The turning processing method is actually a secondary processing method of plastics. Because the sintered product of Teflon PTFE has relatively low hardness and good toughness, it can be processed into Teflon film by metal turning method. Turning generally requires a dedicated lathe, and metal processing lathes and woodworking lathes can also be used.
The cut blank is a sintered PTFE Teflon rod. This kind of rod is sintered and formed at one time, the internal structure and plasticization degree are not very uniform, and sometimes it is inevitable that a small amount of raw material is sandwiched, and this kind of rod is easy to deform due to changes in the environment. not allowed. For this reason, PTFE blanks need to be pretreated.
The pretreatment can be carried out in a sintering furnace, and the general treatment temperature is 360~380℃. After reaching the temperature, keep it for a certain period of time, and then slowly cool to room temperature. For large blanks, it can be kept at 327℃ for 2h, and then dropped to below 250℃ within 5h, and then wrapped and cooled to room temperature. After the processed blank is placed for 3 to 5 days, it can be turned.
PTFE Teflon, like most plastics, has a compressive strength higher than its tensile strength, which is generally 2 to 3 times larger, that is, the compressive breaking force of plastic is always greater than the tensile breaking force. Therefore, in the turning of PTFE, the shape of the tool and turning conditions should be well designed to avoid tensile fracture.
The cutting tool used for turning is made of carbon steel quenching tool. The cutting edge should be sharp. The larger the rake angle, the more favorable it is for tensile fracture to occur from the mechanical point of view, and the turning force can be reduced accordingly. Therefore, the rake angle of the tool should be 20 ~30° above.
If conditions permit, the turning of PTFE Teflon should be carried out in a constant temperature environment, because the size of PTFE varies greatly with temperature. Generally, the processing temperature is usually 22~25℃, and the temperature change is small, which can ensure the uniformity of the film. At the same time, the heat generated during the turning process can easily change the temperature. Therefore, when high film precision is required, spray cooling is required during cutting. The cooling medium is generally liquid fluoride.
The turning speed should be selected appropriately to prevent overheating and cooling. At the same time, the cutting speed also affects the performance of the film, such as smoothness. Generally, the turning speed of PTFE Teflon is 90~225m/min.
The thickness of the Teflon film processed by the turning method can reach about 0.04mm. This kind of membrane has good mechanical properties, no substance is added during processing, low impurity content, non-toxic, and can be used in medicine.