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Volume Two, Number One
Rotomolding fans - this issue offers new information to help design engineers, product managers and others use plastics. Email me with questions and comments. If you need to leave the newsletter, see the end for instructions.
Now boldly mold!
For more information, contact Meese Orbitron Dunne Co., American Rotational Molding Group; 16404 Knott Ave., La Mirada, CA 90638; Phone: 888.724.1228; Fax: 877.904.1670; www.modroto.com.
YOU, TOO, CAN DESIGN FOR ROTOMOLDING (#3 In A Series)
If you need to join parts together and are concerned about strength, seams and leaks then consider there are several different approaches and each one is ideally suited to a range of applications.
Spin welding delivers high quality, permanent joints and hermetic seals by applying heat at the joint line to join parts with rotationally symmetric joints. Since the parts can be handled immediately after welding and no extra materials are needed, spin welding can often be provided without adding significant costs or time to the project. Types of parts or products that are easily spin welded include threaded and bulkhead type fittings.
Drader welding seals seams, blow-bys and voids between either two plastic parts or within a single part. It’s also used to add baffles, flanges and fittings onto tanks and vessels when a secure, leakproof seal is required. Drader weld strength approaches the strength of the virgin material which virtually eliminates the potential for weak spots.
Bolts provide ample strength when attaching parts made from different materials such as metal to plastic (which is a problem for welding) or two plastics with a wide disparity in melt temperatures. In some cases, MOD engineers intentionally specify bolts to permit easy separation of the parts, which isn’t possible once welded. But if the bolted parts are large, assembly may take two people and add to secondary costs.
In many cases, MOD engineers design parts and products in one piece, or with reduced part counts, to eliminate the need for welding and bolting entirely.
See how we bolted arms and legs to E.T. the Extra Terrestrial at here.
See how we welded a fitting at here.
DID YOU KNOW EVEN SMALL PARTS CAN WARP?
Everyone has seen a large plastic panel or bulk tank warp over time but warping is real issue that affects every molded plastic part, not just large ones. The key to preventing your parts from bowing, twisting and getting bent out of shape is to pay careful attention at the design stage.
Consider that material density is critical in how well the part forms. Specifying high density materials such as HDPE and metallocenes helps form and maintain the desired shape over time.
Skilled rotational molding machine operators also contribute to warp prevention. If the operator fails to properly control the molding time and temperature then the material may be forced into a solid state too soon. The part will become either brittle and weak, as well as warped. Operator experience becomes even more important when working with low density materials.
NEW INFORMATIONAL CD
Get one for yourself. It’s an Interactive Capabilities CD using live action video and 3-D photo realistic renderings to highlight some of MOD’s most talked about designs. A football game for swimming pools; a 360 degree playground slide; an upscale laundry cart; plastic, canvas and wire material handling products; and other noteworthy projects are featured.
It’s free. Just call 800.772.7659 or email Bob@modroto.com.
Get a free estimate on your next project at http://www.modroto.com/cgi-bin/request.
For a free brochure, call 800.772.7659 or go to http://www.modroto.com/cgi-bin/request.
Adventures In Rotomolding is published by Meese Orbitron Dunne Co., Saddle Brook, NJ, www.modroto.com; 800.829.3230. Copyright 2004 Meese, Inc. May not be reprinted without permission. Please feel free to pass along to other engineers and colleagues.
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