Method and apparatus for making a contoured muntin bar. A supply of sheet material having a finished surface on at least one side in the form of a coiled ribbon is unwound and fed along a strip path of travel to a punch station. At the punch station a ribbon punching mechanism punches the ribbon at a precisely predetermined locations along the ribbon to form one of a plurality notch patterns that define a portion of a contoured muntin bar. Downstream along the travel path from the punch station the ribbon is fed through a forming station having a succession of forming rolls that define a succession of forming roll nips to bend the ribbon and form a generally closed cross-sectional tube. The rolls form a number of bending stages to produce a muntin bar tube having a contoured shape with raised sides to provide an attractive appearance to a muntin grid.
1. A tubular muntin bar comprising:
a) an elongated tube having a mitred end and a flat end wherein the mitred end includes muntin bar portions adapted to fit over mid portions of other muntin bars to form a part of a grid and where the flat end forms an outer bound of a completed muntin bar grid for contacting a window spacer frame;
b) said elongated tube including side walls that have two relatively narrow top and bottom planar segments and two relatively wider side planar segments wherein the tube also includes a beveled transition portion between each side planar segment and either a top or a bottom planar segment and wherein one of the planar segments is formed by sheet portions of the tube that are bent to abut each other along a seam.
2. The apparatus of claim 1 wherein the top or the bottom planar segment of the muntin bar is formed by inwardly bending a lip portion of an elongated sheet of muntin bar material to form the elongated tube and wherein the sheet is bent in stages and wherein an early bending stage or stages forms two lips on the edges of said sheet and a later bending stage completes the formation of the top or the bottom generally planar surface of the elongated tube by bending two lips toward each other to form a seam and wherein intermediate bending stages after the early stages but before the latter stages leave the lips untouched.
3. The apparatus of claim 2 wherein the last and next to last stages contact the two lips to bend said lips together and form a seam along the elongated tube.
4. The tubular muntin bar of claim 1 , wherein the beveled transition portion includes two beveled surfaces.
5. A tubular muntin bar comprising:
a) an elongated tube having mitred ends wherein the mitred ends include muntin bar portions adapted to fit over mid portions of other muntin bars to form a part of a grid;
b) said elongated tube including side walls that have two relatively narrow top and bottom planar segments and two relatively wider side planar segments wherein the tube also includes a beveled transition portion between each side planar segment and either a top or a bottom planar segment and wherein one of the planar segments is formed by sheet portions of the tube that are bent to abut each other along a seam.
6. The tubular muntin bar of claim 5 , wherein the beveled transition portion includes two beveled surfaces.
7. A tubular muntin bar comprising:
a) an elongated tube having flat ends wherein the flat ends form an outer bounds of a completed muntin bar grid for contacting a window spacer frame;
b) said elongated tube including side walls that have two relatively narrow top and bottom planar segments and two relatively wider side planar segments wherein the tube also includes a beveled transition portion between each side planar segment and either a top or a bottom planar segment and wherein one of the planar segments is formed by sheet portions of the tube that are bent to abut each other along a seam.
8. The tubular muntin bar of claim 7 , wherein the beveled transition portion includes two beveled surfaces.