Beginning in 2005, the glass container company with better efficiency at the time began to select piston machines for air supply to military machines under the recommendation of air compressor dealers. Since 2011, the glass container company that selected the piston machine has felt that the support cost of the piston machine is too heavy and the failure rate remains high, which severely affected the production and made customers miserable. Acquiring screw air compressors in succession with sighs, in order to gradually replace the piston compressors already purchased. Some glass companies, with strong capital, choose a lot of piston machines, although they know that the cost is high, but they also stand firm. Some companies spent millions of dollars, and the piston machines they purchased became hedgehogs in their hands. There are still some companies that are also tempted to acquire piston machines amid the cry that "piston machines are more suitable for glass container companies than screw air compressors." Whether a single-piston machine or a double-piston machine is a compression machine has been debated for 30 to 40 years. In fact, each has its own advantages and disadvantages, and examples of good use.
Now it is time to discuss from practice and theory why the piston engine is not suitable for air supply to the army:
1. Existing piston machines in shopping malls are not suitable for glass container work: small exhaust pipes
1. Existing piston machines in the market
The existing piston engine in the market is a replica of the foreign 7bar exhaust pressure piston engine. The primary standard is the compact piston engine developed for the compressed air user solution with 7bar exhaust pressure. It is not suitable for the air supply of army machines with an exhaust pressure of 2~3bar. The piston engine currently sold in the market is like the Founder’s 4L-20/8 air compressor. It can be used, but it wastes power and costs a lot. The principle of the piston machine and the screw air compressor are different, and the mechanism of compressing the air is different. From the perspective of energy saving, the use of piston compressors to reduce pressure is not as good as the use of MA-20/8 screw air compressors. Some air compressor vendors who don't understand compressors change the motor of the piston engine with an exhaust pressure of 7bar to a smaller one. They mistakenly think how to do it. Lower the exhaust pressure to save electricity. The result is too much current, which not only wastes electricity, but even burns the motor.
2. The flow rate of the exhaust pipe scheme of European and American piston engines (when the exhaust temperature is 80℃ and the exhaust pressure is 7bar) is 10~15m/s. This flow rate is also selected for post-treatment of compressed air. For example: an oil-injected piston engine with an air volume of 30m³/min and an exhaust pressure of 7bar. The inner diameter of the exhaust pipe is usually 80mm. When the exhaust temperature of this pipe is 80℃, the compressed air flow rate is 15m/s. When the exhaust pressure is At 3.5 bar, the flow rate becomes 26.6 m/s. The pipe resistance at this flow rate is 3 times that at 7bar. Exhaust pipe diameter and flow rate of foreign oil-injected screw air compressors in the early 2000s are shown in the following table. Air volume m³/min Exhaust pressure bar Exhaust pipe diameter mm Exhaust pipe flow velocity m/s at 80℃ 10 7 50 13 20 7 76.2 11 40 7 100 12.8 Later, domestic manufacturers widely changed the exhaust pipe diameter of 20 m³/min from 76.2mm to 65mm. The flow velocity of the exhaust pipe at 80°C increased to 14m/s. The gas volume of the modified product is 25m³/min. When the exhaust temperature of the machine is 80℃, the exhaust pipe flow rate increases to 19m/s. When using such an air compressor with an exhaust pressure of 3.5 bar, the exhaust pipe flow rate at 80°C will reach 33.6m/s. A single screw air compressor company supplied the OG(F)D-35.0/3.5 screw air compressor of a glass company with an air volume of 35 cubic meters per minute, an exhaust pressure of 3.5 bar, and an exhaust pipe diameter of 80 mm. When the exhaust temperature is 80°C and the exhaust pressure is 3.5 bar, the air flow velocity of the exhaust pipe contraction is 31 m/s. Such a high pipeline flow rate has severely exceeded the pipeline flow rate standard.
3. Why is it so? Many domestic screw air compressor manufacturers have always advertised that they use German imported heads (or mainframes) or mainframes made with German skills. The exhaust port standard of the oil-injected screw air compressor sold in China is basically the same as Atlas, and the same in the world. The difference is shown in the above table. Domestic screw air compressor manufacturers only need a handful of program talents, and they do not intend to change foreign program standards. 90% of screw air compressor manufacturers are just copying other people's machines. So it presents the scene of the national screw air compressor interface standard. Some air compressor manufacturers propose to participate in the concept of energy saving from the machine's main engine plan, piping plan, heat dissipation plan, oil circuit plan, including noise plan, etc., making it one of the few energy-saving manufacturers in China. This idea is correct. However, no products conforming to the above-mentioned concept were seen.
4 For a wide range of variant products, how to control the exhaust pipe flow rate? An example of a variant product of a screw air compressor company. Exhaust pressure MPa Flow rate m3/min Pipe diameter mm Temperature ℃ Temperature K Exhaust pipe compressed air flow rate m/s Motor power Kw 0.7 10.5 50 80 353.16 13.4283 55 0.7 13.5 50 80 353.16 17.26496 75 0.7 16.5 50 80 353.16 21.10161 90 In this example, in order to promote sales, the manufacturer increased the speed of an air compressor with a capacity of 10 m3/min, seeking a capacity of 13.5 m3/min and 16.5 m3/min. The compressed air velocity of the exhaust pipe increases from 13.4 m/s to 17.3 m/s and 21.1 m/s. The compressed air velocity of 21.1 m/s is already very difficult to tolerate. Assuming that a 16.5 m3/min air compressor is used in an environment with an exhaust pressure of 0.35 MPa, the air flow rate of the exhaust pipe contraction will reach 37.5 m/s, and I can hardly dream of what the result will be.
2. Existing screw air compressors in shopping malls are not suitable for glass container work: screw compressors are not suitable for volume ratio
When the exhaust pressure is 7 bar, the internal volume ratio of the screw air compressor is usually 5.5 distribution. The air supply pressure of the army machine is 1.8~2.8bar, and the exhaust pressure is 3.5bar. It is suitable to use the screw air compressor main body with the internal volume ratio of 3.5. The internal volume ratio is the internal compression ratio, and the internal compression ratio of the screw compressor should be smaller than the intern compression ratio. It is doubtful that the internal compression ratio of the screw compressor is greater than the practical compression ratio, which consumes more power. Because there are not many screw air compressors for glass container work, the manufacturers that produce screw air compressors are reluctant to make other casting models or modify the exhaust port processing standards. It is reasonable to supply air to the military aircraft with a screw air compressor mainframe with an internal volume ratio of 3.5, and the corresponding exhaust port standards should be changed accordingly. Large companies refuse to do it; small companies don’t understand and cannot do it, so "the existing screw air compressors in shopping malls are not suitable for the air supply of glass container units." In summary, the problem with screw air compressors used for air supply to military aircraft lies in the internal volume ratio of the exhaust pipe and the main engine. The questionable parts of the internship are: the main engine body and the exhaust end cover, the exhaust end cover to the oil and gas separator receiving, the oil and gas separator, the oil and gas separator to the aftercooler receiving, the aftercooler, the compressed air exhaust receiving, etc. With regard to the above-mentioned 7 optimization solutions, the flow field of the screw air compressor with an exhaust pressure of 3.5 bar can be smoothed, and the noise and power consumption can be reduced.
3. Existing screw air compressors in shopping malls are not suitable for glass container work: high support costs
Distributors of screw air compressors can't make much money by selling screw air compressors. The main reason for dealers selling screw air compressors is to gain efficiency and profit. It is necessary for customers to accept their performance and consumables (compact oil or coolant, air filter, oil filter, oil and gas separator). Moreover, the user is forced to refuse to accept their performance and consumables, and subsequent repairs and other performances will be rejected. As a result, the screw air compressor cannot maintain the established working conditions, and the vast majority of users have to submit. Because screw compression oils are very different, with a wide range of inferior quality and high prices, the suppliers have made a lot of "articles" here to enable customers to replace the compression oil, oil filter, and oil in a short period of time according to their requirements. Presents a situation where most users are overwhelmed. The question lies in: the glass container company is not good at using the initiative when acquiring air compressors, blindly inquiring about the application situation, the quotation of the air compressor, etc. I neglected to let the air compressor supplier specifically report "annual electricity consumption, oil product costs, three-filter costs, efficiency costs, etc. to summarize consumption → support costs." After all, the supplier was biased because it did not press the air pressure. The support cost of the machine is measured by the supplier, but only relying on the opinions or suggestions of the peers, without scientific analysis and consulting senior experts, and the purchase price as the primary basis for calibration. After all, it can only be slaughtered. The final internship has now been confirmed: In the absence of low-pressure screw air compressors, it is unspeakable to equip multiple screw air compressors in parallel on a large scale to supply air to the army. A military air supply station is equipped with 1 to 2 screw compressors, which are different from the centrifugal air compressor and the piston air compressor to form a different air volume ladder combination. There is no doubt that it is feasible.