Earlier flyers were invariably made of steel, but they are now mostly made of light alloy (Fig. 11). At the high speeds currently considered normal steel flyers would spread at the legs considerably; this is detrimental to the operation of the machine, and even more so to the winding operation. The amount of spreading depends upon the rotation speed. When this varies, e.g. during starting and stopping, the presser arm (5) adopts a continually varying inclination, which causes continual shifting of the winding point of the bobbin. It becomes impossible to ensure a controlled build over the complete package. In addition, light alloy flyers have lower weight. Flyers can have varying sizes, which are specified in inches. The stated sizes are actually winding dimensions, i.e. the maximum height (first number) and the maximum diameter (second number) of a wound package of material. Roving frames are supplied in the following sizes:
12˝ x 5 1/2˝ ; 12˝ x 6˝ ; 14˝ x 6˝
14˝ x 6 1/2˝ ; 16˝ x 6˝, 16˝ x 7˝
As well as imparting the roving twist, the flyer has to guide the very sensitive strand from the flyer top to the package without introducing false drafts – not exactly an easy task. For one thing, the strand has only protective twist and is very liable to break. For another, the flyer is rotating, along with the roving, at a speed of up to 1 500 rpm. The fiber strand must therefore be protected against strong air currents. For this purpose, in most roving frames to date, one of the two flyer legs (4) has usually been „hollow“, i.e. with a deep guide groove that is open in a direction opposite to the direction of rotation. The strand is drawn through this groove. The second, solid flyer leg serves to balance the grooved leg. Newer designs no longer feature this easily accessible, „service-friendly“ groove. Instead, they have a very smooth guide tube set into one flyer leg. In this case, the strand is completely protected against air flows and the roving is no longer pressed with considerable force against the metal of the leg, as it is in the previous designs. Frictional resistance is significantly reduced, so that the strand can be pulled through with much less force. This reduces false drafts and strand breaks while allowing high production speeds. However, piecing of strand breaks is somewhat more difficult.