Couplings

Glass components are connected with one another by flanged joints. All the glass nozzles have special ends known as buttress ends to fix up a backing flange behind the end and connect the two opposite flanges by bolting with each other.

Coring usually gives tapered buttress ends (GARG type) which are backed by a metal flange with matching tapered bore and with a soft asbestos insert in between to prevent excessive point stresses on the glass surface. These joints give excellent performance when the glass and metal tapers are perfectly matched with full concentricity and when the alignment is perfect. In case of sight imperfection, there is a chance of excessive stresses and breakage of glass neck. Secondly, because of the taper fit, the glass to flange joint is mechanically locked and it is difficult to change flanges. 

We give another type of end which we call collared buttress end. This is similar to stub ends used in copper and stainless steel piping. The collar is backed by an asbestos rope, a metal split ring and a metal backing flange. This type of joint is very strong and has flexibility in case of slight misalignment. The overall dimensions of this type of end are kept same as those of tapered end. Hence it is easy top interchange these types of ends; and even fixing tapered end with collared end is possible. 

The following table gives dimensions of both the types of buttress ends