Shrink tunnel for palletized loads

Claim 2

A shrink tunnel to shrink a plastic wrapper covering a palletized load into a substantially tight fitting relationship with the palletized load as the load moves along a path through the tunnel comprising: a tunnel housing including an entrance and exit; apparatus for establishing a shrink zone within the tunnel housing, the apparatus including means for raising the temperature of the shrink zone to a temperature range adequate to shrink the plastic wrapper into a substantially tight fitting relationship with the palletized load as the load moves along the path through the shrink zone; apparatus for generating a combined air door and plastic wrapper preheating zone adjacent the housing entrance, said generating apparatus accepting heated air from the shrink zone and unheated ambient air and combining them to obtain preheating air having a temperature range less than that required to shrink the plastic wrapper, said preheating air being conveyed to the entrance to generate a curtain of air directed across and into the entrance to thereby preheat a plastic wrapper entering the tunnel housing and isolate the shrink zone from an ambient environment.

Claim 3

The combination according to claim 1 wherein said means for raising the temperature in the shrink zone includes: apparatus for heating and circulating air, the apparatus heating the air to a predetermined temperature range adequate to shrink the plastic wrapper onto the palletized load and circulating the shrinking air through the housing to establish a shrink zone at a distance from the entrance thereof containing an adequate volume of shrinking air to shrink the plastic wrapper into a substantially tight fitting relationship with the palletized load.

Claim 4

The combination according to claim 1 wherein the apparatus for generating a combined air door and plastic wrapper preheating zone further includes: a preheating zone blower; a preheating zone air return conveying said preheating air from the tunnel housing to said preheating zone blower; a plurality of preheating nozzles receiving said preheating air from said preheating zone blower and located about the entrance for emission of said preheating air to generate the curtain of air.

Claim 5

The combination according to claim 3 wherein an outlet duct extending from the preheating zone blower to the said nozzles supplies air to the nozzles, said outlet duct having a damper therein adjacent the preheatIng zone blower to exhaust air from the tunnel housing thereby causing ambient air to enter the housing at a predetermined rate thereby controlling the temperature of said preheating air.

Claim 6

The combination according to claim 3 wherein each preheating nozzle has a longitudinally disposed slotted orifice and a pair of lips adjoining the slotted orifice and separated thereby to direct preheating air issuing therefrom across and into the tunnel entrance to generate the curtain of air.

Claim 7

The combination according to claim 5 wherein one of the lips of each preheating nozzle is moveable relative to the slotted orifice to controllably obstruct the orifice and thereby vary the volume of air passing through the orifice.

Claim 8

The combination according to claim 1 including: a cooling zone blower; a cooling zone air return located in the tunnel housing between the shrink zone and the exit conveying air from within the tunnel housing to the cooling zone blower; and a plurality of cooling nozzles receiving the air from said cooling zone blower, the nozzles located about the exit to expel the air therefrom thereby generating a curtain of air adjacent the exit.

Claim 9

A tunnel to shrink a plastic cover on a palletized load into a tight fitting relationship with the load comprising: a tunnel housing including an entrance and exit; a conveyor moving the palletized load through the housing; means heating and circulating shrinking air inside the housing to establish a shrink zone in spaced relation to the entrance, the temperature of the shrinking air being adequate to shrink the cover into tight fitting relationship with the palletized load as the load moves through the shrink zone; second means for supplying an independent preheating zone of air immediately adjacent the entrance and having a temperature substantially less than the shrinking zone air; said heating and circulating means also including a pair of stationary shrink nozzles between the preheating zone and the shrink zone, one nozzle being located on each side of said conveyor adjacent the conveyor and on a vertical level with a pallet moving therealong, the nozzles directing shrinking air substantially horizontally across the housing and at the sides of the pallet as the load passes through the preheating zone to thereby shrink the skirt of the cover to tightly grip the pallet prior to the load entering the shrink zone wherein the remainder of the cover is shrunk onto the load.

Claim 10

A tunnel to shrink a plastic cover on a palletized load into a tight fitting relationship with the load comprising: a tunnel housing including an entrance and exit; a conveyor moving the palletized load through the housing; means heating and circulating shrinking air inside the housing to establish a shrink zone in spaced relation to the entrance, the temperature of the shrinking air being adequate to shrink the cover into tight fitting relationship with the palletized load as the load moves through the shrink zone; second means for supplying an independent preheating zone of air immediately adjacent the entrance and having a temperature substantially less than the shrinking zone air; said heating and circulating means also including a pair of stationary shrink nozzles between the preheating zone and the shrink zone, one nozzle being located on each side of said conveyor adjacent the conveyor and on a vertical level with a pallet moving therealong, the nozzles directing shrinking air substantially horizontally across the housing and at the sides of the pallet as the load passes through the preheating zone to thereby shrink the skirt of the cover to tightly grip the pallet prior to the load entering the shrink zone wherein the remainder of the cover is shrunk onto the load.

Claim 11

The combination according to claim 8 wherein said second means includes a plurality of entrance nozzles arranged to direct preheating air against the top and sides of the palletized load, said second means further including an air return spaced along the tunnel housing from the entrance nozzles so the preheating air flows along and preheats the top and sides of the palletized load, and then enters the air return, the preheating zone extending along the tunnel housing to said air return, the shrink nozzles being disposed in the portion of the tunnel housing containing the preheating zone to shrink the skirt of the cover onto the pallet while preheating air continues to be applied to upper portions of the cover.