GB1419971A - Sealing apparatus - Google Patents

Abstract

1419971 Sealing apparatus for heat-shrinkable film W R GRACE & CO 12 Nov 1973 [17 Nov 1972] 53326/72 Heading B8C [Also in Division B5] Apparatus for heat-sealing together superposed layers of heat shrinkable film comprises a pair of clamping bars 9, 10 and 14, 16 for holding superposed layers of heat-shrinkable film in engagement with one another and associated with heat sealing means for sealing together the clamped layers, a cutting knife, Fig. 7, mounted for movement with one of the clamping bars, means 11 for moving the cutting knife relative to said one clamping bar to cross the plane of contact between the clamping bars to sever the superposed layers of film, means 21-24 for sensing the proximity of the other of the clamping bars to said one clamping bar with which the knife moves, and means for locking the cutting knife against movement relative to said one clamping bar until the sensing means indicates close proximity to the other clamping bar. A longitudinally, and centrally, folded thermoplastic film of shrinkable material is fed, from a supply roll, not shown, and round guide pulleys 3-5 so that the lower, and upper, halves thereof pass respectively below and above a laterallyadjustable guide plate 6 which is located at the loading table and has an upstanding end 7. The supply roll is removably carried on a bar 91, Fig. 3, removably mounted in V-shaped bearings 45 on a carriage 42 which is slidably mounted for withdrawal from beneath the table for replacing a spent roll, the bar 41 having an adjustable bearing member 46 to accommodate rolls of different sizes. The fold of the film is disposed at the rear of the machine so that goods to be packaged, e.g. weighed meat in a tray, can be inserted, by an operator, between the two spaced film layers. With a sealing head, pivoted at 8 to the framework of the machine, in its open position, the film with the enclosed tray, is lifted manually and placed on a sealing table 2 so that the film lies across the side sealing bar 10, Fig. 1, with its free edges overhanging the front sealing bar 9. The sealing head is then pulled down manually, almost to its closed position, whereat a timing cam, not shown, is triggered by levers 21-24 to operate a pneumatic holding jack 11, connected between the sealing head and the framework, Fig. 3. The jack 11 forces the sealing head down with high pressure against the fixed sealing bars 9, 10 to provide a relatively low sealing temperature and a short cooling time. The sealing head carries a resilient plastics pad which, when the head is closed, bears downwardly on the tray and its surrounding layers of film, the sealing bars 9, 10 not meeting at the corner at the front of the sealing head to provide a vent hole for air during a subsequent heat-shrinking operation. The sealing table is mounted on a telescopic tube assembly 12 which is spring-urged upwardly and has a locking handle 13 to set the table 2 for different thicknesses of package. The sealing head, Fig. 4, carries sealing bars 14, 16 which, to assist alignment, are pivotally mounted respectively to the sealing head at their mid-points 15, 17 the head having a handle 19, and the rod of the holding jack 11 being hinged to the head at 18b. The bars 14, 16 are associated with serrated cutting knives, Fig. 7, each of which is unable to descend below the corresponding clamping surface until the sealing head has been almost closed. During the final lowering movement of the sealing head, Fig. 6, the spring-loaded trigger levers 21-24 are pivoted upwardly against their springs as they contact the fixed bars 9, 10 so that locking pins 25 on the levers are moved from the detaining portions 21b-24b of corresponding slots 21a-24b in the knives associated with the sealing bars 14, 15 and into the release portions 21c-24c of the slots, head springs 29, 30 of the sealing bars 14, 15 being compressed and the knife blades 31, 32 being driven down to cut the two layers of film and engage in corresponding grooves in the fixed sealing bars 9, 10. In this manner a knife cannot be operated until all of the associated trigger levers 21-24 have been tripped. Heating wires in the clamping bars are located close to metal bars which act as heat sinks. A pneumatic circuit, with safety precautions, and which regulates the operation of the jack 11 is described with reference to Fig. 8 (not shown) and is housed in a removable control box 40.