Does a milled electronic sample demonstrate RoHS compliance?
No. Compliance depends on the current applicable requirements and the complete testing and assessment process, not the milling operation alone.
In July 2006, the EU Directive Restriction of Hazardous Substances (RoHS) for restricted use of certain hazardous substances such as lead, mercury, cadmium and brominated flameproofing agents in electrical and electronic products became effective. An update in March 2015 (2015/863) added four new substances, mainly present in plastic parts, namely Bis(2-ethylhexyl)phthalate (DEHP); Benzylbutylphthalate (BBP); Dibutylphthalate (DBP); Diisobutylphthalate (DIBP). In July 2019, an amended RoHS Directive with new prohibitions on the use of substances came into force.
All EU countries must adopt the directive through national legislation which will not only affect EU members but also countries which export their products to Europe. In other parts of the world, like California and China, the directive has also been transformed into national regulations. In any case, the manufacturers of electric appliances as well as recyclers and disposers of electronic scrap need to carry out analytical examinations to prove that the RoHS directive is being observed.
Sample preparation of electronic scrap
The industries involved look for testing protocols for these regulated substances and while in most cases approved analytical methods are available, one major issue is often omitted: correct sample preparation. The affected electrotechnical products come in many forms and sizes from relatively simple devices such as toys all the way through to complex instruments and computers each of which contains many different sub-assemblies. Hence, it can be a challenge to produce a representative, neutral-to-analysis laboratory sample for subsequent analysis.
The primary target of investigation are electronic assemblies such as PCBs and individual components, plastic housing parts, mains cables and wiring. In PVC insulation, the detection of cadmium, lead and DEHP is required. It is important to remove any iron and steel components before starting the sample preparation process. These need to be evaluated separately.
To carry out reproducible analyses, and achieve representative results, a completely homogeneous sample with a fineness below 500 µm is required. With such a heterogeneous mixture of materials made from metals, glass, ceramics and plastics, this is no easy task. In addition, electronic components may have different breaking properties which make the selection of a suitable laboratory mill more difficult.
For the initial size reduction of this type of material, a RETSCH Cutting Mill such as the SM 300 (left) is recommended. This high-performance mill has proved to be particularly suitable for the size reduction of a heterogeneous mixture of hard and ductile as well as soft-elastic materials and larger initial feed size up to 80 mm. The complete laboratory sample, which can be as much as 30 liters when a cyclone system is used, is processed to a fineness of less than 7 mm in a first step. The SM 300 is available in a heavy-metal-free version which makes it especially suitable for sample materials which are analyzed for traces of hexavalent chrome. For the typical material mixes found in electronic scrap, the use of the 6-disc rotor is beneficial as it acts more like a shredder than the
parallel section rotor which acts like an axe. Therefore, also electric cables or tough materials are easily comminuted.
Application examples Cutting Mill SM 300
| Sample | Accessories | Starting size and quantity | Speed and grinding time | Final fineness D90 |
|---|---|---|---|---|
| Electronic scrap | • universal hopper • 6-disc rotor with cutting tips tungsten carbide • bottom sieve 4 mm • cyclone | 170 mm 100 g | 3000 rpm 30 s | < 5 mm |
| Electronic scrap with larger metal parts | • universal hopper • 6-disc rotor with cutting tips tungsten carbide • bottom sieve 6 mm | 50 mm 50 g | 1500 rpm 10 s | < 7 mm |
| Keyboard | • universal hopper • 6-disc rotor with cutting tips tungsten carbide • bottom sieve 4 mm • cyclone | 80 mm 1 piece | 1500 rpm 7 min | < 5 mm |
With the help of a sample divider (such as RETSCH’s PT
100, left, or, for sample amounts up to 60 l, the PT 600) a
representative
sub-sample
is obtained
for
further
pulverization to analytical fineness.
The required grind size of 500 µm and less can be easily achieved with the Ultra- Centrifugal Mill ZM 200 (right). The two-stage rotor/ring sieve system is extremely gentle on the material. Equipped with
tungsten-reinforced
grinding tools, wear through abrasion is not an issue with the ZM 200, and the risk of introducing impurities during milling can be avoided. This extremely efficient mill is characterized by very short grinding times and easy and convenient operation. Other RETSCH mills which are suitable for fine grinding of this type of sample material are the Vibratory Disc Mills RS 200 or RS 300 (pulverization of sample amounts of up to 2 l in one go) and the Mixer Mill MM 400 (for small sample volumes of up to 2 x 20 ml).
The new regulations also affect plastic softeners. RETSCH’s
CryoMill
(left)
facilitates
the
pulverization of elastic, ductile materials, which would only be deformed at room temperature, by automatic embrittlement of the sample with liquid nitrogen during grinding. In the ZM 200, the sample material can easily be embrittled with liquid nitrogen or dry ice prior to grinding. The dry ice may be fed into the mill during grinding which
has the additional benefit of chilling the sample while it is pulverized. This not only improves the breaking properties and avoids frictional heat but also ensures that volatile fractions are not adversely affected. The ZM 200 processes prechilled materials without any problems.
Application examples for pulverization of electronic scrap and plastic materials
| Sample | Mill / accessories | Starting size and quantity | Speed and grinding time | Final fineness D90 |
|---|---|---|---|---|
| Electronic scrap | • Vibratory Disc Mill RS 200 • grinding set 250 ml hardened steel | 5 mm; 70 g | 1500 U/min; 4 min | < 500 µm |
| Electronic scrap with larger metal parts | • Vibratory Disc Mill RS 200 • grinding set 50 ml hardened steel | 7 mm; 50 g | 1500 U/min; 1 min | < 500 µm |
| Keyboard | • Ultra-Centrifugal Mill ZM 200 • push-fit rotor 12 teeth, stainless steel • ring sieve 0.5 mm; cyclone • cryokit and LN2 | 5 mm; 1 piece | 18000 U/min; 15 min | < 550 µm |
| Rubber | • CryoMill • grinding jar 50 ml stainless steel • 1 x 25 mm ball stainless steel | 10 mm; 4 g | 8 min pre-cooling, 4 x (2 min grinding at 30 Hz and 30 s intermediate cooling at 5 Hz) | < 200 µm |
| Capacitor | • CryoMill • Grinding jar 35 ml stainless steel • 1 x 20 mm ball stainless steel | 5 mm; 3 g | 10 min precooling, 5 x (2 min grinding at 30 Hz and 30 s intermediate cooling at 5 Hz) | < 150 µm |
Plan the configuration for your material.
Define the component or material being assessed before reducing it. Separation of different materials, tool contact and the final analytical portion can affect interpretation. Discuss preparation with the laboratory performing the test; historic equipment applications do not establish current regulatory scope or compliance.
| Consideration | Information to provide |
|---|---|
| Test material | Component or defined homogeneous material |
| Target analysis | Substances and required method |
| Preparation control | Separation and tool contributions |
How should the application examples be used?
The results describe the materials and configurations discussed here. Confirm equipment options, contact materials and operating conditions for your own sample before adopting a method. A demonstrated endpoint does not guarantee the same outcome for a different material.
Discuss material testing with Glen Mills or request further information or a quote.
Explore the equipment discussed
- RETSCH RS 200 Vibratory Disc Mill
- RETSCH SM 300 Cutting Mill
- RETSCH CryoMill Cryogenic Mixer Mill
- RETSCH PT 100 Sample Divider