If not finished correctly, stainless steel will sometimes develop specks of rust. That’s unsightly and can lead to customer complaints. Corrosion-resistant material isn’t supposed to suffer that problem, and it won’t if the right finishing techniques are used. Plating, electro-polishing and even grinding are some of the ways we prepare perforated tubes for service. Here’s a review of the options.
Fitness for Purpose
Perforated tubes are used primarily for filtration. As such, hole size, shape and “open area,” (the ratio of hole area to total surface,) are critical design parameters. End fittings like caps, flanges and threaded connections may be the next aspects to consider, followed by material choice. In all but a few cases the last point considered, if it’s thought of at all, is how the tube should be finished.
Finishing is key to final appearance, but its impact goes further. Performance, cost, longevity, and customer satisfaction can all be affected by how perforated tubes are finished.
In many fluid applications surface finish influences flow rates with a rougher texture build up a thicker boundary layer. Chemicals will attack some metals, causing corrosion that shortens the life of the tube. And as in the case of stainless, flakes of die steel can lead to unsightly specks of rust on an otherwise pristine surface.
Finishing can also be a way of lowering cost. This is achieved by using an inexpensive, readily formed metal as a base and coating it with a different metal with the characteristics required.
Finishing Techniques for Perforated Tubes
At Perforated Tubes Incorporated the finishing techniques we offer are:
- Plating
- Electro-polishing
- Powder coating
- Centerless grinding
Should a different finishing process be needed, please contact one of our product specialists.
Plating
More properly referred to as electroplating, this is a way of covering a lower cost or more formable metal with a thin layer of a second metal that has more desirable characteristics. In plating electricity flows from an anode to the workpiece, (the cathode,) in the process transferring atoms of the anode material.
Chrome, tin, nickel, zinc and tin are metals commonly plated over mild steel substrates. Chrome plating for example creates the corrosion-resistant, highly reflective finish required in some automotive applications.
One point to note is that some plating processes need an intermediate step to ensure good adhesion. Chrome plating is one such where mild steel is first plated with a thin layer of copper.
Electropolishing
Think of this as electroplating in reverse: rather than transferring metal to the workpiece, this uses electricity to lift atoms off the surface of the workpiece. The key to this process is that current density is greater at corners, edges and high points. Thus, as the name implies, electropolishing smooths the surface of the workpiece and in the process, removes impurities.
Electropolishing is usually reserved for stainless steel perforated tubes. On these it removes embedded flakes of die steel, preventing unsightly rust spots, and leaves a bright, highly reflective surface.
Medical and food perforated tube applications can also benefit from electropolishing. The smooth surface it creates eliminates places where microbial contamination can cling on through cleaning.
Powder Coating
Like spray painting, powder coating entails spraying a thin plastic coating onto the perforated tube. The plastic, which can be any color, forms a strong, waterproof bond to the metal surface and so provides corrosion resistance.
A limitation of powder coating is a lower upper temperature limit. For this reason powder coating is not used in applications like exhaust mufflers.
Centerless Grinding
Less of a finishing technique than a sizing operation, centerless grinding smooths the outside diameter and brings it to a consistent size. The perforated tube rests on a support while a small roller pushes it up against a grinding wheel. High spots are removed and the tube surface is smoothed out. Using centerless grinding it’s possible to maintain tolerances on diameter tighter than +/-0.002” (0.050mm).
Many Ways to Finish Perforated Tubes
While it’s the tube that does the job required, (or more accurately, the holes perforated into it,) finish has a big impact on how the final product looks and performs. As discussed here, at Perforated Tubes Incorporated we can offer several different options to address needs like appearance, corrosion protection, cost control and performance. For more information, contact us today.