METHOD AND INSTALLATION FOR HEAT TREATMENT, ESPECIALLY CASE-HARDENING

Abstract: Method and installation for heat treatment in connection with case-hardening of articles with varying requirements as to heat treatment time. The articles are first heated up in a heating-up furnace (9) to the heat treatment temperature. Thereafter the articles are heat-treated in a ring furnace (10). The articles are removed from the ring furnace after a predetermined holding time independently of the order in which they are inserted, by advancing each article to the discharge opening (11) of the furnace.

Description: Method and installation for heat treatment, especially case-hardening The present invention relates to a method of heat treatment, especially case-hardening, of articles with varying requirements as to heat treatment time. The invention also relates to a heat treatment instal- lation particularly suited to carrying out said method, In continuous case hardening, up to now pusher type installations have been used, in which the articles to be hardened are placed on metal skidding pallets, which are inserted through a feed-in opening at one end of the heat treatment furnace, and after heat treatment has been completed, are taken out through an exit opening at the opposite end of the furnace. In the furnace, the articles are heated to the heat treatment temperature and kept at this temperature as long as is required to achieve the desired carbonization depth. The method is based on the principle: first in - first out, and presupposes that all the articles inserted at the same time into the furnace are to have the same carbonization depth and therefore the same heat treatment time. If the assortment of articles in the heat treatment installa¬ tion contains articles requiring different carboniza¬ tion depths, which is often the case, these cannot be mixed in the furnace, since those articles requiring a short heat treatment time cannot be taken out before those requiring a longer treatment time. The result will be low utilization of capacity, when a few articles are to have a long heat treatment time and the available furnace space cannot at the same time be used for articles requiring a shorter treatment time. The purpose of the present invention is to achieve a method which makes it possible to better utilize available capacity by making it possible to treat at the same time articles which are to have differing carbonization depths. This is achieved according to the invention by a plurality of articles being heated up at the same time in a separate heating-up furnace to a predeter- mined temperature, the articles being thereafter inserted into and kept in a heat treatment furnace for heat treatment, the holding time for each article in the heat treatment furnace being monitored individu¬ ally and the articles being removed individually from the furnace after a predetermined holding time independently of the sequence of insertion. An installation particularly suited to carrying out the method according to the invention comprises a ring furnace known per se with a rotatable carrier for the articles and is characterized in that the discharge opening from a separate heating-up furnace is connected directly to the input opening of the ring furnace. In the method according to the invention, all the articles are heated in the heating-up furnace to the heat treatment temperature of the heat treatment furnace. The articles to be heat-treated for 1.5 hours, for example, can be inserted into the heat treatment furnace after the articles to be treated for 3.5 hours, and be taken out before these, without requiring a change in the temperature or atmosphere of the heat treatment furnace. By using a ring furnace, this can be done quite simply. Each article is time-monitored, preferably via a computer system, and is advanced to the exit point from the ring furnace after heat treatment has been completed. The invention will be described in more detail with reference to an example shown in the accompanying drawing, which shows schematically a heat treatment installation, particularly suited for carrying out the method according to the invention. In the figure, 1 designates a feeding station for articles to be case-hardened. The articles are placed on metal skidding pallets 2, on which the artic¬ les are then transported through the installation. From a conveyor 3 , the pallets are transferred to a conveyor 4 and are conveyed thereon through a washing station 5 and back to the conveyor 3 via a conveyor 6, and from there to a conveyor 7, by means of which the skidding pallets 2 are fed into the heat treatment furnace 8. After preheating, the pallets are advanced to a heating up furnace 9, in which the articles are heated up to their heat treatment temperature, e.g. ca 900°C. The heating-up furnace 9 is attached directly to a ring furnace 10, in which the pallets after heat¬ ing of the articles are placed on a turn-table (as is indicated by the arrows in the figure). Regardless of the order in which the pallets are fed into the furnace 10, anyone of the pallets can now be removed by virtue of the fact that the turn-table can be advanced as many steps as are desired in either direction in order to place the selected pallet at the outlet 11 of the furnace 10. . After treatment has been completed in the ring furnace 10, the articles are.transferred to a diffusion furnace 12 and from there either directly to a packing robot 13 or to an oil bath 14. From the oil bath 14, the articles are conveyed via conveyors 3 and 4 once again through the washing station 5 and finally to a tempering furnace 15, from which the articles are conveyed out to the conveyor 3» The heat treatment installation shown and described is suitably controlled by a computerized control system which keeps track of where each indi¬ vidual pallet is at each moment and times the various operations, so that all of the articles receive the proper heat treatment period independently of the order in which they are fed into the installation.

Claims: CLAIMS 1. Method of heat treatment, preferably case- hardening, of articles with varying requirements as to heat treatment time, characterized in that a plurality of articles are heated up at the same time in a separate heating-up furnace (9) to a predetermined temperature, that the articles are thereafter inserted into and kept in a heat treatment furnace (10) for heat treatment, that the holding time for each article in the heat treatment furnace is monitored individually and that the articles are removed individually from the furnace after a predetermined holding time independently of the sequence of insertion. 2. Method according to Claim 1, characterized in that the articles after heating up are placed on a rotary carrier in a ring furnace (10) and that each article, when the predetermined holding time has expired, is advanced to a discharge opening in the furnace by rotation of the carrier. 3. Method according to Claim 2, characterized in that the articles, after heat treatment in the ring furnace (10), are fed into a diffusion furnace (12) directly connected to the ring furnace. 4. Installation for heat treatment, preferably case-hardening, of articles with varying requirements as to heating-up time, said installation comprising a ring furnace with a rotary carrier for the articles, characterized in that the discharge opening from a heating-up furnace (9) is directly connected to the feeding opening of the ring furnace (10). 5. Installation according to Claim 4, characterized in that the ring furnace has a discharge opening (11) placed diametrically opposite to its feed-in opening and is directly connected to the feed-in opening of a diffusion furnace (12).

Inventors: BARKMAN TOMAS, BARKMAN, TOMAS
Applicants: VOLVO AB, AB VOLVO
Application year: 1985
Main classification: C21D9
IPC codes: C21D9