A houseware moulder has a 220 t machine free and a new mould for an 8 litre round storage tub, 240 mm tall with a 230 mm rim. Clamp is no issue at about 129 to 193 t. The real question is deep mould daylight: will the machine open far enough for the tub to clear a 240 mm core, and can the ejector push it free?
Answering that takes four figures from the machine data sheet and two from the mould: opening stroke, minimum and maximum mould height, maximum daylight and ejector stroke, set against the closed mould thickness and the part height.
Key Takeaways
- Allow an opening stroke of at least 2.5 times the part height, so a 240 mm tub needs about 600 mm.
- On a toggle clamp, maximum daylight equals maximum mould height plus stroke, so the full stroke is there at every mould height.
- For a free drop, the ejector must carry a deep part clear of its core; robot take-out may need less.
- Stripper rings push on the whole rim, which suits deep round parts, but they cost more than pins.
How Much Opening Stroke Does a Deep Houseware Part Need?
At least 2.5 times the part height, by a common sizing rule. The core has to come fully out of the part, and the part then needs room to drop or be gripped between the mould halves. A 240 mm tub needs about 600 mm of opening.
The rule comes from Bruce Catoen's guide to machine sizing in MoldMaking Technology. Treat it as a planning figure. Robot take-out, collapsing cores or a part that leaves sideways can change the real need, but start from 2.5 times and justify any reduction on trial.
Opening stroke at 2.5 × part height for typical deep houseware parts (heights are assumed for illustration)
| Deep part | Part height | Opening stroke |
|---|---|---|
| Casserole outer shell | 120 mm | 300 mm |
| Storage tub | 200 mm | 500 mm |
| 8 litre round tub | 240 mm | 600 mm |
| 10 litre bucket | 260 mm | 650 mm |
| Large tub | 300 mm | 750 mm |
Compare these with the opening stroke on the data sheet. Deep buckets and tubs can run out of stroke at 220 t before they run out of clamp, so stroke belongs at the start of the check, not at the end.
How Do You Check Deep Mould Daylight?
Daylight is the largest gap between the platens. The closed mould must sit between the machine's minimum and maximum mould height, and mould thickness plus the opening you need must not exceed maximum daylight. Toggle and hydraulic clamps arrive at that maximum differently.
Catoen sets out both cases. On a toggle clamp, maximum daylight equals maximum mould height plus stroke, so the full stroke is available at every mould height. On a direct hydraulic clamp, maximum daylight equals minimum mould height plus maximum stroke, so a thicker mould leaves less opening.
Deep parts make thick moulds. The core is as tall as the part, the cavity block surrounds it, and a stripper plate adds a layer. An ejector box, used when the mould's ejector pattern does not match the machine's SPI or EUROMAP layout, adds more. Count every plate when you quote closed thickness.
Check weight as well. Catoen advises confirming the machine's maximum mould weight for both platens, and notes that most moulds locate with a 101.6 mm (4 in) or 120 mm ring. Confirm the ring size on the mould drawing before the mould arrives at your shop.
How Far Must the Ejector Push a Deep Part?
For a free drop, far enough to carry the part clear of its core, which means roughly the part depth plus some clearance. With robot take-out, a shorter stroke that breaks the part free can work. Prove the figure on trial and check it against the machine's ejector stroke.
Deep round parts shrink onto the core and can hold there by vacuum. Air through the core top breaks that vacuum, and a stripper ring spreads the push around the rim instead of loading a few pins, which avoids white stress marks on the wall.
Paul Thal of Thal Precision, writing in MoldMaking Technology, describes stripper systems as ejecting on the part's perimeter and ranks them the most expensive ejection option, as each is custom-made for the part. He advises placing ejection points at the deepest areas of a part and avoiding knockout pins under 3/64 in, about 1.2 mm, in diameter.
Where the ejector stroke falls short of the part depth, a robot that grips the part as the stripper lifts it, or two-stage ejection in the mould, can close the gap. Both add cost and need planning with the mould maker before steel is cut.
Stripper plates need upkeep too. Thal notes that the plate must sit flush with the rest of the mould, and flash at the stripper's parting line is the sign that maintenance is due. On a deep tub, that flash appears on the rim, where customers look first.
Our view: specify ejector stroke and ejector force alongside opening stroke when you order a machine for deep houseware. A machine that opens far enough but cannot push the part clear forces a slower cycle or a manual pick on every shot.
What Should You Check Before Ordering a Deep Mould?
Get the closed mould thickness, part height, ejection method and take-out plan from the mould maker, then compare them with opening stroke, mould height range, daylight and ejector stroke. For deep parts, clamp comes after these. See the 220 ton horizontal injection moulding machine page.
Frequently Asked Questions About Deep Mould Daylight and Ejector Stroke
What is the difference between daylight and opening stroke?
Opening stroke is how far the moving platen travels. Daylight is the largest gap between the platens, which includes the mould's own thickness. On a toggle clamp, maximum daylight equals maximum mould height plus stroke. A deep mould needs enough of both, so check each figure on the data sheet separately.
Does a thinner mould give more opening on a hydraulic clamp?
Yes. On a direct hydraulic clamp, maximum daylight is minimum mould height plus maximum stroke, so a thinner mould leaves more room to open and a thick deep-part mould leaves less. Check the opening available at your actual mould thickness, not the headline stroke figure on the brochure.
Why do deep tubs show white marks after ejection?
White marks are stress whitening, where ejectors push hard on a small area or the part leaves the core too hot. A stripper ring on the rim, air to break the core vacuum, more draft on the walls or a little more cooling time can each cure it.
Do deep food storage tubs need a special resin?
They need a food-contact grade. Under the FSSAI Packaging Regulations, 2018, plastics in food containers must meet the listed Indian Standards, IS 10910 for PP, and food businesses need an NABL lab certificate of conformity for packaging in direct food contact. Choose a grade your supplier lists against IS 10910.
What happens if the ejector stroke is too short?
The part stays partly on the core and does not drop. The operator then pulls it by hand, which slows and varies the cycle, or a robot must grip and pull it, which needs space the opening may not have. Check ejector stroke against part depth before the mould is built.
Related Articles
- What Can You Make on a 220 Ton Household Moulding Machine?
- Larger Buckets and Tubs on a 220 Ton Machine
- Using Recycled PP on a 220 Ton Household Machine
Sources & References
- MoldMaking Technology, B. Catoen: Machine Sizing and Specification for Optimal Mold Performance, Part 1
- MoldMaking Technology, P. Thal (Thal Precision): Three Key Decisions for an Optimal Ejection System
- FSSAI: Food Safety and Standards (Packaging) Regulations, 2018, compendium
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