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Welding method of polypropylene folding filter


Polypropylene folding filter is an ultra-fine filter, referred to as filter element, used for sterilization filtration in the fields of medicine, pharmacy, biochemical inspection, etc., used for separation and purification in chemical engineering, beverage process, semiconductor automatic rinsing, water purification treatment, etc. filter.

The filter element is made of a polymer chemical material through a unique adhesive coating process. The ultra-thin microporous filter membrane is folded on both sides by a support layer, crimped into a cylindrical filter layer, and welded and consolidated with the plastic inner and outer cylinders and end caps. When filtering, the Filter Medium passes through the microporous membrane, and the particles having a larger pore size in the medium are retained, thereby achieving separation. In order to minimize the influence on the high performance of the microporous membrane and the change of the microstructure, special care should be taken when the filter layer is sealed with the inner and outer cylinder end caps, that is, the welding conditions are strictly controlled, and finally the performance of the microporous membrane is required. The test results are used to determine the quality of the filter seal welding.

At present, polypropylene filter welding has formed a particular scale on the market, and the welding quality is also continually improving, but there is still a considerable distance compared with the international brand filter. The sealing welding of domestic filter cores generally adopts hot plate welding, that is, the hot template is first heated to a predetermined temperature, and then adhered to the welding surface of the parts. After a predetermined heating time, the sexy model is quickly evacuated, and the two heated weldings are performed. The cover soon adheres to it, and it can be cooled and solidified. Hot plate welding has certain advantages. The heating and melting time and temperature of the welding surface can be detected and monitored at any time by ordinary timers and temperature sensors. The parameter setting can be adjusted anywhere at any time through the PLC software, and the welding process has a short cycle. Easy to form mass production.

However, this direct contact with the contact heating can easily cause the phenomenon of plasticity. Although the Teflon anti-adhesive coating can be isolated between the plastic welding surface and the hot template, the sealing welding has a high requirement on the temperature and fluidity of the welding surface, that is, the temperature range of the molten layer is narrow and the surface hardening layer is microscopic. Generally, when the room temperature is 22 °C at room temperature if the system response time of the equipment exceeds 3s due to the mechanical structure, the welding process parameters will be difficult to guarantee. This can only rely on increasing the mold temperature to ensure the welding surface requirements, and the membrane temperature is one liter. High will reduce the anti-adhesion of the Teflon coating, leading to premature aging of the sheet and layer, which will affect the quality of the seal weld.

The new single-station welding equipment is mainly designed according to the characteristics of the filter seal welding, from the mechanical hardware and integrated control software, completely changing the way of using the cylinder push welding on the side cover of the conventional equipment, avoiding the resulting The shortcomings of low synchronism precision and poor controllability of welding speed make the machine and electric power more closely cooperate, adequately providing convenient debugging mode, ensuring that the final commissioning process parameters can perfectly meet the welding requirements, respectively, from the mechanical and integration The critical points of control, operation process, etc. are explained.

The microporous membrane is a skinny polymer membrane with a microscopic state of porous sponge. The standard pore size ranges from 0.1 microns to 10 micrometers. The main characteristic parameters are bubble point and flow rate. The bubble point measures the maximum pore size. The quantity and distribution uniformity are generally required to wear latex gloves to prevent membrane damage how to protect the filter layer from damage during the welding process, and to seal very well, to ensure that there is no leakage during the filtration process, which is the critical problem in welding. Analysis of the welding process and the instantaneous action of the solder, it can be known that the plastic melting temperature, depth, fluidity of the welded sealing surface, and the speed of the welding action and the force of the welding are directly related to the final performance of the filter product, and must be improved from here. To meet these debugging requirements, the first introduction of a single light source, infrared heating, a non-contact, uniform radiation heating, so that the temperature, depth, and fluidity of the molten layer become a controllable factor. Secondly, the V-shaped linear guide, bidirectional precision ball screw and motor with rotary encoder and inverter control are selected to drive the end cover to the inner and outer cylinders and the end face of the filter layer according to the predetermined speed and the predetermined insertion depth. The impact on the filter layer is significantly reduced due to the effects during the insertion welding, and the two sides are synchronized at the same speed to ensure the consistency of the solder at both ends, and a reliable hardware guarantee is provided for securing the controllability of the welding parameters.

The integrated control system is the core and soul of the welding equipment. It can be divided into automatic welding control system, manual welding control system, preheating cooling temperature control system, and each part has its own functions and cooperates with each other. The automatic welding control system can automatically complete the whole welding process according to the preset process parameters, mainly for mature technology and mass production; the manual welding control system, as its name implies, can control the execution of the action at any time, mainly used in the debugging of process parameters. During the stage and welding, the preheating temperature of the clamp can be ensured, and the temperature can be lowered in time when solidified and cooled. The integrated control system adopts the easy-to-understand PLC programmable control system design. In the automation control engineering, it has strong versatility and can be designed into a multi-station automated production line, which is controlled and managed by the central control system. The main electrical components are a touch screen, rotary encoder, inverter, PLC programmable controller, driver, input reactor, control unit, and so on.

The parameters of the entire control system are easy to set, modify, save and recall, and can be directly performed on the touch screen, such as heating time, cooling time, fixture preheating and cooling time. Different combinations of process parameters are likely to be required between various products, and the system can be classified and saved and called on demand. As mentioned above, another focus of the welding equipment is the commissioning of the process parameters. The slight variation of each process parameter has a significant influence on the performance of the filter product. For different combinations of filter layers (such as various specifications of the filter film) Suppliers, the number of support layers, order changes, etc.) generally have their own optimal process parameters. The specific values need to be confirmed by a large number of tests. For example, when we established the performance of the equipment, we carried out a series of welding tests and tests. It was found that the preheating temperature change of the fixture has a significant influence on the heating time, melting depth, and temperature of the end cover. Generally, the film can withstand higher heat such as PTFE film. For the welding of PVDF film, it is possible to use a lower preheating temperature such as 40~50 °C, and to withstand lesser temperature films such as PP film, PES film, N66, etc., and use high preheating temperature welding, such as 75 ~ 85 °C. Involving changes in materials, it is even more necessary to debug the corresponding operating parameters. The appropriate data is mainly obtained by experiment.

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