Method For Drying Metal Parts

Abstract

A method for removing water from metal parts, wherein the parts are introduced into a bath of a solvent which displaces the water from the parts, the parts then being conveyed upward on a spiral conveyor through saturated vapors of the solvent. The articles are then conveyed out of the vapor zone and are heated to completely dry them of all traces of the solvent.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention lies in the field of method and apparatus for spot free drying of metal articles and, particularly, a method of spot free drying of metal articles by displacing the water with a halogenated solvent having a specific gravity greater than that of water.

2. Description of the Prior Art

There are many industrial applications wherein metal parts are processed through operations where water is present, resulting in the parts being wet at the end of such processes. For example, finishings such as deburring, burnishing, and decoppering of metal articles in the presence of an aqueous solution results in wet metal parts. To prepare such parts, or articles, for further finishing, such as lacquering, it is essential that the parts be dried completely "spot free". Normal evaporative drying results in spots, which are totally unacceptable on such articles, where appearance is a primary factor. Complete "spot free" drying requires complete displacement of all water on the articles, and must be done without any evaporation of the moisture or water.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a novel and efficient means and method for accomplishing spot free drying of metal objects.

It is a further object of this invention to provide spot free drying of wet metal objects by conveying such objects through a halogenated solvent having a specific gravity greater than that of water, and through a vapor of such solvent.

Accordingly, the method of this invention comprises spot free drying of wet metal objects by immersing such objects in a bath of a halogenated solvent having a specific gravity greater than that of water, which solvent displaces the water which rises to the top of the bath where it is removed. The articles are then transmitted through a solvent vapor area where the articles are surrounded by hot solvent vapors, at a temperature and for a sufficient time such that when the articles are brought out of the vapor area they are warm and dry. The articles are introduced onto a vibrating conveyor which conveys the articles from a bottom pan where they are immersed in the solvent up through and out of a vapor zone and subsequently to a discharge point. The displaced water is separated away from the solvent and discharged from the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view, partly in block diagram form, showing the apparatus of this invention, indicating the flow of articles through such apparatus and the means for achieving the desired solvent cycle.

FIG. 2 is a diagram illustrating a typical article drying cycle for the apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A vibrating spiral elevator, as shown generally at 15, is mounted within a generally cylindrical tank, or housing 10, having a removable head 11 at the top thereof. The conveyor structure is of the helical type such as shown in the U.S. Pat. to White, No. 2,853,180, issued Sept. 23, 1958. The elevator is driven by dual vibratory motors 16, mounted to the hood through rubber drive mounts 17. Applicants make no claim herein covering the specific structure of such vibratory conveyor apparatus.

The wet metal articles, or objects, which are covered, either partially or entirely, with a thin film of water, are introduced into load chute 20, through which they are dropped into a bottom pan of the conveyor, which contains a halogenated water immiscible solvent having a specific gravity greater than that of water. The solvent also must have a viscosity less than that of water, in order to accomplish efficient displacement of the water. Typical solvents which are suitable for use in the method of this invention are perchloroethylene, trichlorotriflouroethane, and trichloroethylene. Perchloroethylene is the generally preferred solvent.

The halogenated solvent is continuously introduced into a well, or shed pan 21, which encompasses the bottom pan of the conveyor, through piping indicated at 46. As the metal articles are immersed into the solvent, the water is displaced from same and carried to the top of the solvent bath, due to its lower specific gravity. The solvent overflow from pan 21, indicated generally at 19, drops into a collecting pan 22 from which it drains through outlet 23. This solvent, carrying the displaced water, is passed through conventional water separator 28, and reintroduced through inlet 29 into the boil chamber 25 located at the bottom of the tank. The solvent in boil chamber 25 is raised to boiling temperature by steam coils 27, and is maintained at a level 26 below the location of collecting pan 22. The vapors which rise from the boil chamber pass upwardly through holes 30 around the periphery of collecting pan 22, and thence upward past the shed pan 21 and into the vapor zone indicated generally at 60. The vapor zone is bounded on top by water-cooled condenser coils 35 which cause formation of vapor condensate which drips into the slopped collecting trough 36 and then runs outward through trough outlet 37. Since some water may be displaced from the articles after they have left the bottom pan, a water separator 40 is provided to separate out any water which was condensed along with the vapor condensate. The purified solvent is then passed through heat exchanger 41 which raises the temperature of the cooled solvent condensate to the preferred temperature which is desired in the bottom pan. For perchloroethylene, for example, the temperature range is 180.degree.F to 220.degree.F. The heated solvent is returned through bottom pan inlet 45 and piping as indicated at 46, to the well, or shed pan 21. Suitable pumping means, not shown, may be utilized in the return path.

As an alternate embodiment, some of the heated solvent condensate may be introduced through upper inlet 47 and carried by suitable piping to a point on the conveyor above the bottom pan, where the solvent is introduced to provide a wash-back rinse of the articles. The counterflow of the clean solvent, along with the vibration of the vibratory conveyor, provides continuous agitation of the parts for complete removal of any water film which had not been displaced at the time the articles were immersed into the bottom pan.

In order to maintain the cleanliness level of the solvent used in the process, solvent is continuously drawn out from the boil chamber as at tank outlet 50, passed through a pump 51 and into a still 52, where purified solvent distillate is obtained. The purified solvent is passed through conventional heat exchanger 53 and introduced back into the system through inlet 45.

In operation, the processed metal parts which are to be spot free dried are introduced through chute 16, and travel rapidly by gravity down the chute into the solvent in the well 21, which is integral with the lower portion of the spiral vibratory conveyor. Due to the lower viscosity and higher density of the solvent, it displaces the water film on both the surfaces of the articles, and out of any indices of the articles, e.g., such as exist in an assembled hinge. The displaced water rises to the top of the solvent bath and overflows to the collecting pan 22. The overflow is continuous, due to the continuous reintroduction of solvent distillate through inlet 45. Thus, water which is displaced from the metal articles is continuously carried away.

As the metal pieces progress up the spiral vibratory conveyor 15, they are completely surrounded by solvent vapors, which vapors are approximately at the boiling point of the solvent. During the time that the articles are exposed to the vapor, they are brought up to the temperature of the vapor so that, when they rise above the vapor zone 60, they leave warm and dry.

In order to ensure complete drying of varied sizes and types of work, auxiliary heat may be supplied to the conveyor by means of steam jackets 65 running along the conveyor track, and supplied through steam pipe 66. The steam jackets are operated to yield a temperature slightly above the boiling point of the solvent used. This additional source of heat ensures that any small quantity of solvent that might be entrapped in or on the work piece will be evaporated before such work piece is discharged from the unit through discharge chute 38.

From the above, it is seen that a method and apparatus are disclosed for efficient spot free drying of metal articles. Since the solvent used efficiently displaces water, there is no evaporation of water from the article, which evaporation is the source of spots. Also, since the solvent does not leave spots when it drys it is necessary only to provide complete drying of the solvent from the articles, which is accomplished by passing the articles first through the vapor zone where they are raised to high temperature, and then through a vapor free zone where they are dried.

A typical processing cycle for a spiral vibratory conveyor as used in this method is illustrated diagrammatically in FIG. 2. While the articles are immersed in the solvent contained in the well 21, they are rotated through approximately one and one-half revolutions by the spiral conveyor. In the embodiment where a wash-back rinse is used, the rinse is applied for approximately two revolutions. Subsequent to that, there are four revolutions during which the articles are solely in the vapor zone, where they are heated by the vapor. Subsequent to that, the articles are transported upward through approximately another five revolutions of the vibrator, prior to unloading through chute 38.

The following example is presented to illustrate the method and apparatus of this invention.

EXAMPLE 1

Miscellaneous hardware, including door pulls, drawer pulls, hinges, etc., are first burnished following a copper plate and oxide treatment. These articles are dried using the method and apparatus of this invention, after which they are assembled and/or lacquered. The parts are fed into the dryer apparatus very wet with water, and are discharged dry and spot free. The solvent used is perchloroethylene. The temperature in the boil chamber is maintained at 250.degree.F, and the temperature of the solvent in the bottom pan of the spiral is maintained at 200.degree.-210.degree.F. Steam requirements are 210 lb./hour at 40-50 PSIG. Solvent usage averages approximately 3/4 of a gallon per hour, for processing 20 to 24 tote pans of articles per hour.

Claims

We claim:

1. A method for treating metal articles covered at least partially with a thin film of water, comprising:

a. immersing said articles in a bath of water-immiscible halogenated solvent having a specific gravity greater than that of water such that said solvent displaces the water from said articles;

b. maintaining said solvent bath in a heated state below its boiling temperature, and continuously introducing solvent into said bath and overflowing water and solvent from said bath;

c. maintaining a vapor zone containing vapor of the same type of solvent as maintained in said bath said vapor being generated in a separate chamber containing substantially water-free solvent;

d. vibrating said articles out of said solvent bath and through said vapor zone;

e. back-washing said articles with the same type of solvent as maintained in said bath while said articles are being vibrated through a portion of said vapor zone; and

f. heating said articles after said back-washing to a temperature above the boiling point of said solvent to ensure complete evaporation of said solvent from said articles.

2. The method as described in claim 1, wherein the solvent is perchloroethylene, and said solvent bath is maintained at a temperature in the range of 180.degree.F to 220.degree.F.

3. The method as described in claim 1, wherein said articles are heated to a temperature above the boiling point of said solvent both while said articles are being vibrated through the upper portion of said vapor zone and also after said articles have been vibrated through said vapor zone.