It is best to start describing this topic with tin and lead separately. Lead, tin and alloys from this material have certain properties that are due to their initial state.
General description of tin
It is important to note here that two types of this raw material are distinguished. The first type is called white tin, and it is a β-modification of this substance. The second type is the α modification, which is better known as gray tin. When passing from one modification to another, namely from white to gray, a strong change in the volume of the substance occurs, since a process such as the scattering of metal into powder occurs. This property is called tin plague. It is also important to note here that one of the most negative properties of tin is its tendency to frost. In other words, at temperatures from -20 to +30 degrees Celsius, a spontaneous transition from one state to another can begin. In addition, the transition will continue, even if the temperature is increased, but only after the process has begun. Because of this, raw materials have to be stored in places with a rather high temperature.
Properties of Tin and Lead
It is worth saying that tin, lead and alloys from these materials have very few common properties. For example, the purer the tin, the higher the chance that it will be affected by the plague. Lead, in turn, does not at all experience allotropic transformations.
However, it is also worth noting that additional substances are used to slow down this kind of transformation in tin. Materials such as bismuth and antimony have proven their best. The addition of these substances in a volume of 0.5% will reduce the rate of allotropic transformation to almost 0, which means that white tin can be considered completely stable. Here it can be noted that to a lesser extent, but nevertheless, an alloy of tin and lead is used for the same purpose.
If we talk about the properties of lead, then it has a higher melting temperature - 327 degrees Celsius than tin - 232 degrees. The density of lead at room temperature is 11.34 g / cm 3 .
Characteristics of Tin and Lead
It is worth starting with the fact that the recrystallization of riveted tin lead and alloys occurs at a temperature that is considered below room temperature. For this reason, their processing is a hot type.
A common indicator was atmospheric corrosion resistance. However, a slight difference lies in the resistance to corrosion under the influence of minor substances. For example, lead is best manifested when interacting with concentrated formulations of certain acids - sulfuric, phosphoric, etc. Tin, in turn, is best opposed to solutions of food acids. The scope of these substances individually is also different. Tin is widely used for tinning tin, while lead has been used for lining equipment for sulfuric acid production.
Alloy systems
Here it is important to start with the fact that the alloy of tin with lead is an even more fusible material than individually. Such mixtures were most widely used as solders, for the manufacture of typographic fonts, cast fuses, etc. A system such as tin-lead belongs to the eutectic type group. An important property of all materials belonging to this category is that the temperature of their smelting is in the region from 120 to 190 degrees Celsius. In addition, there are groups of triple eutectics. An example is the alloy system of tin, lead, zinc. The melting temperature of such materials drops even lower, and its limit is 92-96 degrees Celsius. If you add the fourth component to the alloy, the melt temperature indicator will drop to around 70 degrees. If we talk about the use of an alloy of tin with lead as solder, then most often up to 2% of a substance such as antimony is introduced into their composition. This is done in order to improve solder flowability. It is worth noting that the melting temperature can be controlled by the ratio of tin / lead. The most fusible raw materials melt at a rate of 190 degrees.
Babbits
With what is called the alloy of tin and lead, have already figured out - it's a eutectic. This group of substances with such a composition is most widely used in the production of bearing alloys called "babbits." This material is used as a fill for bearing shells. The most important thing here is to choose the right material so that it can easily run into the shaft. At first glance, it seems that the mass of tin and lead alloys with various solders is an excellent yield. However, in reality this is not entirely true. Such materials turned out to be too soft, and the coefficient of friction between the shaft and such an insert was high. In other words, during operation they were too hot, because of this the fusible metals began to “stick” to the shaft. To avoid this drawback, began to add a small amount of more solid substances. Thus, a material was obtained that is both soft and hard.
Substance composition
In order to achieve such a substance that has directly opposite characteristics, the following substances were used. The most important thing is that they lie immediately in the two-phase region α + β. The crystals of the β phase are enriched with solder such as antimony. They act as solid brittle substances. The crystals of the α phase, in turn, are a soft and plastic base. In order to avoid such disadvantages as the melt of solid crystals and their ascent, another component is added to the mixture - copper. Thus, from a piece of lead and tin alloy with the addition of some other substances, it is possible to create a babbit bearing material that combines two opposite qualities - hardness and softness. The classic and most common product of this brand was the B83 babbit. The composition of this alloy is as follows: 83% Sn; 11% Sb; 6% Cu.
Alternative
It is worth mentioning that from the point of view of saving tin-based babbits are very disadvantageous, since this material costs quite a lot. In addition, tin itself is considered a scarce substance. For these two reasons, alternative bearings have been developed based on lead, antimony and copper. In this composition, antimony crystals act as a solid base. The soft base is a direct alloy of lead and antimony. Copper is used in the same way as lead in the previous composition, that is, to prevent the floating of crystals of a solid base.
However, here it is worth mentioning the shortcomings. A lead and antimony eutectic is not as plastic as the tin phase. Therefore, parts manufactured in this way suffer from rapid wear. In order to level this disadvantage, one still has to add a certain amount of tin. The use of triple eutectics of zinc-tin-lead alloy is not very common.