The importance of a perfect weld
The role of laser welding technology in supporting a reliable heat exchange solution
Author: Jamie Zachary
Simple in its operation yet complex in its design, there’s much more than meets the eye with vertical moving bed heat exchanger (MBHE) technology.
From plate spacing to discharge methods, countless variables ultimately determine the efficacy of this technology. Yet production quality rises to the top in being one of the most significant factors in being able to deliver a final product that meets customers’ final requirements.
While electronic resistance welding (ERW) has been traditionally relied upon in the manufacturing industry for joining metal sheets that are used to produce pillow plates, automation technology has recently led to quantum advances in the accuracy and, in turn, the quality of what’s being used in today’s MBHEs.
“Automated laser welding technology removes the inconsistencies that have long existed with resistance, or spot, welding,” says Jan Steenhuis of Mosman Stainless Steel.
“With more control over parameters such as welding power, penetration depth and even welding speed, there’s much more predictability in high-quality finished welds that are used to produce high-quality and customer-specified pillow plates.”
The background and benefits
Pillow plates used in vertical MBHEs consist of two double-sided stainless-steel plates welded together, between which a hollow space is created when inflated with a high pressure. A heat exchange medium such as water, glycol, steam or thermal oil passes through this hollow space, indirectly cooling or heating the free-flowing bulk solids that pass through the plate channels.
To meet the cooling or heating needs while also avoiding contamination between the product and the heat exchange medium, the plates need to be able to withstand high pressures without the risk of leaking.
One of the key advantages to using the Mosman laser welding technology in the fabrication of pillow plates is its perfect clamping capabilities. For example, the process used to manufacture the plates used in Solex heat exchangers involves a three-axis, CNC-controlled laser welding machine that includes a set of 16 hydraulic fingers on each side that press the sheets together to ensure a perfect seal during welding.
In fact, Steenhuis notes this multi-clamping system guarantees every spot along the two sheets are pressed to its maximum depth, regardless if the material varies in thickness.
“Imagine if the material in one area is slightly thinner than the material in another. One area could be perfectly clamped while another is not,” he says. “To avoid that, the hydraulic fingers press the material together to avoid any fluctuations. This is what we refer to as ‘perfect clamping.’ and this gives us the assurance that the two pillow plates are touching perfectly and welded with 100 per cent accuracy.”
Once clamped and a full row is welded, the fingers will open, the sheet will move, the fingers will close and a new row is then clamped and welded.
In the driver’s seat
Another benefit to laser welding is the ability for greater control over everything from the beam’s intensity and speed to overall operator consistency.
For example, Steenhuis notes that laser welding technology allows operators to achieve a very high degree of control over the beam’s penetration depth, intensity and speed. All three variables will depend on the type of material. For example, a thin material requires less depth and intensity, compared with thicker materials that can afford more depth and greater beam intensity.
“On the other hand, with resistance welding, operators have less control over the temperature of the welding spot as it is dependent on current and resistance. As the resistance cannot be controlled, the quality of the weld can be much more inconsistent,” says Steenhuis, which can lead to bad welding or even leaking plates.
In addition, the automation that comes with laser welding technology removes the potential for user error. The welding parameters are automatically generated from a pillow plate CAD drawing. The operator controls the machine during production on product level and not path level. This means all the corrections and input is given to the machine interface on a high level and not in the machine program (e.g. CNC code).
“It’s all in the drawing,” says Steenhuis. “Once we determine the design of a plate, the image is loaded up to the machine and there’s 100 per cent accuracy in final product.”
Did you know?
One of the final steps before installing pillow plates into a MBHE is the testing phase. All pillow plates used by Solex are pressure tested to confirm if they will meet the customers’ design requirements. Pillow plates are typically inflated with 17 to 23 bar of hydraulic water, depending on the spot pattern.
Ready to talk specifics? Contact a Solex team member today.
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