Development Trend of Propeller Casting Method
|Large propellers are produced almost all over the world in the form of a scraper. In the production of variable-pitch ship propellers, after scraping off the equal-pitch surface with a scraper, the auxiliary pitch plate is also used to scrape the variable-pitch surface|
1. Modeling Method
In the 1960s, pit shapes were generally used when casting large propellers in various countries. Later, through production practice, it was found that when the driving height is sufficient, the ground shape is convenient, so they have changed to ground shape.
The types of foundry sand vary from manufacturer to manufacturer. In general, there are cement sand or CO2 water glass sand. The former is cheap, the latter has a short hardening time, and both can guarantee product quality.
At home and abroad, large-scale propellers are produced by means of scraper modeling. In the production of variable-pitch propellers, after scraping off the equal-pitch surface with a scraper, the variable-pitch surface is also scraped with an auxiliary pitch plate. Use a cross-section template to make a fake blade. There are two methods of the model: one is a fish belly shape, which is placed according to its radius; the other is a linear shape, which is placed according to rectangular coordinates.
The former can be made only by using a scale according to the figure, and the latter can be made only after conversion by an electronic computer. The superiority of the linear model separation modeling method is not obvious, but it adds a lot of conversion procedures, and it does not substantially improve the product quality.
Usually, hot air is used to dry the inner cavity of the casting. The hot air blower is mobile or fixed.
The pouring system is an important part to ensure the casting quality of the product. During the machining castings process, oxide slag is often mixed into the liquid metal. Especially when turbulence or vortex is generated, slag inclusions will be generated in the central area of the vortex.
Therefore, careful consideration should be given when designing the casting system to minimize the possibility of slag inclusion. There is information to introduce a filter in the casting system. The filter screen was first made of molding sand, and later it was made of iron plate drilling. However, after many years of trials in our country, the effect is not good. Because when there is a filter, the liquid metal enters the casting system and is sprayed by the filter, which increases the chance of metal oxidation and significantly increases the oxide slag.
At present, there are people using insulation risers in China. If hot molten steel can be used for supplementary pouring, the supplementary effect of the riser can be brought into full play.
4. Casting Retention
The densest part of the casting is on the surface of the metal.
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