Dual-head belt grinder doing the job
Sep 1, 2003 12:00 PM, By Rick Weber
WESTFALIA Surge Inc is finishing welds on its stainless steel milk storage tanks with a dual-head belt grinder that can accommodate partial sections or complete tanks.
The company is minimizing finishing time and meeting appearance and sanitary standards for seam welds on the tanks with the grinder, which is part of a production cell that also includes a resistance seam welder/planisher.
Once the seams are welded and planished at the company's Galesville, Wisconsin, plant, they are ground to blend in with the base metal and, for inside seams, to eliminate any scratches or pockets in which bacteria could form. To grind the seams, a special top seam weld grinder was built by Grinding & Polishing Machinery Corp of Indianapolis, a specialist in designing and building industrial grinding machinery.
The machine can accommodate sheets up to 20' long and features two 2-hp belt grinders that travel along the seam in tandem. Each grinding head will accommodate an abrasive belt up to 1"×72" and is equipped with a 6"-diameter serrated contact wheel that applies pressure. In addition, each head incorporates adjustable gauge wheels that control the depth of the grind. Down pressure is applied by pneumatic cylinders to maintain grinding uniformity and to keep the welded sheets flat during the process.
Depending on finish requirements, the two belts used on the machine are either 100 grit followed by 150 grit or Norax grade 45 followed by grade 65. Belt speed is 5500 sfpm. For interior seams — which must have a 32 micro-inch finish to meet 3A sanitary standards and prevent bacteria growth — another pass is made with a ScotchBrite belt.
To grind the final seam that creates the tank's cylindrical shape, the machine is designed with dual-releasable outboard supports for the overhead beam. These can be moved away to allow the tank body to be placed under the grinding heads and then replaced to support the beam while the heads pass through the tank and finish the final seam.
Westfalia Surge manufacturing engineer David Robinson says the grinder was designed to meet the company's specific needs, noting that the dual-head design was specified to reduce or eliminate hand finishing and to achieve the desired finish in a single pass, if possible.
“We went with the largest belt we could — a 72" length — to avoid downtime from frequent belt changes,” he says.
Westfalia Surge Inc provides dairy producers with a complete line of milking systems, cooking, sanitation, and dairy supply product lines. The company was created in 1999 with the purchase of Babson Bros Co, the manufacturer of Surge dairy farm equipment and related supplies, by Westfalia Landtechnik GmbH of Germany.
To keep the milk chilled as close to an optimum 34°F as possible, the tanks are built with a double-wall construction, separated by 3" to 6" thick foamed-in-place polyurethane insulation.
Tank bodies are made from Type 304 stainless steel, using .075"-thick material for the inner tank, .035"-thick material for the evaporator plates, and .060" material for the outer jacket.
Formed from 20'-long sheets cut to the proper width, a tank is fabricated with five seams. After evaporator plates are resistance-welded to some of the inner panels, the company expands or “pillows out” these plates to form coolant passageways. Next, the panels are welded together to form the inner or outer tank shell, using a special seam welder manufactured in Denmark.
The butt seams are resistance-welded, and a wire filler is added to the seam. The same machine planishes the weld while it is still warm to reduce the seam's thickness and strengthen it by mechanical working.
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