# Lobster Back Bend Development

Summary

The article discusses how to construct a segmental bend, which is made up of full and half segments to allow for the flow of materials through it. The 90° bend consists of two half and two full patterns, and it is important to ensure the radii/sweep of the bend is designed to specification for smooth flow. A segmental bend can be composed of right cylinders or oblique cylinders, with the development of the pattern differing for each type. The angle for each segment can be calculated by dividing the angle of the bend by the number of segments, and construction begins and ends with a half segment.

Table of Content

The above bend consists of two half patterns and two full patterns. To construct a segmental bend, we begin and end with a half segment (refer to Figure 2). The above bend has three full segments, achieved by adding the two halves to the two full bends. To determine the angle for each segment, we divide the bend’s 90° angle by three, giving us 30°. Therefore, each full segment has a 30° angle, and a ½ segment has a 15° angle. For construction, we first create an angle of 15° at point C and draw the line from left to right. The next segment will be 15° + 30°, resulting in a 45° angle. We then construct an angle of 45° to obtain the second segment. The following segment will be 45° + 30° = 75°, leaving us with a final 15° segment to complete the bend.

Segmental Bends

When creating a segment bend, it is crucial to ensure that the flow of whatever is passing through it is unimpeded. The most critical aspect in achieving this is the radii or sweep of the bend. The engineer responsible for the design will include this in the drawing as part of the specification. A segment is sometimes referred to as a gore, while a segmental bend is known as a lobster back bend. Segmental bends can consist of right cylinders, with the first and last segments being half segments. Alternatively, oblique cylinders can be used to construct segmental bends, in which case all segments are full segments and the development of the pattern differs. The following images illustrate the two types of segmental bends.