In the most common create, the content is sealed between a die of your desired shape and a flat stationary steel plate covered with a brass or aluminum liner. The shaped electrode, too, is usually manufactured from a brass strip a few inches high, as thick as the seal wanted and fastened to a plate attached to the press ram. The type and measurements of press, shaped electrode and minimize platen will, needless to say, depend upon the desired application.
To some degree these factors are independent of merely one another, as an example, a more substantial current or maybe more pressure does not necessarily minimize the sealing time. The type and thickness of material and the total are in the unlock electronic seal determine these factors.
When you start up the energy, the fabric gets hotter and its temperature rises, naturally, as the temperature rises, heat is carried out off with the dies as well as the air until a stat of heat balance is reached. At this point, the volume of heat generated inside the plastic material remains constant. This temperature, indicating a kind of equilibrium condition in between the heat generated and the heat loss to the seal must be over the melting reason for the plastic.
This is basically the time required (measures in seconds or fractions of the) to arrive at this melting point described as the “heating time”.
The temperature loss is naturally greater with thinner material and fewer with thicker material. Indeed, very thin materials (lower than .004″) lose heat so rapidly that it becomes hard to seal them. Out of this we could realize that, overall, thicker materials require more heating efforts and less power than thinner materials. Furthermore, it was actually found that certain poor heat conductors that do not melt of deteriorate easily under the impact of high frequency can be used buffers. Bakelite, Mylar, silicone glass and Teflon, for instance, are fantastic in improving the seal.
The standard heating period ranges from one to four seconds. To minimize failures, we advise that the timer determining the heating cycle must be set slightly over the minimum time found needed for an excellent seal.
The electrodes supply the heating current to melt the material and the pressure to fuse it. Generally, the lower pressure the poorer the seal. Conversely, an increased pressure will usually produce a better seal. However, a lot of pressure will lead to undue thinning from the plastic material as well as in an objectionable extrusion over the sides from the seal. Arcing might be caused due to two electrodes moving closer to one another thus damaging the plastic, the buffer and / or perhaps the die.
To acquire high-pressure nevertheless prevent the above disadvantages, s “stop” in the press restrains the moving die in their motion. This really is set to stop the dies from closing completely if you find no material between them. And also this prevents the die from cutting completely from the material and as well gives a seal of predetermined thickness. Each time a tear-seal type of die is utilized, the stops are not set in the press, since a thinning from the tear seal area is wanted.
To insure a uniform seal, the correct pressure should be obtained at all points of your seal. To insure this, they grind the dies perfectly flat and held parallel to one another from the press. They must also rigidly construct the dies to prevent warping under pressure.
Power essential for an excellent seal is directly proportional for the part 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 highest portion of the seal obtainable with each unit. However, bear in mind that these figures are calculated for concentrated areas. The sealable area will be less for too long thin seals and also for certain materials that are challenging to seal.
When establishing a new sealing job, the 1st test should be with minimum power, moderate time and medium pressure. In case the seal is weak, you need to increase power gradually. For greatest freedom from burning or arcing, the power needs to be kept only possible, consistent with good sealing.
The dies has to be held parallel to produce even pressure at all sections. If you have too much extrusion or maybe if the seal is just too thin, the press sealing “stop” ought to be used. Setting the stop, place half the total thickness of material being sealed about the lower plate. Close the press and adjust the stop-nut finger tight. Then insert the total thickness of material in the press and make up a seal. Check the result and lower or enhance the “stop” as required.
If the seal is weak at certain spots, the dies are not level. The leveling screws should be checked and adjusted. If these adjustments will still be unsatisfactory, the die might have to be surface ground.
After making many seals, the dies then heat substantially along with the some time and power might need readjustment after several hours of operation. To remove readjustment, they equip many machines with heated upper platens to pre-warm dies to operating temperatures. Utilization of heated platens is desirable when doing tear seals applications.
If you do not have the various adjustments correctly, arcing through the material may occur. Arcing might also occur if the material to be sealed has different thickness at various parts of the seal or the location where the die overlaps the advantage of the material. When this happens, there could be arcing from the air gaps between the material and also the die. Increasing the power can occasionally remedy this.
Arcing could also occur because of dirt or foreign matter around the material or dies. To prevent this, care needs to be delivered to keep your material along with the machine clean.
Sharp corners and edges on dies may also cause arcing. The die edges ought to always be rounded and smooth. When arcing occurs, the dies must be carefully cleaned and smoothed with fine emery cloth. Never try and seal material containing previously been arced.
Because they are now making sealing electrodes larger and more complex, it is vital that no damage as a result of arcing occurs in the die. Although dies are repairable, the loss of production time sea1 repairs might be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The purpose of this device is always to sense the opportunity of an arc after which shut off the R.F. power before a damaging arc may appear. Before full production runs are made, usually a sensing control (that may be set for various applications and sealing areas) is preset. The Container monitoring will not prevent arcing but senses the arc, then shuts off the power that prevents injury to the die.
For an option, an Arc Suppressor Tester can be put into the unit, which tests the arc suppressor before each cycle to insure proper operation.
Typically rf heating is improved from a thin layer of insulating material referred to as a Buffer. You attach this to 1 or both dies to insulate the material to become sealed from your die. This will a number of things: it lowers the high temperature loss from the materials to the dies; it compensates for small irregularities in the die surface and may help make a good seal even if your die is not really perfectly flat; it decreases the tendency to arc when too much time or pressure is utilized. Overall, it will make a better seal with less arcing. Buffer materials should have a very good heat resistance and voltage breakdown. Of the numerous materials used (Bakelite, paper, glassine, Teflon, glass Mylar, silicone, fiberglass, etc.). Bakelite (grade xx about .010 to .030 inches thick) works extremely well successfully typically. A strip of cellulose or acetate tape adhered to the shaped die can be utilized with successful results.