Pinch seals

Electric lamp and radio valve pinch seals usually have two or more wire leads passing through the glass. A simple form is shown in Fig. 7.3. 

Complete siftproofness can be had by the tape-over-sewn procedure, whereby the tape is glued onto the finished sewn closure by a device downstream from the sewing head. For siftproofness at high production rates, the pinch-style glued closure is used. The pinch-bag closure has the adhesive preapphed to the open end by the Bagmaker. After the bag has been filled, the closing machine reactivates the adhesive by heat prior to sealing. 

Mold construction FRP spray metal, cast aluminum gusket seal, air vents, self-sealing injection port FRP FRP, spray metal, cast aluminum, pinch (land) Metal, shear edge High grade steel shear edge... 

The prepared flattened section is inserted into a glass sleeve shaped to fit, and the glass is fused on to the metal, pinched with tweezers and strongly heated. The seal must be carefully annealed. With soft glasses the copper glass interface is coloured red, while with harder glasses the colour is more of a yellowish red. 

Consequently, more elaborate designs had to be tested and/or developed for this application of pneumatic conveying. The following two valves have been found useful in particular areas. Note that in each case it is imperative to ensure fast actuation time (e.g., 1 second for a 100 mm nominal bore NB valve and a few seconds for a 300 mm NB valve, if possible). Large-bore solenoid valves and quick-exhaust valves usually are required for this purpose. Also, note that each one of the following valves provides a full cross-sectional area of flow in the open position and a 100% seal in the closed position. One of the major problems of air-on-sleeve pinch valves is that they do not provide these important features for pneumatic conveying applications (e.g., a small hole in a closed sleeve quickly erodes due to the subsequent high velocities of air and solids). 

Cut off the delivery tube at a distance of about 1.5 cm. from the neck and seal on a tube B of thin glass 1.3 cm. in diameter and 50 cm. to act as an air condenser, bending the tube as shown in the figure. Make a tube C shaped like a pipette the wide part of which will just slip into the neck of the flask. The lower end is of very small tubing drawn to a capillary at the tip. When the tip is almost at the bottom of the flask, the upper part of the narrow tube should be just above the outlet into the condenser tube. The wide tube should extend about 3 cm. above the end of the neck of the flask and should then contract to a short, narrow tube over which a short piece of rubber tubing, provided with a pinch cock F, is slipped. 

Fig. 14.15 Schematic representation of the blow molding process, (a) The extruder head with the blowing pin and open mold (b) the extrusion of the parison (c) the mold closed with the parison pinched in the bottom and sealed at the top (d) the inflated parison forming a bottle.

Pinch one end of the straw shut and seal it with epoxy or by using the edge of a hot knife blade to melt the plastic. 

In the continuous extrusion design process, the parison is continuously extruded between the open mold halves from an accumulator head. When the required length of parison has been produced, the mold is closed, trapping the parison that is severed usually by a hot knife from the die. Figure 6.7 provides a simplified schematic of a continuous BM process. Land or pinch-off areas on the mold compress and seal the upper and lower ends of the parison to make an elastic airtight part. Compressed air is introduced through the blow pin into the interior of the sealed parison that expands to take up the shape of the mold cavities. The cooled mold chills the blown object that can then be ejected when the mold opens. 

---