US 2754729 A
Description (OCR text may contain errors)
July 17, 1956 R. L. EMERY MOLDING 0F PERFORATED PULP ARTICLES Filed Sept. 15, 1953 IN VEN TOR.
United States Patent MOLDING 0F PERFORATED PULP ARTICLES Richard L. Emery, Fairfield, Maine, assignor to Keyes fibre Company, Portland, Maine, a corporation of ame Application September 15, 1953, Serial No. 380,155
4 Claims. (Cl. 92-54) The present invention relates to the preparation of molded pulp articles that have one or more perforations, more particularly to the method and apparatus for effecting such molding.
Among the objects of the present invention is the provision of a novel method and novel apparatus of the above type which are very well suited for commercial use.
The above as well as additional objects of the present invention will be more readily understood from the following description of several of its exemplifications, reference being made to the accompanying drawings where- 'Fig. lis a sectional view of a pair of molding dies pursuant to the present invention, the dies being shown in an early stage of the pulp molding process;
Fig. 2 is a view similar to Fig. 1 showing the dies in a later stage of the process, and
Figs. 3 and 4 are views of the respective dies of Figs. 1 and 2, the view being taken from the faces of these dies.
According to the present invention a perforated molded pulp article is made by suction-forming a mass of pulp on a forming die surface having an upstanding non-porous formation-preventing plug at the location of the desired perforation, pressing the formed mass on the forming die surface with a mating pressing die having a recess that receives the upstanding plug, and separating the formed mass from the pressing die while discharging a blast of air out of the blind end of the recess to clear out stray pulp fibers and cause them to be blown against the pressed mass as it is separated. 1.,
It has been found that by using the above process, the molding dies and particularly the pressing die, keeps quite free of any appreciable build-up of stray pulp fibers that would require interruption of the molding for cleaning. In other words maintenance of the apparatus is exceedingly low.
Referring now to the figures there is here shown a section of a forming die and a cooperating pressing die 12. The forming die can be generally of conventional suction-forming type, as shown for examplein Shepard U. S. PatentNo. 2,192,937 granted March 12, 1940, with an outer or forming face 14 lined with-wire screening 16 and backed up by a die plate 18 that has a large number of small passageways (not shown) drilled through it so that suction applied. behind the platewill be communicated to the outer surface'14 of screen 16. The die plate '18 is mounted on a die holder that is controllablyconnected to a source of compressed air." I l The forming die 10 is also provided with perforationdefining elements shown as animpervious plug. 20. fixed in place to stand up from the forming surface? 14. One such plug is used for each perforation desired-.inithe molded pulp product, and two such plugs are included in the die portion illustrated in Fig. 1. The plugs can be fixed in place in any desired manner as by being brazed to the tops of fiat-head bolts 22 that have inverted frustoconical seats 24 clamping a projecting margin of screen wire 16 against a suitably countersunk portion of the face of die plate 18. The clamping action can be provided as the conveyor of a tunnel drier.
2,754,729 Patented July 17 1956 byfnuts 26 threaded on the shanks of the bolts or by any other arrangement such as the resilient outwardly biased plate-gripping locking fingers shown in copending Harper patent application Ser. No. 233,833 filed June 27, 1951, now Patent No. 2,698,557, granted January 4, 1955.
v The pressing die 12 has a die face 28 formed generally by a plate 30 that is also provided with drilled passage- Ways or pores (not shown) establishing communication between the face 28 and the back of the plate. As with the forming die the plate 30 is mounted on a holder that is controllably connected to a source of suction and a source of compressed air. In addition plate 30 carries recess inserts 32 that define recesses or sockets 34 to mate with and receive plugs 20. In the construction illustrated in the figures the recess inserts have their outer faces flanged at 36 and fit into corresponding seat-shaped openings 38 extending entirely through the plate 30. They are fixed in place as by a slotted flat-head screw 40 threadedly-engaged in the plate with a portion of the screw head overlapping a suitably shaped portion of flange 34.
, I The fiat head of screw 40 can be aligned flush with the die face 28 or it can be projected out or relieved back somewhat if desired. The inserts 32 have at the blind end of the recesses 34, a passageway 42 that connects the recess with the space behind the plate 30.
The molding operation of the present invention is practiced by first immersing the forming die in a suitable aqueous slurry of pulp fibers and applying suction to this die.
This causes slurry to be sucked against the screen 16,
the liquid portion of the slurry passing through the screen and die plate 18 while the fibers are trapped against the face of the screen to deposit as an interfelted layer shown at 44 in Fig. l. The plugs 20 being non-porous, the layer is interrupted at their locations, although by reason of the porosity of the layer itself the effects of the suction are transmitted along the layer and cause it to extend somewhat up along the plugs, as indicated at 46.
This extension is particularly annoying since it generally tapers down to practically a feather edge of very loosely held fibers.
After a sufficientdeposit of fibers, the forming die is withdrawn from the pulp slurry, the fiber layer 44 remaining in place as by continuing the suction.
The pressing die 12 is then brought into pressing engagement with the forming die to squeeze the fibrous layer as illustrated in Fig. 2. This squeezing expresses a large amount of the water carried by the fibrous layer and thereby greatly reduces the amount that must be evaporated olf to produce the final dried article.
When the desired amount of liquid removal has been completed by the squeezing, the dies are separated. The squeezed layer of fibers 14 can then be arranged to be lifted of the forming die 10 and transferred to the pressing die12, as by simultaneously stopping the application of suction to the forming die while applying suction on the pressing die. If desireda puff of compressed air applied to the forming die will assist in the transfer. The pressing die can then be arranged to carry the layer of felted fibers to and deposit it on a drying apparatus such The fibrous layer is conveniently deposited by cutting off the suction applied to the pressing die and at the same time making at least a momentary application of compressed air. The deposited layer can then be dried and after-treated as desired to produce the final article.
A feature of the present invention is the fact that the final puff of compressed air applied to the pressing die acts as a cleaning operation that assists in removing any stray fibers that otherwise tend to be left behind in the sockets 34. This tendency is heightened by the expression of liquid during the squeezing, some of the liquid so expressed apparently acting to wash away the loosely held fibers previously formed at the thin edge of the fibrous layer around the plugs 20.
Not only does the passageway 42 in each socket enable the blowing away of the loose fibers, but some of these fibers are forcefully blown back onto the fibrous layer that is simultaneously being blown off the die 12. As a result the loose fibers which are still wet are actually caused to adhere to thetdeposited layer which is also quite wet. However the loose fibers thus blown back do not adhere in such a position as to bridge or otherwise restrict or spoil the appearance of the perforation in the layer. Apparently the blowing action takes place so readily through the opening in the fibrous layer that any loose fiber ends blown against the opening are blown completely through so that they adhere to the outer face of the layer or are blown completely out of engagement. In any event the resulting perforation in the finished article is very clean and trim and does not require any touching up. 7
Another feature of the present invention is that the cleaning puff is provided without any complication. By merely connecting the blind end of the recess with the back face of the die plate, the same compressed air application used to blow off the fibrous layer will effect the cleaning. Furthermore, the connection does not interfere with the application of suction to the pressing die or the forming die.
The above technique is particularly adapted to make perforated molded pulp articles such as the ventilated fruit packing trays described in copending U. S. patent application Serial No. 350,630, filed April 23, 1953.
The advantages of the present invention are also obtained if the pressing die is used merely for pressing and is then simply removed from engagement with the fibrous layer on the forming die. The puff of compressed air still etfects the desired cleaning of the sockets 34 while it assists in the separation of the fibrous layer from the engagement with the pressing die and at the same time blows away loose fibers back onto the body of the layer. In this modification of the present invention the pressed layers of fibers can be subsequently transferred from the forming die onto a second pressing or hot drying die or directly blown off onto a conveyor belt or the like for further treatment.
Best results are obtained in accordance with the present invention when the recesses 34 are made generally frustoconical in cross section as shown in Fig. 1 and generally circular in plan as shown in Fig. 3, the blow passageways 42 being located at the extreme blind end of the recess, being positioned tangentially to the conic surface and directed at an angle toward the opening of the recess. When the finished article is blown from the pressing die 12, the passageways 42 being positioned as described dircct a stream of air generally in the form of a conical helix, thus sweeping stray fibers from the surfaces of the recess 34. Where non-circular perforations are desired in the finished pulp product it is accordingly preferred that the recesses be rounded into generally circular form at least at their blind end. However, noncircular recesses can be used even with formation-limiting plugs that are rectangular throughout or merely at the formation level. H
Good cleaning is effected however with non-tangential blow passageways and/or with non-circular recesses, although in such cases higher blast pressures of about ten to twenty pounds per square inch are then preferred. With the tangential and circular arrangement, blast pressures of about five pounds per square inch are completely satisfactory.
The blast passageways 42 can also be tapered if desired so that the end opening into the hollow center of the pressing die is bigger in size than the opposite end. This has the effect of increasing the air velocity of the blast without changing the actuating pressure and thereby improves the blasting action.
Improvements can also be obained if the surface of recess 34 is made very smooth,.as by a high polish or a chromium plating operation, This smoothness makes it easier for loose fibers to be blown out. The blast pressure can accordingly be lowered somewhat and still effect good cleaning.
The dies of the present invention can be made in any desired form varying from those having one-piece dicplate structures as shown in U. S. Patent No. 2,585,049, granted February, 12, 1952, to those having an assembly of die plate sections as in U. S. Patent 2,192,937, granted March 12, 1940. Even laminated constructions as shown in U. S Patent 1,984,384, granted December 18, 1934, can be used. I V The particular manner in which the recess or plug is mounted in place forms no part of the present invention and any suitable anchoring arrangement is satisfactory. lf convenient, these parts may be integral portions of the respective dies. 7 As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof except as defined in the appended claims.
What is claimed is:
1. A method of molding a perforated pulp article which method includes the steps of suction forming a mass of pulp on a die surface having an upstanding non-porous formation-preventing plug at the location of each of the desired perforations, pressing the formed mass on the die surface with a mating pressing die having a blind recess that receives the upstanding plug, separating the pressing die from the forming die surface while transferring the molded mass onto the pressing die removing the pressing die from the vicinity of the forming die, and blowing the transferred mass off from the pressing die while discharging a blast of air out of the blind end of the recess to clear out stray pulp fibers and cause them to be blown against the pressed mass as it is transferred.
2. In apulp molding apparatus for preparing perforat'ed molded pulp articles, a forming die having a forming surface with an upstanding formation-preventing plug, and a perforated pressing die having a pressing surface shaped for mating with the forming surface, said pressing surface having a recess open at one end for receiving the plug, a b lind end wall, and imperforate side wall area and an air blastpassage opening into said blind end wall.
3; The invention of claim 2 in which the plug and the recess are both generally circular in cross section perpendicular t o th eir axes, and the air blast passageway is directed substantially tangentially of the circular recess cross section. I v I v 4. The invention of claim 2 inwhich the plug and the recess' a re both generally frustoconical, and the air blast passageway is directed tangentially of the recess.
References Cited in the file of this patent UNITED STATES PATENTS 877,579 Lorenz Jan. 28, 1908 961,214 Crane June 14, 1910 1,415,649 Jagenburg May 9, 1922 1,655,878 Reif Jan. 10, 1928 2,320,789. Montague et al. June 1, 1943 2,363,107 Young Nov. 21, 1944