Closing tubes with round ends

In this method the internal tube is in two pieces and there is less likelihood of making a joint with pinholes in it. The first step is the preparation of the internal tube a length of tubing is drawn off, the end blown out and polished smooth in the flame. The projecting part of the internal tube should be prepared in the same way. The outer tube should be prepared by closing one end to a round end. 

In this method a mandrel is placed in the mould of an injection moulding machine, the mould heated, and thermoplastic forced in to flow round the mandrel and form a tube with a closed end mandrel and plastic then are removed and passed while still hot to the blowing mould, where air introduced through the mandrel blows the material to the shape required. 

A closed-end tube with a round orifice spaced near the closed end as shown in Fig. 8C. 

The furnace and thermostatic mortar. For heating the tube packing, a small electric furnace N has been found to be more satisfactory than a row of gas burners. The type used consists of a silica tube (I s cm. in diameter and 25 cm. long) wound with nichrome wire and contained in an asbestos cylinder, the annular space being lagged the ends of the asbestos cylinder being closed by asbestos semi-circles built round the porcelain furnace tube. The furnace is controlled by a Simmerstat that has been calibrated at 680 against a bimetal pyrometer, and the furnace temperature is checked by this method from time to time. The furnace is equipped with a small steel bar attached to the asbestos and is thus mounted on an ordinary laboratory stand the Simmerstat may then be placed immediately underneath it on the baseplate of this stand, or alternatively the furnace may be built on to the top of the Simmerstat box. 

---