Flange box

Split jacket around a pair of flanges, closed by two flat annular rings — and the collar's strain calculated honestly.

Exact flat patternInside dimensions22 dimensions8 presets

Trade(10)Teknisk isolatoer …

Teknisk isolatoer Amu teknisk isolering Vvs energi Smed Metalsmed Industritekniker Skibsmontoer Procesoperatoer Industrioperatoer Teknisk designer

Trade areas(2)Insulation · Plumbing

Insulation Plumbing

Also known as(10)flangekasse · flangehætte …

flangekasse · flangehætte · flangeboks · flangekappe · flangedæksel · flangeisolering · endeskive · ventilkasse · aftagelig isoleringskappe · flange box

How true is the flat pattern?

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.

The vocabulary of bending

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.

The dimensions you type

22 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.

Dimension in mm	Interval	Standard	Explanation
Installation length of the flange pairflangelaengde	80–800 mm · step size 5	260 mm	Measured from the flange's back edge to back edge, including nuts and bolt ends. That is the length the casing must be able to accommodate — not the flanges' thickness alone.
Side allowance at each endsidetillaeg	0–150 mm · step size 5	30 mm	Extra shell length beyond the flange pair, so the end disc can finish AGAINST the pipe's insulation instead of on top of the flange's edge. The shell length becomes flange pair + 2 × this figure.
Inside Ø of the shellkappe_d	100–1.500 mm · step size 5	400 mm	INTERNAL dimension — the hole the flange and the insulation must be able to fit in. The blank is calculated on the neutral axis D_i + t; if the figure is read as an external dimension, each turn will be 2π·t too long.
Pipe outside Øroer_d	25–1.000 mm · step size 0,1	114,3 mm	The bare pipe's outer dimension — DN100 is Ø114.3 mm, DN200 is Ø219.1 mm. The pipe's dimensions are EXTERNAL; it is a foreign body the casing must go around, not sheet we are cutting.
Insulation thickness on the pipeiso_t	0–200 mm · step size 5	50 mm	The thickness of the insulation on the adjoining pipe section. The end disc's hole is sized around its shell, i.e. around Ø pipe + 2 × this figure.
Air space around the pipe insulationluft	2–20 mm · step size 1	5 mm	Radial clearance between the pipe's shell and the end disc's hole. Without clearance the casing binds, and it can neither be slid into place nor removed without tearing the pipe's own shell.
The cladding is divided intokappedeling	2 shells (180°) · 3 shells (120°) · 4 shells (90°)	2 shells (180°)	A flanged box is ALWAYS split — the pipe is already assembled. The number determines both the arch width on the blank and how many longitudinal seams must be riveted.
The end disc is split intoringdeling	Full ring (one piece) · To halvringe (kan monteres om samlet rør)	To halvringe (kan monteres om samlet rør)	—
Collar in towards the pipekrave_h	0–40 mm · step size 1	0 mm	0 = no collar. A collar is a 90° upward bend along the end disc's HOLE, axially beyond the pipe's shell. It is stretch flanging, ε = +b/r₀ — above 5% the rim must be cut into radial slits.
Ends of the shellendekant	Skarp (klippet af) · Rullet stivrille (sikke) · Opkant indad — griber om endeskiven	Rullet stivrille (sikke)	—
Upstand heightconditionalopkant_h	4–20 mm · step size 1	8 mm	External dimension on the inward-facing edge. The shrinkage is b/R_n — keep it under 5% of the shell's neutral radius, otherwise the edge cannot be bent in one piece.
Number of stiffening beads per endconditionalsikke_antal	1–3 stk · step size 1	1 stk	More grooves stiffen more, but also eat more of the blank length.
The longitudinal seam is closed withfastgoerelse	Blind rivets · Pladeskruer · Spot welding	Blind rivets	—
Pitch c/c in the longitudinal seamdeling	20–200 mm · step size 5	100 mm	Desired spacing between the fixings. The number is rounded up, and the ACTUAL pitch is distributed evenly between the outer points. Below 7 per metre (143 mm) the shell will bulge out between the rivets.
Overlap widthoverlaeg	BAI efter færdig Ø (20/35/50 mm) · Fast bredde (tastes)	BAI efter færdig Ø (20/35/50 mm)	—
Goods thicknesst	0,4–1 mm · step size 0,05	0,7 mm	Cladding sheet is 0.5–0.8 mm indoors and 0.8–1.0 mm where it is walked on or knocked. Thicker sheet is no longer an insulation shell.
Cladding materialblik	Hot-dip galvanised steel sheet DX51D+Z · Aluminium AlMg3 (5754) · Aluminium, pure (1050A) · Stainless 1.4301 / AISI 304 · Stainless 1.4404 / AISI 316L	Hot-dip galvanised steel sheet DX51D+Z	—

Advanced fields

Hidden by default — they have a sensible default, and most parts do not need them.

Dimension in mm	Interval	Standard	Explanation
Stiffening groove depthconditionalsikke_h	1–6 mm · step size 0,5	2 mm	The groove's height above the sheet. The extra length grows with the square: 8·h²/(3·w).
Stiffening groove widthconditionalsikke_w	4–20 mm · step size 1	8 mm	The beading wheel's width. If the depth is more than half the width, the flat-arc formula underestimates the extra length.
Rivet/screw Øconditionalnitte_d	Ø2.4 mm · Ø3.0 mm · Ø3.2 mm · Ø4.0 mm · Ø4.8 mm · Ø5.0 mm · Ø6.4 mm	Ø4.0 mm	The insulation trade's standard is Ø4 blind rivets. The edge-allowance layer's automatic choice (nearest standard ≥ 2·t) hits Ø2.4 on 0.7 mm sheet — too small for a shell that must be removable.
Fixed overlap widthconditionaloverlaeg_b	10–80 mm · step size 5	30 mm	At least 4 × the rivet diameter, otherwise the hole tears out at the edge of the strap.
Number of identical flange boxesantal	1–50 stk · step size 1	1 stk	Counts in the parts list and weight. The sheet plan nests one blank at a time.

Ready-made presets

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.

Flange box DN100 heating pipe — Ø400, two-part

Ø114.3 pipe with 50 mm insulation gives a pipe cladding of Ø214.3, a hole of Ø224.3 and a ring just under 88 mm wide

Also known as: flangekasse · flangehætte · flangeboks · flangekappe · flangeisolering

Small flange cap DN50 domestic water — Ø200

Ø60.3 pipe with 30 mm insulation gives a Ø128.3 hole and a ring just under 36 mm wide — the overlap is 20 mm at Ø ≤ 350

Also known as: flangehætte · lille flangekasse · ventilkasse · brugsvandsisolering · flangedæksel

Steam flange DN100 with 80 mm insulation — aluminium

80 mm insulation lifts the pipe cladding to Ø274.3 and the hole to Ø284.3 — the ring is just under 58 mm wide in 0.7 mm AlMg3

Also known as: dampflange · flangekasse damp · aluminiumskappe · procesisolering · flangehætte alu

DN200 with 15 mm collar round the pipe cladding

The collar stretches the hole edge by 8.3 % — over 5 %, so it must be cut in radial slits

Also known as: demands · flangekasse med krave · muffekant · endeskive med krave · strækflangning

DN300 process flange — Ø800 in three shells

Ø800 split in 3 gives 838 mm arc per shell versus 1,257 mm when split in two — and 50 mm overlap

Also known as: tredelt kappe · stor flangekasse · procesflange · tankstuds-kasse · Ø800 kappe

New installation — whole end disc, pulled over the pipe end

Ø300 cladding around a Ø88.9 pipe: full ring without a split line — but it can only be fitted BEFORE the flange is bolted together

Also known as: hel endeskive · hel ring · nyanlæg · monteret før samling · ubrudt skive

Outdoor Ø600 with upstand that holds the disc

6 mm upstand on Ø600 is 2.0 % shrinkage — just below the strain limit, so it can be bent in one piece

Also known as: udendørs kappe · opkant · vejrbestandig flangekasse · regnsikker kappe · endekant

Cooling pipe DN80 with 120 mm insulation — Ø700, four-part

Thick cold insulation: the hole becomes Ø344.9, the ring just under 178 mm wide, and the cladding is split into four to be manageable

Also known as: kuldeisolering · kølerør · firedelt kappe · tyk isolering · kølekasse

Reservation

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

The flange box is an INSULATION SHELL, not a pressure-bearing part. The sizing of the flange joint, the bolts' preload and the gasket's tightness belong to EN 1092-1 and EN 13480 and are not calculated here — the figure supplies the sheet metal around it.
The insulation's thickness, density, fire class and retention are NOT in the piece. The shell is the sheet metal on the outside; the thickness is determined by DS 452 and the insulation supplier's instructions, not by this figure.
Personal protection against touch is not sized. Surface temperature and the permitted contact times follow DS 452 and EN ISO 13732-1 — a shell that is geometrically correct can still be too hot to touch.
Corrosion under insulation (CUI) is not assessed. The choice between galvanised, aluminium and stainless steel, and the need for a vapour barrier or coating on the pipe itself, belongs to a corrosion assessment of the specific installation.
The watertightness outdoors depends on the overlaps facing DOWNWARDS and with the wind direction, and on the seams being caulked. The figure calculates the geometry; it says nothing about sealant or about where the seam should lie in relation to the weather.
The rivet and screw spacings are GUIDANCE-ONLY workshop practice from the blind-rivet suppliers' installation instructions (edge distance ≥ 2·d, strap width ≥ 4·d, pitch ≤ 8·d) — not a standard. Only the hole diameter is standard-backed (DIN 7337 / ISO 15977).
Fire insulation of flanges and penetrations in fire separations is not covered. Fire dampers and fire seals follow EN 15650 and EN 1366 and cannot be replaced by a sheet-metal shell.
The collar's tabs are a subsequent CUTTING operation. A radial slit has no width and therefore cannot be included in the cutting contour; the number, depth and position are given in the table and in the check dimensions.