When the temperature rises, the basic properties of thermal shrinkable pipe insulation materials, such as resistance, electrical breakdown strength, mechanical strength, etc., will become smaller, and the dielectric loss, stress and deformation will increase. Therefore, it is of great practical value to improve the heat resistance of insulating materials.

(1) To ensure the safe operation of motors and electrical appliances, reduce maintenance and replacement of spare parts;

(2) Without changing the shape size of motor and electrical appliances, the insulation grade and power can be increased, or the amount of insulation materials can be reduced while the original shape size of motor and electrical appliances is maintained, thus reducing the manufacturing cost and weight.

(3) In the electrical equipment of substation, coal mine, petroleum, chemical industry and other departments, the use of insulating materials with high heat resistance can achieve good results in explosion-proof and fire-proof.

Some names used to express the heat resistance of insulating materials and their meanings are as follows:

1. Thermal aging of insulation (high temperature FEP heat shrinkable tube)

In a short time, when the temperature rises or under the action of high temperature for a long time, the chemical changes (deterioration) of insulating materials or insulators occur slowly or sharply, which is called thermal aging. For example, the formation of oxides in transformer oil, the hardening, brittleness and cracking of paint film are all manifestations of thermal aging.

In addition to temperature, factors accelerating thermal aging include ozone, sunlight, electric field, mechanical load and so on.

2. thermal conductivity

It represents the heat transfer performance of dielectrics (insulators). That is, the heat transmitted in a second from the material cross section (]cm') wheel with a distance of 1 cm and a temperature difference of 10 C, in units of cards/centimeters/seconds.0C0.

3. Heat Resistance (High Temperature Resistant Heat Shrinkage Tube)

It represents the ability of materials to withstand high temperature, that is, the ability of insulating materials to withstand short-term or long-term thermal action without changing dielectric, mechanical, physical and chemical characteristics.

The maximum service temperature of insulating materials depends on this property. The use of insulating materials with high heat resistance can reduce the size, weight and cost of manufacture and maintenance of motors and electrical appliances within the prescribed capacity (output) range.

4. Martin's heat resistance

It indicates that the standard sample of the material can bear the bending moment load of 50 kg/cm and reach the temperature of bending deformation in the environment where the temperature rises by 50 C per hour (i.e. Martin's heat-resisting tester), that is, Martin's heat-resisting index.

5. Thermal Stability (High Temperature Resistant Insulated Thermal Shrinkage Tube)

It means that the material does not change its physical, chemical, mechanical and dielectric properties and can maintain its ability to work when the temperature changes repeatedly (from high to low).

For insulating coatings, it refers to the performance that does not change the appearance color, delamination, spalling and crack under the specified temperature and duration.

6. thermal elasticity

It indicates that the material can maintain its flexibility for a long time under high temperature.

The difference between thermoelasticity and thermal stability is that the former represents the lifetime of the material in dynamic state and is determined by bending strength, while the latter represents the stability of the material in static state to thermal action, and is determined by weight loss.

High thermoelasticity is an important sign of excellent new insulation materials.

7. Weight loss

It represents the amount of weight lost by a material after a period of time at a specified temperature. There is a limit value for different materials. If it exceeds the limit value, it indicates that there are too many volatiles in the material, or there are pyrolysis, aging and altogether chemical changes. If it is serious, the material can not be used.

In practice, the comparison of weight loss between two kinds of materials is often used as the basis for the high or lower thermal stability of the material A than that of the material B.

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热缩管绝缘材料的耐热特性

当温度升高时，热缩管绝缘材料的基本性能，如电阻、电击穿强度、机械强度等，都会变小，介质损耗、应力变形等，都将增大。因此，提高绝缘材料的耐热性能，具有重大的实用价值:

(1)能够保证电机、电器的安全运行，减少维修和零、部件的更换;

(2)在不改变电机、电器外形尺寸的情况下，可提高其绝缘等级和功率，或者在保持原有电机、电器外形尺寸的情况下，可减少绝缘材料的用量，从而降低制造成本和减轻重量;

(3)在变电站、煤矿、石油、化工等部门的电工设备中，采用耐热性高的绝缘材料，可收到防爆、防火的良好效果。

用来表示绝缘材料耐热性能的一些名称及其含义如下:

1.绝缘热老化（耐高温FEP热缩管）

在短时间内温度升高或在高温长期作用下，绝缘材料或绝缘体发生缓慢或急剧的化学变化(劣变)，称为热老化。如变压器油内氧化物的形成，漆膜的变硬、发脆及出现裂纹等，都是热老化的表现。

除温度外，加速热老化的因素，还有臭氧、日光照射、电场、机械负荷等。

2.导热性

它表示电介质(绝缘体)的传热性能，即在相距为1厘米、温差为1 0C的材料横断面(]厘米’)轮向上，于1秒钟内所传导的热量，其单位为卡/厘米·秒·0C0

3.耐热性（耐高温热缩管）

它表示材料承受高温作用的能力，即绝缘材料在短期或长期热作用下，不改变介电、机械、理化等特性的能力。

绝缘材料的最高使用温度，取决于这一性能。采用耐热性高的绝缘材料，可使电机、电器在规定的容量(出力)范围内，缩小外形尺寸，减轻重量和降低制造及维修成本。

4.马丁氏耐热性

它表示材料的标准试样，在每小时升高温度50℃的环境(即马丁氏耐热试验器)中，承受50公斤/厘米²的弯曲力矩负荷并达到弯曲变形时的温度，即马丁氏耐热性指标。

5.热稳定性（耐高温绝缘热缩管）

它表示材料在温度反复(忽高忽低)变化的情况下，不改变理化、机械、介电性能，并能保持本身工作的能力。

对于绝缘涂层，是指在规定温度和持续时间下，不改变外观色泽、不脱层、无剥落和裂纹的性能。

6.热弹性

它表示材料在高温作用下，能长期保持其柔韧状态的性能。

热弹性与热稳定性的区别是:前者表示材料在动态下的寿命，以抗弯曲强度来确定;后者表示材料在静态下对热作用的稳定性，以重量损失的大小来确定。

热弹性高，是优良的新型绝缘材料的一个上要标志。

7.重量损失

它表示材料在规定温度下经若干时间后，损失其重量的数量。对不同的材料，各有一个极限值。如果超过极限值，则表明材料内挥发物过多，或有热裂解、老化及共他化学变化，严重时，该材料不能使用。

在实际工作中，往往以两种(或儿种)材料重量损失的对比值，作为甲种材料的热稳定性高或低于乙种材料的根据。