Article by Steven Adang, Laarmann Group B.V.
Determining the quality of purchased or produced goods is dependent on how a representative sample is obtained and the preparation of this sample. In-line sampling is crucial to monitor and control the production process. Incorrectly obtained or processed samples will lead to false analyses, resulting in goods being wrongly approved (false positive) or declined (false negative). In the last nine years Laarmann Group BV has specialised in advising, designing and building solutions for the representative sampling and processing of bulk materials.
Cost savings at various levels
The company strongly encourages companies to implement their own sampling process rather than outsourcing it. Outsourcing creates a range of expenses, including the amount of product that is lost during the process. For instance to ensure that an external laboratory has a representative amount of material for sampling, companies are usually required to send around 25 kilograms of product, even though the actual chemical analysis requires only a few hundred grams. Apart from the question of whether the laboratory produces a representative sub-sample, the left over (rejected) material is never returned.
The question is; what happens to this often costly material? Obviously it would be preferable for companies to be able to process and prepare their own sample, particularly when large quantities of precious materials are at stake. With a good sample preparation process, the quantity required for analysis can be reduced to a few hundred grams. Furthermore, processing the samples in-house make it possible to take multiple samples, thereby more accurately determining the quality of the material. Finally, companies who successfully implement their own sampling system not only reduce their material costs but also transport costs.
The stainless steel industry
Laarmann Group has developed an efficient and reliable system for sample processing of raw materials. In this specific case we look at the production of stainless steels which requires precise additions of e.g. chrome, nickel, titanium and molybdenum to iron. These high value materials are bought as ferroalloys. Correct determination of the metal content within these alloys is crucial when producing stainless steel. A shortage of certain elements will lead to an inferior quality of stainless steel, while an excess will only increase the costs of the production.
Companies who successfully implement their own sampling system reduce both material and transport costs.
The traditional method to determine the quality of the ferroalloys requires 60-70mm pieces of alloy to be sampled then reduced in size by crushing. The steel company used a jaw crusher to reduce 25 kg of material to pieces measuring ~10 mm. After the primary crushing the operator then manuallyh removes the material and puts it into a roller crusher where the product is further reduced to small pellets of < 2mm. The sample is finally sent to an external laboratory for analyses.
Push of a button
Laarmann Group B.V. has simplified the size reduction process to the push of a button. This removes the need for an operator to lift any heavy materials or perform multiple actions; the process is more efficient, resulting in more samples and an overall higher quality. The operator puts 25 kilograms of material into the inlet funnel and starts the process at a central control box. A vibratory feeder underneath the inlet funnel evenly feeds the bucket elevator. The bucket elevator lifts the material and feeds the jaw crusher (type LMFC250) which reduces thematerial to < 2mm. The pelleted material in transported, using a flexible connection, to a rotary sample divider which divides the sample into ten equal parts of 2.5 kilograms (sub samples).
The alloys have a density between 3 and 8 kg/liter, giving a partial sample volume of 500 to 800 ml. This sample is pulverised in a ring mill (type LM2000) to reach the desired end size of 125 microns. The external lab needs just 12 to 15 grams of this product to make into a tablet which can then be analysed with an XRF-machine (X-ray fluorescence). The funnel above the LMFC250 jaw crusher can be moved aside so that the installation can handle smaller quantities of material without contamination of the bucket elevator. Sliding the funnel aside also makes the crusher easily accessible for cleaning although this is not required on a regular basis; the pieces entering the bucket elevator are quite large, resulting in very little dust.
The advantages of the installation for a steel manufacturer can be summarized as:
- The amount of material to be sent to an external laboratory is reduced from 25 kg to 400 gram.
- The working conditions of the operator are considerably improved. His work load is reduced, freeing him up for other tasks.
- The efficiency of the installation allows multiple samples to be taken, improving the overall quality and representability of the process.
- A more accurate analysis of the purchased good triggers the suppliers to deliver high quality raw material as inferior quality will be spotted in an early stage.
- The installation can operate in an oxygen free environment to eliminate the chances of explosion which is common for some Ferroalloys.
About Laarmann Group
In addition to providing laboratory equipment, Laarmann Group offers a complete assessment of the sampling processes for clients. Their specialists can map the entire process in one day, from receiving the material in bulk to final analyse of the sample. For information see www.laarmann.eu