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The use of diamond in the stone processing industry continues to grow. And one of the main factors for this growth has been the development of diamond synthesis technology that allows better control of crystal structures so that the diamonds can be tailored to specific applications.
Coupled with this, advanced processing of diamonds has allowed products to be delivered with synthetic diamond particles that are selected to a consistent quality and stringent particle distribution criteria.
Processing quality control is extremely important and particles are sorted not only by size and shape but also crystal purity, strength and thermal stability.
Large differences in particle sizes and strengths within a product range can have detrimental and unexpected effects on performance in operation.
The reason Element Six have become a leader in the supply of products to the stone processing industry is not simply because they are able to produce a variety of different synthetic diamond products. They also have the ability to deliver those products to consistent qualities within stated and stringent particle distribution criteria.
The physical properties important to the use of diamond in stone processing – ie its hardness and wear characteristics – relate to the structure of the diamond crystal and its chemical bonding.
At the atomic level diamond has a cubic structure with each carbon atom covalently bonded with four other carbon atoms. Suffice it to say that this results in huge molecules with a particularly rigid structure.
Diamond synthesis aims to make diamonds that have properties – shape, inclusions, size – such that they perform well in sawing and grinding applications for a wide range of products.
For applications in the stone industry, synthetic diamond is produced by a high-pressure high-temperature process (HPHT).
In essence, HPHT emulates the way in which natural diamonds are created deep in the earth where the enormous pressure means that carbon crystals with the denser structure of diamond are thermodynamically more stable than those of other carbon forms such as graphite.
Recreating such processes came through understanding the relationship between the graphite and diamond forms of carbon and the conditions for transforming one into the other.
A phase diagram, plotting pressure against temperature, revealed the regions where each type of carbon was likely to be the preferred form.
What is known as the Berman-Simon line defines the boundary between these regions and gives scientists the first clues to the conditions under which graphite might be converted into diamond.
At room temperature and normal pressure, while graphite is the thermodynamically stable form, diamond is only slightly less stable. But making the transition between these states requires overcoming a huge intermediate energy barrier. This, figuratively speaking, was the hurdle that scientists had to be able to jump in order to synthesise diamond.
It is the combination of high pressures measured in fifty or more kilobar, tens of thousands of times normal atmospheric pressure and temperatures of around 1,400°C that create the conditions for diamond synthesis.
The science of catalysis has also contributed to commercial diamond synthesis.
The addition of a catalyst allows presses to run at lower pressures than would otherwise be needed to produce diamond.
Certain molten metal catalysts such as iron, cobalt and nickel dissolve graphite and this facilitates diamond precipitation when the other conditions for diamond formation are met.
Two main press designs have been developed to synthesise diamond on a commercial scale: the belt press and the cubic press.
The belt press is popular because a relatively large volume of material can be produced in a single press run.
In this design, a ceramic canister tube that contains the starting materials for diamond fits into a ring or belt of tungsten cobalt that is further restrained by a large steel band. This ensures that the pressure is confined so that the pressure delivered by two upper and lower anvils acts only over the top and bottom surfaces of the canister. The belt is profiled so it fits snugly in contact with the anvils.
The tapered anvil design results in the delivery of higher pressures at the point of contact with the canister. Pressures of around 80 tonnes per square metre are concentrated over an area one hundred times smaller at the heart of the machine.
Thick copper cables deliver electric current to resistively heat the metal canister to the required temperature.
The second type of press, the cubic press, has six anvils that provide pressure simultaneously on to all faces of a cube-shaped volume.
Cubic presses are typically smaller than belt presses but can achieve the pressure and temperature necessary to create synthetic diamond faster. However, cubic presses cannot easily be scaled up to larger volumes.
What goes into the canister and the length of press runs largely depends on the size, morphology and type of diamond you want to get at the end of the process.
Generally diamond-makers are like wine-makers and jealously guard their particular recipes. However, the principles are well known. If you want to create diamonds less than one millimetre in size – such as those required for use as abrasives in grinding and cutting – the aim is to produce lots of tiny, individual diamonds as quickly as possible.
In this case, the canister is loaded with ‘slugs’ comprising blended catalyst metal and graphite powders. The inclusion of diamond seeds also ensures that nucleation (the tendency to gather and grow) occurs on the seeds. Each recipe tends to produce one particular type of diamond structure, though other forms may be also be present.
At the end of each press run, the synthetic diamond produced has to be extracted, or recovered, from the mixture of residual graphite and catalyst metal in the canister. This is a chemical process.
Finally, the synthetic diamond is graded by size and shape.
For the majority of sawing applications in the stone industry, particle strength is a key factor that influences performance, durability and efficiency in the tool.
Strength is generally a property of the crystal structure and normally the more regular or crystalline the structure, the higher will be the strength.
Size is another factor and in this case small is best because the smaller the particles the higher the strength.
In addition, the diamond will also contain certain impurities or inclusions which have an impact on the properties of the diamond.
It is important that the diamond material is carefully selected for the application so that in the tools this will translate into good integrity and predictable breakdown characteristics and good performance.
Generally, synthesising diamond with the appropriate crystalline structures requires careful control of the growth parameters and there is also the matter of yield for each of the various crystal structure permutations.
For consistent performance in an application, then, synthesis is coupled with stringent grading and quality control procedures to ensure that each product batch is of a consistent quality.
This is why tools made using carefully produced, graded and selected diamonds are regarded as premium ones and tend to command the highest prices.
A new diamond tool company has come into the UK market and made a major (and successful) bid for expansion at the Natural Stone Show at ExCeL London last month (March).
Based near Ashford in Kent, Granite Tool Supplies Ltd (GTS) were incorporated on 6 February 2006 by Jason Barnard and Greg Wise, both previously with diamond tool company DK Holdings.
Jason says they had not wanted to overstretch themselves too early, but by the time of the Stone Show in March were ready to expand. And the show has already helped them do that by bringing in new accounts.
“We had previously been involved in selling tooling and consumables into the stone industry with DK Holdings, which helped give us a good understanding of the needs of stone fabricators,” Jason told NSS.
“We didn’t want to go out into the market place and sell any old product, so we took the decision that each and every product within our programme would be rigorously tested by our panel of approved stone fabricators, which includes well known companies such as Butterfield Natural Stone, Classico Marble and Prima Marble & Granite.
“Each item was tested, then, based on the written feedback received from our panel, modifications were made such as changes to the diamond bonds of our blades and polishing discs, increasing the diameter of the central waterfeed holes in our drills, and adding slots to our dry cores. Put simply, our products have been developed by stone fabricators for stone fabricators.”
Since starting out, their range has virtually doubled in size. Their 2008 catalogue and website with an online shopping cart have been designed for ease of use, with clear headings, colour photos, product descriptions and prices.
“We offer our customers a next day delivery service throughout the UK and Eire, supported by weekly call van sales in the South East and quarterly visits elsewhere,” says Jason.
As well as their own-brand GTS range, they are also official partners of Abratech, KDrills, SKE and Saint-Gobain Abrasives (with brands such as Flexovit and Norton).
Jason says: “Our aim is to offer high quality products, in stock availability, excellent prices and on time delivery.”
Stuart Cleary of Cranden Diamond Products makes a lot of one-off solutions for customers. One such product was a 400mm diameter wheel designed to make drainage grooves in a 75m length of replacement path through the estate of Bodnant Gardens in Conwy Valley, Wales.
The path was constructed of Anglesey Marble – the same stone that was used to build Birmingham Town Hall. It is exceptionally hard.
The wheel is 66% electroplated in D427 natural diamond grit supplied by Element Six. It was designed to grind a concave groove 125mm wide and 75mm deep into 1m lengths of the Anglesey Marble. These sections would lay between path slabs either side of them to act as a drain for rainwater. This is precisely how the original path was configured when the gardens were created in their current form in the 19th century.
Another popular product from Cranden Diamond Products is a two tool resin-bonded set for cutting drainage grooves in granite and quartz kitchen worktops using a radial arm saw. This was a bit of a departure for Cranden as they more commonly make electroplated tools for processing softer marble and limestone. “We have done pretty well with them,” says Stuart.
With Cumbrian machinery company Accurite having taken over the sales of the entire Ghines marque in the UK, and Ghines making diamond tools as well as machinery and dust extraction, diamond tools supplied by Accurite are now from Ghines.
Ghines have taken advantage of each tool-making technique (sinterization, vacuum-brazing, electroplating, vulcanization) to obtain a set of shaped wheels where each tool represents what they believe is the best possible solution for its function.
Ghines have the maximum control on the entire production process, from the manufacturing of the metallic supports to the diamond application.
The geometry of each tool is achieved with the necessary increment so that all the steps can be accomplished without modifying the spindle trim.
Thanks to the accurate manufacture and ability of their tools to keep their shapes, replacing a single wheel is now possible without resetting all the other tools, saving time and money and consistantly achieving the best finish.
Ghines wheels are suitable for any stone material and can be used on any machine, manual or CNC, with the simple modification of dimensions and connection.
A technical chart with the characteristics and working parameters of the Ghines tools is provided to customers when they purchase a tool. And Ghines technicians are available and ready to demonstrate the tools on manual and CNC machines.
Diamond tooling has played a major part in the development of stone processing, not least for granite worktop manufacture. And with the economies of increased production and developments of the tools the price of them has fallen at the same time as they have been developed to last longer and work quicker without compromising the finish.
Now stone companies are bombarded with emails from the Far East with offers of cheap tools. Those who have bought them report various degrees of satisfaction, while those supplying diamond tools in the UK, some of which are indeed sourced in the Far East, say most customers these days are more concerned with performance than purchase price because their priority is to maximise machine up-time and minimise the amount of time each slab spends on the machine or being finished by hand.
Barrie Whorrall of Encore Diamonds cites his ‘Space’ blades as an example.
They are manufactured with a consistent pattern of diamond throughout the segment. The benefit of that, says Barrie, is a cut up to 50% faster than a standard blade with 30% longer life and the ability to work on a wider range of materials.
Barrie says: “Because of the placement of the diamonds in the segment the diamond grit works 100%. As a performance-based product it is necessary to use the highest quality diamond grit with high concentration, making it marginally more expensive than a standard blade.
“Hard and soft bond consideration still applies, but because the Space blades are more efficient they cut a wider range of materials. With faster cutting times and longer life, this more than offsets any extra costs.”
Another example is Encore’s Thickness-Maker for calibrating stone, natural and artificial. Its lightweight acrylic centre and reinforced arbour reduces weight on the machine bearings and is quiet.
This is not a new concept, but design improvements to reduce weight and noise while retaining a robust structure have re-awakened interest in this tool.
Segment bond is designed for the expected workload providing optimum performance and life.
Apart from the use of the Thickness Maker to reduce slab thickness to 20mm for splashbacks, it is used widely for calibrating slabs before edge profiling, guaranteeing thickness to allow for accurate shaping.
With the increased demand for architecturally shaped stone, multi-pass profiling has become popular. In order to remove the saw marks from the shaped material, Encore Diamond have designed a range of routers with replaceable tips, manufactured in metal bond, PCD and electroplated – sometimes a mixture of two of the technologies being used on one tool.
Barrie says: “The demand for off the shelf standard or general purpose tools has diminished, with customers demanding premium products. With this in mind, Encore Diamond offer a design service, providing individual tools for customers with specific requirements, enabling them to achieve the finished products required.”
Higher productivity and quality are paramount to success in the stone industry – an industry that is still growing but experiencing increasing competition, say diamond tool specialists Stonegate.
This puts the spotlight on diamond tooling, says the company’s Peter Hazell. “At Stonegate, we spend a lot of time developing and improving our tooling and our range. Here’s an example: Our new Evo blade [pictured above] is a blade with laminated segments. The outer wall of them is harder than the inner wall. This causes the top of the segment to wear into a concave shape instead of convex, creating a sharp double cutting edge.”
The result, say Stonegate, is faster and cleaner cutting, less load on the saw, longer life and the ability to cut a greater range of granites.
They also have a new range of tooling from Nicolai Diamant offering high speed cutting, long life and improved product finish. “This is just an example of our continually progressing programme,” says Peter.
Stonegate work closely with many small manufacturing companies in Europe that make tooling to Stonegate’s own specifications to meet the exact requirements of customers.
“We are always glad to hear from our customers with a view to working together with them to mutual advantage,” says Peter.
Tel: 01482 620007
