§ 16
How thick will the shell be, and what plate should I choose?
Answer: When a warm PP or PE sheet is drawn over a plaster model it doesn't make more plastic. The sheet is stretched over a larger area and gets thinner, most where it's stretched furthest, e.g. at heel and ankle on an AFO. The average wall thickness after forming is start thickness times sheet area divided by formed area. The calculator shows thinning and which sheet you should choose to end with a specific thickness.
Plastens volumen er den samme før og efter: tykkelse før × pladeareal = tykkelse efter × formet areal
Tykkelse efter = tykkelse før × pladeareal ÷ formet areal
Plade der kræves = ønsket tykkelse × formet areal ÷ pladeareal
| Symbol | Meaning | Unit |
|---|---|---|
| start_mm | Sheet thickness | mm |
| pladeareal_cm2 | Sheet area within the frame | cm² |
| formet_cm2 | Area of the formed surface (model + edge) | cm² |
| oensket_mm | Desired average thickness after forming | mm |
| = | Average wall thickness after forming | mm |
| = | Thinning | % |
| = | Sheet thickness giving the desired thickness | mm |
Does not apply when
The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.
Substituted
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Du bruger den, når du vælger pladetykkelse til en dybtrukket ortose, fx en AFO i polypropylen. Pladen bliver tyndere, når den strækkes over modellen.
En plade på 4 mm og 1.200 cm² trækkes over en model, der giver 1.800 cm² formet flade.
It means: Den gennemsnitlige tykkelse bliver 2.67 mm, altså 33 % udtynding. For at få 3 mm i snit skal pladen være 4.5 mm.
En plade på 5 mm og 1.200 cm² over en høj model på 2.100 cm².
It means: Tykkelsen bliver 2.86 mm i snit, med 43 % udtynding.
Bliver arealet halvanden gang større, bliver pladen to tredjedele så tyk.
Mål skallen med tykkelsesmåler ved malleolerne og hælen.