Manual blowing nesting process

Nesting is a decorative molding method that nests two or more glasses, such as colorless glass, color glass, colorless glass, color glass, and milky white glass. When multiple colors are used, the expansion coefficients must match each other. Otherwise, the product will burst. When designing the glass composition, the expansion coefficient is calculated to match it. Due to the fluctuation of raw material composition, melting temperature, and volatility, the expansion coefficients of various color materials may change. They can be produced within ±3×107℃¹. The dilatometer or tablet matching method can determine whether the linear expansion coefficients match. If these two detection methods are used after production, the damage has already occurred when the problem is found, and the loss is significant. If they are used before production, the tested sample must be annealed for several hours before it can be judged. Especially for the production of color glass, it isn’t easy to have so much time to wait in actual operation. In this case, a test method that can play a warning role in advance of production is urgently needed, and the double-line method has such a role. The double-wire method fuses two glasses and draws them into wires, thus forming a system similar to bimetal.
Measurement method: Some materials suggest that the glass to be tested needs to be made into a flat shovel with a blowtorch and drawing pliers. Here is a simpler and more practical method: you don’t need to use drawing pliers.
The glass to be tested and the standard glass with known linear expansion coefficient are made into glass rods with a length of 200-400mm and a diameter of 1-3mm. The two glass rods are overlapped at the joints with an overlap of 5-10mm. The two glass rods are melted together with the help of a blowtorch flame, as shown in Figure 4-17 (a) and (b). The flame is removed while the glass is softening, and the glass is immediately pulled parallel to both sides without deflection or rotation. The glass rods are pulled into double wires with a length of 400-800mm and a diameter of 0.1-0.3mm. The wires are then cut from the middle. When the linear expansion coefficients of the two glasses are the same, the double wire is a straight line after cooling; otherwise, the double wire will bend. The linear expansion coefficients of the two glasses are compared based on the chord length and chord height of the glass wire when bent.

Suppose it is to check whether the linear expansion coefficients of different colour materials in production match. In that case, it is generally used to take a clear glass rod as a standard rod, take a matching colour glass rod, overlap the two glass rods, and weld them on the flame of a blowtorch. Leave the flame before melting, pull the two rods flat in two opposite directions, and pull the welded part into a filament with a 0.1-0.3mm thickness.
Cut the filament from the middle. If the filament is straight, the two glass materials match. If the filament is bent, the bending degree can be used to judge whether the two glass materials are usable. Draw a ruler on the glass plate or other flat surface. The ruler length is 200mm, and the two sides of the centre are 100mm each. Hold the glass rod to overlap the bent glass filament with the two ends of the ruler, and measure the bending height. When the bending height between the general soda-lime glass explicit material and the colour glass material is less than 5mm, the two materials will not burst when used together. Otherwise, the glass products will still be damaged no matter how long the annealing time is. The bending height between the explicit material and the opal porcelain material is more variable, and the maximum limit varies according to the glass composition and annealing temperature. This needs to be determined by the manufacturer according to the glass composition, and the maximum limit is determined by the double-wire method.
When the linear expansion coefficient of the transparent material changes by the double wire method, it can be inferred that the composition of the explicit material fluctuates. Many samples of the transparent material rods are kept as standard rods at a particular time. After that, samples are taken daily or at intervals for matching tests with the standard rods to check whether the expansion coefficient of the transparent material changes.
They take the explicit material and the colour material on the day of production and use the double wire method to determine whether the two materials match, which has excellent guiding significance for production. If the two materials do not match, the production department can be notified to stop using this colour material before production to prevent losses.

(2) The outer sleeve method involves inserting different coloured glass on the outside of the product. Usually, the glass must be ground and carved to show the effect of colouring. It can be single-layer or multi-layer colouring. The outer sleeve method is divided into the skin method and the blowing skin method.
The skin method is to dip a large amount of coloured glass into the small bubble of the selected material and then make it into a trumpet shape by blowing, baking, and opening it. Then another worker dips the blowpipe into a large amount of colourless transparent material in the clear material crucible, inserts it into the trumpet-shaped coloured glass skin, makes it adhere, and then puts it together at the mouth of the crucible to bake the sample (to soften the glass), roll the material, blow the material, repeat several times, and put it into the model to blow it into shape. The skin can form more oversized glass products and engraved blanks.
The skin-blowing method uses a blowpipe to dip a proper amount of coloured glass material, put it in a semi-elliptical mould, and blow it into a uniform bowl-shaped skin. The thickness depends on the product and the colour depth. Then, another technician dips a certain amount of colourless transparent glass from the clear material crucible
and inserts it into the bowl-shaped iron mould. At the same time, it is red hot, adheres to the colour glass material skin, and then takes out the clear material bubble with the colour material skin as a whole, heats it to the moulding temperature at the crucible mouth or in the oven, and then puts it into the mould for blowing. When inserting the clear material bubble into the skin, prevent air bubbles from being sandwiched between the colour glass skin and the explicit material. The outer sleeve method is suitable for small glass products and has high production efficiency.
Although the skin-blowing and skin-covering methods involve more processes, they can evenly distribute the colour layer, and multiple layers of materials can be used, such as the first layer being explicit material, the second layer being milky white material, the third layer being colour material, and the fourth layer being explicit material. Multiple layers of colour material can also be used.
If the skin is not blown or covered, the transparent material bubble can be directly dipped into a thin layer of colour material and then baked for moulding. Although this method is simple, it quickly causes uneven distribution of the colour material layer, which is unsuitable for large, deep products.
The glass products made by the outer coating method have a multi-layered colour effect after carving or grinding, with a strong three-dimensional sense and rich colours.