FAQ

1. What are the alternatives to hard chrome plating? 
2. How can the processing time be shortened? 
3. How long is the processing time for one surface treatment?  
4. Which base materials can be surface treated with hard chrome? 
5. If there are weak spots in the component's base material (blowholes, pores), can the
component still be coated? 
6. How resistant is a hard chrome surface treatment to corrosion and wear? 
7. To which media is hard chrome resistant? 
8. Which characteristics can be influenced by the procedures used at STI Group? 
9. Is hard chrome suitable for the effects of high temperatures? 
10. Which types of mechanical processing can STI Group offer? 
11. What size components can STI Group process? 
12. Which levels of hardness can be achieved with hard chrome plating? 
13. What is the maximum surface pressure for chrome plated surfaces? 
14. What is the maximum weight of the components? 
15. Which surface treatments are available from STI Group?
16. Which component geometries cannot be hard chrome plated?
17. Which parameters need to be considered during the surface treatment process?
18. What factors are considered with regard to the quality of a surface treatment?
19. Which plating structures can be produced by STI Group?
20. What happens to a hard chrome surface in the event of temperature/shock/load?
21. What is the difference between hard chrome plating and bright chrome plating?
22. What is the difference between heavy chrome plating and chrome plating to size?
23. What is the difference between technical hard chrome plating and "hardening"?
24. When/why do components need surface treatment? 

1. What are the alternatives to hard chrome plating? 
In considering the adhesion requirements (high surface pressure) individually and in combination with corrosion and wear resistance, there are hardly any two surface treatments which are qualitatively identical. Depending on the application specifications, hard nickel, nickel dispersion coatings, nickel phosphorous, nickel alloys, various CVD and PVD surfaces as well as thermal spray surfaces may represent good alternatives.

2. How can the processing time be shortened? 
By assured quality of the base material and prior notice of the surface treatment requirements needed.

3. How long is the processing time for one surface treatment?  
It's hard to give a standard answer to that question, since the processing time depends greatly on the following factors: 

• Quality of the base material 
• Size and form of the component 
• Complexity of the particular procedure 
• The extent to which STI Group can plan the preparations
• Plant availability/capacity

4. Which base materials can be surface treated with hard chrome? 
Almost all base materials can be hard chrome plated. However, they rarely take into account the time and cost considerations required for your successful industrial processes. The longstanding know-how of the STI specialists makes it possible to offset the disadvantages of a basic material, to increase its positive characteristics and to create additional properties.

• Steel (alloyed and unalloyed)
• Cast steel (nitrated and induction-hardened) 
• Cast iron 
• Casting in iron moulds 
• Copper 
• Nickel 
• Brass 
• Bronze 
• Aluminium (alloys)
• Spray coatings 
• Build-up welding 
• Upon request: 
• Titanium
• Synthetics (such as epoxy composites, CFRP/GRP, etc.)
• etc.

5. If there are weak spots in the component's base material (blowholes, pores), can the component still be coated? 
In most cases, yes, it can. STI Group uses various processes and technologies, so we can even process problematic base materials which result in a non-porous surface treated product. Profitability might have to be assessed on a case-by-case basis.

6. How resistant is a hard chrome surface treatment to corrosion and wear? 
In general, hard chromium is extremely wear and corrosion resistant. Since resistance is influenced by many factors, we will be happy to provide you with additional information upon request.

7. To which media is hard chrome resistant? 
The resistance characteristics of hard chrome plating depend on the area of use, the base material and the plating specifications. The characteristics are controllable in the surface treatment process (coating thickness, fissure shape, structure and base material). Each individual application should be clarified separately. In general, hard chromium is resistant to many media and acids, with the exception of chlorides.

8. Which characteristics can be influenced by the procedures used at STI Group? 

• Corrosion resistance
• Wear resistance
• Adhesive properties 
• Wettability (from hydrophilic to hydrophobic) 
• Precision 
• Surface topography (from mirror finishes to defined structures) 
• Hardness 
• Friction coefficient 
• Demoldability 
• Impact resistance 
• Temperature resilience 
• Gloss level
• and many others

9. Is hard chrome suitable for the effects of high temperatures? 
In general, a hard chromium surface is consistent against static temperature loads up to 400°C, assuming that the component can be heated up slowly. After 400°C static load, a gradual loss of hardness and after 700°C a rapid loss of hardness of the chromium coating occurs. However, many parameters influence temperature resistance and can possibly change it. To some extent, hard chrome coatings are successfully used for temperatures over 1000°C. We will be happy to provide additional details upon request.

10. Which types of mechanical processing can STI Group offer? 

• External circular grinding
• Flat grinding 
• Grinding in operating conditions (pressure and temperature) 
• Special curve grinding 
• Belt grinding

Polishing:

• extra fine grinding: CNC circular grinding with polishing discs
• "super finishing“: Polishing with vibrating advance by means of belt, stones or 
  mulsions/suspensions, respectively 
• Honing
• Lathing/Cutting

11. What size components can STI Group process? 
Without technical fixture or infrastructure adaptations, the following dimensions apply: Chrome plating: Components of up to more than 12,000 mm (40 feet) in length with a diameter of 4,500 mm (more than 14 feet). Grinding: Components of up to 27,000 mm (88 feet) in length and a diameter of 6,000 mm (19 feet). Because of our highly efficient and flexible infrastructure it is entirely possible to process even larger parts. Details are available upon request.

12. Which levels of hardness can be achieved with hard chrome plating? 
Hardness levels of up to 1,100 HV0.1 can be achieved while maintaining a flawless (and non-porous) surface.
However, hardness levels of between 800 and 1,000 HV0.1 are usually more sensible.

13. What is the maximum surface pressure for chrome plated surfaces? 
Under ideal conditions a hard chromium coating can withstand a static surface pressure of up to 1000 N/mm2. The distortion risks are greatly influenced by the overall conditions, such as the base material or the rigidity of the construction.

14. What is the maximum weight of the components? 
Our infrastructure will accommodate components of up to 64 tons, depending on the geometry.

15. Which surface treatments are available from STI Group? 
Galvanic Surface Procedures

• Hard Chrome 
• Triplex Chrome
• Structure Chrome
• Dispersion Coating
• Nanochrom
• Chromium/PTFE
• Chrome-ceramics
• Galvanic Nickel
• Chemical Nickel
• Nickel chrome

Thermal Spray Coatings

• High Velocity Oxygen Fuel Spraying
• Plasma Spraying

Further Coating Procedures

• Cadmium coating
• Thermal treatments/ Dehydration
• Electropolishing
• Burnishing
• Silver-plating
• Tin-coating
• Stainless steel passivation
• Zinc phosphating
• Magnesium phosphating

Our Specialisations

• Dimensional corrections
• Homogenisation of basic materials
• Interior chrome plating

16. Which component geometries cannot be hard chrome plated? 
From a technological and infrastructure perspective, STI Group can treat parts with almost any conceivable geometry (form and size).

17. Which parameters need to be considered during the surface treatment process?
There are countless parameters, both in the plating as well as in the later mechanical processing. To keep to every parameter within the most stringent limits is imperative for the quality and precision of a surface. Close monitoring and adherence to these parameters is of utmost importance in the recipe STI | Hartchrom's success.

18. What factors are considered with regard to the quality of a surface treatment?
The quality of a surface treatment depends on a combination of many factors. These can be easily classified into two groups:

One factor is the quality of the surface treatment systems and processes. The ability to keep the process within very narrowly defined limits determines the precision with which all requirements can be met. The second factor is whether or not the plating can be done from one mould.

The quality of a surface treatment is indicated by the following factors:

• Coating strength and structure 
• Homogeneity of the coating 
• Pore number and depth 
• Fissure structure and number 
• Hardness 
• Surface quality 
• Adhesion to the base material and cohesion in the coating 
• The ability to treat components without damage or modifications to untreated areas.

19. Which plating structures can be produced by STI Group?
With regard to the surface topography, Hartchrom AG Steinach can manufacture almost any type of desired structure (from mirror finish coatings and mirror pocket coatings to individually defined structures). Regarding a coating's structure, the following structures can be primarily produced:

• Multi-layer chrome plating
• Micro- and macro-fissure layers 
• Non-porous coatings, and many more

20. What happens to a hard chrome surface in the event of temperature/shock/load?
Thin layer chromium plating will not change. For thick chromium plating there is a danger of fissure formation and a loss of the corrosion resistance, etc. These risks can be greatly reduced through technical procedural measures.

21. What is the difference between hard chrome plating and bright chrome plating?
Hard chromium plating, as practiced at STI Group, is used for protecting machine parts against any and all types of stress. Such stress includes wear due to abrasion and surface pressure, as well as corrosion from the effects of materials, high temperatures, etc. Hard chromium plating also provides these parts with functional characteristics such as non-adhesive qualities, wettability, precision, surface structures, etc.

With the aid of hard chrome plating, not only can the service life of a machine be improved, by reducing wear and corrosion, but the functionality can be improved as well.

Bright chrome plating, also called decorative or adornment chrome plating, is used primarily for visual effects and to protect from corrosion. It provides the part with only very minimal wear protection. The parts to be chrome plated are often pre-polished, in many cases, manually. The chrome layer itself is wafer thin (usually 0.3 - 1.5µm). It is most often used for an attractive and long-lasting optical effect. Decorative chromium plating is often found on the decorative components of cars, motorcycles, household fixtures, utility objects, etc.

22. What is the difference between heavy chrome plating and chrome plating to size?
In the heavy chromium plating process we strive to achieve coating geometry, precision, coating thickness and surface roughness in precision grinding. In chromium plating to size, coating thickness and plating sequence in the galvanic process are determined. After surface treating, the work pieces are polished or ground again if needed, during which only the roughness of the surface is impacted, and not its geometry or thickness.

If there are weak spots in the component's base material (blowholes, pores), can the component still be treated? In most cases, yes, it can. STI Group uses various processes and technologies, so we can even process problematic base materials which result in a non-porous surface treated product.

23. What is the difference between technical hard chrome plating and "hardening"?
Technical hard chrome plating is done at lower temperatures. Therefore, distortion (i.e. sheathing of the part) does not take place as it can with hardening. Hardening is normally a process whereby the structure of the component is actually changed. There is usually no corrosion protection in the hardening process. Only components made from materials that can be hardened (e.g. nitrided steel) can also be hardened. The progression of the hardening process is not homogenous. Hard chromium plating, however, can be deposited on many base materials in a wide variety of desired layer thickness. Hard chromium plating is consistent throughout the entire layer. Corrosion and wear properties are excellent. In addition, when using the heavy chrome plating process, it is possible to provide the component with many other properties, such as anti-adhesive and topographical properties.

24. When/why do components need surface treatment?
Components are usually treated for two reasons: The first reason is to provide the component with (additional) functional properties, which are not inherent in the base material. A good example of this is the hard chromium plating of CFRP and GRP rolls. CFRP and GRP are very light substrates and are therefore well suited for high speed rolls. As these materials are non-homogeneous, porous and require wear protection, they often cannot be used at all without a surface treatment. The second reason is to extend the lifetime of a component. The service life of the components previously being used in an untreated condition (such as piston crowns) can thus be lengthened considerably.