| 1. Introduction:Mechanical properties | | | | the tool was done by indirect cooling |
| like hardness, wear resistant, tensile | | | | and with no direct contact with liquid |
| strength are very important for cutting | | | | nitrogen. The Cryo-treatment is a |
| tool. The Cryogenic treatment on metal | | | | doubled walled stainless steel container |
| has been extensively employed since many | | | | with inter-spaced filled with |
| years for various application like | | | | Polyurethane foam. The top cover made of |
| stabilizing dimension of precision | | | | stainless steel has a double end shaft |
| machined part and gauges with change in | | | | fan motor assembly mounted centrally. |
| temperature, removal of internal | | | | The liquid nitrogen, connecting valve, |
| stresses, improving wear resistant and | | | | pressure gauzes, feed through and outlet |
| hardness.Cryogenic treatment of metal | | | | connections are all mounted on the top |
| parts means cooling these parts at a | | | | flange.Below the top cover a cylindrical |
| predetermined rate, up to a given | | | | buffer tank is mounted where the liquid |
| Cryogenic temperature (-80C), | | | | nitrogen get collected and evaporated |
| maintaining these parts at that lowest | | | | vapour are vented through a vent pipe. |
| temperature for a given duration of time | | | | The shaft of the fan motor assembly |
| and then allowing these parts to warm-up | | | | passes through this buffer tank and has |
| at a given warming-up rate to room | | | | fan blades mounted on both sides. A |
| temperature.So the main variable of the | | | | copper disk has been fixed to the bottom |
| Cryogenic treatment are:a. Rate of | | | | of the buffer tank to ensure better heat |
| cooling.b. The lowest maintained | | | | transfer. Aluminium fans are fixed at |
| temperature for a given duration.c. The | | | | the bottom to ensure forced convection |
| duration for which the specimen are | | | | cooling of the space inside the |
| maintained at the lowest temperature.d. | | | | Cryo-treatment chamber. The specimen |
| The rate of warming up(Chillar, Agarwal. | | | | kept in the stainless steel tray can be |
| 1995)Cryogenic treatment has been | | | | cooled by two ways:i. A circulating fan |
| successfully applied on steel to improve | | | | housed below the buffer tank, induce |
| its mechanical properties. This occurs | | | | forced convection currents picking up |
| because of transformation of almost all | | | | cold from stored liquid nitrogen in the |
| the retained Austenite in steel to | | | | buffer tank downward over the specimen. |
| Martensite thereby making the steel more | | | | The cold gas moving down to the bottom |
| Wear resistant.2. Literature | | | | of the chamber gets cooled and moves |
| Survey:Evidence of Cryogenic treatment | | | | radially sideways. These gases re-enter |
| was found during 1937 in Soviet Union | | | | on the fan region through the opening of |
| (Carry and Robert 1980). Metals are | | | | the slots in the aluminium fins. Thus |
| gradually cooled to cryogenic | | | | forced convection current loop is |
| temperature (-80C), soaked for a | | | | established within the chamber.ii. Part |
| prolonged period and warmed to room | | | | of the liquid nitrogen stored in the |
| temperature at a predetermined rate, the | | | | buffer tank is made to circulate over |
| lattice structure of the atoms change | | | | the shroud by thermo-syphon effect. To |
| due to stress being relived during | | | | facilitate this a copper tube is |
| Cryogenic treatment. In case of ferrous | | | | connected to the buffer tank and is |
| metal, the soft ductile FCC structure | | | | brazed on the outer wall of the shroud |
| Austenite gets converted into strong and | | | | over its entire length. A solenoid valve |
| harder BCC structured Martensite. Apart | | | | is operated by a PID controller with |
| from this, a wide precipitate of newly | | | | predetermined set points, is used to |
| formed Eta-Carbides (responsible for | | | | regulate the liquid nitrogen supply to |
| increased wear resistance) into the hard | | | | the chamber. The temperature of the |
| Martenside structure induces a dense | | | | specimen is measured using temperature |
| lattice structure.Some theories by Zhmud | | | | sensors.Another method can be by using |
| (1980) are:a. Cryogenic treatment was | | | | refrigerator with ethyl alcohol and dry |
| effective for intemperate and adequate | | | | ice as refrigerant for Cryogenic |
| tempered tool.b. The soaked time (5min | | | | treatment. The specimen to be treated |
| to 10 hrs) had no effect on the tool | | | | was placed in a clean and dry thermocol |
| life.c. A decrease in tool life within | | | | box. The specimen with the thermocol box |
| 5-7 days after treatment and increases | | | | were then kept in a refrigerator for |
| again with repeated treatment.Cryogenic | | | | duration of 12hrs to bring down the |
| treatment can be performed by different | | | | temperature of the specimen to |
| methods.One of such methods consists of | | | | 0C. After a period of 12 hrs, |
| a Cryo-treatment chamber and an | | | | dry ice was added into the thermocol box |
| auxiliary liquid nitrogen supply system. | | | | using a spatula. |
| In this set-up Cryogenic treatment of | | | | |