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Selecting mesh bonding systems: Frame surface preparation As with any adhesive, surface must be clean, dry, and free of any flaws. Wood can easily be sanded or planed. Aluminum is best sandblasted, but can be sanded or ground. The finely roughened surface provides the best anchor, but can hold contaminants and residues. Residues can be removed with non-oxidizing, fast evaporating solvents and moisture-free pressurized air to scrub the surface clean and dry. Adhesives Instant-set Cyanoacrylates Best known as "super glue", this adhesive sets by using spray or brush-on accelerators, before or after glue application. Basically a liquid acrylic plastic, it's assets are speed, and high tensile strength in small surface area bonding. Drawbacks are cost vs. coverage (especially on coarse mesh counts) and sensitivity to moisture before hardening. From an engineering standpoint, the wide range of viscosities available allow fine tuning of the bonding process.
2-part Urethane Adhesives This solvent-based curable system is much like an epoxy. Proportional parts of glue and hardener are mixed, and a certain time-frame is available before solidification; usually accelerated when exposed to air. It's cost-effective in high-coverage demands, and results in a more pliable surface than cyanoacrylates, but requires more time to bond. Even distribution of tension load. Mesh stretches differently at various points on the frame surface. Long threads to the center stretch more than short threads to the corners. Even tension is basically circular in nature. With the need for evenness in the rectangular format of a frame, more slack needs to be picked up at the middle of each frame side vs. the corners. This forms an arc if you draw a straight line before starting. The degree of the arc's curve is relative to the target tension level intended; the higher the tension the stronger the arc. Mesh Tension vs. Format Size As a frame gets larger, longer and longer threads extend to the center. This increase in the amount of elasticity extends the time frame for reaching mesh stability. The smaller the frame, the easier it is to achieve higher tensions and stabilization. Low-elongation threads are prestressed to remove some of this elasticity. Mesh Tension vs. Side-Bar Deflection If your tension level reaches the point of deflecting (bowing) side-bars on your frame, any additional tensioning will escalate corner tension as the center of the side-bar stretches and the center of the mesh does not. Always insure that adequate frames are used to support the tension you want to maintain. Mesh Tension vs. Mesh Material Although tensioning methods are similar for different materials, the time factors involved are impacted by how rigid or pliable the mesh is. Steel hardly elongates at all, Nylon seems to just keep stretching, Polyester eventually stops stretching but in its multifilament form it has a long term "springy" response. Mesh Stretching Techniques Given the elastic nature of mesh, slack is pulled up using mechanical or pneumatic equipment, or tensioning features that exist in the frame. Frame format size and QC limits often dictate the type of system used. Fundamental in any stretching process is a knowledge of the degree to which a particular mesh elongates: Traditional Work-Hardening As you pull up slack, the mesh stretches out more. This relaxation becomes smaller with each subsequent tensioning. Eventually stabilization is reached, or close enough, for use in production. The arrival of HT/LE threads had a big impact on the time it takes to work-harden monofilament polyester. Pulse and Rapid Tensioning Advances in screen mesh technology have developed materials that are highly predictable. This allows the ability to quickly stretch in a few stages, even exceeding intended tension level. By knowing how much elongation will occur you can often stretch up to a tension that then settles to your target level.
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