| EUROPLEX® PPSU - Processing
EUROPLEX® PPSU sheets can be processed similarly to other thermoplastic materials.
Machining
The tools used for machining (sawblades, drills, milling cutters) must be well ground. During machining, any vibration of the material must be avoided by means of suitable clamping and retaining devices.
For sawing, we recommend conventional unset, carbide-tipped sawblades. Drilling is also simply performed using conventional metal drills or special drills for plastics.
Trimming and machining of moldings should be done with special multi-purpose milling cutters and high-speed milling machines (approx. 30,000 rpm)
Thermoforming
EUROPLEX® PPSU sheets must be dried in an air-flow oven before thermoforming, and be positioned in such a way that the air can circulate freely around them. The sheets should therefore not be stacked since this unnecessarily prolongs the drying process. The oven temperature must be controlled. The following drying times are recommemded:
Thickness (mm) |
Drying time in hours at 175°C (± 5)* |
1,0 |
4 |
2,0 |
8 |
3,0 |
12 |
4,0 |
16 |
5,0 |
20 |
6,0 |
24 |
Since different air-flow ovens have different tolerances, the stated temperatures refer to the actual oven temperature (to be established by separate measurements if necessary). |
*These times are determined for sheets stored under standard conditions (23°C, 50 % RH). If the sheets are stored in particularly humid rooms, the drying times may be up to 50 % longer than those stated here. |
To enable problem-free thermoforming, the machines should be equipped as followed:
a) heating from above and below. In particular, it must be possible to control the performance of the individual radiators at the top.
b) a means of retaining the heated sheets automatically by air support
c) output per surface area approx. 43-54 kW/m2 (possibility to heat sheets to approx. 300° C). Min. 22 kW/m2
d) if necessary a possibility to heat the molds
The forming range of EUROPLEX® PPSU sheets is between 270 and 285° C, the optimum forming temperature being approx. 275° C, since this ensures good shaping, preservation of the surface texture and low deflection).
Owing to the narrow forming temperature range, it should be possible to constantly control the sheet temperature during heating. Suitable means are radiation pyrometers that are already incorporated into the center of the top heater in some thermoforming machines. In general, the edges of the sheets should be heated to higher temperatures than the center, especially if they are flat.
The thermoformed items shrink when cooling to room temperature. EUROPLEX® PPSU shows uniform, predictable shrinkage that must be considered when designing the mold so that the finished item has the desired dimensions. Since different materials have different coefficients of linear thermal expansion, the shrinkage values for EUROPLEX® PPSU were determined as the difference between the dimensions of the mold at operating temperature and the dimensions of the component after at least 24 hours’ cooling and conditioning under standard conditions. The shrinkage of EUROPLEX® PPSU determined by this method is approx. 0.8 – 1 %.
Molds
In principle, molds made from almost all materials (wood, epoxy resin, aluminum) are suitable. However, owing to the high forming temperatures, closer attention must be paid to the properties of the mold materials.
(a) Wood: used in general for small series and prototypes. Choose low cycle times to avoid overheating and ensuring damage to the mold.
(b) Epoxy resin: used in general for average-sized and small series. Ensure a constant mold temperature (c. 90°C or more), since the mold becomes increasingly hot during production and the moldings may therefore show different dimensions.
(c) Aluminum: used in general for large series and intricate moldings. It should be possible to heat the mold to a temperature of 140 – 200° C by means of suitable temperature-control devices.
Annealing
All parts that have been thermoformed (forming, line bending etc.) or machined (by drilling, milling or grinding) should be annealed to release internal stress.
The following times and temperatures are recommended:
Temperature: 190 +/- 5° C: 8 h
Residual frozen-in stress can be determined by dipping the component (e.g. a reject from the production series) in a series of solvents that attack polyphenyl sulfone in differing degrees.
This is done by dipping the component into a given solvent for one minute or wetting the component with the solvent, then rinsing it off and examining the component visually for stress cracking. The following table lists various solvents and the corresponding stress level that leads to cracking:
Solvent Approximate |
Stress Level |
100 % ehyl acetate |
12,0 MPa |
100 % methyl ethyl ketone (MEK) |
8,3 MPa |
5 % N-methyl pyrrolidone + 95 % MEK |
5,5 MPa |
Example:
A component with a stress level higher than 8.3 Mpa shows stress cracking after immersion in methyl ethyl ketone.
Joining
EUROPLEX® PPSU sheets can be bonded with solvent-based adhesives or solution adhesives and some 2-component PUR adhesives. The parts to be bonded should be stress-free (see annealing) to prevent stress cracking.
Apart from PUR adhesives, the following are also suitable: Scotchweld 3532 from 3M and Uralane from Ciba Geigy, as well as 2-component epoxy resins, e.g. EA 9303.3NA from Dexter HYSOL. The fat-free bonded surfaces show the usual shear strength.
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