By JOHN HOLUSHAAUG. 28, 1991 This is a digitized version of an article from The Times's print archive, before the start of online publication in 1996. To preserve these articles as they originally appeared, The Times does not alter, edit or update them. Occasionally the digitization process introduces transcription errors or other problems. Please send reports of such problems to . As complex plastics increasingly replace metals in cars and appliances, recycling these products becomes a larger problem. Attention is now turning to a high-temperature process called pyrolysis that breaks down plastics into burnable oil and gas.Auto makers and plastic suppliers hope to demonstrate within a few years that this technique has great commercial potential. Environmental advocates question whether pyrolysis is truly recycling, but backers of the technique say it is far better than throwing the plastic away.Pyrolysis breaks materials down by heating them at high temperatures in the absence of air. Because no oxygen is present, plastics and rubber left over from cars do not burn, as they would in an incinerator. Instead, the heat, about 1,300 degrees Fahrenheit, breaks the complex hydrocarbons down into simpler molecules, producing a liquid resembling heating oil and a combustible gas, along with some ash. Potential for PollutionBecause nothing except the fuel for the pyrolysis reactor is burned, the technique may cause less air pollution than incinerators. But if the gas produced by pyrolysis is used to heat the reactor once it reaches operating temperature, as most plans envision, pollution will result from plastic and rubber that contain chlorine or sulfur, said Raymond Machacek, of A. D. Little, a consulting firm.AdvertisementVinyl plastics contain chlorine, and sulfur is used in the vulcanization of rubber. The chlorine and sulfur atoms tend to form hydrochloric and sulfuric acids, which are toxic pollutants, Mr. Machacek said.AdvertisementThe growing amount of plastic in automobiles causes grumbling among metal recyclers, because it results in more worthless material that must be disposed of in landfills, at additional cost. Unlike plastic soda bottles, which can easily be reprocessed, most of the plastics left after cars are shredded and the metals extracted are composites of materials that have been further contaminated by paint and adhesives."Very often you will have incompatible plastics glued together," said Richard L. Klimisch, an environmental specialist at the General Motors Corporation's Technical Center here. In addition, many of the plastics are a type known as thermosets, which cannot be melted down and used again, like the material in soda bottles.A car on exhibit at the technical center, cut away to display new sound-deadening insulation materials, also inadvertently illustrates how difficult these new materials might be to recycle. Several of the insulating materials are simply labeled, "Complex blend of various stuff."Researchers at the G.M. Technical Center are running perhaps the largest pyrolysis trials, but an association that includes several major plastic and rubber makers, including Goodyear Tire and Rubber, Dow Chemical, Eagle-Picher, Allied-Signal and Owens-Corning Fiberglas, is also experimenting with the technique.Industry trends make it clear that metal recyclers are going to have to find ways to cope with more plastic. "Cost is driving the industry to greater use of plastic," said Irvin E. Poston, a plastics specialist at G.M.He notes that plastic body parts are lighter than steel, requiring less costly tooling to shape and improving fuel economy. The entire outer body of G.M.'s new line of mini-vans, like the Chevrolet Lumina APV, is made of composite plastic. Pyrolysis recovers the energy content of plastic after its useful life is finished, he said.Please verify you're not a robot by clicking the box.Invalid email address. Please re-enter.You must select a newsletter to subscribe to.View all New York Times newsletters.Plastics suppliers say they may be able to use the ash produced in pyrolysis as well, particularly if the feedstock is uncontaminated scrap from the production process. Since some of the composites used in auto body panels consist of 50 percent inert filler, clean ash might be substituted for the limestone used now. But it is less likely that ash from shredder residue contaminated with other substances could be used.Industry officials have been quick to label pyrolysis a form of recycling, but some environmentalists say it is similar to incineration, because the material is destroyed and some energy is used. "We do not consider incineration as recycling on this side of the environmental fence, and a lot of people put pyrolysis in the same category," said Lisa Collaton, a solid-waste specialist at the Environmental Action Foundation in Washington.AdvertisementAdded John Ruston of the Environmental Defense Fund in New York, "Pyrolysis is not recycling; it is pyrolysis."Mr. Poston said G.M. and some plastic suppliers had run pyrolysis tests on shredder residue at two operations for processing old tires. He said that once the material reached operating temperature, it gave off enough gas to be self-sustaining without external fuel. The recovered oil is available for sale.He said the company and its suppliers planned larger-scale tests to see if the approach was technically and economically feasible in commercial quantities. "We have done 5,000 pounds; now we are going to do a run of 50,000 pounds so we can see the true economics," Mr. Poston said. More Plastic in CarsA group of plastic parts suppliers predicts that the amount of thermoset materials going into cars will almost double by 1995, to 423 million pounds, from 242 million pounds in 1990. That is in addition to thermoplastic materials, which can be melted and used again.Officials involved in recycling say pyrolysis may have a place in materials disposal, after more valuable plastic parts of old cars and appliances have been pulled out for recycling. "Pyrolysis can be part of the waste-management approach, but we should not give up on recovering various plastic streams for re-use," said Michael Fisher, a technical director at the Council for Solid Waste Solutions, a plastics industry group.Noting that it took metal recyclers several decades to refine techniques for separating different metals and alloys, he said that the plastics industry was just beginning the process. "There are 20 different types of plastic on an automobile," he said. "Some will be recycled, and some will go for pyrolysis."Herschel Cutler, executive director of the Institute for Scrap Recycling Industries, said the institute was interested in pyrolysis, despite economic, technical and pollution problems with some other experiments. "There have been some plants in the past that were dismal failures," he said.Nevertheless, he said, with the amount of plastic in cars rising, "we are still looking at it." He added, "We may see a new generation of pyrolytic activity that really can convert materials to oil, gas and carbon black."A version of this article appears in print on August 28, 1991, on Page D00009 of the National edition with the headline: . Order Reprints| Today's Paper|Subscribe

In modern manufacturing, CNC (computer digital control) processing technology plays a vital role. Among them, turning, milling, cutting and turning milling combined processing are common process methods. They each have unique characteristics and scope of application, but also have some advantages and disadvantages. In-depth understanding of the similarities and differences of these processing technologies is of great significance for optimizing the production process and improving the processing quality and efficiency.


Advantages and disadvantages of machining processes such as CNC turning, milling, cutting and turn-milling combined machining


CNC turning

(1) Advantages

1. Suitable for processing rotary parts, such as shaft, disk parts, can efficiently realize the outer circle, inner circle, thread and other surface processing.

2. Because the tool moves along the axis of the part, the cutting force is usually more stable, which is conducive to ensuring the machining accuracy and surface quality.

(2) Disadvantages

1. For non-rotating parts or parts with complex shapes, the processing capacity of turning is limited.

2. A clamping usually can only process one surface, for multi-sided processing requires multiple clamping, which may affect the processing accuracy.



CNC milling

(1) Advantages

1. Can process various shapes of parts, including plane, surface, cavity, etc., with strong versatility.

2. High precision machining of complex shapes can be achieved through multi-axis linkage.

(2) Disadvantages

1. When processing slender shaft or thin-walled parts, it is easy to deform due to the action of cutting force.

2. The cutting speed of milling is usually higher, the tool wear is faster, and the cost is relatively high.



CNC cutting

(1) Advantages

1. High machining accuracy and surface roughness can be obtained.

2. Suitable for processing materials with high hardness.

(2) Disadvantages

1. The cutting speed is slow, and the processing efficiency is relatively low.

2. Higher requirements for tools and higher tool costs.



CNC turning and milling composite processing

(1) Advantages

1. Integrated turning and milling functions, a clamping can complete the processing of multiple processes, reduce the clamping times, improve the processing accuracy and production efficiency.

2. Can process complex shape parts, make up for the lack of a single turning or milling process.

(2) Disadvantages

1. The equipment cost is high, and the technical requirements for the operator are also high.

2. Programming and process planning are relatively complex.



CNC turning, milling, cutting and turning milling combined processing processes each have advantages and disadvantages. In the actual production, the processing technology should be reasonably selected according to the structural characteristics of the parts, precision requirements, production batch and other factors to achieve the best processing effect and economic benefits. With the continuous progress of technology, these processing processes will also continue to develop and improve, providing stronger support for the development of the manufacturing industry.


The similarities and differences of CNC turning, milling, cutting and turning milling combined machining are analyzed from different angles


1. processing objects and shapes

1. Turning: mainly suitable for processing rotary parts, such as shaft, disc, sleeve parts, can efficiently process outer circle, inner circle, cone, thread and so on.

2. Milling: better at processing planes, steps, grooves, surfaces, etc., with advantages for non-rotating parts and parts with complex contours.

3. Cutting: It is usually used for fine machining of parts to obtain high precision surface and size.

4. Turning and milling composite processing: It integrates the functions of turning and milling, and can process parts with complex shapes and both rotary and non-rotary characteristics.

2. tool movement mode

1. Turning: The tool moves in a straight line or curve along the axis of the part.

2. Milling: The tool rotates around its own axis and does translation movement along the surface of the part.

3. Cutting: The tool makes precise cutting action relative to the part.

4. Turning and milling composite processing: on the same machine tool, to achieve different movement combinations of turning tools and milling tools.

3. processing accuracy and surface quality

1. Turning: When processing the surface of the rotary body, it can achieve higher accuracy and better surface quality.

2. Milling: Machining accuracy for flat and complex profiles depends on machine tool accuracy and tool selection.

3. Cutting: Very high precision and excellent surface roughness can be achieved.

4. Turning and milling composite processing: combining the advantages of turning and milling, it can meet the high accuracy requirements, but the accuracy is also affected by the comprehensive impact of the machine tool and process.

4. Processing efficiency

1. Turning: For large quantities of rotary parts processing, high efficiency.

2. Milling: When machining complex shapes and polyhedral parts, the efficiency depends on the tool path and machine performance.

3. Cutting: Because the cutting speed is relatively slow, the processing efficiency is generally low, but it is indispensable in the demand for high precision.

4. Turning and milling composite processing: one clamping to complete a variety of processes, reduce the clamping time and error, improve the overall processing efficiency.

5. Equipment cost and complexity

1. Turning machine: relatively simple structure, relatively low cost.

2. Milling machine: According to the number of shafts and functions, the cost varies, and the cost of multi-axis milling machine is higher.

3. Cutting equipment: usually more sophisticated, high cost.

4. Turning and milling composite processing machine: integrated with a variety of functions, high equipment cost, complex control system.

6. Application fields

1. Turning: widely used in automobile, machinery manufacturing and other industries of shaft parts processing.

2. Milling: It is often used for the processing of complex parts in mold manufacturing, aerospace and other fields.

3. Cutting: Often used in precision instruments, electronics and other industries with high precision requirements.

4. Turning and milling composite processing: in high-end manufacturing, medical equipment and other fields, it has important applications for the processing of complex and high-precision parts.

CNC turning, milling, cutting and turning milling composite processing in many aspects of the similarities and differences, should be based on the specific processing needs and production conditions to choose the appropriate processing technology.




Comparison of efficiency of turning and milling combined machining with turning and milling


The efficiency comparison of turning and milling combined machining, turning and milling cannot be simply generalized, but is affected by many factors.

Turning has high efficiency in the processing of rotary parts, especially for large quantities of standard shaft and disk parts. Its tool movement is relatively simple, the cutting speed is high, and continuous cutting can be achieved.

Milling has advantages for machining planes, steps, grooves and complex contours. However, when processing simple rotary parts, its efficiency may not be as good as turning.

The combination of turning and milling machining combines the advantages of turning and milling, and can complete the turning and milling processes in a single clip, reducing the number of clips and positioning errors. For the parts with complex shape and both rotary and non-rotary characteristics, the combined turning and milling machining can significantly improve the machining efficiency.

However, the efficiency benefits of combined turning and milling may not be evident in the following cases:

1. When processing simple parts that only need to be turned or milled in a single process, due to the high cost and complexity of the turn-milling complex machine tool, it may not be as efficient as the specialized turning or milling machine.

2. In small batch production, the adjustment and programming time of the machine tool account for a large proportion in the entire processing cycle, which may affect the efficiency advantage of the turn-milling composite processing.

In general, for the medium and large volume production of complex parts, the turn-milling composite machining usually has a higher overall efficiency; For simple parts or small batch production, turning and milling may be more efficient in certain situations.

CNC turning, milling, cutting and turning milling combined processing technology is an important means in modern manufacturing industry. Turning is good at processing rotary parts, milling can deal with complex shapes and polyhedra, cutting can achieve high-precision surface treatment, and turn-milling composite processing is a combination of the two, can complete a variety of processes in a clip. Each process has its own unique advantages and scope of application, high turning efficiency in rotary body machining performance, milling versatility to meet the needs of complex contours, cutting accuracy is excellent, turning and milling combined processing is both precision and efficiency. In actual production, according to the characteristics of parts, accuracy requirements, batch size and other factors, reasonable selection of processes to achieve high quality, high efficiency and low cost manufacturing goals, to promote the continuous development and progress of the manufacturing industry.