Casting and operation of finished silver ingots

Silver finished cast ingot starting material, mostly silver electrolysis. Purified using a variety of chemical and hydrometallurgical process silver bullion to whether the requirements for the quality standards.

The method of casting the finished silver ingots is similar to each factory. A silver powder containing 99.86%~99.88% of silver produced by a factory is melt-cast ingot in a 100-gauge graphite crucible. The grate is pre-sawed and gated, and after inspection, it is determined that there is no damage. electrolytic silver drying approximately 90kg, the use of coal gas is heated atomizing air pressure of [98.066 ~ 196.133kPa (1 ~ 2kg / cm 2) ] after the molten cast 5 370 × 135 × 30mm, each weighing 15 ~ 16kg Silver ingots containing 99.94% to 99.96% of silver.

The charge was filled with about 0.3% sodium carbonate and a piece of live pine. Pine wood is added to reduce the solubility of oxygen in silver. The pine used should contain low rosin to prevent the carbon particles produced by the turpentine from affecting the quality of the silver ingot.

Since the density of silver powder is small and large, it should be added to the crucible in several stages. The temperature in the furnace is 1200~1250 °C, and each smelting is 1~1.5h, and a piece of wood is added before burning. When the silver is completely melted, the silver liquid is cyan and transparent, and the liquid wood block is cast out when it is rotated abruptly.

A combination of vertical ingot mold mold pig iron, the inner surface is machined into a flat and smooth surface. Before using the mold, use gas to bake to 130-160 ° C. After cleaning, ignite the acetylene and evenly smoke a layer of smoke on the mold wall, then clamp the mold, and cover each gate with silver or stainless steel. use. Each time the acetylene is smoked once per casting, the mold is completely cleaned once every 14 times of casting.

When casting silver, remove the slag from the liquid surface and the wall of the furnace (the wooden block is not taken out), remove the sputum, use the stainless steel piece to pull the residual slag and the wooden block near the shovel to the back, and put a piece in the sputum. The old hoe saws about 150×100mm and is preheated to a graphite block above 300°C, and a large bowl of straw ash is poured into the liquid surface, which is cast. The addition of grass ash and graphite blocks is mainly for the purpose of adsorbing the separation slag and also for burning oxygen removal and heat preservation.

The casting uses a combined vertical mold top injection method, the liquid temperature is about 1200 ° C, and the mold temperature is 90 to 160 ° C. The injected metal should be aligned with the core, and the speed will be slower and slower. That is to start the trickle, and then quickly increase the flow of silver, until the metal is about three-fifths of the height of the mold, and gradually slow down, so that the gas freely escapes. When it is five-fifths of the height of the mold, it will decelerate again. After the molten metal enters the cap, it will continue to flow through the cap until it fills the cap to ensure that the silver fills the upper corners of the mold. The condensation of silver creates shrinkage pits below the hat opening, and it is necessary to add silver liquid in time. It takes about 10 to 18 seconds to cast a piece of ingot. After pouring the second piece, pour the sample into the sample and send it to the test. After the pouring of 5 pieces, the grass ash and graphite pieces in the crucible were taken out, and then the next crucible was cast.

After the ingot is condensed, the mold is opened with steel brazing, the silver ingot is taken out with stainless steel pliers, and placed on a smooth and smooth cast iron mold. At this time, the ingot is still at a high temperature and is soft, and special care must be taken not to collide with the ingot side and the spindle angle. Heat the surface of the silver ingot with a thick steel wire. After the initial self-inspection, the unqualified ingot is recast, and the qualified ingot is marked with the steel code. . After the ingot is cold, use a saw to remove the ingot and place it on the bottom of the ingot. . Remove the flash burrs into the warehouse. Then the factory inspector will re-examine the factory standard, and the unqualified ingot will be recast. The qualified ingot will be marked with the serial number, the year and month, and the inspection mark. The block weight code (accuracy of one hundred grams, the current standard stipulates the repair to 0.1 g) ), fill in the pound code single billing delivery. The position of the silver ingot steel code is shown in Figure 1.

Figure 1 Silver chain steel code position and meaning

Waste ingots and spindles were returned to recast. After the batch is poured, the remaining waste ingots, spindles, and sawdust are all billed into the warehouse for recasting.

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