Technical Note No: 1013

Subject: Vacuum Encapsulation with Liquid Inlet Valve Two part resin mixes will cure inside valves and pipework used to convey such mix and so doing render the valve and pipework unusable until it is cleaned out. Not an easy task due to the nature of the cured resin. To overcome this problem, Island Scientific produces a Vacuum Encapsulation system which has a liquid inlet valve for the mixed resin with a replaceable liner/connecting tube which can be economically replaced between batches of encapsulation. The Unit Comprises: A cylindrical vacuum chamber of standard construction and suitable size, fitted with a Liquid Inlet Valve and the expendable liner. This is fixed in by a brass nut and captive sealing ring which forms a vacuum tight seal. Evacuation is by means of a suitable Vacuum Pump outfit. Operation The resin is freshly mixed, degassed, then drawn in via the inlet pipe and valve from a beaker outside of, and next to, the Vacuum Chamber to fill the capsule inside the Vacuum Chamber. Procedure 1) Set up the Vacuum Chamber and Pump as described in the appropriate notes. 2) To fit the replaceable liner, loosen the brass nut on the valve, open fully the valve by turning anti-clockwise, push the end of the pipe through the brass nut/valve and into the Vacuum Chamber. Pull through and position a sufficient length. Cut off outside allowing sufficient to reach the bottom of the resin beaker. Tighten the brass nut to seal the tube. Turn the valve handwheel several turns clockwise to close the pipe. 3) Prepare the item to be encapsulated or mould to be filled and put aside ready. 4) Mix and degas the resin mixture (see other notes) 5) Place the container of degassed resin mix outside the Vacuum chamber with the outer section of expendable pipe dipping to the bottom of the container. 6) Put the mould inside the Vacuum Chamber and position the inside section of expendable pipe so that the resin flowing from it will flow into and fill the mould. 7) Evacuate the chamber until a suitable degree of vacuum is reached. 8) Slowly open the liquid inlet valve and allow the mould to fill with the resin. Take care that the resin in the bucket does not reach too low so that air is drawn in. 9) Release the vacuum and remove the mould. Use paper tissue to catch drops of resin coming from the end of the pipe. 10) Top up the mould using resin left in the mixing container and put aside to set. 11) Open the liquid inlet valve and replace the pipe. Or use again if the resin has sufficient pot life. Repeat as needed. Precautions and Notes 1) The liner/pipe can be used more than once. Use it until the resin begins to gel and no more will flow. 2) The unit performs as a standard Vacuum Chamber without the expendable pipe by closing the liquid inlet valve. 3) Do not leave the pipe in position closed (by the liquid inlet) or it will >set= and be very difficult to remove and may not open again. 4) Open the liquid inlet valve carefully to avoid excessive flow of resin. 5) Ensure that the external end of the pipe is well below the level of the resin otherwise air can be drawn in. 6) Always remove pipe from the unit immediately after use and before resin starts to set. 7) Never allow resin or any such material to enter the working parts of a vacuum pump. Even the smallest quantities can cause considerable damage. The use of a pipeline trap or inlet filter is strongly recommended if this is likely to occur. 8) Components i.e., transformers and coils etc., should be baked before evacuation to assist drying and removal of all moisture. Trapped moisture subsequently encapsulated can harm the finished items. Ideally the components should be pre-heated in a vacuum oven before encapsulating. The pumping time should be sufficient for this drying out process. If the components are warm when evacuated then they will dry out much quicker. 9) Ensure that there are no sealed sections at atmospheric pressure in the article to be encapsulated. They could split under vacuum due to the pressure inside them, e.g., ampoules, sealed bottles, sealed cans. 10) Once the mould is filled, do not delay releasing the vacuum. The atmospheric pressure exerts up to 14.7 psi on the surface of the resin in the mould which helps to push it into the finest detail in the mould surface and fill any voids to encapsulate the components. 11) Remember, light weight objects may float if not securely fixed. 12) Always clean up after use. 13) To reduce the risk of the fluid entry valve diaphragm sticking to the outside wall of the plastic pipe we suggest that either the inside surface of the diaphragm or the outside of the pipe is coated with silicone grease or silicone oil. If the valve diaphragm is not able to lift freely when the valve is opened (i.e., it is stuck to the pipe), then the diaphragm lifting bolt will tear out of the diaphragm and require replacing. To Fit Fluid Entry Valve to Your Chamber The Vacuum Chamber should have 1/2" BSP threaded nipple which is unused and blanked off. 1) Remove the blank, clean off residues of sealing compound. 2) Apply fresh sealing compound such as a PTFE Tape or a jointing paste. 3) Screw on the Valve until tight, with the handle in a convenient position for easy operation. 4) Check that the Valve is clean inside. 5) Close the Valve by rotating the handwheel clockwise. The Vacuum Chamber is now ready for degassing as it was when the blank was in place. Resins: For a list of Resin Manufacturers and Stockists, please contact our Sales Office. Copyright 1988 NB: The information in this pamphlet is offered in good faith and is based on our general experience. The method of use of Island Scientific Ltd equipment and materials are outside our control, the responsibility to ensure that the equipment is properly used and suitable for intended application rests with the user. No responsibility will be accepted by this company nor any person or other company associated with this leaflet for loss or consequential losses as a result of them using this information. For advice, information, general literature, prices or a discussion of your needs, telephone 01983 855822, fax 01983 852146 or E-Mail: sales@island-scientific.co.uk. A full list of Technical Notes is available free on request.