Flatwire, often referred to as ribbon wire, is commonly used in devices designed to reduce catheter profiles or increase available lumen size. Typical applications include safety wires in a catheter guidewire, helical coils in a catheter guidewire and braiding wire. Fort Wayne Metals uses two manufacturing techniques to yield different types of radius edged flatwire: rolled flatwire and drawn flatwire.
Both products exhibit a smooth bright surface finish and tight size tolerances. However, each has its advantages. Rolled flatwire has a larger cast, less camber, less stress induced in the wire and a lower cost versus drawn flatwire as the width/thickness ratio increases. While drawn flatwire has the advantage of improved size tolerances, it’s often specified for applications requiring more consistent and tighter dimensions.
The maximum available width for both types of flatwire depends on the thickness and the alloy. The maximum width/thickness ratio of rolled flatwire is approximately ten to one, alloy allowing. Rolled flatwire is available as thin as 0.0003". Drawn flatwire is available as thin as 0.0015". Standard tolerances for each wire type are described below. Depending on width, thickness, alloy and width/thickness ratio, both drawn flatwire and rolled flatwire may be offered.
±10% of the thickness rounded up to the next 0.0001", with a minimum of ±0.0002".
±10% of the width rounded up to the next 0.0001".
|Width or Thickness||Tolerance|
|Over||Including||Plus or Minus|
The tensile strength of flatwire is determined by manufacturing techniques. Tensile strength ranges from annealed to spring temper in most alloys. The maximum tensile strength is a function of both the alloy itself and other requirements of the specified wire, such as cast.
When determining tensile strength, it’s necessary to properly calculate the cross-sectional area using the flatwire conversion factors (see chart below). Because both rolled and drawn flatwire have full radius edges, necessary adjustments to remove the corners of the rectangle from the area calculation must be determined. Accurate calculation is vital because minute differences in cross-sectional area can make significant differences in tensile strength.
The first column is width divided by thickness. The factor is to be used to calculate cross-sectional area (i.e. 0.010" ÷ 0.003" = 3.3; look up 3.3 to get 0.984; 0.003" x 0.010" x 0.984 = 0.0000295; this is the cross-sectional area).
|Width Thickness||Factor||Width Thickness||Factor|
If straightness is critical to the flatwire application, then a minimum cast and/or maximum camber may be specified. Cast is measured by cutting a three foot piece off the spool and laying it on its edge on a flat surface so it forms a circle or an arc. The size of the circle or arc is the cast. To determine camber, a short length of flatwire is cut. Next it is placed on its width rather than its edge. Then, by holding the wire in the middle against a straight line, the distance that the free ends extend from the line is measured as camber.
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