V.A.V. Group has introduced a new vertical silicone extrusion line, enabling us to produce more complex silicone profiles faster. The vertical line is more energy efficient than the traditional horizontal line and will also facilitate quality control.
Project Manager Hannu Veijola and Production Line Operator Arttu Juntunen answer questions about the vertical extrusion line and its current and future role in our production.
How does a vertical extrusion line work?
The vertical extrusion line uses production technology that differs from the traditional horizontal furnace. On the current line, the profile is run horizontally along a conveyor belt in a 12-metre-long furnace. On the vertical line, the profile is driven vertically upwards and steered in the air through the furnace.
The profile is quickly heated by the infrared lamps. The infra-red furnace heats up in about 15 minutes, unlike the horizontal furnace, which has to be heated for several hours before it is ready to vulcanise the profiles and stays on all day. „Although the vertical furnace uses almost as much energy as the horizontal basic furnace, the energy savings are still high as the heating time is reduced and once a profile has been run through the furnace, the furnace can be switched off until the next use,“ says Veijola. Therefore it only consumes energy during the time the profile is fed through it, plus the 15 minutes before it heats up.
The vertical furnace is just under three metres tall, with a half-metre diameter tube that opens vertically in the centre. The vertical furnace is heated by the lamps and reflector panels inside it, whereas the old furnace runs on resistors. Because the vertical furnace is shorter, it does not need as long of a feedline for the finished profile, which is led down by two coils and then gathered.
What can the vertical extrusion line do that the horizontal furnace can’t?
According to Veijola, on the regular production line, the profile is driven horizontally, and runs on a belt made of wire mesh that runs for 12 metres through the furnace: „When the silicone seal comes out of the extruder, it’s still soft like plasticine, so there’s always a spot where it sticks to the belt and the pattern on the belt gets pressed into the seal itself.“ The surface is left with a dotted pattern left by the mesh, which does not affect the profile but can be aesthetically undesirable. In the horizontal furnace, an attempt is made to drive the profile through the furnace so that the pattern remains on a side that is not visible when installed, but this is not always possible.
In a vertical furnace, the seal is driven upwards, floating in the air as it bakes inside the furnace. In a vertical furnace, the profile cooks fast enough to stay in shape and pass easily through the furnace. The sealant is soft when it is fed from the bottom of the furnace, and by the time it comes out of the top, it has already hardened.
In addition, it can be difficult or even impossible to run a geometrically complex profile with a conventional line. According to Veijola and Juntunen, a challenging shape could be, for example, one where the centre of the profile is circular with three whiskers coming out of it. A profile of this shape is challenging to place in any orientation on a horizontal belt without any of the whiskers bending. As the profile travels through the air inside the vertical furnace, nothing can press on it and even the most complex seal will hold its shape. “In short, the vertical extrusion furnace allows us to make more geometrically difficult profiles, leaves no marks on the profile and is more energy efficient than a traditional furnace.”
If a vertical extrusion line is more efficient and faster, why not do all profiles with it?
Not all seals can be produced on a vertical line. Sometimes you will find seals with, for example, a very thin, millimetre-long whisker on one side, but a thicker one on another side. In a vertical furnace, such profiles exit the nozzle in a different way and there is a risk that the profile starts to spiral and ends up vulcanising in that shape.
As we come to learn which seals are easiest and most efficient to make in the vertical furnace, it will probably be faster to run them in the vertical furnace than in the horizontal one. Juntunen says that as our experience with the furnace grows, at some point, the situation may change, and we might be making most of our seals on the vertical extrusion line.
Veijola and Juntunen agree that the vertical furnace has shown its potential for even the most difficult sealing applications. The seal can be vulcanised quickly, which speeds up the entire production chain. When using a horizontal furnace to produce geometrically challenging profiles, the gasket is heated with LPG to help keep its shape before it goes into the furnace. If asymmetric seals can be transferred to the vertical extrusion line, the use of gas can also be omitted.
How have you got on with the new furnace?
According to Juntunen, a welcome feature of the vertical furnace is the laser width measurement: „The gauge reads the width of the seal as it passes through the furnace, and the machine automatically adjusts the feed according to the variations it detects in the readings. We can give the machine precise tolerances for the gasket width, which it then monitors throughout the production of the profile.“ From a quality control point of view, this vertical line makes monitoring easier, compared to the horizontal production line, where quality cannot be monitored in real-time and the gasket has to be manually checked at regular intervals.
On the use of the vertical furnace, Veijola says that so far it has mainly been used to produce symmetrical profiles. Running larger profiles for example has been noticeably faster. „While we’re still learning the machine, it has been worthwhile to stick to simple shapes, but the more we use it, the more we can try out new things,“ says Veijola. „The goal is to be able to produce the asymmetric, complex seals that we know some of our customers already have need of.“