In the most frequent put in place, the content is sealed between a die from the desired shape plus a flat stationary steel plate covered with a brass or aluminum liner. The shaped electrode, too, is usually created from a brass strip a couple of inches high, as thick as the seal wanted and fastened into a plate placed on the press ram. The type and size of press, shaped electrode and minimize platen will, naturally, rely on the necessary application.
To some degree these factors are independent of merely one another, for example, a larger current or maybe more pressure does not necessarily reduce the sealing time. What type and thickness of material and also the total are of the electronic seal device determine these factors.
When you activate the strength, the content heats up and its temperature rises, naturally, as the temperature rises, heat is carried out off with the dies and the air until a stat of warmth balance is reached. At this stage, the quantity of heat generated in the plastic material remains constant. This temperature, indicating a kind of equilibrium condition involving the heat generated along with the heat loss to the seal should be higher than the melting reason for the plastic.
This is basically the time required (measures in seconds or fractions with this) to attain this melting point understood to be the “heating time”.
The warmth loss is naturally greater with thinner material and much less with thicker material. Indeed, very thin materials (under .004″) lose heat so rapidly it becomes very difficult to seal them. With this we can see that, overall, thicker materials require more heating efforts and less power than thinner materials. Furthermore, it had been found that certain poor heat conductors which do not melt of deteriorate easily beneath the impact of high frequency can be used buffers. Bakelite, Mylar, silicone glass and Teflon, as an example, are fantastic in boosting the seal.
The typical heating period ranges from a to four seconds. To reduce failures, we suggest how the timer determining the heating cycle ought to be set slightly higher than the minimum time found essential for a great seal.
The electrodes provide you with the heating current to melt the material as well as the pressure to fuse it. Generally, the reduced pressure the poorer the seal. Conversely, an increased pressure will usually develop a better seal. However, too much pressure will lead to undue thinning out from the plastic material as well as in an objectionable extrusion over the sides in the seal. Arcing could be caused as a result of two electrodes moving closer to one another thus damaging the plastic, the buffer and / or perhaps the die.
To obtain high pressure however prevent the above disadvantages, s “stop” in the press restrains the moving die in their motion. This can be set to stop the dies from closing completely if you have no material between them. This too prevents the die from cutting completely through the material and concurrently gives a seal of predetermined thickness. When a tear-seal sort of die is commonly used, the stops are certainly not set in the press, since a thinning of the tear seal area is wanted.
To insure a uniform seal, the appropriate pressure has to be obtained in any way points of the seal. To insure this, they grind the dies perfectly flat and held parallel to one another within the press. They should also rigidly construct the dies to stop warping under pressure.
Power essential for a great seal is directly proportional on the area of the seal. Moreover, thicker materials require less power than thinner materials because thinner materials lose heat for the dies more rapidly. Our sealability calculator shows the utmost section of the seal obtainable with each unit. However, be aware that these figures are calculated for concentrated areas. The sealable area is going to be less for too long thin seals and for certain materials which can be difficult to seal.
When setting up a new sealing job, the first test needs to be with minimum power, moderate time and medium pressure. If the seal is weak, you ought to increase power gradually. For greatest freedom from burning or arcing, the strength must be kept only possible, consistent with good sealing.
The dies should be held parallel to create even pressure whatsoever sections. When there is too much extrusion or maybe the seal is just too thin, the press sealing “stop” must be used. Setting the stop, place half the complete thickness of material to get sealed in the lower plate. Close the press and adjust the stop-nut finger tight. Then insert the entire thickness of material within the press and create a seal. Look into the result minimizing or enhance the “stop” as required.
When the seal is weak at certain spots, the dies will not be level. The leveling screws ought to be checked and adjusted. If these adjustments remain unsatisfactory, the die may need to be surface ground.
After making many seals, the dies then warm-up substantially and the time and power may need readjustment after a few hours of operation. To eliminate readjustment, they equip many machines with heated upper platens to pre-warm dies to operating temperatures. Usage of heated platens is desirable when performing tear seals applications.
Unless you make your various adjustments correctly, arcing throughout the material may occur. Arcing may also occur when the material to get sealed has different thickness at various areas of the seal or the location where the die overlaps the edge of the material. In these instances, there could be arcing within the air gaps between your material as well as the die. Boosting the power will often remedy this.
Arcing may also occur due to dirt or foreign matter in the material or dies. To prevent this, care needs to be delivered to retain the material and the machine clean.
Sharp corners and edges on dies can also cause arcing. The die edges should be rounded and smooth. When arcing occurs, the dies needs to be carefully cleaned and smoothed with fine emery cloth. Never try and seal material that has previously been arced.
Because they are now making sealing electrodes larger and much more complex, it is important that no damage because of arcing occurs around the die. Although dies are repairable, the decline of production time sea1 repairs might be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The purpose of this gadget is usually to sense the possibility of an arc and then shut down the R.F. power before a damaging arc can take place. Before full production runs are made, usually a sensing control (which is often set for various applications and sealing areas) is preset. The Fuel sensor does not prevent arcing but senses the arc, then shuts away from the power that prevents problems for the die.
As being an option, an Arc Suppressor Tester may be put into the device, which tests the arc suppressor before each cycle to insure proper operation.
Typically rf heating is improved from a thin layer of insulating material known as a Buffer. You attach this to just one or both dies to insulate the information to become sealed in the die. This does many things: it lowers the high temperature loss from your materials towards the dies; it compensates for small irregularities inside the die surface and could help to make a great seal even if the die will not be perfectly flat; it decreases the tendency to arc when a long time or pressure is used. Overall, this makes an improved seal with less arcing. Buffer materials should have a good heat resistance and high voltage breakdown. Of many materials used (Bakelite, paper, glassine, Teflon, glass Mylar, silicone, fiberglass, etc.). Bakelite (grade xx about .010 to .030 inches thick) may be used successfully in most cases. A strip of cellulose or acetate tape followed the shaped die works extremely well with very successful results.