Dynamic stress-strain testing of ribbons of film

Claim 3

The method of claim 1 wherein said controlled constant tension is about 10 percent or less of the elongation induced tension.

Claim 4

The method of claim 1 further comprising winding said film into a roll of film after said measuring and recording.

Claim 5

The method of claim 2 further comprising winding said film into a roll of film after said measuring and recording.

Claim 6

The method of claim 4 wherein: A. said distensible polymeric film is polyethylene having nominal thickness of 0.001 inch; B. said controlled constant tension is approximately two ounces per inch of width of said ribbon of film; and C. said predetermined elongation is in the range from about 2 to about 6 percent.

Claim 7

The method of claim 5 wherein said predetermined elongation is about 4 percent.

Claim 8

The method of claim 6 wherein said film is supplied from a rolled ribbon of film.

Claim 9

The method of claim 4 wherein said predetermined elongation is about 4 percent and said film is maintained under constant tension during said winding into said roll of film, whereby said film is uniformly stressed until subsequently used.

Claim 10

The method of claim 8 wherein said film is supplied from a rolled ribbon of film.

Claim 11

Apparatus to non-destructively measure and record stress versus strain characteristics parallel to the direction of movement of a continuous ribbon of film of uniform width, said apparatus comprising: A. a frame structure; B. a tension-sensing roll; C. means for mounting said tension-sensing roll in said structure so that it is freely rotatable on its axis; D. stretching means for imparting uniform elongation to said film parallel to the direction of movement, said stretching means comprising two pairs of nip rolls rotatably secured to said structure with their axes substantially parallel to the axis of said tension-sensing roll, forming a first nip intermediate one said pairs and a second nip intermediate the other said pairs, said nips being spaced so that the film traverses a substantially constant length, constant geometry looped path including a circumferential portion of said tension-sensing roll intermediate said first nip and said second nip, said stretching means including means for driving said nip rolls at constant surface velocities so that their surface velocity at said second nip is a fixed percent greater than their surface velocity at said first nip whereby said film is elongated as it traversed the looped path; E. means for sensing and recording the tension in said film intermediate said nips by measuring the forces tending to displace the axis of said tension-sensing roll; F. means for maintaining constant tension in said film feeding into said first nip, said constant tension means comprising a controllable torque brake secured in part to said frame structure, closed-loop control means for controlling the controllable torque of said brake, and means for causing said brake to induce tension in said film proportional to the controllable torque; and G. means for winding said film into a roll of film after it passes through said second nip.

Claim 12

Apparatus to non-destructively measure and record stress versus strain characteristics parallel to the direction of movement of a continuous ribbon of film of uniform width, said apparatus comprising: A. a frame structure; B. a tension-sensing roll; C. means for mounting said tension-sensing roll in said structure so that it is freely rotatable on its axis; D. stretching means for imparting uniform elongation to said film parallel to the direction of movement, said stretching means comprising two pairs of nip rolls rotatably secured to said structure with their axes substantially parallel to the axis of said tension-sensing roll, forming a first nip intermediate one said pairs and a second nip intermediate the other said pairs, said nips being spaced so that the film traverses a substantially constant length, constant geometry looped path including a circumferential portion of said tension-sensing roll intermediate said first nip and said second nip, said stretching means including means for driving said nip rolls at constant surface velocities so that their surface velocity at said second nip is a fixed percent greater than their surface velocity at said first nip whereby said film is elongated as it traversed the looped path; E. means for sensing and recording the tension in said film intermediate said nips by measuring the forces tending to displace the axis of said tension-sensing roll; F. means for maintaining constant tension in said film feeding into said first nip, said constant tension means comprising a controllable torque brake secured in part to said frame structure, closed-loop control means for controlling the controllable torque of said brake, and means for causing said brake to induce tension in said film proportional to the controllable torque; and G. means for winding said film into a roll of film after it passes through said second nip.

Claim 13

The apparatus of claim 10 wherein each said pairs of nip rolls comprise a driving roll and a freely-rotatable nip idler forming a said nip therebetween, said nip rolls being suitably urged towards one another by actuators whereby sufficient force can be applied to said film passing through said nips to impart the required tensions to said film.

Claim 14

The apparatus of claim 11 whereIn said film is polyethylene having a thickness of about 0.001 inch and width of about 16 inches, said nip roll having a surface velocity of about 375 feet per minute at said first nip, said nip rolls having a surface velocity about 4 percent greater at said second nip than said first nip, said actuators being air operated are each sized to develop a maximum nip force of 500 pounds when supplied with 80 p.s.i. air, and said constant tension in said film feeding into said first nip is about 2 pounds, whereby the tension induced by said elongation is in the order of ten times said constant tension.

Claim 15

The apparatus of claim 12 wherein said winding means comprises means for maintaining substantially constant tension on said film parallel to the direction of moving as it is wound into said roll of film, and means for preventing wrinkles in said film beyond said second nip of said stretching means.

Claim 16

The apparatus of claim 13 wherein said constant winding tension is approximately 2.5 pounds and said wrinkle prevention means comprises a non-rotating smooth, curved transverse member secured to said frame structure having its center displaced upwardly and downstream from its ends, said member contacting the underside of said film across its full width intermediate said second nip and said roll of film whereby said film is bowed upwardly from its edges towards its middle causing transverse stress in said film that substantially prevents wrinkling of said film as it is wound into said roll of film.