In the most common set up, the content is sealed from a die in the desired shape along with a flat stationary steel plate engrossed in a brass or aluminum liner. The shaped electrode, too, is usually made of a brass strip a few inches high, as thick since the seal wanted and fastened to some plate placed on the press ram. The type and dimensions of press, shaped electrode and reduce platen will, needless to say, depend upon the specified application.
To some degree these factors are independent of one another, by way of example, a larger current or even more pressure will not necessarily lessen the sealing time. The type and thickness of material as well as the total are in the unlock electronic seal determine these factors.
As you switch on the energy, the material heats up as well as its temperature rises, naturally, as being the temperature rises, heat is conducted off with the dies along with the air until a stat of warmth balance is reached. At this point, the quantity of heat generated throughout the plastic material remains constant. This temperature, indicating a kind of equilibrium condition involving the heat generated as well as the heat loss for the seal must be over the melting point of the plastic.
It will be the time required (measures within minutes or fractions of this) to arrive at this melting point understood to be the “heating time”.
The warmth loss is naturally greater with thinner material and less with thicker material. Indeed, very thin materials (less than .004″) lose heat so rapidly that this becomes very difficult to seal them. Using this we could notice that, overall, thicker materials require more heating time as well as less power than thinner materials. Furthermore, it was found that certain poor heat conductors that do not melt of deteriorate easily underneath the impact of high frequency can be used as buffers. Bakelite, Mylar, silicone glass and Teflon, as an example, are great in enhancing the seal.
The typical heating period ranges in one to four seconds. To lower failures, we advise how the timer determining the heating cycle must be set slightly above the minimum time found necessary for an excellent seal.
The electrodes give you the heating current to melt the fabric as well as the pressure to fuse it. Generally, the reduced the strain the poorer the seal. Conversely, an increased pressure will most likely produce a better seal. However, excessive pressure can result in undue thinning out from the plastic material and also in an objectionable extrusion along the sides of the seal. Arcing can be caused due to the two electrodes moving closer to each other thus damaging the plastic, the buffer and / or perhaps the die.
To acquire high-pressure however prevent the above disadvantages, s “stop” on the press restrains the moving die in the motion. This can be set to prevent the dies from closing completely should there be no material between them. This also prevents the die from cutting completely from the material and at the same time offers a seal of predetermined thickness. Every time a tear-seal kind of die can be used, the stops will not be set about the press, since a thinning of the tear seal area is wanted.
To insure a uniform seal, the proper pressure must be obtained by any means points in the seal. To insure this, they grind the dies perfectly flat and held parallel to each other in the press. They should also rigidly construct the dies in order to avoid warping under pressure.
Power necessary for a good seal is directly proportional towards the section of the seal. Moreover, thicker materials require less power than thinner materials because thinner materials lose heat on the dies more rapidly. Our sealability calculator shows the highest part of the seal obtainable with every unit. However, keep in mind that these figures are calculated for concentrated areas. The sealable area will probably be less for too long thin seals and for certain materials which are hard to seal.
When generating a new sealing job, the very first test should be with minimum power, moderate efforts and medium pressure. In case the seal is weak, you ought to increase power gradually. For greatest freedom from burning or arcing, the energy must be kept only possible, consistent with good sealing.
The dies has to be held parallel to make even pressure by any means sections. If you have an excessive amount of extrusion or if the seal is too thin, the press sealing “stop” must be used. To create the stop, place half the total thickness of material to become sealed on the lower plate. Close the press and adjust the stop-nut finger tight. Then insert the full thickness of material from the press and create a seal. Examine the result and reduce or increase the “stop” as required.
In case the seal is weak at certain spots, the dies will not be level. The leveling screws needs to be checked and adjusted. If these adjustments are still unsatisfactory, the die might have to be surface ground.
After making many seals, the dies then warm up substantially as well as the some time and power may require 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. Consumption of heated platens is desirable when conducting tear seals applications.
Should you not have the various adjustments correctly, arcing from the material may occur. Arcing may also occur if the material being sealed has different thickness at various areas of the seal or where die overlaps the edge in the material. In these cases, there can be arcing inside the air gaps between your material and also the die. Improving the power can often remedy this.
Arcing can also occur as a result of dirt or foreign matter around the material or dies. To prevent this, care needs to be taken up retain the material and the machine clean.
Sharp corners and edges on dies could also cause arcing. The die edges should invariably be rounded and smooth. When arcing occurs, the dies must be carefully cleaned and smoothed with fine emery cloth. Never attempt to seal material which includes previously been arced.
As they are now making sealing electrodes larger and much more complex, it is crucial that no damage as a result of arcing occurs in the die. Although dies are repairable, the loss of production time sea1 repairs could be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The purpose of this piece of equipment is always to sense the chance of an arc after which shut down the R.F. power before a damaging arc can happen. Before full production runs are manufactured, normally a sensing control (which can be set for various applications and sealing areas) is preset. The Fuel sensor will not prevent arcing but senses the arc, then shuts from the power that prevents injury to the die.
For an option, an Arc Suppressor Tester may be included in the system, which tests the arc suppressor before each cycle to insure proper operation.
Typically rf heating is improved by way of a thin layer of insulating material termed as a Buffer. You attach this to a single or both dies to insulate the content to become sealed from the die. This will many things: it lowers the temperature loss from your materials towards the dies; it compensates for small irregularities within the die surface and may even help to make a good seal even when the die is just not perfectly flat; it decreases the tendency to arc when too much time or pressure is used. Overall, it can make a greater seal with less arcing. Buffer materials should have a very good heat resistance and high voltage breakdown. Of the many materials used (Bakelite, paper, glassine, Teflon, glass Mylar, silicone, fiberglass, etc.). Bakelite (grade xx about .010 to .030 inches thick) works extremely well successfully in many instances. A strip of cellulose or acetate tape followed the shaped die can be utilized with very effective results.