Drying Seam Welded Steel Tube – How We Did It

The Process

To make high quality seam welded steel tube, a flat steel plate is passed through a series of forming rollers to create the tubular shape. The seam is then welded and trimmed – throughout this process the tube is cooled and lubricated using water or water based coolant. Finally, the information relevant to the job such as heat number, dimensions, material and part number needs to be inkjet printed onto the surface of the tube. However, before the printing can take place the surface needs to be dried – that’s where we come in.

The Challenge

The customer contacted us to see if we could dry the tube by removing the water / coolant prior to the printing process. Sounds easy enough, right? Think again.

The steel tube currently has swarf on it as a result of the welding and trimming process. So we need to dry the tube, but without blowing anything back towards the rollers which are very expensive – if a piece of trim swarf gets onto the rollers it can indent them resulting in an expensive re-grinding operation for the customer.

Space on process lines is always at a premium so it is not surprising that the available space between the rollers and printing was just 200mm.

We couldn’t physically touch the surface of the tube to create a barrier – when air hits a surface it latches to it, pushing water and swarf back up the process line. This meant it was a problem we couldn’t solve with our range of energy efficient airknives and nozzles because these use high velocity air to strip water from the surface.

We needed to come up with something new…

The Solution

So we put our heads together and arrived at a novel solution – we would vacuum the water and swarf off the tube.

This is not as easy as it sounds – the reason we use blown air for stripping water from surfaces is that you can deliver a focussed jet of air onto a surface so it strips the water. When you use a vacuum it draws the air from all around and there is no focus, making it a bit more difficult. As an example, when you blow on your hand you can feel it but with your hand at the same distance and you suck in the air you feel no movement at all.

We developed a new product called a vacuum box. It effectively removes the liquid and swarf from the tube without creating any spray. A passage through the box is created for the tube with a clearance hole. With the correct design of the clearance hole, a high velocity jet of air squeezes between the tube and the clearance hole stripping the water from the surface of the tube into the vacuum box. All removed water and swarf is collected into a drum and the water is then simply pumped back to the process line after swarf is filtered out.