Page 39 - MetalForming September 2017

How to Trim a Flap Disc
Some flap discs feature a trimmable backing plate that can be removed pro- gressively to establish the desired flap overhang. This feature provides an operator with a more versatile product for multiple jobs, and can extend the product life.
Every flap-disc manufacturer has recommendations for trimming. A com- mon one is a maximum trim of 3⁄8 in. from the edge of the original backing plate. Remember that not all plastic- backed flap discs are trimmable. Those that are use composite or glass-filled nylon back plates—not plastic—that allow the edges to be trimmed without shattering. Before trimming any flap disc, the disc must be marked or rated as trimmable. Operators also need to read and understand the manufactur- er’s recommendations.
To achieve the best results, follow these steps:
1) Select a sharp piece of scrap material.
2) Ramp the flap disc up to speed.
3) Slowly lift the flap disc until the
flap’s top (or overhang) contacts
the scrap.
4) Push directly into the corner of
the metal with consistent, con-
trolled pressure.
The process may take some practice
to perfect, but in the long run it can save time and money.
To maximize effectiveness and longevity of a flap disc, use the proper pressure at the proper angle.
Choosing the Material: Three Choices
Aluminum oxide is a common choice when a consistent, low-cost product is needed, but the most com- mon flap disc used today is zirconia alumina. This type of flap disc provides a blend of zirconia-alumina and alu- minum-oxide grains as well as the most versatility. Although it is slightly more expensive upfront than an aluminum- oxide flap disc, it is more heat-resistant and more durable, and it maintains its sharpness longer.
Another choice is ceramic alumina. The grains on these flap discs micro- fracture to enable a continuous supply of the sharpest edges, and they are more resistant to heat. Ceramic-alu- mina flap discs are the most expensive option, but they last the longest of the three types.
In the end, the goal is to find a flap disc that accomplishes the application’s requirements within a desired time- frame and budget.
Using the Correct Technique
To maximize a flap disc’s effective- ness, it’s important to use the proper pressure at the proper angle.
Putting too much pressure on a flap disc when it does not work rapidly enough can cause premature wear or lead to gouging, undercutting or heat buildup, and discoloration. If you find yourself needing to push harder to have a disc perform, consider a coarser grain. Using too much pressure also can undercut, gouge or damage the workpiece. Premium cutting grains such as ceramic alumina require max- imum tool speed. Excessive pressure can cause the grinder to bog down, actually reducing the grain’s cut rate. Glazing or dulling of the grain also can occur, limiting the disc’s ability to cut. Once this happens, the disc must be discarded—even if it’s only partially used.
Similarly, grinding at too steep of an angle causes operators to work much harder because they’re not using the full width of the cloth. Grinding steep also places increased pressure and stress on the flap overhang, which can reduce product life.
When finishing thin-weld material in particular, do not remove too much of the metal, as this creates a weak point. This is another good reason to select the least aggressive disc that will do the job, especially when tighter tol- erances are required. Undercutting or gouging the thin material could ulti-
mately ruin the workpiece. In appli- cations where these issues are real con- cerns, it is usually best to use a higher grit —such as 60 or 80—rather than a 36- or 40-grit disc.
Lengthening Usability
Flap discs are designed to be used to the point where you can see glue through the flap, so don’t try to judge whether a disc has been fully used based on flap wear. When used prop- erly, a flap disc will continue to cut until this glue is visible. This insight, when shared with all operators, can result in significant cost savings.
Remember, even though flap discs are disposable, steps can be taken to lengthen their usability. The result is less downtime, more work accom- plished, and greater savings. MF
When choosing a flap disc, find one that accomplishes the application’s requirements within a desired timeframe and budget.
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