Processing in general
PLEXIGLAS® can be bonded with PLEXIGLAS® and some other plastics by means of ACRIFIX® adhesives. Small-sized parts can be bonded to wood or metal using contact adhesives. For larger components and major differences in temperature / moisture content, an elastic adhesive such as a compatible silicone rubber must be used owing to the different coefficient of linear thermal expansion and moisture absorption.
PLEXIGLAS® can be machined without any problems using suitable tools. These must be equipped with carbide-tipped blades (sawblades, for example). PLEXIGLAS® can be thermoformed, blow-molded etc., as well as cold-curved. The minimum bending radius (R > 150 x D) must be observed during cold-curving. Moreover, PLEXIGLAS® surfaces can be upgraded by treatment such as screening, painting, embossing, abrasion-resistant coating, etc.
Parts made from PLEXIGLAS® can be sterilized by means of gamma radiation or ethylene oxide gas. However, in the event of repeated sterilization, the following disadvantages are known to occur:
- gamma radiation: yellowing of moldings
- ethylene oxide gas: stress cracking.
For use in the medical field, we recommend our CYROLITE® molding compound, which was optimized for sterilization purposes.
Standard PLEXIGLAS® and impact-modified PLEXIGLAS® can be combined with each other at will. Naturally, the respective product properties are changed in the process. PLEXIGLAS® can be mixed fairly well with ABS, PC, PLEXIGLAS® hw55 and PVC. However, mixing of different polymeric materials produces haze in the end product.
PLEXIGLAS® molding compound is usually employed to manufacture highly transparent, brilliant moldings. Even the tiniest impurities (e.g. fines from feed piping) may reduce the brilliance or optical properties. It is therefore very important to select the optimum material for building silos.
Since PLEXIGLAS® pellets are very hard and therefore have an abrasive effect, silos made of plastics should not be used. All feed pipes to the silo and from the silo to the consumer equipment (e.g. drier, machine, etc.) should be made of stainless steel (V2A 1.4541 or V4A 1.4571). The air used for conveying the material should be cleaned via a 5-micrometer filter.
- All bends in the feed pipes should have a radius = 10 D
- It must be ensured that no gaskets protrude into the pipes.
- Silo throat cone: The cone should not be too flat, so as to ensure regular product discharge (so-called mass flow). An angle of 60° has proved suitable. Flatter angles pose a risk of core flow, and finely dispersed compound (fines) accumulates along the sides. These fines then enter the product flow in batches, and may cause clogging or processing problems, especially when the silo is emptied.
We assist our customers with special, detailed advice and planning for the construction of silos.
If PLEXIGLAS® moldings are to be further fabricated, it is advisable to anneal them at about 20°C below the Vicat softening temperature. The duration depends mainly on the wall thickness of the molding. Whereas 30 minutes are sufficient for thin-walled parts, the time increases disproportionately at high thicknesses. It is important for the parts to cool down slowly afterwards, to avoid introducing renewed stresses.
Freedom from stress can be examined by means of the alcohol test. The part is immersed in concentrated alcohol for 5 minutes. If no crazes can be discerned after drying, the part is virtually stress-free.
A high standard of cleanliness should be observed at all processing machines and downstream equipment. There is a risk of feedstock contamination with dust and foreign material particularly during conveying and drying. Only filtered air should be used for conveying the molding compound, and the air that enters the pipe subsequently must also be filtered. Aluminum pipes and hoppers are unsuitable owing to material abrasion. Only stainless steel components should be used in conveyor equipment.There is usually no need to predry PLEXIGLAS®, provided it has been stored in a dry place for not too long (up to six months). Corresponding temperatures and drying times can be taken from the respective product information leaflets.
PLEXIGLAS® moldings can be joined by all conventional welding processes (hot-gas, high-frequency, ultrasonic, friction or laser welding). During welding, it must be ensured that the contours to be joined are identical. If not, the welded PLEXIGLAS® part may be exposed to permanent mechanical stress after welding. Such mechanical stress cannot be relieved subsequently even by means of annealing.
Internal stress is usually generated even if welding is properly performed. It is therefore recommended to anneal welded parts.
All well-known methods can be used to decorate PLEXIGLAS® moldingss.
To obtain colored moldings, it is advisable to injection mold them from colored molding compound.
Painting may be useful to obtain moldings in several colors. It should be ensured that paint solvents do not attack the PLEXIGLAS® parts too strongly. Annealing is advised before painting to avoid stress cracking.
PLEXIGLAS® moldings can also be screened, hot embossed, metallized or provided with an abrasion-resistant coating to excellent effect. The surfaces to be treated must be clean and free from grease or mold release agents. The sensitive metallized surface is usually applied to the back of the item and can be additionally protected by a layer of varnish. This metallized coating applied in a high vacuum can be applied directly to the molding, with and without varnishing.