• Quality assurance

Quality assurance

 

In addition to checks throughout the production process, the finished products are tested so as to guarantee the quality that our customers expect. Basically, the number of specimens tested is in line with the applicable standard or with the customer's specification.

Destructive testing

The quality of HUNDT & WEBER products is verified by means of destructive testing, i.e., spectroscopic analysis, wet chemical analysis, mechanical material testing and metallographic methods.

Spectroscopic analysis
In order to ensure perfect quality of the melting process, the melt is analysed prior to casting using a vacuum spark emission spectrometer. If there is a deviation from the reference value, corrections can be swiftly made so that the melt always complies with our customers' specifications. We have a fully equipped wet chemical laboratory to meet particular requirements.

Mechanical testing
Hardness is the most commonly used property to define the condition of the cast material. It describes the resistance of a body to penetration by a testing device. In the case of the Brinell method (EN 10003-1), which is typically applied to copper alloys, the hardness is determined using a steel ball or a hard metal ball.
For the Charpy impact test (EN 10045-1), a notched specimen is broken in one single stroke and the impact load is measured. The test serves to evaluate the material toughness. However, it is less suitable for nonferrous metals.
Mechanical characteristics (0.2 proof stress, tensile strength, and elongation at rupture) are determined by means of tensile testing (EN 10002-1) in our own material laboratory. The condition of the material can hence be precisely described.

Metallograpy
Using optical procedures and test methods, defects in a component, as well as their nature and cause, can be observed. Furthermore, the structure and grain size indicate the material properties. For metallographic testing, which is carried out using a reflected light microscope (metallurgical microscope), a plane surface is ground on the specimen which is then prepared for microscopic or macroscopic examination by polishing and etching.

Non-destructive testing

Pressure tightness, conductivity, and magnetic permeability are checked by means of non-destructive testing. Furthermore, radiographic (X-ray) testing, ultrasonic testing, and dye penetration tests enable defects to be detected in castings without the need for destruction.

Radiographic testing
Using radiographic testing (X-rays and gamma rays), defects inside a casting may be detected. While the rays penetrate all kinds of material in a straight line, they are weakened on encountering discontinuities in the actual material and their magnitude. Defects (such as gas bubbles or inclusions of moulding materials) show as a dark spot on the radiosensitive film.

Ultrasonic testing
By means of ultrasonic testing, invisible defects inside the material may be detected. It also allows easy determination of material thickness.
Bundles of sound waves pass through the test specimen until they are reflected by the rear wall. The echo level indicates the extent of hidden defects inside the casting (e.g., blowholes, slag, porosity, etc.).

Permeability check
The magnetic permeability µ is another important material characteristic. The magnetic prop-erties of copper alloys are affected by the actual chemical composition, in particular by the iron content. Magnetic permeability is of major significance for copper-aluminium alloys used for marine applications.

Conductivity test
Electrical conductivity is the reciprocal value of specific resistance. As a large amount of copper will be used in the field of electrical engineering, understandably electrical conductivity is considered as the most important property of this metal. However, even small contents of other elements that form mixed crystals will lead to a reduced electrical conductivity.
The unit is m/Ohm x mm² (Siemens units, SE) or % IACS.
100% IACS equal 58 m/Ohm x mm².
At a temperature of 20°C, the highest grade of copper has a conductivity of 59.62 m/Ohm x mm².
At room temperature, there is almost a linear correlation between thermal and electrical conductivities. Therefore, components made from a high grade of copper are particularly used in metallurgical furnaces for their excellent thermal conductivity.

Leak tests
For armature housings or specially formed castings, a leak test is an essential component of production monitoring. In order to ensure pressure tightness of these parts, they are tested by applying a multiple of the intended operating pressure (rated pressure) over a defined period of time. Technical details of the leak tests required should be specified individually in the order.
For flow testing, the water flow in m³/h together with the pressure drop in the component are determined and documented on an automatically registered diagram.

Dye penetration test
The dye penetration test is used to detect micro cracks and porosity. As a result of the capillary effect, dye penetrates into defects, which are open towards the surface. When using a developer, these defects display a clearly visible colour.
Prerequisites:
  • The defect starts from the surface
  • The defect is open towards the surface so that the testing agent penetrates inside
The findings are then documented by photographs. Using reference photographs or series, round or linear indications on a reference surface can be classified according to their frequency and size.
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