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A small detail has a great impact on the quality of castings!!!!!!!
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A small detail has a great impact on the quality of castings!!!!!!!

Views: 29     Author: Site Editor     Publish Time: 2018-10-09      Origin: www.fuchun-casting.com

The quality of molding sand has a great influence on the quality of castings and the rejection rate. In sand casting, especially in clay sand green casting, the properties of molding sand have a significant influence on the quality of castings and the rejection rate.

Good molding sand needs not only high strength, suitable compaction, suitable moisture and composition, but also suitable temperature. Therefore, it is very important to adjust the sand temperature for the sand treatment system of large-scale continuous production workshop. Excessive sand temperature will lead to the formation of casting defects.

Harmfulness of excessive molding sand temperature

1、Molding sand requires low temperature and stability when molding. Most old sand temperatures are much higher. If the sand is not cooled, the performance of the sand will be unstable, so it is impossible to produce uniform compactness sand moulds on the moulding machine. The lower the temperature of molding sand, the higher the compactness. Because of the high sand temperature and the deterioration of compactness, a lot of problems such as sand mold rupture, viscous mold and sand mass appear in the sand, which reduces the molding speed and increases the waste mold.

2、Too high sand temperature leads to poor quality of sand mold, resulting in quality problems of castings and high reject rate. Casting defects such as pinholes, inclusions, sand washing and surface roughness often occur when the sand temperature is too high. If these defects are not found until sand drop, cleaning, shot blasting or machining, it will cause greater waste.

3、When hot sand is added to the sand mixer, water vapor condenses in the sand mixer and absorbs dust that should have entered the dust collector, as well as clay that should have been mixed into the sand mold. Dust accumulates in the mixer and reduces the efficiency of the mixer. The excessive evaporation of water during sand mixing requires higher water addition, which results in longer sand mixing period and lower productivity of sand mixer.

In order to prevent and solve the hot sand problem, the most important measure is to increase the actual capacity of sand system, reduce the number of cycles of sand use, and adopt humidifying ventilation cooling treatment in the design stage of sand treatment system, which can greatly reduce casting defects.

molding sand



  • What is 'multiple certification'?

    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.

  • What surface finishes are available on stainless steels?

    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.

  • Can I use stainless steel at high temperatures?

    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:

    1. Maximum temperature of operation
    2. Time at temperature, cyclic nature of process
    3. Type of atmosphere, oxidising , reducing, sulphidising, carburising.
    4. Strength requirement

    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.

  • Can I use stainless steel at low temperatures?

    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. 

  • Is stainless steel non-magnetic?

    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.

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