 Why use quality Cube Moulds?Cube Testing has, over the years, become the routine standard test for checking that concrete conforms to design specification.
Traditionally, Cube Moulds have been constructed from steel and cast iron and are manufactured to extremely tight engineering tolerances.
Of these tolerances the most important has been shown to be that for flatness of the sides. Some years ago a research project was carried out to compare results obtained with the same concrete mix using some Cube Moulds with flatness's inside the old BS tolerance for new Moulds of 0.03mm ("the best") and some approaching the maximum in use tolerance of 0.06mm ("poorer"). Results showed that samples made from the same batch of Concrete in "the best" Moulds were giving noticeably better results in compression tests than the "poorer" Cube Moulds.
This difference in results is because on samples made in "the best" Moulds, the compression load is spread uniformly across the two parallel faces of the sample, but samples made in the "poorer" Moulds which have imperfect faces (possibly convex or concave), the compression forces are applied unevenly to only parts of the faces.
Cube strengths are adjusted by changes to the concrete mix design; to make the concrete stronger usually more cement (the most expensive component of the mix) is added. Therefore, a company using top quality Capco Cube Moulds will need to use less cement in their concrete to achieve test results inside specification than another company who are using poor quality Cube Moulds. The cost of this additional cement will be significantly more over time than the cost of using top quality Moulds.
In recent years we have seen the availability of plastic Cube Moulds, which are lightweight and often disposable. Plastic by its nature is flexible and cannot produce cube samples with engineering tolerances (especially flatness) even approaching that of Cast Iron Moulds. All the concrete samples which we have seen from plastic moulds have had sides so badly bowed that measuring equipment showed flatness imperfections measured in millimetres rather than the hundredths of millimetres we are used to. Naturally this is reflected in much poorer compression test results.
The European Standard for concrete testing EN12390-1 requires each concrete cube sample to be accurately measured and recorded for size, squareness and flatness prior to compression testing unless the sample has been prepared in a Mould that has been certified to meet all tolerance requirements, in which case only a rapid dimensional check and the Mould number needs to be recorded.
Capco Cube Moulds are recognised worldwide as the market-leading product, and we are continually updating and improving them. We are the only Cube Mould supplier still manufacturing in the UK and have a quality control system overseen by a quality manager where every Mould is individually checked.
We can confidently say that using top quality Capco Cube Moulds is more economical in the long term for the following reasons:
* More accurate concrete strength results.
* Unnecessary cement will not need to be added to concrete mix designs to make up for the poor results obtained from inferior testing methods.
* Moulds are easier and quicker to use and clean, saving on technician's time (or allowing them to do more in the day!!).
* Moulds last longer before they need replacement.
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 A Brief Guide to Using Ball MillsPrinciple of operation
The Ball Mill Jar is filled with grinding media and the product to be ground. Rotation of the Jar causes the grinding media and product to move around the wall of the jar creating a grinding process.
Choosing the Ball Mill Jar and Grinding Media Material
Materials available include:
Porcelain/Steatite - A hard ceramic, fairly inert when mixed with most products.
Alumina - A high alumina ceramic which is harder than porcelain but again fairly inert when mixed with most products.
Mild Steel - Hard wearing but corrodes (rusts) in water and can react with some products.
Stainless Steel - Harder than mild steel and does not corrode with most products, however it can still react with some products.
The material should be chosen to suit the product being ground, remember that the nature of the milling process means that the inside of the jar and the grinding media wear away leaving small amounts of material in the finished product. The size of grinding media again is dependent on the product being ground; larger balls will have more impact energy but there will be a large gap between adjacent balls. Small balls will grind finer but have less impact energy and if the product is viscous are more likely to "stick" to the jar walls. It is ideal to use a mixture of different sized balls to ensure even and effective grinding. We sell Ball Charge Sets containing a mixture of ball sizes to suit different sizes of jar.
Filling the Jar
The grinding process will not work if the jar is overfilled, there must be an air gap to give the grinding media and product room to move around. Ideally the Jar should be approx 50% by volume full of grinding media and 25% by volume of product to be ground [measure the volume by water displacement to allow for the voids between the grinding media - balls or cylinders).
Selecting the Rolling Speed
As the jar rotates the media gets pulled up the side of the jar by friction. Rotate too slowly and the charge will only go part way up the side of the jar before rolling back down. Rotate too fast and the charge will "stick" to the jar walls by centrifugal force. The ideal speed is somewhere in between so that the balls carry almost to the top of the rotating jar and fall or "cascade" back down impacting on to the product and media below. This "cascade" effect is reached when the grinding noise is at its loudest.
Grinding Time
This is found purely by trial and error, if a very fine grind is required and time is not a critical factor then leave for several hours or overnight. To increase throughput check after a shorter time and see what grinding result has been achieved.
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