WO2015081478A1

WO2015081478A1 - Device for treatment of parts at low temperatures

Info

Publication number: WO2015081478A1
Application number: PCT/CN2013/088366
Authority: WO
Inventors: Edward Feng; Pierre Foret; Entela Diamanti
Original assignee: Linde Aktiengesellschaft
Priority date: 2013-12-03
Filing date: 2013-12-03
Publication date: 2015-06-11

Abstract

The invention relates to a device for treatment of parts, especially metallic parts, at low temperatures, comprising a cooling chamber (102) with an inlet (110) for a cooling medium (111), wherein there is provided a means (112, 113, 120, 130, 132) for controlled high velocity injection of gas (128).

Description

DEVICE FOR TREATMENT OF PARTS AT LOW TEMPERATURES

The invention relates to a device for treatment of parts especially metallic parts, at low temperatures. Further, the invention relates to a corresponding method.

Processing of steels at sub-zero temperatures can improve various mechanical properties such as hardness and strength, wear resistance and dimensional stability. There are different methods to cool steel parts down to a desired temperature: For example, the parts can be cooled in a toploaded cryogenic box freezer. The cryogenic box is loaded and de-loaded manually or by a crane from the top. The inner volume of the box is cooled by liquid nitrogen or cold gaseous nitrogen. The cryogenic box freezer is an economic solution for cooling small production volumens. Since loading and de-loading require both man power and consume time this method is not suitable for higher production volumes.

A sub-zero cabinet, standing on the floor or on legs, which can be loaded from the front partly solves this problem since it is easier to load and de-load. Further it can be integrated in a heat treatment processing line.

EP 1 842 929 A1 describes a cooling chamber for treatment of parts, especially metal parts, at low temperatures comprising an inlet for a cooling medium and an outlet for vent gas, an entrance door, and a separate exit door and transportation means for transporting said parts from said entrance door to said exit door.

Cooling chambers conventionally use fans to distribute a cooling medium throughout the cooling chamber. The aim is to achieve a homogenous temperature distribution in the chamber. The object of the invention is to provide a device for treatment of metallic parts, in which a homogenous temperature distribution in the chamber is more easily achieved. This object is achieved by a device comprising the features of claim 1 as well as a method comprising the features of claim 7.

The invention improves convection within a cooling chamber as compared to prior art solutions. Also, use of circulating fans within the cooling chamber can be avoided, thus reducing mechanical movement and minimizing wear and tear. According to the invention, a faster process and cost savings are achievable.

Advantageous embodiments of the invention are the subject matter of the dependent claims.

Expediently, the device comprises an outlet for vent gas and at least one door through which parts to be treated can be brought into and taken out of the cooling chamber. Preferably, there is provided an entrance door and a separate exit door. In this case, it is possible to provide a transportation means for the parts to be treated from said entrance door to said exit door, whereby handling of the parts is simplified.

According to a preferred embodiment of the invention, a liquid nitrogen source is connected to the cooling medium inlet of the cooling chamber. Liquid nitrogen has the advantage that it is relatively cheap as a cooling medium, and enables the provision of extremely low temperatures. It is preferred to lead the liquid nitrogen into the cooling chamber with a pressure of between 1 and 10 bar, preferably 1 to 4 bar.

Preferably, the liquid nitrogen is sprayed into the cooling chamber. The evaporation or vaporisation cold which is generated thereby and the resulting cold gaseous nitrogen lower the temperature inside the cooling chamber and of the parts that are to be treated.

The invention is preferably used to cool down parts to a temperature between +60 °C and -196 °C, more preferred to sub-zero temperatures and most preferred to a temperature between -10°C or -20 °C or -30 °C or -503 or -50 °C or -60 °C and -180°C. For example, for shrink fitting of metals according to the invention it is often sufficient to provide a temperature between -40 °C and -80 °C. Neaty the same temperature range, for example -70°C to -120°C, is utilized for cold rteatment of steel, that is to complete the metallurgic phase transformation of austenite into martensite during the hardening of steels via quench and temper heat treatment. The inventive method may also be used to subject metal parts, especially steel parts, to a cryotreatment at extremely low temperatures down to -180°C for an extended period of time, sometimes as long as 48 hours.

The inventive method can improve various properties of metal parts, especially of steel parts, namely hardness and strength, wear resistance and dimensional stability.

Preferably the invention is included into a line for heat treatment of metals. Advantageously, the gas injected into the cooling chamber at high velocity is provided in a recipient, which is connected to the cooling chamber by means of a relief valve. Such a relief valve will open when a defined pressure within the recipient is reached. For example, the relief valve can open when a pressure between 4 and 10 bar or between 5 and 8 bar, for example 6 bar, is reached. In this case, the gas within the recipient will be released into the cooling chamber. Such a recipient is, preferably, operated at room temperature, i. e. not cooled, whereby handling is facilitated.

Preferably, the gas is released into the cooling chamber via a high speed nozzle. The nozzle is designed to increase the gas speed by reducing the outlet diameter to a minimum. The orientation of the nozzle outlet enables a controlled circulation in the box.

Preferably, the recipient is adapted to handle liquid nitrogen. As the recipient is not further cooled, liquid nitrogen will vaporize to provide gaseous nitrogen, thus increasing the pressure within the recipient. As explained, when the pressure within the recipient reaches a value defined by the relief valve, this gaseous nitrogen can be effectively ejected into the cooling chamber.

Preferably, the gas, especially gaseous nitrogen is injected into the cooling chamber with velocities of 200 to 400 m/s, especially 200 to 300 m/s. Such velocities ensure a sufficient turbulence and consequently a mixing of liquid nitrogen and/or cold gaseous nitrogen within the cooling chamber, to ensure a more even temperature distribution.

Preferred applications of the invention are the following: shrink fitting of metal parts, in particular steel parts, by causing a contraction on cooling in order to facilitate the assembly of parts which have very close tolerances, cold treatment of steel, in particular of higher-alloy (e.g. tool steels) and carburized steel, in order to complete the transformation of the metal microstructure from austenite to the stronger and harder martensitic structure

cryotreatment of metals at liquid nitrogen temperatures

The invention as well as further details of the invention are described in the following with reference to the accompanying drawing wherein a cooling chamber according to the invention is shown.

Figure 1 shows a schematic side view of a device of a preferred embodiment of a device according to the invention Figure 2 shows, in schematically simplified form, a preferred arrangement of supply lines for liquid and gaseous nitrogen.

The preferred embodiment of a device according to the invention is shown in Figure 1 and generally designated 100. It is provided with a cooling chamber 102. The cooling chamber 102 shown in figure 1 is designed as a leg standing unit. It is also possible to place the cooling chamber directly on the floor.

The cooling chamber 102 comprises an entrance door 104 and an exit door 106 which is positioned opposite the entrance door 104. At the bottom of the cooling chamber several reels 107 are arranged in order to transport parts which enter the cooling chamber through the entrance door 104. The cooling chamber is provided with an inlet 1 10 for liquid nitrogen 1 1 1 . The liquid nitrogen 1 1 1 is sprayed or otherwise brought into the cooling chamber 102. The evaporation cold that is generated and the resulting 102 cold gaseous nitrogen lower the temperature inside cooling chamber and of any parts therein to be treated.

It is to be noted that the cooling chamber depicted in Figure 1 shall merely serve as an example, with which the invention can be implemented. Especially, the construction with entrance door, exit door and reels is optional. The device further includes a closed recipient 120, which is adapted to hold and handle liquid nitrogen 122, which can be brought into the recipient 120 via an inlet 124.

The recipient 120 is not subjected to any further cooling (i. e. apart from that caused by liquid nitrogen 122). Thus, liquid nitrogen 122 will be vaporized to form gaseous nitrogen (designated 128).

The recipient 120 is connected to an inlet 1 12 of the cooling chamber 102 by means of a conduit 130, in which a pressure relief valve 132 is provided. If necessary or expedient, a further conduit 131 can be provided (as shown in Figure 2) via which for example a further cooling medium, in liquid or gaseous form, can be provided. For example, gaseous nitrogen can be provided via conduit 131 . Hereby for example, the temperature within recipient 120 can be controlled. Due to the vaporization of liquid nitrogen 122 within recipient 120, the pressure in recipient 120 and conduit 130 increases. Up to a certain pressure, for example up to 4 bar, up to 5 bar or up to 6 bar, the pressure relief valve 132 remains closed.

When a certain pressure is reached, for example 6 bar, valve 132 opens and gaseous nitrogen enters cooling chamber 102 via inlet 1 12. Inlet 1 12 is provided with a schematically shown nozzle 1 13, which is designed to increase the velocity of the gas entering the cooling chamber via inlet 1 12. Recipient 120 can be provided with a vent 121 . The vent 121 can be used in case the nozzle 1 13 is blocked. This vent can be provided with a further pressure relief value, which can have a higher pressure relief value than valve 132, and thus will open only if nozzle 1 13 or valve 132 is blocked.

Due to the high pressure of this gaseous nitrogen 128, it will enter the cooling chamber at velocities of about 250 to 300 m/s. Due to this high velocity, it will rapidly spread and circulate within the cooling chamber 102 (symbolised by dotted line 128'), and will cause turbulances and thus enhance convection of liquid nitrogen 1 1 1 entering cooling chamber through inlet 1 10 as well as cold gaseous nitrogen 1 1 1 resulting therefrom. Preferably, as symbolized by the slanting inlet 1 12, a first impingement of gaseous nitrogen 128 from recipient 120 on liquid nitrogen 1 1 1 will occur in a region of cooling chamber 102 in the vicinity of inlet 1 10. By means of said interaction between gaseous nitrogen 128 entering chamber 102 via inlet 1 12 initially liquid, and subsequently also gaseous nitrogen 1 1 1 entering chamber 102 via inlet 1 10 will be evenly distributed throughout the cooling chamber 102, resulting in an even temperature distribution.

Gaseous nitrogen can escape from chamber 102 via a gas outlet 1 14.

As explained above, the pressure relief valve 132 will open upon reaching a defined pressure in recipient 120 and conduit 130. After gas (especially liquid nitrogen) is thus injected into the cooling chamber 102, this pressure will decrease, so that the valve

132 will again close, until the pressure in conduit 130 again reaches said defined value, resulting in a further opening of relief valve 132. Hereby, an effective control of injection of gas via conduit 120 can be effected. In order to effectively prevent gas injected via inlet 1 12 to be too warm, which would result in an unwanted temperature increase in the cooling box 102, a recirculation duct 134 is provided, by means of which gaseous nitrogen 128 from recipient 120 or conduit 130 can be recirculated into recipient 120. This aspect is shown only schematically in figure 1 , and will be further explained in connection with figure 3.

For example by providing a temperature sensor 140 in conduit 130, the temperature of gaseous nitrogen can be ascertained. In case the temperature is too high, recirculation can be effected. Expediently, a controllable valve 142 is provided in recirculation conduit 134.

The use of liquid and gaseous nitrogen 1 1 1 and 128 for effecting the main cooling within cooling chamber 102 as well as the convection within cooling chamber 102, as described above, is advantageous in that only one medium (i.e. nitrogen) is used. Thus, handling is facilitated. There is no need to provide convection fans within chamber 102.

A preferred feeding system for liquid and gaseous nitrogen is, schematically, shown in Fig. 2. A liquid nitrogen source 200 provides liquid nitrogen through a conduit 202, leading to (symbolically shown) inlet 1 10. From conduit 202, a conduit 204 branches off, which leads to inlet 124 for recipient 120. Thus, cooling chamber 102 and recipient 120 can be provided with liquid nitrogen from the same source.

As described above, gaseous nitrogen exits recipient 120 via conduit 130, and enters into the cooling the chamber 102 via (symbolically shown) inlet 1 12.

As mentioned, figure 3 shows a preferred solution for recirculating gaseous nitrogen 128 into recipient 120.

Here, recirculation duct 134 leads to a heat exchanger 135 provided in the lower part of recipient 120, i. e. within liquid nitrogen 122. Gaseous nitrogen 128 can thus be effectively cooled, if for example temperature sensor 140 indicates too high

temperatures. Thus cooled gaseous nitrogen can be recirculated into conduit 130 via further conduit 136. Additional control valves 132 may be provided, for example at the positions indicated in figure 3.

Claims

1 . Device for treatment of parts, especially metallic parts, at low temperatures, comprising a cooling chamber (102) with an inlet (1 10) for a cooling medium (1 1 1 ), characterised in that there is provided a means (1 12, 1 13, 120, 130, 132) for controlled high velocity injection of gas (128).

2. Device according to claim 1 , comprising an outlet (1 14) for vent gas and at least one door (104, 106) through which parts to be treated can be brought into the chamber (102) and removed therefrom.

3. Device according to any one of the preceding claims, wherein a liquid nitrogen source (200) is connected to the inlet (1 10) and/or the means for controlled high velocity injection of gas.

4. Device according to any one of the preceding claims, wherein the means for controlled high velocity injection of gas include a recipient (120) for holding and vaporizing liquid gas, especially liquid nitrogen, a conduit (130) for transporting vaporized gas into the cooling chamber (102), a pressure relief valve (132) provided in conduit (130) and a nozzle (1 13).

5. Device according to any one of the preceding claims, comprising a recirculation conduit for recirculation of vaporized gas into the recipient (120).

6. Device according to claim 5, comprising a heat exchanger (135), through which recirculated vaporized gas can be led.

7. Method for treatment of parts, especially metallic parts, at low temperatures, comprising

- placing parts to be treated in a cooling chamber (102),

- injecting gas into the cooling chamber at high velocity, such that convection of the cooling medium within the cooling chamber is achieved.

8. Method according to claim 7, wherein a cooling medium is injected into the cooling chamber.

9. Method according to claim 7 or 8, wherein the gas injected into the cooling chamber is gaseous nitrogen, and/or the cooling medium is liquid nitrogen.

10. Method according to claim 7to 9, wherein gaseous nitrogen is injected at

velocities of 200-400 m/s, preferably 200-300 m/s.

1 1 . Method according to claim 7 to 10, wherein a liquid gas, especially liquid

nitrogen, is vaporized in a recipient (120) and the vaporized nitrogen is injected into the cooling chamber (102) when the pressure of the vaporized nitrogen exceeds a predefined value.

12. Method according to claim 1 1 , wherein the vaporized nitrogen is injected into the cooling chamber (102) when the pressure of the vaporized nitrogen exceeds 4 bar, 5 bar or 6 bar.