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How to control the quality of precision castings?
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How to control the quality of precision castings?

Author: Site Editor     Publish Time: 2017-10-18      Origin: www.fuchun-casting.com

Casting quality inspection is an important process in foundry production. Its main functions are:

1. Provide quality information for casting production and management department;

2. Put forward the project for the quality management activities.

3. Guarantee the quality of the product.

 

The total quality management of the foundry includes two parts, the quality control of the castings and the quality assurance of the castings. It is the quality system carried out in the factory under the premise of the comprehensive and reasonable specification of the technical requirements of the castings.

 

Casting quality inspection is an indispensable part in the casting production process. Its purpose is to ensure that the quality of castings meets the technical requirements of delivery and acceptance. The quality inspection of castings is based on casting drawings, casting process documents, relevant standards and technical conditions for delivery and acceptance of castings.

 

For the foundry industry, it is characterized by many processes, strong coherence, and many variables in each process. These variables are difficult and difficult to control, and may eventually be reflected in the causes of the defects.Therefore, as far as defect control is concerned, the prevention of defects should be put in the first place, and the quality problems should be studied and solved continuously.

 

Through active market research, we should constantly grasp the quality requirements of consumers or users, and carry out serious after-sales service to ensure the quality of the market. Quality management is a comprehensive collection of research and development, production inspection and sales services in one of the activities of the total.

 



According to the quality inspection results of castings, castings are usually divided into three categories: qualified products, repaired products and unqualified products.


Qualified products refer to castings that conform to the relevant standards or delivery conditions.


Rework means that the appearance and internal quality are not fully conformed to the standard and acceptance conditions, but the rework is allowed and the castings can meet the requirements of the standard and the technical requirements for the delivery acceptance of the castings after the rework.

 

Unqualified products refers to the disqualification of both the appearance quality and the internal quality, and the castings that are not allowed to be repaired or after reworking still fail to reach the standard and the technical requirements for the casting acceptance

 

In order to ensure the quality of the castings, different inspection methods should be adopted according to the different uses and requirements of the castings so as to detect the impermissible defects in time. The inspection of castings mainly includes the surface quality inspection, the internal quality inspection and the comprehensive identification quality. The surface quality includes surface defects, dimensional accuracy, quality deviation, surface roughness and so on. The appearance quality affects the subsequent processing and subsequent processing, and also affects the performance. All castings must be checked according to the specified standards for appearance quality inspection, which often need to be completed several times. Therefore, there are different inspection systems for different precision casting parts.


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Products

FAQS

  • 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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