The requirements on the base material for electronic contacts refer to its physical, mechanical and technological properties. The combination of strength, conductivity and relaxation resistance is vital. For spring-loaded contacts, additional specific spring properties such as spring bending limit, flexural strength and stress relaxation are important due to increased ambient temperatures. Furthermore, ductility (ratio between radius and thickness) is a constructive property that is critical for the contact's design and size.
EMC
We offer different metals for applications in the field of electromagnetic compatibility where the ambient temperature is crucial.
A spring only maintains its damping in the MHz and GHz frequency field if it can hold its nominal force elastically by compression, no matter how the ambient temperature evolves.
The relaxation behaviour of the spring material is the decisive factor. For EMC applications, the following metals have proven themselves:
• Stainless steel 1.4310
• Copper beryllium
• Inconel in sheet metal mould
• Monel as mesh
These materials cover a wide range of temperature requirements from -200 °C bis +700 °C ab.
Contact corrosion and surface coatings
In a second step the material combination of the contact surfaces is to be checked for possible contact corrosion. The environment of the respective application plays an important role here. By means of modern surface coatings we are able to fulfil any of your requirements in collaboration with our partners.
Ampere
For current-carrying contacts, the material of the spring element and the body is required to have high electrical and thermal conductivity which is proportional to the amperage. In the design process, care must be taken to keep the temperature rise of the current as little as possible since this limits the maximum current rating. Therefore, carrier materials made from copper alloys are preferably used, as they are excellent current (% IACS) and heat (W/m∙K) conductors. If flexural strength is required additionally, the following materials are available:
CuTiFe; CuNiSnMnFe; CuBe2; CuNi3SiMg; CuNi2Be; CuCrSiTi; CuCrSiAg
Conductivity and spring function
To ensure the spring function, copper alloys that show high mechanical strength are required. In particular miniaturized contacts need a high stiffness, which is achieved by a modulus of elasticity in the range of 110 to 140 kN/mm². Additionally, high flexibility is required in order to be able to produce contact parts as stamped bending parts in an economic and precise way.
Temperature resistance
The ability to ensure a stable nominal contact force in the long term, even with increased temperatures, depends on the relaxation behaviour of the spring material. For an elastically loaded spring that is exposed to temperatures above 100 °C over a longer period of time, the stress relaxation can cause a significant decrease in spring force, depending on the material.
The temperature resistance to stress relaxation limits the spring element's maximum permitted ambient temperature decisively.
Temperature limits of different materials:
- Brass: can be used up to approx. 100 °C
- Tin brinzes (e.g. CuSn6): below 150 °C
- High performance copper alloys like CuNiSi, CuTiFe and CuBe: suitable for permanent temperatures between +200 °C and +250 °C
- CuBe: especially temperature-resistant between +270 °C bis -253 °C
- Alloy 718 (Inconel): can be used up to 704 °C
Spring bending limit
Flexibility is a property that is decisive for the constructive design and therefore the size.
The spring bending limit is defined as the bending stress on the tension side leading to a permanent deflection of 0,05 mm after a specimen was loaded and subsequently unloaded. Thus, a spring has a high spring bending limit if there is hardly plastic deformation after being highly stressed.
Spring-hard materials
For spring-hard materials, there is no direct relation between tensile strength and spring bending limit, since the tensile test load and the bending test load are different. Spring-hard rolled materials are usually not uniformly hardened over the entire cross-section.
Theoretically, the spring bending limit is slightly below the 0,2 % yield strength, approximately at the 0,1 % yield strength. In practice, it is often lower because of internal stresses inside the material. Only when being heat-treated with temperatures between 200 °C and 350 °C, these stresses can be normalized. How often the material is hardened and at which temperature it is relaxed, influences the price. Therefore, we have a variety of hard materials available that we will check for the specific application concerning their input costs and thermoelectric stresses.
With regard to material costs, hardenable alloys are superior to naturally hard materials, since we carry out precipitation hardening under safety glass at ZILLKON.
Our product line comprises:
- CuBe-types
- CuNi2Be
- CuCrSiTi
- Inconel Alloy
Flexural strength
Flexural strength is a decisive factor for contact springs subjected to dynamic loads. How much the flexural strength is stressed, depends on the strength, particle size and tape thickness. It decribes the highest bending stress a repeatedly loaded specimen can withstand without breaking.
The measurement is carried out by means of S-N curves (so-called Woehler curves) showing that the number of load cycles to failure decreases with increasing bending stress. The influence of the number of cycles is negligible above 10 to the power of 7, and this value is defined as flexural strength.
Copper materials can be classified into three groups by their flexural strength:
- Brasses: 130-160 MPa, suitable for static plug-in contacts.
- Phosphor bronzes (e.g. CuSn6, CuSn8, CuSn10): 180-220 MPa, ideal for spring contacts with medium load cycles and medium spring deflection.
- High-strength copper alloys:
- CuNiSnMnFe: 300 MPa
- CuBe2: 300 MPa
- CuTiFe: bis zu 400 MPa
These alloys are suitable for applications with high spring cycles and dynamic loads.
Alternative spring materials
The following pages provide an overview of “Additional Spring Materials,” including detailed descriptions of their respective application areas and properties.
CuBe2CuNi2BeCuSn6CuSn8CuSn10TeFiCuK55K75Inconel 718Edelstahl 1.4310