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Volume 7   Issue 2               February 2006

AAMA Analysis

New Guidelines Enhance 
Integrity of Welded Vinyl Corners

by Rich Walker 

Extended research into the integrity of welded corners in vinyl windows concluded recently. As a result of these studies, a comprehensive resource has been published by the AAMA Vinyl Material Council titled, “AAMA 320-05: General Guidelines for Troubleshooting Welded Vinyl Corners.” This resource should help window manufacturers identify and correct the many factors that can affect the durability of welded corners, which range from ambient environment in the plant and manufacturing processes through post-manufacturing testing, packaging, shipping and installation practices. While information of this nature has been available in bits and pieces from welding equipment manufacturers, a single comprehensive document on the subject has never existed.

Specific quality issues identified at each step of the fabrication process resulted in the following recommendations: 

Incoming Extrusions

• Check outside dimensions and surfaces that will contact machine fixtures at multiple points against die drawings to ensure they are within accepted tolerances;
• Check for moisture or contamination from debris; and
• If cold, acclimatize the extrusions gradually to at least 59° Fahrenheit before processing. 

Ambient Factory Conditions
• Maintain factory temperature between 65° Fahrenheit and 70° Fahrenheit;
• Keep voltage supplied to processing equipment at ± 10 percent of nominal;
• Keep incoming compressed air dry and at a pressure between 87 and 116 psi; and 
• Keep storage areas clean.

Sawing and Processing
• Verify dimensional tolerances of cut lengths and notches and that cut angles (typically 45° and 90°) are within ± 1/4° of the specification;
• Prevent inaccurate length or angle dimensions that can cause weak welds by checking fixture surface for wear or damage, keeping the saw blade free of dust accumulation and properly clamping the material; and
• Reject profiles that have burrs, chipping or burning of cut edges.

• Verify quality of sawed parts before welding;
• Check for proper seating in the welding fixture. Pieces should not move when weld pressure is applied;
• Check that burn is even using a weld block or precision-measured reference line;
• Verify squareness of the finished product by comparing diagonal dimensions;
• Check visually for a uniform seam and evenly matched corners;
• Perform a melt test to verify welder performance; and
• Perform destructive tests at set intervals daily.

Corner Cleaning
• Ensure adequate cooling before cleaning;
• Check scarfing knives for sharpness; and 
• Keep cleaning area free of debris and dust accumulation.

Assembly and Glazing
• Avoid undue stress on welded corners by ensuring proper removal of weld seam material in the glazing pocket, observing proper setting block placement practices and avoiding sealant application too close to corner joints (so that expansion during curing will not add stress).

Warehousing and Shipping
• Avoid heat build-up during shrink-wrapping;
• Stack units vertically with adequate ventilation between them;
• Utilize shipping blocks to protect corners from impact; and
• Use air ride shipping trailers with climate control if warm weather is expected.

The guidelines provide details on how to implement these and other measures by identifying methods for inspection and offering solutions for quality issues.
Manufacturers experiencing weld integrity problems should review the entire production system when hunting down quality issues. Quite often, a quality issue shows up further down the production line. The cause of a detected problem may, in fact, be related to an earlier process or ambient conditions in the factory.

Last, but not least, windows should be installed according to InstallationMasters™ specifications. InstallationMasters, based on ASTM E 2112 installation protocols, is an independent program (originally developed by AAMA) that trains and certifies window installers in proper installation methods to minimize future field failures and callbacks. For more information, visit www.installationmastersusa.com.
The new guidelines were reviewed and approved by a wide mix of welding process and materials specialists, including equipment manufacturers, window manufacturers, vinyl extruders, test labs and other material suppliers. 

For more information on AAMA 320-05, visit the Publications Store at www.aamanet.org. 

Rich Walker serves as executive vice president for the American Architectural Manufacturers Association in Schaumburg, Ill. He may be reached at rwalker@aamanet.org. 

© Copyright 2006 Key Communications Inc. All rights reserved. No reproduction of any type without expressed written permission.