🧪 Vicat softening temperature (VST) of thermoplastic materials — the temperature at which a flat-ended 1 mm² indenter under a force of 10 N or 50 N penetrates 1 mm when heated at 50 °C/h or 120 °C/h (methods A50, B50, A120, B120); PN-EN ISO 306

Materials and NDT PN-EN ISO 306

Overview

WHAT THE STANDARD COVERS. ISO 306:2022 (clause 1) specifies four methods for determining the Vicat softening temperature (VST) of thermoplastic materials: A50 — force 10 N and heating rate 50 °C/h; B50 — 50 N and 50 °C/h; A120 — 10 N and 120 °C/h; B120 — 50 N and 120 °C/h. The methods are applicable only to thermoplastic materials, for which they give a measure of the temperature at which the material starts to soften rapidly. VST (definition 3.3) is the temperature at which a flat-tipped indenter penetrates the specimen to a depth of 1 mm under a specified load at a selected uniform rate of temperature increase; it is given in °C as the temperature of the specimen measured as close as possible to the point of indentation at the moment 1 mm is reached. The "Scope" field of the PKN card of PN-EN ISO 306:2023-05 (English version, scope description in Polish): "(1.1) This document gives four methods for determining the Vicat softening temperature (VST) of thermoplastic materials: — Method A50 using a load of 10 N and a heating rate of 50 °C/h — Method B50 using a load of 50 N and a heating rate of 50 °C/h — Method A120 using a load of 10 N and a heating rate of 120 °C/h — Method B120 using a load of 50 N and a heating rate of 120 °C/h. (1.2) The methods described are applicable only to thermoplastic materials and allow the measurement of the temperature at which thermoplastic materials start to soften rapidly" (our translation).

APPARATUS (clause 5). A rigid metal frame with a vertically movable rod (with a load plate on one end and an indenter on the other) — materials with low thermal expansion are recommended; when the frame is manufactured, repaired or replaced, a blank test is carried out on a specimen of a rigid material with low expansion (e.g. invar, borosilicate glass) over the test temperature range, and a correction of 0.02 mm or more is recorded with its sign and added algebraically to the reading. Indenter: hardened steel, length at least 2 mm, circular cross-section with an area of (1.000 ± 0.015) mm² (diameter (1.128 ± 0.008) mm), perpendicular to the rod, free from burrs. Heating: a liquid bath, a fluidized bed or a heating block with direct contact; with a medium other than air the specimen is immersed to at least 35 mm, with stirring; the liquid shall be stable over the temperature range and shall not affect the material (e.g. cause swelling or cracking) — suitable are, among others, paraffin oil, transformer oil, glycerol and silicone oils, and for a fluidized bed aluminium oxide powder. The liquid method is the reference method in case of doubt. Heating rate (50 ± 5) °C/h or (120 ± 10) °C/h — met when in every 6-minute interval the increase is (5.0 ± 0.5) °C or (12.0 ± 1.0) °C; the first 10 minutes or the first 40 °C of the ramp may be outside the tolerance (PID controllers). The weights give a total force of (10 ± 0.2) N (methods A) or (50 ± 1.0) N (methods B). Temperature sensor: resolution 0.1 °C, accuracy ±1 °C, calibrated at the immersion depth of the apparatus, not further than 12.5 mm from the point of contact of the indenter with the specimen, without touching the specimen or the frame (thermocouples according to IEC 60584-1 and -3, resistance thermometers according to IEC 60751). Penetration sensor: dial gauge or transducer (e.g. LVDT) with a reading of 0.01 mm; the total thrust of the rod, the indenter and the gauge spring shall not exceed 1 N. Micrometers for specimen dimensions — reading 0.01 mm, according to ISO 16012.

SPECIMENS (clause 6). At least two specimens per sample of material, 3–6.5 mm thick, at least 9.5 mm × 9.5 mm or 9.5 mm in diameter, with flat, parallel surfaces free from flash; from moulding materials — moulded according to ISO 293, ISO 294 or ISO 20753, if there is no material specification. Sheets thicker than 6.5 mm are reduced by machining one side to 3–6.5 mm (according to ISO 2818), testing the unmachined side; sheets thinner than 3 mm are stacked in not more than three layers (the top one at least 1.5 mm), although stacking layers does not always give the same result. Specimens from products are taken from flat, preferably non-textured places, with the texture facing away from the indenter. The result may depend on the moulding conditions of the specimens.

EDITIONS. The sixth edition ISO 306:2022 (ISO/TC 61/SC 2 with CEN/TC 249) replaced ISO 306:2013; according to the foreword, it allows commercial universal apparatus (for ISO 75 and ISO 306) and current testing practice. In the iTeh catalogue (read on 27.10.2026) ISO 306:2022 has the status "Published" and the stage "9092 – International Standard to be revised" (standard to be revised), and EN ISO 306:2022 — "Published".

STATUS (PKN card as of 27.10.2026). The card of PN-EN ISO 306:2023-05 (English version) has no withdrawal label: publication 10-05-2023, 28 pages, Chemistry Sector, KT 141 Plastics, "Adopts: EN ISO 306:2022 [IDT], ISO 306:2022 [IDT]", "Replaces: PN-EN ISO 306:2014-02 - English version", ICS 83.080.20. PKN search, search term "ISO 306" (27.10.2026): the editions PN-EN ISO 306:2002, 2005, 2006 (the last one in the Polish version) and 2014-02 are withdrawn; there is no Polish version of the 2023 edition in the results.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database refreshed from the production server on 27.10.2026 and current PCA documents downloaded on that day). Number 306 (form "PN-EN ISO 306") appears in 6 records at 6 Polish laboratories: AB 005, AB 023, AB 128, AB 163, AB 237, AB 1256. In all 6 current PCA documents the standard is in the same entries; none is suspended. Forms: "PN-EN ISO 306:2023-05" (AB 005, AB 163, AB 237, AB 1256) and "PN-EN ISO 306" without the year (AB 023, AB 128). In four laboratories the standard is in one entry with standards for pipes: PN-EN ISO 2507-1, -2 and -3:2017 (AB 005, AB 163, AB 237, AB 1256) and PN-EN 727:1998 (AB 005, AB 1256). The "Laboratories" tab ("PN-EN ISO 306") shows 10 laboratories: these 6 Polish ones and 4 Czech ones (tab query on labcoda.pl, 27.10.2026).

WHAT THE LABORATORIES TEST (database copy and PCA documents). Thermoplastic materials (AB 005: 50–250 °C; AB 163: up to 150 °C, loads of 10 N and 50 N; AB 237: 50–150 °C with heating liquid), products of thermoplastics (AB 1256: 50–150 °C, heating liquid), plastic products (AB 023: method B50, liquid as the heating medium, range given as 0–90 °C), plastics and products (AB 128: "heat resistance", up to 300 °C).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — method: A50, B50, A120 and B120 differ in force (10 or 50 N) and heating rate (50 or 120 °C/h); a result without the method stated is not comparable, and most scope entries do not state the method (AB 023 does so explicitly — B50, and AB 163 gives both loads). Second — heating medium: the reference method is the liquid bath; the liquid must not affect the material, and the specimen must be immersed to at least 35 mm. Third — temperature measured too far from the indenter: the sensor shall be not further than 12.5 mm from the point of contact, because VST is the temperature of the specimen at the indenter. Fourth — expansion of the apparatus: without a blank test and correction (when it is at least 0.02 mm), the elongation of the frame and rod on heating adds to the apparent penetration. Fifth — specimens from sheets and products: stacking thin layers does not always give the same result, and a textured surface must face away from the indenter. Sixth — scope: the methods concern thermoplastic materials only.

WHAT WE DO NOT GIVE. The fragment of ISO 306:2022 we read ends at point 6.4. We do not give the conditioning, the course of the determination (clauses 7–8), the expression of results, precision or the report requirements.

Method principle

A flat-ended indenter with an area of (1.000 ± 0.015) mm² acts perpendicularly on a specimen of thermoplastic material (thickness 3–6.5 mm) with a force of 10 N (methods A) or 50 N (methods B), and the specimen is heated uniformly at 50 °C/h or 120 °C/h in a liquid bath, fluidized bed or heating block; VST is the temperature of the specimen measured as close as possible to the indenter at the moment the penetration reaches 1 mm (ISO 306:2022, clauses 1, 3–5).

Applications

• Thermoplastic materials — a measure of the temperature at which the material starts to soften rapidly (ISO 306:2022, point 1.2)
• Products of thermoplastics, including pipes and fittings — in the scopes together with PN-EN ISO 2507 and PN-EN 727
• In accreditation scopes: 6 Polish laboratories, temperature ranges up to 150, 250 and 300 °C

Key parameters

Standard

Standard number

PN-EN ISO 306:2023-05 (wersja angielska; wprowadza EN ISO 306:2022 i ISO 306:2022 [IDT])

Title (PL)

Tworzywa sztuczne — Tworzywa termoplastyczne — Oznaczanie temperatury mięknienia metodą Vicata (VST)

Title (EN)

Plastics — Thermoplastic materials — Determination of Vicat softening temperature (VST)

Step-by-step procedure

1. Specimens

   At least 2 specimens 3–6.5 mm, ≥ 9.5 × 9.5 mm, flat and parallel; from sheets — machining one side or not more than 3 layers (top one ≥ 1.5 mm) (clause 6).

2. Apparatus

   Blank test and expansion correction (recorded when ≥ 0.02 mm); calibrated temperature sensor ≤ 12.5 mm from the indenter (points 5.1, 5.5).

3. Loading and heating

   Force 10 N or 50 N, heating at 50 °C/h or 120 °C/h with control of the increase in 6 min intervals (points 5.3–5.4). WE DO NOT GIVE the course from clause 7.

4. Result

   VST = temperature at a penetration of 1 mm, in °C, with the method stated (A50, B50, A120, B120). PN-EN ISO 306:2023-05 — current (PKN card as of 27.10.2026; English version).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The heating liquid shall be stable over the whole test temperature range and shall not affect the material (point 5.3)
• TECHNICAL NOTE: the VST result always with the method symbol — A50, B50, A120 and B120 give different temperatures

Frequently asked questions