Hello Graham, I do not know which information you studied already but I found this one at a physics-forum here https://www.physicsforums.com/threads/making-an-electret.180622/https://rimstar.org/materials/electrets/Since I ware raised as a son of a gold- and silver-smith I worked at my fathers workshop starting at the age of 8 ( in 1957 ) where I learned some of the basic manual techniques of casting gold and silver into special moldes he was producing himself - at that period after WWII you had to self-manufacture almost every tool. From theses years of practical experience I can tell you that you are bound to get into problems the way you casted the wax into the mold. You need to provide different air-channels for the air to esxcape because the air must leave fast ( in addition : its expanding rapidly as it is heated up ) otherwise you will have bubbles of any size trapped in the wax which spoils the end-product. In the above thread the technique does not use a closed mold. And by the way pay attention to the paragraph "Testing electrets" : after the electret is cooled down and finished you need to attach an aluminium-foil on one side and fold it and attach it to the other side ( close contact ) in order to close the field-lines and thus strengthen the electret - as you would do with a permanent magnet ( attaching a iron bar across the two poles of a horseshoe-magnet) So therefore it makes sense to use aluminium-foil in the mold to cast the wax on right during the manufacture process so that it sticks to the wax right from the beginning. Hope this helps Mike Edit: did you read this on the scientific forum webseite: "If the electret's polarity is measured directly after its manufacture, its charge will be just what theory predicts it should be. The negative surface of the electret will be that which made contact with the positively charged polarizing electrode, and vice versa. This agrees with the north-south polarity of a bar of steel magnetized by contact with a permanent magnet. In contrast with the behavior of a magnet, however, the charge on the electret begins to diminish immediately, and in about a week it will have fallen to zero. The charge then begins to build up in opposite polarity to a final value that may be several times as large as the original charge. This may take as long as three months. The negative surface of the stabilized electret will be the face that made contact with the negatively charged polarizing electrode."List of Oleg Jefimenkos documents http://electretscientific.com/author/jrnl.html
« Last Edit: 2018-01-05, 20:45:08 by Kator01 »
|
Author
Topic: Making an Electret. (Read 10333 times)
