The faucets in the marketplace are mainly copper materials, but there is lead element in copper alloys, which is harmful to people’s health. Therefore, it is a kind of trend to develop stainless steel faucets. The stainless steel faucet has not been widely used owing to its complicated production process and expensive materials. But now in the kitchen,these utensils are contacted with food directly,such as vegetable basins, pots and spatulas are all made of stainless steel and even a straight drinking fountain is also equipped with stainless steel faucets. Stainless steel faucets can meet the requirements in terms of decoration, environmental protection, greenness, health and practicality.
Stainless steel faucet was produced by investment casting. Through adopting new core making, the core could be cleaned smoothly by shell-vibration and ball throwing. During production process, the shrinkage porosities (holes) could be avoided or eliminated by optimizing assembling-tree design and gating system. After hydraulic examination, the faucet meets the requirements.
Faucet Structure Analysis
The water channel of the faucet is curved and irregular. There is a deep inner hole in it and the shape of the water channel cavity is narrow and deep, and its mouth is small while its inner space is big. The faucet structure is shown in below. It is impossible to produce with a mold, which is a typically complicated and difficult to cast part. Traditionally,the faucet was produced by copper alloy because the main body of the faucet is cast by gravity, the pouring temperature is only about 1100°c , the sand core is easy to clean and this process is better controlled.It requires a large amount of stamping die, labor cost and processing time if the forming methods such as processing sheet metal and blank metal and welding and sealing were adopted. However, the processing allowance of blank metal is large and the process is complicated, resulting in inconsistent outer surface of the batch parts, which is affecting its appearance.What is more,the deformation is easily caused by the local overheating during welding, and therefore, the product quality is not high.With stainless steel casting, the wax patterns can be welded. But it is easy to cause problems such as steel leakage due to the inner shell and the sand dripping as well as insufficient strength and the scrap rate is high. However,with the sand core molding method, the problem of mold ejection and shell making can be better solved, and the alkali core cooking and alkali explosion process are avoided to clean the core.It does not react with metals and oxides at high temperatures if the ceramic core is used, and its porosity rate is generally 40%~50%.It has good gas permeability and good collapsibility and solubility. The core becomes loose after pouring molten steel and most of the core can be removed only by shaking the shell. The inner cavity of the casting can be cleaned by ball throwing or sand blasting, which has the features of high efficiency and low energy consumption. Stainless steel faucets are not allowed to leak water. After hydraulic examination, the product must not have any defects ,such as shrinkage and cracks.
Stainless Steel Casting Design
The inner gating channel is generally designed in the highest thick part of the casting. It not only leads to effective feeding, but also reduces the possibility of stress, deformation and crack. At the same time, it is considered to open the gate to avoid the formation of new heat knots.It is good to hang pulp, sanding and drying during the shell making process and convenient to cut the inner gating channel. We should try to improve the product yield under the premise of ensuring the quality of castings .This part is designed with two ingates after a comprehensive consideration, see blow picture.
There are 6 pieces in each group and 3 pieces per side when using bottom pouring process, the weight of the wax part of the die head is about 580 g while the wax part weight is about 50.2 g, and the process yield rate is 50.2%.
Considering the moistening slurry and dewaxing, an ingate at the bottom was opened , because any part of the dewaxed part will cause casting defects such as chipping and slag holes, so try to keep the residual wax to a minimum. The size of the ingate should be minimized under the premise of ensuring the quality of the casting, which can reduce the sanding of the ingate. The height of these two ingates is set to 10. 5 mm, because on one hand, the casting and the die head can be tightly combined to increase the strength of the die head and prevent the breakage of the product after hanging pulp and sanding, and on the other hand it is convenient to cut in the subsequent process, but it will easily damage the casting during the cutting when the ingate is too short, while it will increase the cost and affect the casting feeding if it is too long.
Roasting and Smelting
Basic lining was selected while choosing smelting furnace. It is necessary to pay attention to deoxidation and slag removal during the production. The operators are required to operate in strict accordance with the specifications in the processes of batching, melting, adjusting components, deoxidizing and removing slag. The casting piece is cast at the bottom, the molten steel passes through the pouring cup and the entire cavity is filled from the bottom in order to avoid the impact of the molten steel on the shell and prevent the slag and other inclusions from entering the cavity.Since the surface of the faucet after stainless steel investment casting needs to be polished, the casting is likely to appear black spots after polishing. The first step to prevent the black spots is to dewaxing thoroughly, the second is to control the melting time and temperature. The work of deoxidation and slag removal is also considered and pay attention to the deoxidation and refining effect and purify the melted stainless steel effectively ,this is because the molten stainless steel contains a variety of easily oxidized alloying elements. When molten steel is exposed to air for a long time during smelting, it will react with oxygen in the air and form oxidized impurities and produce black spots. The third is to control the impurity content of the regenerated stainless steel, reduce non-metallic inclusions and control the amount of die metal added. The die metal material is allowed to be used after ball throwing . The raw materials should not be placed in a damp, oily or moisture place to prevent impurities from seeping.
It is necessary to extend the roasting time appropriately because the stainless steel faucet module is not easy to burn thoroughly. After repeated tests, the temperature of the roasting shell is about 1 100 V, and the shell roasting time is 50 min. It is necessary to keep the furnace door opened for 6 to 8 min after roasting if it is roasting in an electric furnace and adding some oxygen so as to let the gas generated after the core and shell roasting is quickly discharged from the roaster,while it is roasted with oil, it is poured as much as possible within 10 s when the roasting temperature of the shell is reached. To some extent,the slag inclusion, pores and cold insulation are affected by the pouring speed.Therefore, it should be poured quickly so as to it can be filled with a mass flow and a low flow speed. Since there is a core inside the faucet, the surrounding wall thickness is about 2.5 mm, so the pouring temperature of the molten steel should be around 1 580 V.It will cause coarse grains and defects such as hot cracks, pores and burnt-on sand if the pouring temperature is too high. The surface of the casting will be prone to black spots, causing water leakage.It will easily cause cold separation and insufficient pouring if the temperature is too low. An appropriate amount of covering agent is placed into the pouring cup to protect the molten steel after casting, which is beneficial for feeding and absorbing the non-metallic inclusion oxide on the molten steel surface and isolating the air to prevent secondary oxidation, thereby,it improved the products’ quality.
CFS Stainless Steel Foundry is skilled at investment casting stainless steel faucets, which are mainly exported to USA, UK, Canada, Australia, ect. Thanks to our good quality and timely delivery, we are always keeping good business cooperation with our customers. If you have any stainless steel investment casting demands, pls get in touch with us!