Line Bending Acrylic Sheet

This brief gives advice for:

  • Equipment
  • Procedures
  • Trouble Shooting

Equipment

Straight Nichrome Resistance Wire Heater

straight nichrome resistance wire heater

To bend ACRYLITE® sheet up to 1/8" (3 mm) thick, the most commonly used piece of equipment is a straight nichrome wire resistance heater. The unit functions similarly to a household electric toaster by passing electricity through a wire.

You can bend material thicker than 1/8" (3 mm) on this unit, but the material must be flipped over halfway during the heating cycle.

In constructing the heater, use plywood for the base. The top surface should be insulation board or aluminum sheet to provide a smooth surface, helping prevent mark-off marks on the sheet as a result of contact. Aluminum is selected as the metal alternative because it is durable and does not absorb and re-radiate heat.

The heating element is a 17-gauge nichrome (nickelchrome) wire. Attach the wire to a 120-volt, 20-amp variable transformer. Provide a spring as shown to keep the wire under tension. Allow space around the wire for free air flow to aid heat transfer from the wire to the part. Position the wire so it remains at least 1/8" from the sheet during heating. Ceramic stand-offs are useful in supporting the wire at a consistent height from the base.

CAUTION: An unguarded nichrome wire is a burn/ shock hazard. Provide a guard to prevent contact with the wire.

 

Modification for Multiple Line Bends

 modification for multiple line bends

To perform multiple line bends, modify the heater as shown on previous page. Where the wire joins the spring, include an insulation ring. Raise the unit’s base so convection air from below flows through slots routed in the base as shown.

Coiled Resistance Wire

Coiled resistance wire can be substituted for straight wire as a heating element. Because coiled wire must be supported and because it is difficult to position the coils evenly, temperatures across the sheet’s width may vary, causing uneven stresses and distortion. See the following section entitled Line Bending with Coiled Resistance Wire.

Tubular Rod Heaters

To heat sheet thicker than 1/8" (3 mm), use a tubular-rod heater with a heating rod like the heating element of an electric stove. Power the heater with a variable transformer. Place a reflector, preferably of split aluminum conduit for its good reflectivity, beneath the rod. For shorter heating cycles, mount heaters above and below the sheet. Use water-cooled supports to avoid marks on the acrylic.

Radiant Quartz Tube Heaters

Quartz tube heaters are among the most efficient sources of radiant energy. They look like a thin fluorescent light bulb. These units provide capability to bend ACRYLITE® sheet 1/4" (6 mm) thick or greater. The heater consists of a coiled resistance wire housed in a quartz-coated glass tube.

Use a reflector with a quartz tube heater for most efficient heating. For short heating cycles, mount heaters above and below the sheet. Power the heater(s) with a variable transformer.

Cooling Jigs

Use a cooling jig like the one shown at left to assure that your bend is at the proper angle and to prevent the piece from “springing back” into its original shape. This is an all-purpose jig for 90° bends - you can modify it to suit the part. A cooling jig which exposes both sides of the heated sheet to air will accelerate cooling and reduce stresses.

Procedures

Be sure to follow the manufacturer’s safety recommendations for equipment and materials used with ACRYLITE® sheet.

Bending with a Straight Nichrome Wire Heater

Heat the material until it bends easily. Experience will teach you how long to heat each part. Don’t overheat or lay ACRYLITE® sheet directly on the heating element - doing so will blister and/or mark the sheet.

Bend the heated part to the desired shape and quickly place it in a cooling jig. To retain the bend while you do other work, secure the part in the jig with weights or clamps. Cooling time normally equals heating time.

When line bending with only one heating element, be sure to bend away from the heated side. For example, if the nichrome wire is on the bottom, bend upwards.

Line Bending with Coiled Resistance Wire

Follow the procedures above for nichrome resistance wire line bending. Flip the piece over while heating to prevent uneven stresses in the bend area.

Long Line Bends

When a bend line exceeds 24 inches in length, there is a tendency for the part to bow across the bend. This can also happen when a bend is made close to the edge of a sheet. To minimize bowing, restrict the width of the heated area or, v-groove the sheet along the desired bend line, as shown at right. When a line bend exceeds 36" in length, the part tends to bend unevenly (slight wave) along the bend due to shrinkage. To minimize this tendency, make the bend perpendicular to the manufacturing direction. You can tell manufacturing direction when the label or masking paper is still attached to the sheet. If there is a label, manufacturing direction is from top to bottom as you read it. If masking paper is still on the sheet, manufacturing direction is from top to bottom as you read the words on the masking.

directions for long line bends when bending acrylite acrylic sheet

 

Sharp Line Bends

For sharp line bends with no deflection, it is a good idea to v-groove the sheet, as shown at left. Use a v-rabbet router bit or a table saw, making two opposed 45° cuts. V-grooving the sheet reduces the material cross section at the point of bending, reducing stresses and making bending easier. A wire heater beneath the cut will help create a sharp angle bend without deflections or bowing.

sharp line bends

Bending with a Tubular Heater

Bend the part as outlined above for a nichrome wire heater. The ACRYLITE® sheet should be at least half an inch from the rod to avoid overheating.

Bending with Quartz Tube Heaters

Bend the part as outlined above for a nichrome wire heater. The ACRYLITE® sheet should be at least a half inch from the tube to avoid overheating.

Gentle Bending

By changing the distance between supports, the worker can increase or decrease the width of the heated area, thus varying the curvature of the bend. In this way, the part can be bent with a gentle curve instead of a right angle bend.

Trouble Shooting

Problem Cause Solution
Bubbling or Blistering Overheating

Lower heat; Reverse or turn over work

Increase sheet heater distance

Wet Material Pre-dry sheet
Wrinkling Narrow heating

Widen heated area

Increase bend radius (bend radius at least twice sheet thickness)

Bending part the wrong way Bend away from heated side
Mark-off (stray marks

on sheet surface)

Surface contact

Avoid overheating

Cover jig with felt

Reduce areas of contact in cooling jig

Bow Effect

Stresses for, heated and unheated areas Use straight nichrome wire to decrease width of heated area

Design reverse curve in cooling jig

Heat entire part in oven

Use a v-groove bend line

Inherent shrinkage in sheet

Bend sheet perpendicular to direction of manufacture-see foregoing drawing


Fire Precautions

ACRYLITE® sheet is a combustible thermoplastic. Precautions should be taken to protect this material from flames and high heat sources. ACRYLITE® sheet usually burns rapidly to completion if not extinguished. The products of combustion, if sufficient air is present, are carbon dioxide and water. However, in many fires sufficient air will not be available and toxic carbon monoxide will be formed, as it will when other common combustible materials are burned. We urge good judgement in the use of this versatile material and recommend that building codes be followed carefully to assure it is used properly.

Compatibility

Like other plastic materials, ACRYLITE® sheet is subject to crazing, cracking or discoloration if brought into contact with incompatible materials. These materials may include cleaners, polishes, adhesives, sealants, gasketing or packaging materials, cutting emulsions, etc. See the Tech Briefs in this series for more information, or contact your ACRYLITE® sheet Distributor for information on a specific product.

This information and all further technical advice is based on our present knowledge and experience. However, it implies no liability or other legal responsibility on our part, including with regard to existing third party intellectual property rights, especially patent rights. In particular, no warranty, whether expressed or implied, or guarantee of product properties in the legal sense is intended or implied. We reserve the right to make any changes according to technical progress or further developments. The customer is not released from the obligation to conduct careful inspection and testing of incoming goods. Performance of the product described herein should be verified by testing, which should be carried out only by qualified experts in the sole responsibility of a customer. Reference to trade names used by other companies is neither a recommendation, nor does it imply that similar products should be used.

These products are sold under the registered trade name ACRYLITE® in the Americas and under the PLEXIGLAS® trade name on the European, Asian, African and Australian continents.

EVONIK CYRO LLC, Acrylic Products 1796 Main Street Sanford, ME 04073 USA Phone +1 800 631-5384 www.acrylite.co

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