The liner material processing of electromagnetic flow meter
Author:vacorda Source:vacorda.com Date: 2016-12-21 16:27:10
In the production and manufacture of electromagnetic flowmeter, in order to meet the roughness of the requirements of measuring tube, we often need to choose the qualified lining material according to the type of fluid. Different lining materials need to use an excellent processing technology for processing.
（Intelligent electromagnetic flowmeter）
Commonly used lining materials are: neoprene, EPDM rubber, polyurethane, PTFE and PFA. In accordance with the requirements of measurement specifications, there are following types of the measuring liner media:
Neoprene for large diameter sensor (≥DN300), often used for measuring water, sewage, weak acid, weak alkaline .etc. Generally directly bonding with a film and attached to the inside wall of the stainless steel pipe, then made by curing. This process, the surface roughness of the rubber lining is generally high, when operation it should pay special attention to the seam at the formation, but the relative roughness to be low. For neoprene and EPDM rubber lining for small diameter , it is best to use the mold pressure, attached to the inner wall of the catheter and then curing. Reducing the surface roughness of the liner depends on the surface roughness of the die mandrel and the pressing and vulcanization processes.
At present, foreign rigid polyurethane often use polyurethane rubber, an important technological point of forming is to remove the bubbles involved in the injection process, make the chemical reaction be stable. When adopt the centrifugal casting process, ensure that the raw materials are kept in a dry state during storage, and the raw materials are mixed and stirred uniformly and smoothly. In order to remove the bubbles involved in the raw materials, set the appropriate rotation speed of the conduits, good control the temperature of raw material handling, hardening, and cross-linking. Lining materials with low roughness should be made of fluoroplastics.
For the electromagnetic flowmeter, the excellent fluoroplastic lining is PFA. Which is mainly used in the injection of molten resin, and then injection (injection injection). Injection molding method is a seamless one forming. PFA lining has good chemical resistance, heat resistance, resistance to adhesion (surface finish). Especially in the chemical resistance, heat resistance, the use of unique manufacturing technology, can reduce the internal stress and internal bubbles and avoid cracks, so that the flow meter can remain high reliability even used in harsh environments.
For this reason, in the manufacturing process of the PFA lining, the important control points are control of the injection temperature (resin viscosity, metal mold temperature), cooling control of the metal mold (cooling time, temperature), and the control of resin pressure. The injection molding temperature should be set as low as possible to reduce the thermal degradation of the PFA resin. In the injection molding, the temperature of the metal mold is uniformly maintained to be greater than the melting point of the resin. Due to the need for high-precision cooling control, it should set a number of cooling circuit in the metal mold, and independent cooling control operation. While the cooling control, it should also control the resin pressure.