# Acetal homopolymer

Specify POM-H by grade and manufactured form; interpret short-term properties, creep, thermal expansion and chemical compatibility without transferring resin data to finished-part guarantees.

Reviewed: 2026-11-01

Tags: materials, polymers, acetal, pom-h, engineering-plastics

## Identify the polymer, grade and manufactured form

For MCG's **Acetron / Ertacetal H POM-H** stock-shape data, the **95 µm/(m·K)** mean coefficient over **23–60°C** gives **0.3515 mm** free expansion of a **100 mm** length. The result assumes uniform heating and free movement. Account for restraint, gradients and moisture in a fit calculation. [MCG POM-H physical and thermal data](https://www.mcam.com/mcam/products/pom)

**Acetal homopolymer**, or **POM-H**, is a semi-crystalline engineering thermoplastic. It is distinct from acetal copolymer, POM-C. Mitsubishi Chemical Group describes the homopolymer as generally offering stronger mechanical performance, while the copolymer offers broader chemical resistance. [MCG acetal comparison](https://www.mcam.com/mcam/products/pom)

For procurement, record critical dimensions, conditioning, surface requirements, traceability and the intended service. Require the relevant lot or product documentation when food contact, medical use, electrical classification or another approval matters. Such suitability belongs to an identified product and application basis; the family name POM-H does not establish it.

## Stock-shape data: a bounded example

MCG's comparison identifies its standard unfilled **Acetron™ / Ertacetal™ H POM-H** shapes as the basis for the following data:

| Quantity | Published POM-H entry |
| --- | --- |
| Density, ISO 1183-1 | 1.43 g/cm³ |
| Tensile strength, ISO 527-1/-2 | 78 MPa |
| Flexural modulus, ISO 178 | 3450 MPa |
| Mean CLTE, 23–60°C | 95 µm/(m·K) |

These named-product data are not finished-part acceptance limits. [MCG stock-shape property tables](https://www.mcam.com/mcam/products/pom)

## Sustained loads: creep and stress relaxation

Delrin's technical guide distinguishes **creep under constant load**, where deflection increases with time, from **stress relaxation under constant strain**, where transmitted force decreases. Composition, temperature, stress and moisture affect the response. Short-term tensile data do not resolve either behavior. [Delrin creep and stress-relaxation guide, pp. 3–4](https://www.delrin.com/wp-content/uploads/2023/01/Delrin-Solution-Series-Creep-and-Stress-NA-FNL.pdf)

For a loaded bracket, bushing or spacer, define duration, temperature, allowable deformation and unloading history. For a snap-fit or retained-force feature, define how much force must remain after the intended exposure. Use data appropriate to the actual grade and stress level rather than a universal reduction factor applied to room-temperature modulus.

The guide's material examples are bounded: its Delrin 100 modulus-versus-time example identifies **23°C and 10 MPa constant stress**, while another comparison uses **accelerated flexural creep at 23°C with DMA** and is labeled for reference. Do not transfer a plotted advantage to an arbitrary resin or component. [Delrin example conditions, pp. 4 and 6](https://www.delrin.com/wp-content/uploads/2023/01/Delrin-Solution-Series-Creep-and-Stress-NA-FNL.pdf)

Qualify representative parts where geometry, molding or machining differs from the specimen basis. Assess both initial performance and retained function. An accelerated test requires a justified relationship to the actual service; increasing temperature also changes material response.

## Temperature and chemical exposure

MCG lists **180°C melting temperature by ISO 11357-1/-3 with a 10°C/min DSC rate** for its POM-H comparison. A melting measurement is not a loaded-part operating-temperature rating. [MCG thermal-test table](https://www.mcam.com/mcam/products/pom)

For selection, distinguish melting, heat-deflection testing, short excursions, continuous exposure and performance under load. Define the temperature/time history and required dimensional, mechanical and electrical behavior. A part can lose useful stiffness or fit without melting. Evaluate expansion mismatch, local frictional heating and constraints in the actual assembly.

MCG also flags **centerline porosity in homopolymer stock shapes** and reduced chemical resistance compared with its copolymer products. Check whether machining exposes the stock center. [MCG stock-shape and chemical guidance](https://www.mcam.com/mcam/products/pom)

Specify the actual substance, concentration, temperature, duration, cleaning cycles and stress state. A generic chemical-family or pH description cannot qualify every formulation. Obtain the supplier's applicable compatibility evidence and, where needed, test the finished part under representative exposure. Do not interpret low moisture uptake as zero dimensional change or unlimited hot-water service.

## Manufacturing and functional qualification

Delrin explicitly labels its design guide a **legacy reference** and directs users to current grade-specific technical data sheets for current product and test information. Use the current grade's processing instructions rather than extracting a generic melt temperature or shrinkage number from an older manual. [Delrin design-guide qualification](https://www.delrin.com/delrin-design-guide/)

For molding, establish drying/handling as required, process window, tool geometry, shrinkage, weld-line effects and inspection. For machining stock, qualify workholding, heat input, material removal sequence and any supplier-recommended intermediate treatment. Measure critical dimensions at the specified temperature and conditioning state. Do not assume a dimension measured immediately after machining represents equilibrium service dimensions.

For sliding parts, identify counterface, finish, contact pressure, speed, duty, temperature, lubricant and contamination. A low-friction or wear-resistant material description is not a universal pressure-velocity limit or permission to run every bearing dry. Test the actual pair and geometry when wear or friction controls function.

Define joining and assembly requirements separately: press fits, threaded fasteners, bonded joints and snap-fits impose different stresses and acceptance needs. Require an appropriate joining procedure and assess retained load over time. Parent-material tensile strength alone cannot establish joint capacity.

## Release record and source dates

Retain product identity, lot, supplied form, drawing and process revisions, conditioning, dimensional results and functional acceptance. Review substitutions against chemical, thermal, time-dependent and manufacturing requirements together.

Sources reviewed November 1, 2026. Delrin's creep guide prints **Copyright 2023** and **Form No. HMC1223**. Website post/update dates and upload paths are not treated as PDF revisions. The cited MCG comparison page gives no explicit technical revision date; the legacy design guide is used for its stated applicability warning, not current grade specifications.

## Related reference

[Material selection through production](../grades-tempers-and-conditions.md)