Abstract:
The present invention describes a blade assembly for use with side-sealing and lap-sealing machines, which are used to seal thermoplastic film. Briefly, the cutting element is oval in shape, and has its entire outer edge profiled. This provides four distinct cutting surfaces, depending on the mounting orientation of the cutting element in the machine. This cutting element is held against a heating block, and its temperature is continuously monitored by a temperature sensor. The sensor is spring-loaded to insure solid contact with the cutting element, and thus, accurate temperature measurements. This entire assembly is then encased in insulation. Additionally, the cutting element is mounted on an adjustable platform, which permits vertical adjustments relative to the film. Thus, the specific portion of the cutting element which actually engages the film can be adjusted to improve the cutting quality or further extend the useful life of the cutting element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Machines used to wrap and seal articles and packages in thermoplastic film are well known in the art. Two types of machines are commonly referred to as side-sealing and lap-sealing machines. In the typical side-sealing configuration, an article or set of articles travels, typically via a conveyer belt, toward the machine. A sheet of center-folded plastic film, having two layers, is fed from a direction which is preferably perpendicular to the direction of the conveyer. The two layers of the film are then separated such that the article is placed between the lower layer and the upper layer. On one side of the article is the center-fold, while on the other side, there is an open edge where the two layers are not attached. The machine has a side sealing mechanism, which typically comprises several sets of belts to hold and guide the film, a heating/sealing element that fuses or welds the two layers together and a cutting element that removes the excess material. Thus, as the article passes by the side sealing mechanism, this open edge is sealed by welding the two layers together, the plastic is cut and the waste is removed and discarded. At this point, the plastic film resembles a tube, with openings at both the leading and trailing ends of the article, but sealed along both sides. As the article continues to advance, an end sealing mechanism is then employed to seal the film at the leading end of the article. The article is then advanced and the end sealing mechanism then seals the film at the trailing end of the article.  
         [0002]     Incomplete, inconsistent or sloppy welds can be problematic with these types of machines. One specific issue is caused by the temperature and sharpness of the cutting element. If the temperature is too low, or the cutting surface becomes dull, the ability to create a high quality seal is reduced. Thus, to maintain a satisfactory output, it is necessary to replace the cutting element when it wears. In machines of the prior art, the cutting element is typically a single blade, typically with a cutting surface having a radius. Once this blade wears or becomes covered with film, it must be replaced. Replacement of the cutting element requires removal of the used blade and the insertion of a new blade.  
         [0003]     The cost associated with replacement blades can be significant. Also, it is imperative that a supply of replacement blades be available, since the sealing machine is completely inoperative without a blade.  
       SUMMARY OF THE INVENTION  
       [0004]     The problems associated with the prior art have been overcome by the present invention, which describes a blade assembly for use with sealing machines, which are used to seal thermoplastic film. Briefly, the cutting element is oval in shape, and has its entire outer edge profiled. This provides four distinct cutting surfaces, depending on the mounting orientation of the cutting element in the machine. This permits the cutting element to have roughly four times the useful life of conventional blades. This cutting element is held against a heating block, and its temperature is continuously monitored by a temperature sensor. This sensor measures the actual temperature of the cutting element, as opposed to that of the heating block. The sensor is spring-loaded to insure solid contact with the cutting element, and thus, accurate temperature measurements. This entire assembly is then encased in insulation. Additionally, the cutting element is mounted on an adjustable platform, which permits vertical adjustments of the cutting element relative to the film. Thus, the specific portion of the cutting element which actually engages the film can be adjusted to improve the cutting quality or further extend the useful life of the cutting element. To further simplify the replacement process, the entire heater block assembly can be removed and replaced without the use of any tools. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  illustrates a representative side-sealing machine of the prior art;  
         [0006]      FIG. 2  illustrates the side-sealing mechanism in accordance with the present invention;  
         [0007]      FIG. 3  illustrates a top view of the side-sealing mechanism shown in  FIG. 2 ;  
         [0008]      FIG. 4  illustrates an exploded view of the cutting element and associated heater block assembly;  
         [0009]      FIG. 4   a  is a top view of the heater block assembly;  
         [0010]      FIG. 4   b  is a cross-section of the heater block assembly at line A-A shown in  FIG. 4   b ; and  
         [0011]      FIG. 5  illustrates a perspective view of the heater block assembly and the adjustable platform.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  illustrates a representative side-sealing machine used to encapsulate or wrap an article in thermoplastic film, as described in U.S. Pat. No. 6,526,728. The machine  10  utilizes a conveyer belt  12  operating at a relatively constant speed to deliver articles  8  that are to be encapsulated. The thermoplastic film  1  is center-folded, such that the side with the fold is closed, while the opposite side  6  is open. On this opposite side, there are two layers of film  4 ,  5 , which will later be sealed. This center-folded thermoplastic film  1  is fed from a reel (not shown) that is preferably mounted perpendicular to the direction of travel of the conveyer belt  12 . The film is then inverted and separated by an inverter  13  such that the article is enveloped between the two layers  4 ,  5 . At this point, the film  1  on one side of the article is closed, while the opposite side  6  remains open. Also, the film at both the leading and trailing ends of the article are not sealed. Downstream from the inverter is the side-sealing mechanism  20 . After proper relative positioning of the article between the layers of the film  4 ,  5 , the enveloped article approaches the side-sealing mechanism  20 .  
         [0013]     The side-sealing mechanism  20  is located on the open side  6  of the enveloped article. The mechanism holds the two layers of film  4 ,  5  together, and guides the layers through the heating and cutting means. It then welds the two layers together, and cuts off the surplus material. The surplus material is pulled away so as not to reattach to the film while it is still at an elevated temperature.  
         [0014]     As shown in  FIG. 2 , to perform these actions, the mechanism  20  preferably comprises two sets of cooperating pulleys, an upper set  101  and a lower set  102 . These sets work in unison to pull the two layers of film into the mechanism and hold the layers in place. In the preferred embodiment, each of the pulleys has teeth  110  in its channel so as to accept one or more, preferably two, timing belts  120 . The presence of teeth  110  ensures that the timing belt does not slip relative to the pulleys; a common problem with the prior art. However, V belts can also be utilized with this invention, as well. The first set of pulleys  101  is located above the layers of film, while the second set  102  is located below the layers. Each set comprises a drive pulley  101   a ,  102   a  and a tail pulley  101   b ,  102 b. There may optionally be one or more idler pulleys (not shown). Each of these pulleys also has one or more, preferably two, O-rings mounted in the channel where the belts are located, so as to provide individual channels for each of the timing belts.  
         [0015]     Each of the timing belts preferably has a special gripping outer surface, that is bonded to a truly endless steel or Kevlar reinforced timing belt. Each corresponding set of belts has upper and lower pressure plates that are preset to insure good contact between the pair of belts.  
         [0016]     In the preferred embodiment, as shown in  FIG. 3 , one set of O-rings  200  is positioned such that the movement of the outermost belt  210  is made to be parallel to the direction of the film movement. The outer wall of the pulley  240  and this first set of O-rings  200  provide the guides for the outermost belt  210 . As shown in  FIG. 3 , O-ring  200   a  and O-ring  200   b  are equidistant from the outer wall of their respective pulleys. A second set of O-rings  201  is used to guide the innermost belt  220  in a path that diverges away from the direction of the film and the outermost belt. This can be accomplished in a number of ways. For example, a combination of one O-ring and the inner wall of the downstream pulley  250   b  can be used to define the channel for the innermost belt  220 , as shown in  FIG. 3 . Similarly, two O-rings may be inserted on the upstream pulley to define a channel for the innermost belt. Alternatively, a single O-ring  201   a , as shown in  FIG. 3 , can be used to define the inner wall of the channel for the innermost belt  220 . Because of the divergence angle, there are no forces pushing the innermost belt  220  toward the outermost belt  210 , thus the second O-ring may be eliminated. In other words, in the channel associated with the upstream pulley  240   a , the O-ring  201   a  provides the inner guide for the belt  220 . In the channel associated with the downstream pulley  240   b , the O-ring  201   b  provides the outer guide for the belt  220 . As a result, the innermost belt  220  is closest to the outermost belt  210  at the upstream pulley, and farthest away from it at the downstream pulley. The cutting element  230  is preferably located between the upstream and downstream pulleys. Thus, as the film passes the upstream pulley, it is still intact; however, it is cut before it reaches the downstream pulley. By introducing this divergence angle, the innermost belt  220  helps guide the unwanted surplus away from the film after it is cut. In the preferred embodiment, the innermost belt  220  is guided in the channel of the downstream pulley a distance further away from the film than on the upstream pulley sufficient to force the surplus plastic away from the film. One such suitable distance is about ¼ inch. This ensures that the surplus material does not reattach itself to the film while still at an elevated temperature. This surplus material is then held under tension and fed into a reel, which is later discarded. While the use of multiple belts, with a divergence between them is preferred, the use of a single belt, or multiple parallel belts is also within the scope of the present invention.  
         [0017]     As shown in  FIG. 4 , the heater block assembly  400  comprises a heater block  410 , which preferably contains a cartridge style heater  420 . This heater block  410  is constructed of a heat conductive material, preferably copper. The cutting element  430  is mounted to the heater block  410 , allowing it to be in good thermal contact with the heater block  140  so that it may be heated directly by the heater block  410 . In the preferred embodiment, the cutting element  430  is oval shaped, with the mounting holes  440  positioned such that it can be installed in any of four possible mounting orientations. The cutting element is preferably roughly 6 inches long and 2-3 inches high. To produce a satisfactory seal, the cutting element is preferably maintained at a temperature between 400° and 800° F. The speed at which the film passes the cutting element is useful in determining the optimal temperature of the cutting element. For example, as the film speed increases, the optimal temperature of the cutting element increases as well. The heater block  410  and cutting element  430  are encased in an insulating block  450  such that only the lower portion of the cutting element  430  is exposed. The insulating block  450  is used to envelope the heater block  410  and cutting element  430  so as to concentrate and localize the heat. In the preferred embodiment, a refractory material such as a ceramic fiber paper, most preferably FiberFrax®, is used as the insulating material  460 , although other insulators are within the scope of the invention. Fiberfrax® is a ceramic fiber paper, having a heat flow rate of 0.57 BTU/hr×in/sq. ft @800° F. and a temperature range of −425° F. to 2300° F. Another insulating material, Alumina Silica Board, has a heat flow rate of 0.85 BTU/hr×in/sq. ft @800° F. and a temperature range of 0° F. to 2192° F., and is also suitable for this application.  
         [0018]     A temperature sensing probe  470  is used to monitor the temperature of the cutting element  430 . In the preferred embodiment, a hole  480  is bored through the heater block  410 , and the probe  470  is placed within this hole  480 . To ensure satisfactory contact between the probe  470  and the cutting element  430 , the probe is preferably spring loaded, such that it is biased toward the cutting element  430 . The temperature of the cutting element  430  can thus be monitored and the energy supplied to the heater block  410  can be adjusted in response to the monitored temperature. By measuring the temperature of the cutting element  430  directly, the thermal lag and uncertainty associated with monitoring the temperature of the heater block  410  is eliminated.  
         [0019]     In one embodiment, the cutting element  430  and heater block  410  are constructed from copper to maximize the conductivity between the two elements. In this embodiment, the copper cutting element  430  is highly polished and then coated so as to prevent film buildup. Compositions such as, but not limited to, titanium nitride, and Nedox® from General Magnaplate Corporation can be used to provide this coating. Nedox® coatings are created by the controlled infusion of various polymers within a proprietary nickel alloy plating. It has a frictional coefficient of 0.09 and a temperature range of −250° F. to 550° F. A Nedox® coating will survive temperatures of 1400° F., but all lubricant will dissipate above 800° F. In a second embodiment, the cutting element  430  is constructed with highly polished aluminum with a hard anodized coating with TFE or other similar temperature release coating infused into the anodized coating. Alternatively, aluminum oxide coatings such as Tufram® from General Magnaplate Corporation can be used to coat the polished aluminum blade. Tufram® has a frictional coefficient of 0.05 and a temperature range of −360° F. to 800° F.  
         [0020]     As described above, the temperature probe  470 , cutting element  430 , heater block  410  and insulating box  450  comprise the heater block assembly  400 . This heater block assembly  400  is mounted to a retractable platform, such that it can be moved away from the film when the machine has stopped. In the preferred embodiment, the blade assembly  400  is mounted to an adjustable platform  370 , as shown in  FIG. 2 . This adjustable platform  370  preferably comprises an air cylinder with guide rods and a manually adjustable stroke-limiting device  380 . Alternatively, the adjustable platform can be a basic motor, a servo motor or stepper motor, or can be pneumatically or hydraulically controlled. The adjustable stroke enables the operator to reposition the blade with respect to the film during sealing, thereby changing the portion of the blade in contact with the film. By repositioning the blade, the operator can improve the seal quality, which can be degraded by film build-up or contamination of the portion of the blade in contact with the film. This technique can be used several times on each of the four sealing edges of the blade, thus greatly extending the life of the blade.  
         [0021]     In another embodiment, a control system (not shown) is used to control the movement of the adjustable platform. For example, a control system actuates a stepper motor, which in turn causes the blade to be dynamically repositioned with respect to the film. The blade is continuously moved upward and downward such that the entire useable portion of the blade is equally exposed to the film. This technique maximizes the useful life of the blade without any intervention by the operator. This embodiment is applicable to all kinds of motors and is not limited to stepper motors.  
         [0022]     In the preferred embodiment shown in  FIG. 5 , heater block assembly  400  is secured to the adjustable platform  370  without the use of any tools. Mounted to the top side of heater block assembly  400  are several, preferably two, mounting pins  490 . Mounted to the underside of the adjustable platform  370  is a mounting plate  500 . This mounting plate  500  preferably has latches  510  on each end, which are adapted to hold a clamping plate  520 . The clamping plate  520  has latch keepers  530 , adapted to interact with the latches  510  on the mounting plate  500 . Each of these plates has an incomplete hole, formed such that when the plates are latched together, there are several, preferably two, mounting holes formed, which hold the mounting pins  490 . The mounting pins  490  are designed such that the diameter at the free end is greater than that of the shaft. The mounting holes formed by the assembly of mounting plate  500  and clamping plate  520  have a diameter which is roughly equal to that of the shaft of the mounting pins  490 , but less than the diameter at the free end of the mounting pins  490 . Thus, to install the heater block assembly  400 , the mounting pins  490  are positioned in the incomplete holes of the mounting plate  500 . The clamping plate  520  is then drawn to the mounting plate  500  using latches  510 . This mating completes the formation of the mounting holes and these holes surround the mounting pins  490 , thereby holding the heater block assembly  400  in place. To further simplify the assembly and disassembly of the clamping plate  520 , one or more, preferably two alignment pins  540  can be used. These pins  540  extend from the edge of the mounting plate to which the clamping plate is mated. The clamping plate  520  has corresponding guide holes  550 , through which the alignment pins  540  pass. In the preferred embodiment, the alignment pins  540  are ¼″ diameter and extend one inch from the mounting plate  500 . The free ends of the alignment pins preferably have retaining rings which serve to keep the mounting plate  500  and clamping plate  520  attached.  
         [0023]     To replace the existing heater block assembly  400 , the user simply unlatches the mounting plate  500  from the clamping plate  520 . This action will release the heater block assembly. A new assembly can be installed by placing the mounting pins  490  in the incomplete holes of the mounting plate  500 . The clamping plate  520  is then aligned via the aligning pins  540 . The latches are then engaged, thereby securing the new heater block assembly in place.  
         [0024]     Returning to  FIG. 1 , after the article passes the side-sealing mechanism  20 , it encounters a second heating element  48 . This element  48  is used to seal and cut the leading and trailing edges of the film surrounding the article. When the article  8  is properly positioned, the second heating element  48  descends so as to contact the thermoplastic film. This serves to weld the layers together. The film is then cut, preferably in the middle of the newly created seal. The article is then advanced so as to position the trailing edge of the article under the second heating element  48 . This process is then repeated, thereby completely sealing the article in thermoplastic film.