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Views: 3 Author: Site Editor Publish Time: 2018-04-07 Origin: Site
H2. Sand type precision casting is preferred.According to statistics, in our country or international, in total casting production, 60 ~ 70% of casting is made of sand,and about 70% of them are made of clay sand.The main reason is that sand casting is cheaper than other casting methods、the production process is simple and the production cycle is short.Therefore, the engine cylinder block, cylinder head, crankshaft and other castings are produced by using clay wet sand molding process.When the wet type cannot meet the requirements, consider using clay sand table dry sand type, dry sand type or other sand type.The weight of castings in wet sand moulds can range from a few kilograms to dozens of kilograms, while the casting of clay dry type can weigh tens of tons.In general, for medium and large castings, cast iron pieces can use resin self-hardening sand mold casting parts can be production of water glass sand mold, can obtain the size precision, smooth surface castings, but the cost is higher.Of course, the casting precision, surface finish, material density and metallographic structure and mechanical properties of sand mold casting are often poor.Therefore, other casting methods should be adopted, such as investment casting, die-casting, low-pressure casting, etc., when the performance requirements of the casting are higher.
H3. Low pressure casting, die-casting, centrifugal casting and other casting methods, due to the high price of equipment and mold, suitable for mass production.For small castings, the production line and real model of the non-box high pressure molding machine with horizontal parting or vertical parting are high and the area is small.In order to adapt to the requirements of fast and high-precision molding production line, we can choose a variety of production line and air-shock molding line of various boxes of high-pressure molding machines.Core method can be used: cold core box, hot core box, shell core and other efficient core method.Medium batch large castings may consider the application of resin from hard sand molding and core.Single small batch production of heavy castings, hand modeling is still an important method, manual modeling can adapt to various complex requirements more flexible, do not require a lot of technological equipment.Water glass sand type, VRH water glass sand type, organic ester water glass self - hard sand type, clay dry type, resin self - hard sand type and cement sand type can be applied.For heavy castings of single parts,the method is low cost and fast in production.Batch production or long-term production of finalize the design product box, split box shape modelling method is appropriate, although high mould and sand box to start investing, but from compensated save modelling cycle time, improve the quality of its products.
Investment casting products, lost wax casting suppliers
This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimise stock levels.
For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.
There are many different types of surface finish on stainless steel. Some of these originate from the mill but many are applied later during processing, for example polished, brushed, blasted, etched and coloured finishes.
The importance of surface finish in determining the corrosion resistance of the stainless steel surface cannot be overemphasised. A rough surface finish can effectively lower the corrosion resistance to that of a lower grade of stainless steel.
Various types of stainless steel are used across the whole temperature range from ambient to 1100 deg C. The choice of grade depends on several factors:
In the European standards, a distinction is made between stainless steels and heat-resisting steels. However, this distinction is often blurred and it is useful to consider them as one range of steels.
Increasing amounts of Chromium and silicon impart greater oxidation resistance. Increasing amounts of Nickel impart greater carburisation resistance.
Austenitic stainless steels are extensively used for service down to as low as liquid helium temperature (-269 deg C). This is largely due to the lack of a clearly defined transition from ductile to brittle fracture in impact toughness testing.
Toughness is measured by impacting a small sample with a swinging hammer. The distance which the hammer swings after impact is a measure of the toughness. The shorter the distance, the tougher the steel as the energy of the hammer is absorbed by the sample. Toughness is measured in Joules (J). Minimum values of toughness are specified for different applications. A value of 40 J is regarded as reasonable for most service conditions.
Steels with ferritic or martensitic structures show a sudden change from ductile (safe) to brittle (unsafe) fracture over a small temperature difference. Even the best of these steels show this behaviour at temperatures higher than -100 deg C and in many cases only just below zero.
In contrast austenitic steels only show a gradual fall in the impact toughness value and are still well above 100 J at -196 deg C.
Another factor in affecting the choice of steel at low temperature is the ability to resist transformation from austenite to martensite.
It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1.
It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.
In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.
Martensitic, ferritic, duplex and precipitation hardening steels are magnetic.