US3698098A - Method for drying articles having a low heat tolerance - Google Patents

Abstract

A method for drying articles having a low heat tolerance, such as parachutes fabricated of synthetic fibers, comprising the steps of first heating a hermetically sealable chamber to a predetermined temperature which the article can tolerate, then evacuating the chamber to create a vacuum therein for substantially reducing the boiling-point of any moisture in the article, and exhausting the boiled-off moisture to complete the drying cycle.

Description

United States Patent Ramsay 4] METHOD FOR DRYING ARTICLES HAVING A LOW HEAT TOLERANCE [72] Inventor: James M. Ramsay, Yuma, Ariz,

[73] Assignee; The United States of America as represented by the Secretary of the Navy '22 Filed: March 29, 1971 [2]] Appl. No.2 129,062

Related us. Application Data [62] Division of Ser. No. 861,104, Sept. 25, 1969,

Pat. No. 3,605,278.

[52] US. Cl ..34/15, 34/92 [51] Int. Cl ..F26b 5/04 [58] Field of Search ..34/15, 92, 103, 104

[5 6] References Cited UNITED STATES PATENTS 3,615,310 10/1971 Long ..34/92 1 Oct. 17, 1972 3,057,078 l0/1962 Gold.. ..34/92 FOREIGN PATENTS OR APPLICATIONS 1,378,202 10/1964 France ..34/15 18,018 8/1912 Great Britain ..34/15 Primary Examiner-Frederick L. Matteson Assistant ExaminerW. C Anderson Attorney-R. S. Sciascia, George J. Rubens and J. W; McLaren [s7 ABSTRACT' A method for drying articles having a low heat tolerance, such as parachutes fabricated of synthetic fibers, comprising the steps of first heating a hermetically scalable chamber to a predetermined temperature which the article can tolerate, then evacuating the chamber to create a vacuum therein for substantially reducing the boiling-point of any moisture in the article, and exhausting the boiled-off moisture to complete the drying cycle.

2 Claims, 5 Drawing Figures PATENTEDncr 11 I972 3 6 98 O9 8 SHEET 1 0F 2 METHOD FOR DRYING ARTICLESHAVING A LOW HEAT TOLERANCE CROSS-REFERENCE TO RELATED APPLICATIONS The invention is a divisional application of Ser. No.

861,104 filed on Sept. 25, 1969, now U.S. Pat. No. 3,605,278.

STATEM ENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION I paratus has contributed to malfunctioning of deployed parachutes. This malfunctioning occurs when a damp parachute is repacked, flown to a high altitude where it freezes, and the parachute is again deployed on landing before it has the opportunity to defrost. The accepted standard for the amount of humidity in a parachute is 5 percent of the dry weight, and if the humidity is at this level or less, the parachute can be repacked. The problem of adequately drying parachutes has long been a problem in the U.S. Naval Service particularly on board aircraft carriers where available space for towertype drying is limited and costly. Conventional clothes drying methods all have serious limitations. Because of the low heat tolerance of nylon, being the conventional parachute material, hot air drying is time consuming and inefficient especially where the ambient air is hot and humid. Dehumidification does not work efficiently were it is cold and humid. Tests have indicated that the combination of tumbling the parachute with an air flow is not satisfactory because the fibers separate and give the parachute a nap-like angora.

Although prior art devices have allegedly used vacuum techniques in association with heat for drying purposes, the vacuum was used solely as a suction means to draw off the moistened air from the drying chamber into which ambient air was introduced during the drying process.

SUMMARY OF THE INVENTION The problem of drying an article, such as a parachute, has beensolved by employing a method using a high vacuum for boiling-off the moisture without the requirements of tumbling, circulating hot air, or relying on ambient air or other climatic conditions. The parachute is inserted into a stationary, hermetically sealed chamber which is then heated to a temperature that the article can tolerate. The heating is preferably supplied by a flexible blanket inside the chamber into which the article is folded back-andforth, and by an external blanket around the chamber, if needed. The chamber is thereafter subjected to a substantially high vacuum, preferably, the highest vacuum that is obtainable from commercially available pump equipment, which is about 29.5 inches Hg. With such a vacuum, the boiling point of the moisture in the parachute can be reduced to about 60 F. Obviously, the higher the parachute can be heated safely over the boiling point of the moisture, the quicker the article can be dried. For example, with the chamber heated to 125 F., and a vacuum of 29.5 inches Hg a normal drying cycle will comprise a 10 minute heat build-up, a 25 minute vacuum phase, and a 5 minute pressure dump and cool-down phase. The latter phase dissipates the vacuum in the chamber to permit access to the chamber, and cooling of the parachute to a handling temperature. The length of the heat phase, vacuum phase, and cool phase can be manually or automatically varied in length and is controlled by a timer in an electrical circuit. I

STATEMENT OF THE OBJECTS OF THE INVENTION A principal purpose of the invention is to provide a method for drying articles having a low heat tolerance quickly, effectively, for use in an apparatus occupying a minimum of space making it particularly suitable for shipboard use. I

Another important object of the invention is to provide a drying method which does not require the apparatus to be rotated for tumbling the article to be dried and which dies not require the introduction of ambient air into the apparatus during the drying cycle.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is a perspective view of drying apparatus employing the novel method with the chamber partially broken away to show the internal heating blanket'in a slightly extended position, the parachute being omitted;

FIG. 2 is a side elevation of the drying chamber and pump assembly;

FIG. 3 is a partial elevation in section of the drying apparatusshowing the internal heat blanket connections; and

FIGS. 4 and 5 are schematic wiring diagrams of a power circuit and a control circuit, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings where like reference numerals refer to similar parts throughout the figures there is shown in FIG. 1 the vacuum drying apparatus 10 disclosed in applicants above-identified pending ap plication and now patent number 3,605,278 which is designed principally, although not necessarily limited, to drying articles having a low tolerance to heat and to tumbling. An example of articles of this type are parachutes made of synthetic fibers, such as nylon. It has been found that a normally wet standard 28 ft diameter Navy service type parachute contains about 4 pounds of water that should be removed. A normally wet parachute is considered one that has been subjected to rain. It has been determined that when the chamber is maintained at 125 F., 333 cu ft of vapor must be off-gassed for each pound of water. To maintain the temperature of 125 F. requires an additional heat of 7 1,000 BTUs per pound, regardless of the degree of vacuum that is to be maintained.

Dryer 10 comprises a drum-shaped chamber 12 fabricated of a tubular metal side wall 14 having welded thereto a bottom plate 16, and an upper neck collar 18 to which a door 20 is hinged at 22. Door 20 is provided with an O-ring 24 for sealable contact with collar 18 making the chamber hermetically air tight when closed. In the particular installation being described because of the high vacuum being employed the chamber is fabricated of heavy plate aluminum, the

side walls being one-eighth inch in thickness, the top door being five-eighths inch thick and the bottom plate being 1 inch thick. Because of the vacuum being employed no latches are needed to lock the door in a closed position. The door has a large diameter to provide maximum access to the chamber for loading and unloading the parachutes which are somewhat bulky, and to facilitate folding of the parachute within the chamber in a manner to be described. Chamber 12 is supported on a base cabinet 26 having leveling legs 28. A console 29 is mounted on cabinet 26 adjacent chamber 12 and contains the operating controls as will be described. Chamber 12 may be heated by an external and internal heating means singly or in combination as the heating requirements may dictate. External heating is performed by an electric blanket 30 which is snugly wrapped externally around chamber 12 and is provided with cutout portions at 31 to accommodate a heating junction box 32 and other elements attached to the chamber. An external heater blanket 30a is also secured to the bottom surface of plate 16. An'insulating jacket 33 is mounted around the external heater blanket 30 and is held in position by a thingsplit tubular metal shroud'34 held together by a plurality of bands 36 and fasteners 38. A bottom insulation pad 33a is also provided for the bottom heater blanket 30a.

A feature of the drying apparatus is the employment of a flexible internal heater blanket 40, preferably electrically controlled, which blanket serves principally to supply the additional heat to the parachute, approximately 4,000 BTU, to maintain the drying temperature .of 125 F. The internal temperature of the chamber is indicated at gauge 41 on console 29. In the specific installation herein described the combined internal and external heat sources have a capacity of 12,000 BTU/hr. For a chamber having an internal diameter of 30 inches, internal blanket 40 is dimensioned 22 inches in width and approximately 120 inches in length. The internal heater blanket is constructed as flexible as possible to allow folding to a 1 inch minimum radius, the space between the sides of the blanket and the inside wall of the chamber allowing room for the parachute when folded. The technique of folding the parachute back-and-forth within the internal heater blanket ensures maximum heating contact as well as providing voids to permit the escape of the vapor being generated.

As shown in FIG. 3, one end of internal heater blanket 40 is secured to a chamber floor plate 42 by a pair of bolted straps 44. Floor plate 42 is secured to bottom plate 16 in spaced relation thereto by bolts 46and spacers 48 providing a sump 50 for any water draining from the wet parachute when initially placed in the chamber. There is no need to drain sump 50 as the moisture will be quickly evaporated when the chamber is subjected to the drying cycle.

lntemal blanket 40 is suitably controlled in automatic or manual operation by a control circuit to be described, being connected by conductor 51 to receptacle 52 mounted on the chamber wall and grounded by strap 54 (FIG. 2). The openings through chamber 12 for the electrical connections are sealed by epoxy so that the installation is helium tight.

As previously described, the chamber is subjected to a very high vacuum to reduce substantially the boiling point of the moisture in the parachute and, of course, the more perfect the vacuum the quicker the drying cycle. For example, it has been found that the boiling point of the moisture can be reduced to 30 F. when the chamber is subjected to a vacuum of 29.8 inches Hg, whereas the boiling point increases to 105 F. when a vacuum of 27.8 inches Hg is employed. However, for the contemplated use of drying parachutes the employment of exotic equipment to obtain the highest vacuum is not considered warranted. The best results that can be obtained with present day commercially available equipment achieves the operating vacuum of about 29.5 inches Hg which reduces the boiling point of the water in the parachutes to about 60 F. The equipment employed in the described installation includes a 10 HP motor 56 which drives a 200 cfm pump 58 having a muffler 60 to keep the noise level at 55 db or lower. The pump is connected to chamber 12 via a 3 inch flexible pipe 62 and through a solenoid operated vacuum valve 64 and outlet 66 which controls the vacuum in chamber 12 and the dumping of the vapor being formed. A direct reading vacuum gauge 67 is conveniently mounted in the front of the chamber 12.

A guard plate 68 is welded tothe inside of chamber 12 in spaced relation to outlet 66 to prevent the parachute from accidentally blocking the outlet when folded into the chamber, (FIG. 1). After the completion of the vacuum drying cycle, the chamber is relieved of the vacuum by a solenoid operated pump valve 70 mounted to chamber 12 (FIG. 2).

The various valves and heating elements in the drying apparatus are operated in a controlled circuit and a controlling circuit having common relays, and the circuits are separately illustrated for clarity. The 220V power circuit is diagrammatically illustrated in FIG. 4, being the controlled circuit, and-the 1 10V controlling circuit is diagrammatically illustrated in FIG. 5. Referring to FIG. 4, line voltage of 220V (3 phase, 20 amp) is connected through suitable circuit breakers 72 across resistance- type heating elements 74, 76, and 78 of the internal, external and bottom heater blankets 40, 30, and 30a,'respectively. Each line to the respective heating elements are provided with suitable thennostatic relay switches 80, 82, and 84, each relay being a double-pole double-throw type and preset to limit its respective blanket to a predetermined temperature and controlled in operation by the control circuit in FIG. 5. Solenoid operated vacuum valve 64 and dump valve 70 are separately connected in parallel across the line voltage, and each are provided with a relay switch 86 and 88, respectively.

The control circuit in FIG. 5 is also connected to 220V line voltage through a step-down transformer 90 which reduces the 220V line voltage to 110V. A fuse 91 protects the control circuit. The control circuit includes three toggle switches 92, 94, and 96 arranged in parallel circuits for controlling the power circuits to the heaters, and the circuits including the vacuum valve and the dump valve, respectively. Each toggle switch has three positions, namely, AUTOMATIC, MANUAL, and OFF. A timer 98 (0-60 minute scale) is connected to each AUTOMATIC position of the switches for automatically controlling the operation of the various respective circuit components in accordance with the selected cycle. The MANUAL position of each toggle switch is connected in the control circuit in a manner to by-pass the timer to permit manual operation of the individual components when desired.

As is apparent from the drawings, the solenoid portions for the various relay switches in the power circuit of FIG. 4 are located in the control circuit of FIG. 5. Heater switch 92 controls the three parallel heater circuits. The internal heater circuit includes relay 80 and a variable temperature control 100 (0300 F.) which permits a manual mode of the internal heater. The external heater control circuit includes relay 82 and a variable temperature control switch 102, while bottom heater control circuit includes relay 84 and a variable control switch 104. Likewise, the vacuum valve toggle 3 switch 94 includes solenoid 86, and dump valve toggle switch includes solenoid 88.

As previously stated, one drying cycle that has been found to work satisfactorily for drying standard parachutes includes a minute heat build-up stage by the various heater elements to achieve a 125 F. temperature in the drying chamber which is thereafter maintained by the thermostatic controls. Normally, it is not desirable to commence evacuating the chamber prior to the heat build-up phase because it would be more difficult and take much longer time to reach the desired temperature of 125 F. After the heat build-up stage, a minute vacuum phase is commenced. During the vacuum stage the internal heater is one primarily involved in maintaining the 125 F. temperature to replace the heat lost in evaporation. Obviously, the internal heater is cycled more often during the initial vacuum stage. After the vacuum phase a 5 minute dump phase is initiated in which the dump valve is operated to admit ambient air into the chamber to dissipate the vacuum and to cool the parachute to permit the chamber to be opened and the parachute removed.

The various valves for the vacuum, temperature and phase duration of the heating cycle heretofore described are intended to be only illustrative, and may vary depending on the specific article to be dried and the amount of moisture to be removed.

The novel method satisfies a long-felt requirement for drying articles quickly and efficiently, especially articles that cannot tolerate high drying temperatures. The drying operation is achieved without the need for moving parts in the chamber, the use of ambient air, or the need for blowers which might otherwise damage sensitive fabrics. These results are achieved by the use of a high vacuum and the unique arrangement of heater elements, particularly the flexible internal heater, to enable the removal of moisture in the article by a boilin E rocess.

%)%vi usly many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: 1. A method of drying a parachute fabricated of synthetic fibers having a lowheat tolerance comprising 0 the steps of:

inserting the parachute in a chamber;

first heating the chamber to a predetermined temperature between 60 to F. below which the article can tolerate;

evacuating said chamber to create a vacuum of between 27 inches Hg to 29.5 inches Hg therein for substantially reducing the boiling-point of any moisture in said article;

exhausting the boiled-off vapor from said chamber until the article is dry;

relieving the vacuum within the chamber to complete the drying cycle.

2. The method of claim 1 wherein the heating is achieved by external and internal means, the latter by folding the article within a flexible electric blanket position within the chamber.

Claims (2)

1. A method of drying a parachute fabricated of synthetic fibers having a low heat tolerance comprising the steps of: inserting the parachute in a chamber; first heating the chamber to a predetermined temperature between 60* to 140* F. below which the article can tolerate; evacuating said chamber to create a vacuum of between 27 inches Hg to 29.5 inches Hg therein for substantially reducing the boiling-point of any moisture in said article; exhausting the boiled-off vapor from said chamber until the article is dry; relieving the vacuum within the chamber to complete the drying cycle.

2. The method of claim 1 wherein the heating is achieved by external and internal means, the latter by folding the article within a flexible electric blanket positioned within the chamber.

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