US2338438A

US2338438A - Apparatus for coating sheet metal

Info

Publication number: US2338438A
Application number: US363652A
Authority: US
Inventors: John D Keller
Original assignee: Wean Engineering Co Inc
Current assignee: Wean Engineering Co Inc
Priority date: 1940-10-31
Filing date: 1940-10-31
Publication date: 1944-01-04
Anticipated expiration: 1961-01-04

Description

Jan. 4, 1944. J. D. KELLER APPARATUS FOR COATING SHEET METAL 2 Sheets-Sheet 1 Filed Oct. 31, 1940 H W Q? 0% Q m w ,l w 5 a 5 Fig. 2A.

25 INVENTOR v (la/7n D. /\e//e/" Z2 [Z7 v m M 46% Jan. 4, 1944. J. D. KELLER 2,338,438

APPARATUS FOR COATING SHEET METAL Filed Oct. 51, 1940 2 Sheets-Shet 2 INVENTOR (70/70 0. Kefler Patented Jan. 4, 1944 UNITED STATES PATENT OFFICE APPARATUS FOR COATING SHEET METAL John D. Keller, Pittsburgh, Pa., assignor to The wean Engineering Company, Inc., Warren, Ohio, a corporation of Ohio Application'october 31, 1940, Serial No. 363,652

(Cl. ill-12.5)

4 Claims.

This invention relates to the coating of sheet or strip metal and, particularly, to the tinning of steel sheets.

It is desirable for various reasons that the protective coating of tin applied to steel sheets or strip be as thin as possible. One of these reasons, of course, is the cost of the tin itself. Another reason is that a thin coating exhibits better adherence than a thick coating under deformation of the coated material.

It is the general belief that the tin coat on a steel sheet includes a bottom alloy layer and an outer layer of tin several times thicker than the alloy layer. Attempts have been made heretofore to reduce the thickness of the tin layer by increasing the pressure exerted on the coated strip by the exit rolls of the conventional tinning apparatus. It has been found, however, that when the adjustment of the exit rolls is such as to reduce the amount of tin applied to the sheets below about 1.35 pounds per base box, the surfaces of the tin sheets are not uniformly bright in appearance, but, instead, are dull and streaky. This condition, known as scruff streaks or bands, appears to be the result of wiping off the tin layer clear down' to the alloy layer. Regardless of its cause, it precludes the sale of the coated sheets as prime material. For this reason, it has been generally believed that the thickness of the tin layer cannot be reduced much below that corresponding to a. total weight of tin per base box of about 1.35 pounds.

I have invented a novel apparatus whereby the thickness of the layer of pure tin formed on steel sheets or strip by passage through a bath of molten tin or by some other method of applying molten tin may be reduced considerably below that usually obtained heretofore, without producing scruff streaks. In a preferred embodiment and practice of the invention, I subject the material emerging from the bath of molten tin to the action of a pair of wiping members each including a flexible wall. I am thus able to exert enough pressure on the emerging sheet to wipe off more of the excess tin than it has been possible to remove heretofore but at the same time, I avoid solid contact between the wiping members and the material and thereby prevent removal of the tin clear down to the alloy layer which would produce scruff streaks as explained above. The wiping surfaces are preferably urged against the coated sheet passing therebetween under fluid pressure which can be accurately controlled and is uniform at all points.

The wiping members are immersed in a palm oil bath floating on the tin bath, as in the conventional tin pot. The palm oil being at substantially the same temperature as the molten tin, keeps the tin coating on the sheets or strip fluid while it is subjected to the action of the wiping members. The latter may take the form of hollow rolls having their bodies formed of thin, flexible material or may be constituted by elongated box-like members having one wall composed of such material. Further details of the apparatus of .my invention will become apparent during the following complete description and explanation which refers to the accompanying drawings illustrating a typical form and practice. In the drawings:

Fig. 1 is a longitudinal central, vertical section through a tin pot which is largely of conventional design but is modified to embody my invention;

Fig. 2 is a portion of Fig. 1 enlarged considerably to illustrate diagrammatically the manner in which the apparatus functions to remove excess tin;

Fig. 2a is a plan view of the wiping rolls and backing rolls therefor;

Fig. 3 is a view similar to Fig. 2 showing a modified construction;

Fig. 4 is a similar view showing a still further modification; and

Fig. 5 is a diagram of the piping employed in connection with the. modification of Fig. 4.

Referring now in detail to the drawings, a tin pot I0 is largely of conventional construction, including feed-in rolls ll, l2 and I3 and guide rolls l4 journaled in spaced side frames IS, the side frames I5 being removably disposed in the entering end of the pot l0.

In the exit end of the pot l0, side frames l6 are disposed having feed rolls l1 journaled therein. Wipers ll engage the rolls I! to remove any solidified particles or tin-iron crystals which may adhere thereto. A curved guide plate l8 extends through an opening in the center wall [9 of the pot to direct a sheet from the rolls l3 to the rolls I1. Above the'roll I'I, wiping rolls 20 are disposed in pairs, being journaled in the side frame IS. The rolls 20, as more clearly shown in Fig. 2, comprise body portions 2| having end closures 22 secured thereto. The end closures have bearing trunnions 23 projecting therefrom.

The body portions 2| of the rolls 20 are composed of thin-walled tubes sufficiently flexible to be deformed, as shown, under the wiping pressures exerted on the sheet metal emerging from the coating bath, as indicated at 24. To permit this deformation, the rolls are preferably constructed as shown in Fig. 2a, the end closures 23 being smaller than the roll bodies and the latter being contracted adjacent their ends.

Backing rolls 25 are journaled in the side frame l6 and engage the body portions of the'rolls 2G. The backing rolls on one side of the wiping rolls are journaled in bearing blocks 25 adjustable relative to the side frames by screws 21. 7

One of the rolls of each pair has a gear 28 thereon and is driven by a motor (not shown) through

gears

29 and 30, the latter meshing with one of the gears 28. The backing rolls may also be driven if desired. The rolls l1 preferably have a separate drive including a gear 3| mounted on one of the rolls and a gear 30a meshing therewith driven bya suitable motor. This permits the rolls 20 to be driven at a peripheral speed different from that of rolls I! if desired.

Above the wiping rolls, the apparatus i largely of conventional construction including converging guides 32, traction rolls 33 and a deflector 34. The emerging sheets are finally de-' livered down a chute 35 to suitable apparatus for further processing. Rolls 33 may be driven at a surface speed differing rolls 20, if desired.

The level of molten tin two sides of the pot II) at about the elevations indicated by chain lines 36. The level of the palm oil in the exit end of the pot is s milarly indicated at 37. The entire pot is disposed in a suitable setting 38 which may be of conventional construction. An immersion heater 39 is disposed in the entry end of the pot.

In order to cause the rolls 20 to exert suflicient pressure on the emerging sheet or strip 24, to remove the desired amount of surplus tin therefrom, I provide connections 40 cooperating with 'the bearing trunnions 23 to supply fluid under pressure to the interior of the wiping rolls. The bodies of the rolls 20 are, of. course, fluid-tight whereby the pressure exerted on the sheet may be controlled by varying the pressure of the fluid on the interior of the roll bodies. This pressure,

is maintained in the from that of the furthermore, is uniform throughout the length of the rolls.

Referring now particularly to Fig. 2, the sheet 24 as it leaves the tin bath carries an excessively thick adherent layer of molten tin 4|. The flexible-walled tubes may be made of very thin metal such as stainless steel or of a rubber composition suitable for withstanding the action of the temperature and the oil. The rolls 25 are preferably, but not necessarily, composed of non-tinning metal.

As the sheet or strip 24 ascends between the roll 20, the excess tin is wiped oil. as indicated at 43 and the strip emerges from the nip of the rolls with a very thin coating of tin indicated at 44. As clearly shown in Fig. 2, the rolls 20 do not make mechanical contact with the sheet or strip. At the same time, the pressure of the fluid such as air or oil -on the interior of-the rolls 20, may be regulated to equalize the fluid pressure exerted by the molten tin adhering to the sheet, for any desired thickness of tin coating on the finished sheet. The molten tin acts like a lubricant to maintain separation between the sheet and the rolls, the actual separation and hence the final thickness of the tin layer depending on the pressure maintained within the rolls 20 and the adjustment of the backing rolls '25.

Fig. 3 illustrates a modification wherein the rolls 20 are replaced by elongated box-like ento the other as by screws such as those shown at 21. The thickness of the tin coating on the finished product, however, is pref- It will be apparent that the rolls 20 and the box-like members 45 serve to wipe oil excess tin nated.

Fig. 4 illustrates a further modification generally similar to that of Fig. 3, except that the flexible walls 46' of the box-like members 45' have slots 47a therein and conduits 48 extending therealong through which hot palm oil may be discharged onto the sheet emergence from the pot, and means mounting said r the sheet metal through the bath, said device comprising a pair oi wiping members above the bath between which the sheet metal passes alter emerging from the bath, at least one of said wiping members being a roll having a body presented to the emerging sheet metal and composed of a tube of flexible metal deformable under the pressure or the molten coating metal adhering to the emerging sheet metal, and means mounting said roll for rotation at a peripheral speed difierent from that of the feed rollers.

,3. A device for removing excess coating material, for use in an apparatus for coating sheet metal including a tank for holding a bath of liquid coating material, and feed rollers for passing the sheet metal through the bath, said device comprising a pair of wiping members above the bath between which the sheet metal passe after emerging from the bath, at least one of said wiping members being a roll having a body presented to the emerging sheet metal and composed of a tube of flexible material deformable under the pressure of the coating material adherin to the emerging sheet metal, and means mounting said roll for rotation at a peripheral speed different 5 from that of the feed rollers.

4. A device for removing excess coating material, for use in apparatus for coating Sheet metal including means for conveying the sheet metal and means for forming a coating of liquid material thereon, said device comprising a pair of wiping members between which the strip passes after traversing the coating apparatus, at least one 01 said wiping members being a roll having a body presented to the ongoing sheet metal and composed of a tube of flexible material deformof the liquid coating material adhering to the sheet metal, and means mounting said roll for rotation at a peripheral speed different from that of said conveying 20 means.

JOHN D. KEIJLER.