EP3839099A1

EP3839099A1 - Manufacturing process for enamel container and enamel container

Info

Publication number: EP3839099A1
Application number: EP19835216.3A
Authority: EP
Inventors: Victortsangtong LIEN
Original assignee: Sohome Houseware Nanjing Co Ltd
Current assignee: Sohome Houseware Nanjing Co Ltd
Priority date: 2019-10-25
Filing date: 2019-10-28
Publication date: 2021-06-23
Also published as: WO2021077445A1; CN110625535A; KR20230002019A; EP3839099A4

Abstract

The invention discloses a manufacturing method -of an enameled container and an enameled container, wherein the manufacturing method comprises the following steps: removing oil stains on the inner wall of the metal container; sandblasting the inner wall of the metal container; electrostatically spraying glaze powder on the inner wall of the metal container; and placing the metal container in a sintering furnace for sintering. The enamel layer of the enameled container obtained by the manufacturing method of enameled container has uniform thickness and smooth surface and is free of the defects of charring, porcelain chipping, powder deposition and the like.

Description

Field of the invention

The present invention relates to the field of enamel manufacturing, in particular to a manufacturing method of an enameled container and an enameled container.

Background of the invention

An enameled container is an apparatus formed by melting an inorganic material to a metal surface of a substrate and firmly bonding to the metal, wherein the container comprises a base and side walls surrounding the base, such as a cup and the like. The conventional enamel preparation method comprises the steps of glaze preparation, green body preparation, enameling, drying, sintering, inspection and the like. The glaze is prepared by mixing dry glaze powder such as silicate, boron oxide, aluminum oxide, alkali metal oxide and the like with water in advance to form glaze slurry, and enameling is that the glaze slurry is coated on the surface of the green body. The defects of the prior art are as follows: (1) glaze slurry is often not uniformly coated on the green body, resulting in uneven thickness of the enamel; (2) the drying process occupies the manufacturing time, and prolongs the production cycle; (3) sometimes the drying is insufficient and cracks easily occur during the sintering process.

Summary of the invention

In order to solve the defects in the prior art, the present invention provides a method for manufacturing an enameled container, which comprises the following steps:

S1: removing oil stains on the inner wall of the metal container;
S2: sandblasting the inner wall of the metal container;
S3:electrostatically spraying glaze powder on the inner wall of the metal container;
S4: placing the metal container in a sintering furnace for sintering.

The invention has the beneficial effects that: enamel powder is coated in an electrostatic manner, the thickness of the enamel is uniform, the surface is smooth, the defects of porcelain chipping, powder accumulation and the like are avoided, and the production efficiency is improved by electrostatically spraying glaze powder; the drying process is eliminated, the quality of the enameled container is improved, and the process flow is shortened.
In certain embodiments, in step S1, the oil stains on the inner wall of the metal container is removed by a heating method at a heating temperature of 400-450°C and a heating time of 30 minutes. The beneficial effect of the invention is that oil stains can be removed cleanly and environmentally.
In certain embodiments, in step S2, the surface roughness Ra of the sandblasted container body is not less than 2. The invention has the beneficial effect of facilitating the adhesion of glaze powder to the inner wall of the metal container.
In certain embodiments, the sandblasting is performed using No. 46 emery, the air pressure of the sandblasting is not less than 0.6 MPa, and the sandblasting time is 35-50 seconds. The beneficial effect is that the inner wall of the metal container can obtain suitable surface roughness.
In certain embodiments, the thickness of the glaze layer on the surface of the container body is from 100 to 150µm.
In certain embodiments, electrostatically spraying glaze powder is carried out with an electrostatic spray gun at a voltage of 30-60kV, a current of 20-30µA, and an atomizing gas pressure of 2-4MPa. The method has the beneficial effects that the powder coating rate is high, and the powder coating is uniform.
In certain embodiments, the container opening of the metal container faces upward and the electrostatic spray gun is tilted toward the inner wall of the metal container which rotates about its central axis. The method has the beneficial effects that the compressed air sends the glaze powder into the metal container. When the metal container rotates, the glaze powder carrying the static charge can be adsorbed around the inner wall of the metal container, the glaze powder can completely cover the inner wall of the metal container, and the glaze powder coating efficiency is also improved.
In certain embodiments, the electrostatic spray gun swings in a vertical direction. The apparatus has the beneficial effects that the scanning of the glaze powder spraying cone on the inner wall of the metal container is realized, the uniformity of powder coating is improved, and a higher powder coating rate and a higher powder coating uniformity can be achieved at the corner position where the side wall of the container is connected with the bottom of the container.
In certain embodiments, the sintering temperature is 820 ± 10°C and the chain speed is 2 meters per minute. The invention has the beneficial effect that a good sintering effect is achieved.
According to another aspect of the present invention, an enameled container prepared by the enameled container manufacturing method is provided. The enameled container is smooth in surface and free of the defects of charring, porcelain chipping, powder deposition and the like.

Brief description of the drawings

Figure 1 is a flow diagram of one embodiment of the present disclosure.
Figure 2 is a schematic diagram of an electrostatically spraying dry powder system used in one embodiment of the present disclosure.
Figure 3 is a schematic diagram of an electrostatically spraying dry powder system used in another embodiment of the present disclosure.
Figure 4 is an illustration of the location of points taken for thickness measurements of the enameled container made in accordance with one embodiment of the present disclosure.

Detailed description of the invention

According to one aspect of the present disclosure, a method for manufacturing an enameled container is provided, with reference to Figure 1, comprising the following steps:

S1: removing oil stains on the inner wall of the metal container;
S2: sandblasting the inner wall of the metal container;
S3: electrostatically spraying glaze powder on the inner wall of the metal container;
S4: placing the metal container in a sintering furnace for sintering.

Oil stains on the inner wall of the metal container are removed, so that on one hand, the oil stains on the inner wall of the metal container can be prevented from reducing the adsorption force of the glaze powder on the wall of the container, and on the other hand, the oil stains can be prevented from decomposing into gas and forming gas hole defects or causing the glaze powder to fall off during sintering. In certain embodiments, heating method is used to remove oil stains from the inner walls of the metal container. And setting the opening of the metal container upright, heating the container to a certain temperature, and evaporating and decomposing the oil stains on the inner wall of the metal container. Specifically, in the step of heating and degreasing the metal container, the heating temperature is from 400 to 450°C, the heating time is at least 30 minutes. Under the condition, the oil stains on the inner wall of the metal container can be removed completely. In certain alternative embodiments, an organic solvent may also be used to dissolve the oil stains, although the method has low efficiency in removing the oil stains and the organic solvent may cause environmental pressure, it is also capable of removing the oil stains.
The purpose of the sandblasting is to increase the roughness of the inner wall of the metal container and improve the adhesion of glaze powder and enamel on the inner wall of the metal container. In addition, sandblasting can also remove impurities from the inner wall. For example, the roughness Ra of the inner wall of the metal container after sandblasting is not less than 2. The inner wall having the roughness value facilitates adhesion between the glaze powder and the inner wall of the metal container. In particular, No.46 emery is used for sandblasting, the air pressure of the sandblasting is not less than 0.6MPa, the sandblasting time is 35-50 seconds, and under these conditions, the inner wall of the metal container can obtain suitable surface roughness.
The electrostatically spraying glaze powder is realized by an electrostatic glaze powder spraying system, and referring to Fig. 2, the electrostatic glaze powder spraying system comprises an electrostatic spray gun 1, a powder supply system 2 and a rotatable carrier 3. The electrostatic spray gun 1 and the powder supply system 2 may be of the prior art. For example, a high-voltage generating device is arranged in the electrostatic spray gun 1, a needle-shaped electrode electrically connected with the high-voltage generating device is arranged at the outlet of the electrostatic spray gun 1, and an auxiliary air inlet is arranged on the electrostatic spray gun 1. And the powder supply system 2 is connected with the electrostatic spray gun 1 through a hose 5. The powder supply system 2 mainly comprises a powder barrel, a fluidized bed and a venturi powder pump. Air is blown into the powder barrel, the powder in the powder barrel is fluidized through the fluidized bed, and the fluidized powder is pumped by the venturi powder pump to form powder flow which is conveyed into the electrostatic spray gun 1 through the hose 5. During operation, air is input from the auxiliary air inlet of the electrostatic spray gun 1 to atomize glaze powder, the needle-shaped electrode is connected with a negative electrode, the high-voltage generating device releases high voltage to the needle-shaped electrode so that it discharges, and the atomized glaze powder is electrostatically charged. The carrier 3 is used for fixing the metal container 4 and driving the metal container 4 to rotate around the central axis of the metal container 4. The carrier 3 is made of a conductive metal material, the metal container 4 is in electrical communication with the carrier 3, and the carrier 3 is grounded. The end of the metal container is grounded, so that an electric field is formed between the spray gun and the metal container, the electrostatically charged glaze powder reaches the inner wall of the metal container 4 under the double pushing of electric field force and the compressed air pressure, and the electrostatic attraction is carried out on the inner wall of the metal container 4 to form a uniform layer of glaze powder. Preferably, the thickness of the glaze power layer on the surface of the container is from 100 to 150µm.
In certain embodiments, the electrostatic voltage of the electrostatically spraying glaze powder is 30-60 kV, the electrostatic current of the electrostatically spraying glaze powder is 20-30 microamperes, and the spray gun atomization pressure is 2-4 MPa. If the electrostatic voltage is too high, the glaze powder rebounding and pitting on the edge are easily caused, and if the electrostatic voltage is too low, the powder coating rate is low. Excessive electrostatic current is easy to generate discharge which can break down powder coating, and too low current can cause low powder coating rate. The atomizing air pressure of the spray gun provided by the embodiment of the invention can enable the thickness of the glaze powder layer to be uniform.
In certain embodiments, the container opening of the metal container faces upward and the electrostatic spray gun is tilted toward the inner wall of the metal container, the metal container rotates about its central axis. In the electrostatic spraying process of glaze powder, the container opening of the metal container faces upwards, the electrostatic spray gun is arranged above the metal container and obliquely faces the inner wall of the metal container, compressed air sends glaze powder into the metal container, when the metal container rotates, the glaze powder carrying electrostatic charge can be adsorbed around the inner wall of the metal container, the glaze powder can completely cover the inner wall of the metal container, and the powder coating efficiency is also improved.
Furthermore, the electrostatic spray gun swings in the vertical direction. The powder-gas mixture sprayed from the spray gun is in the shape of a cone, and the electrostatic spray gun slowly swings clockwise or anticlockwise, so that the spray cone scans the inner wall of the metal container up and down. For example, in the embodiment shown in Figure 3, the dashed line of the electrostatic spray gun represents the initial position of electrostatic spray gun and the solid line of the electrostatic spray gun represents the position of the electrostatic spray gun after swing. In the radial direction of the spray cone, the distribution density of the glaze powder near the center of the spray cone is higher, but far away from the center of the spray cone, the distribution density of the glaze powder is lower. For the container with higher height, in order to enable the glaze powder to be uniformly coated, the spray gun swings to realize that the spray cone scans on the inner wall of the metal container so as to improve the uniformity of powder coating, and the corner position where the side wall of the container is connected with the bottom of the container can also achieve higher powder coating rate and higher powder coating uniformity.
In certain embodiments, the sintering temperature is 820±10°C and the chain speed is 2 meters per minute. After the dry powder is sprayed by electrostatic spraying, the metal container is hung on the sintering frame. During the process, the container should be lightly held and lightly hung, and the green body cannot be damaged. A continuous tunnel kiln is adopted for sintering, the metal container moves at the speed of 2m/min, which can avoid the falling of glaze powder. The sintering time in a continuous tunnel kiln is typically 6-7 minutes.
In accordance with one aspect of the present disclosure, an enameled container prepared by the manufacturing method described herein is provided. The enameled container disclosed by the invention has the advantages of smooth surface and no defects of charring, porcelain chipping, powder deposition and the like.

Example 1

The metal container of this embodiment is a stainless steel container. It has a height of 10 cm and a cylindrical side wall. The stainless steel container was placed in a heating furnace and heated for 30 minutes at a temperature of 400°C. After the stainless steel container is cooled, the inner wall of the stainless steel container is sandblasted with No.46 emery, the air pressure of sandblasting is 0.6MPa, and the sandblasting time is 35 seconds. The roughness of the inner wall of the stainless steel container is measured to be Ra2. The electrostatic glaze powder spraying process comprises the following steps:

S311: providing an enameled container electrostatically spraying glaze powder system, wherein the system comprises an electrostatic spray gun and a carrier capable of rotating;
S312: fixing a metal container on a carrier, wherein the metal container is electrically communicated with the carrier, and the carrier is grounded;
S313: adjusting the inclination angle of the electrostatic spray gun to enable the outlet of the electrostatic spray gun to face the vicinity of the middle of the inner sidewall of the metal container;
S314: rotating the carrier at a rotation speed of 5 revolutions per minute, spraying glaze powder on the inner wall of the stainless steel container by the electrostatic spray gun, wherein the voltage is 30kV, the current is 20µA, and the air pressure of the spray gun is 2MPa.

Sintering the stainless steel container obtained by electrostatically spraying glaze powder in a high-temperature furnace, wherein the sintering temperature is 820±10°C, the chain speed is 2 meters per minute, and after the sintering, the enameled container is obtained.
Four positions of the enameled container are selected, and the thicknesses of the enamel layer of the four positions are measured. The selected four positions are respectively the A position near the upper end of the container wall, the B position at the middle of the container wall, the C position at the lower end of the container wall, and the D position at the middle of the bottom of the container. The thickness of the enamel layer is calculated by subtracting the thickness of the metal container when it is not enameled from the thickness of the enameled container. The thickness of the enamel layer at the four positions is 115µm, 117µm, 115µm, and 116µm respectively, and the data reflected the present embodiment's uniformity of the powder coating on the enameled container.

Example 2

The metal container of this embodiment is featured as a stainless steel container. It has a height of 20 cm and a cylindrical side wall. The stainless steel container was placed in a heating furnace and heated for 30 minutes at a temperature of 450°C. After the stainless steel container is cooled, the inner wall of the stainless steel container is sandblasted with No.46 emery, the air pressure of sandblasting is 1MPa, and the sandblasting time is 50s. The roughness of the inner wall of the stainless steel container is measured to be Ra3.2. The electrostatically spraying glaze powder process comprises the following steps:

S321: providing an enameled container electrostatically spraying glaze powder system, wherein the system comprises an electrostatic spray gun and a carrier capable of rotating;
S322: fixing a metal container on the carrier, wherein the metal container is electrically communicated with the carrier, and the carrier is grounded;
S323: adjusting the inclination angle of the electrostatic spray gun to enable the outlet of the electrostatic spray gun to face the vicinity of the upper part of the inner side wall of the metal container;
S324: rotating the carrier at a rotation speed of 5 revolutions per minute, spraying glaze powder onto the inner wall of the stainless steel container by the electrostatic spray gun, wherein the voltage is 60kV, the current is 30µA, and the atomization air pressure is 4MPa;
S325: the electrostatic spray gun is swung in a vertical plane at a rate of 0.5 revolutions per minute. When the electrostatic spray gun is swung to the end point, its outlet faces the center of the bottom of the metal container, and it is then swung in the reverse direction, and the cycle repeats.

Sintering the stainless steel container obtained by electrostatic spraying glaze powder in a high-temperature furnace, wherein the sintering temperature is 820±10°C, the chain speed is 2 meters per minutes, and after the sintering, the enameled container is obtained.
Selecting four positions of the enameled container, and measuring the thickness of the enamel layer at the four positions, wherein the selected four positions are respectively a position close to the upper end of the container wall, a position at the middle of the container wall, a position at the lower end of the container wall and a position at the middle of the bottom of the container. The thickness of the enamel layer is calculated by subtracting the thickness of the metal container when it is not enameled from the thickness of the enameled container. The thickness of the enamel layer at the four positions is 136µm, 135µm, 136µm, and 137µm respectively. The data reflected the present embodiment's uniformity of the powder coating on the enameled container.
What have been described above are only some embodiments of the invention. It will be obvious to those skilled in the art that various changes and modifications can be made without separating from the inventive concepts herein, which fall within the scope of the invention.

Claims

An enameled container manufacturing method is characterized by comprising the following steps:
S1: removing oil stains on the inner wall of a metal container;

S2: sandblasting the inner wall of the metal container;

S3: electrostatically spraying glaze powder on the inner wall of the metal container;

S4: placing the metal container in a sintering furnace for sintering.
The enameled container manufacturing method according to claim 1, characterized in the step S1, oil stains on the inner wall of the metal container are removed by a heating method, the heating temperature is 400-450 °C, and the heating time is at least 30 minutes.
The enameled container manufacturing method according to claim 1, characterized in the step S2, after sandblasting, the surface roughness Ra of the container body is not less than 2.
The enameled container manufacturing method according to claim 3, characterized in that sandblasting is performed with No.46 emery, the air pressure of the sandblasting is greater than or equal to 0.6MPa, and the sandblasting time is 35-50 seconds.
The enameled container manufacturing method according to claim 1, characterized in that the enamel layer on the surface of the container body has a thickness of 100-150µm.
The enameled container manufacturing method according to claim 1, characterized in the step S3, electrostatically spraying glaze powder is performed with an electrostatic spray gun, the voltage of electrostatically spraying glaze powder is 30-60kV, the current is 20-30µA, and the atomizing pressure is 2-4 MPa.
The enameled container manufacturing method according to claim 6, characterized in that the container opening of the metal container faces upwards, the electrostatic spray gun is inclined toward the inner wall of the metal container, and the metal container rotates about its central axis.
The enameled container manufacturing method according to claim 6, characterized in that the electrostatic spray gun swings in a vertical direction.
The enameled container manufacturing method according to claim 1, characterized in that the sintering temperature is 820 ± 10°C and the chain speed is 2 meters per minute.
Enameled container, characterized in that it is prepared by the enameled container manufacturing method according to any one of claims 1-9.