Tank and vessel

The surface is developable and the flat pattern is solved in closed form. Cut the part to the drawing and it fits — the whole uncertainty sits in the K-factor, which belongs to the material and the machine, not to the geometry.

Dimensions are entered as: Inside dimensions. The flat pattern itself is always computed on the neutral fibre — at Ø800 in 3 mm sheet the difference between the inside and the outside dimension is 18.8 mm of developed width, and then the seam does not meet.

En vandret trykbeholder: et cylindrisk kappe-rør lukket i hver ende af en buet bund. Modellen viser en glat tank med to udadbuede ender.

Tankbygning og apparatbyg — fx trykluft-, vand- og procesbeholdere. Som øvelse demonstrerer den en sammensat del, hvor en cylinder og to kupler udvikles hver for sig og samles.

Smed, industritekniker, skibsmontør og procesoperatør — tank- og apparatbyg; teknisk isolatør kapsler tanken udenom.

Stål eller rustfri kappeplade 2–8 mm (1.4404 i fødevarer/klor-CIP); kuplede ender presses. Isoleringskappe udenom: alu/rustfri 0,5–1,0 mm.

Source: Fremstillingsfælder: docs/PLAN-UDFOLDNINGSBIBLIOTEK.md §9.2/§4. Materialer/tykkelser: src/lib/kasse/materialer.ts (DIN 6935 for stål; massefylder og handelstykkelser; springback). Yderkappe: src/lib/sortiment.ts (pladekappe alu/alu-zink/rustfri 0,5–1,0 mm) + src/lib/calculations.ts (overlæg, «Faglig Regning», BAI 2024).

Diameter — Kappe-diameter

Cylinderens udvendige diameter i mm. Bestemmer både kappens omkreds (π·diameter) og bundenes radius.

Cylinderlængde — Cladding length

Den lige del af kappen i mm, målt mellem de to bunde. Bliver højden på kappe-rektanglet når kappen rulles ud.

Step by step with compass and square — in cardboard first, in sheet metal after.

1. 01Tegn kappen som ét rektangel (parallel-linje): bredden = π·diameter (den udrullede omkreds), højden = cylinderlængden.
2. 02Del rektanglets bredde i 12 lige store felter og træk lodrette stationslinjer — de bliver valse-/rulle-linjer. Læg en smal limflap langs den ene lodrette søm.
3. 03Udvikl hver bund som en halvkugle i gore-blade (appelsinbåde): del kuglefladen i 12 ens, spidse blade.
4. 04For hvert gore-blad afsættes meridianbuen (R·90°) som lodret midterlinje med stationer; i hver station måles bladets halve bredde ud til begge sider og forbindes til et symmetrisk blad. Alle 12 blade er ens.
5. 05Skær 12 blade til hver ende, buk hvert blad let skålformet og lim bladene kant-mod-kant til to halvkugle-bunde.
6. 06Rul kappe-rektanglet til et rør om stationslinjerne og lim sømmen langs flappen.
7. 07Sæt en bund i hver ende af kappen og lim hele vejen rundt.

Gore-bladene er en buildbar tilnærmelse til den buede bund — let at samle i pap og plade. Placér kappens lodrette søm væk fra, hvor delen belastes, og pas de to bunde nøje til kappens omkreds, så samlingen lukker tæt.

• ·Denne tank er ATMOSFÆRISK. Trykbærende beholdere over klassegrænsen er certificeret udstyr efter PED/EN 13445 — geometrien her er ikke en trykberegning.
• ·Cylinderkappen udrulles rent (parallel-linje), men de kuplede ender kan ikke foldes ud (Theorema Egregium) — de presses eller petal-svejses.
• ·På en LIGGENDE tank: sømmen må aldrig ligge kl. 6 (bundfald og kondens samler sig der); default klokken 12.

The words and formulas the trade uses for a flat pattern. The symbols are the same throughout Discebo: α is the bend angle in degrees, R the inside bend radius, t the sheet thickness and K the K-factor — all in millimetres.

Flat pattern (development)

The part's surface laid out flat as one continuous cutting outline — the way the sheet looks BEFORE it is bent or rolled. Only a developable surface can be unfolded exactly; a doubly curved surface cannot be laid flat without stretching the material.

Flat length

The flat length the part must be cut to so the dimensions come out right once it is bent. It is either the sum of the outside dimensions minus the bend deductions, or the sum of the flat legs plus the bend allowances — both routes must give the same number.L = Σ(udvendige mål) − Σ(BD) = Σ(flade ben) + Σ(BA)

Bend allowance

The length of material that sits in the bend itself, measured along the neutral fibre. The bend allowance is always positive and is added to the flat legs.BA = (π/180) · α · (R + K · t)

Bend deduction

The amount subtracted from the sum of the outside dimensions, because the two outside dimensions between them count the corner twice. Here the bend deduction is taken as POSITIVE and subtracted; DIN 6935 writes the same quantity as the compensation value v with the opposite sign.BD = 2 · OSSB − BA

Outside setback

The distance from the theoretical outside corner point in to where the bend starts. Above 90°, tan(α/2) is clamped to at most 1 per DIN 6935, so the number does not explode towards 180°.OSSB = tan(α/2) · (R + t)

Compensation value v to DIN 6935

The standard's own way of writing the same corner loss: the flat length is a + b + v, where v is negative. Our bend deduction is therefore the same quantity with the opposite sign — never flip one without the other.L = a + b + v ⇒ v = −BD

K-factor

Where the neutral fibre sits in the sheet, given as a fraction of the sheet thickness. DIN 6935 writes the correction factor k, which applies to the neutral line in the form (R + t·k/2); the American CAD convention writes (R + K·t), so K = k/2.k = 0,65 + 0,5 · log₁₀(R/t), k ≤ 1,0 ⇒ K = k/2

Neutral fibre

The layer in the sheet that is neither stretched nor compressed when the part is bent. The flat pattern is always computed on the neutral fibre — which is why it matters whether the drawing's dimensions are inside or outside.

Bend angle

The angle the material is turned through, not the angle between the legs. The bend angle is 180° minus the included angle, so a square corner is 90° and a seam fold is 180°.α = 180° − åbningsvinklen

Inside bend radius

The radius on the inside of the bend. It is set by the tooling and the material, not by the drawing — too small a radius cracks the part in the outer fibre.

Sheet thickness

The thickness of the material. It enters every single bend allowance, so sheet delivered 0.2 mm thicker than ordered shifts the flat length at every bend.

Fold line

The line on the flat pattern where the part is to be bent. It is drawn but never cut through — in a laser file it therefore sits on its own layer.

Test bend

A strip of known raw length, bent in the material and the tooling that production will use. Measure the two outside legs afterwards and the bend deduction and K-factor can be worked back. The machine's own measured bend table beats any table.BD_målt = (A + B) − L₀

DIN 6935 covers only cold bending of flat products in structural steel. Stainless, aluminium, copper, brass and titanium zinc are not included — there the formulas are an extrapolation, and a test bend in the actual material settles it.

38 fields. The starting values belong to the figure itself — they live in one place in the code, so the tool, the share link and the smoke test can never disagree about what «default» means.

A preset sets every dimension at once. The name is often the word the part goes by in the workshop — the library's search knows them all.

Read them before the part is cut. They are here because they cannot be calculated away — not as legal text, but as craft.

• The figure describes an ATMOSPHERIC tank. It is not pressure-bearing and must not be used to size a pressure vessel — vessels above PED 2014/68/EU's class limits are certified equipment and must be calculated in accordance with EN 13445.
• Fuel tanks for road vehicles are type-approved equipment (ECE R34 / ADR) and must not be manufactured according to this figure.
• The saddle and support figures (A ≤ 0.2·L, wear plate θ + 12°, b ≥ 1.56·√(R·t)) are GUIDANCE ONLY and must be verified against EN 13445-3 ch. 16 or ASME VIII App. G before being used as requirements.
• The hygiene rules follow EHEDG's principles (fall ≥ 3°, R ≥ 3 mm, dead leg ≤ 2·d_i, Ra ≤ 0.8 µm). They do not replace an approval under Regulation (EC) 1935/2004 or a HACCP assessment.
• The straight edge h₁ on a dished head is an ENTERED dimension. Look it up in DIN 28011 or DIN 28013 respectively for your diameter and thickness — the tool does not invent it.
• The thickness after pressing a dished head is not the sheet thickness: the material thins by 10–20% at the knuckle. Strength and weight calculations must use the pressed thickness.