The enlargement of presses has been operating in China for over ten years, which has greatly promoted the development of China's superhard materials industry. Previously, it was generally believed that it was almost impossible for China's diamond industry to catch up with and surpass the world's advanced level. However, after the enlargement of presses, along with new technologies such as powder catalyst, indirect heating, high-precision control, and scientific synthesis processes, the overall quality of China's diamond, including variety, color, transparency, roundness, surface finish, TI, TTI, and strength, has significantly improved. It can be said that it has reached the international advanced level. In this process, the enlargement of presses has made indispensable contributions. If there had not been equipment enlargement, it would be difficult to imagine that other new processes and technologies could be implemented so quickly and improve the quality of diamond so rapidly.
Because the enlargement of equipment has truly brought benefits to colleagues, continuous enlargement has become a hot topic in the superhard materials industry in recent years. However, in the second half of 2011, some difficult problems hindering continuous enlargement gradually emerged. This article will discuss these problems in detail and provide reference suggestions for related issues.

From Figure 1, it can be seen that the force applied in a belt type press is in the upper and lower two directions, which we call primary pressure, and is active. The surrounding pressure is a reaction force formed due to the limitation by the cylinder after being subjected to the upper and lower forces (as shown by the solid line in Figure 1a). This forms the pressure cavity. This pressure cannot be actively adjusted; it is passive, and we call it secondary pressure. That is to say, the high-pressure cavity in a belt type press is composed of primary pressure and secondary pressure.
The cubic press, on the other hand, is completely different. The cubic press can be actively adjusted in all six directions. Especially when we have the relative balance theory and a high-precision control system, the pressure in each direction of this type of press can be arbitrarily adjusted by people. It must be pointed out here that this arbitrary adjustment must comply with the relative balance theory; mutual balance in all directions is required to form a high-pressure cavity. Here, all pressures are primary pressures, so the degree of adjustment freedom is completely superior to the belt type press. With the relative balance theory and high-precision control system, our cubic press can make appropriate adjustments based on the deformation state of the synthesis column, so everything is under control, fully demonstrating its true advantage! This is what we often say is the reason why the cubic press has more advantages in force application than the belt type press!
As everyone knows, the anvil consumption of large domestic presses has been controlled at a relatively low level. The author predicted 5-6 years ago that with our progress in high-pressure theory and practice, we could completely control anvil consumption to below 1 kg/10,000 ct. In fact, a very small number of units had already achieved this target at that time, and the continuous monthly statistics were stable between 0.3 and 0.5 kg/10,000 ct. So, the question was only whether it could be widely promoted. The author recently visited many medium and large enterprises with hundreds or even thousands of presses and saw that many enterprises can achieve the target of 0.5 kg/10,000 ct. Better ones have already controlled it at the advanced target of 0.3 kg/10,000 ct. It should also be noted here that this does not refer to the anvil consumption of low-quality diamond synthesis processes, but rather the anvil consumption of medium and high-quality diamond synthesis processes!
According to the information we have, this target is difficult to achieve on belt type presses. Most belt type presses have anvil consumption of 5-8 kg/10,000 ct. The fundamental reason for this is their inherent deficiency. Because belt type presses, like cubic presses, require "centering" adjustment, but this adjustment is even more difficult than with cubic presses! Due to this, belt type presses also experience the phenomenon of "explosion". This can cause damage to the anvils and cylinders, especially large cylinder loss. Because when it breaks, it is systemic. Once damaged, it can be over a hundred kilograms; how much diamond needs to be synthesized to make up for this?
The cubic press is different. Unlike the belt type press cylinder, its non-heating cylinder anvils are divided into four segments. When one is damaged, it is impossible for all four to be damaged (although complete damage in one instance also occurs). So sometimes damaging one saves 3/4, damaging two saves 1/2, and even damaging three can still save 1/4. Therefore, the advantage in anvil consumption is fully demonstrated!
Everyone knows that anvil design follows the principle of large support. The cubic press applies the principle of large support by just increasing and thickening the anvil appropriately. A belt type press, to effectively use the large support principle, must thicken the entire cylinder. As everyone knows, if the outer diameter is increased, the weight increases quadratically, which further adds to the disadvantages of the belt type press!
The biggest previous doubt about cubic presses producing single crystal diamond was the belief that high-quality single crystal diamond could not be produced. At that time, there was insufficient understanding of powder catalysts, assembly methods, and most importantly, severe insufficient control precision of the equipment. Therefore, for a long time, single crystal diamond comparable to that produced by belt type presses could not be obtained. Through continuous observation, experiments, and research on the theory and practice of high-quality diamond in recent years, a deep understanding of this issue has been gained fundamentally. Although large presses were available at first, the high-quality diamond we envisioned was not obtained. But with technological progress, the proportion with 250-300 N, or even ≥ 400 N, has been gradually increasing. It started at 5%, then 10%, followed by 15%, and now can reach 20%-30%. The operators' control ability and judgment ability have also been greatly improved. It should be said that the assertion of foreign countries having an advantage in high-quality diamond no longer exists! This part is also achieved by large scale cubic presses.

Why have cubic presses developed strongly in recent years, while belt type presses, both domestically and internationally, have not achieved rapid development? The fundamental reason is still cost, or economic efficiency. When various types of superhard materials can be produced normally and belt type presses do not have a special advantage, cubic presses have a special advantage in terms of cost.

It can be simply known from a case study of a domestic enterprise that an investment of over 300 million yuan at that time only yielded six belt type presses. Let's perform a simple calculation for it. With relatively full load production, it produces 24 synthetic blocks per day. Each synthetic block produces 600-800 ct, so it can produce 48,000 ct of diamond per day. Calculated on an annual basis of 11 months, each equipment can produce 5.64 million ct per year. Six pieces of equipment can produce about 33.84 million ct in total (we cannot consider factors like price index and USD exchange rate over a decade later here).
What if we invest 300 million yuan today? The main equipment investment is 220 million yuan, which can obtain about 150 presses with a Φ700 mm cylinder diameter (already配套 - meaning 'with matching components' or 'fully equipped'). Including land and other matching facilities, the total investment is 80 million yuan. Based on a 40-minute synthesis process, the average single yield is about 300 ct. Synthesizing 30-35 synthetic blocks per day, the average daily production per press should be about 9600 ct. Calculated on an annual basis of 11 months, a single press can produce over 3 million ct per year. The annual output of 150 presses should reach 450 million ct. It should be noted that if producing good 20/25, 25/30, 30/40 diamond, the yield will decrease appropriately. From the above data, the difference is nearly 13 times. With such an input-output ratio, we are completely confident that the chance for belt type presses to make a comeback is now very, very small. Why do I elaborate on this here? Because in some high-level discussions analyzing the situation, some people say: Britain and the United States are using your resources, and when your resources are almost used up, belt type presses will make a comeback and rise again. The author believes this is absolutely impossible.
Furthermore, domestically, in terms of products, adjustments can be made as needed according to market demand. This includes adjustments in particle size; adjustments in quality; adjustments in variety (fine material, superfine material, composite sheets, large single crystal particles, etc.). Many of our enterprises have moved away from the state of selling whatever they produce. Instead, they are all pursuing a rational development path that adapts to market demand and combines market demand with economic efficiency. Producing featured products is the only way for some small and medium-sized enterprises to survive and develop.

Let's use another set of data comparison to further illustrate. A 6000-ton belt type press cylinder weighs about 150 kg, with a price of 240,000 yuan (RMB, same below). A single anvil weighs about 75 kg, with a price of 130,000 yuan, and two are about 260,000 yuan. The single yield is about 600 ct, and the average anvil lifespan is 2000-3000 cycles, with the best being around 5000 cycles. Anvil consumption is 5-8 kg/10,000 ct. The current main domestic presses are shifting towards Φ700-750 mm. The anvils used here are also gradually shifting towards Φ(160-175) mm. A Φ160 mm anvil weighs 27 kg, with a unit price of 13,000-15,000 yuan. A set of anvils is about 78,000-90,000 yuan. Generally, the anvil lifespan is over 10,000 cycles, and the best can reach 40,000-50,000 cycles. Assuming they are used for synthesizing Φ(52-59) mm cavities, the single yield can reach about 300 ct or more. The quality is close to or comparable to belt type presses. Thus, it seems that after the presses are enlarged, China's cubic presses are more advantageous! (A Φ175 mm anvil weighs about 31 kg, with a unit price of 23,000-28,000 yuan, and a set is about 150,000 yuan, but it is currently not stable enough.)
The above is only about the original price. In addition, cubic presses have "explosions," and belt type presses also have "explosions". If a belt type press explodes, besides the cylinder and anvils being damaged, the press ring outside the cylinder is also often damaged. A set of press rings costs another 30,000-40,000 yuan, and domestically it is currently difficult to supply, which has a significant impact, directly affecting the operating rate.
In terms of anvil consumption, it has generally dropped to below 1 kg/10,000 ct in China. Good ones are controlled at only 0.3-0.5 kg/10,000 ct, and the best have achieved ≤ 0.3 kg/10,000 ct. This has greatly reduced the cost of diamond production in China. The average lifespan of a belt type press cylinder is 4000-5000 cycles, while the average lifespan of the anvils is 2000-3000 cycles. The average lifespan of cubic press anvils has already reached over 10,000 cycles, with the best reaching tens of thousands of cycles. This is actually 1/10 of the anvil consumption of belt type presses. This is another important factor why foreign belt type presses have lost their competitive advantage!

Due to the specificity of belt type presses, they still have some advantages in synthesizing coarse-grained, high-strength diamond. They can be designed with a track for pulling in and out, or with a three-position planar turntable for feeding material blocks. Other automated designs seem ineffective, and arbitrary enlargement is indeed the case. However, cubic presses frequently need to be opened and closed, so from the beginning, we paid great attention to their automated control. For a long time, this has become an advantage for synthesis processes that require only a short time. For example, producing 80/120, 120/140-140/170, 170/230-230/270, 270/320-320/400 products. Recently, some units' featured products are synthesized on presses into cubic-octahedral polyhedral crystals with quite perfect morphology. The particle size is only 400/500, 500/600, 600/700, and the finest has reached 800/900. Of course, at this point, dispersion, deagglomeration, etc., have the same difficulty as with nanodiamonds, and the quality is also significantly worse. These special processes for medium-fine, fine, and superfine particles, as well as processes specifically for producing RVD, and synthesizing small particle polycrystals, all require short or extremely short production cycles. Using belt type presses greatly increases labor, so the belt type press becomes a clear disadvantage, while the advantages of the cubic press are displayed.

Why has the enlargement of presses not declined in recent years? Simply put, it is driven and tempted by economic efficiency. Every investment is a challenging test for large presses – dare or not dare? That requires courage and boldness. Invest or not invest? Invest in which cylinder diameter? These investments are large, ranging from tens of millions to over a hundred million or even several hundred million yuan for a single investment. Without experience, one is walking a path never walked before, so risk and benefit coexist, and science and reality coexist. "The rainbow is always after the storm" is not just lyrics. Our industry has gone from hundreds of companies being eliminated to dozens today, with only about ten companies having over a hundred presses.
When the author was at a certain enterprise, after installing 100 presses with Φ500 mm cylinder diameter, there was a repeated discussion about whether to install presses with Φ560 mm or Φ600 mm cylinder diameter. Finally, it was decided to install Φ600 mm cylinder diameter presses. Later, it was successful, and it was felt that the repeated discussions and research at that time were scientific. Similarly, two or three years later, when installing a new batch of presses at another unit, the question was whether to install Φ650 mm or Φ700 mm cylinder diameter presses. After research, it was decided to install Φ700 mm cylinder diameter presses, which led to the current set of data. Whether this is the most reasonable can only be verified by time, but at least for now, it seems successful. Why has the author been relatively successful in proposing successful parameters that were accepted by enterprises? This is related to the author's consistent work on the front lines for many years. When the cavity size developed from Φ(8-10) mm to Φ(15-18) mm, the author's biggest discovery was that increasing the cavity size was not just an act of increasing single yield, but also further improving the quality of diamond while increasing the single yield. This understanding is very important; it has realized a process from quantitative change to qualitative change. The changes in presses with Φ(600-650-700) mm cylinder diameter further confirm this point. This is shown in Table 1.

The biggest problem is not the manufacturing technology of large presses. According to reliable information, two Φ850 mm cylinder diameter presses have already been produced domestically and are undergoing tests in the areas of single crystal diamond and diamond composite sheets. This indicates that the R&D and production of China's cubic presses have entered a mature stage and can be scientific and serialized.
But is it problem-free to achieve successful mass production? The author has repeatedly used "hardware" and "software" to describe the relationship between diamond presses and the配套 (matching) synthesis processes. "Hardware" should not simply be said to be the main machine and booster, but should include their design, basis, and rationality. Based on investigations, the following conclusions are drawn:
Firstly, at cylinder diameters of Φ750-Φ800 mm, especially ≥ Φ800 mm, operations are already felt to be inconvenient. Increased opening is an important aspect, but it is not comprehensive. Besides taking out and placing synthetic blocks, which are necessary operating procedures, inspection is the biggest difficulty. Therefore, we believe that simply increasing the size of the press to enlarge the cavity is not a reasonable choice.
Secondly, regarding the current problems with large anvils. The main purpose of enlarging the press is to enlarge the cavity, which necessitates enlarging the anvils. As for existing domestic anvils, the relatively good ones should be in the Φ140-Φ160 mm range. Anvils of Φ175 mm clearly show instability, with significantly higher anvil consumption, mostly reaching 1 kg/10,000 ct. If belt type presses are not good, cubic presses are also not good if consumption is high. This becomes a clear disadvantage compared to anvil consumption maintained at 0.3-0.5 kg/10,000 ct.
Thirdly, regarding the current problems with pressure medium. Another important aspect of the continued development of superhard materials nationwide is that the supply of high-quality pressure medium is decreasing. Prices have risen from several hundred yuan/ton to 1200-1400 yuan/ton, even to 2200-2400 yuan/ton, and recently reached 5000-6000 yuan/ton. Furthermore, Beijing has enforced restrictions on its production to protect the environment, which are major national policies. Therefore, the application of red pyrophyllite in recent years, as well as the selection and research of other new pressure media, have been placed in important positions. It is thus necessary to discuss the feasibility of continuous press enlargement.

Is continuous enlargement necessary? According to relatively reliable information, the enlargement of belt type presses abroad was also a hot topic for a while. After the completion of 5000-6000 ton presses, a 10,000-ton press plant was built in Ireland, and a 12,000-ton press was also tested. During a discussion, a foreign high-level expert stated that they had tested a 30,000-ton press. However, information obtained from different sources indicates that the 10,000-ton press did not fully function and was the first equipment to stop production. The 5000-6000 ton presses, however, could be used up to about 90% of their tonnage, meaning the actual pressure used was up to 5400 tons. Learning from foreign experience, must we necessarily try to outperform each other and see which enterprise has the largest cylinder diameter? Currently, great importance should be placed on cost-effectiveness, which is more important than anything else! And it should be considered from multiple aspects: yield, quality, consumption, and more!
Given that China's superhard materials industry holds an absolute advantage globally, domestic counterparts do not need to engage in cruel internal competition. Focusing on quality and yield, building brands, and having distinguishing features are more important.

Is it feasible to increase tonnage without increasing press weight and volume? This is another important issue that should be considered currently. The author repeatedly emphasized this more than ten years ago. Later, this viewpoint was elaborated in detail in the book "New Technologies and Progress in Superhard Materials in China". An article was also jointly published with Lu Fengnong. When visiting Guilin this time, the author saw that the largest diamond press manufacturer in the country, Guilin Metallurgical Machinery General Plant, has begun working in this area, which is very noteworthy!
We emphasize increasing tonnage without increasing press weight and volume based on the principle of using advantageous steel materials for the main stress-bearing parts of the press, and also working on heat treatment and precision machining. For example, many press hinge beams currently use 35CrMo, while the Guilin plant has already adopted 35NiMoCr for some presses. The strength difference between these two after heat treatment is over 29%, so the strength of a hinge beam with the same arm thickness will also increase by over 29%. If our originally designed hinge beam could only withstand 100 MPa, a hinge beam of the same size can now withstand 120-130 MPa. This level of high pressure state has been frequently used by us before and should not cause any problems.

This is another new concept. The author previously widely applied this process on presses with Φ230-Φ320 mm cylinder diameter, but later abandoned it due to being led by some incorrect ideas. In recent research, it was found that some units are applying this idea in designing synthesis cavities, thereby achieving good synthesis results. Therefore, anyone who adopts this idea to design synthesis assembly blocks can enlarge the cavity, increase yield, and improve quality on existing Φ500-Φ750 mm cylinder diameter presses. For example, a unit using a Φ700 mm cylinder diameter press achieved the yield of a Φ750 mm cylinder diameter press, and some even exceeded the yield of typical Φ750 mm cylinder diameter presses. The author believes this is very worth promoting.