Méthodologie pour gérer les propriétés mécaniques et dimensionnelles liées à l'humidité dans les polyamides

Transcription

1 Méthodologie pour gérer les propriétés mécaniques et dimensionnelles liées à l'humidité dans les polyamides Jean-Marie MALDJIAN Material expert / Design Expertise / Innovation Efficiency Michel RAPEAUX, Material expert, Partner. Innov Days Dijon 20 Novembre 2014

2 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 2

3 Creating a truly global enterprise, close to our customers Western Europe North America Asia Pacific Rest of World 2013: 6.6bn 2013: 5.9bn 2013: 6.5bn 2013: 4.6bn 2003: 4.1bn 2003: 2.3bn 2003: 1.2bn 2003: 1.2bn 44,000 29,300 61,000 28, Published figures restated to reflect country-market view; Source: McKinsey Global Footprint 90 Data Base 2. Headcount incl. supplementary staff in FTE + Delixi & Fuji JVs

4 Les marchés de Schneider Electric 4

5 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) 5

6 Introduction Decision taken Corrective action mold modification Preventive action identify other unfilled PA46 parts design rules for Polyamide parts Guide for designers 6

7 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) 7

8 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 8

9 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 9

10 Humidity absorption in Polyamides (PA) climatic survey for year 2009 Paris (France) temperature High humidity during winter: less water in air Bangkok (Thaïland) temperature High humidity during hot season : more water in air Humidity Humidity 10

11 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 (H 2 O) absorbed Water absorption is inherent to polyamide structure 11

12 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 2.5 Humidity absoprtion (% weight) mm 2 mm 1 mm Exposition duration (days) humidity absorption kinetics for PA6 GF20 at accelerated conditions (70 C, 62% RH) 12

13 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 Dim ensional change at saturation (%) PA46 PA66 PA66 GF30 PAA GF50 Dry Europe Asia 13

14 Consequences Change in mechanical properties 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 Tensile modulus (MPa) at 35 C - 65% RH 6000 PA6 GF20 FR(30), 4mm thick Exposition duration (days) 14

15 Consequences Change in mechanical properties tensile strength at 23 C / 50% RH is only 50% of the dry value Stress (MPa) PA6 GF20 FR(30), 4mm thick 23 C dry 80 C dry 23 C / 50% RH Deformation (%) and is equivalent to the value obtained for 80 C / dry!! 15

16 Best Practices A 3-step process Step 1 Step 2 Step 3 Design Dimensional verification of component Functional verification of product 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) 16

17 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. 17

18 1: Design: Correction coefficients to apply to dry properties Material Tensile Modulus Tensile Strength Unotched Charpy impact Tensile Modulus Tensile Strength Unotched Charpy impact PA6 PA6 FR PA6 MD25 FR 0,40 0,40 0,60 0,50 NB 0,25 0,20 0,50 0,30 NB PA6 GF30 PA6 GF30 FR PA66 0,60 0,50 0,60 0,70 1,10 NB 0,50 0,25 0,50 1,20 NB PA66 GF25 FR PA66 GF30 FR PA6.66 0,70 0,60 0,70 0,60 1,20 NB 0,60 0,40 0,60 0,50 NB PA6.66 GF30 0,60 0,60 1,30 0,50 0,50 PAA GF50 PAA GF50 FR 23 C, 50% HR 32 C 80% HR 0,90 0,80 1,80 0,60 0,50 2,00 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 coefficient to apply to Dry As Molded Properties Example: PA6 GF30 FR: Tensile Modulus Dry As Molded MPa Europe 23 C, 50% HR 6600 MPa (40% drop) Asia 32 C 80% HR 5500 MPA (50% drop) 18

19 Best Practices in Design Dimensional tolerance Corporate rules: tolerancing shall comply with NFT 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 Tolerance according to NFT58000 for a 40mm part Normal Reduced Tight NFT58000 Filled PA 0.87% 0.40% 0.30% Humid environment PA6 GF20 PA6 GF30 0.4% - 0.6% 0.4% - 0.2% Mechanical simulation in extreme conditions using mechanical properties available in the Guide 19

20 2: Best Practices in Part verification Verification of molded part dimensions Parts are stored dry in humidity-tight bag Stress Relaxation Dimensional Verification. 48h Molding Dry As Molded 20

21 3: Best Practices in Product verification Product Verification Conditioning Conditioning Environment 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 Accelereted conditioning duration 3 days (b) 16 hours 6 days (b) (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 shortcircuit) (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

22 Any questions? 22

23 Data Annex, Dimensional change PA46 PA6 PA66 PA6.66 PA6 FR PA6 MD25 FR PA46 GF30 FR PA6 GF20 FR PA6 GF30 PA66 GF25/30 Europe Asia PPA GF30 FR PA6.66 GF30 PAA GF50 FR Dimension change (%) 23