Shaving head
A mechanical shaving head is part of an electric razor and consists of the components blades and shaving foil. The shaving foil is firmly attached while the blades move underneath as a blade block.
Modern shaving heads have a complex structure and often consist of several smaller shaving units, which together have a strong influence on shaving behavior. Individual shaving units are flexibly stored, which means that the whole shaving unit can adapt to different ergonomic face shapes and achieve a more thorough shave result.
The shearing process is significantly influenced by the shearing partner blade and shaving foil. Factors that influence shaving, such as wear and tear, shear behavior and possible skin irritations, are determined by different geometries and the choice of material.
Shaving foil
geometry
Modern shaving foils (2014) have a similar hexagonal hole structure to historical shaving foils (1959). While the structure of the old model is uniform across the entire film, the current model has a distortion of the pattern towards the outside. This manifests itself both in a distortion of the hexagons and in a partial reduction to five corners. This geometry is reminiscent of the interplay of pentagons and hexagons and ensures a seamless structure like that of a football ( truncated icosahedron ). In addition, the holes in the new shaving foil are much smaller than before.
Materials and manufacturing
Shaving foils are made from nickel . There has been no change in this regard in the last 50 years. It makes sense to use it in the course of shaving and especially wet shaving because this material has a high level of corrosion resistance, especially when it comes into contact with alkalis (soaps). The shaving foil has a high hardness, which in the case of nickel materials can mainly be produced by cold forming. A high degree of hardness is essential for the edge retention of the cutting edges. Due to the good cold formability and the high ductility , it can be assumed that the foil was first rolled as a thin sheet and then brought into the final structure by a punching process.
The use of nickel should be noted despite a large number of consumers with a corresponding allergy. This can be justified with the advantages in production and with the fact that skin contact with nickel only poses an actual risk of allergic reaction from a migration limit of 0.5 μg / cm² / week. Furthermore, the risk only arises when it comes into contact with sweat, as nickel ions are then released and these enter the body through the skin.
At the end of the 1950s, the shaving foil was coated with precious metal , which was used for advertising purposes under the term "platinum-coated". In an energy-dispersive X-ray spectral analysis , however, it can be determined that the coating consists of the elements platinum and palladium . The proportion of palladium is higher than that of platinum. Palladium was believed to have been used to reduce manufacturing costs. The coating ensures increased scratch resistance. It is possible that the newer models do not have a precious metal coating for cost reasons.
wear
The analysis of the coating carried out in the Materials section explains why the surface of the new film shows increased wear compared to the older model . In SEM images it can be seen that there are significantly fewer scratches on the outside of the shaving foil from 1959. The increased scratch resistance is due to the material of the coating and not to the Vickers hardness of the base material. In the test of the cross-section, the hardness values are in the same range of 634 HV 0.05 for the newer model and 595 HV 0.05 for the older model . A higher hardness due to the coating cannot be determined, as it is very thin with a thickness of less than 1 μm.
On the inside of the two models, grooves can be seen in the direction of movement of the blades, which indicate the direct interaction between blade and film during the shearing process. On closer inspection of the hexagonal holes, it is noticeable that there is more wear in the corners than in the bars. This can be attributed to the meeting of hair, shaving foil and blade in the corner.
Sound
geometry
In a razor that was examined in 1959, 24 blades with a rectangular cross-section were embedded in a block of metal. These are not arranged perpendicular to the direction of shear, but slightly angled. The much smaller razor block from 2014 is produced as a cast part and consists of 31 individual blades. These have a trapezoidal cross-section with concave side surfaces and are perpendicular to the direction of movement.
While the blade radii of around 1.5 μm are the same for both models, there are clear differences when comparing the cutting angles, which presumably have a significant influence on the shaving result. With an angle of approx. 55 ° you can speak of a cutting shearing of the whiskers with the newer blade, whereas with the older blade with an angle of approx. 90 ° a blunt shearing takes place.
Materials and manufacturing
A chrome steel was used for the blades of the blade blocks manufactured in the middle of the 20th century . In the course of a die-casting process, the blades were embedded in a tertiary aluminum-silicon alloy. This has excellent properties in terms of castability. In the etched section, the AlSi alloy shows an irregular, two-phase mixed structure.
During the die-casting process, the heat from the aluminum block is dissipated from the liquid interior to the outside. This heat flow influences the cooling of the cast material, which is evident in the structure. Due to the external cooling of the excess material, which can sometimes be found on the side of the blades, this area cools down very quickly and a disordered structure is created with little diffusion processes when cooling. The result is a disordered, small-grain structure. A V-shaped area of aluminum grains is formed in the vicinity. There is a pronounced dendrite structure, the formation of which suggests a slower cooling rate. Due to the slowed solidification, larger aluminum grains are present in the third area in a matrix of an AlSi phase. In the Vickers hardness curve of the martensitic blade cross-section, which ranges from a hardness value of 600 HV 0.05 in the interior to a value of 683 HV 0.05 in the outer area of the blade, there is a tempering effect of the steel due to the die casting.
The shrinkage of the aluminum when it cools creates cavities between the blade and the AlSi mount, so that there are only partial contacts between the components and there is therefore an inadequate connection. This can lead to component failure in the course of use. The further development shows an optimization of this problem for a blade from 2014 by reducing it to a component element in the shear blade. Despite a low material thickness of around 0.3 mm, this blade is a cast part, as can be seen in the etched cross-section and the side view. The hard martensitic structure (720 HV 0.05) has the same structure in both directions and thus provides information about the manufacturing process described. The ratios of the peaks in the EDX spectrum are very similar to those of the material X153CrMoV12. Due to the high carbide density in the structure, the material is particularly resistant to adhesive and abrasive wear and is therefore well suited for fineblanking tools . In addition, once it has been cast in a mold, the material shows little dimensional change and is well suited for a subsequent coating. Such an additional refinement in the form of a thin chrome hard coating is visible in the image from the SEM and as a peak in the EDX spectrum. This layer of around 1 μm can also be seen in the cross-section.
wear
On closer inspection of the two blades, the one from 1959 shows a comparatively higher degree of wear than the one from 2014. The defects of the older blade can be seen in deeper scratches and crumbly areas, which are probably due to corrosion .
Only grinding marks and slight scratches can be seen on the surface of the newer blade. More serious signs of wear and tear are presumably prevented by the material properties mentioned above. When comparing the hardness of the two blades, there are only minor differences (683 HV 0.05 - blade 1959; 720 HV 0.05 - blade 2014 with the hardness test of the base material in the cross-section), which is why most of the wear is due to the missing hard chrome layer and the lower alloyed material in the model from 1959 is due.
Individual evidence
- ↑ a b c d e f g h i Material science investigations on Braun SM3 and Braun Series 9 at the WAM of the TH Köln Campus Gummersbach
- ↑ Gert Redlich: Max Braun's razor - part 5. In: HiFi Museum. Artur Braun, January 2014, accessed May 31, 2018 .
- ↑ Pure Nickel & Other Alloys. In: Nickel Institute. Nickel Institute, accessed May 31, 2018 .
- ↑ Peter Rauch: The properties and uses of nickel and its alloys. Accessed May 31, 2018 .
- ^ Heinrich Oettel, Hermann Schumann: Metallography . Ed .: Heinrich Oettel, Hermann Schumann. 15th edition. WILEY-VCH, Weinheim 2011, ISBN 978-3-527-32257-2 , pp. 371 .
- ^ Heinrich Oettel, Hermann Schumann: Metallography . Ed .: Heinrich Oettel, Hermann Schumann. 15th edition. WILEY-VCH, Weinheim 2011, ISBN 978-3-527-32257-2 , pp. 789 f .
- ↑ Nickelfrei.de: Distribution :: Nickelfrei.de - The information portal for people allergic to nickel. Retrieved May 31, 2018 .
- ↑ https://eur-lex.europa.eu/legal-content/DE/TXT/PDF/?uri=CELEX:32006R1907
- ↑ Nickelfrei.de: Definition :: Nickelfrei.de - The information portal for people allergic to nickel. Retrieved May 31, 2018 .
- ↑ Die WELT (Ed.): Die WELT - Edition of December 3rd, 1968 . No. 282 , December 3, 1968, pp. 5 .
- ↑ Platinum coating and palladium coating | surpro. Accessed May 31, 2018 .
- ↑ Standard DIN EN ISO 4957 - tool steels . DIN, March 31, 2017.
- ↑ a b Heinrich Oettel, Hermann Schumann: Metalography . Ed .: Heinrich Oettel, Hermann Schumann. 15th edition. WILEY-VCH, Weinheim 2011, ISBN 978-3-527-32257-2 , pp. 818 ff .
- ↑ a b Dörrenberg Edelstahl GmbH: material no.1.2379. (PDF) In: Dorrenberg.es. Dörrenberg-Edelstahl GmbH, accessed on June 7, 2018 .
- ↑ hard chrome | Ernst Meuter GmbH & Co. KG. Retrieved June 8, 2018 (German).