In the most common put in place, the material is sealed between a die of the desired shape as well as a flat stationary steel plate engrossed in a brass or aluminum liner. The shaped electrode, too, is usually created from a brass strip 1 or 2 inches high, as thick because the seal wanted and fastened to some plate attached to the press ram. The type and dimensions of press, shaped electrode and reduce platen will, naturally, depend upon the specified application.
To some degree these factors are independent of a single another, for example, a greater current or maybe more pressure will not necessarily lessen the sealing time. What type and thickness of material and also the total are of the electronic seal device determine these factors.
As you switch on the ability, the material gets hotter along with its temperature rises, naturally, as the temperature rises, heat is conducted off with the dies and the air until a stat of warmth balance is reached. At this point, the quantity of heat generated inside the plastic material remains constant. This temperature, indicating a kind of equilibrium condition between your heat generated along with the heat loss towards the seal has to be above the melting point of the plastic.
It is the time required (measures within minutes or fractions of the) to reach this melting point considered the “heating time”.
The high temperature loss is of course greater with thinner material and less with thicker material. Indeed, very thin materials (under .004″) lose heat so rapidly that this becomes tough to seal them. Using this we can notice that, overall, thicker materials require more heating time and less power than thinner materials. Furthermore, it absolutely was discovered 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 excellent in increasing the seal.
The normal heating period ranges from a single to four seconds. To minimize failures, we propose how the timer determining the heating cycle ought to be set slightly on top of the minimum time found necessary for an excellent seal.
The electrodes supply the heating current to melt the content and also the pressure to fuse it. Generally, the reduced the stress the poorer the seal. Conversely, a greater pressure will normally develop a better seal. However, excessive pressure will result in undue thinning out from the plastic material and then in an objectionable extrusion over the sides of your seal. Arcing might be caused because of the two electrodes moving closer to each other thus damaging the plastic, the buffer and / or perhaps the die.
To acquire high-pressure but steer clear of the above disadvantages, s “stop” around the press restrains the moving die in its motion. This is set to prevent the dies from closing completely when there is no material between them. And also this prevents the die from cutting completely with the material and as well gives a seal of predetermined thickness. When a tear-seal form of die is commonly used, the stops are certainly not set on the press, since a thinning of your tear seal area is wanted.
To insure a uniform seal, the correct pressure has to be obtained at all points of the seal. To insure this, they grind the dies perfectly flat and held parallel to each other inside the press. They should also rigidly construct the dies to avoid warping under pressure.
Power needed for a good seal is directly proportional for 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 maximum section of the seal obtainable with each unit. However, bear in mind that these figures are calculated for concentrated areas. The sealable area will likely be less for long thin seals as well as for certain materials that are hard to seal.
When starting a new sealing job, the first test ought to be with minimum power, moderate time as well as medium pressure. In case 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 has to be held parallel to create even pressure at all sections. When there is a lot of extrusion or maybe if 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 about 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. Check the result minimizing or raise the “stop” as required.
When 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 continue to be unsatisfactory, the die may need to be surface ground.
After making many seals, the dies then warm-up substantially and also the time as well as power might require readjustment after several hours of operation. To remove readjustment, they equip many machines with heated upper platens to pre-warm dies to operating temperatures. Usage of heated platens is desirable when doing tear seals applications.
If you do not have the various adjustments correctly, arcing with the material may occur. Arcing can also occur when the material to become sealed has different thickness at various areas of the seal or where the die overlaps the advantage of your material. When this happens, there could be arcing in the air gaps in between the material as well as the die. Enhancing the power can often remedy this.
Arcing might also occur as a result of dirt or foreign matter about the material or dies. To avert this, care must be taken up maintain the material along with 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 needs to be carefully cleaned and smoothed with fine emery cloth. Never try to seal material which has previously been arced.
As 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 loss of production time sea1 repairs might be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The purpose of this product is always to sense the chance of an arc and then shut off the R.F. power before a damaging arc may appear. Before full production runs are produced, commonly a sensing control (which can be set for various applications and sealing areas) is preset. The Container Tracker will not prevent arcing but senses the arc, then shuts away from the power that prevents damage to the die.
Being an option, an Arc Suppressor Tester might be added to 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 known as a Buffer. You attach this to one or both dies to insulate the content to get sealed from your die. This will many things: it lowers the temperature loss from the materials towards the dies; it compensates for small irregularities within the die surface and may even help to make an excellent seal whether or not the die is just not perfectly flat; it decreases the tendency to arc when too much effort or pressure is used. Overall, it will make an improved seal with less arcing. Buffer materials should have a 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) can be utilized successfully in many instances. A strip of cellulose or acetate tape adhered to the shaped die can be used with very successful results.