Various types of heat stabilizers heat discoloration Comment

Ideal thermal stabilizer should also absorb HCL, remove the active site, the addition of a conjugated polyene chain, destruction carbenium salts and prevent auto-oxidation, etc., which does not produce a product of catalytic degradation of PVC. The actual result of  Circuit breaker  have different functions and behave in a different thermal stability characteristics, can be divided into early-type, long type, intermediate type and versatile four categories.

1) cadmium, zinc soap is typical of early-type heat stabilizers, can quickly absorb HCL, and Cd, Zn in the catalyst to effectively replace PVC chain carboxylate unstable chlorine atom, thereby effectively suppressing the initial degradation and coloring , but because of consumption of fast transformation products CdC12, ZnC12, but also off the HCL PVC efficient catalysts, which will lead to degradation of the material PVC vicious suddenly darkened, so long-term thermal stability.

2) barium, calcium soap is a typical long-term thermal stabilizers, only the function of absorbing HCL, PVC can not effectively suppress coloration, but the transformation products BaC12, CaC12 non-catalytic activity, does not cause a sudden black PVC, long-term heat stability better.

3) fatty acids, organic tin are intermediate, both absorbs HCL, can effectively replace PVC with chain carboxylate unstable chlorine atoms, and transformation products do not have catalytic activity.

4) an organotin mercaptide is a all-round characteristics in various mechanisms simultaneously stabilize PVC, transformation products nor a catalytic activity, thus both excellent initial and long-term thermal stability results.

3 is a kind of heat stabilizers to prevent or reduce the polymer in the course of processing by heat degradation or crosslinking, additives to extend the life of the composite material. Stabilizers commonly be divided into categories according to the main component base, fatty acid soaps, organic tin compounds, composite heat stabilizer and pure organic compounds.

1) base heat stabilizers: base with stabilizers is the "base" of the lead salt of inorganic and organic acids, such stabilizer having excellent heat resistance, weather resistance and electrical insulation properties, low cost , poor transparency, toxicity, the dosage is generally 0.5% to 5.0%.

2) fatty acid-based heat stabilizer: These heat stabilizers is defined by the fatty acid composition of roots and metal ion compounds, also known as metal soap-based heat stabilizer, and its performance with the radical species and metal ions, generally an amount of 0.1% ~ 3.0%.

3) Organic tin-based heat stabilizer: These heat stabilizers may be unstable PVC and chlorine atoms in the molecule to form a ligand, the ligand and the organic tin carboxylate group and a chlorine  circuit breakers replacement. Such heat stabilizers are characterized by high stability, good transparency, heat resistance, deficiencies are more expensive.

4) composite heat stabilizer: This class is the base class of heat stabilizers or metal soap-based compound and a liquid or solid organic tin-based compound, wherein the metal salts of calcium - magnesium - zinc, barium - calcium - zinc, barium - zinc and barium - cadmium; commonly used organic acids such as organic acids, naphthenic acid, oleic acid, benzoic acid and salicylic acid.

5) organic heat stabilizers: These heat stabilizers can be used alone except for a few main stabilizers (mainly nitrogen-containing organic compounds), but also includes high boiling polyols and phosphite, phosphite often associated with metal stabilizers used, composite materials can improve the weather resistance, transparency, improve the surface color.

PVC heat stabilizer mechanism

Where to improve the thermal stability of the polymer added for the purpose of heat stabilizer additives are known. In addition to a small amount of heat stabilizers used in rubber and other resin processing, mainly used for thermal stability problem is very prominent PVC processing. Thus, said heat stabilizer is usually refers to a copolymer of PVC and PVC heat stabilizer. In the process of thermal degradation of PVC, almost no monomer, but generate a lot of HCl. PVC thermal degradation mechanism is very complicated, the same, the mechanism of thermal stabilizer is also very complicated. Comprehensive results of the current study, thermal stabilizer preventive action can be summarized as (and in HCl, Cl atoms instead of unstable and preventing auto-oxidation) and remedies type (with PVC, the unsaturated site reactions, damage  circuit breakers ) two kind. As follows: 1. Absorption and HCl, inhibit its catalytic automatically. Such stabilizers include lead salts, organic acids, metal soaps, organic tin compounds, epoxy compounds, amines, metal alkoxide and a phenolic salts and metal thiolate salt. They are available with HCl to de-HCl reaction inhibition PVC. (2) replacement of PVC unstable allylic chlorine molecule or a tertiary carbon atom chlorine atom, inhibit de PVC. Such as organic tin stabilizer of PVC unstable molecule of chlorine  Circuit breaker  binding occurs, the ligand, organic tin substitution with an unstable chlorine atoms. 3 with the addition reaction of a polyene structure, damage the formation of a large conjugated system and reduce coloration. A salt of an unsaturated acid or ester containing double bonds, and the PVC molecules conjugated diene double bond addition reaction, thereby destroying the conjugated structure, and color. 4 capture free radicals and prevent the oxidation reaction. Such as adding phenolic heat stabilizer can block off HCl, is due to give phenol H atom radical degradation of PVC macromolecules with radical coupling reaction with O2 to form a substance can not be, and has a thermal stability. Such thermal stabilizers may have one or several functions of both. Ideal PVC heat stabilizer should be a multi-functional substance, or a mixture of some materials, they can achieve the following functions: 1. Replacement lively, unstable substituent, such as the connection on the tertiary Cl Cl atom or allyl chloride, to form a stable structure; 2 absorbed and the PVC during processing and release of HCl, HCl elimination autocatalytic degradation; 3 and in catalytic degradation or passivating the metal ions and other harmful impurities; 4 by chemical reaction forms an unsaturated bond can block the continued growth of the degradation suppressing coloration; 5. preferably a protective shielding to ultraviolet light.

Breaker selection

1, the general principle of selection
     
      (1) Select the circuit breaker according to the application type and number of poles;
      Selected according to the maximum Circuit breakeroperating current of the circuit breaker rated current; need to select the type of release, attachment type and size. Specific requirements are:
     
      ① breaker rated voltage ≥ circuit rated voltage;
      ② breaker rated short-circuit breaking capacity ≥ calculate the load current;
      ③ breaker rated short circuit breaking capacity ≥ maximum possible short-circuit current (generally based on RMS calculation);
      ④ opposite end of the line single-circuit current ≥ 1.25 times the circuit breaker instantaneous (or short delay) tripping setting current;
      ⑤ breaker undervoltage release voltage rating equal to the rated line voltage;
      ⑥ shunt trip circuit breaker rated voltage equal to the control power supply voltage;
      ⑦ electric transmission mechanism rated working voltage equal to the control power supply voltage;
      ⑧ breaker for lighting circuits, transient electromagnetic release setting current generally take the load current of 6 times.
     
      (2) taken as a single motor circuit breaker short-circuit protection, instantaneous tripping setting current for the motor starting current of 1.35 times (DW series circuit breaker) or 1.7-fold (DZ series circuit breaker).
     
      (3) using the breaker as a multi-stage motor short-circuit protection, instantaneous tripping setting current of 1.3 times the maximum starting current of a motor coupled with the rest of the motor operating current.
     
      (4) used as a distribution Air circuit breakertransformer low voltage side of the circuit breaker main switch when its breaking capacity should be greater than the low-pressure side of the transformer short-circuit current value, release of not less than the rated current of the transformer rated current, short circuit protection setting current is generally 6-10 times the rated current of the transformer; overload protection setting current is equal to the rated current of the transformer.
     
      (5) initially selected circuit breaker type and grade, they still had the upper and lower switch with protective characteristics, so as not to override trip, expanding scope of the accident.
     
      2, motor protection circuit breaker selection
     
      Motor protection circuit breaker can be divided into two categories:
      A class is only for circuit breaker protection without the burden of normal operation; another means breaker protection and do not require frequent operation doubles purposes. After the class of cases to be considered operating conditions and electrical life. Motor protection circuit breaker selection principles are:
     
      (A) long delay current setting equal to the motor rated current.
     
      (2) Instantaneous setting current: the protection cage motor circuit breaker instantaneous setting current is equal to (8-15) times the rated motor current, depending on the model of the motor to be protected, capacity and start conditions; wound rotor motor for the protection of breaker instantaneous setting current is equal to (3-6) times the rated motor current, depending on the wound rotor motor protected model, capacity and launch conditions.
     
      (3) six times the current setting of the long delay to return time is greater than equal to the actual motor startup time. Severity of the load at startup, you can choose to return to the time of 1,3,5,8,15 S in a file.
     
      3, the conductor selection circuit breakers
     
      Lighting, living with a wire protection circuit breaker is used to protect the life of the building distribution system circuit breaker, the choice should be considered:
     
      (A) time-lapse setting value less than or equal line calculation load current.
      (2) instantaneous action setting value equal to (6-20) times the line calculated load current.