In the most prevalent put in place, the material is sealed from a die in the desired shape as well as a flat stationary steel plate engrossed in a brass or aluminum liner. The shaped electrode, too, is generally manufactured from a brass strip a few inches high, as thick since the seal wanted and fastened into a plate placed on the press ram. What type and dimensions of press, shaped electrode and minimize platen will, obviously, depend upon the required application.
To some extent these factors are independent of one another, as an example, a bigger current or even more pressure will not necessarily minimize the sealing time. The type and thickness of material as well as the total are in the Container Tracker determine these factors.
As you may switch on the ability, the content warms up and its temperature rises, naturally, because the temperature rises, heat is conducted off from the dies along with the air until a stat of heat balance is reached. At this time, the quantity of heat generated throughout the plastic material remains constant. This temperature, indicating a sort of equilibrium condition involving the heat generated and the heat loss on the seal has to be higher than the melting reason for the plastic.
This is basically the time required (measures within minutes or fractions with this) to achieve this melting point defined as the “heating time”.
The high temperature loss is naturally greater with thinner material and much less with thicker material. Indeed, very thin materials (under .004″) lose heat so rapidly that this becomes very difficult to seal them. With this we can see that, overall, thicker materials require more heating some time and less power than thinner materials. Furthermore, it had been learned that certain poor heat conductors which do not melt of deteriorate easily under the impact of high frequency can be used buffers. Bakelite, Mylar, silicone glass and Teflon, by way of example, are great in increasing the seal.
The standard heating period ranges from one to four seconds. To reduce failures, we advise how the timer determining the heating cycle needs to be set slightly over the minimum time found needed for an excellent seal.
The electrodes provide the heating current to melt the fabric along with the pressure to fuse it. Generally, the lower the stress the poorer the seal. Conversely, a higher pressure will most likely develop a better seal. However, an excessive amount of pressure can result in undue thinning out from the plastic material and also in an objectionable extrusion along the sides of the seal. Arcing might be caused as a result of two electrodes moving closer to one another thus damaging the plastic, the buffer and / or even the die.
To have high-pressure and yet stay away from the above disadvantages, s “stop” on the press restrains the moving die in its motion. This is set in order to avoid the dies from closing completely when there is no material between the two. This too prevents the die from cutting completely throughout the material and simultaneously provides a seal of predetermined thickness. Whenever a tear-seal type of die can be used, the stops will not be set on the press, since a thinning from the tear seal area is wanted.
To insure a uniform seal, the appropriate pressure needs to be obtained whatsoever points from the seal. To insure this, they grind the dies perfectly flat and held parallel to one another within the press. They need to also rigidly construct the dies to avoid warping under pressure.
Power essential for a good seal is directly proportional on the section 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 every unit. However, be aware that these figures are calculated for concentrated areas. The sealable area will likely be less for too long thin seals as well as for certain materials which are hard to seal.
When establishing a new sealing job, the initial test needs to be with minimum power, moderate efforts and medium pressure. In case the seal is weak, you need to increase power gradually. For greatest freedom from burning or arcing, the energy should be kept only possible, consistent with good sealing.
The dies should be held parallel to make even pressure at all sections. When there is an excessive amount of extrusion or if perhaps the seal is way too thin, the press sealing “stop” ought to be used. To set the stop, place half the whole thickness of material to be sealed about the lower plate. Close the press and adjust the stop-nut finger tight. Then insert the complete thickness of material within the press and create a seal. Look into the result and reduce or raise the “stop” as required.
If 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 have to be surface ground.
After making many seals, the dies then heat substantially and the time and power might need readjustment after several hours of operation. To remove readjustment, they equip many machines with heated upper platens to pre-warm dies to operating temperatures. Consumption of heated platens is desirable when doing tear seals applications.
If you do not make your various adjustments correctly, arcing with the material may occur. Arcing might also occur if the material to get sealed has different thickness at various elements of the seal or where the die overlaps the advantage in the material. In such cases, there could be arcing in the air gaps in between the material as well as the die. Improving the power can sometimes remedy this.
Arcing could also occur as a result of dirt or foreign matter on the material or dies. To avert this, care needs to be come to maintain the material along with the machine clean.
Sharp corners and edges on dies could also cause arcing. The die edges ought to always be rounded and smooth. When arcing occurs, the dies should be carefully cleaned and smoothed with fine emery cloth. Never try to seal material that has previously been arced.
Considering they are now making sealing electrodes larger and more complex, it is essential that no damage due to arcing occurs about the die. Although dies are repairable, the losing of production time sea1 repairs may be prohibitive.
We supply all Thermatron equipment with arc suppression devices. The function of this piece of equipment is always to sense the opportunity of an arc and then switch off the R.F. power before a damaging arc can occur. Before full production runs are produced, often a sensing control (which is often looking for various applications and sealing areas) is preset. The Container monitoring does not prevent arcing but senses the arc, then shuts off of the power that prevents problems for the die.
As being an option, an Arc Suppressor Tester could be added to the device, which tests the arc suppressor before each cycle to insure proper operation.
Typically rf heating is improved by a thin layer of insulating material referred to as a Buffer. You attach this to just one or both dies to insulate the content to get sealed from the die. This will many things: it lowers the heat loss from your materials for the dies; it compensates for small irregularities from the die surface and may help to make an excellent seal whether or not the die is not perfectly flat; it decreases the tendency to arc when a long time or pressure is used. Overall, it makes a much better seal with less arcing. Buffer materials should have a great heat resistance and 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 followed the shaped die can be utilized with very effective results.