Claims
- 1. A method for the direct white enameling of steel parts using a single enamel coating particularly suited for the direct white enameling of steel parts of the type comprising steel sheets of aluminum stabilized continuously cast sheet material, said method comprising the steps of:
- applying a single coating of an enamel slurry to the surface of the steel part to be enameled;
- drying the slurry on the slurry coated steel part;
- degasifying substantially simultaneously the slurry and the steel part coated with the slurry by heating the slurry coated steel part to a degasifying temperature which degasification temperature is at a temperature less than the firing temperature of the enamel coating wherein the slurry coated steel part is held within the degasifying temperature range for a time period sufficient to diffuse hydrogen gas from the steel part and the slurry coating, said diffused hydrogen gas passing from the steel part through the unfired enamel slurry coating to the atmosphere;
- firing the degasified enamel slurry coating on the degasified steel part by increasing the temperature of the degasified enamel slurry coated steel part to the enamel firing temperature directly from the degasifying temperature without cooling the degasified slurry coated steel part between the degasifying step and the firing step;
- maintaining the temperature of the slurry coated steel part at the enamel firing temperature for a time period sufficient to fire the single enamel coating, and
- cooling the fired enamel coated steel part wherein the temperature of the fired enamel coated steel part is lowered from the enamel firing temperature to a lower cooling temperature during a predetermined cooling time interval.
- 2. A method for the direct white enameling of steel parts using a single enamel coating as defined in claim 1 wherein the degasifying step includes maintaining the heated slurry coated steel part within the degasifying temperature range of 680.degree. C. to 760.degree. C. for two (2) to six (6) minutes.
- 3. A method for the direct white enameling of steel parts using a single enamel coating as defined in claim 1 wherein the degasifying step includes maintaining the heated slurry coated steel part at the degasification temperature of 720.degree. C. for three(3) to five(5) minutes.
- 4. A method for the direct white enameling of steel parts using a single enamel coating as defined in claim 2 wherein the enamel firing step includes firing the enamel coated steel part at a firing temperature of 800.degree. C.
- 5. A method for the direct white enameling of steel parts using a single enamel coating as defined in claim 2 wherein the enamel firing step includes firing the enamel coated steel part at a temperature within the range of 810.degree. C. to 840.degree. C.
- 6. A method for the direct white enameling of steel parts using a single enamel coating particularly suited for the direct white enameling of steel parts of the type comprising steel sheets of aluminum stabilized continuously cast sheet material, said method comprising the steps of:
- applying a single coating of an enamel slurry to the surface of the steel part to be enameled;
- drying the slurry on the slurry coated steel part;
- degasifying substantially simultaneously the slurry and the steel part coated with the slurry by heating the slurry coated steel part to a degasifying temperature which degasification temperature is at a temperature less than the firing temperature of the enamel coating wherein the slurry coated steel part is held within the degasifying temperature range of 680.degree. C. to 760.degree. C. for two(2) to six(6) minutes to diffuse hydrogen gas from the steel part and the slurry coating, said diffused hydrogen gas passing from the steel part through the unfired enamel slurry coating to the atmosphere;
- preventing the heated enamel slurry coated steel part from being cooled after the degasifying step and prior to an enamel firing step;
- firing the degasified enamel slurry coating on the degasified steel part by increasing the temperature of the degasified enamel slurry coated steel part to the enamel firing temperature;
- maintaining the temperature of the slurry coated steel part at the enamel firing temperature of 800.degree. C. for a time period sufficient to fire the single enamel coating, and
- cooling the fired enamel coated steel part wherein the temperature of the fired enamel coated steel part is lowered from the enamel firing temperature to a lower cooling temperature during a predetermined cooling time interval.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 3400619 |
Nov 1984 |
DEX |
|
Parent Case Info
This is a continuation of co-pending application Ser. No. 689,390 filed on Jan. 7, 1985 now abandoned.
The invention concerns a method for firing enamel on steel parts, especially on steel sheet of aluminum stablized continuously cast steel material and an enameling oven with a firing zone and an inlet zone serving as a prewarming zone for the firing of enamel, especially on steel parts, for carrying out the process.
Methods for enameling steel parts and steel sheet are known in different forms and enameling ovens are also known. A disadvantage both with direct white enameling as well as with base and superimposed layer enameling is the formation of so called blow-outs which most usually are observed at welding seams, cut edges, and radii of the parts to be enameled. Such blow-outs especially appear at welded seams in the direct enameling of aluminum stablized sheet, for example continuously cast thin sheet subsequently decarbonized in open coil. After the firing of the enamel open pockets appear in the enamel layer at the welded seam which commonly are referred to as blow-outs.
Another typical fault recognized on enameled steel surfaces is generally referred to as fish scales. Such fish scales are caused by the release of hydrogen from the material of the workpieces. An especially unpleasant characteristic of this release of hydrogen is that it often first appears weeks after the firing of the enamel so that the fault containing parts are already assembled with other parts or are already packaged. Thus the faults may be first detected by customers. To avoid the mentioned faults on enameled steel parts or sheets very often only steel parts of special quality are used or the workpieces are enameled on only one side so that released substances, for example hydrogen, can escape from the non-enameled surface. In case of dip enameled workpieces these possibilities do not exist and moreover for corrosion protection an enameling of all sides of the workpieces is very often required. In these cases therefore only expensive special steel was previously used. Blow-outs and fish scales are examples of typical enamel faults which are grouped under the heading "hydrogen faults". Hydrogen unavoidablly arises during the firing process from the enamel frit and is absorbed by the steel. During the cooling process the hydrogen partially escapes. Some remains however, depending on the cooling conditions, the thickness of the sheet etc. as well as on the room temperature supersaturated condition of hydrogen in steel.
For avoiding enamel failures caused by hydrogen Dietzel[1]recommends bringing as little possible water vapor into contact with the red hot steel plate and to allow the hydrogen still in the steel to diffuse out of it during a long cooling period, or to hold it as H.sub.2 in the smallest of hollow spaces. The named measures do not however give the slightest hint as to the described features of the invention.
The invention has as an object the provision of a method of the foregoing type by means of which the mentioned faults at welding seams, cut edges and radii of enameled parts are avoided, especially in the case of direct white enameling of aluminum stablized thin sheet made of continuously cast steel. The invention has as a further object the provision of an enameling oven for firing enamel in the carrying out of the process of the invention.
These objects are solved in accordance with the invention in that the heating of the steel part or steel sheet to the firing temperature, before reaching the firing temperature the heating is interrupted, in that the hydrogen dissolved in the steel is released during the time of the interruption, in that the steel part subsequently is heated further to the firing temperature, is held at this temperature and then is cooled in a known way. The enameling oven of the invention is so built that between the firing zone and the prewarming zone a degasing zone is interposed in which the workpieces coated with enamel are held for a certain minimum time at a certain temperature. Further advantageous refinements of the inventive method as well as the enameling oven are apparent from the following description as well as from the dependent claims.
The advantage of the method of the invention as well as of the enameling oven is especially to be seen in that certain types of faults, produced by a gas from the steel used, especially the hydrogen content of the steel parts or sheet to be enameled, are avoided. Moreover additional costly special measures in the manufacture of the steel are avoided in relatively simple manner.
The invention is explained hereafter in comparison to the state of the art in connection with preferred embodiments explained in detail.
US Referenced Citations (8)
Foreign Referenced Citations (3)
| Number |
Date |
Country |
| 2257280 |
Jun 1973 |
DEX |
| 624967 |
Jun 1949 |
GBX |
| 626008 |
Jul 1949 |
GBX |
Non-Patent Literature Citations (1)
| Entry |
| Deringer, "Relation of Hydrogen to Adherence of Sheet Enamels", J. of the American Ceramic Society, vol. 26, No. 5, pp. 151-159, May 1, 1943. |
Continuations (1)
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Number |
Date |
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| Parent |
689390 |
Jan 1985 |
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Patent Grant
4707385
