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Plastics Profile

PVC: A Versatile Polymer

By Diana Roman

Polyvinyl chloride — better known to industry experts and consumers alike as PVC or vinyl — is a remarkable polymer. Used commercially since the 1930s, PVC is still the most popularly used plastic material in the world after polyethylene. Over 14 billion pounds of this material are produced annually in everything from flexible calendered sheets to rigid extrusions.

Global markets rely on PVC because of its strength and machining characteristics. PVC is versatile and strong, offering converters a broad processing window. It is resistant to moisture, corrosion and abrasion. In terms of bonding, it can be sealed to itself using heat, radio frequency or solvent sealing. It also is readily welded.

Fire-resistance Properties

One of the major components in PVC is salt, a plentiful, inexpensive and renewable resource. PVC resin manufacture is said to be more energy efficient than other polymers and gives off fewer emissions. Also, with less reliance on petrochemicals for raw materials and production, PVC pricing is less affected by the volatility of the world oil market.

Thanks to its considerable salt content, it is inherently self-extinguishing and is electrically non-conductive. Concerns about fire propagation and resultant damage in silicon wafer fabrication plants led to the development of fire retardant plastics for wet benches. PVC’s performance characteristics — its inherent fire resistance, strength, corrosion resistance and relative low cost — make it particularly suitable for wet bench cabinetry.

A new, specially-modified PVC material that meets the UL2360 Standard Test Method for Determining the Combustibility Characteristics of Plastics Used in Semiconductor Tool Construction is also now available. This sheet offers fire resistance and low smoke generation.

Processing methods

Extrusion is a popular processing method for PVC. The rigid sheets are fabricated into tanks, ductwork, hoods, scrubbers, lab equipment and other industrial applications.

While care needs to be given to avoid overheating the sheet and the introduction of stress, observation of good working procedures and practice will ensure a long-lasting, attractive end product.

PVC is user friendly and most fabricating shops have experience with the basic operations of cutting, bonding, welding and bending. Guidelines are also available from sheet and profile manufacturers. The material can be customized for specialty uses and stringent specifications.

Diana Roman is the director of marketing for HPG Corp. For more information, contact her at 800/344-6080, ext. 4235, romand@hpg-intl.com or visit www.hpg-intl.com.

Fabricating Rigid PVC Foam Board

Rigid PVC foam board is ideal for use in signage, displays, props and photo mountings. It offers impact resistance, low water absorption, high corrosion resistance and UV resistance, combined with a light weight.

Ordinary tools may be used for drilling, sawing and welding. A spiral drill with an angle twist of 30 degrees works best for drilling. The point angle should be between 80 to 100 degrees and the orthogonal angle at about 10 degrees. The cutting speed and forward feed will depend on the depth of the hole to be cut. HPG recommends that high cutting speeds should be set in the case of thin-walled workpieces.

Circular saws are suitable for straight cuts. High speed steel saw blades should be concavely ground, and for cutting sheets 8mm or larger, the teeth should be slightly pitched in the opposite direction. Bandsaws can also be used. A clean cut can be produced with a tooth division of 3/16 inch and a feed speed of 6-10 fpm.

To weld the board, hot air welding, ultrasonic welding and heated tool welding can be used successfully for joining. The values of the welding parameters — heating temperature, heating time and joining pressure — can vary depending on the welding method. Fabricators should consult with their welding or material supplier for the exact guidelines.

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Plastics Machining & Fabricating
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