In the 1970s, around the time of the inception of fused silica capillary columns for gas chromatography, production began at SGE. When Hewlett Packard introduced the concept of flexible thin walled fused silica columns we immediately recognised the importance of mass producing high quality GC capillary columns. We then set out to develop the necessary skills for producing fine tubing. After all, our name was Scientific Glass Engineering. |  |
| Now the SGE fused silica drawing operation is quite substantial and very sophisticated with four drawing towers producing many millions of meters per year. The operation has gone well beyond just meeting the needs of the SGE's GC capillary column production, with other manufacturers of GC capillary columns now using SGE produced tubing. Tubing is also provided for a range of other applications including high throughput DNA sequencing. Our contributions to this part of the Genome Project have brought significant value to the project. Along with some other special material skills within the SGE organisation, the drawing of fused silica capillary tubing is now one of our core technologies centers. |
Understanding the process
| To put it in simple terms, fused silica capillary tubing is made like drawing a Pasteur pipette, except to very tight tolerances. The parent tube (preform) is made from high purity, halogen free fused silica glass. Its outer diameter (OD) to inner diameter (ID) ratio is virtually identical to that of the finished capillary tubing. In fact, for every one meter length of preform, it's possible to continuously draw over 10,000 meters of capillary tubing. Our drawing facility has the capacity to produce more than 50,000,000 meters per year. That's enough capillary tubing to wrap around the earth 1¼ times. During the drawing process the fused silica preform is heated to 2000 °C, at this temperature it enters a plastic state where it can be reduce by more than 200 times its original size. The size of the capillary tubing is monitored during the drawing process by laser measuring devices, which control the entire operation to within a few microns of tolerance. Continuous drawing times of up to 15 hours are typical. The capillary tubing is coated with either polyimde resins or acrylate-based solutions. It's even possible to coat with pure aluminum. Coated fused silica capillary tubing exhibits remarkable flexibility, with most sizes capable of being looped around a pencil without the glass fracturing. The key to this flexibility comes from the coating material that protects the glass from abrasive damage. The resins we use are semiconductor grade polyimides that posses excellent high temperature and electrical insulating properties. These resins offer exceptional scuff resistance, which is important for applications where the capillary tubing is frequently handled. Once the drawing process is complete, the capillary tubing is subjected to stresses many times above general handling levels to ensure it's free from structural defects. Prior to packaging, a final inspection is performed to ensure conformance to dimensional and aesthetic specifications. Back to scientific manufacturing |  |
