Thermal couple protector tube processing technique

Abstract

The invention relates to a process for producing protecting pipes of thermocouples, which is composed of three parts of a process for producing cores, a process for dip-coating and a process for combining boxes to cast. The invention comprises firstly, producing sand cores in a wood-made box which is composed of an upper half and a lower half, arranging sand cores which are produced into an iron slot which contains coating materials and dip-coating, reserving after drying, lastly, arranging the sand cores which are dip-coated with the coating materials on an upper sand box and a lower sand box, molding closely, and casting, finishing steps of cutting, hole-filling and wire-coning on a turning machine after polishing, and obtaining qualified protecting pipes of the thermocouples. The invention has the advantages that firstly, a plurality of common casting defects can be avoided and eliminated, finished product rate is increased from 70% to 95%, secondly, the preciseness of casts can be increased greatly, un-straightness is 0.5%, and the tolerance of wall thickness is +-1.5, thirdly, mechanical processing has good performance with non hard points which are easy to appear on thin-wall casts and hard phases of carbides, the conditions of surface electric plating and enamels are good with no tiny defects such as needle holes which affect electric plating, enamels and sand holes, and fourthly, the finished product rate of casting processes can reach 85%.

Description

technical field [0001] The invention relates to a production process of a cast iron hollow tube, in particular to a production process of a thin-walled slender thermocouple protection tube with one end closed as a blind hole. Background technique [0002] Thermocouple temperature measurement is the main component of temperature control devices widely used in metallurgy, chemical industry, materials, food, light industry and other industries. When used at lower temperatures, dipole materials such as NiCr-NiAl and NiCr-NiSi are often used , to convert the temperature signal into a potential difference output. When measuring temperature, a full-package protection tube must be added and fixed in the heating device to maintain its safety and stability. The full-package protection tube can be made of ceramic materials, which are heat-resistant and corrosion-resistant. , anti-oxidation, but the production process of the ceramic protective tube is complicated, the cost is high, and ...

AI Technical Summary

Problems solved by technology

[0002] Thermocouple temperature measurement is the main component of temperature control devices widely used in metallurgy, chemical industry, materials, food, light industry and other industries. When used at lower temperatures, dipole materials such as NiCr-NiAl and NiCr-NiSi are often used , to convert the temperature signal into a potential difference output. When measuring temperature, a full-package protection tube must be added and fixed in the heating device to maintain its safety and stability. The full-package protection tube can be made of ceramic materials, which are heat-resistant and corrosion-resistant. , anti-oxidation, but the production process of the ceramic protective tube is complicated, the cost is high, and the brittleness is relatively large. It is suitable for the working environment with direct or direct contact with the medium at a higher temperature. Insufficient sensitivity to changes

[0003] Cast iron, especially gray cast iron, has the characteristics of good thermal conductivity and excellent mechanical properties. It is used as a thermocouple protection tube for direct contact at lower temperatures. It has high sensitivity for temperature measurement, long service life, and low price. Cheap, but as a thermocouple protection tube, its shape is generally long and thin, with a thin wall and one end is closed. If it is produced by conventional casting technology, it is very difficult to produce, casting defects often occur, the scrap rate is high, and the quality is difficult. ensure

[0004] 1. It is produced by clay coal powder sand mold. Because the pipe wall is very thin (10mm-12mm) and slender, it is prone to casting defects such as insufficient pouring and cold shut.

[0005] 2. Ordinary sand cores are used to form the inner hole. Since the gas can only be discharged from one end of the core, the gas path is too long, the resistance is large, and the exhaust is not smooth. Often there will be casting defects such as choking, blowholes, etc.

[0006] 3. Adopting the traditional process of concentrated introduction of molten iron, it is easy to form shrinkage cavity and shrinkage defects at the inner runner, and because the inner runner is small, the flow of molten iron is long, which promotes the occurrence of insufficient pouring and cold shut

[0007] 4. Due to the thin wall and fast solidification speed, the molten iron is easily overcooled to form a hard and brittle carbide structure, which affects the machinability of the pipe end connection

[0008] 5. Due to the slender pipe, the impact kinetic energy and buoyancy of the molten iron during the filling process often cause floating cores to increase the thickness difference of the pipe wall, that is, the wall thickness is uneven

[0009] 6. With conventional horizontal pouring, the rising speed of the liquid level is slow, the top of the cavity is baked by high-temperature molten iron for too long, the quartz sand expands, the surface of the mold is cracked and deflected, and casting defects such as sand inclusions and rat tails occur

[0011] The thermocouple cast iron protection tube is also not suitable for the centrifugal process of casting pipe fittings, because the outer diameter of the tube is small, the inner diameter is also small, the inner hole of the centrifugal casting is extremely rough, and cannot be processed, and the required centrifugal speed is extremely high, the equipment performance and production safety sex is not guaranteed

[0012] Thermocouple protection tubes are also unsuitable for the production process of metal molds, because metal molds produce such slender pipes in batches, the device is very complicated, the cost is high, the casting is more difficult, and it is more likely to cause the formation of chills in the metallographic structure, so that the product cannot Machining

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