A customer sends a thermoware range to quote: three casserole outer shells of 160, 180 and 200 mm diameter, 100 to 120 mm deep, in glossy ABS, with PP lids. Can a 150 t machine run casseroles and thermoware shells of this size? In PP, yes, all three. In ABS, all three fit at a factor of 3, but only the 160 mm shell fits at the datasheet's upper factor of 4.
Clamp is one of three checks for these parts. Deep shells also need a long opening stroke, and ABS needs drying before it reaches the hopper. This article works through all three, with a worked example for the largest shell.
Key Takeaways
- A 200 mm round shell projects about 314 cm² and needs about 146 t at a factor of 3, with a 10% reserve.
- Allow an opening stroke of at least 2.5 times the shell height, so a 120 mm shell needs 300 mm or more.
- One ABS datasheet lists drying at 71 to 88 °C for 2 to 4 hours to below 0.10% moisture.
- Where a lid or inner part touches food, use a PP grade listed against IS 10910 and IS 16738:2018.
Will Each Shell Size Fit the Clamp?
In PP, every shell up to 200 mm diameter fits a 150 t clamp as one cavity, even at a factor of 3. In ABS, the answer depends on the factor: up to 200 mm at 3, but only about 160 mm at 4. Confirm the factor for the grade.
Clamp needed for one round shell, sprue gated (no runner area), with a 10% reserve (a starting margin, not a rule)
| Shell diameter | Projected area | At factor 2 (PP low end) | At factor 3 (PP high end) | At factor 4 (ABS high end) |
|---|---|---|---|---|
| 160 mm | 201 cm² | 62 t | 93 t | 124 t |
| 180 mm | 254 cm² | 79 t | 118 t | 158 t |
| 200 mm | 314 cm² | 97 t | 146 t | 194 t |
| 220 mm | 380 cm² | 118 t | 176 t | 235 t |
| 240 mm | 452 cm² | 140 t | 210 t | 280 t |
The figures use the projected area method explained in the applications article in this series. An SPE Plastics Engineering article puts PP at 2 to 3 US t/in². The INEOS datasheet for Lustran ABS 248, a grade it lists for small appliance housings, gives a clamp tonnage of 2.0 to 4.0 US t/in².
Shells larger than about 200 mm in PP, or 160 mm in ABS at the upper factor, are where 150 t runs out. A family mould that pairs a shell with its lid adds the lid's area too, which pushes even the smaller sizes past the limit.
How Much Stroke and Daylight Do Deep Shells Need?
Allow an opening stroke of at least 2.5 times the shell height, so the shell clears the core. A 120 mm deep shell needs 300 mm or more. Then confirm that the mould thickness sits inside the shut height range and that daylight covers thickness plus stroke.
These checks come from Bruce Catoen's MoldMaking Technology article on machine sizing. On a toggle clamp, maximum daylight is maximum shut height plus stroke, so the full stroke is there at every mould thickness. On a direct hydraulic clamp, maximum daylight is minimum shut height plus maximum stroke.
Deep shells make thick moulds. The core must be as tall as the shell, and a stripper plate or air ejection adds more plates. The same article advises checking the maximum mould weight for both platens and lists a dry cycle of 3 to 5 seconds for conventional machines, which a long stroke uses fully.
Ejection needs the same care. A deep, round shell shrinks onto its core and can hold there by vacuum. An air valve in the core top breaks that vacuum, and a stripper ring pushes on the whole rim instead of a few pins, which avoids white stress marks on a gloss part.
Our view: on deep houseware, check stroke and daylight before clamp. A 150 t machine can hold a 200 mm PP shell shut easily, and still be the wrong machine if the shell cannot leave the core.
What Changes When Moulding Casseroles and Thermoware Shells in ABS?
ABS must be dried, runs hotter than PP, and needs a warm mould for gloss. The Lustran ABS 248 datasheet lists drying at 71 to 88 °C for 2 to 4 hours, melt at 246 to 266 °C and mould at 43 to 66 °C. Plan a dryer early.
The same datasheet suggests a shot size of 50% to 75% of barrel capacity and allows up to 20% regrind. Gloss shells show every flaw, so weld lines around knob or handle holes and sink marks over bosses matter more than on a matte PP part. Gate location and an even wall decide most of that.
Where the inside of a casserole or its lid touches food, the resin needs food-contact credentials. Reliance's Repol B120MA, a PP impact copolymer, lists compliance with IS 10910 and IS 16738:2018, the Indian positive list of constituents for PP and PE in food contact. Its notched Izod is 85 J/m at 23 °C.
If the space between an outer shell and an inner liner is foam-filled for insulation, the shell must hold its shape while the foam expands. Ribs or a slightly thicker wall can help, but a thicker wall also lengthens cooling, which the baskets and trays article in this series explains.
What Should You Send Before Quoting a Thermoware Range?
Send the drawings for every shell size with height, wall thickness, part weight and resin grade, plus the lid and any knob or handle parts. Each shell then gets a clamp, stroke and drying check before the moulds are ordered. See the 150 ton horizontal injection moulding machine page.
Frequently Asked Questions About Casseroles and Thermoware Shells
Why do glossy casserole shells show flow lines?
Flow lines on a gloss part usually mean the melt front is cooling too fast against the steel. A warmer mould within the resin's range, a higher injection speed and a polished cavity all help. The Lustran ABS 248 datasheet lists a mould range of 43 to 66 °C, so check where your setting sits.
Do PP thermoware shells need a dryer as well?
PP absorbs little moisture, so a dryer is not usually needed for it. ABS is different and must be dried to the supplier's moisture limit before moulding, or splay marks appear on the surface. If your range mixes PP and ABS shells, budget a dryer for the ABS jobs.
How much regrind can go into an ABS shell?
The Lustran ABS 248 datasheet allows up to 20% regrind. On a gloss shell, colour and surface can shift before that limit, so trial the regrind ratio on the actual part. Keep regrind dry and clean, because wet or contaminated regrind shows first on high-gloss surfaces.
Can the knob and handles run on the same 150 t machine?
They can, but small parts on a large machine use little of its capacity and can sit in the barrel too long. Small knobs and handles in a multi-cavity mould often suit a smaller machine better. If they must share the 150 t machine, check the shot against the barrel first.
Why does a deep shell come out oval instead of round?
Uneven cooling and a single side gate are the usual causes. If the core runs hotter than the cavity, or one side fills first, the wall shrinks unevenly and pulls the rim out of round. A centre gate on the base and balanced core cooling keep the shell round.
Related Articles
- What Can You Make on a 150 Ton Household Moulding Machine?
- 45 mm or 50 mm Screw? Choosing for Household Articles
- Baskets and Trays: Flow, Venting and Cycle Time on a 150 Ton Machine
Sources & References
- MoldMaking Technology, B. Catoen: Machine Sizing and Specification for Optimal Mold Performance, Part 1
- INEOS ABS via UL IDES: Lustran ABS 248 datasheet
- Reliance Industries: Repol B120MA Technical Data Sheet
- SPE Plastics Engineering, A. Urbina: Mastering Clamping Force Calculation
Technical Disclaimer
Disclaimer: The information provided in this document is for general informational and educational purposes only. It is based on technical references and industry information available at the time of preparation and may be subject to change. It does not constitute engineering, technical, commercial or professional advice, nor does it constitute a quotation, specification, warranty or contractual commitment by Pratishna Engineers.
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