Method and machine for welding thermoformed sheets of plastics material

Abstract

In this method, hot air at a particular temperature is blown onto lands ( 25, 26 ) for welding films ( 19, 21, 22 , etc) two by two with transverse pressure (P) applied to the sheets to press them together, after which cold air is blown onto the welding lands. The machine welds a cellular block ( 18 ) of sheets ( 19, 21, 22 ) stacked by means of their mutual contact lands, the sheets delimiting horizontal cells ( 27, 28 ) between them. The machine comprises two batteries ( 23 ) of horizontal tubes ( 24 ) mobile horizontally and adapted to be introduced laterally into the horizontal cells of the block, the tubes being provided with nozzles ( 29 ) for blowing air onto the lands. This method heats the plates without contact and therefore dispenses with a cycle of cleaning the heat source. It easily welds cellular blocks of profiled polypropylene or polyethylene sheets without the drawbacks of other welding methods known in themselves.

1 . A method of welding thermoformed sheets ( 1 ,  2 ;  9 ,  11 , etc) of plastics material characterized in that hot air at a particular temperature is blown onto lands ( 3 ,  4 ;  25 ,  26 ) for welding the sheets two by two while applying transverse pressure (P) to the sheets to press them together.  
     
     
         2 . A method according to    claim 1    characterized in that tubes ( 12 ,  13 ;  24 ) for blowing hot air and then cold air are disposed in a machine for vacuum thermoforming plastics material sheets ( 9 ,  11 ;  19 ,  21 , etc) in line with lands ( 3 ,  4 ;  25 ,  26 ) for welding two stacked sheets and the sheets are first thermoformed and then welded by blowing hot air either onto only one side of the two sheets to be welded or onto both sides simultaneously.  
     
     
         3 . A method according to    claim 2    characterized in that two sheets ( 9 ,  11 ;  19 ,  21 , etc) are first welded together after which subsequent sheets are welded to them one by one to produce a cellular block ( 18 ).  
     
     
         4 . A method according to any one of claims  1  through  3  characterized in that after blowing hot air cold air is blown onto the welding lands ( 3 ,  4 ;  25 ,  26 ), either onto one side only of the two sheets to be welded ( 9 ,  11 , etc) or onto both sides simultaneously.  
     
     
         5 . A method according to    claim 1    characterized in that a series of thermoformed sheets ( 19 ,  21 ,  22 , etc) are stacked to constitute a cellular block ( 18 ) delimiting a set of horizontal cells ( 27 ,  28 ) separated by contact lands ( 25 ,  26 ) between the sheets after which batteries ( 23 ) of tubes ( 24 ) equipped with nozzles ( 29 ) for blowing hot air and then cold air are introduced laterally into said cells from each side of the block for the purpose of welding the lands ( 25 ,  26 ) together.  
     
     
         6 . A method according to    claim 5    characterized in that the length of the tubes ( 24 ) is such that only the lands ( 25 ,  26 ) on the periphery of the cellular block ( 18 ) are welded.  
     
     
         7 . A machine for implementing the method according to any one of claims  1  through  6  characterized in that it comprises two dies ( 7 ,  8 ) for thermoforming plastics material sheets ( 9 ,  11 ), said dies being stacked symmetrically on either side of a horizontal plane and connected to vacuum means (H) for the purpose of thermoforming sheets disposed between the dies and in that said machine includes tubes ( 12 ,  13 ) for blowing hot air and then, if necessary, cold air onto contact lands ( 3 ,  4 ) between two thermoformed sheets ( 9 ,  11 ) in order to weld the latter together at their contact lands.  
     
     
         8 . A machine according to    claim 7    characterized in that air blowing tubes ( 12 ,  13 ) are associated with each die ( 7 ,  8 ) and oriented perpendicularly to the plane of the contacting surfaces ( 3   a ,  4   a ) of the lands ( 3 ,  4 ) of the sheets ( 9 ,  11 ).  
     
     
         9 . A machine according to    claim 7    characterized in that it includes means for pressing the dies ( 7 ,  8 ) together in their areas of contact with the thermoformed sheets, for example vertical cylinders ( 16 ,  17 ), the dies being substantially horizontal.  
     
     
         10 . A machine for implementing the method according to any one of claims  1  through  6  for welding a block ( 18 ) of thermoformed sheets ( 19 ,  24 ,  22 ) stacked via their mutual contact lands ( 25 ,  26 ), said sheets delimiting horizontal cells ( 27 ,  28 ) between them, characterized in that it comprises at least one horizontally mobile battery ( 23 ) of horizontal tubes ( 24 ) adapted to be inserted laterally into said horizontal cells and each provided with nozzles ( 29 ) for blowing hot air and then, if necessary, cold air onto the contact lands ( 25 ,  26 ) between the sheets of the block, and means for applying to the top sheet ( 19 ) of the block a pressure (P) transmitted to all the contact lands of the block.  
     
     
         11 . A machine according to    claim 7    characterized in that each tube ( 24 ) has two air blowing nozzles ( 29 ) separated by a distance equal to the distance (e) between two consecutive contact lands ( 25  or  26 ) of a sheet ( 19 ,  21 , etc).  
     
     
         12 . A machine according to    claim 9    characterized in that it comprises two batteries ( 23 ) of tubes ( 24 ) movable laterally to the block ( 18 ) of sheets ( 19 ,  21 , etc) and horizontally on each side of said block, the lengths of the tubes inside the block being at least equal to the distance (e) between two consecutive contact lands ( 25  or  26 ) between the sheets.