ISO 7850:1986

Overview

ISO 7850:1986 specifies a laboratory method for the determination of compressive creep of rigid cellular plastics (rigid foams). The standard defines how to apply a steady compressive load to rectangular or circular test specimens between two flat plates and measure deformation over time under controlled load, temperature, relative humidity and time. Test results quantify both the initial compressive deformation and the time-dependent creep for comparative evaluation and product qualification.

Key Topics and Requirements

• Specimen geometry and preparation

  • Test specimens are rectangular parallelepipeds or circular sections; surfaces must be undamaged and, where integral skins are part of the product, retained.
  • Standardized specimen thickness is 50 ± 1 mm (minimum thickness 20 ± 1 mm). Minimum loaded surface area is specified (generally ≥ 25 cm²); for thicknesses > 50 mm the loaded area must be at least the square of the thickness.
  • Specimens must be cut without damage and conditioned per ISO 291 (normal atmosphere: 23 ± 2 °C, 50 ± 5 % RH) for at least 24 hours.

• Apparatus

  • Dial micrometer (precision 0.1 mm) compliant with ISO 1923 or equivalent.
  • Temperature and humidity test chamber capable of ±2 °C and ±5 % RH control.
  • Compression machine with two flat plates (one mobile), plates guided to limit lateral movement and avoid bending; plate separation measured to 0.1 mm.

• Test procedures

  • Procedure A: Load applied under standard conditions; initial thickness measured (H1), load applied and thickness measured at 60 ± 10 s (H2), then thickness measured at specified intervals.
  • Procedure B: Specimen and load device stabilized at agreed temperature/RH, after 24 h the load is applied and measurements taken (H4 at 60 ± 10 s; subsequent H values at chosen intervals).
  • Recommended test conditions include temperatures (23, 40, 60, 80, 100, 120, 140 ± 2 °C), stresses (10–150 kPa ± 5 %), humidities (0–5 %, 50 %, 90 ± 5 % or ambient) and times (1, 2, 7, 14, 28 days ± 5 %).

• Calculations and reporting

  • Initial deformation (%) and compressive creep (%) are calculated from measured thicknesses. Test reports must list specimen identification, dimensions, skin type (if any), test mode (A or B), load, temperature, RH, duration, and results.

• Notes on accuracy

  • Interlaboratory data are not available; repeatability and accuracy are therefore not established in the standard.

Applications and Users

ISO 7850 is used for:

• Material selection and quality control of rigid cellular plastics (thermal insulation, sandwich cores, packaging foam).
• Product specification, comparative testing, and accelerated aging evaluation. Primary users: materials engineers, QA/test laboratories, foam manufacturers, building-product developers, and research organizations.

Related Standards

• ISO 291 - Plastics - Standard atmospheres for conditioning and testing
• ISO 1923 - Dimensional measurement for rigid cellular plastics

Keywords: ISO 7850:1986, compressive creep, rigid cellular plastics, cellular plastics testing, compressive creep test, plastics testing, ISO standards.