use of polyamides under humid conditions

Jean-Marie MALDJIAN Material expert / Design Expertise / Innovation Efficiency

Michel RAPEAUX, Material expert, Partner.

Innov’ Days Dijon 20 Novembre 2014

Méthodologie pour gérer les propriétés

mécaniques et dimensionnelles liées à

l'humidité dans les polyamides

Schneider Electric 2 - M. Rapeaux & JM Maldjian – March 2011

Summary

● Introduction

● Field issue

● Preventive actions

● Objective of the Guide «Use of Polyamides under humid conditions»

● Humidity absorption in Polyamides (PAs)

● Mechanisms

● Influencing factors

● Consequences

● Best Practices to design PA parts

● How to use data

● Conclusions


Creating a truly global enterprise,

close to our customers

1. Published figures restated to reflect country-market view; Source:

McKinsey Global Footprint Data Base

2. Headcount incl. supplementary staff in FTE + Delixi & Fuji JVs

North America

2013: €5.9bn

2003: €2.3bn

29,300

46

Rest of World

2013: €4.6bn

2003: €1.2bn

28,000

46

Western Europe

2013: €6.6bn

2003: €4.1bn

44,000

90

Asia Pacific

2013: €6.5bn

2003: €1.2bn

61,000

76


Les marchés de Schneider Electric


Introduction

● Field issues on Polyamide based circuit breakers during tests in Asia

(Hong-Kong & Shanghai, August 2009)

● Failure mode: handle not in TRIP position after activating trip button,

incomplete closing or opening

● Root cause

normal operation prevented by an increase in size of an unfilled

Polyamide PA46 part due to moisture absorption (30°C / 85 – 95% RH

measured on sites)


Introduction

● Decision taken

● Corrective action

● mold modification

● Preventive action

● identify other unfilled PA46 parts

● design rules for Polyamide parts

Guide for designers


Objectives of the design guide

● Provide Designers with details about humidity absorption issue

● explain humidity absorption

● identify influencing factors

● detail consequences on material mechanical properties and part dimension

● Provide Designers with rules about Polyamide part design

● tolerance class selection

● part verification

● Provide data to evaluate change in material performance

● in moderate climate (Europe… for which data are usually available from material suppliers)

● in humid climate (Asia, US for which very few data are available from material suppliers)


Humidity absorption in Polyamide (PA) Mechanism

● What is relative humidity ?

Relative Humidity (RH) is the ratio between the water content in the air Pv and

the water content at saturation Pvs at a given temperature

RH (%) = Pv / Pvs

For example, relative humidity RH is:

- 100% when it rains, whatever the temperature

- and in average

80% in South East Asia, for an average temperature of 32°C

50% in Europe, for an average temperature of 23°C


Humidity absorption in Polyamide (PA) Mechanism

● Pvs increases largely at high temperature: for 1 Kg of air, we have:

15 g of water at 23 °C

32 g of water at 32 °C

● This is why issues mainly come from humid countries


Humidity absorption in Polyamides (PA) climatic survey for year 2009

Paris (France) Bangkok (Thaïland) High humidity

during winter: less

water in air

High humidity

during hot season

: more water in air temperature temperature

Humidity Humidity


Humidity absorption in Polyamides (PA)

Why does Polyamide absorb humidity

● All polyamides trend to absorb humidity, this is the result of the

chemical structure

● amide polar function CONH in polyamide molecule exhibits a strong affinity

for water

Amide function CONH

Water (H2O)

absorbed

Water absorption is inherent to polyamide structure


Humidity absorption in Polyamides (PA)

absorption kinetics

● Humidity absorption increases with exposure time, up to the saturation

or equilibrium state

● water absorption rate depends on temperature and thickness

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20

4 mm

2 mm

1 mm

Exposition duration (days)

Humidity absoprtion (% weight)

humidity absorption kinetics for PA6 GF20 at accelerated conditions (70°C, 62% RH)


Consequences Change in dimensional stability

● Water absorption changes part

dimensions and may

● induce issues during part

dimensional qualification and/or

part assembly

● prevent normal operating

conditions of the product during

product life 0

1

2

3

Dry Europe Asia

PA46

PA66

PA66 GF30

PAA GF50

Dimensional change at saturation (%)


● Moisture absorption significantly modifies mechanical properties of

polyamide parts

● part might become too brittle under dry environment or too soft under

humid conditions

● main issue is the drop of both elastic modulus ( stiffness) and tensile

strength

Consequences Change in mechanical properties

Tensile modulus (MPa) at 35°C - 65%RH

4000

4500

5000

5500

6000

0 2 4 6 8 10 12

Exposition duration (days)

PA6 GF20 FR(30), 4mm thick


● tensile strength at 23°C / 50% RH is only 50% of the dry value…

…and is equivalent to the value obtained for 80°C / dry !!

Consequences Change in mechanical properties

0

20

40

60

80

100

0 5 10 15 20

23 °C dry

80 °C dry

23°C / 50% RH

Deformation (%)

Stress (MPa)

PA6 GF20 FR(30), 4mm thick


Best Practices

● A 3-step process

1. Design

● tolerance & functional verification by simulation (dimensional and mechanical)

●Include high humidity mechanical properties in our internal database : ( 32°C / 80 % HR)

2. Molded part verification

● how to control dimensions ?

3. Product verification

● conditioning (temperature, humidity level and duration)

Step 1

Design

Step 2

Dimensional verification of

component

Step 3

Functional verification

of product


1: Design: Use high humidity properties measured in material lab

●Humid properties (32°C,

80% RH) added in our

internal database MEZZO

●These data to be used by

designers for simulation

and dimensional

calculation.


1: Design: Correction coefficients to

apply to dry properties

Example: PA6 GF30 FR: Tensile Modulus

● Dry As Molded 11000 MPa

● Europe 23°C, 50% HR 6600 MPa (40% drop)

● Asia 32°C 80% HR 5500 MPA (50% drop)

Tensile

Modulus

Tensile

Strength

Unotched

Charpy

impact

Tensile

Modulus

Tensile

Strength

Unotched

Charpy

impact

PA6

PA6 FR

PA6 MD25 FR 0,40 0,50 0,20 0,30

PA6 GF30

PA6 GF30 FR

PA66 0,50 0,70 NB 0,25 NB

PA66 GF25 FR

PA66 GF30 FR

PA6.66 0,60 0,60 NB 0,40 0,50 NB

PA6.66 GF30 0,60 0,60 1,30 0,50 0,50

PAA GF50

PAA GF50 FR

PA46 0,30 0,60 NB 0,20 0,50 NB

PA46 GF30 FR 0,70 0,70 1,30 0,65 0,60 1,20

0,70 0,70 1,20

0,90 0,80 1,80 2,000,60 0,50

0,60 0,60

0,60 0,60 1,10 0,50 0,50 1,20

Material

23°C, 50% HR 32°C 80% HR

0,40 0,60 NB 0,25 0,50 NB

coefficient to apply

to Dry As Molded

Properties


Best Practices in Design

● Dimensional tolerance

● Corporate rules: tolerancing shall comply with NFT 58-000

category 3 for unfilled PAs, category 4 for the rest of PAs

● In addition,

● normal tolerance is the first choice

● reduced tolerance for critical applications

● tight tolerance has to be avoided

● Mechanical simulation in extreme conditions

● using mechanical properties available in the Guide

Normal Reduced Tight

NFT58000 Filled PA 0.87% 0.40% 0.30%

PA6 GF20

PA6 GF30

Humid

environment

0.4% - 0.6%

0.4% - 0.2%

Tolerance according to

NFT58000 for a 40mm part


2: Best Practices in Part verification

● Verification of molded part dimensions

Molding Dry As Molded

Dimensional Verification ….

48h

Parts are stored dry in humidity-tight bag

Stress Relaxation


3: Best Practices in Product verification

● Product Verification Conditioning

● (a) severe conditions to use only when risk is high for customer (for instance, if

degradation of impact performance may induce breakage in case of product drop or short-

circuit)

● (b) for internal parts, it is recommended to condition parts and then assembly the product

or make sure conditioning duration is long enough to get saturation

● (c) according to standard ISO 111

Dry (a) Europe Asia

Standard 23°C / 50% RH 35°C / 80% RH

Accelerated 80°C 70°C / 62% RH (c) 55°C / 95% RH (d)

Thickness

1mm

2mm 6 days (b)

Environment

Accelereted conditioning duration

Conditioning

3 days (b)16 hours


Any questions ?


Data Annex, Dimensional change

0.0 0.5 1.0 1.5 2.0 2.5 3.0

PAA GF50 FR

PA6.66 GF30

PPA GF30 FR

PA66 GF25/30

PA6 GF30

PA6 GF20 FR

PA46 GF30 FR

PA6 MD25 FR

PA6 FR

PA6.66

PA66

PA6

PA46

Europe

Asia

Dimension change (%)

use of polyamides under humid conditions

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