| US5252273A | 1993-10-12 | |||
| GB2424610A | 2006-10-04 | |||
| CN215549536U | 2022-01-18 | |||
| US6409954B1 | 2002-06-25 |
| CLAIMS 1. A method of making a hollow ceramic article having different wall thicknesses at different sections by slip cast moulding comprising: preparing a mould in negative 3-dimensional configuration of said article wherein said mould comprises a plurality of sections; each section is disposed to contain moulding material within said section to substantially reduce overflow into adjacent sections for at least a predetermined period; said plurality of sections are allowed to set to form said mould integrally; allowing the set mould to dry; and slip casting said hollow ceramic article with the dried mould . 2. A method according to Claim 1 wherein the moulding material in each section are prevented from setting until all sections have been filled and ready to be set so as to form the mould integrally. 3. A method according to Claim 1 wherein adjacent sections are separated by a removable barrier (12) . 4. A method according to Claim 3 wherein the barrier (12) is removed upon each section' s moulding to allow the moulding material of adjacent sections to interface each other to facilitate integral setting of all sections to form an integral mould . 5. A method according to Claim 3 wherein the barrier (12) comprises set thin walls of the same moulding material as that of the mould. 6. A method according to Claim 3 wherein the barrier (12) is dissolvable upon contact with the admixture of moulding material being poured into said sections. 7. A method according to Claim 1 wherein the moulding material is prevented from setting by vibratory means. 8. A method according to Claim 1 wherein the moulding material in different sections of the mould has different absorption rate, with increasingly higher absorption rate toward the shank (26) section. 9. A method for making a mould for slip casting a hollow ceramic article having different wall thicknesses at different sections, said method comprising: preparing a mould in negative 3-dimensional configuration of said article wherein said mould comprises a plurality of sections; each section is disposed to contain moulding material within said section to substantially reduce overflow into adjacent sections for at least a predetermined period; said plurality of sections are allowed to set to form said mould integrally; allowing the set mould to dry. 10. A method according to any one of the preceding claims wherein the hollow ceramic article is a former for dip forming of thin-walled, elastic rubber articles. 11. A method according to Claim 10 wherein the former (20) is a hand glove former. 12. A mould made according to any one of Claims 9 to 11. 13. A hollow ceramic article made from a mould according to Claims 9 to 11. 14. The hollow ceramic article according to Claim 13 wherein the wall thickness of the ceramic article is thinnest at the finger section and thickest at the shank section, the wall thickness gradually increasing in thickness from finger (22) section to shank (26) section. 15. A thin-wall elastomeric article produced with a hollow ceramic article according to any one of Claims 13 to 14. 16. A thin-walled elastomeric article according to Claim 15 wherein the wall thickness of the elastomeric article is generally uniform throughout the whole length of the article. |
FIELD OF INVENTION
This invention relates to a ceramic former for forming thin walled latex articles with uniform wall thickness by slip casting and a method of its manufacture.
BACKGROUND OF INVENTION
Thin walled latex products such as gloves or condoms are manufactured by dipping formers into tanks of liquid latex and admixed chemicals. Typically, formers used for dip-formed polymeric products uses formers made of wood, ceramic, glass, porcelain, plastic and aluminium. The formers are firstly heated and then dipped into the latex bath, usually fingers first in the case of a glove former, where the latex adheres to the former. The "wet" formers are then dried in a heated oven and the latex cured on the mould.
For ease of reference, we will refer to thin-walled latex products as glove products. This does not serve to limit the thin-walled latex products to only glove products, as other products such as condoms are applicable.
During the dipping process, the fingers of a glove former are dipped first into the liquid latex bath, followed by other parts of the former, and the fingers will be the last to be removed from the latex bath. Since the finger section of the glove former enters first into and leaves last from the latex bath, the dwelling time of this section is the longest when compared to other sections of the former. By having more dwelling time in the latex bath, more latex will adhere onto this section, and as a result, the finished article has a non- uniform wall thickness; i.e. being thicker at the finger section and thinnest at the part where the dwelling time of the former is shortest in the liquid latex bath.
It is therefore desirable to produce ceramic former with non- uniform wall thickness such that the ceramic former is thickest at the area that has shortest dwelling time, and thinnest at the area that has the longest dwelling time. This will produce latex products with uniform wall thickness.
Ceramic formers are made from a method known as slip casting whereby the moulds used for making the formers are made of plaster of paris. The plaster of paris has a cavity with a negative 3-dimensional configuration of the intended former, and the slip; i.e. clay in the form of a pourable suspension, are poured into the cavity. The water present in the slip will be absorbed by the plaster of paris, leaving a layer or a cake of clay on the cavity wall. Once the preferred thickness of the layer or cake is achieved, the remaining slip is poured from the mould to maintain the desired wall thickness formed.
Little is known to enable the ceramist to know that the desired wall thickness has been formed on the wall cavity. Common methods used by ceramist are tilting the mould so that the clay wall formed on the wall cavity is revealed and the thickness is judged by the eye. Another method used by ceramist is to take a sample of the wall formed from the top edges of the moulds with a thin spatula. US 5, 670, 180 teaches a method of accurately judging the wall thickness by using a "dam" of a desired wall thickness, placed on the flat surface of the mould to contain the slip. The mould will absorb the water from the slip in the cavity as well as in the dam simultaneously and the dam will allow a visual indication that the desired wall thickness is achieved. Further to that, little is known to enable the ceramist to form a ceramic article with variable wall thickness.
The present invention therefore provides a method of producing a ceramic article with variable wall thickness.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is drawing of the cross-sectional view of a former according to an embodiment of the present invention.
Figure 2 is a photograph showing a top view of the mouldforming chassis according to an embodiment of the present invention .
Figure 3 is a photograph showing a side view of the mouldforming chassis according to an embodiment of the present invention .
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, this invention provides a method of producing a hollow ceramic article with variable wall thickness for producing a thin-walled latex article with uniform wall thickness . A mould or mould halves for a negative 3-dimensional configuration of the desired article is made from plaster of paris. The mould of this invention has different rates of water absorption at different parts or sections of the mould, thereby enabling formation of glove former with different wall thickness .
This mould is achieved by firstly forming different sections of the mould separately with different mould material, namely the admixtures of plaster of paris for each section. The mould is formed in a chassis (10) as shown in Figure 2 and Figure 3. The section that is intended to form a thicker ceramic article may be made of high porosity plaster of paris. Each section is prevented from flowing into other sections by means of a barrier (12) and the plaster of paris admixtures of each section is prevented from setting by constant stirring or vibration. Once the sections of the mould have been prepared, the barriers (12) are then removed to allow the plaster of paris admixtures for limited borderline integration or adhesion between sections moulding admixtures so that all the sections integrally set to form the mould.
The barrier (12) that is used to separate the sections of the plaster of paris can be in the form of a cardboard. The barrier can be a thin wall made from the same moulding material admixture, which is to be poured into said sections so that when the plaster of paris admixture sets, the barrier (12) also forms a part of the mould. Another type of barrier that can be used for this purpose is made from a dissolvable material such that the barrier (12) dissolves upon contact with the admixture of moulding material being poured into said sections. As seen in Figures 2 and 3, the barrier (12) can be inserted into one of the slots (14) in the chassis (10) for partitioning the sections in the chassis (10) . The mould can be formed with two to five sections of different plaster of paris admixtures, depending on the barriers (12) inserted into the chassis (10) for partitioning.
The mould or mould/halves made from this method will absorb water at different rates at different sections of the mould, creating a hollow ceramic former (20) with variable wall thickness. Plaster admixture of higher absorption rate will render a thicker wall formation on the former (20) , and vice versa. The thickest part of the former (20) wall will be the part that has the least dwelling time in the latex bath and the thinnest will have the longest dwelling time. The thickest part will have more heat retained for curing purposes.
The plaster of paris admixture is a hemihydrate of calcium sulphate (CaSOv^lhO) . The ratio of calcium sulphate to water can be varied from 2:1 to 1:1. A higher ratio of the calcium sulphate translates into lower absorption rate. For example, a ratio of 1.69: 1 of plaster of paris to water is used for the fingertip section, and a ratio of 1.38:1 used for the shaft end. In another example, the ratio of calcium sulphate to water of 2:1 is used for the palm and finger section, and the ratio of plaster to water is 1.6 : 1 for the shaft end or shank section .
Therefore, e.g. when a glove former (20) is made from the mould according to this invention, the walls of the glove former (20) will be thinnest at the fingers section and thickest at the shaft or shank. When this former (20) is heated, the heat retained by the former is least at the finger section and most at the shaft. In an embodiment with reference to Figure 1, the former is formed in three sections of the finger (22) , palm (24) , and the shank (24) , with the wall thickness highest at the shank (26) section, intermediate thickness at the palm (24) section, and lowest thickness at the finger (22) section.
In a further embodiment, no adjoining line will be visible externally between the adjacent sections of the former (20) with different wall thickness, as the barriers are removed before the mould is set in each section and the entire mould is integrally set together.
For example, the thickness of the glove former (20) in different sections are shown below.
Table 1 shows the wall thickness of the surgical glove former (20) .
Table 2 shows the wall thickness of the examination glove former (20) . The glove former (20) is firstly heated before dipping, fingers first, into a liquid latex bath. The section of the glove former (20) that will be dipped last will be the shaft or shank of the ceramic former (20) . As the dwelling time of the shaft is relatively short, the thicker wall compensates by retaining more heat, thereby allowing more latex to adhere to the ceramic former. The opposite will apply for the fingers section.
Therefore, a glove with more uniform wall thickness is produced from a former made from the mould of this invention. It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims .