Die plates (land or face plates) for thermoplastic profile extrusion · Die body, spider and mandrel, pre-land and die plate, die swell and drawdown, land length to opening ratio, flow balance across sections, calibrator interface, and re-cut trials
A polymer extrusion die plate (also called the face plate or land) is the last plate in a profile die: molten resin leaves it with the profile shape, then swells or is drawn down before a calibrator cools it to size. Its opening and land length set how the profile comes out. Ask three things first: what profile and resin the plate is for, how die swell or drawdown and flow balance between sections have been allowed for, and how many trial and re-cut rounds are included before the profile is in tolerance.
Die plates, pre-land plates and complete profile dies for extruding thermoplastic profiles, including their opening and land design and their fit with the die body, spider, mandrel and calibrator. Sheet and film dies, pipe heads, pelletiser die plates and aluminium extrusion dies (see aluminium extrusion die) are outside this page except where compared.
CNFX editorial research · Sources checked October 12, 2026 · 4 sources
European patent application EP 0 835 735 A1 (General Electric, A method for designing a profile extrusion die plate) describes a profile extrusion line as extruder, die and calibrator. In the die, the die body gives the basic profile shape, a spider plate holds a mandrel, a pre-land adds shaping, and the die plate (face plate or land), which may be one or more plates, gives the final shape. The resin then crosses a gap where it expands or contracts according to the relative speed of resin and puller, and enters the calibrator, where water cooling and vacuum fine-tune the dimensions. [1]
It explains that viscoelastic resins swell after leaving the die plate through two effects: a memory effect, overcome by keeping the resin in the die land length longer, and a flow-rate effect in which higher shear, as with thinner sections and higher rates, causes more swell. Die swell occurs if resin velocity at the die exit exceeds puller speed; drawdown occurs if puller speed exceeds it. [1]
US patent 5,608,637 (Method for designing a profile extrusion die plate) models die swell against shear rate and the ratio of die land length to die opening thickness; for its polymer resin, die swell diminishes as that ratio increases and begins to remain constant at a ratio of about 20, and for a profile with sections of different thickness the maximum thickness should be used to calculate land length. [2]
Editorial calculation: at the ratio of about 20 found for that resin, a profile whose thickest section is 3 mm would need a land length of about 3 × 20 = 60 mm; the right ratio for your resin must come from the supplier's data or trials. [2]
Give the supplier the profile drawing with tolerances, resin grade and any filler, extruder size and output, line speed and puller, die body or adapter interface, plate count (pre-land and die plate), calibrator design, steel grade and surface finish of flow surfaces, heating, and the number of trial and re-cut rounds included.
02
Balance flow between sections and plan trials
EP 0 835 735 A1 states that profile dies are designed by experience-based rules, then extruded and evaluated to see whether land length, opening thickness and opening width give the desired profile, with repeated iterations of re-cutting; every dimension change or new resin means modifying the die again. Its method links the flow and force balance inside the die with die swell or drawdown at the exit to predict die dimensions for each section of a multi-section profile from operating conditions, section width and thickness, and resin data. [1]
US 5,608,637 builds design charts for selecting die opening thickness, opening width and land length from modelled results and experimental data on draw speed, shear rate and die swell measured with an experimental die. [2]
Editorial note: ask the supplier which resin data and design method it uses, how it balances flow between thick and thin sections, and how trial results are recorded so a later resin change does not start from scratch.
Die plate dimensions must allow for shrinkage in the calibrator that follows. US 2020/0130247 A1 (Innovative Plastic Products) describes calibrators built in sections of 4 to 15 inches long from wire-EDM-cut plates, with slots that alternately apply partial vacuum and cooling water. For rigid PVC used for vinyl window lineals it gives a coefficient of expansion of 0.000035 in/in/°F up to a Tg of about 165 °F, so a 1 in strip cooled from 165 °F to 65 °F shrinks 0.0035 in, and a larger 0.00015 in/in/°F above Tg, which governs cooling from the melt. In its example a flange that cooled too slowly forced the line down to about 2.5 ft/min; with the patented calibrator the line ran at 5 ft/min while holding the critical gap. [4]
Editorial calculation: the patent's two PVC coefficients differ by 0.00015 / 0.000035 ≈ 4.3 times, so each degree of cooling above Tg, in the gap and calibrator, shrinks the profile about 4.3 times as much as a degree below Tg; size the die opening with the calibrator maker, not from room-temperature part dimensions. [4]
03
Use flow-balance optimisation results to judge L/t choices
Nóbrega, Carneiro, Pinho and Oliveira (University of Minho and University of Porto, International Polymer Processing XIX, 2004) optimised a profile die for polypropylene (Novolen PPH 2150) whose cross-section was split into six elemental sections 2–4 mm thick. The trial die used a constant land length to thickness ratio L/t of 15 at 20 kg/h with melt and die walls at 230 °C. Two automatic strategies were compared: changing section lengths (DieL) or section thicknesses (DieT). [3]
Measured and predicted pressure drop and flow rate agreed within 8% and 6%. The authors note that length optimisation gave much shorter lands (L/t down to 3.5), and that a die with low L/t is more sensitive to processing conditions because its parallel zone is too short to damp upstream oscillations; thickness optimisation produced profiles more prone to distortion. After about 4 hours of calculation all variables were within 5% of their final values. [3]
Editorial calculation: in the trial die the slowest section ran at 1/7.46, about 13% of the fastest section's velocity; after length optimisation the worst section was within about 15% (1/1.15 ≈ 0.87).
Result reported
Trial die
Length-optimised (DieL)
Thickness-optimised (DieT)
Maximum ratio of fastest to section velocity
7.46
1.15
1.68
Objective function
About 0.4
0.03
0.01
L/t range across sections
15
3.5–15
12.4–18.8
Computation time
—
43 h
111 h
Ask the die maker which balancing strategy it uses, the final L/t of each section, and the predicted velocity spread at your output and melt temperature.
04
Die body, spider and mandrel, pre-land, die plate and calibrator
Opening, land length, L/t by section and calibrator shrink allowance
Land length carries the published guidance: about 20 × opening thickness for the resin in the GE patent, and L/t of 3.5–15 or 12.4–18.8 per section after the two optimisation strategies tried on the Minho–Porto polypropylene die. [2][3]
1 company lists this product among what they make. Company figures are quoted from each
company's own website; every card states where the relationship came from.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
Share this page
Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
What is a die plate in profile extrusion?
The final shaping plate (face plate or land) after the die body, spider, mandrel and pre-land (EP 0 835 735). [1]
How long should the die land be?
For the resin in US 5,608,637, die swell stopped falling at a land length about 20 times the opening thickness, using the thickest section. [2]
Why do profile dies need re-cutting?
EP 0 835 735 says experience-based designs can need repeated cut-and-test rounds before land and opening dimensions give the profile. [1]
How well can computer flow balancing predict a profile die?
In one polypropylene case study, measured and predicted pressure drop and flow rate agreed within 8% and 6%, and the velocity spread fell from 7.46 to 1.15. [3]
How much does a PVC profile shrink after the die?
US 2020/0130247 A1 gives rigid PVC for window lineals an expansion coefficient of 0.000035 in/in/°F below a Tg of about 165 °F and 0.00015 in/in/°F above it; a 1 in strip cooled from 165 °F to 65 °F shrinks 0.0035 in. [4]
Sources and what still needs a direct check
Sources checked 2026-10-12. Two General Electric patent documents (European application 1998; US patent) describe a die design method in their own terms, and the ratio of about 20 applies to the resin they studied. The University of Minho and Porto study reports one optimised polypropylene die, and the Innovative Plastic Products patent describes calibrator sizing for rigid PVC profiles.
