Method for determining tightness of film shrunk over a container or an assembly of containers
&#39; nited States Patet 1191 Miller Apr. 15, 1975 METHOD FOR DETERMINING TIGHTNESS OF FILM SHRUNK OVER A CONTAINER OR AN ASSEMBLY OF CONTAINERS [75] Inventor: Anderson Miller, Saxonville, Mass.  
 [73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.  
  22 Filed: Dec. 6, 1973 211 Appl. No.: 422,492  
  52 11.5. CI 73/159; 73/95 51 1111.01. ..G0ln 3/08 581 Field of Search 73/159, 95, 102, 141 R,  
 [56] References Cited UNITED STATES PATENTS 2,106,407 l/1938 Hensley 73/453 Clarke 73/14! AB Delker 73/141 AB X Primary ExaminerJerry W. Myracle Attorney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Charles C. Rainey [5 7 ABSTRACT Apparatus and method for determining the tightness of a pellicular wrapper, particularly a heat-shrunk film wrapper, on a container or assembly of containers, comprising a force gage and a needle, the force gage comprising a suction cup by means of which the force gage is detachably attached to the pellicular wrapper to enable the pulling of the wrapper away from a particular portion of the surface of the container or the surface of a particular container in an assembly of containers enclosed by the pellicular wrapper.  
 4 Claims, 4 Drawing Figures METHOD FOR DETERMINING TIGHTNESS OF FILM SI-IRUNK OVER A CONTAINER OR AN ASSEMBLY OF CONTAINERS The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.  
 BACKGROUND OF THE INVENTION This invention relates to an apparatus for determining the tightness of a film type wrapper encasing or partially enclosing a load comprising a container or an assembly of containers. The invention also relates to a method of determining the tightness of such a film type wrapper which has been applied to the load by being shrunk thereover, preferably by heat shrinking.  
  For a number of years the Armed Forces have packaged a great many of the supplies required by troops in the field or at numerous bases in paperboard containers which for convenience in handling and storage are stacked on pallets. These pallets can then be moved from place to place by means of forklift trucks, thus saving much manual labor. These paperboard containers must be held in place on the pallets and they require protection from water and desirably they need protection from dust. A relatively recently developed method of providing such protection involves placing a large heat-shrinkable plastic bag, e.g. a heat-shrinkable polyethylene film bag, over the stack of containers on a pallet and heat-shrinking the plastic bag over the top and sides of the stack of containers until a reasonably tightly fitting wrapper is produced around the top and sides of the stack. Also where it has been found unnecessary to protect the top of a container or assembly of containers from rain or dust or other contaminants, the practice of heat-shrinking a plastic tubing about the periphery of a container or assembly of containers has been adopted by some industrial concerns to facilitate handling of such containers. This heat-shrinking may be carried out in shrink tunnels specially devised for this purpose or by means of portable heaters which produce a blast of heat which can be moved about over the external surface of the plastic bag to cause shrinkage thereof. The latter method results in appreciably less uniform shrinkage of plastic film than the former method and thus may result in the wrapper fitting too loosely over certain areas of the containers. It has, therefore, become necessary to provide some means for determining when such a plastic film wrapper has been heat-shrunk to a sufficient degree and sufficiently uniformly over the exterior surfaces of the stack of containers to maintain the containers in place through any handling of the pallet and stack of containers that may be anticipated.  
  It is, therefore, an object of the invention to provide an apparatus for determining the tightness of a substantially non-porous pellicular wrapper surrounding or encasing a container or an assembly of containers.  
  It is also an object of the invention to provide a method for determining the tightness of a substantially non-porous pellicular wrapper surrounding or encasing a container or an assembly of containers.  
  More particularly, it is an object of the invention to provide an apparatus and a method for determining the tightness of a heat-shrunk plastic film wrapper surrounding or encasing a container or an assembly of containers.  
  Other objects and advantages will be apparent from the following description of one embodiment of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.  
 SUMMARY The apparatus of the invention comprises a force gage and a needle, the force gage comprising means for gripping a pellicular structure, such as a plastic film, shrunk in place about a container or assembly of containers. The gripping means is preferably a suction cup. The needle serves to penetrate the pellicular structure and is provided with a handle the lower end of which may serve as a stop for the pellicular structure at a preselected distance along the needle. The needle may also be provided with distance or length graduations to indicate when the pellicular structure being penetrated by the needle has been pulled various distances from the exterior surface of the container or one of the assembly of containers in carrying out a determination of tightness of the pellicular wrapper on the container or assembly of containers.  
  The method of the invention may be carried out in two ways, the first way comprising detachably attaching a force gage to a pellicular wrapper, which surrounds or encases a load, at a predetermined point, pulling the force gage and the pellicular wrapper attached thereto a predetermined distance away from the load, and measuring with the force gage the force required for pulling the pellicular wrapper the predetermined distance away from the load. The second way of carrying out the method comprises detachably attaching a force gage to a pellicular wrapper, which surrounds or encases a load, at a predetermined point, pulling the force gage and the pellicular wrapper attached thereto away from the load until the force gage registers a predetermined force, and measuring the distance from the load to which the pellicular wrapper is pulled when the force gage registers the predetermined force.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing shows the preferred embodiment of the invention.  
 In the drawing:  
  FIG. 1 is a perspective view of a force gage in accordance with the invention.  
  FIG. 2 is a perspective view ofa needle in accordance with the invention.  
  FIG. 3 is a perspective view of a cutaway portion of a shrink-wrapped container with the force gage and needle being held in position preparatory to determina tion of the tightness of a film wrapper on the container.  
  FIG. 4 is a perspective view similar to FIG. 3, but showing the container, wrapper, force gage, and needle during the determination of the tightness of the film wrapper on the container.  
  Referring to the drawing, wherein like characters designate like parts in all views, 10 designates generally a force in accordance with the invention. The force gage comprises a suction cup 11 made of elastomeric material, e.g. rubber, for detachably attaching the force gage to a pellicular material by the formation of a partial vacuum between the suction cup and the pellicular material. The suction cup is supported by rod 12, which extends into the force gage and operates hand 13 so as to cause registration on dial 14 of the force being applied in pulling a pellicular material 15 away from a container 16. The force gage also comprises adjusting knob 17 for adjusting the original setting of hand 13 to indicate zero force prior to the application of a pulling force to the force gage by means of the operators left hand 18. The apparatus also comprises needle 19 which has distance or length graduations 20 thereon and which is attached to a handle 21 by which the needle is held by means of the operators right hand 22 during a determination of the tightness of the pellicular material on the container.  
  In the use of the apparatus of the invention, a container, such as 16, or assembly of containers about which a pellicular wrapper 15 has been shrunk, usually by heat-shrinking, is subjected to a determination of the tightness of the pellicular wrapper 15, which may be a heat-shrinkable plastic film, such as heatshrinkable polyethylene film of from about 5 mils to about 8 mils thickness, on the container. The container may be completely enclosed within the pellicular wrapper; or it may be enclosed or covered over the top and plurality of sides without being covered over the bottom thereof, particularly when the container or assembly of containers enclosed by the pellicular wrapper is resting on a pallet or other type of base; or it may be covered only with respect to its sides. The second arrangement is gaining greater usage every day since it provides for ease of handling and good protection against rain, snow, dust and other contaminants while holding an assembly of containers tightly together, provided the pellicular wrapper is thick and strong enough and has been sufficiently tightly shrunk about or over the assembly of containers.  
  As shown in FIG. 3, in determining the tightness of the pellicular wrapper on the container or assembly of containers, the force gage is brought into engagement with the exterior surface of pellicular material 15 with the suction cup being pressed against the pellicular material at a preselected position with respect to the corners and edges of the container or assembly of containers. The force gage is held by the left hand of the operator and pushed toward the container until the suction cup flattens out and then is permitted to expand to or toward its original condition, thus producing a partial vacuum between it and the exterior surface of the pellicular wrapper material. The needle 19, is then held as in FIG. 3 with its point resting against the exterior surface of the pellicular wrapper at a point close to the edge of the suction cup, the needle being held in place by means of the right hand of the operator grasping the handle 21 which supports the needle.  
  If need be, the hand 13 of the force gage is adjusted to zero by means of the right hand of the operator prior to holding the needle against the pellicular wrapper material before any force is applied in pulling the force gage and the pellicular wrapper to which it is attached.  
  When all is in readiness, the force gage is pulled with the left hand of the operator away from the container or assembly of containers, the point of the needle as a result thereof penetrating the pellicular wrapper material as the pellicular wrapper material is pulled away from the container surface until the pellicular wrapper material comes to a preselected distance graduation on the needle, which may be the end of the handle which may serve as a stop means for the pellicular wrapper material if desired; and the pulling force required to pull the pellicular wrapper material that distance from the container or assembly of containers in that particular area is read off of the dial 14 at the point registered by hand 13 thereon. The portion of the needle which has penetrated the pellicular wrapper material is designated by 19 and is shown in phantom in FIG. 4. If desired, the force gage may be provided with a catch for setting the hand at the maximum force applied in pulling the pellicular wrapper material a preselected distance away from the container surface. Such a determination may be made at a plurality of points over the exterior surface of the pellicular wrapper material to obtain an average value for the tightness of the pellicular wrapper on the container or assembly of containers or to plot such values as to location with respect to the container or assembly of containers.  
  Alternatively, the tightness of the pellicular wrapper on the container or assembly of containers may be determined by preselecting a force at which determinations will be made of the distance from the container to which the pellicular wrapper material is pulled. This type of determination may be repeated at various points on the exterior surface of the pellicular wrapper material and an average value obtained for the distance to which the pellicular wrapper material is pulled away from the container or assembly of containers in developing the preselected force; or the values may be plotted with respect to location on the pellicular wrapper in relation to the container or assembly of containers.  
  Although the invention has been described in terms of a force gage comprising a suction cup for detachably attaching the force gage to the exterior surface of a pellicular wrapper material, it is to be understood that various other means may be employed for attaching the force gage to the pellicular wrapper material. The preferred forms of the apparatus and method apply only to their use with substantially non-porous pellicular wrapper material since in the use of the suction cup it is necessary that air not be able to pass through the pellicular material at a substantial rate, otherwise the suction cup would not be able to maintain a partial vacuum sufficiently long to permit accurate force measurements to be made.  
  While certain thicknesses of film have been disclosed by way of example in connection with the encasing or surrounding of containers or assemblies thereof by means of heat-shrinkable film, it is to be understood that films of other thicknesses may be employed, the essential requirement being that the films be sufficiently thick and strong to hold the load of containers under any anticipated set of conditions of handling or shipping after having been shrunk in place about the containers.  
  The apparatus and method of the invention are very useful in determining whether a pellicular wrapper has been shrunk over or around a container or assembly of containers in such a manner as to produce relatively uniform tightness thereof and whether the wrapper has been shrunk sufficiently to insure that an assembly of containers will not topple over or shift to an excessive .degree while it is being handled while assembled on a pallet by means of a forklift truck, or on any other type of base, or that it will not shift too much during shipment. The apparatus and method place this matter on a quantitative basis, whereas, heretofore, it has involved a question of guessing whether an assembly of the sides of a load comprising a container or an assembly of containers which comprises the steps of:  
 a. detachably attaching a force gage to said pellicular wrapper at a predetermined point,  
 b. pulling said force gage and said pellicular wrapper attached thereto a predetermined distance away from said load, and  
 c. measuring with said force gage the force required for pulling said pellicular wrapper said predetermined distance away from said load.  
  2. Method according to claim 1, wherein said step of pulling said force gage and said pellicular wrapper said predetermined distance comprises inserting a needle graduated in terms of distance through said pellicular wrapper with the point of said needle held against said load and permitting said pellicular wrapper to move along said graduated needle until said pellicular wrapper is pulled said predetermined distance away from said load as determined by the position of said pellicular wrapper relative to said graduated needle.  
 3. Method of determining the tightness of a substantially non-porous pellicular wrapper encasing at least the sides of a load comprising a container or an assembly of containers which comprises the steps of:  
 a. detachably attaching a force gage to said pellicular wrapper at a predetermined point,  
 b. pulling said force gage and said pellicular wrapper attached thereto away from said load until said force gage registers a predetermined force, and  
 c. measuring the distance from said load to which said pellicular wrapper is pulled when said force gage registers said predetermined force.  
  4. Method according to claim 3, wherein said step of measuring the distance from said load to which said pellicular wrapper is pulled comprises inserting a needle graduated in terms of distance through which said pellicular wrapper is pulled with the point of said needle held against said load and said pellicular wrapper caused to move along said graduated needle as said needle penetrates said pellicular wrapper until said force gage registers said predetermined force.