Temperature-sensitive dielectric material for flame detector and preparation method of temperature-sensitive dielectric material

Abstract

The temperature-sensitive dielectric material for the flame detector is prepared from the following components in parts by weight: 8 to 9.5 parts of a BPT ferroelectric material, 8 to 9.5 parts of a BPTFeCr ferroelectric material, 15 to 19 parts of an MCT semiconductor ceramic material, 7.5 to 8.5 parts of Fe2O3, 6.5 to 7.5 parts of MnCO3, 0.5 to 1 part of Cr2O3, 2.3 to 3.5 parts of NaCl, 1.5 to 2.5 parts of Ni2O3 and 42 to 50.7 parts of Al2O3.

Description

Technical Field

[0001] The invention relates to the field of flame detectors, and in particular to a temperature-sensitive medium material for flame detectors and a preparation method thereof. Background Art

[0002] In some special occasions, such as the closed engine compartment of special vehicles (high-end passenger cars, VIP cars, internal combustion locomotives, special vehicles, etc.), due to the long-term operation of the engine, the excessively high temperature can easily ignite the oil seepage and oil leakage in the compartment, causing a fire. In order to ensure the safety of such equipment, it is necessary to install a protection system with a high-performance flame detector. In the photovoltaic industry of the new energy industry, the polysilicon ingot furnace has its own defects, unreasonable loading, unreasonable heating parameter settings, etc., causing the crucible containing silicon materials to rupture during heating or cooling, and silicon liquid overflow occurs. If the silicon liquid overflow is not discovered in time, the overflowed silicon liquid will accumulate in large quantities over time, and it is very likely to melt through the bottom of the furnace. If it encounters a water cooling pipeline, the large amount of water vapor will easily cause a safety accident. The air preheater is an important heat exchange equipment for thermal power generators. The unburned components are deposited on the heating surface, which is easy to produce hot spots. If the hot spots are not discovered in time, there is a huge risk of causing fire. Open-air coal piles have many disadvantages such as floating dust, sewage, loss, and coal quality degradation. The state requires that all coal-using units will gradually adopt coal storage bunkers to store coal, and the oxidation and spontaneous combustion of coal in the coal storage bunkers must be monitored at all times. If the refractory material of a high-temperature and high-pressure boiler (pipeline) lined with refractory material falls off, the high temperature and high pressure will directly act on the metal of the furnace shell (tube wall), and the reduced thermal strength of the metal may lead to serious consequences such as explosion.

[0003] At present, the commonly used sensors mainly include wired temperature sensors, thermocouple wire temperature sensors, original dual-parameter wire flame detectors, etc. These sensors have the following problems: 1. Wire temperature sensor Distributed optical fiber measures the average temperature of the distribution area, but it has low resolution, too large a temperature sensing area, and large measurement errors; Generally, optical fibers are protected by organic materials and have low operating temperatures. If gold optical fibers or armored protection is used, the cost is high and it is difficult to afford the cost for ordinary applications or large quantities. 2. Thermocouple type wire temperature sensor The detection signal of the thermocouple type linear temperature sensor is a thermoelectric potential signal, so its use environment is only suitable for static state. In the vibrating use environment, the stress produces a piezoelectric effect on the temperature sensitive medium, which causes the thermoelectric potential signal to jump easily. The existing thermocouple type linear temperature sensor is mostly used in relatively static equipment such as coal gasification furnaces, coal storage bins, and air preheaters. There is no application report in the application environment with large vibration; 3. Dual parameter line flame detector The original dual-parameter line flame detector has the function of jointly judging fire alarms with two temperature characteristic parameters, resistance and capacitance, and has the advantages of strong environmental adaptability and high reliability. However, the capacitance change rate C 500℃ / C 25℃ The original dual-parameter linear flame detector capacitance change ratio C 500℃ / C 25℃ The test data is shown in the table below:

[0004] As a new type of industrial sensor, flame detectors are used in many occasions involving personal and property safety. They are extremely important new sensors with broad application prospects. The use of high-performance flame detectors is a convenient, reliable and relatively inexpensive method. Among them, the composition design of temperature-sensitive dielectric materials used in flame detectors and their preparation methods are particularly critical in high-performance flame detectors. Summary of the invention

[0005] The purpose of the present invention is to provide a temperature-sensitive dielectric material for flame detectors and a preparation method thereof in view of the corresponding deficiencies of the prior art. The dual-parameter line flame detector made of this temperature-sensitive dielectric material has two temperature characteristic parameters of resistance and capacitance with high sensitivity, can reliably realize fire detection, and can adapt to application environments such as impact, vibration, and humidity, and has good environmental performance.

[0006] The object of the present invention is achieved by adopting the following scheme: a temperature-sensitive dielectric material for a flame detector, wherein the weight proportions of the components in the temperature-sensitive dielectric material are: 8 to 9.5 parts of BPT ferroelectric material, 8 to 9.5 parts of BPTFeCr ferroelectric material, 15 to 19 parts of MCT semiconductor ceramic material, 7.5 to 8.5 parts of Fe2O3, 6.5 to 7.5 parts of MnCO3, 0.5 to 1 part of Cr2O3, 2.3 to 3.5 parts of NaCl, 1.5 to 2.5 parts of Ni2O3, and 42 to 50.7 parts of Al2O3.

[0007] The weight proportions of the components in the BPT ferroelectric material are 8 to 10 parts of BaO, 30 to 40 parts of TiO2, and 50 to 62 parts of Pb3O4.

[0008] The weight proportions of the components in the BPTFeCr ferroelectric material are 8-10 parts of BaO, 29-34 parts of TiO2, 49-54 parts of Pb3O4, 1-2 parts of Fe2O3 and 7-9 parts of Cr2O3.

[0009] The weight proportions of the components in the MCT semiconductor ceramic material are 70-75 parts of Cr2O3, 24-28 parts of MgO and 1-3 parts of TiO2.

[0010] The preparation method of the temperature-sensitive medium material for the flame detector comprises the following steps: 1) Preparation of BPT ferroelectric materials; 1-1) Ingredients: Take each component according to the ratio of BPT ferroelectric material, add anhydrous ethanol, stir and mix, and dry; 1-2) Pre-sintering: pre-sinter the powder obtained in step 1-1) at 1000-1100° C. for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder; 1-3) Sintering: The powder obtained by pre-sintering is sintered at 1200-1300°C for 1.5-2.5 hours, cooled to room temperature, taken out, and ball-milled into powder to obtain BPT ferroelectric material; 2) Preparation of BPTFeCr ferroelectric materials; 2-1) Ingredients: Take each component according to the ratio of BPTFeCr ferroelectric material, add anhydrous ethanol, stir and mix, and dry; 2-2) Pre-sintering: pre-sinter the powder obtained in step 2-1) at 1000-1100°C for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder; 2-3) Sintering: Sinter the powder obtained by pre-sintering at 1200-1300°C for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder to obtain BPTFeCr ferroelectric material; 3) Preparation of MCT semiconductor ceramic materials; 3-1) Ingredients: Take each component according to the ratio of MCT semiconductor ceramic materials, add anhydrous ethanol, stir and mix, and dry; 3-2) Pre-sintering: pre-sinter the powder obtained in step 3-1) at 1000-1100°C for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder; 3-3) Sintering: The powder obtained by the pre-sintering treatment is sintered at 1250-1350°C for 1.5-2.5 hours, taken out after cooling to room temperature, and ball-milled into powder to obtain MCT semiconductor ceramic material; 4) Ingredients: Take the components according to the proportions described in claim 1, put them into an agate pot, add anhydrous ethanol, stir and mix at high speed, and dry for later use; 5) Sintering: The powder prepared in step 4) is sintered at 1250°C to 1300°C for 45 hours, cooled to room temperature, and then taken out and high-speed ball-milled into powder to obtain a temperature-sensitive dielectric material.

[0011] During the preparation process, a corundum crucible is used to load the powder into a high-temperature sintering furnace for sintering.

[0012] Application of temperature-sensitive dielectric materials for flame detectors in the preparation of temperature-sensitive cables for flame detectors.

[0013] BPT ferroelectric materials and BPTFeCr ferroelectric materials are used to form dielectric material capacitance temperature sensitive components. If their content exceeds the upper limit, the initial resistance value and resistance temperature coefficient of the temperature sensitive dielectric material will be excessively reduced. If their content is lower than the lower limit, they cannot effectively play the role of forming capacitance temperature sensitive components. MCT semiconductor ceramic materials, Fe2O3, MnCO3, Cr2O3, Ni2O3, and Al2O3 are dielectric material resistance temperature sensitive components. The reason for limiting the upper and lower limits is that they have suitable resistance values ​​and suitable NTC resistance temperature coefficients within the component range. NaCl is an additive for dielectric materials, which can further increase the temperature change rate of resistance and capacitance, thereby further improving sensitivity. The reason for limiting its upper and lower limits is that it has suitable NTC resistance temperature coefficients and capacitance temperature coefficients within the component range.

[0014] The advantages of the present invention are: 1. The material of the present invention has sensitive resistance and capacitance temperature characteristic parameters, wherein the change multiple C of the capacitance temperature characteristic parameter is 500℃ / C 25℃ Reach more than 250; 2. The material of the present invention is a powder material with a stable microstructure synthesized by high-temperature sintering, so it has good vibration and impact resistance, good environmental adaptability, and can work in a frequent vibration environment such as a tracked vehicle; 3. The temperature-sensitive dielectric material produced by the present invention has a wide range of use. All materials can be used within 900°C. The normal temperature resistance of the Φ2mm dual-parameter temperature-sensitive cable produced is between 1MΩ·m and 20MΩ·m, and the normal temperature capacitance is ≤0.5nF / m. It can be used for over-temperature alarm or fire detection within room temperature to 700°C, thereby improving the reliability of detection. 4. The interaction and promotion between the materials of the present invention make it have good adaptability. All component materials will not oxidize and corrode the electrodes and the outer protective sleeve. The resistance and capacitance parameters of the dual-parameter temperature-sensitive cable are uniform and consistent. 5. The present invention eliminates the chemical reaction between the sensitive dielectric material and the electrode and the protective tube below 900°C, eliminates the influence of heat treatment on the performance of the product, has good process stability, and can be prepared using a larger raw material outer tube, the length of the prepared finished product is doubled, the efficiency is greatly improved, and the cost is greatly reduced. The overall content of Pb3O4 in the sensitive dielectric material is reasonably designed, and the pre-sintering and sintering process of BPT ferroelectric materials, BPTFeCr ferroelectric materials, MCT semiconductor ceramic materials, and temperature-sensitive dielectric materials for flame detectors are reasonably designed to obtain temperature-sensitive dielectric materials with stable phase structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a temperature-sensitive medium material for flame detectors. DETAILED DESCRIPTION

[0016] like Figure 1 As shown, a temperature-sensitive dielectric material for flame detectors, the weight parts of each component in the temperature-sensitive dielectric material are 8-9.5 parts of BPT ferroelectric material, and the weight parts of each component in the BPT ferroelectric material are 8-10 parts of BaO, 30-40 parts of TiO2, and 50-62 parts of Pb3O4. 8-9.5 parts of BPTFeCr ferroelectric material, and the weight parts of each component in the BPTFeCr ferroelectric material are 8-10 parts of BaO, 29-34 parts of TiO2, 49-54 parts of Pb3O4, 1-2 parts of Fe2O3, and 7-9 parts of Cr2O3. 15-19 parts of MCT semiconductor ceramic material, and the weight parts of each component in the MCT semiconductor ceramic material are 70-75 parts of Cr2O3, 24-28 parts of MgO, and 1-3 parts of TiO2. Fe2O3 7.5~8.5 parts, MnCO3 6.5~7.5 parts, Cr2O3 0.5~1 part, NaCl 2.3~3.5 parts, Ni2O3 1.5~2.5 parts, Al2O3 42~50.7 parts.

[0017] The preparation method of the temperature-sensitive medium material for the flame detector comprises the following steps: 1) Preparation of BPT ferroelectric materials; 1-1) Ingredients: Take each component according to the ratio of BPT ferroelectric material, put it into an agate pot, add anhydrous ethanol, stir and mix at high speed, and dry for use; uniform mixing can ensure that BPT ferroelectric material with uniform composition is obtained.

[0018] 1-2) Pre-sintering: The powder obtained in step 1-1) is pre-sintered at 1000-1100° C. for 1.5-2.5 hours, and after cooling to room temperature, it is taken out and high-speed ball-milled into powder for later use; pre-sintering can further ensure that the materials are mixed evenly, and a BPT ferroelectric material with uniform composition is obtained.

[0019] 1-3) Sintering: The powder obtained in step 1-2) is sintered at 1200-1300°C for 1.5-2.5 hours, and after cooling to room temperature, it is taken out and high-speed ball-milled into powder to obtain BPT ferroelectric material. Sintering can ensure that the components react to form BPT ferroelectric material.

[0020] 2) Preparation of BPTFeCr ferroelectric materials; 2-1) Ingredients: Take the components according to the ratio of BPTFeCr ferroelectric material, put them into an agate pot, add anhydrous ethanol, stir and mix at high speed, and dry for use; uniform mixing can ensure that the BPTFeCr ferroelectric material with uniform composition is obtained.

[0021] 2-2) Pre-sintering: The powder obtained in step 2-1) is pre-sintered at 1000-1100° C. for 1.5-2.5 hours, cooled to room temperature, and then taken out for high-speed ball milling into powder for later use; pre-sintering can further ensure that the materials are mixed evenly, and obtain a BPTFeCr ferroelectric material with uniform composition.

[0022] 2-3) Sintering: The powder obtained in step 2-2) is sintered at 1200-1300°C for 1.5-2.5 hours, and after cooling to room temperature, it is taken out and high-speed ball-milled into powder to obtain BPTFeCr ferroelectric material. Sintering can ensure that the components react to form BPTFeCr ferroelectric material.

[0023] 3) Preparation of MCT semiconductor ceramic materials; 3-1) Ingredients: Take each component according to the ratio of the MCT semiconductor ceramic material, put it into an agate pot, add anhydrous ethanol, stir and mix at high speed, and dry for use; uniform mixing can ensure that the MCT semiconductor ceramic material with uniform composition is obtained.

[0024] 3-2) Pre-sintering: The powder obtained in step 3-1) is pre-sintered at 1000-1100° C. for 1.5-2.5 hours, cooled to room temperature, and then taken out by high-speed ball milling into powder for later use; pre-sintering can further ensure that the materials are mixed evenly, and obtain MCT semiconductor ceramic materials with uniform composition.

[0025] 3-3) Sintering: The powder obtained in step 3-2) is sintered at 1250-1350°C for 1.5-2.5 hours, and after cooling to room temperature, it is taken out and high-speed ball-milled into powder to obtain MCT semiconductor ceramic material. Sintering can ensure that the components react to form MCT semiconductor ceramic material.

[0026] 4) Ingredients: Take the components according to the proportions described in claim 1, put them into an agate pot, add anhydrous ethanol, stir and mix at high speed, and dry for later use; uniform mixing can ensure that the temperature-sensitive medium material with uniform composition is obtained.

[0027] 5) Sintering: The powder prepared in step 4) is sintered at 1250°C to 1300°C for 45 hours, and after cooling to room temperature, it is taken out and high-speed ball-milled into powder to obtain the temperature-sensitive dielectric material. Sintering can ensure that the components react to form the temperature-sensitive dielectric material.

[0028] During the preparation process, a corundum crucible is used to load the powder into a high-temperature sintering furnace for sintering.

[0029] Application of temperature-sensitive dielectric materials for flame detectors in the preparation of temperature-sensitive cables for flame detectors.

[0030] 1) Preparation of BPT ferroelectric material: weigh 500g of BaO, 1800g of TiO2, and 3000g of Pb3O4, add 2000ml of anhydrous ethanol, stir at high speed and dry, place the dried material in a corundum crucible and put it in a high-temperature sintering furnace for pre-burning at 1070℃ for 2 hours, cool to room temperature and take out and high-speed ball mill into powder, place the powder in a corundum crucible and put it in a high-temperature sintering furnace for sintering at 1200℃ for 2 hours, cool to room temperature and take out and high-speed ball mill into powder, thus obtaining BPT ferroelectric material.

[0031] 2) Weigh 1400 g of Cr2O3, 550 g of MgO, and 110 g of TiO2, add 2000 ml of anhydrous ethanol, stir at high speed and dry, place the dried material in a corundum crucible and put it in a high-temperature sintering furnace for pre-firing at 1070°C for 2 hours, cool it to room temperature and take it out and high-speed ball grind it into powder, place the powder in a corundum crucible and put it in a high-temperature sintering furnace for sintering at 1260°C for 2 hours, cool it to room temperature and take it out and high-speed ball grind it into powder, thus obtaining MCT semiconductor ceramic material.

[0032] 3) Weigh 1400 g of Cr2O3, 550 g of MgO, and 110 g of TiO2, add 2000 ml of anhydrous ethanol, stir at high speed and dry, place the dried material in a corundum crucible and pre-sinter it in a high-temperature sintering furnace at 1070°C for 2 hours, cool it to room temperature and take it out and grind it into powder by high-speed ball milling, place the powder in a corundum crucible and sinter it in a high-temperature sintering furnace at 1260°C for 2 hours, cool it to room temperature and take it out and grind it into powder by high-speed ball milling, thus obtaining MCT semiconductor ceramic material.

[0033] Example 1

[0034] According to Example 1 in Table 2, the components of the temperature-sensitive dielectric material were weighed, 4000 ml of anhydrous ethanol was added, the mixture was uniformly stirred at high speed and then dried, the dried material was placed in a corundum crucible and then placed in a high-temperature sintering furnace for sintering at 1300° C. for 5 hours, and after cooling to room temperature, the material was taken out and high-speed ball-milled into powder to obtain a temperature-sensitive dielectric material for a flame detector.

[0035] As shown in Table 3, Table 3 is the test result of the flame detector made of the temperature-sensitive dielectric material prepared in Example 1 at the China Testing Technology Research Institute. The capacitance change rate C of the linear flame detector made of this temperature-sensitive material is measured. 500℃ / C 0℃ Reach more than 250.

[0036] Example 2

[0037] According to Example 2 in Table 2, the components of the temperature-sensitive medium material were weighed, 4000 ml of anhydrous ethanol was added, the mixture was uniformly stirred at high speed and then dried, the dried material was placed in a corundum crucible and then placed in a high-temperature sintering furnace and sintered at 1260° C. for 5 hours, and after cooling to room temperature, the material was taken out and high-speed ball-milled into powder to obtain a temperature-sensitive medium material for a flame detector.

[0038] As shown in Table 4, Table 4 shows the detection results of the flame detector made of the temperature-sensitive dielectric material prepared in Example 2. The capacitance change rate C of the linear flame detector made of this temperature-sensitive material is 500℃ / C 25℃ Reach more than 250.

[0039] Example 3

[0040] According to Example 3 in Table 2, the components of the temperature-sensitive dielectric material were weighed, 4000 ml of anhydrous ethanol was added, the mixture was uniformly stirred at high speed and then dried, the dried material was placed in a corundum crucible and then placed in a high-temperature sintering furnace for sintering at 1250° C. for 5 hours, and after cooling to room temperature, the material was taken out and high-speed ball-milled into powder to obtain a temperature-sensitive dielectric material for a flame detector.

[0041] As shown in Table 5, Table 5 is the detection results of the flame detector made of the temperature-sensitive dielectric material prepared in Example 3. The capacitance change rate C of the linear flame detector made of this temperature-sensitive material is measured. 500℃ / C 25℃ Reach more than 250.

[0042] Example 4

[0043] According to Example 4 in Table 2, the components of the temperature-sensitive dielectric material were weighed, 4000 ml of anhydrous ethanol was added, the mixture was stirred at high speed and then dried, the dried material was placed in a corundum crucible and then placed in a high-temperature sintering furnace and sintered at 1280° C. for 5 hours, and after cooling to room temperature, the material was taken out and high-speed ball-milled into powder to obtain a temperature-sensitive dielectric material for a flame detector.

[0044] As shown in Table 6, Table 6 is the detection results of the flame detector made of the temperature-sensitive dielectric material prepared in Example 4. The capacitance change rate C of the linear flame detector made of this temperature-sensitive material is measured. 500℃ / C 25℃ Reach more than 250.

[0045]

[0046] It can be seen from the above embodiments that the capacitance change rate C of the flame detector made of the temperature-sensitive dielectric material in these embodiments in Embodiment 1 is 500℃ / C0℃ Above 250, the capacitance change rate C of the flame detectors of Examples 2, 3, and 4 500℃ / C 25℃ The capacitance change rate C of the flame detector made of the temperature-sensitive dielectric material in Example 3 is above 250. 500℃ / C 25℃ All above 300.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A temperature-sensitive dielectric material for a flame detector, characterized in that: The weight proportions of the components in the temperature-sensitive dielectric material are: 8-9.5 parts of BPT ferroelectric material, 8-9.5 parts of BPTFeCr ferroelectric material, 15-19 parts of MCT semiconductor ceramic material, 7.5-8.5 parts of Fe2O3, 6.5-7.5 parts of MnCO3, 0.5-1 part of Cr2O3, 2.3-3.5 parts of NaCl, 1.5-2.5 parts of Ni2O3 and 42-50.7 parts of Al2O3.

2. The material according to claim 1, characterized in that: The weight proportions of the components in the BPT ferroelectric material are 8 to 10 parts of BaO, 30 to 40 parts of TiO2, and 50 to 62 parts of Pb3O4.

3. The material according to claim 1, characterized in that: The weight proportions of the components in the BPTFeCr ferroelectric material are as follows: 8 to 10 parts of BaO, 29 to 34 parts of TiO2, 49 to 54 parts of Pb3O4, 1 to 2 parts of Fe2O3, and 7 to 9 parts of Cr2O3.

4. The material according to claim 1, characterized in that: The weight proportions of the components in the MCT semiconductor ceramic material are: 70-75 parts of Cr2O3, 24-28 parts of MgO, and 1-3 parts of TiO2.

5. The method for preparing the temperature-sensitive medium material for flame detector according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) Preparation of BPT ferroelectric materials; 1-1) Ingredients: Take the components according to the proportions described in claim 2, add anhydrous ethanol, stir and mix, and dry; 1-2) Pre-sintering: pre-sinter the powder obtained in step 1-1) at 1000-1100° C. for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder; 1-3) Sintering: The powder obtained by pre-sintering is sintered at 1200-1300°C for 1.5-2.5 hours, cooled to room temperature, taken out, and ball-milled into powder to obtain BPT ferroelectric material; 2) Preparation of BPTFeCr ferroelectric materials; 2-1) Ingredients: Take the components according to the proportions described in claim 3, add anhydrous ethanol, stir and mix, and dry; 2-2) Pre-sintering: pre-sinter the powder obtained in step 2-1) at 1000-1100°C for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder; 2-3) Sintering: Sinter the powder obtained by pre-sintering at 1200-1300°C for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder to obtain BPTFeCr ferroelectric material; 3) Preparation of MCT semiconductor ceramic materials; 3-1) Ingredients: Take the components according to the proportions described in claim 4, add anhydrous ethanol, stir and mix, and dry; 3-2) Pre-sintering: pre-sinter the powder obtained in step 3-1) at 1000-1100°C for 1.5-2.5 hours, cool to room temperature, take out, and ball-mill into powder; 3-3) Sintering: The powder obtained by the pre-sintering treatment is sintered at 1250-1350°C for 1.5-2.5 hours, taken out after cooling to room temperature, and ball-milled into powder to obtain MCT semiconductor ceramic material; 4) Ingredients: Take the components according to the proportions described in claim 1, add anhydrous ethanol, stir and mix, and dry; 5) Sintering: Sinter the powder prepared in step 4) at 1250°C to 1300°C for 4 to 5 hours, cool to room temperature, take out and grind into powder, and obtain the temperature-sensitive dielectric material.

6. The method according to claim 5, characterized in that: During the preparation process, a corundum crucible is used to load the powder into a high-temperature sintering furnace for sintering.

7. Application of temperature-sensitive dielectric materials for flame detectors in the preparation of temperature-sensitive cables for flame detectors.

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