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An Open & Shut Case

Lid opening and bag closing are run-of-the-mill requirements in the process industries, but they also critically manage the rate and portion control of an expensive process.

Hazards lurk around every process equipment design and manufacturing decision. Because not “sweating the small stuff” sometimes backfires, design engineers are wary of simple solutions. Yet, finding a way to make the job easier is the implicit desire of any good design engineer.

Lid opening and bag closing are run-of-the-mill requirements in the food and pharmaceutical industries, but they also critically manage the rate and portion control of a long and expensive process. A Canadian company employs a simple motion control solution that is often overlooked. Perhaps the simplicity of the solution is the very reason it is overlooked.

Italy’s Loss Is Americas' Gain

Case in point: The custom stainless steel equipment fabricator, Pure Ingenuity Equipment Design & Fabrication Group (known as E.K. Purdy Ltd. until 2000). Pure Ingenuity was approached by a representative in 2002 that had a customer in the Kingston, Ontario area. He had seen Pure Ingenuity’s ad stating that they were manufacturers of stainless steel equipment, so he dropped in to see what they did.

He had been ordering lipstick-mixing equipment from Italy. When Pure Ingenuity proved they could design and build a jacketed and insulated kettle for cosmetics, Italy lost the rep’s business. This process equipment is specifically for components for making lipstick that are dropped into the kettle. Then the agitator starts running. The kettle is jacketed with an oil bath in order to heat the ingredients and melt them. Then the liquid lipstick is dispensed into the molds at the bottom.

During this process, the machine operators need to lift the lid four or five times a day to add products or to see what is going on. Since the lid is 24 inches in diameter and made of stainless steel, it is quite heavy — weighing fifty or sixty pounds. Therefore, lifting the lid has to be done mechanically, using rods that raise the lid along with the mixing paddles that are attached to it. It has to be raised about 20 inches.

Effortless Solution to a Vertical Challenge

After considering alternate solutions, Pure Ingenuity decided against bearings that involved a great deal of time and effort in the mounting process. They did not want to have to make their own housing to mount a bushing.

They decided on the linear flange ball bushing, so that they could just bore a rough hole and tap it, then bolt the linear flange ball bushing down to the top of the base to which the tank is mounted. Because the bushing is supported by the linear flange, the bore-through hole — the main hole that the bushing slides in — doesn’t need to be accurate or tight against the bushing, so the machining is much easier.

Steven Dean, a project manager at Pure Ingenuity, explains, “We needed a bearing to help us move a couple rods up and down that could bear the weight of the lid. The linear flange ball bushing we chose does that. The linear flange bushings lift the lid 20 inches. We use two linear flange bushings to raise the lid.

“We started using it about eight years ago. In all these years we’ve not had to replace the linear flange bushings in our customers’ kettles. The linear flange bushing is easy to work with. You might say, compared to mounting a non-linear flange bearing, that they are effortless.”

RotoPrecision Inc., a Canadian specialist in precision linear motion products and design, helped Pure Ingenuity specify the SWF 20 GWUU manufactured by the NB Corp. of America. The linear flange ball bushing they chose is about 4 inches and can travel 30 inches for clamping. It’s a linear flange double-wide bushing with a resin retainer that has seals on both sides.

Synchronizing Movement

The two ball bushings in one cylinder give it all the strength and uniformity of movement needed to handle the weight of the heavy lids. Uniform movement keeps the movement smooth, and prevents shaking and rattling as the lid goes up and down.

For the ultimate in vertical movement precision, some companies, such as those that manufacture measuring tables, use four linear flange ball bushings — ensuring complete rigidity. But, the linear flange bushing advantage for measuring tables isn’t the weight they can bear, it is their accuracy. An uneven measuring table won’t yield accurate measurements. All four sides have to be going down equally to be able to measure precisely. This is also why linear flange ball bushings are frequently specified for mating molds for injection-molding machines and moving stamping die sets. For these applications, linear flange ball bushing precision is critical.

Should Pure Ingenuity design a larger jacketed and insulated kettle with, say, a 100-pound lid, the triple-wide cylinder with the additional space between its two bushings would be the linear flange ball bushing for the job. It can handle extremely high moment loads.

Pure Ingenuity manufactures all sorts of stainless steel processing equipment for the production of well-known brands in the food, cosmetics and pharmaceutical industries around the globe. Think Kraft, Nestle, Parmalab, Pfizer, L’Oreal, Clairol, etc. 

1,200 Choices

Bushings are, typically, sized by bore/shaft diameter. In NB’s line of 1,200 linear flange ball bushing combinations, the smallest inner diameter — which dictates the shaft diameter to be used — is 6 mm. NB bushing inner diameters are precisely controlled to eliminate unwanted clearance between the shaft and bushing. The inner diameter is controlled from 0 to 5 microns or larger, depending on the size.

NB also offers the Fit Series because choosing proper linear shafting is so critical. The Fit Series is a combination of NB shaft and NB ball bushing as a set, appropriate when customers do not have to use their own shafting. Both NB-supplied linear flange bushing and shaft are precisely controlled to fit together. This avoids mismatches, such as using a non-hardened, non-linear grade shafting that would not take advantage of NB ball bushings’ precision.

The Fit Series assures customers that their shaft and bushing combinations’ fit tolerance is precise. This is essential since, if the shaft diameter is not properly fitted to a ball bushing’s inner diameter, the motion control will not be accurate. NB linear flange ball bushings range in size from 19 in length up to 310 mm. Single, double-wide, triple-wide or center-mount configurations are available. Linear flange types are available in inch, Asian or European metric dimensions.

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