In the most prevalent setup, the fabric is sealed between a die of the 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 1 or 2 inches high, as thick since the seal wanted and fastened to your plate mounted on the press ram. What type and measurements of press, shaped electrode and reduce platen will, naturally, depend upon the desired application.
At some level these factors are independent of a single another, by way of example, a greater current or more pressure is not going to necessarily minimize the sealing time. What type and thickness of material as well as the total are of the Container Tracker determine these factors.
As you switch on the strength, the fabric warms up and its temperature rises, naturally, since the temperature rises, heat is carried out off with the dies along with the air until a stat of heat balance is reached. At this moment, the quantity of heat generated throughout the plastic material remains constant. This temperature, indicating a kind of equilibrium condition involving the heat generated along with the heat loss for the seal should be over the melting point of the plastic.
It is the time required (measures within minutes or fractions of this) to attain this melting point described as the “heating time”.
The heat loss is of course greater with thinner material and much less with thicker material. Indeed, very thin materials (lower than .004″) lose heat so rapidly that this becomes tough to seal them. With this we can easily realize that, overall, thicker materials require more heating some time and less power than thinner materials. Furthermore, it was actually learned that certain poor heat conductors that do not melt of deteriorate easily underneath the impact of high frequency can be used buffers. Bakelite, Mylar, silicone glass and Teflon, for instance, are excellent in increasing the seal.
The usual heating period ranges from one to four seconds. To reduce failures, we advise that this timer determining the heating cycle needs to be set slightly above the minimum time found needed for an excellent seal.
The electrodes provide you with the heating current to melt the material as well as the pressure to fuse it. Generally, the low the stress the poorer the seal. Conversely, a higher pressure will normally develop a better seal. However, an excessive amount of pressure can lead to undue thinning out from the plastic material and then in an objectionable extrusion along the sides of the seal. Arcing could be caused as a result of two electrodes moving closer to each other thus damaging the plastic, the buffer and / or it could be the die.
To obtain high pressure however avoid the above disadvantages, s “stop” in the press restrains the moving die in its motion. This really is set to stop the dies from closing completely if you have no material between the two. And also this prevents the die from cutting completely from the material and simultaneously provides a seal of predetermined thickness. Every time a tear-seal sort of die is used, the stops are not set about the press, since a thinning of your tear seal area is wanted.
To insure a uniform seal, the right pressure has to be obtained at all points in the seal. To insure this, they grind the dies perfectly flat and held parallel to each other within the press. They should also rigidly construct the dies in order to avoid warping under pressure.
Power required for an effective seal is directly proportional for the part of the seal. Moreover, thicker materials require less power than thinner materials because thinner materials lose heat towards the dies more rapidly. Our sealability calculator shows the utmost part of the seal obtainable with every unit. However, keep in mind these figures are calculated for concentrated areas. The sealable area will likely be less for very long thin seals as well as for certain materials which can be hard to seal.
When setting up a new sealing job, the 1st test must be with minimum power, moderate efforts and medium pressure. In the event the seal is weak, you must increase power gradually. For greatest freedom from burning or arcing, the strength needs to be kept only possible, consistent with good sealing.
The dies needs to be held parallel to produce even pressure at all sections. If you have excessive extrusion or if perhaps the seal is too thin, the press sealing “stop” should be used. To create the stop, place half the total thickness of material being 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 make a seal. Look into the result minimizing or enhance the “stop” as required.
In case the seal is weak at certain spots, the dies usually are not level. The leveling screws ought 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 heat up substantially along with the 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. Utilization of heated platens is desirable when you are performing tear seals applications.
Should you not make your various adjustments correctly, arcing from the material may occur. Arcing could also occur once the material being sealed has different thickness at various elements of the seal or in which the die overlaps the edge in the material. In these cases, there can be arcing in the air gaps in between the material and the die. Enhancing the power can often remedy this.
Arcing can also occur because of dirt or foreign matter about the material or dies. To avoid this, care must be come to maintain the material and the machine clean.
Sharp corners and edges on dies could 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 attempt to seal material which has previously been arced.
Because they are now making sealing electrodes larger and much more complex, it is essential that no damage on account of arcing occurs in the die. Although dies are repairable, losing production time sea1 repairs might be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The function of this piece of equipment is to sense the opportunity of an arc and then turn off the R.F. power before a damaging arc may appear. Before full production runs are produced, normally a sensing control (which 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 of the power that prevents harm to the die.
As being an option, an Arc Suppressor Tester may be included in the device, 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 just one or both dies to insulate the content to become sealed from your die. This may numerous things: it lowers the temperature loss in the materials towards the dies; it compensates for small irregularities from the die surface and might help to make an effective seal even if your die is not perfectly flat; it decreases the tendency to arc when too much effort or pressure is used. Overall, it makes an improved 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 adhered to the shaped die can be utilized with very effective results.