What Is White Metal?

White alloy, also known as Barbie alloy, is a white alloy containing tin, lead, antimony and copper. It can be used as anti-friction metal for shaft sleeves and bearings. Barbie alloy bearings are suitable for applications where the temperature and pressure are not high. This alloy is a cubic crystal containing hard copper and antimony, or a compound of lead and antimony on a medium-hard matrix. Abrasion causes the softer substrate to sag quickly, leaving the hard crystals exposed and bearing the load. The exposed area of the hard crystals is small, thus reducing friction, and the sinking matrix makes it possible for the lubricant to circulate between the hard crystals. ^[1]

Also called Barbie. According to the chemical composition generally: tin white alloy, which is an alloy of tin, antimony, copper. Lead white alloy, it is lead antimony steel with lead as the main body. It was invented by Barbie, so it was called white alloy. It is a fusible bearing alloy. It is characterized by small hard particles distributed on a soft substrate and strong heat resistance. However, due to its low strength, it cannot be used as a self-loading structure. Usually cast on cast iron or bronze bushings. Tin white alloy works under high load and high speed and generates little heat, making air compressors, centrifuges, etc. In addition, there are more widely used lead white alloys containing calcium, barium, strontium and nickel. ^[2]

Tin-based and lead-based wear-resistant alloys are called white alloys or babbitt alloys, and are generally used to cast bearings or bearings.

Various waste alloys, intermediate alloys, prepared alloys and primary metals can be used as raw materials in the production of lead white alloys. The lead waste used should contain no less than 0.2% tin and no less than 0.3% antimony.

Due to the different chemical composition of lead and its alloy waste, the raw materials (lead and white alloy waste, tin-containing waste, alloy chips, printing alloy, etc.) must first be smelted to form a prepared alloy. After measuring its chemical composition, it can be used as the ingredient of the white alloy required for smelting.

Prepared alloys are usually smelted in pig iron, blast furnaces or reverberatory furnaces. When melting, charcoal is used as the covering flux, and the ground asphalt is used as the reducing agent to prepare the alloy. The melting process is: heating the alloy crucible with a capacity of 3t in a resistance furnace, and adding coarse hard lead and 15-20 kg of charcoal. After the crude lead is melted, asphalt is added and the melt is stirred until dry scum is produced. Remove the dry dross, add the white alloy old material, lead old material and alloy shavings to the crucible, and stir the alloy melt. When the crucible is filled with alloy, it is heated to 550 ~ 600 ° C. After the stirrer and centrifugal pump are installed in the crucible, the melt is cast on a belt ingot casting machine.

When smelting a lead-tin white alloy containing copper, nickel, tellurium, and other components, these components are difficult to melt or easily oxidize, so they cannot be added to the ingredients in a pure state. These components need to be previously smelted into an intermediate alloy. In order to produce the required grade of lead-containing tin white alloy, prepared alloys, master alloys, regenerated or primary tin and antimony are added to a crucible resistance furnace for melting. Its proportion is calculated according to the chemical composition of each component of the charge.

The production process of white alloy includes two basic operations: feeding and adjusting alloy composition. During the feeding operation, the most refractory charge components are melted into a liquid melt; in the process of adjusting the alloy composition, the alloy composition is adjusted to the specified composition standard range.

For example, the production of white alloy B16 (its chemical composition (%) is: Sb15 ~ 17, Cu1.5-2.0, Sn15-17, the balance is Pb), the approximate composition of the charge (%) is: Sn15.7, Sb16. 5, Cu1.76, the rest is lead; the charge composition (%) for the production of BH white alloy is: Sn9.55, Sb14.10, Cu1.77, Ni0.50, As0.72, Cd0.60, the rest is lead. Lead-tin alloys are prone to segregation, so appropriate amounts of copper should be added. Because copper, tin, and antimony all form stable intermetallic compounds Cu ₂ Sn, CuSn, and Cu ₂ Sb. When the alloy is cooled, these intermetallic compounds precipitate in the form of primary crystals, forming an alloy skeleton, which can prevent small-density products from floating. The alloy is cast at a temperature of 360 to 400 ° C. At this time, the alloy must be continuously stirred to ensure uniform composition. The raw materials for the production of white alloys include various intermediate alloys such as tin, antimony, arsenic, and cadmium, and prepared alloys, as well as return materials (dross, spatter, and scrap) for each process. ^[3]

The chemical composition (%) of calcium white alloy is: Ca 0.85 ~ 1.15, Na 0.6 ~ 0.9, and the balance is Pb. During production, metallic calcium is added to the lead. At this time, calcium and lead form PbCa crystals, which form a hardening component in the white alloy. This component bears the main load in the bearing. To increase the strength of the alloy body, sodium metal is also added to the lead. Sodium and lead form a very fine-grained compound Na ₂ Pb ₅ , which is evenly distributed in lead.

Recycled calcium white alloys can be produced from old alloys and scraps containing sodium-calcium and various recycled lead raw materials. The standard impurity content (%) is: Bi 0.1, Sn 0.25, Mg 0.02, and other impurities 0.3. Therefore, only soft lead materials containing antimony not exceeding 0.3% can be used as raw materials. There are three methods for producing calcium-containing white alloys in industrial practice, namely the calcium chloride method, the metal calcium method, and the electrolytic method. Here, only the metal calcium method is introduced.

Metal calcium method is to add metal calcium to molten lead, and then add metal sodium. The production equipment consists of upper and lower pot. The lead with the lowest impurities was melted in the upper pot, and half of the lead residue was placed in the lower pot at 800 ° C. Calculated by adding 13.5 to 14 kg of calcium per ton of alloy, and adding metallic calcium to the lower pot. Lead and calcium form an intermetallic compound Pb ₃ Ca, which reacts strongly and emits a lot of heat. Therefore, calcium should be added to the lower part of lead to reduce calcium burn. Then put the lead in the upper pot (at 350 ~ 370 ) into the binary alloy in the lower pot to reduce the temperature of the Pb-Ca binary alloy. Calculated based on 7 to 8 kg per ton of alloy. Add sodium metal to the alloy that has cooled down, while stirring the alloy vigorously. It is required to add calcium before adding sodium, otherwise sodium will be lost due to the severe reaction between lead and calcium. The disadvantage of this method is that it generates a large amount of scum with high lead content. ^[3]