 150 | 41.3 | 184.1 | down 31% |
| 200 | 31.0 | 173.8 | down 35% |
Between 50 and 200 pieces the only compressible line is the tool; powder and machine time will not negotiate.
Below 50 pieces, pay for the tool separately and keep title. Most rotomolded plastic case manufacturers accept this, and the mold serves the next run.
4. Five Lines Missing From the Quote
Rotomolded quotes arrive as one unit price with a note reading tax included. What appears at settlement sits in five places.
- Repowdering: uneven wall needing a second fill, charged at half rate
- Mold changes: adding a rib or moving a latch, from 800 CNY
- Colorant: moving from cream to olive or black, 0.8 to 1.2 CNY per kilo
- Packing: large bodies need a timber frame at 35 CNY each, pallet extra
- Sampling: 1,200 CNY for the first article, two revisions included, credited on volume
Together they add 8 to 15 percent. Asking whether each is included works better than bargaining at the end.
One more item never reaches paper: mold title. An aluminum tool at 6,200 CNY is not a large sum, but whose name sits on it decides whether you can ask a second rotomolded plastic case manufacturer for a price next time.
Conclusion
Rotomolded cost traces back to each gram of powder and each minute in the oven: powder by weight, time by minute, finishing by operation, tooling by lot size. Only the tool line responds to volume, so a small order should negotiate a separate tool charge and a fixed wall tolerance, not a lower unit price. Pick the rotomolded plastic case manufacturer that shows you those four blocks first.
This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.
Related Reading
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- Rotomolded cases against injection molded ones
- Six criteria on a supplier scorecard
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