Nozzle in a shell

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 studs (afgrenings-rør) der gennembryder en cylindrisk kappe i en skrå vinkel. Hvor studsens runde rør møder kappens runde flade, opstår en buet skæringslinje — et saddel-snit.

Tilslutninger på tanke og beholdere — studse til rør, ventiler, mandehuller og instrumenter. Et klassisk udfoldnings-stykke, fordi to cylindre skærer hinanden i en rumlig kurve.

Smed, industritekniker og skibsmontør — studse til rør, ventiler, mandehuller og instrumenter på tanke og beholdere.

Kappe- og studsplade 2–8 mm i samme materiale; rustfri 1.4301/1.4404 i proces og fødevarer.

Source: Fremstillingsfælder: docs/PLAN-UDFOLDNINGSBIBLIOTEK.md §9.2/§4. Materialer/tykkelser: src/lib/kasse/materialer.ts (DIN 6935 for stål; massefylder og handelstykkelser; springback).

Kappe-Ø — Kappe-diameter

Den gennembrudte cylinders diameter i mm. Kappens krumning bestemmer formen på saddel-snittet i bunden af studs-mønstret.

Studs-Ø — Studs-diameter

Studs-rørets diameter i mm. Sætter studsens omkreds (π·studs-Ø) = bredden på det udrullede studs-rektangel.

Studs-højde — Studs-højde

Studs-rørets længde fra kappens flade og udad i mm. Bliver den maksimale højde på studs-mønstret før saddel-snittet trækkes fra.

° — Studs-vinkel

Studsens hældning i grader fra vandret. Jo skråere studsen sidder, jo mere asymmetrisk bliver saddel-snittet.

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

1. 01Tegn studsens tværsnit (en cirkel = studs-Ø) og del omkredsen i 12 lige store dele — ur-metoden — og nummerér generatricerne 1–12.
2. 02Afsæt ved siden en udrullet grundlinje = π·studs-Ø, delt i samme 12 dele, og rejs en lodret stationslinje fra hvert delepunkt.
3. 03Tegn opstalten af studsen mod kappen og find for hver af de 12 generatricer dens sande længde fra studs-ende ned til skæringen med kappens buede flade (saddel-snittet).
4. 04Overfør hver generatrices sande længde ud på dens stationslinje i mønstret.
5. 05Forbind de 12 endepunkter med en jævn kurve — det giver studsens saddel-formede nederste kant; den øverste kant er studs-højden.
6. 06Skær mønstret ud med en limflap langs den ene søm, rul til et rør og lim sømmen.
7. 07Pas studsens saddel-kant mod hullet i kappen og lim/svejs hele vejen rundt.

Sømmen kan flyttes rundt om studsen med klokkemålet. Læg sømmen øverst eller på siden — væk fra studsens lavpunkt — så samlingen afviser vand og bliver nem at komme til.

• ·Hullet i hovedrøret er hverken en cirkel eller en ellipse: X = a·cos φ, Y = R_m·arcsin((a/R_o)·sin φ). Ellipse-tilnærmelsen holder kun for a/R_o < 0,3.
• ·Forstærkningspladen er en CYLINDERFLIG (en cirkel skåret fladt bliver en ellipse efter valsning), ikke en flad ring — den valses til R_o + t_pad/2.
• ·Ligament-vagt ved store gennemføringer: κ = s/(π·R_m) skal helst være over 0,30, ellers svækkes kappen for meget.

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.

15 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 vessel or an unpressurised pipe. It is not a pressure calculation: vessels above PED 2014/68/EU's class limits are certified equipment and must be sized in accordance with EN 13445.
• The reinforcement plate's area ratio ρ is GEOMETRY — the removed cross-section against the plate's. The required thickness follows from a pressure calculation in accordance with EN 13445-3, and neither the nozzle wall's nor the weld throats' contribution has been included. The figure is a lower, conservative estimate.
• The ligament limits κ ≥ 0.30 and κ ≥ 0.50 are a geometric safeguard against the shell becoming perforated through. They do not replace a strength calculation, and they do not apply to pressure, wind or vacuum load.
• Welding data — joint preparation, electrode, preheating, weld build-up and testing of the saddle seam — is not covered. A fully welded set-in joint in thick-walled material requires a welding procedure (WPS) in accordance with EN ISO 15614.
• Insulation shells (trunnion) are not pressure-bearing, but they are part of an insulation build-up: vapour barrier, spacers and water-shedding overlap belong to the insulation trade and are not in the figure.
• The circumferential seams against the rest of the vessel lie outside the piece. The shell section's two end edges are declared sharp; if they are to carry a seam, the piece belongs to the figure ‘Tank and vessel’.
• The nozzle's free end is supplied without an edge allowance. A flange or bead on a round rim is shrinking (ε = −b/r_n), not bending — the press brake's bend allowance does not apply there.