In the most prevalent put in place, the fabric 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 often made of a brass strip a few inches high, as thick as the seal wanted and fastened to some plate installed on the press ram. The type and measurements of press, shaped electrode and lower platen will, of course, rely on the required application.
To some extent these factors are independent of merely one another, by way of example, a larger current or even more pressure is not going to necessarily reduce the sealing time. What type and thickness of material as well as the total are from the unlock electronic seal determine these factors.
As you may activate the power, the content gets hot along with its temperature rises, naturally, since the temperature rises, heat is conducted off from the dies and also the air until a stat of heat balance is reached. At this stage, the volume of heat generated in the plastic material remains constant. This temperature, indicating a sort of equilibrium condition between the heat generated and also the heat loss to the seal must be over the melting point of the plastic.
This is the time required (measures within minutes or fractions of the) to achieve this melting point defined as the “heating time”.
The temperature loss is of course greater with thinner material and less with thicker material. Indeed, very thin materials (lower than .004″) lose heat so rapidly that this becomes very difficult to seal them. From this we can realize that, overall, thicker materials require more heating time and less power than thinner materials. Furthermore, it had been discovered 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 typical heating period ranges from a to four seconds. To minimize failures, we advise how the timer determining the heating cycle needs to be set slightly above the minimum time found essential for a good seal.
The electrodes provide the heating current to melt the content and also the pressure to fuse it. Generally, the low the pressure the poorer the seal. Conversely, a higher pressure will most likely generate a better seal. However, too much pressure will lead to undue thinning out of your plastic material and in an objectionable extrusion across the sides of your seal. Arcing could be caused due to two electrodes moving closer to each other thus damaging the plastic, the buffer and / or even the die.
To have high-pressure but steer clear of the above disadvantages, s “stop” on the press restrains the moving die in its motion. This is certainly set to prevent the dies from closing completely when there is no material between the two. This too prevents the die from cutting completely with the material and concurrently provides a seal of predetermined thickness. When a tear-seal type of die is commonly used, the stops are not set around the press, since a thinning in the tear seal area is wanted.
To insure a uniform seal, the right pressure should be obtained at all points in the seal. To insure this, they grind the dies perfectly flat and held parallel to one another inside the press. They have to also rigidly construct the dies to avoid warping under pressure.
Power needed for an effective seal is directly proportional on 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 highest section of the seal obtainable with each unit. However, be aware that these figures are calculated for concentrated areas. The sealable area will likely be less for long thin seals and then for certain materials that are tough to seal.
When setting up a new sealing job, the 1st test should be with minimum power, moderate some time and medium pressure. In case the seal is weak, you should increase power gradually. For greatest freedom from burning or arcing, the ability ought to be kept only possible, consistent with good sealing.
The dies should be held parallel to make even pressure by any means sections. If you find excessive extrusion or maybe the seal is simply too thin, the press sealing “stop” needs to be used. To create the stop, place half the entire thickness of material to get sealed in the lower plate. Close the press and adjust the stop-nut finger tight. Then insert the entire thickness of material in the press and create a seal. Look into the result and minimize or enhance the “stop” as required.
In the event the seal is weak at certain spots, the dies are not level. The leveling screws must be checked and adjusted. If these adjustments continue to be unsatisfactory, the die may have to be surface ground.
After making many seals, the dies then warm-up substantially and also the some time and power may need readjustment after a few hours of operation. To reduce readjustment, they equip many machines with heated upper platens to pre-warm dies to operating temperatures. Consumption of heated platens is desirable when performing tear seals applications.
If you do not make your various adjustments correctly, arcing with the material may occur. Arcing may also occur once the material to be sealed has different thickness at various elements of the seal or where the die overlaps the edge of the material. In these instances, there could be arcing within the air gaps in between the material and the die. Improving the power can sometimes remedy this.
Arcing may also occur due to dirt or foreign matter around the material or dies. To avert this, care has to be come to maintain the material and the machine clean.
Sharp corners and edges on dies can also cause arcing. The die edges should always be rounded and smooth. When arcing occurs, the dies needs to be carefully cleaned and smoothed with fine emery cloth. Never make an effort to seal material that has previously been arced.
Because they are now making sealing electrodes larger plus more complex, it is important that no damage on account of arcing occurs about 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 function of this device would be to sense the potential of an arc after which switch off the R.F. power before a damaging arc can take place. Before full production runs are produced, often a sensing control (which may be looking for various applications and sealing areas) is preset. The Fuel sensor fails to prevent arcing but senses the arc, then shuts from the power that prevents damage to the die.
As being an option, an Arc Suppressor Tester could be put into the unit, 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 known as a Buffer. You attach this to one or both dies to insulate the content being sealed from your die. This does numerous things: it lowers the temperature loss in the materials for the dies; it compensates for small irregularities inside the die surface and may even help make an excellent seal even when the die is not perfectly flat; it decreases the tendency to arc when a long time or pressure can be used. Overall, this makes a better seal with less arcing. Buffer materials should have a 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 most cases. A strip of cellulose or acetate tape adhered to the shaped die may be used with very effective results.