Frequently Asked Questions
See below a list of our most frequently asked questions.
What is the difference between Arylic, Plexiglas and Perspex, and why use it?
PolyMethyl MethAcrylate (PMMA) has the common name Acrylic. Plexiglas, Perspex and Polycast are brand names for Acrylic from suppliers such as Rhom and Lucite. Acrylic has excellent optical properties with light transmission typically around 92% and a refractive index of 1.49. It has good abrasion resistance, is easier to process versus glass and approximately half of it’s weight. It has good chemical resistance to many common chemicals and good flexural strength. It is also relatively widely available and cost effective versus many engineering plastics.
My parts are cracking and crazing, why is this?
The majority of times you see cracking and crazing in plastics such as Acrylic/Perspex/Plexiglas (PMMA), Polycarbonate (PC) and Ultem (PEI) is due to lack of the correct heat treatment. These such plastics need careful normalising and annealing steps throughout the machining, bonding and polishing process.
How thermally stable is Acrylic / Plexiglas / Perspex PMMA?
Acrylic has a coefficient of thermal expansion at 7.7 x 10-5. It is possible to produce a 100mm diameter component to a tolerance of +/- 0.1mm, however, a change in ambient temperature of 15⁰C would take this component out of limits. Consideration should be given to working tolerances and the end application when selecting the correct plastic materials and considering the use of plastic component. To ensure component stability, it is important to heat treat both the base material and finished component to ensure that they are stress free and will remain stable over a long period of time.
How to join or bond Acrylic / Plexiglas / Perspex PMMA?
Common techniques to join acrylic would be with the use of solvents or adhesives which can achieve a strong joint, however, the visual results may not be as desired and joints can suffer from shrinkage or dry back over time. These additives are also considered contaminants and are often unsuitable for medical, life science and food applications. They are also not ideal for manifolds as the solutions often bleed into the tracks and block them.
Carville have a process called High Accuracy Diffusion Bonding (HADB) which bonds the parts at a molecular level and avoids any contaminants.
Should I specify Cast or Extruded Acrylic / Plexiglas / Perspex PMMA?
Cast Acrylic has far less stress in the material than extruded Acrylic due to the nature of manufacture, so should be used whenever possible as it is of far higher quality. Extruded Acrylic is also dimensionally less stable, can stretch or burn more easily, is softer and is far more prone to cracking even with heat treatment. You can source rods or tubes of Acrylic as a base material in a cast form, but these still go egg shaped with heat treatments, so Carville normally produce our own rods and tubes from sheets of cast Acrylic after in-house heat treatment by turning as we can then guarantee dimensional stability.
Are the parts Carville supply suitable for medical devices or IVD applications?
Carville have been producing precision machined plastic parts and bonded manifolds for medical devices for almost forty years. These are often critical to function components in class III medical devices so must adhere to the strictest standards in terms of processes, materials and procedures. We support our client’s ISO14385 requirements with full documentation and full traceability on the entire process from certified in bound material to final despatched parts including full dimensional reports when required. We are also subject to unannounced audits by notified bodies including the FDA to support our clients.
Do Carville support consignment and schedule delivery agreements?
Carville work in many fast paced and demanding industries and therefore understand the needs to a secure and reliable supply chain as well as guarantee lead times and stock availability. Carville have supply framework agreements with a range of customers in Europe, Asia and the USA. These are always tailored to the individual client’s needs including features such as stock holding at Carville, consignment stock on client’s site, kan ban systems, bespoke packaging guaranteed call-off windows.
Do you produce prototype quantities and high volumes?
Carville work’s with clients from early concept prototypes, through to high volume series production. A key advantage of Carville’s approach to precision machined plastic parts and bonded manifolds, is the same fundamental process is used for the early, low volume prototypes as with the series production, so any test results from early development work can be directly translated to production volume performance. We can produce one-off parts up to volumes of 2,000 pcs per day depending on the complexity.