In the most common setup, the fabric is sealed between a die in the desired shape and a flat stationary steel plate covered with a brass or aluminum liner. The shaped electrode, too, is generally manufactured from a brass strip one or two inches high, as thick as being the seal wanted and fastened to a plate attached to the press ram. What type and measurements of press, shaped electrode and reduce platen will, of course, rely on the required application.
To some degree these factors are independent of merely one another, for example, a larger current or higher pressure does not necessarily reduce the sealing time. What type and thickness of material along with the total are of the electronic seal device determine these factors.
As you turn on the power, the content gets hotter along with its temperature rises, naturally, as the temperature rises, heat is conducted off with the dies and also the air until a stat of heat balance is reached. At this stage, the volume of heat generated within the plastic material remains constant. This temperature, indicating a sort of equilibrium condition involving the heat generated along with the heat loss for the seal has to be higher than the melting reason for the plastic.
This is basically the time required (measures in seconds or fractions on this) to reach this melting point defined as the “heating time”.
The heat loss is naturally greater with thinner material and much less with thicker material. Indeed, very thin materials (below .004″) lose heat so rapidly that it becomes hard to seal them. With this we are able to notice that, overall, thicker materials require more heating some time and less power than thinner materials. Furthermore, it absolutely was learned that certain poor heat conductors which do not melt of deteriorate easily under the impact of high frequency can be used as buffers. Bakelite, Mylar, silicone glass and Teflon, as an example, are great in increasing the seal.
The normal heating period ranges from a to four seconds. To reduce failures, we advise that this timer determining the heating cycle needs to be set slightly higher than the minimum time found required for an excellent seal.
The electrodes give you the heating current to melt the fabric and also the pressure to fuse it. Generally, the reduced pressure the poorer the seal. Conversely, a better pressure will usually create a better seal. However, too much pressure can result in undue thinning from the plastic material and then in an objectionable extrusion across the sides in the seal. Arcing might be caused due to two electrodes moving closer to each other thus damaging the plastic, the buffer and / or perhaps the die.
To obtain high pressure and yet stay away from the above disadvantages, s “stop” on the press restrains the moving die within its motion. This is certainly set to prevent the dies from closing completely if you have no material between the two. This prevents the die from cutting completely through the material and at the same time gives a seal of predetermined thickness. Each time a tear-seal sort of die is commonly used, the stops are not set about the press, since a thinning of the tear seal area is wanted.
To insure a uniform seal, the appropriate pressure needs to be obtained by any means points of your seal. To insure this, they grind the dies perfectly flat and held parallel to one another in the press. They have to also rigidly construct the dies in order to avoid warping under pressure.
Power required for a good seal is directly proportional towards the area of the seal. Moreover, thicker materials require less power than thinner materials because thinner materials lose heat to the dies more rapidly. Our sealability calculator shows the highest area of the seal obtainable with each unit. However, be aware that these figures are calculated for concentrated areas. The sealable area will probably be less for long thin seals and also for certain materials which can be challenging to seal.
When setting up a new sealing job, the initial test should be with minimum power, moderate time as well as medium pressure. In the event the seal is weak, you should increase power gradually. For greatest freedom from burning or arcing, the energy ought to be kept as low as possible, consistent with good sealing.
The dies should be held parallel to create even pressure at all sections. If there is an excessive amount of extrusion or if perhaps the seal is way too thin, the press sealing “stop” needs to be used. To create the stop, place half the whole thickness of material to be sealed in the lower plate. Close the press and adjust the stop-nut finger tight. Then insert the full thickness of material within the press making a seal. Look into the result minimizing or boost the “stop” as required.
In the event the seal is weak at certain spots, the dies will not be 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 heat substantially and also the some time and power may need 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.
Unless you make the various adjustments correctly, arcing throughout the material may occur. Arcing might also occur when the material to become sealed has different thickness at various areas of the seal or the location where the die overlaps the advantage from the material. When this happens, there might be arcing inside the air gaps between the material and the die. Boosting the power can sometimes remedy this.
Arcing can also occur due to dirt or foreign matter about the material or dies. To avoid this, care needs to be delivered to keep the material and also 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 must be carefully cleaned and smoothed with fine emery cloth. Never try to seal material which includes previously been arced.
Since they are now making sealing electrodes larger and much more complex, it is vital that no damage due to arcing occurs on the die. Although dies are repairable, the decline of production time sea1 repairs could be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The purpose of this gadget is to sense the opportunity of an arc and after that shut off the R.F. power before a damaging arc can happen. Before full production runs are produced, commonly 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 injury to the die.
As being an option, an Arc Suppressor Tester may be added to the system, which tests the arc suppressor before each cycle to insure proper operation.
Typically rf heating is improved by a thin layer of insulating material called a Buffer. You attach this to one or both dies to insulate the material to become sealed through the die. This does numerous things: it lowers the temperature loss from your materials for the dies; it compensates for small irregularities in the die surface and may even help to make an effective seal even if the die is not perfectly flat; it decreases the tendency to arc when too much time or pressure is commonly used. Overall, it will make a greater seal with less arcing. Buffer materials should have a very good heat resistance and voltage breakdown. Of the numerous materials used (Bakelite, paper, glassine, Teflon, glass Mylar, silicone, fiberglass, etc.). Bakelite (grade xx about .010 to .030 inches thick) can be used successfully typically. A strip of cellulose or acetate tape followed the shaped die works extremely well with highly effective results.