US 2894869 A
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July 14, 1959 J. E FooTE MOLDING PULP ARTICLES 2 Sheets-Sheet Filed Aug. 6. 1956 INVENTOR ATTORNEY July 14, 1959 J. E. FOOTE 2,894,869
, I MOLDING PULP ARTICLES File dAu'g. '6, 1956 2 Sheets-Sheet 2 FIG 4 J. E.FOOTE INVENTOR Bf. Bani. UJ FLMKs ATTORNEY r 2,894,869 rateniedntym; 1959 MODDING PULP ARTICLES :James E. Foote, Westport, Conn., assignor to Diamond Gardner Corporation, a corporation of Delaware Application August 6, 1956, Serial No. 602,372
4 Claims. (Cl. 162-224) This invention relates to the molding of pulp articles. IMore particularly, the invention relates to methods of :molding in which a series of foraminous molds are advanced successively through an aqueous pulp slurry in -which the articles are formed initially by the deposition 'of layers of wet pulp on the molds, and the articles are subsequently compressed and dried to produce a z-smooth-surfaced finish thereon.
In the commercial manufacture of molded pulp arti- L cles, such as !pie plates, it is customary to impart a smooth- :surfaced finish to the articles by employing either one of two well known methods. In one of these methods, :the wet initially formed articles are transferred directly ffrom the foraminous forming molds to a pair of heated compression drying dies, in which all of the excess Water Eris expressed from the articles while simultaneously imparting a smooth finish thereto. In the other one of athese methods, the wet initially formed articles are transfferred from the foraminous forming molds to a drier in which substantially all of the moisture is first removed :1from the articles by heated air without compressing the :articles, and then the dried articles are subjected to -compression between heated finishing dies. The second ;-method does not produce the desired surface smoothness fin the finished articles, and the first method is not sulfitciently economical and rapid for the mass production of low unit cost items, such as pie or household plates, in rtodays highly competitive markets.
An object of this invention is to provide a new and improved method for molding pulp articles.
Another object of the invention is to provide a new rand improved method for rapidly producing a superior smooth-surfaced finish on molded pulp articles.
Still another object of the invention is to provide a highly economical and very rap-id method for mold- ;ing pulp articles having a superior smooth-surfaced finish.
A method illustrating certain features of the invention :may include the step-s of initially forming a molded pulp article by depositing a layer of wet pulp onto a :foraminous mold, free or form drying the initially formed .article to reduce its moisture content to about 45 to 55% L-by weight, and then subjecting the article to compres- :sion between heated dies to complete the drying operation .and impart a smooth surface finish thereto.
Other objects and the nature and advantages of the iinstant invention will be apparent from the following description taken in conjunction with the accompanying -.-drawings, wherein:
Fig. l is a side elevation of a pulp molding machine :suitable for initially forming articles in accordance with nnethods embodying the invention;
Fig. 2 is an enlarged vertical section of a transfer .mechanism and an adjacent conveyor belt located at the discharge station of the molding machine illustrated in Fig. 1;
Fig. 3 is a rear elevational view of the transfer mechanism shown in lfig. 2; and v 2 Fig. 4 is a schematic side elevation of one suitable arrangement of apparatus, including a pulp molding machine, a drying tunnel, and a final compression, and dry.-. ing machine, designed to perform all of the steps of methods embodying the invention. The invention may be utilized either in connection with intermittent (step-by-step) or continuously moving machines.
The pulp molding machine illustrated in Fig. 1 is of the intermittently operable type. It includes a series of foraminous forming molds 10 located on the periphery of a circular carrier 12 which is disposed vertically and mounted rotatably on a fixed horizontal shaft 14 journalled on the main frame 15 of the machine. Each of the molds 10 is secured to the outer end of a hollow arm 16 projecting radially from the carrier 12, and all of the arms 16 are connected to a central vacuum pump (not shown) which applies suction to the molds 10 during rotation of the carrier 12. The molds are advanced in a circular path in which they successively be come immersed in an aqueous pulp slurry contained in a tank 18. The suction applied to the molds 10 while they are immersed in the tank 18 causes layers of wet pulp to be deposited thereon, thereby initially forming the pulp articles. In the case of the machine illustrated, the articles being produced are pie plates, but
' other molded pulp articles could be formed thereon.
The molds 10 are advanced in a counterclockwise direction, as viewed in Fig. 1, from the tank 18 of .pulpslurry through an arc of about 270 to a discharge station where a take-off or transfer mechanism 20 is located. The advancement of the molds 10 is in a uniform step-by-step movement, each step bringing another one of the molds to the transfer mechanism 20. A Geneva stop motion is employed for this purpose. A driven member 22 secured to the carrier 12 is engaged by a driving member 24 aflixed to a shaft 26 which is operatively connected by gears 28 with a gear 30 secured to a main driving shaft 32. The driven member 22 is temporarily locked at the end of each stepwise movement by means of a bolt 34 which projects from one end of a periodically movable crank lever 36 fulcrumed on the main frame 15. A face cam 38 connected to the main driving shaft 32 oscillates the lever 36 in timed relation to the intermittent movement of the carrier 12.
The transfer mechanism 29 removes the initially formed pulp articles from the molds 10 and transfers them one at a time to an adjacent split endless belt conveyor 40. As is best shown in Fig. 3, the transfer mechanism 20 includes three cooperating spaced segments 42 shaped to receive a pie plate. The segments 42 are secured to three correspondingly spaced parallel rocker arms 44 which are aflixed to a hollow rock shaft 46 journalled on the main frame 15 of the molding machine. The three rocker arms 44 are movable as a unit through an arc of about between limits adjacent to the paths of the molds 10 and the conveyor 40. The spaces between the segments 42 are aligned with the parallel sections of the split belt conveyor 40, and the arms 44 together with their supported segments 42 can be swung slightly below the level of the belt conveyor 40, as shown in Fig. 2, to deposit a molded pulp pie plate 48 thereon.
In order to enable the transfer mechanism 20 to engage and remove the molded pulp articles from the molds 10, means is provided for applying suction to one of the segments 42. The central segment 42 is provided with a pair of suction orifices 50 communicating through a duct 52 in its supporting rocker arm 44 with the interior of the hollow shaft 46, which is connected to a suction pump (not shown). An automatic .valve (not shown) is associated with the transfer mechanism 20 for interrupting the suction when the mechanism is tilted to deposit a molded pulp article on the belt conveyor 40.
An oscillatory movement is imparted to the shaft 46 to rock the transfer mechanism 20 in timed relation to the intermittent movement of the mold carrier 12. This may be accomplished by securing to the shaft 46 a gear segment 54 which engages a rack 56 formed on the lower end of an inclined movable bar 58 supported on a roller 60 mounted on the main frame 15. The upper end of the bar 58 is bifurcated and engages a face cam 62 operatively associated with the main driving shaft 32 of the machine.
The molded pulp articles, such as the pie plate 48 produced by the molding machine illustrated in Fig. 1, are still quite wet at the time they are placed on the belt conveyor 40 by the transfer mechanism 20. At this stage of the manufacturing process, the molded pulp articles may contain from about 70% to about 75% by weight of excess moisture. The wet pulp articles are rather pliable and soft at this time, yet they are sufiiciently compacted to hold together during the transfer operation. The articles are compacted slightly by the suction applied to the molds It? during the initial forming action. The suction is applied to the molds while they are immersed in the aqueous pulp slurry contained in the tank 13. This slurry is a water suspension of pulp fibers having a solids content of about /2 to about 3% by weight. The suction extracts the pulp fibers from the slurry and deposits the fibers in layers on the molds, thereby initially forming the molded articles. Suction on the molds 10 is continued while they are advanced by the intermittently rotatable carrier 12 through an arc of about 270 to the discharge station where the transfer mechanism 20 is located. Thus, excess moisture is sucked from the initially molded articles during the entire time required for their travel through the 270 arc to the discharge station, reducing their moisture content to about 70% to 75% by weight.
At this stage of the molding process, the wet pulp articles are ready to be further dried and compressed to produce the finished articles desired, and at this point the treatment of the articles in methods embodying the invention involves important differences over the treatments employed in the well known methods of the prior art.
In one of these prior art methods, the wet articles are transferred directly from the forming molds to a pair of heated compression drying dies in which all of the excess water is expressed from the articles while simultaneously imparting a smooth finish thereto. Due to the relatively large amount of water which must be expressed by the heated compression dies in this method, relatively high temperatures andv pressures must be employed. Consequently, the equipment required is complicated, massive and expensive. Even more important is the fact that the compression drying step is necessarily unduly slow. As the dies compress the wet pulp it becomes progressively more difficult to remove the remaining moisture (due, at least in part, to the insulating effect of the pulp) and as the efficiency of the drying operation decreases there is a corresponding increase in the time required to attain dryness. Furthermore, even if a plurality of drying presses were employed to speed up the operation due to practical limitations on manufacturing floor space, only a limited number of drying presses could be employed. Hence, in any event this method of drying imposed a severe limitation on manufacturing capacity.
In another well. known prior are method, known as the semi-smoothing process, the wet articles are transferred from the forming molds to a drier in which the preponderantly major portion or substantially all of the moisture is first removed from the articles by heated air without compressing the aricles, and then the substantially dry articles are subjected to compression between heated finishing dies. The hot air drier reduces the moisture content of the pulp from about 70% down to less than 10%, and the finishing dies remove all of the remaining moisture. It is evident that the drying equipment required for this method is less complicated and expensive than the previously described equipment. However, the finish produced by this method is inferior to that produced by the other prior art method described. In attempting to compress pulp containing less than 10% moisture, enormous resistance to compression is encountered. Hence, the product is compressed to a lesser degree, resulting in decreased density and inadequate surface smoothness. In an effort to improve the surface smoothness, the surfaces of the articles are sometimes sprayed with additional moisture just before placing them in the heated finishing dies, but this results in little or no improvement.
In accordance with methods embodying the present invention, the wet articles are transferred from the forming molds to a free drier in which the moisture content of the articles is reduced from about 70 to 75% by weight down to about 45 to 55% by weight, and then the articles are subjected to compression between heated dies to complete the drying operation and impart the desired surface smoothness thereto. By first reducing the moisture content to about 45 to 55%, the work required to extract the remaining moisture is considerably reduced, thereby effecting a substantial simplification of the equipment required for final drying, and greatly increasing the rate of production. Yet suflicient moisture remains to maintain the pliability and softness required to produce good surface smoothness. In fact, the surface smoothness produced by methods embodying the invention is much superior to that heretofore obtainable.
One type of apparatus suitable for performing all of the steps of methods embodying the invention is illustrated schematically in Fig. 4. This apparatus includes a pulp molding machine 70 which may correspond in structure and in operation to the previously described pulp molding machine illustrated in Fig. l. The machine 70 comprises a series of foraminous molds 72 mounted on the periphery of an intermittently rotatable circular carrier 74. Rotation of the carrier 74 advances the molds 72 through an arcuate path in a counterclockwise direction, as viewed in Fig. 4, from a tank 76 containing liquid pulp slurry to a transfer mechanism 78, which corresponds to the mechanism 20 illustrated in Figs. 1, 2 and 3. Suction applied to the molds 12 while they are submerged in the pulp slurry causes the deposition of layers of pulp on the molds, to initially form the articles. The suction is continued while the molds 72 are advanced successively from the tank 76 to the transfer mechanism 78, thereby lightly compacting the molded articles and reducing their moisture content to about 70 to 75 by the time they reach the transfer mechanism 78 and are transferred to an endless belt conveyor 80.
The wet articles are advanced by the conveyor 80 through an elongated horizontal drying tunnel 82 in which the articles are subjected to any suitable free drying treatment. For example, the articles may be subjected to a current of heated air therein. This treatment reduces the moisture content of the articles from about 70% down to about 45 to 55% by weight. A value of about 50% moisture is preferred, a value between 45 and 55 is desired and is considered optimum, and values ranging between 35 and 65% may in some instances be considered acceptable.
After emerging from the tunnel 82, the partially dried articles are advanced by the conveyor 80 to a transfer mechanism 84, which is similar to the transfer mechanism 78. Here the articles are transferred one at a time from the conveyor 80 to a final compression and drying machine 86 comprising a series of male compression dies 88 mounted on the periphery of an intermittently rotatable carrier 90 which advances the articles to a vertically reciprocable female compression die 92. During each dwell in the step-by-step movement of the carrier 90, one of the pulp articles is subjected to final compression and drying between the male die 88 carrying the article and the female die 92. Another transfer mechanism 94 then discharges the completed articles from the machine 86 to a conveyor 96 which transports the articles to a suitable stacking and storage area (not shown).
The type of apparatus illustrated in Fig. 4 is particularly suitable for performing methods embodying the invention at a relatively high rate of production. However, it is evident that other types of apparatus may also be employed for this purpose. It is contemplated that the pulp molding machine employed may be of the continuously operable type instead of the step-by-step type machine illustrated and described herein. In order to increase the production capacity of the step-by-step type of machine, it may be considered desirable to employ a pair of alternately operable transfer mechanisms instead of the single mechanism shown. In such case, it may be possible to double the capacity of the production line by employing two drying tunnels and two final compression and drying machines.
Regardless of what type of apparatus may be employed, methods embodying the present invention provide a highly economical and rapid system for the mass production of low unit cost items, such as molded pulp pie or household plates. In the production of such items in immense quantities, it is vital to reduce manufacturing costs to the strictest minimum. Even a small fraction of a cent shaved from the cost of producing each item is worthy of careful consideration. Among the primary advantages obtainable from methods embodying the invention are a substantial simplification of the equipment required for final drying and a greatly increased rate of production, while at the same time producing a superior final product.
It will be obvious to those skilled in the art that various changes may be made Without departing from the spirit of the invention and therefore the invention is not limited to what is shown in the drawings and described in the specification but only as indicated in the appended claims.
What is claimed is:
1. A method of molding pulp articles, comprising the steps of immersing into a liquid pulp slurry a formainous mold under suction to deposit a layer of wet pulp thereon which initially forms a molded pulp article, removing the mold from the slurry While continuing the suction to reduce the moisture content of the deposited pulp article to about 70% to 75% by weight free drying the wet pulp article to reduce its moisture content down to about to by weight without compressing the article, and then subjecting the partially dried article to compression between heated dies to remove the remaining moisture and impart a smooth surface finish to the article.
2. The method defined by claim 1, in which the moisture content of the articles is reduced to about 50% by weight in the free drying step.
3. A method of molding pulp articles, comprising the steps of continuously advancing a series of foraminous molds through a liquid pulp slurry while applying suction to the molds to deposit layers of wet pulp thereon which initially form molded pulp articles, successively removing the molds from the slurry while continuing the suction to reduce the moisture content of the deposited pulp articles down to about to by weight, subjecting the articles to a current of heated air to reduce their moisture content down to about 45% to 55% by weight without compressing the articles, then successively transferring the articles to heated compression dies, and compressing the articles between the heated dies to remove the remaining moisture and impart a smooth surface finish thereto.
4. The method defined by claim 3, in which the moisture content of the articles is reduced to about 50% by weight by the current of heated air.
References Cited in the file of this patent UNITED STATES PATENTS 2,369,488 Perry Feb. 13, 1945 2,559,945 Chaplin July 10, 1951 2,704,493 Randall Mar. 22, 1955 2,746,358 Emery May 22, 1955