Patent Publication Number: US-6210309-B1

Title: Sheet folding method and apparatus utilizing convex folder and guide

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 372,770 filed Jan. 13, 1995 (now U.S. Pat. No. 5,807,228), entitled “Sheet Folding Method and Apparatus”. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to machinery for folding sheet material and, more particularly, to method and apparatus for folding sheet material in forming envelopes and the like. 
     2. Description of the Prior Art 
     In automated envelope forming operations, it is well known to utilize at one of the envelope forming stations a folding mechanism which folds a web of sheet material or blanks cut in preselected lengths. A common folding mechanism includes plow-share-type folding guides which extend a preselected length along the envelope feed line. The web of sheet material or cut blanks are conveyed through the plowshare folder by a vacuum table or a combination of overlying conveyors and pinch rolls. 
     U.S. Pat. No. 5,094,658 discloses a plowshare folder in an envelope forming machine where individual envelope blanks are conveyed through the folding mechanism by a vacuum table. The vacuum table includes a series of spaced apart conveyor belts that are driven over the surface of a vacuum table in the direction of feed of the blanks. The vacuum table includes a plate having apertures which draw in air as a result of a vacuum created by the evacuation of air from a vacuum plenum created below the surface of the vacuum plate. The plowshare folder includes a thin wall of rigid material having at the front end an initial planar surface which gradually bends in a 180° turn. Through the 180° turn, blades of the plowshare engage the seal flap region of the envelope blank. The flaps to be folded extend parallel to the axis of movement of the blank across the vacuum table and are folded into overlying relation with the main body of the blank. 
     As further disclosed in U.S. Pat. No. 5,094,658 a pair of plowshares are oppositely positioned in the feed line to simultaneously fold opposite side flaps. This operation is routinely performed in the formation of large open end envelopes. 
     U.S. Pat. No. 4,994,010 also discloses a machine for forming large open end envelopes having clasps to maintain the seal flaps of the envelope closed. Prior to attaching the clasp the lateral flaps of the blank are folded into overlapping relation to form the back side of the envelope. Then the clasp is attached to the folded flaps. 
     The folding operation in U.S. Pat. No. 4,994,010 is performed by a plowshare-type folding mechanism that includes fold loops and folding blades. During the folding operation, the lateral flaps converge and are glued together in an overlapping area by means of an adhesive layer which has been previously applied with the result that the folded and overlapping flaps form the back side of the envelope. The lateral flaps are simultaneously folded by folding blades which have an inner curvature that evolves from an initial point where the side flaps extend horizontally to a point where the flaps are folded in a tubular configuration. The guide surfaces of the folding blades curve progressively through 180° along travel of the blank. 
     The progressive folding of side flaps of an envelope blank in a plowshare-type folder is accomplished by the envelope blank advancing through zones of the folding blades. The curvature of the blades progressively changes from 0° to 180° through zones that extend in the direction of the feed line. The blades have a width which corresponds to the full width of the flap being folded. Consequently the entire surface of the flap being folded is in contact with the blades through the 180° folding. 
     During the progressive folding, the flap moves from a horizontal position at the 0 20   position through an angle of 180° to a position horizontally in overlying relation on the body of the blank. At the downstream end of the folding operation, the flap is moving downwardly to the 180° position while at the upstream end the flap is moving upwardly to the 90° position. 
     Over its entire length the flap is required to move in different directions during the folding operation. The sheet material forming the flap has a natural tendency to resist a change in direction of the fold. This resistance to folding introduces stress into the blank, making it difficult to maintain the fold aligned with the score line where the fold is to take place. 
     The nature of sheet material to resist bending or folding increases as the length of the blank being folded increases. U.S. Pat. Nos. 1,851,061 and 2,054,832 disclose plowshare-type folding mechanisms for envelope making machines in which the sheet material is folded before it is cut into segregated blanks for forming envelopes. The plowshare blades disclosed in these patents contact the full width of the flap being folded. At one point in the folding operation, the flap is bent upward toward 90° and at another point the flap is folded downwardly toward 180°. Particularly for an extended length of sheet material being folded, the sheet material resists folding which can result in misalignment of the fold at the score line. 
     In U.S. Pat. No. 2,077,952, individual blanks are cut from a continuous web and then folded by the provision of upwardly inclined converging arms which serve to turn the side flaps through approximately a quadrant. Downstream of the converging arms a pair of belts act on the flaps. Active stretches of the belts are twisted from substantially upright to horizontal positions to fold the flaps into overlying relationship with the body of the envelope blank. 
     With the envelope making machine disclosed in U.S. Pat. No. 2,077,952 and the other patents discussed above, the folding mechanisms attempt to support the entire width of the flap being folded. Consequently folding forces are directed at the free edge of the flap a distance substantially removed from the score line where the fold is to be formed. Particularly for envelopes with large flaps to be folded, the folding process commences at even a greater distance from the score line. Therefore, the greater the width of material in contact with the folding device and the further the folding operation commences from the score line, the greater the difficulty in maintaining the fold aligned with the score line. 
     Therefore, there is need in sheet folding machinery, such as envelope forming machines, for apparatus that initiates the folding operation and applies the folding forces closely adjacent to the score line. The free edge of the flap should be supported as the fold is accomplished without applying the folding forces to the flap free edge. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided sheet feeding apparatus that includes a guide bar extending longitudinally in a feed path for conveying individual sheets of material for folding. The guide bar has a receiving end portion and a discharge end portion with a folding edge extending therebetween and positioned parallel to the feed path. A folding face is formed integral with the folding edge and extends between the receiving and discharge end portions. The folding face has a convex profile projecting upwardly from the folding edge and extending the length thereof. The folding face follows a helical path through an angle of 180° relative to the feed path beginning in a horizontal plane at the receiving end portion and ending in a horizontal plane at the discharge end portion. 
     Further in accordance with the present invention, there is provided a method for folding a sheet of material that includes the steps of conveying a sheet of material for folding in a longitudinal feed path. A bending force is applied at a score line in a leading edge of the sheet by a convex folding surface as the sheet is conveyed in the feed path. The leading edge of the sheet is directed in a helical path on the convex folding surface extending longitudinally in the feed path as the sheet is conveyed. The sheet is captured against the convex folding surface to maintain the score line in contact with the convex surface. The sheet is advanced in the helical path to bend the sheet through a angle of 180° in the longitudinal feed path to fold the edge of the sheet along the score line to form a flap on the sheet. 
     Additionally, the present invention is directed to apparatus for folding a flap on a blank of sheet material that includes a bar having a folding edge extending longitudinally in a feed path of a blank of sheet material. The bar has a profile surface positioned transverse to the folding edge. The profile surface has a convex configuration projecting in a radial path upwardly from the folding edge. The profile surface extends in the direction of feed of the sheet material along a helical path through an angle of 180° beginning at about an angle of 0° relative to the feed path and terminating at an angle of 180° relative to the feed path. 
     Accordingly, a principal object of the present invention is to provide method and apparatus for folding sheet material along a score line where the folding forces are applied to the sheet material closely adjacent to the score line and the free edge of the sheet follows the direction of the fold to insure that the fold is maintained in alignment with the score line. 
     Another object of the present invention is to provide an envelope blank folding mechanism that includes a folding bar having a convex profile positioned in overlying relation with the score line of an envelope blank and following a helical path to initiate folding of the envelope blank at the score line with the remainder of the flap portion following the direction of fold at the score line. 
     A further object of the present invention is to provide a folding mechanism for forming a side flap in an envelope blank where the flap is folded along the score line by advancing the blank on the convex surface of a plowshare folder that follows a helical path through 180° and maintaining the score line in contact with a folding edge of the folder. 
     Another object of the present invention is to provide method and apparatus for forming flaps in an envelope blank where the flap is folded on a score line by maintaining the fold on the score line and the remaining portion of the flap follows the direction of the fold. 
     These and other objects of the present invention will be more completely disclosed and described in the following specification, the accompanying drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary isometric view of a folding mechanism of an envelope forming machine, illustrating a plowshare-type folding device for forming a flap in an envelope blank. 
     FIG. 2 is a schematic isometric view of the folding mechanism shown in FIG. 1, illustrating a plowshare extending in a helical path and a guide assembly that follows the helical path to support the blank being folded. 
     FIG. 3 is a further isometric view of the plowshare folder, schematically illustrating a pinch roll assembly at the discharge end of the plowshare. 
     FIG. 4 is a fragmentary isometric view, illustrating the adjustable mounting of the plowshare on a conveyor in the envelope feed path. 
     FIG. 5 is an isometric view of the progressive folding of the envelope blank by the plowshare, schematically illustrating the folding of a side flap from an initial position of the flap at 0°, upwardly to 90°, and then downwardly to 180° where the fold is completed 
     FIGS. 6-12 are schematic sectional views of the plowshare taken at selected points in the feed line shown in FIG. 5, illustrating the helical path followed by the plowshare convex face from approximately 0° at the receiving end portion shown in FIG. 6 to 180° at the discharge end portion shown in FIG.  12 . 
     FIGS. 13-17 are schematic sectional views of the plowshare at selected points during the folding operation, illustrating a forming blade positioned oppositely of the plowshare in overlying relation with the blank closely adjacent to the score line. 
     FIG. 18 is a schematic sectional view of the plowshare, illustrating completion of the fold downstream of the forming blade. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings and particularly to FIG. 1, there is illustrated a folding mechanism generally designated by the numeral  10  for forming envelopes from blanks of sheet material cut from a continuous web of material fed through an envelope forming machine. The details of the envelope forming machine are beyond the scope of the present invention which is limited to the folding mechanism  10 . In a conventional envelope forming machine, individual blanks of sheet material are fed from a stack in a feed line through a number of different stations. 
     Envelopes are formed from blanks or sheet material cut from a web which is first fed to a printing station where a selected portion of both sides of the blank are printed. The printing is followed by the formation of score lines along the top and bottom edges of the blank. From the scoring mechanism, the blanks are moved to a seal gummer. Following the application of adhesive to the flaps to be folded, the blanks are conveyed by a suitable transport device generally designated by the numeral  12  in FIG.  1  through the folding mechanism  10 . 
     The folding mechanism  10  folds the side seam of the blank. A folding mechanism for folding only one flap of the blank is shown in FIG. 1. A duplicate folding mechanism is provided on the opposite side of the machine for simultaneously folding opposite side flaps into overlying relation with the body of the envelope blank. From the folding mechanism  10 , the blanks are fed through creasing rollers generally designated by the numeral  14  that complete the folding operation. From the creasing rollers  14  the envelope blanks are fed to additional folding mechanisms to fold the seal flaps and subsequent stations to complete the envelope forming operation. The formed envelopes are then fed to a delivery station for stacking of the completely formed envelopes in preselected quantities for shipment. 
     The transport device  12  for advancing the blanks in a longitudinal, horizontal feed path through the folding mechanism  10  includes, as illustrated in FIG. 1, a vacuum table formed by a plurality of parallel continuous endless belts  16 . The belts  16  extend around rollers  18  which are driven by suitable drive mechanisms (not shown). The belts  16  are rotated to advance the spaced apart envelope blanks in the feed path identified by the arrow  20 . 
     Each belt  16  includes an upper conveying surface  22  which is positioned above the surface of a vacuum table  24 . The vacuum table  24  is a suitably supported by the envelope machine frame and includes a plurality of apertures  26 . Air is drawn through the apertures  26  by a vacuum created by the evacuation of air from a vacuum box positioned below the table  24 . The vacuum box is connected by pipes to a vacuum creating mechanism (not shown). Details of a suitable vacuum table for use with the present invention are disclosed in U.S. Pat. No. 5,094,658 which is incorporated herein by reference. 
     As the belts  16  are driven above the surface of the vacuum table  24 , the vacuum force is applied to the envelope blanks to frictionally engage the blanks to the surface  22  of the belts  16 . The belts  16  advance in the direction of the feed path indicated by the arrow  20  through the folding mechanism  10 . The vacuum force is exerted at a magnitude to maintain the blanks fixed on the belts  16  so that when the blanks pass through the folding mechanism  10  the edge portions of the blanks are folded along the desired score line. 
     It should also be understood in accordance with the present invention that other types of transport devices  12  are operable for use with the folding mechanism  10 . Rather than a plurality of parallel continuous belts  16 , a single perforated belt is positioned to advance above the surface of the vacuum table  24 . The vacuum force created by the vacuum box draws air through the holes in the perforated belt and the surface of the vacuum table  24  to retain the blanks in a fixed position on the perforated belt as the belt conveys the blanks through the folding mechanism  10 . 
     In a further embodiment of the folding mechanism  10 , a conventional conveyor is used to transport the blanks. The blanks are held in place on the conveyor by suitable holddown devices positioned above the conveyor. Rollers, brushes, grippers and the like are commonly used, as known in the art, as holddown devices to secure the blanks in position on the conveyor through the envelope machine. Accordingly, the folding mechanism  10  is not limited to a specific embodiment of conveyor to transport the envelope blanks. 
     PLOWSHARE SUPPORT FRAME 
     The folding mechanism  10  is supported by a frame  28  of the envelope machine above the surface of the transport system  12 . The folding mechanism  10  is mounted on a bridge generally designated by the numeral  30  which is connected to and extends upwardly from the frame  28  and transversely across the feed path above the vacuum table  24 . It should be understood that the end portions of the bridge  30  are connected to the machine frame  28 . For clarity of illustration, only one end portion of the bridge  30  is shown connected to the frame  28  in FIG.  1 . An identical connection of the bridge  30  to the frame  28  is provided on the opposite side of the transport system  12 . 
     The bridge  30  supports the folding mechanism  10  for adjustment above the transport system  12  in three directions. The folding mechanism  10  is vertically and horizontally adjustable in a direction transverse to the feed path  20 . In addition, the folding mechanism  10  is angularly adjustable about an axis vertical to the vacuum table  24 . The bridge  30  includes at its opposite ends an upright member  32  which is suitably bolted to the frame  28 . A support beam  34  is connected at end portions  36  to the upper end of member  32  to extend transversely to the longitudinal axis of the transport system  12 . 
     The support beam  34  includes a longitudinally extending slot  38  that extends substantially the length of the beam  34 . A plurality of guides  40 ,  42 , and  44  are mounted on the beam  34  for slidable movement along the length of the beam. Each guide  40 - 44  includes an adjustable fastening device  46  that extends through the respective guide into locking engagement with the slot  38 . Advancing the fastening device  46  through the guide into the slot  38  fixes the guide in position on the beam  34 . To move the respective guides  40 - 44  to a desired position along the length of the beam  34 , the fastening device  46  is loosened to permit the guide to slide to the desired position on the beam. 
     The guide  40  is connected to a plowshare-type folder generally designated by the numeral  48 . The plowshare folder  48  folds the envelope blank along a score line as will be described later in greater detail. By adjusting the position of the guide  40  on the beam  34  the plowshare folder  48  is positioned to receive a selected size of envelope blank for folding as it is conveyed along the feed path  20  on the transport system  12 . 
     A sheet control guide generally designated by a numeral  50  is similarly supported above the transport device  12  by the guide  42  for movement along the length of the beam  34 . The sheet control guide  50  is positioned laterally and above the plowshare  48 . The control guide  50  stabilizes movement of the blank trailing edge as the leading edge of the blank is engaged by the plowshare  48  to fold the blank on the score line. 
     A forming blade generally designated by the numeral  52  is adjustably positioned on the support beam  34  by connection to the guide  44 . The forming blade  52  includes an elongated bar  54  that is positioned to extend the length of the plowshare  48  at a preselected angle thereto. The bar  54  is connected to a coupling  56  extending between the bar  54  and a rod  58  that extends through the guide  44 . The rod  58  is supported for rotational movement in the guide  44  and includes conventional means for locking the rod in a desired position to adjust the angular position of the forming blade bar  54  relative to the plowshare  48 . The lateral position of the bar  54  is also adjustable relative to the plowshare  48  by loosening the fastening device  46  to slide the guide  44  in the slot  38  to a desired position on the beam  34 . 
     PLOWSHARE FOLDER 
     As illustrated in FIGS. 1-4 the plowshare folder  48  extends parallel to the direction of feed of the envelope blanks on the transport system  12 . The plowshare folder  48  includes an elongated guide bar  60  having a longitudinally extending folding edge  62  parallel to the feed path  20  of the envelope blanks on the transport system  12 . The folding mechanism  10  of the present invention is adjustable relative to the conveying surface of the transport system  12  to position the folding edge  62  at the desired location to fold the blank along a score line for a wide range of blank sizes at high speed, for example  300  envelopes per minute, through the folding mechanism  10 . 
     To accommodate variations in the width of the flap to be folded on the blank, the guide bar  60  is adjustable laterally relative to the conveying surface  22 . The folding edge  62  is positioned in substantially overlying relation with the score line on the envelope blank that defines the location of the fold in the blank to form a flap of desired width. Further, the length of the plowshare  48  permits flaps of a substantial length to be folded on each envelope blank as they are conveyed on the transport system  12 . 
     As further illustrated in FIGS. 1 and 4, the guide bar  60  forming the plowshare folder  48  extends substantially the length of the upper surfaces  22  of the endless belts  16  between the rollers  18  supporting the conveyor belt  16 . The guide bar  60  has a receiving end portion generally designated by the numeral  64  where envelope blanks are first engaged by the bar folding edge  62 . A discharge end portion generally designated by the numeral  66  defines the end of the plowshare  48  where the folding operation is completed. As shown in FIG. 3, a flap  72  is folded into overlying relation with the body of envelope blank  70  at the plowshare discharge end portion  66 . 
     FIG. 5 illustrates three of the series of steps in the folding sequence in which an unfolded blank  70  is conveyed by the transport system  12  to the receiving end portion  64  of the folding mechanism  10 . One example of an envelope blank  70  is shown in FIG. 5 which has been formed by the envelope machine to include a body portion having a pair of side flaps  72  and  74  defined by score lines  76  and  78  respectively. A pair of end flaps  80  and  82  are separated from the envelope blank body portion by score lines  84  and  86 . Also prior to conveying the unfolded envelope blank  70  to the folding mechanism  10 , the side flaps  72  and  74  and end flaps  80  and  82  are applied with a suitable adhesive for sealing the flaps in folded position. 
     The envelope blank  70  is advanced to the folding device  10  in the direction indicated by the arrow  20  in FIGS. 1 and 5. With the blank  70  conveyed in the direction of arrow  20 , a leading edge generally designated by the numeral  88  of the flap  72  first engages the receiving end portion  64  of the guide bar  60 . A trailing edge generally designated by the numeral  90  of the flap  72  follows the flap leading edge  88  in the folding process. 
     In accordance with the present invention, the leading edge  88  of the flap  72  is initially acted upon by the folding edge  62  of the plowshare guide bar  60  at the score line  76 . Folding of the flap  72  is accomplished by the plowshare folding edge  62  applying bending forces along the score line  76  which is the weakest point on the blank  70  to resist folding. The flap trailing edge  90  does not engage the plowshare folding edge  62  nor does a free edge  92  of side flap  72  engage the folding edge  62 . As it will be explained later in greater detail, the free edge  92  of side flap  72  and the trailing edge  90  follow the folding movement of the flap leading edge  88  at the score line  76 . 
     As shown in FIGS. 1 and 4, the plowshare  48  is supported by the bridge  30  at a selected elevation above the transport device  12  so that the leading edge  88  of the envelope blank  70  engages the guide bar folding edge  62  in alignment with the side flap score line  76 . The plowshare  48  is adjustably connected to the bridge  30  by the provision of an angle bracket  94  bolted to a rear vertical face  96  of the guide bar  60 . The bracket  94  receives a base  98  of a support arm  100  that is suitably connected to the beam  34  for longitudinal movement along the length thereof and vertically relative thereto. With this arrangement, the guide bar  60  is vertically and transversely movable relative to the surface of the transport device  12 . This allows the folding edge  62  of the plowshare  48  to be positioned for engaging the leading edge  88  of the blank  70  to fold the flap  72  precisely on the score line  76 . 
     Not only is the plowshare  48  vertically and transversely movable relative to the longitudinal feed path, it is also angularly movable relative thereto by the feature of removably bolting the support arm base  98  to the angle bracket  94 . As illustrated in FIG. 4 the support arm base  98  includes a pair of holes  102  that are aligned with selected holes or a slot (not shown) in the angle bracket  94 . A plurality of holes or a slot is provided on the angle bracket  94  to permit variations in the position of the base  98  on the bracket  94 . Bolts extend through the holes  102  to securely connect the support arm  100  to the bracket  94 . 
     As seen in FIG. 4, the support arm base  98  is connected to the bracket  94  with the edge of the base extending substantially parallel to the edge of the bracket  94 . However, the base  98  is positioned angularly displaced from the position shown in FIG. 4 on the bracket  94  to angularly displace the folding edge  62  of the plowshare  48  relative to the longitudinal feed path  20  of the envelope blank. With the above described apparatus, the plowshare folding edge  62  is adjustably positioned relative to the score line  76 . Regardless the width of the flap to be folded, the plowshare folding edge  62  is positioned in alignment with the flap score line to fold the flap along the score line. 
     PLOWSHARE FOLDING EDGE 
     As illustrated in FIGS. 1,  3  and  5 , the plowshare folding device  10  is supported by the bridge  30  to position the guide bar folding edge  62  parallel to the center line of the envelope machine and in axial alignment with the score line of the envelope blank. For example, the folding edge  62  is aligned with the score line  76  about which the side flap  72  is to be folded. The plowshare  48  is adjusted on the bridge  30  to align the folding edge  62  at the receiving end portion  64  of the folding mechanism  10  with the score line  76 . The folding edge  62  of the guide bar  60  extends the complete longitudinal length of the folding mechanism  10  from the receiving end portion  64  to the discharge end portion  66  as shown in FIGS. 3 and 5. 
     At the receiving end portion  64 , the envelope blank is introduced to the folding mechanism  10  with unfolded flaps. As the blank  70  advances the length of the plowshare  48  a flap, for example the side flap  72 , is folded on the score line  76  into overlying relation with the body of the envelope blank by the time the blank reaches the discharge end portion  66 . From the discharge end portion  66 , as illustrated in FIG. 3, the folded blank  70  is conveyed by the transport device  12  to the creasing rollers  14 . A pinch roller  104  is mounted in overlying and frictional engagement with a driven roller  106 . With this arrangement, the folded envelope blank  70  is advanced from the discharge end  66  of the folding mechanism  10  into the bight formed between the rollers  104  and  106 . 
     As the folded envelope blank passes between the rollers  104  and  106 , the folded edge of the flap at the score line  76  passes between the rollers to complete and set the fold in the envelope blank at the score line  76 . The creasing rollers  14  close the side flap  72  in a tightly folded position on the blank  70 . Preferably the creasing rollers  14  are spaced a preselected distance downstream of the plowshare discharge end  66  so as to avoid jamming of the blanks as they pass through the folding mechanism  10 . From the creasing rollers  14  the envelope blanks  72  are conveyed to subsequent stations to complete folding of the blank. 
     As illustrated in FIGS. 1-3 and  5 , the plowshare folder  48  includes the elongated guide bar  60  having a base  108  that extends perpendicularly relative to the rear vertical face  96 . The base  108  extends from its intersection with the rear vertical face  96  laterally a preselected width to the folding edge  62 . The plowshare folder  48  is supported by the bridge  30  so that the base  108  is positioned coplanar with a horizontal plane  110  of the conveyor feed path, schematically illustrated in FIG. 2, of the envelope blank  70  positioned on the transport system  12 . 
     Positioning the plowshare base  108  in the plane  110  of the envelope blank  70  assures that the folding edge  62  of the plowshare acts upon the blank leading edge  88  in alignment with the score line  76 . The longitudinal edge forming the folding edge  62  extends parallel to the center line of the envelope machine and in coaxial alignment with the score line  76  where the fold is to be executed on the blank  70 . 
     As will be explained later in greater detail, as the fold is executed the score line is captured or maintained in a position contacting the folding edge  62 . This prevents the score line  76  from moving away from the folding edge  62  as the flap is being folded and assures that the fold in the sheet flap  72  is maintained on the score line  76 . The tendency for the score line  76  to move away from the folding edge  62  occurs principally when the bending stresses in the flap are the greatest. The bending stresses are the greatest during the folding cycle when side flap  72  approaches a 90° angle (FIG. 14) with the plane  110  of the conveyor feed path and passes through 90° to a position approaching 180° (FIG.  17 ). During this folding cycle, the score line  76  is maintained in contact with folding edge  62  to prevent a misfold, i.e., the side flap  72  not folded on the score line  76 . 
     As illustrated in FIG. 2, the forming blade  52  in the embodiment of a longitudinally extending bar  54  is supported by the rod  58  connected to the bridge  30 . As shown in FIG. 1, the bar  54  is supported in a preselected position adjacent to and extending at an angle relative to the plowshare folding edge  62 . 
     During the folding operation, the side flap  72  moves from a planar position at the plowshare receiving end portion  64  upwardly and downwardly to a folded planar position at the discharge end portion  66  through an angle of about 180°. During this movement, an upward lifting force is applied to the body of the blank conveyed by the transport device  12 . If the body of the blank is lifted from the surface of the transport device  12 , then the driving force on the blank is reduced thereby reducing the feed rate of the envelope blank and displacing the score line  76  from contact with the folding edge  62 . This causes the envelope blank  70  to be misaligned on the transport device  12  and prevents a precise fold of the flap  72  along the score line  76 . 
     To prevent the blank  70  from being lifted from the transport device  12  and the score line  76  moved out of contact with the folding edge  62  as the flap  72  is being folded, the blank  70  passes in the plane  110  (FIG. 2) beneath the bar  54 . Thus the body of the blank  70  adjacent to the score line  76  is maintained in driving contact with the transport device  12 . This assures that the blank  70  is maintained in the required aligned position on the transport system  12  relative to the plowshare folding edge  62  and travels at the required speed for formation of the fold on the score line  76 . 
     PLOWSHARE HELICAL FACE 
     As illustrated in FIG. 5, the plowshare folding device  48  acts on the leading edge  88  of the flap  72  to be folded. The blank  70  is conveyed in the feed path in the direction of arrow  20  into contact with the plowshare  48  which is supported by the bridge  30  The plowshare  48  is positioned to align the folding edge  62  substantially axially with the score line  76  about which the side flap  72  is folded. As the blank  70  is conveyed into contact with the folding edge  62 , the leading edge  88  at the score line  76  is lifted from the planar position of the blank  70  shown in FIGS. 5 and 6. In this initial position, the blank leading edge  88  is at an angle close to but greater than 0° relative to the plane  110  (FIG. 6) of the transport device  12 . The leading edge  88  and side flap  72  then move upwardly and then downwardly through an angle of 180°. The side folding operation is completed at the discharge end  66  of the plowshare  48 . As a result, the score line  76  is maintained in required alignment with the folding edge  62  so that the side flap  72  is folded on the score line  76  in overlying relation with the body of the envelope blank  70 . 
     The progressive lifting of the blank  70  through an angle of 180° relative to the plane  110  of the blank on the conveying surface of the belts  16  is accomplished by a convex face  112  of the guide bar  60 . The convex face  112  extends upwardly from the folding edge  62  at an angle of 0° with respect to the plane of the envelope blank  70 . The angle that the convex face  112  forms with the horizontal plane  110  changes progressively along the length of the plowshare  48  from an initial angle of slightly greater than 0° (FIG. 6) to an angle of 180° (FIG. 12) at the plowshare discharge end portion  66 . The face  112  of the plowshare  48  follows a longitudinal helical path in the linear direction of travel of blank  70  as it progresses through the 180° angular displacement. Consequently, the position of the blank side flap  72  relative to the plane  110  of the conveying surface is the sum of two angular components. As the blank is fed the side flap  72  is bent into a convex profile. The convex profile is maintained as the side flap  72  is bent 180° in the linear feed path between receiving end portion  64  and discharge end portion  66 . 
     As seen in FIG. 5, the convex face  112  displaces the leading edge  88  of the envelope blank at the side flap  72  through an angle of 180° to fold the side flap  72 . The leading edge  88  follows the profile of the face  112  from the receiving end portion  64  at just above 0° to the discharge end portion  66  at 180°. During the folding sequence, the trailing edge  90  of the flap  72  follows the angular displacement of leading edge  88 . The flap trailing edge  90  does not come in contact with the folding edge  62  or the convex face  112  of the plowshare  48 . Similarly, the flap free edge  92  is not acted upon by the folding edge  62  or face  112 . 
     The free edge  92  of the blank side flap  72  follows the direction of movement of the flap leading edge  88  as it is folded so that the entire flap  72  moves through an angle of 180°. However through the entire range of movement of the flap, the folding forces are exerted upon the flap  72  at the leading edge  88  along the score line  76  by the provision of the plowshare  48 , which assures that the fold is maintained on the score line  76 . 
     As illustrated in FIG. 5, the folding operation progresses through an angle of 180°. The side flap  72  is engaged by the profile face  112  of the plowshare  48  in a position coplanar with the envelope blank  70  at the receiving end portion  64 . As the blank  70  advances along the plowshare  48 , the body of the blank  70  is bent from a flat profile to a convex profile and remains in contact with the surface of the transport device  12  by the provision of the forming blade  52  (FIG. 2) and the hold down device used by the transport device  12 . 
     The side flap  72  is lifted from a substantially horizontal position upwardly by the plowshare convex face  112 . The face  112  progressively bends the side flap  72  from a flat contour in the horizontal plane  110  to a convex profile and then back to a flat profile. See FIGS. 13-18. At approximately the midpoint of the plowshare  48  the side flap  72  is moved to a vertical position extending 90° from the plane of the transport device. Thereafter, the flap  72  moves downwardly toward the surface of the blank  70  to where the flap  72  is positioned in overlying relation with the blank  70  at the discharge end portion  66 . During this folding cycle the side flap  72  is maintained in a convex profile with the score line  76  captured in a position relative to the plowshare  48  to assure that the flap  72  is folded on the score line  76 . 
     The folding of the side flap  72  maintained in a convex profile through an angle 180° is accomplished by extending the face  112  along a helical path that varies in length based upon the nature of the folding operation being performed. For example, in one envelope machine the length of the helical path followed by the flap  72  extends approximately 6 feet. Over this length the flap  72  is folded through an angle of 180°. 
     The fold is initiated by the change in the angle of the plowshare face  112  from the receiving end portion  64  to the discharge end portion  66 . The rate of change in the angle of the face  112  varies over the length of the bar  60 . The rate of change is not constant so that flap  72  is initially lifted rapidly from approximately the 0° position to the 90° position, as illustrated in FIG. 5, over a distance less than one half of the bar  60 . From the 90° position, the flap  72  is folded downwardly to a horizontal position on the blank  70 . 
     It should be understood that any rate of rise of the flap along the length of the plowshare  48  can be controlled by the angle formed on the face  112 . One factor in determining the rate of rise in the side flap  72  from the 0° position is the length of the plowshare  48 , which length is determined in part by the structure of the envelope forming machine. 
     The helical path followed by the convex face  112  of the plowshare  48  between 0° and 180° is schematically illustrated in FIGS. 2,  3  and  5 . In FIGS. 6-12 sectional views of the plowshare  48  are illustrated along the length thereof from the receiving end portion  64  in FIG. 6 to the discharge end portion  66  in FIG.  12 . As described above, the plowshare  48  is in the configuration of a bar  60  which guides the flap leading edge  88  on the convex face  112  to fold the flap on the score line  76 . In accordance with the present invention, the flap is folded on or as closely as possible to the score line  76 . 
     The folding operation is initiated in the body of the flap  72  adjacent to the score line  76 . The folding forces on the flap  72  are not concentrated at the free edge  92  of the flap  72 . 
     The convex face  112  acts on the flap  72  to capture the score line  76  in contact with the folding edge  62 . As a result, the body of the flap  72  adjacent to the score line  76  initiates the folding movement of the flap  72 . The free edge  92  of the flap  72  follows the direction of fold initiated at the score line  76 . This assures that the flap  72  is not misfolded by movement of the score line  76  out of contact with the plowshare folding edge  62 . This problem is encountered with the prior art devices that initiate folding the flap  72  by the application of forces at the flap free edge  92  creating stresses in the flap  72  that move the score line  76  out of contact with the plowshare. 
     With conventional plowshare-type folding devices used in envelope forming machines, the fold is initiated at the free edge  92  of the flap  72 . This requires that the folding force be applied at the furthest possible point from the score line  76 . This results in folding the blank into a tubular configuration, trapping a substantial volume of air inside the flap. In this configuration, the stresses applied to the flap are increased, reducing the stability of the blank on the transport device  12 . Consequently the blank becomes misaligned with respect to the plowshare so that the flap score line is displaced from the plowshare. The flap is not folded on the score line. This problem is aggravated at machine speeds in excess of  300  envelopes per minute and with larger size envelope blanks. 
     An envelope blank has a natural tendency to resist folding. When the folding is initiated a substantial distance from the weakest point of the blank, the fold has a greater tendency to be misaligned from the score line because of the stresses acting on the blank. The stresses tend to urge the blank away from the plowshare and remove the score line from the required position for folding the flap. 
     With the present invention, the fold is initiated at the weakest point on the flap which is at the score line. The plowshare profile face  112  initiates the fold at the score line and maintains the score line in position so that the flap breaks across the score line prior to the flap free edge  92 . By maintaining the flap score line  76  captured in contact with the folding edge  62  the adverse effects of creating a pocket of air within the folded flap are eliminated because the air is expelled or pushed out of the folded flap by the convex face  112 . 
     The structure of the plowshare  48  that provides for improved folding of an envelope blank includes an elongated bar  60  having a base  108  of a substantially constant width along its entire length Extending upwardly from the base  108  on one side of the bar  60  is the rear vertical face  96 . The base  108  includes on the side adjacent to the feed path the folding edge  62 . The edge  62  extends the entire length of the plowshare from the receiving end portion  64  to the discharge end portion  66 , as illustrated in FIGS. 6-12. 
     The folding edge  62  is maintained substantially in the plane  110  of the envelope blank  70  on the transport system  12 . From the folding edge  62  the plowshare includes the profile face  112  which extends upwardly from the edge  62  to the rear vertical face  96 . In accordance with the present invention, profile face  112  is positioned at an angle with respect to the plane  110 . The angle evolves through a helices beginning at substantially 0° illustrated in FIG. 6 to 180° as illustrated in FIG.  12 . At substantially the midpoint in the plowshare  48  between the receiving end portion  64  and the discharge end portion  66  the profile face  112  approaches an angle of 90° with the plane  110 . 
     FIG. 8 illustrates the profile face at a point along the plowshare  48  before the flap  72  reaches an angle of 90° with respect to the plane  110 . FIG. 9 illustrates the profile face  112  at an angle which urges the flap  72  downwardly toward the body of the blank  70  after the flap has passed through an angle of 90° with respect to the plane  110 . During the travel of the envelope blank from the 0° position to the 90° position, the flap  72  moves upwardly from the surface of the transport device  12 . At the 90° point, the profile face  112  moves the flap  72  downwardly toward the body of the blank  70 . 
     As seen in FIGS. 6-12, the convex profile face  112  follows a helical path from one end of the plowshare  48  to the other. The angle the profile face  112  makes with the plane  110  of the envelope blank progressively varies from 0° to 180°. The rate at which the angle of the profile face  112  rises from 0° to 90° and from 90° to 180 is substantially uniform along the length of the plowshare  48 . In one embodiment the rate of rise from 0° to 90° takes place over a shorter length of the plowshare  48  than the rate at which the angle falls from 90° to 180°. 
     The rate of rise and the rate of fall of the angle of the profile face  112  between 0° and 180° is selective based on such factors as the machine speed, length of the envelope blank, and width of the flap to be folded. For example, in one embodiment of a plowshare having a length of 76⅝ inches the angle of the profile face  112  rises 60° in a first  24  inch section. In a second 24 inch section, the face  112  moves an angle of 60° to 120°. In a third 24 inch section, the profile face  112  moves through an angle of 120° to 180°. The profile face along a length of 4⅝ inches is maintained at 180° or in a position parallel to the plane  110  of the blank  70  on the transport system  12 . 
     As schematically illustrated in FIG. 7, the angle of the profile face  112  of the plowshare  48  is formed by an end mill tool  114 . As known in the art, the tool  114  has a cutting surface  116  with a concave radial surface which forms the face  112  having a convex radial configuration. In one embodiment the radius of curvature of the profile face  112  is 8 inches. The angle at which the face  112  is cut in the body of the bar  60  with respect to the base  108  determines the angle formed by the face  112  with the plane  110  of the envelope blank  70 . The angle at which the face  112  is formed is controlled by the relative position of the end mill tool  114  during the cutting operation. 
     FIG. 7 schematically illustrates the angle at which the tool  114  is positioned to cut the face  112  at an angle which is positioned in the feed path  20  at a point on the plowshare  48  downstream a short distance from the plowshare receiving end portion  64 , as illustrated in FIG.  5 . As discussed above FIG. 8 illustrates a section of the plowshare taken at a point where the flap  72  is continuing to rise from the plane  110  of the envelope blank  70  toward the vertical position or the 90° position. It should be pointed out that while the angle formed by the profile face  112  with the blank plane  110  evolves progressively through a helix, the convex configuration of the face  112  along its length remains at a fixed radius, for example 8 inches. 
     The convex configuration of the profile face  112  serves to execute the folding movement of the blank  72  closely adjacent to the score line  76 . The folding forces exerted on the flap  72  are thus concentrated at the score line  76  which is the weakest point on the flap. The folding forces are not applied to the flap free edge  92  in the folding operation. 
     With the provision of the present invention of maintaining the fold of the flap  72  on the score line  76 , the free edge  92  follows the movement of the flap  72  as it is being folded. A folding force need not be applied to the free edge  92 . In fact, the free edge  92  does not come in contact with the surface of the face  112 . This relieves the stresses acting on the flap  72  so that the stability of the flap is maintained as it is folded. With movement of the flap  72  controlled, the fold can be kept on the score line  76 . 
     The free edge  92  extends above the face  112  and is removed from contact with face  112 . Consequently, no bending or folding forces are applied by the face  112  to the flap free edge  92 . In this respect, the convex shape of the plowshare face  112  initiates folding of the flap  72  at the flap leading edge  88  adjacent to the score line  76  where the resistance to folding is the weakest. The fold on the score line  76  is not initiated by applying a folding force at a point substantially removed from the score line, such as at the flap free edge  92 . 
     In the folding cycle between 0° and 90°, the convex profile face  112  vertically raises the flap  72  from the plane  110  of the envelope blank  70 . FIGS. 9-11 illustrate the progressive movement of the flap  72  as it is urged downwardly from the 90° position. During this cycle of movement of the flap  72  the convex configuration of the face  112  in combination with the forming edge  62  serves to maintain the bending forces applied to the flap  72  closely adjacent to the score line  76 , overcoming the stresses that tend to urge the score line  76  away from the folding edge  62 . The portion of the flap adjacent to the score line  76  leads the folding operation. The flap free edge  92  follows the movement of the flap leading edge  88 . The edge  92  does not lead the folding operation. FIG. 12 illustrates the completion of the fold at the discharge end portion  66  where the face  112  is substantially parallel to the plane  110  of the blank  70 . At this point, the flap  72  is folded into overlying relation with the blank  70  along the score line  76 . 
     The provision of the plowshare  48  having a convex profile face  112  extending upwardly from the folding edge  62  to initiate the fold closely adjacent to the score line  76  departs from the folding method and apparatus described above for the prior art. With the prior art devices, the plowshare blade initiates the fold at the outer free edge of the side flap to bend the blank into a tubular configuration. At high feed rates, the prior art approach results in misfolding of the blank. The flap is not folded on the desired score line. 
     The present invention overcomes the problems encountered with the prior art devices by utilizing a plowshare with a convex face extending upwardly from a folding edge where the forces for folding the flap are concentrated closely adjacent to the score line. Precision in forming the fold is achieved by concentrating the bending forces applied to the flap at the point where the flap is the weakest to resist bending, which is along the score line. This allows greater control of the folding operation to overcome the stresses generated in the flap when folded to maintain the folding edge  62  in contact with the score line  76 . Also, with the bending force applied to the leading edge of the flap, the fold follows the score line. 
     FORMING BLADE 
     Another factor of the present invention that contributes to precision in folding a flap of an envelope blank and prevents misfolding is maintaining the blank in a preselected position on the transport device  12  with respect to the folding edge  62  of the plowshare  48 . If the blank  70  moves from a desired position on the conveyor surface as it advances through the folding mechanism  10 , the flap  72  is not folded on the score line  76 . It is misfolded. As described above, the transport device  12  includes a vacuum table or a series of overlying drive rolls. 
     It is essential that the body of the envelope blank  70  remain in contact with the conveying surface so that the feed rate of the envelope blanks through the folding mechanism  10  remains constant. If the feed rate should deviate as the blank advances through the folding mechanism  10 , the flap will be misfolded. The flap is first lifted vertically from the plane of the envelope blank and then turned in an opposite direction to complete the fold. An upward lifting movement is imparted to the body of the envelope blank. 
     Lifting the blank from the conveying surface  22  reduces the surface area of the envelope blank in contact with the conveying surface. This results in a reduction in the feed rate of the blank through the folding mechanism. To overcome the natural tendency of the blank to be raised from the conveying surface as it is being folded, the present invention utilizes the forming blade  52  to maintain the blank in contact with the conveying surface and the score line  76  positioned opposite the folding edge  62  of the plowshare  48 . 
     As schematically illustrated in FIGS. 1 and 2 and in further detail in FIGS. 13-17, the forming blade  52  has an elongated configuration in the shape of a relatively thin bar  54  having a fixed width along its length. The bar  54  forms a breaking edge opposite the score line  76  of the envelope blank  70  to facilitate folding the flap  72  by the plowshare  48 . The bar  54  maintains the body of the envelope blank  70  adjacent to the score line  76  in contact with the conveying surface  22 . 
     The bar  54  has longitudinally extending edges  116  and  118  where the edge  116  is positioned oppositely of the plowshare folding edge  62 . The bar  54  has an upturned receiving end portion  120  raised above the plane  110  of the envelope blank  70 . The raised end portion  120  permits the leading edge  88  of the envelope blank  70  on the transport device  12  to pass beneath the bar  54 . A discharge end portion  122  is provided at the opposite end of the bar  54  from which the body of the envelope blank  70  passes. 
     The bar  54  is supported above and closely adjacent to the surface of the transport device  12  by the rod  58  adjustably connected to the guide  44  which is slidably positioned on the bridge  30 , as above described and illustrated in FIG.  1 . The bar  54  is positioned non-parallel relative to the plowshare  48 . The bar edge  116  converges toward the plowshare edge  62  in the direction from the receiving end portion  120  to the discharge end portion  122 . In other words, the discharge end portion  122  of the bar  54  is closer to the plowshare edge  62  than the bar receiving end portion  120 . The angular position of the bar  54  relative to the longitudinal edge of the plowshare  48  is schematically illustrated in FIGS. 13-17. 
     As illustrated in FIG. 13, the forming blade  52  is suspended above the surface of the envelope blank  70  to permit the blank to pass under the bar  54 . The bar  54  maintains the blank in contact with the transport device  12  to overcome the tendency of the blank  70  to be lifted from the conveying surface  22  as the flap  72  is folded by the plowshare  48 . As shown in FIG. 14, the edge  116  of the bar  54  exerts a downward force on the body of the envelope blank adjacent to the score line  76 . This prevents a reduction in the conveying force applied to the blank  70  when the flap  72  is lifted from the conveying surface. 
     As shown in FIGS. 14 and 15, the blank  70  progresses along the plowshare  48  and the flap  72  is raised from the plane  110  of the blank  70 . The edge  116  of the bar  54  progresses closer and closer to the score line  76  to resist the lifting forces applied to the blank  70 . During the folding cycle between 0° to 90° the lifting forces on the blank  70  are the greatest. To counter the lifting forces the bar  54  maintains the body of the envelope blank  70  in contact with the transport device  12  and in close proximity to the score line  76 . The flap  72  is caught between the convex face  62  of the plowshare  48  and the longitudinal edge  116  of forming blade  52 . 
     The score line  76  is also captured in the position of folding by the plowshare edge  62  by the provision of a vertical surface extending upwardly from the plowshare base  108  on the edge  62 . The vertical surface is formed integral with the convex surface  112 . See FIGS. 14-18. With this arrangement of the convex surface  112  and vertical surface on edge  62 , the score line  76  is maintained in position to assure folding of flap  72  on score line  76 . With the score line  76  captured in position for folding, the flap is stabilized to resist the stresses from folding that tend to urge the score line  76  out of alignment with folding edge  62 . 
     As illustrated in FIGS. 13-15 the forming blade  52  has a rectangular cross section from the receiving end portion  120  a preselected length along the bar  54  to the point approximately where the profile of the plowshare face  112  begins to bend the side flap  72  downwardly from the 90° position. During this folding cycle the flap  72  moves upwardly from the plane  110  and a lifting force is applied to the body of the envelope blank  70  adjacent to the score line  76 . Unless the body of the envelope blank  70  is restrained from being lifted upwardly with the flap  72 , the conveying force applied to the blank  70  is decreased. This results in a decrease in the feed rate of the blank on the transport system  12  and subsequent misfolding of the flap  72 . 
     With the present invention, the upward movement of the blank is restrained by the edge  116  of the bar  54  positioned adjacent to the score line  76 . The bar  54  traps the envelope blank  70  in close proximity to the score line  76  and maintains the blank in contact with the conveying surface  22 . This serves to maintain the feed rate of the envelope blanks on the transport system  12  constant. The vertical surface on folding edge  62  also serves to trap or capture the flap  72  against the plowshare  48  in position for folding the flap  72  on score line  76 . 
     When the blanks reach the point in the folding cycle where the flap  72  is positioned at the 90° angle and moves toward 180°, the plowshare face  112  commences the helical path from 90° to 180°. During this cycle, when the stresses acting on the flap  72  are the greatest, the folding of the flap  92  is maintained under control as the flap moves downwardly toward the blank on the conveying surface  22 . The score line  76  remains aligned with folding edge  62 . 
     After the 90° point in the helical folding path, the face  112  applies a downward force upon the flap  72 . During the first 90° cycle in the helical path, the forming blade  62  operates in combination with the plowshare profile face  112  to capture the score line  76  in position to break or fold the flap  72  about the score line  76 . 
     At the 90° point, the fold is partially formed in the blank  70 . The flap  72  follows the fold as it is urged downwardly through the second 90° cycle of folding. Once a crease is formed in the blank along the score line  76 , the position of the blank is stabilized so that the flap  72  moves downwardly about the score line  76  to complete the folding operation. The folding cycle is schematically illustrated in FIGS. 8-18. 
     In addition to capturing the score line  76  against the folding edge  62 , flap folding is facilitated by the edge  116  of the forming blade  52  progressing closer and closer to the plowshare folding edge  62  at the discharge end  66  of the plowshare  48 . During this cycle air between the folded flap  72  and the body of the blank  70  is expelled, rather than captured which would displace the position of the blank relative to the plowshare  48 . At the discharge end portion  122  of the forming blade  52 , the edge  116  is located at its closest position opposite the folding edge  62 . As shown in FIGS. 16 and 17, the fold at the score line  76  passes through a wedged shaped opening formed by bar edge  116  converging toward the plowshare folding edge  62 . This wedging effect is achieved with the forming bar  52  positioned in non-parallel relation to the plowshare folding edge  62 . 
     At the point along the forming blade  52  where the flap  72  is moved to the 90° position and a crease is formed in the flap  72  along the score line  76 , a top surface  124  of the bar  54  is provided with a beveled edge  126 , as shown in FIG.  16 . The beveled edge  126  extends upwardly at an angle from the edge  116  to the bar top surface  124 . The beveled edge  126  of the forming blade  52  begins on the bar  54  at a point opposite the plowshare  48  where the flap trailing edge 90° has passed the 90° angle. From this point to the completion of the fold, the trailing edge  90  falls downwardly behind the leading edge  88  toward the surface of the envelope blank  70 . 
     FIG. 16 illustrates an early point in the downward folding of the flap  72  where the bar  54  is beveled on surface  126 . As the beveled edge  126  progresses toward the bar discharge end portion  122 , the angle of the bevel decreases. This arrangement is shown in FIG. 17 where the beveled edge  126  extends the full width of the top of the bar from the edge  116  to the edge  118 . A bevel of this angle is required adjacent the discharge end portion  122  of the bar  54  to provide the necessary clearance for the flap  72  to pass beneath the profile face  112  as illustrated in FIG.  17 . 
     The discharge end  122  of the bar  54  is spaced upstream from the point where the plowshare face  112  is positioned at an angle of 180°, as shown in FIG.  18 . At the 180° position in the folding cycle, the flap  72  is closed. The end of the bar  54  is positioned upstream of this point so as not to interfere with the closing of the flap  72  onto the envelope blank  70 . Once the flap  72  is closed, the blank  70  is advanced beyond the discharge end  66  of the plowshare  48 . At this point, the blank  70  enters the creasing rollers  14  where the crease is permanently set in the envelope blank  70 . 
     SHEET SUPPORT FRAME 
     With conventional plowshare-type folders, the plowshare includes a blade having a surface that acts on the entire width of the flap being folded to form the fold by bending the flap in a tubular configuration. This requires that the blade have a surface area that supports the entire width of the flap. The bending of the flap then commences at the free edge of the flap which is spaced the furthest point on the flap from the score line. When the bending forces are applied to the flap at this distance from the score line, the potential for misfolding the flap is the greatest. 
     One prior art approach to envelope blank folding is to construct the blade or forming surface of the plowshare to meet the dimensions of the side flap. This approach may be moderately successful for side flaps that do not exceed, for example, 2½ inches in width. However, problems occur with this approach in accurately controlling the flap folding operation when the width of the flap approaches, for example, 10 inches as encountered with large open end envelopes. 
     With the present invention, the active surface of the plowshare  48  is confined to the convex profile face  112 . The face  112  extends the length of the plowshare. The face  112  has a relatively short active width that extends upwardly from the folding edge  62  along a radial path. The width of the convex face  112  for most envelope blanks is less than the width of the flap to be folded. 
     In one embodiment of the present invention, the width of the face  112  upwardly from the edge  62  along the radial path is approximately 2 inches. This is the active surface of the plowshare  48  in accordance with the present invention regardless the width of the flap to be folded. The flap width may vary between about 2 inches to 10 inches and wider and be precisely formed by the plowshare  48 . 
     Regardless the width of the flap  72 , the plowshare  48  of the present invention is capable of completing a fold where the forces applied to the flap are initiated at the leading edge  88  closely adjacent to the score line  76 . The plowshare  48  of the present invention deviates from the prior art plowshares having an active surface that supports the entire width of the flap. The active surface of the plowshare  48  has a relatively short width. Therefore, the sheet support apparatus  50  serves as an extension of the face  112  to support the free edge  92  of the flap  72  as the body of the flap adjacent to the score line  76  is folded. 
     The sheet support apparatus  50  includes a support frame  130  as schematically illustrated in FIGS. 1-3 and extends substantially the length of the plowshare  48 . The support frame  130  begins downstream of the plowshare receiving end portion  64  and ends upstream from the plowshare discharge end portion  66 . In accordance with the present invention, the support frame  130  is mounted on the guide bar  60  to form a support surface for the portion of the side flap  72  that is not actively engaged by the convex plowshare face  112 . 
     It is a feature of the present invention that by concentrating the forces for folding the flap  72  at the blank leading edge  88  adjacent to the score line  76  the entire width of the flap is not required to be actively folded. The prior art devices bend the entire flap into a tubular configuration to form the fold. This requires active folding of the entire flap width which becomes difficult for flap widths above three inches. This also captures air in the fold which destabilizes the position of the flap relative to the plowshare folding face. For the reasons discussed above, this method of folding the flap is difficult to control, and misfolding is frequently encountered. 
     With the present invention, the folding is effectively controlled by confining the active surface of the plowshare  48  to a portion of the flap width and not the entire flap width. The plowshare convex face  112  applies the folding forces on the flap at the point where the flap is the weakest which point corresponds to the score line  76 . The flap is captured in this position by the provision of the vertical surface on the plowshare folding edge  62 . 
     Because the plowshare face  112  concentrates the folding forces on only a portion of the flap  72 , the remaining portion of the flap is only required to be supported to follow the flap leading edge  88  as it is being folded. The folding forces are not applied to the entire surface area of the flap. Once the folding is initiated adjacent to the score line  76 , the remaining portion of the flap follows the formation of the fold on the score line  76 . The flap remains under control during the 180° folding operation. In one example, the side flap  72  is engaged by the convex face  112  for a width of about 2 inches. The remaining width of the side flap  72  lies on the surface of the support frame  130 . 
     As schematically illustrated in FIG. 2, the support frame  130  includes a plurality of brackets  140  mounted in spaced relation along the length of the plowshare  48 . The plowshare bar  60 , as described above, includes the convex face  112  formed on a radius which intersects at its upper edge a mounting surface. The brackets  140  are connected to the mounting surface of the plowshare to form a supporting surface that approximates an extension of the convex surface of the face  112 . 
     Each bracket  140 , as shown in FIG. 2 is connected at its lower end portion to connect to the plowshare bar  60 . The brackets  140  are adapted to receive and secure in place a plurality of flexible, elongated elements  146 , such as wires, rods, splines, and the like. The flexible elements  146  are connected to the brackets  140  to form an expanded platform that projects from the upper edge of the convex plowshare face  112 . 
     The brackets  140  and elongated elements  146  form a supporting surface that lies in a plane coextensive with the convex face  112 . With this arrangement the supporting surface formed by the brackets  140  and elements  146  extends the supporting surface of the plowshare  48  beyond the active convex face  112 . While the face  112  is convex the elements  146  lie in a plane which substantially follows the radial path of the face  112  to form an extension of the active face  112 . 
     Preferably the flexible elements  146  are spaced apart to form a grid that is pitched upwardly. The flap free edge  92  lies on this grid. The grid supports the flap free edge  92  without snagging the edge. In essence, the flap  72  combs across the surface of the elements  146  as the blank  70  advances along the plowshare  48 . 
     While the flexible elements  146  supported by the brackets  140  extend the active surface of the face  112 , the elements  146  do not act on the flap  72  to generate the folding forces. The elements  146  support the flap free edge  92  and trailing edge  90  to follow the helical path generated by the active face  112  bending the flap  72  adjacent to the score line  76 . Consequently the entire width of the flap  72  is supported but without the requirement of applying bending forces to the flap free edge  92 . 
     By confining the bending forces to the area immediately adjacent to the score line  76 , formation of the fold about the score line  76  is most efficiently accomplished. Again this permits the bending forces to be applied to the area of the flap which has the least resistance to bending, i.e. at the score line, and not at the outer free edge  92  of the flap  72 . With this method of supporting the free edge of the flap  72 , the plowshare  48  can accommodate envelope blanks with a wide range of flap widths without having to construct a plowshare with an active face that supports an entire width of the flap  72 . 
     The grid arrangement of elongated elements  146  supported by the spaced brackets  140  extends the active face of the plowshare by a lightweight frame which is easily erected. The frame  130  provides a supporting surface that accommodates a wide range of flap widths. By mounting all the brackets  140  in the same angular position on the plowshare  48 , the supporting surface formed by the grid of wire elements  146  follows the helical path of the face  112  as schematically illustrated in FIGS. 1-3. 
     The grid-like structure of the support frame  130  as seen in FIG. 2 permits unobstructed observation of the envelope blank as it advances the length of the plowshare  48 . With conventional blade-type plowshares where the blank is rolled into a tubular form, viewing the folding operation is partially obstructed. However, with the present invention viewing the plowshare face  112  is not obstructed by the support frame  130 . The operator is able to observe at all times folding of the flap along the intended score line. 
     The support frame  130  stabilizes the flap during the folding operation and the envelope blank is viewable through the grid-like structure of the support frame  130  as the blank advances along the face  112  of the plowshare  48 . In the event blanks become jammed in the folding mechanism  10 , the operator can readily locate the point where the jam has occurred because the folding operation is not concealed. It is completely visible along the entire length of the plowshare  48 . Also the operator is able to observe at all times whether the flap  72  is being folded in alignment with the score line  76 . These advantages apply regardless of the size of the envelope blank and the width of the flap being folded. 
     It should be understood that the present invention also includes, as an alternative, to the grid-like structure of the support frame  130 , a thin flexible plate for supporting the side flap free edge  92  as the side flap  72  is folded on the score line  76 . The flexible plate is secured to the upper edge of the plowshare  48  to follow the helical path of the convex face  112  and form a supporting surface for the side flap free edge  92 . 
     The thin flexible plate does not apply a bending force to the side flap free edge  92 . The bending forces, as discussed above, are applied by the plowshare folding edge  62  immediately adjacent the score line  76  of the blank  70 . The structure that extends above the plowshare face  11 . 2  for supporting the flap free edge  92  does not function as a folding surface. This overcomes the prior art deficiencies of initiating the folding operation at a point substantially removed from the score line. 
     SHEET CONTROL GUIDE 
     During the folding operation the blank trailing edge  90  does not come in contact with the plowshare face  112 . The edge  90  follows the folding path of the blank leading edge  88  through the 180° helical path. During the folding cycle, the trailing edge  90  has a tendency to be thrown downwardly and forwardly of the movement of the blank leading edge  88 . The leading edge  88  adjacent to the score line  76  remains in contact with the plowshare face  112 . The free edge  92  of the flap above the face  112  is supported by the support frame  130  shown in FIG.  1 . The sheet control guide  50  resists the tendency of the flap trailing edge  90  to move downwardly toward the plane  110  of the blank  70  as the leading edge  88  is folded on the score line  76 . It is important to maintain movement of the flap trailing edge  90  behind the leading edge  88 ; otherwise, the flap  72  will move out of control and the fold will not be completed on the score line  76 , resulting in misfolding flap  72 . 
     As the flap trailing edge  90  follows the leading edge  88 , the trailing edge  90  is displaced from the plowshare  48  and the support frame  130  a distance which is approximately equal to the change in the angle of the helix over the length of the envelope blank  70 . The control guide  50  includes a flexible guide plate supported by a frame connected to the guide  42  which is adjustably positioned on the bridge  30  shown in FIG.  1 . The guide plate  150  follows a helical path as shown in FIG.  1 . 
     The guide plate  50  is maintained spaced from the support frame  130  a distance which is approximately equal to the change in the angle of the helix formed in the blank between the leading edge  88  and the trailing edge  90  as the blank is folded. By maintaining the guide plate  50  in this position relative to the support frame  30 , the flap trailing edge  90  is prevented from falling away from the plowshare  48  and “out running” the flap leading edge  88 . 
     For envelope blanks with flaps having a width, for example of 10 inches, the flap trailing edge  90  has a tendency to move ahead of the leading edge  88 . The problem of the trailing edge  90  running out of control is also encountered due to the effects of air currents generated when the envelope blanks are fed at relatively high speed through the folding mechanism  10 . 
     The guide plate  50  is movable in a first direction transverse to the feed path  20  on the bridge  30  and vertically relative to the plane  110  of the envelope blank  70 . In this manner, the plate  50  is positioned a preselected distance from the support frame  130 . The distance between the flexible plate  50  and the support frame  130  is approximately equal to the change in the angle in the helix formed in the envelope blank during the folding operation between the blank leading edge  88  and the trailing edge  90 . 
     As seen in FIG. 1, the plate  150  extends in a helical path which is complementary to the helical path followed by plowshare  48 . With the flap leading edge  88  maintained in contact with the plowshare face  112  and the flap free edge  92  supported by the support frame  130 , the flap trailing edge  90  is displaced from the plowshare  48  and the support frame  130 . Uncontrolled forward movement of the trailing edge  90  is restrained by contact with the plate  50 . 
     As the flap  72  advances the length of the plowshare  48 , the leading edge  88  does not contact the guide plate  50 . However, the flap trailing edge  90  contacts the plate  50  and is prevented from bending forwardly ahead of the leading edge  88 . This arrangement assures that the trailing edge  90  does not run out of control and cause the blank to become misaligned in the feed path. With provision of the sheet control guide  50 , the flap trailing edge  90  remains in position to assure precise folding of the flap  72  on the score line  76 . 
     According to the provisions of the patent statutes, we have explained the principle, preferred construction, and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.