US 2960147 A
Description (OCR text may contain errors)
Nov. 15, 1960 w. FERRELL HEAT SEALING DEVICE Filed April 15, 1958 2 Sheets-Sheet l INVENTOR. WEJZE) Ff/P/Pf y wa AGENT United States Patent HEAT SEALING DEVICE Wesley Ferrell, Fair Lawn, N.J., assignor to United States Rubber Company, v New Jersey Filed Apr. 15, 1958, Ser. No. 729,050 '1 Claim. (Cl. 154-42) New York, N.Y., a corporation of sheets under conditions where both sides of the sheet are f not readily accessible to conventional heat sealing equipment. Such conditions are encountered in the COHSU'UC'. tion of plastic bags or containers. It is also useful in bag construction where the opening or port into the bag is very small.
The invention will be described with reference to the accompanying drawing, wherein:
Fig. l is a cross sectional view of a device of the invention;.
Fig. 2 is a longitudinal line 2-2 of Fig. 1 and,
Fig. 3 is a cross sectional 'view of a modification of a portion of the device.
Referring to the drawings, the particular embodiment sectional view taken along the tightly together against of the invention shown includes a support assembly 10 v on which are laid plastic sheets 11, 12 to be sealed with a lap joint having an overlying plastic strip 13. A pressurizing assembly 14 is disposed over the joint, in alignment with the support assembly.
The support assembly is essentially an electromagnet comprising an iron channel or U-shaped elongated member 15, the web or cross-piece of which is cut back at each end to accommodate an electrical winding 16 made of copper tubing coiled around the web. The conductive winding is insulated with a non-conductor of electricity capable of withstanding high temperatures, such as glass fiber. During operation this coil is energized by passing direct current through it, by means of electrical terminals 17, 18 at each end of the coil. The iron channel is thereby magnetized, the two legs of the channel serving as pole pieces. During operation cooling water is passed through the copper coil to keep the coil temperature down. A piece of rigid heat resistant material 19, such as asbestos-cement board, spans the area between the two legs giving a flush surface between the pole pieces. An electric heater strip 20 imbedded in this surface supplies heat to the area being spliced. Such heater may be energized with alternating current applied at terminals 21, 22 at each end of the strip.
The pressurizing assembly 14 comprises a shallow channel 24 closed on both ends to form a box or housing for a flexible heat resistant air bag 25. The housing 24 is open at its lower face and is made of or at least includes iron or similar magnetic material of high permeability, capable of being strongly attracted by the eleetromagnetic support assembly. The air bag may be inflated with air or other fluid, introduced under pressure through a connecting means 26, thus applying pressure to the splice. The connecting means 26 is located toward one end of the air bag, and a similar connecting means 26a is provided toward the opposite end of the air bag, for the purpose of circulating fluid through the bag if desired.
A splice may be made on this apparatus as follows:
- is then turned on the magnetic coil 16 2,960,147 Patented Nov. 15, 19 60 The edges to be spliced are lapped over each other and aligned over the heater strip in the electromagnetic member 10. The pressurizing section 14 containing the air bag is then placed on the sheet so the legs of the upper and lower channels are in alignment. The heatingstrip is relatively narrow compared to the air bag. The power and the support section, which is made at least in part of magnetic material, becomes magnetized, the flux lines running up the legs of the support channel through the plastic sheet or gap up into the pressurizing section, forming a closed magnetic circuit with the sheet forming the only gap. The support and pressurizing sections therefore rigidly clamp the plastic. The air bag is then inflated to apply sealing pressure to the splice. The box-like casing confines the air bag, except at the face in contact with the splice. The heater is then turned on to complete the splice. The time. cycle andthe temperature are varied depending on the type of plastic being sealed.
For sealing bags or containers having a very small opening, a modified form of pressurizing assembly 28 (Fig. 3) may be used. In this assembly the box or enclosure for a flexible pressurizing bag 29 is cut lengthwise into narrow strips 30, which are held in position by a plurality of loose fitting pins 31. In operation, the magnetic flux is strong enough to hold all the strips the opposing pressure of the air bag, After completion of the splicing the air bag is deflated and the magnetism turned ed. The box assembly then falls apart into strips which can easily be removed drawn through the same orifice.
Example excellent splice was produced usingthe equipment just described as follows:
Two sheets of polyvinyl chloride polymer containing 40% plasticizer were lapped over each other of an inch and placed in position over the support member of the sealer equipment. The pressurizing member containing the air bag was then positioned over the splice in alignment with the support or magnetic section. A DC. potential of 12 volts was then applied to the water cooled coil causing a current of amperes to flow through the copper coil. The support and pressurizing sections are thereby magnetically attracted to each other clamping the sheet with a pressure in excess of 500 lbs. The air bag was then inflated to 5 lbs. per square inch to apply this pressure to the lapped splice. Two volts A.C. were then applied to the heater strip causing a current of 200 amperes to flow. This current was maintained for a period of 12 minutes heating the lapped splice to 390 F; at the end of this time the pressure in the air bag was released and air was allowed to blow through the air bag for two minutes to assist cooling. The magnet was then turned ofi and the sealer removed. Splices formed following the above are essentially molded joints having the strength of the sheet material, and are slightly thicker at the joint, feathering out gradually to the sheet thickness.
From the foregoing, it will be apparent that the invention affords numerous advantages over prior heat sealing devices. The invention afiords a unique means for applying clamping pressure to both sides of plastic members being heat sealed, without having any mechanical connection between the clamping members. Electromagnetic force is uniquely utilized in the present invention to permit clamping members, not otherwise physically connected, to be urged toward each insuring good contact of the plastic The advantages of the air bag scribed will be appreciated when it other forcibly, thus heating strip actually melts the plastic sheets along the seam, and the material coalesces (under pressure) to form the bond. During the time when the plastic is fluid, it is confined by the air bag and cannot allow away froth the seam. The ability of the air bag to conform to the exact shape and volume of the plastic insures formation of 'a proper seam. The bag arrangement shown prevents the melted plastic from being squeezed out, which would cause the seam to be thin and therefore weakened. At the same time the air bag insures that proper pressure is applied to the seam. In practice the amount of plastic material at the seam region will vary, and the air bag (not being a solid or rigid member, but being extensible and conformable) is capable of accommodating such variable amounts of material at the seam region.
Another advantage of the fluid expansible member or bag is that it tends to feather out the joint gradually to the sheet thickness, thus resulting in a seam of better appearance.
Havin thus described my invention, desire to protect by Letters Patent is:
A heat sealing device for joining plastic sheets comprising in combination a supporting assembly "having an elongated generally U-shaped body made of magnetic material, the opposite :arms of which include fiat end surfaces forming a first plane wherein the plastic sheets to be joined may be supported, an electrical winding Wrapped around the cross member of the U-shaped body for operating the U-shaped body as an electromagne't, the said electrical winding comprising an electrically conductive tube through which a cooling fluid can be circulated, a supporting member of insulating material extending across the arms of the U-shaped body for supporting the plastic sheets at the area to be joined, said supporting member having a surface in alignment with the end surfaces of said opposite arms and constituting therewith a planar surface for supporting the plastic what 'I claim and sheets to be joined, a heating element contained in said supporting member for heating the plastic to a molten state at said area, a pressurizing assembly, said pressurizing assembly being disposed in operation above the opposite side of the plastic sheets from said supporting member at the area to be joined, said pressurizing assembly comprising an elongated box-like enclosure made of magnetic material and openat its lower face, said enclosure including sidewall members having fiat end sursaid sidewall members befaces foriifin'g a second plane, ing spaced apart from each other by an amount equal to the spacing between the arms of said U-shaped body whereby when plastic sheets to be joined are positioned between the U-shaped body and the enclosure, and the electrical winding of the 'U shaped body is energized, the arms of the U-shaped body and the sidewalls of the enclosure will be drawn together to clamp the plastic sheets in 'proper'lposition for sealing, a fluid-expansible bag disposed 'within said enclosure, the said bag having an opening for introduein'g an inflating fluid to cause the bag to conform to and confine the plastic at the area to be joined, the said ba'ghaving an additional opening whereby a cooling fluid can be passed through the bag at the conclusion of the splice to cool the said area, the said supporting assembly and pressurizing assembly being held together by the electromagnet during the splicing operation against a separating force'exerted by the fluid-expansible bag.
References Cited in the file of this patent UNITED STATES PATENTS 2,305,010 Kenney et al. Dec. 15, 1942 2,646,195 Langer July 21, 1953 2,713,379 Sisson July 19, 1955 2,725,091 Miner Nov. 29, 1955 2,796,914 Park June 25, 1957 2,822,029 Hoagland -t. Feb. 4, 1958 2,835,776 Blessing May 20, 1958