Answer: The primary reasons are that:
Glass with poor edging tends to blast during the process of heating or cooling due to excessive concentration or uneven distribution of stress caused by edge defects. This may lead to significant damage to the glass tempering furnace.
When the glass sheet is sent into the chamber before edging or with only rough edging done, the edge will carry small glass particles that may fall on the rollers when transported or moved by the conveyor. In case that the particles fall on the ceramic rollers inside the furnace, they will be sintered on the rollers due to the high temperature in the chamber. As a result, glass being transported by these rollers will be seriously pitted.This type of problem can only be resolved by shutting down the furnace and having the ceramic rollers thoroughly cleaned after they are cooled down. While frequent downtime definitely leads to the increase of operating cost, it will also result in adverse effects on the useful life of the tempering furnace. When glass with poor edging treatment gets transported on the rollers, it will cause some degree of damage to the roller surface. Some damages, especially to ceramic rollers are permanent and irreparable.
For the same reason, specially shaped glass or glass undergone cutting, drilling, and cold processing should always have the processing areas through edging or chamfering to ensure the glass free of edge cracks.