US2469270A - Apparatus for setting finishing compositions - Google Patents

Description

May 3, 1949. R. A. LIEBEL APPARATUS FOR SETTING FINISHING COMPOSITIONS Filed Aug. 21, 1945 WWW IBY

ATTORNEY Patented May 3, 1949 UNITED STATES OFFICE APPARATUS FOR SETTING FINISHING COMPOSITIONS 1 Claim.

This invention relates to apparatus for setting finishin compositions after application in fluid form to the surface of a continuously moving article. The invention relates particularly to setting the finishing composition in such manner as to give smoothness of surface of the set composition and economy and speed of operation.

The invention is particularly useful in coating flexible steel in the form of long continuous strips and will be first illustrated by description in connection with such article.

In setting the finishing composition upon sheet steel, the sheet is drawn through a baking oven. In order that the baking oven may be of reasonable length and yet complete the baking, it is desirable that the sheet be returned through the oven, so as to pass two or more times through the. oven until the coating is final1y hardened. This repassage may be efiected by equipment including a change of direction roller over which the sheet is passed before it is returned through the oven. Many of the finishing compositions, however, are soft at the elevated temperature of the baking oven. Passage of the sheet with the coating composition in soft condition over a roller would lead therefore to marring of the surface of the composition.

The present invention provides an effective method of overcoming this difficulty and also cooling the surface of the partially set finishing composition, so that it may be passed over a smooth roller, while the under parts of the composition are in warmer and therefore more readily yieldable condition than the surface.

As a result the surface may be smoothed against a yielding backing layer of the enamel. The invention provides also means of decreasing heat loss from the baking oven.

Briefly stated, the invention comprises the herein described apparatus and method including a combination of means for moving an article in coated. condition continuously through a baking oven, through an opening in a wall of the oven, and over a roller, and means for directing a stream of cooling air against the surfaces of the roller and the coated article so as to cool not only the roller but also the coating continuously from the time of emergence from the oven up to and including the time of passage over the roller, this cooling causing hardening of the surface of the coating more than the interior thereof.

In the preferred embodiment, the invention comprises an upright baking even provided with a plurality of spaced openings in the top thereof, a roller disposed above the openings, a hood ntting over the upper end or the oven in substantially air-tight manner and communicating with the said openings, means for drawing the coated flexible article continuously through the oven upwardly through one of the said openings, then over the roller, and then downward through another of the openings, and a blower for maintaining within the hood a pressure of air somewhat greater than the pressure of warm air at the level of the said openings and also for directing a stream of cold air against the roller and the coated flexible article at a position between the first opening and the roller.

The invention comprises also the method of finishin which comprises chilling the surface of a hot finishing composition applied to a flexible article, the composition being hardenable by cooling, and then passing the article with adhered coating and cooled surface over the roller.

The invention will be further illustrated by description in connection with the attached draw- Fig. 1 is a side view partly diagrammatic and partly in section of a preferred form of my app-aratus.

Fig. 2 is a sectional View of the coated sheet of Fig. 1 exaggerated in thickness as compared to the Width of the sheet, so as to show more clearly the normally thin coating on the sheet.

There are shown a bakin oven 2 provided in its upper end with spaced openings 4 and seated at its lower end on any conventional type of structure such as the roof of a building (not shown) through which a hole has been cut to match the dimensions of the lower end of the baking oven.

Fitting upon the upper end of the oven is a hood or enclosure 6. This forms a chamber that is substantially closed or air-tight except for the fact that the chamber is in communication with the openings 4.

Disposed within this chamber is the change of direction roller 8 mounted suitably upon a shaft and either driven by conventional means which are not shown or turned by friction of the article passing over the roller. The roller may be faced with a usual type of fabric cover (not shown).

The article being coated is an elongated flexible member it] that may be for instance a thin sheet of flexible steel. This article is coated in a usual manner with coating II, as by being passed through a conventional coating machine (not shown) before it is drawn into and upward through the baking oven.

A blower l2 delivers a stream of air, as through the open end delivery pipe l4, against the face and back of the coated sheet at all positions between that of emergence of the sheet from one of the openings 4 in the upper wall or top of the oven, up to and including contact with the roller 8. The blower is so selected that it will create within the chamber 6 a pressure somewhat greater than the upward pressure .of the Warm air at the position of the openings 4, so that movement of air through the openings is downward.

Temperatures within the oven are maintained by a usual type of heating or baking equipment. Thus there may be used an electrical heater 10 including means for withdrawing some air from the baking oven, passing this air upwardly through the heater, and returning the thus heated air to the oven.

Various dimensions may be used. The height of one baking oven which I have used to advantage is 40 feet.

A typical pressure within the chamber 6 is that equal to the pressure of an inch or two of water above the upward pressure of the hot gas at the top of the baking oven.

The positive pressure of cold air in chamber 6 causes sealing of the openings 4 against upward movement of hot gases and attendant heat loss through the openings 4. 1

Furthermore, the movement of cold air against the surface of the coated member after emergence from the oven gives a differential cooling of the coating composition so that the surface becomes non-sticky before it passes over the roller 8, whereas the under portions of the enamel are warmer and somewhat yieldable, so as to promote smoothing of the coating without sticking to the roller.

Temperatures within the baking oven are those that are usual for the particular coating composition selected. Thus, temperatures with a baking enamel may be 250 to 400 F. and with some compositions ma vary, for exampl fr m 200 to 1000 F. .It will be understood that, for a given coating composition, the selected temperatures for baking, that is, baking or drying, are usually made higher for higher speeds of movement of the article through the oven.

In a typical operation, thin sheet steel is passed through coating equipment of usual kind (not shown) which applies oleo-resinous finishes and then is drawn upwardly through the baking oven, through the opening, over the roller 8, downwardly, through the other of the openings, through the baking oven again, and out. It may then be cut into pieces of desired size or recoiled for use subsequently. A typical rate of movement of the strip metal through the baking oven is 100 to 200 feet a minute, at a temperature of the oven of 400 to 500 F. maintained by means of a proper setting of conventional heating equipment.

After emergence from the final passage through the baking oven, the coating on the metal sheeting is set and, when cool, is hard and smooth of surface. Furthermore the coating is practically uniform in thickness.

In place of the finishing material described, there may be used other finishing compositions as, for instance, air drying lacquers or enamels (these being force dried) and those having a base of alkyd or urea resins with drying oils, phenolformaldehyde lacquers and enamels, vinyl resin finishes, and others that when partially or fully set are thermoplastic, that is, soft when hot. These compositions as first applied to the sheet metal may be cut with a usual solvent or thinner or may be softened by heat to flowable condition, an in accordance with usual practice for the particular coating composition selected.

In place of the sheet metal that has been used in the illustrative example, there may be used wire, woven wire screen, paper, cloth, sheets or webs of plastic material, or the like, provided the article is sufiiciently flexible to be flexed over the roller 8.

Also my apparatus and method may be employed in heat treating flexible material, particularly sheet metal or wire carrying a tin, zinc, or other coating to be smoothed or otherwise modified by the heat treatment.

In place of air within the oven, there may be used nitrogen, carbon dioxide, or other gas conveniently used in connection with the heat treatment of a given kind of material. In such case, the blower should deliver the same kind of gas.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departure from the spirit and scope of the invention.

What is claimed is:

Apparatus for hardening a coating of heathardenable finishing material on strip metal, the apparatus comprising a gas-filled, heated oven, a wall of the oven provided with openings of size somewhat larger than the cross section of the coated strip metal, an enclosure forming with the said wall an air space, an inlet for air to the said space, the space being closed except for the said openings and inlet, a roller, means mounting the roller within the said space, means for drawing the coated strip metal in succession through the said oven, through one of the said openings and over the roller, and then through another of the said openings, and means for introducing air through the said inlet and delivering it to a position between the said one of the openings and the said roller and at a positive pressure above that of the gas in the oven at the level of the said openings, the said openings during use of the apparatus permitting free escape of the air through them and round the heated strip material.

ROBERT A. LIEBEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 273,013 Bedford Feb. 27, 1883 806,270 Lubbertsmeier Dec. 5, 1905 1,296,010 Robinson Mar. 4, 1919 1,632,760 Jones June 14, 1927 1,799,375 Jones Apr. 7, 1931 2,065,636 Whipple et al Dec. 29, 1936 2,273,740 Terry Feb. 17, 1942 2,316,984 Boockel Apr. 20, 1943 2,362,309 Ross Nov. 7, 1944

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