The temperature cascade control method of metal powder injection molded vacuum degreasing fritting furnace
Technical field
The present invention relates to metal powder injection molded vacuum degreasing fritting furnace, particularly relate to a kind of temperature cascade control method of metal powder injection molded vacuum degreasing fritting furnace.
Background technology
The temperature control design of general metal powder injection molded vacuum degreasing fritting furnace as shown in Figure 1, sintering furnace body 1 inside arranges thermal insulating material 9 and heater 2, hopper 3 is placed in middle part in sintering furnace body 1, is provided with the flitch 4 for putting product 5 in hopper 3, and it is outside that thermocouple 6 is arranged on hopper 3.Operation principle as shown in Figure 2, adopt single loop control system, wherein SV is desired temperature, PV is thermocouple 6 actual temperature monitor value, adjuster PID is according to SV and the PV of input, automatically calculate, result of calculation is defeated by power controller, power controller carries out power percentage and exports the heating power controlling heater 2.Thermocouple 6 called after Thc.
The heat conduction of metal powder injection molded vacuum degreasing fritting furnace is mainly by heat radiation, heater generates heat, heat radiation is on hopper, hopper is made up of graphite, because graphite is at infrared region at the wavelength that low temperature section (≤600 DEG C) radiation is the strongest, the heat that hopper wall is radiated on product can seldom, and product temperature is more delayed than control temperature.And when pressurizeing, Secondary Disturbance (gaseous exchange) is comparatively large on the impact of single loop control system, makes upper and lower temperature difference in sintering furnace body comparatively large, affecting properties of product.
In single-loop system controls, if when thermocouple location is placed on the temperature of namely monitoring product itself in hopper, due to graphite low-temperature zone heat radiation reason, expect that the temperature inside the box causes heater constantly to heat than the delayed meeting of control temperature and occurs temperature overshoot phenomenon.Such as desired temperature is 400 DEG C, material the temperature inside the box is 300 DEG C, thermocouple is placed in hopper, with 300 DEG C for PV value, and actual existing 400 DEG C of box outside temperature will be expected, but now heater can strengthen power heating, when causing material the temperature inside the box to reach desired temperature like this, and actual material box outside temperature has exceeded desired temperature, material box outside temperature can be radiated in hopper, causes material the temperature inside the box to exceed desired temperature.So thermocouple to be arranged on hopper outer and near hopper outer wall, can monitor hopper outside wall temperature on the one hand, be monitoring heater heating-up temperature on the other hand.Can only be waited for by the process time with the temperature difference outside hopper in hopper and balancing, the material box outside temperature such as detected when thermocouple is 400 DEG C, when now expecting that the temperature inside the box is 300 DEG C, heater stops intensification to be namely incubated a period of time or heater programming rate slows down, and waits for that material the temperature inside the box rises to and expects that box outside temperature is close.But thermocouple is placed on outside hopper has following shortcoming: the stand-by period of heating up is longer, and need artificial supposition, cause its precision not high.Because the temperature needed for product and actual monitoring temperature have different, properties of product are caused to decline.In addition, under the state of strong gaseous exchange, the upper and lower temperature fluctuation of hopper is comparatively large, affects properties of product.
Summary of the invention
The present invention is directed in prior art and can not truly show material the temperature inside the box, the intensification stand-by period needs artificial supposition, accuracy is not high, cause the shortcoming that properties of product decline, provide a kind ofly can truly show the temperature inside the box, the temperature cascade control method of the metal powder injection molded vacuum degreasing fritting furnace that improves the followability of temperature.
In order to solve the problems of the technologies described above, the present invention is solved by following technical proposals:
The temperature cascade control method of metal powder injection molded vacuum degreasing fritting furnace, temperature cascade control method carrys out detection and control with the primary heat transport system formed in hopper by master selector, the subloop system that detection and control formed with hopper is carried out outward by secondary controller, primary heat transport system is control object region, subloop system is energy subject area, user is by the good heating-up temperature of technology controlling and process target setting, this heating-up temperature is desired temperature SV1, desired temperature SV1 and the temperature value PV1 of the primary heat transport system detected are input to master selector, master selector calculates automatically according to the input value of SV1 and PV1, again using the setting value SV2 of the output valve of master selector as secondary controller, secondary controller calculates automatically according to SV2 and the temperature value PV2 of the subloop system detected, calculate the heating power that heater needs, again this heating power is transported to power controller, power controller carries out power percentage output, power controller controls the heating power of heater by this output, make PV1 and SV1 close.
As preferably, master selector is PID1, and secondary controller is PID2.
As preferably, the temperature value PV1 of primary heat transport system is monitored by the first thermocouple, and the temperature value of subloop system is monitored by the second thermocouple.
As preferably, power controller is IGCT SCR.
The present invention, owing to have employed temperature cascade control method to control the programming rate of sintering furnace body internal heat generation body, compared with controlling, has following three advantages with single-loop system:
1. the temperature in true display hopper, i.e. the temperature of product itself.
First thermocouple inserts in hopper, close with product, just truly can show the temperature in hopper.
2. improve the dynamic characteristic of process, improve the followability of temperature, be beneficial to improving technique, shorten man-hour.
Had serials control, can monitor constantly the temperature in hopper, and by the heating of IGCT SCR fast-response control heater, the value that material the temperature inside the box and user are set is close, namely improves the followability of temperature.
3. can overcome rapidly the Secondary Disturbance entering subloop system.
When pressurizeing, have gaseous exchange outside hopper to produce, serials control is disturbance large for acute variation design in subloop system, and Secondary Disturbance makes it very little on the impact of main controlled volume by the adjustment of primary heat transport system and subloop system, can be overcome rapidly.
Accompanying drawing explanation
Fig. 1 is temperature control design drawing in prior art.
Fig. 2 is the schematic diagram of Fig. 1.
Fig. 3 is temperature control design drawing of the present invention.
Fig. 4 is temperature cascade control method theory diagram of the present invention.
Fig. 5 is the profile before the thermal expansion of thermocouple hole device.
Fig. 6 is the profile that thermal expansion causes the parts movement such as hopper and thermocouple hole device.
Fig. 7 is temperature-time curve figure.
The toponym that in accompanying drawing, each number designation refers to is as follows: wherein 1-sintering furnace body, 2-heater, 3-hopper, 4-flitch, 5-product, 6-thermocouple, 7-first thermocouple, 8-second thermocouple, 9-thermal insulating material, 10-stopple, 11-cock cap, 12-first pad, 13-second pad, 14-the 3rd pad, 15-protecting tube, 16-expansion gap, 17-ceramic wafer.
Detailed description of the invention
Below in conjunction with accompanying drawing and embodiment, the present invention is described in further detail.
Embodiment 1
The temperature cascade control method of metal powder injection molded vacuum degreasing fritting furnace, as shown in Figures 3 to 6, comprise the thermal insulating material 9 be arranged in sintering furnace body 1, heater 2 and hopper 3, in hopper 3, be provided with flitch 4, flitch 4 is provided with ceramic wafer 17, and product 5 is placed on ceramic wafer 17.Also comprise master selector, the first thermocouple 7 that the secondary controller of connecting with master selector signal output part, power controller, front end are placed in hopper 3 inside and front end are placed in the second thermocouple 8 in sintering furnace body 1, first thermocouple 7 is arranged on hopper 3 by the thermocouple hole be opened on hopper 3 wall, and power controller is connected with the output of secondary controller.First thermocouple 7 is connected with the input of master selector, and the second thermocouple 8 is connected with the input of secondary controller.First thermocouple 7 is arranged on thermocouple hole by thermocouple hole device.
Thermocouple hole device comprises the stopple 10 be arranged in thermocouple hole, is provided with cock cap 11 below stopple 10, is provided with pad in the gap between stopple 10 and cock cap 11.Pad comprises the second pad 13 that the first pad 12 of being connected with stopple 10 is connected with cock cap 11 and the 3rd pad 14 be arranged between the first pad 12 and the second pad 13.First pad 12, second pad 13 and the 3rd pad 14 all adopt ceramic material.Ceramic material has the effect of end face and end face seal.
On first thermocouple 7, cover has protecting tube 15.Expansion gap 16 is had between protecting tube 15 and stopple 10.Expansion gap 16 is had between protecting tube 15 and the 3rd pad 14.Expansion gap 16 is all had between the sidewall of cock cap 11 and the first pad 12, second pad 13.
The thermocouple hole device be provided with has the effect sealing and avoid to cause the first thermocouple 7 stressed by thermal expansion, has very little gap between the first pad 12 top and stopple 10, instead of locking, and pad can be made like this to cause movement by expansion; First pad 12 internal diameter and the gap between the second pad 13 internal diameter and protecting tube 15 very little, such gas enters can seldom, on hopper 3 inside and outside differential pressure without impact; When expansion gap 16 is used for preventing temperature from raising, because thermal expansion causes hopper 3 and thermocouple hole apparatus parts to move and make the stressed breakage of protecting tube 15.
Temperature cascade control method carrys out detection and control with the primary heat transport system formed in hopper 3 by master selector, detection and control is carried out with the outer subloop system formed of hopper 3 by secondary controller, primary heat transport system is control object region, subloop system is energy subject area, user is by the good heating-up temperature of technology controlling and process target setting, this heating-up temperature is desired temperature SV1, desired temperature SV1 and the temperature value PV1 of the primary heat transport system detected are input to master selector, master selector calculates automatically according to the input value of SV1 and PV1, again using the setting value SV2 of the output valve of master selector as secondary controller, secondary controller calculates automatically according to SV2 and the temperature value PV2 of the subloop system detected, calculate the heating power that heater 2 needs, again this heating power is transported to power controller, power controller carries out power percentage output, power controller controls the heating power of heater 2 by this output, make PV1 and SV1 close.
In the present embodiment, the temperature value PV1 of primary heat transport system is monitored by the first thermocouple 7, and control object is product 5, and the data that the first thermocouple 7 records are closest to the true temperature of product 5; The temperature value of subloop system is monitored by the second thermocouple 8.
In the present embodiment, power controller is IGCT SCR, and master selector is PID1, and secondary controller is PID2.
In the present embodiment, the output valve called after SV2 of PID1, the first thermocouple 7 called after Thc1, the second thermocouple 8 called after Thc2.
In Fig. 7, A is the curve of desired temperature, and B is the actual temperature curve that temperature cascade controls, and C is the actual temperature curve of control of the prior art.
In a word, the foregoing is only preferred embodiment of the present invention, all equalizations done according to the present patent application the scope of the claims change and modify, and all should belong to the covering scope of patent of the present invention.