US3680215A

US3680215A - Continuous thickness measuring apparatus for veneer and other web material

Info

Publication number: US3680215A
Application number: US85418A
Authority: US
Inventors: Irving L Plough
Original assignee: Black Clawson Co
Current assignee: Black Clawson Co; Acrowood Corp
Priority date: 1970-10-30
Filing date: 1970-10-30
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01

Abstract

In apparatus including a pair of relatively movable feeler wheels for continuously measuring the thickness of a traveling web, the stationary part of the transducer which detects the movements of the movable wheel is mounted on a supplemental frame fixed with relation to the support for the stationary wheel and capable of sufficient movement with respect to the structure supporting the movable wheel to be independent of shock and vibration forces affecting that structure.

Description

United States Patent Plough 51 Aug. 1, 1972 [54] CONTINUOUS THICKNESS MEASURING APPARATUS FOR VENEER AND OTHER WEB MATERIAL [72] Inventor: Irving L. Plough, Everett, Wash.

[73] Assignee: The Black Clawson Company,

Hamilton, Ohio [22] Filed: Oct. 30, 1970 [21] Appl. No.: 85,418

[52] U.S. Cl ..33/143 L, 33/147 L, 33/147 N [51] Int. Cl. ..G01b 5/02, GOlb 5/04, GOlb 5/06 [58] Field of Search..33/l43 F, 143 L, 143 R, 147 R,

[56] References Cited UNITED STATES PATENTS 3,140,545 7/1964 Murtland ..33/143 L 2,955,358 10/1960 Walking ..33/143F Primary Examiner-Leonard Forman Assistant Examiner-Paul G. Foldes Attorney-Marechal, Biebel, French and Bugg 57] ABSTRACT ln apparatus including a pair of relatively movable feeler wheels for continuously measuring the thickness of a traveling web, the stationary part of the transducer which detects the movements of the movable wheel is mounted on a supplemental frame fixed with relation to the support for the stationary wheel and capable of sufficient movement with respect to the structure supporting the movable wheel to be independent of shock and vibration forces affecting that struc- 7 Claims, 5 Drawing Figures PATENTEDAus 1 I972 SHEET 1 0F 2 Illli w mm F INVENTOI? IRVING L. PLOUGH IOT I55 ISI A TTORNEYS CONTINUOUS THICKNESS MEASURING APPARATUS FOR VENEER AND OTHER WEB MATERIAL BACKGROUND OF THE INVENTION Wood veneers of the types most used in the manufacture of plywood are produced on a lathe wherein a log or bolt of wood is rotated about its longitudinal axis with respect to a knife which peels the wood to form a continuous web. Commonly a nose bar engages the wood at a position close to the edge of the knife, and the thickness of the veneer is primarily determined by the spacing of the knife edge with respect to this nose bar. The web is carried from the lathe on a conveyor system which includes a table where a clipper of the guillotine type cuts the web into sections of predetermined width in the direction of travel, and also cuts out sections containing holes or other defects rendering them unfit for plywood use.

It is important to a veneer producer to maintain the thickness of the veneer as nearly as possible uniform within predetermined tolerances, for a number of reasons. One such reason is that when several layers of veneer, sometimes of different thicknesses and types, are combined in plywood, any significant variation in the thickness of one or another layer could cause unacceptable thickness variations in the plywood. Further, it is customary in the industry to grade veneer for sale in accordance with a guaranteed minimum thickness, e.g., 543 inch veneer is all at least one-eighth inch in thickness but may vary above that thickness. Since the veneer producer is paid only on the basis of the rated minimum thickness, any excess thickness represents a loss to him of potential additional income.

A related factor is that the smoothness of veneer directly affects its sales value, and this is a property which is in large measure determined by the sharpness of the lathe knife. As the knife edge wears in use, the thickness of the veneer will tend to increase unless the knife is readjusted to bring its edge closer to the nose bar, and also roughening of the veneer surface will tend to increase, both of which are economically undesirable conditions. Since, therefore, the operating condition of the knife is reflected in the thickness and surface condition of the veneer, continuing accurate measurement of the veneer thickness would serve as a constant source of information as to the need for readjustment, sharpening or replacement of the knife.

The usual practice has been to caliper the sheet at fairly frequent intervals, but there is obviously a lag between the time when information is obtained in this manner and the time when action could be taken on the basis of that information. Further, calipering requires that the veneer be stationary, which means that the measurement must be made on a piece pulled away from the conveyor. Continuous measuring apparatus, however, must compete with a variety of operating difficulties, including the presence of pitch or gum on the surface of many woods, and also the excessive shock and vibration forces incident to the normal operating conditions of a veneer mill, and particularly contributed to by the frequent and rapid blows of the clipper blade on its complementary anvil.

SUMMARY OF THE INVENTION It is the primary objective of this invention to provide apparatus which will continuously and accurately measure the thickness of a veneer web by continuously monitoring the web as it travels from the lathe to the clipper, and which will supply a continuous record of the thickness information in a convenient form for use. To accomplish this objective, the invention successfully overcomes the major difficulties noted above, and including particularly the presence of pitch and other substances on the surface of the veneer, and the shock and vibration forces generated by the clipper and other apparatus customarily present in a veneer mill.

The apparatus of the invention includes a pair of feeler members such as measuring wheels arranged for movement toward and away from each other while respectively engaging the bottom and top surfaces of the advancing veneer web. The bottom wheel is provided with a relatively firm mounting, the upper wheel is biased downwardly into engagement with the surface of the veneer web riding on the lower wheel, and the thickness of the web is monitored by continuously measuring the movements of the upper wheel toward and away from the lower wheel. The effects of foreign substances on the surface of the veneer are minimized by arranging the wheels at a small angle to each other and the direction of web travel, such that they are essentially self cleaning.

As already noted, a major problem affecting any such measuring apparatus is that its accuracy depends upon the extent to which the movements of the movable measuring member are due solely to variations in the thickness of the material being measured, as distinguished from movements caused by the environmental forces such as shock and vibration which are particularly prevalent in a veneer mill. At the same time, however, since a veneer web is normally somewhat more than eight feet in width, the mountings of measuring wheels on opposite sides of the web are necessarily spaced a substantial distance from each other. Notwithstanding this difficulty, the invention successfully minimizes shock and vibrational elfects by a construction and arrangement such that the stationary member of the transducer which senses movements of the upper measuring wheel is effectively rigidly interconnected with the mounting for the lower measuring wheel so that movements of the upper frame due to shock or vibration do not affect the accuracy of the continuous measurement of web thickness.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view illustrating an installation of the measuring device of the invention for continuously measuring the thickness of a traveling web of veneer near one edge thereof;

FIG. 2 is an enlarged fragmentary side view, partly in section, of the installation of FIG. 1;

FIGS. 3 and 4 are enlarged fragmentary sections on the lines 3-3 and 44 respectively of FIG. 1; and

FIG. 5 is a somewhat diagrammatic elevation showing another form of installation of the invention for continuously measuring thickness at a plurality of spaced positions across the width of a traveling web.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The installation of the invention illustrated in FIG. 1 is arranged for continuous monitoring of the thickness of a web W of veneer carried by multiple conveyor belts 10. Preferably the measuring will be done at a location between the veneer lathe and the clipper, in order to provide a continuous measuring operation uninterrupted by the separation of adjacent pieces. The measuring is accomplished by continuous monitoring of the relative displacement of a pair of wheels 11 and 12 which respectively engage the lower and upper surfaces of the web. The supporting structure for wheels 11-12 is designed to limit measurement of the relative movements of these wheels to the travel caused by variations in the thickness of the veneer, as distinguished from shock, vibration and other forces incident to operation of the mill.

The main frame in FIG. 1 comprises an end stand 13 from which lower and

upper frame arms

14 and 15 are cantilevered in vertically spaced relation to define an open ended slot 17 for receiving the veneer web W therethrough. The stand 13 is mounted on base means, such as angles 18,-in predetermined relation to the path of the veneer so that the

arms

14 and 15 extend above and below the veneer at a location such that the lower measuring wheel engages a portion of the veneer between conveyor belts 10 at a location spaced inwardly from the adjacent edge of the web, for example about 36 inches.

The lower measuring wheel 11 is provided with a fixed mounting on top of the inner end of the lower frame arm 14. This mounting comprises a fork 20 which carries the axle 21 for wheel 11 and is in turn bolted on top of a mounting pad 22 forming in effect a part of the frame arm 14.

The upper measuring wheel 12 is supported in the upper frame arm 15 in such manner that it is free to move vertically as required by variations in thickness of the veneer, independently of any movements of the frame resulting from shock or vibrational forces. Referring particularly to FIG. 2, the wheel 12 is mounted by an axle 24 in a fork 25 which is in turn bolted to the head 26 of an elongated cylinder 30. The barrel portion of the cylinder 30 is in turn supported by bearings 33 and a spacer 34 for free movement in a housing 35 bolted or otherwise mounted on the end wall 36 of the frame arm 15. It has been found desirable in the practice of the invention to use ball bushings as the bearings 33, protected by a suitable seal 37 at the lower end of the housing 35.

A piston rod 40 includes an enlarged head 41 bolted or otherwise securedv in stationary relation with the upper end of the housing 35. The cylinder 30 is accordingly movable axially with respect to the piston rod 40, and its movements are guided along a substantially straight vertical path by a roller follower 42 supported in a fork 43 mounted on a bracket 44 secured to or forming a part of the cylinder head 26. The roller 42 rides in a slot 45 in the end wall 36 and thus maintains the wheels 1 1-12 in the desired arrangement shown in FIGS. 1-2 wherein their central planes are aligned at small angles to each other and to the direction of travel of web W to provide a continuous self-cleaning action with respect to pitch, gum or the like on the surface of the veneer.

The piston rod 40 has a threaded lower end portion on which a piston 46 is mounted by a nut 47, and the 5 piston 46 carries an O-ring 48 in sealing engagement with the inner surface of the cylinder 30. The piston 46 and O-ring 48 thus divide the interior of the cylinder 30 into lower and

upper portions

50 and 51 which are provided with pressure and venting connections for selectively biasing the cylinder 30 in the desired direction. A passageway 52 leads from a port 53 in the piston rod head 41 through the lower end of the piston rod into the chamber 50, and a second passage 55 leads from a port 56in the side of the piston rod 40 above the piston 46 to a port 57 in the upper end of the piston rod. In normal operation, the port 53 is connected to a source of pressure air to supply pressure to the chamber 50 while the port 57 is connected to atmosphere. Preferably, however, the pressure system will include provisions for reversing these connections to supply pressure to the chamber 51 while chamber 50 is connected to atmosphere, as indicated by the pressure control valve 58.

With this construction and control system as thus far described, the cylinder 35 will in normal operation be pressure loaded downwardly so that the upper measuring wheel 12 will be biased into engagement with the upper surface of a veneer sheet traveling between wheels 11-12. Any variations in the thickness of the veneer will produce corresponding up or down movement of the wheel 12 and cylinder 30, and these movements are constantly monitored by a transducer mechanism 60 as described below. It should be noted first, however, that when the pressure supply connections are reversed, the cylinder 30 will rise and thereby separate the measuring wheels 11-12 to the extent of the upward'travel of the cylinder 30, thereby providing corresponding clearance between the two wheels for maintenance purposes and the like.

It is essential to the success of the invention that the mechanism 60 for measuring movement of the upper wheel 12 toward and away from wheel 1 1 respond only to movement of wheel 12 caused by variations in the thickness of the veneer passing therebetween, and that it be able to ignore all forces causing movement of upper frame arm 15 with respect to other parts of the frame, a particular problem being the tendency of the

arms

14 and 15 to move toward and away from each other with a tuning fork effect. The transducer 60 is accordingly supported by a supplemental frame in the form of a generally C-shaped yoke 65 positioned within the frame parts 13-15 and mounted on the lower frame arm 14 in close proximity to the lower measuring wheel 11. As best seen in FIGS. 1 and 3, the lower end of the yoke 65 is forked to provide a pair of short arms 66 which straddle the mounting pad 22 and are supported for limited pivotal movement with respect to the frame arm 14 on a pivot axis extending in the direction of travel of the veneer web and essentially coinciding with the vertical center line of the wheel 10.

The pivotal mounting for one of the fork arms 66 is shown in detail in FIG. 3. It includes a pivot block 70 having is upper surface tapered to form a knife bearing 71 on which the lower surface of the fork arm 66 rests. The fork arm 66 is provided with a tapered bore 72 which receives a complementary tapered rubber grommet or washer 73 enclosing a metal sleeve 84, and a bolt 75 extends through this sleeve and is threaded into a tapped bore in the upper wall of the frame arm 14. With this construction, which is duplicated for the other fork arm 66, the yoke is held firmly against the blocks and thereby substantially located in the horizontal plane, but at the same time, it can have limited pivoting movement on the blocks 70 to the extent permitted by distortion of the grommet 73, which will normally be no more than a minor fraction of a degree.

The yoke 65 is designed to possess a high degree of rigidity such that its two end portions will at all times remain in essentially fi-xed spaced relation, and the series of spaced holes 77 are provided to decrease its overall weight without detracting from the desired rigidity. Its upper portion is therefore guided in the end stand 13 and upper frame arm 15 but is not rigidly connected to either of those frame parts. A pair of links 80 are pivoted at 81 to the upper arm of the yoke 65 and at 82 to the frame arm 15 to permit this part of the yoke to move as required to accommodate vertical movement of the arm 15 with respect to the bearing blocks 70.

An additional flexible support 85 is provided for the mid-portion of the yoke 65 in the end stand 13 and is shown in detail in FIG. 4. One end of a rod 88 is supported for limited movement on the wall of end stand 13 by a flat bar 90 secured to the wall by screws 91 and clamped between a pair of rubber bushings 92 and nuts 93 on the rod 88. The other end of the rod 88 extends through a hole in the yoke 65 and is similarly clamped to the yoke by a second pair of rubber bushings 92 and nuts 93. This supporting arrangement stabilizes the yoke in position within the end stand 13 while still providing for such limited movement as may be required to compensate for vibration and shock effects on the frame.

The transducer mechanism 60, which is mounted in a bracket portion 99 on the outer end of the upper arm of the yoke 65 may be selected from a number of commercially available units capable of converting movement of its movable part into electrical signals proportional to the extent of the movement. The transducer 60 is shown somewhat diagrammatically in FIG. 3 as a linear differential transducer Model 7DC DT-25O manufactured by the Sanborn Division of Hewlett- Packard Company, and comprising a stationary coil assembly 100 and a central probe 101 attached to the core (not shown) which is movable axially within the coil assembly 100. Movement of the probe 101 is guided by the inner wall of the annular housing 102, and a coil spring 105 normally biases the probe 101 upwardly with respect to the coil assembly. The electrical leads 106 to the coil assembly 100 are brought out through the wall of the housing 102 and through an annular spacer 107 positioned between the coil assembly 100 and the spring 105.

The transducer housing 102 is in turn provided with an adjustable but firm mounting in the end of the upper arm of the yoke 65. An annular mounting plate 110 is screwed or otherwise secured to the lower end of the housing 102, and this plate includes a tubular stem 111 mounted for axial movement in a bore in the annular bracket portion 99 at the end of the yoke 65. The mounting plate 110 is provided with a key 112 preventing it from rotating in the bracket 99, and a coil spring 113 is positioned between the upper surface of the bracket 99 and the under side of the mounting plate 110. An adjusting knob 115 engages the under side of the bracket portion 99, and its screw portion is threaded into the tapped interior of the stem 11]. The spring 113 biases the mounting plate 110 upwardly from the bracket portion 99, and rotation of the knob 1 15 in one direction or the other will cause corresponding movement of the housing 102 with respect to the bracket 111 for accurate positioning and calibration of the transducer.

The movements of the upper measuring wheel 12 are transmitted to the probe 101 by a wand of generally Z-shape which is screwed or otherwise mounted on the bracket portion 44 of the cylinder head 26. The upper end of the wand 120 overhangs and engages the upper end of the probe 101, and the adjusting knob 115 is used to adjust the relationships of the parts to a desired reference position of wand 120 and probe 101. This entire mechanism is shielded within the frame arm 15 except for the portion depending below the frame arm, which is enclosed within a shield depending from the frame arm 15 and open at its lower end for access to the adjusting knob 115.

In operation, the adjusting knob 115 is used to establish the desired reference position of the probe 101 and wand 120 corresponding to a predetermined relative spacing of the wheels 11-12. For example, this reference position may correspond to the guaranteed minimum thickness of the veneer to be monitored or to a selected intermediate position in the tolerance range above such minimum thickness. Then with the system in operation and the veneer web traveling between the measuring wheels, whatever vertical movements occur on the part of the upper wheel 12 will be sensed by the probe 101 and translated into electrical signals in accordance with the characteristics of the transducer 60.

The physical and mechanical arrangements of the parts are such that the vertical movements of the wheel 12 will be effectively independent of relative movements of different parts of the frame structure, and will therefore truly represent various thicknesses in the web W. This result is achieved because the coil 100 and housing 102 are held in effectively rigid relation, through the yoke 65, with the lower measuring wheel 11 and do not follow movements of the upper frame arm 15 such as may be caused by shock, vibration and other environmental and operational conditions. Further, the upper measuring wheel is also independent of such frame movements, because it is continually pressure biased against the upper surface of the veneer web, and while movements of the frame arm 15 could cause the housing 35 to move up and down, the cylinder 30 will remain in fixed relation with the upper surface of the veneer web. The flexible supports for the yoke 65 provided through the links 80 and rod 88 also contribute to the desired result of maintaining the yoke 65 and the parts supported thereby in rigid relation with the lower frame arm 14 and isolated from relative movements of the end frame 13 and upper frame arm 15.

The electrical inputs to the transducer 60 are dictated by the electrical characteristics of the transducer, as recommended by its manufacturer. The output 130 of the transducer may take a variety of forms and used for different selected purposes. For example, it may take the form of a digital read out or a tape or other permanent read out record. Alternatively, as indicated at 131, it may be employed to control mechanical means for implementing the monitoring function, such for example as an adjusting mechanism for the nose bar of the veneer lathe, a device for marking the veneer to indicate thick and thin areas, or the actuating control for the clipper to cause it to separate lengths of veneer web in accordance with their variations from the desired thickness.

FIG. illustrates the application of the invention to an installation for monitoring the thickness of a traveling veneer web at a plurality of locations spaced across its width, and particularly useful where the width of the web is such that the cantilevered construction of FIGS. l-4 may not be practical. In FIG. 5, the main frame comprises a base 150 and a pair of end stands 151 connected at their upper ends by a top frame 152 which is spaced above the base 150 to define the opening 153 through which the web travels on conveyor tapes 10. The installation shown in FIG. 5 includes three pairs of measuring wheels 155-156, each of these pairs being individually essentially the same as the wheels 11-12 and cooperating in similar fashion to provide continuous measuring of the thickness of the web traveling therebetween.

In accordance with the invention, each of the pairs of measuring wheels 155-156 and their associated apparatus are supported in essentially the same relation with the base 150 as the wheels 11-12 and their associated apparatus already described. More specifically, each lower wheel 155 has a pivotal support fixed on the base 150, and each of the upper wheels 156 is supported on the top frame 152 for vertical movement with respect to its complementary lower wheel. Thus the mounting 158 for each upper wheel 156 may be of essentially the same construction as the mounting for wheel 12 described in connection with FIG. 3.

The transducer 160 for each pair of wheels 155-156 includes a stationary part mounted in essentially stationary relation with the base 150 by a supplemental frame 165 which corresponds in function to the yoke 65 but is a complete annulus proportioned for enclosure within the four components. of the frame in similarly enclosing relation with the opening 153. As in the case of the yoke 65, the supplemental frame 165 is preferably as light in weight as is compatible with high rigidity under the operating conditions of the invention, and it is similarly provided with multiple holes for reducing its overall weight.

The supplemental frame 165 is mounted in the base 150 at locations close to one or more of the lower measuring wheels, and two such mountings 166 are shown as desirable in view of the overall dimensions of the installation. Each of the mountings 166 should secure the frame 165 in metal-to-metal supported relation with the base 150 to retain the lower measuring wheel 155 in vertically fixed position with respect to the base 150. For example, the mounting 166 could include a knife edge support of the same operating characteristics as the mounting for the yoke 65 as shown in FIGS. 2 and 3. In order to allow for relative movement of the upper portion of the frame 165 and the top frame 152, the upper part of the supplemental frame 165 may be provided with stabilizing supports like the assembly shown in FIG. 4, and two such supports are indicated diagrammatically at 170.

The upper portion of the supplemental frame which lies within the frame top 152 and in the upper portion of the opening 153 corresponds in function to the end of the upper arm portion of the yoke 65, and the stationary portion of the transducer associated with each of the upper measuring wheels is mounted thereon, by means which may be essentially the same as described in connection with FIG. 3. Accordingly, since the supplemental frame 165 is essentially independent of movements of the end frames 151 and top frame 152 with respect to the base 150, it supports the transducers in'essentially stationary position offering the same advantages as described in connection with FIGS. l-4.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. Apparatus for continually measuring the thickness of a moving web comprising:

a. a main frame including a base and a top connected in vertically spaced relation to define an opening for receiving the web therethrough,

b. a lower wheel having a fixed mounting on said base and engageable by the under surface of the web,

c. an upper wheel engageable by the top surface of the web,

(1. means on said frame top supporting said upper wheel for movement toward and away from said lower wheel in accordance with variations in the thickness of the web traveling therebetween,

e. a supplemental frame of rigid construction including upper and lower portions connected in spaced relation defining an opening coinciding with at least a portion of said opening in said main frame,

f. means mounting said lower frame portion in fixed relation with said base at a location adjacent said lower wheel,

g. transducer means including a pair of relatively movable members for measuring movement of said upper wheel toward and away from said lower wheel,

. means securing one of said transducer members to said upper portion of said supplemental frame, and

i. means connecting the other of said transducer members to said supporting means for said upper wheel for movement therewith with respect to said frame top.

2. The apparatus defined in claim 1 wherein said means connecting said lower frame portion to said base comprises resilient means providing for limited movement of said supplemental frame about a horizontal axis substantially aligned with the vertical center lines of said wheels.

frame with respect to said main frame within the limits 1 established by said resilient means to isolate said supplemental frame from the effects of relative movement of said base and top.

5. The apparatus defined in claim 1 wherein said upper and lower portions of said supplemental frame are interconnected by a mid-portion defining therewith a substantially C-shaped yoke with said upper and lower portions extending substantially normal to the direction of movement of said upper wheel on said frame top.

6. The apparatus defined in claim 5 wherein said mounting means (f) comprises 1. pivot means mounted on said frame base in sup porting engagement with said lower frame portion, and

2. resilient spacer means connected between said lower frame portion and said pivot means to limit relative movement of said supplemental frame about said pivot means.

7. The apparatus defined in claim I wherein said upper and lower portions of said supplemental frame are interconnected at both ends thereof by end portions cooperating therewith to enclose said opening for receiving the web therethrough.

Claims

1. Apparatus for continually measuring the thickness of a moving web comprising: a. a main frame including a base and a top connected in vertically spaced relation to define an opening for receiving the web therethrough, b. a lower wheel having a fixed mounting on said base and engageable by the under surface of the web, c. an upper wheel engageable by the top surface of the web, d. means on said frame top supporting said upper wheel for movement toward and away from said lower wheel in accordance with variations in the thickness of the web traveling therebetween, e. a supplemental frame of rigid construction including upper and lower portions connected in spaced relation defining an opening coinciding with at least a portion of said opening in said main frame, f. means mounting said lower frame portion in fixed relation with said base at a location adjacent said lower wheel, g. transducer means including a pair of relatively movable members for measuring movement of said upper wheel toward and away from said lower wheel, h. means securing one of said transducer members to said upper portion of said supplemental frame, and i. means connecting the other of said transducer members to said supporting means for said upper wheel for movement therewith with respect to said frame top.

3. The apparatus defined in claim 1 comprising means forming a guiding connection between said main frame and said upper portion of said supplemental frame providing for limited movement of said supplemental frame with respect to said frame top.

4. The apparatus defined in claim 2 comprising means forming a guiding connection between said main frame and said upper portion of said supplemental frame providing for movement of said supplemental frame with respect to said main frame within the limits established by said resilient means to isolate said supplemental frame from the effects of relative movement of said base and top.

6. The apparatus defined in claim 5 wherein said mounting means (f) Comprises

7. The apparatus defined in claim 1 wherein said upper and lower portions of said supplemental frame are interconnected at both ends thereof by end portions cooperating therewith to enclose said opening for receiving the web therethrough.