In the most typical setup, the material is sealed between a die from the desired shape and a flat stationary steel plate engrossed in a brass or aluminum liner. The shaped electrode, too, is usually made of a brass strip 1 or 2 inches high, as thick because the seal wanted and fastened to some plate mounted on the press ram. What type and dimensions of press, shaped electrode and minimize platen will, of course, depend upon the specified application.
At some level these factors are independent of just one another, for instance, a larger current or more pressure is not going to necessarily decrease the sealing time. The type and thickness of material as well as the total are in the electronic seal device determine these factors.
When you switch on the power, the information gets hotter and its temperature rises, naturally, because the temperature rises, heat is conducted off through the dies as well as the air until a stat of warmth balance is reached. At this stage, the volume of heat generated within the plastic material remains constant. This temperature, indicating a kind of equilibrium condition in between the heat generated and also the heat loss to the seal needs to be higher than the melting point of the plastic.
It will be the time required (measures in seconds or fractions of the) to attain 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 (below .004″) lose heat so rapidly that this becomes tough to seal them. From this we can easily see that, overall, thicker materials require more heating time as well as less power than thinner materials. Furthermore, it was learned that certain poor heat conductors that do not melt of deteriorate easily under the impact of high frequency bring buffers. Bakelite, Mylar, silicone glass and Teflon, as an example, are great in boosting the seal.
The normal heating period ranges in one to four seconds. To lessen failures, we recommend that this timer determining the heating cycle ought to be set slightly on top of the minimum time found needed for an effective seal.
The electrodes supply the heating current to melt the fabric and also the pressure to fuse it. Generally, the lower pressure the poorer the seal. Conversely, a better pressure will normally create a better seal. However, an excessive amount of pressure can lead to undue thinning out from the plastic material and also in an objectionable extrusion over the sides from the seal. Arcing can be caused because of the two electrodes moving closer to one another thus damaging the plastic, the buffer and / or possibly the die.
To obtain high pressure however stay away from the above disadvantages, s “stop” on the press restrains the moving die in the motion. This is set to avoid the dies from closing completely when there is no material between them. This too prevents the die from cutting completely throughout the material and simultaneously offers a seal of predetermined thickness. When a tear-seal sort of die is commonly used, the stops are certainly not set about the press, since a thinning of your tear seal area is wanted.
To insure a uniform seal, the proper pressure has to be obtained whatsoever points of your seal. To insure this, they grind the dies perfectly flat and held parallel to each other from the press. They must also rigidly construct the dies to avoid warping under pressure.
Power required for an excellent seal is directly proportional towards the part 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 maximum area of the seal obtainable with every unit. However, keep in mind these figures are calculated for concentrated areas. The sealable area is going to be less for long thin seals and then for certain materials that happen to be tough to seal.
When establishing a new sealing job, the first test ought to be with minimum power, moderate time as well as medium pressure. If the seal is weak, you need to increase power gradually. For greatest freedom from burning or arcing, the power must be kept as low as possible, consistent with good sealing.
The dies should be held parallel to generate even pressure whatsoever sections. If there is an excessive amount of extrusion or if perhaps the seal is too thin, the press sealing “stop” ought to be used. Setting the stop, place half the whole thickness of material to get sealed about the lower plate. Close the press and adjust the stop-nut finger tight. Then insert the complete thickness of material from the press and make up a seal. Look into the result and reduce or increase the “stop” as required.
In case the seal is weak at certain spots, the dies are not level. The leveling screws should be checked and adjusted. If these adjustments continue to be 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 might require readjustment after several hours of operation. To get rid of readjustment, they equip many machines with heated upper platens to pre-warm dies to operating temperatures. Use of heated platens is desirable when performing tear seals applications.
Should you not have the various adjustments correctly, arcing throughout the material may occur. Arcing can 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 your material. In these instances, there may be arcing within the air gaps in between the material and also the die. Boosting the power can sometimes remedy this.
Arcing can also occur as a result of dirt or foreign matter around the material or dies. To avoid this, care must be taken up keep your material along with the machine clean.
Sharp corners and edges on dies may 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 containing previously been arced.
Because they are now making sealing electrodes larger and more complex, it is vital that no damage due to arcing occurs about the die. Although dies are repairable, the loss of production time sea1 repairs can be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The purpose of this device is usually to sense the chance of an arc after which shut off the R.F. power before a damaging arc can occur. Before full production runs are produced, usually a sensing control (that may be looking for various applications and sealing areas) is preset. The Container monitoring does not prevent arcing but senses the arc, then shuts from the power that prevents damage to the die.
As an option, an Arc Suppressor Tester may be added to the device, which tests the arc suppressor before each cycle to insure proper operation.
Typically rf heating is improved with a thin layer of insulating material called a Buffer. You attach this to just one or both dies to insulate the fabric to become sealed in the die. This will numerous things: it lowers the temperature loss through the materials towards the dies; it compensates for small irregularities within the die surface and may even help to make an excellent seal even if your die is not perfectly flat; it decreases the tendency to arc when a lot of time or pressure is utilized. Overall, it makes a better seal with less arcing. Buffer materials should have a very good heat resistance and 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 generally. A strip of cellulose or acetate tape adhered to the shaped die can be utilized with highly effective results.