A wedge wire screen from one manufacturer may “look” similar to that from another. However, there can be significant quality differences between the two which will not only influence their relative selling price but may determine the suitability of one wedge wire screen over another for a particular application.

K.M.E. supply “Premium Quality” wedge wire screens and the degree to which a competitor’s screen can conform to all of the tenets below is an indication of the quality of their screens compared with the screens supplied by K.M.E. Where the two differ, may provide a very basic indication regarding the suitability, or otherwise, for a particular application. It may also indicate what price you should be paying for a competitive wedge wire screen relative to our own, as the screen price may be influenced by the screen quality on offer and whether the price difference is warranted. 

1.  The shape of the profile wire is important

Only sharp triangular corners on the surface profile wire can impart a wedge wire screen with the optimum non- clogging feature. Most profile wires have corner radii in excess of 0.45mm whereas our profile wire radii range from only 0.15 to 0.10mm so they are extremely sharp. Round cornered profiles can have a tendency to plug and consequently flow through the screen can enter into turbulent conditions with associated low screen permeability and a high skin effect. Sharp cornered profiles allow particles to bridge across Venturi-shaped slot openings. Thus the slot remains open, allows laminar flow conditions across the whole screen length with high screen permeability and low skin effect. 

Wedge Wire Profiles

Wedge Wire Rod Profiles

To achieve such a degree of sharpness, the (initial) round bar from which the profile wires are drawn needs to be run through successive dies. However, the sharper the radius of the profile wire the more die runs required, and hence the longer the manufacturing and therefore the greater the unit cost. The benefit is that the screen will be less prone to blockage and will be more hydraulic, as evidenced by a high screen permeability factor which is the main yardstick by which to judge a wedge wire screen. 

2.  Metallurgical compatibility between profile wire and support rod is important

In order to ensure that there is a 100% fusion bond between the profile wire and the support rods the material of both must conform to a certain tolerance. To achieve the optimum specification for tensile strength and hardness a considerable amount of annealing is required but this increases the manufacturing cost. However strict adherence to proper metallurgical compatibility between the profile wire and support rods does result in a more robust screen. 

The fusion weld between our profile wire and a support rod is by a submerged arc process in order to exclude air totally from the weld.

3.  Screen material is important

Our screen material used is 316L stainless steel.

4.  The number of support rods in cylindrical screen is important

The screen surface profile wire mainly determines the collapse strength of a screen whereas the screens support rods provide not only the tensile and compressible strength but also determine the mechanical integrity of the whole screen assembly. This is because the “end fittings” for a complete assembly, be they a closure plate at the one end or a pipe etc at the other, are connected to the wedge wire by the welds between the screen support rods and the end fittings themselves. The greater the number of screen supports onto which to weld the more robust the screen assembly as a whole can be. 

Usually our “Premium Quality” wedge wire screens have double the number of internal supports compared with other manufacturers. However, the increased number of our support rods does not affect the performance of our screens. This is because the main criterion is the screen permeability factor for a particular screen. Open area alone is of no relevance because it does not include the hydraulic radius of the inflow area. The friction losses due to the mechanical structure of screen and the viscosity of a liquid passing through it can result in very different flow gradients than a simple open area calculation will indicate. 

Having more internal supports means that the aperture control is, and remains, far more exact (especially at 25 micron aperture which is the smallest) and the slot length is shorter. This fact is reinforced by our wedge wire screens being “polygon” in shape, rather than completely round as most of our competitors, since the profile wire is pulled taut against the support rods during the manufacturing process. In high flow situations, such as those encountered in the demin plants of power stations where entrance velocities can reach 1.8m/sec or more there is obviously a danger of vibrational disintegration of the screen where the support rod interval is large and unsupported circumferential wires are relatively long. 

In our view the benefits afforded by having the optimum number of internal screen support rods outweighs the disadvantage that our screens will obviously be more expensive than others due to increased material content and manufacturing time. 

5.  Welding at the optimum rate for the material concerned is important

To ensure that the fusion weld between the profile wire and the support rods has bonded properly, a certain welding speed is required for each material. If the speed is too fast, for instance in order to reduce the manufacturing time and thereby minimize the unit cost, then the structural members will be inadequately melted and hence the screen profile wire and support rods will only be “tack welded together” rather than fully welded with a deep penetration weld. Not only will this affect any associated fabrication that may be necessary on the screen itself, it will also have repercussions to the collapse strength of the screen and as such the possibility of loss of product and damage to ancillary plant equipment. The integrity of the welds is critical because they are the areas most susceptible to chemical attack and/or mechanical stress in many applications. Furthermore, aperture control tends to deteriorate when wedge wire screens are manufactured at high speed.

Contact K.M.E. today to find out more information on our Wedge wire screen solutions.