DE19549422C2 - Mfg. cores for sand casting - Google Patents

Abstract

Resin-bonded sand cores are set by the action of hardener- or catalyser-gas. Exhaust gases are collected for controlled disposal. Liquid hardener or catalyser gas are mixed with transport gas so that the dew-point of the mixture is below room temperature. The mixture is fed into the core either under pressure or partial vacuum supplied by the delivery or suction of a blower.

Description

The invention relates to methods and devices for Production of sand cores or sand molds net), as z. B. in metal casting for internal and external limits tion of the casting can be used. The sand comes in a first Step into the cavity of a core or molding box (tool be draws) and then in a second step by hardening reaction (hardener, catalyst, in the following in common sam as hardener / hardener gas) solidified.

Hardener liquid is first an evaporator that ent air holds, added, then inserted into the sand bale with compressed air The introduction of the mixture into the sand bale is called Bega designated process. Then the airflow continues maintained to re-evaporate hardness to distribute the mixture in the bale of sand and hardener from the To carry out bales of sand again, what is called a rinsing process becomes. A clear separation, gassing and flushing is not possible. Both processes are referred to here as the curing process, at the exhaust air with the gaseous gases involved in the curing process Fabrics.

A fumigation device of conventional design leads the fumigation and Flushing through.

Dossmann (WO 92/18267 A1) suggests a cycle management an evaporator in which hardener liquid is evaporated in air (Mixture formation) and the bales of sand. The use of additional Purge gas is not required.

In order to make the hardening process particularly efficient, i.e. to keep the dosage and consumption of hardener liquid small, several ventilation channels, which suggest the entry of the mixture into the sand bale (exit zone 1 ), are first directed into collecting chambers, the mixture exit of which is included a gas valve can be closed.

The ventilation channels furthest away from the mixture inlet (designated exit zone 2 ), i.e. the zones in the sandball that are most difficult to reach from the flow point of view, are constantly open during core shooting and gassing, while the gas outlet from the collecting chambers (outlet zone 1 ) is closed during gassing being held. This prevents that through the ventilation channels of the exit zone 1 when gassing Ge emerges from the sand bale and tool mixture and is lost for the hardening process, but not that within the collecting chambers an uncontrolled flow of the sandball lens sets, which sets the hardening process affected in certain areas of the bale of sand.

The invention has set itself the goal of guiding the supplied mixture more completely than previously known and for the hardening process more effectively through the sand bale in order to achieve the following advantages:

• - Reduction in the use of hardener to reduce material costs and expenses for exhaust air purification.
• - Reduction of curing times to increase production and Minimize investment costs.

The object is achieved by a method with the features of Claim 1 or by a device with the features of Claim 5.

The following are some effective individual measures explained that serve and combine the above objectives can be.

First action Reversal of the flow of the tool

An essential content of the invention is a reversal of the direction flow of the tool, d. i.e., the inflow point of the mixture to the outflow point and vice versa. This ensures that the originally disadvantaged areas in terms of flow nearby the mixture inflow come to rest and at the beginning of the flow be supplied. The directional reversal is done by valve scarf tung.

Fig. 1 shows the piping and apparatus diagram to perform the Dosie tion, the inner and outer circuit and also to reverse the flow direction of the tool.

Fig. 2 shows the cross section of a two-part tool, which is fastened on the clamping housings of the machine, with the flow paths during gassing in the normal flow direction. With this, the mixture enters via the gassing plate and the mixture exits via the most distant ventilation nozzles.

FIG. 3 shows the cross section of a two-part tool analogous to FIG. 2, which is fastened on the clamping housings of the machine, but with the flow paths during the gassing in the reverse flow direction. In this case, the mixture enters via the most distant ventilation nozzles.

Second measure External circuit with the help of a gas pump pump / compressor

The mixture that has passed through the ball of sand is collected, led to the suction side of a gas feed pump / compressor and again passed through the bale of sand. This makes a multiple flow through the hardener in the sand bale reached, so that the hardener terdosing can be withdrawn accordingly, moreover there is no exhaust air during fumigation.

The pressure is preferably generated after the game ralkammerprinzip working fluid machine that largely has a delivery volume that is independent of back pressure and high  Can create overpressures: rotor and stator have spiral Walls that form gas chambers separated by narrow gaps; the Runner makes circular wiping motions, causing the gas chambers moving from one end of the spirals to the other, doing so decrease in size so that gas flows from one end of the spiral to the other is transported and compacted in the process.

Third measure Location of the dew point and internal circulation

We have the type of mixture preparation before the curing process significant influence on the course of the curing process. Size Hardener quantities lead in the evaporator of conventional gassing devices too high concentrations, which are only evident from the use of temperature Lich above the room temperature in the evaporator air volume full can be continuously evaporated, which also takes a noticeable time span is needed.

When the mixture is cooled down to room temperature in the evaporator back condensation occurs, d. that is, the dew point of the mixture is above room temperature.

At least at the start of curing, i.e. when the highly con centered mixture in the i. R. unheated supply line and in Back condensation occurs at the inlet area of the sand bale. This has the consequence that the curing process takes longer because for less hardener gas is available in the rest of the sand bale and with conventional gassing devices, the recondensed hardness terfluid first through the relaxing and then off cooling compressed air must be evaporated again.

In areas of recondensed cold-box catalyst As the experience shows, the bale of sand remains soft and in the remaining areas will be underpinned due to the shortage tereaction not yet initiated, so these areas too stay soft.

For large and complicated, especially heavily structured Bale of sand is a larger use of hardener, combined with length Ren hardening times necessary to the on partial flow branches to avoid curing problems to be attributed. Through optimism The position and size of the venting nozzles can use hardeners and curing times are reduced until the time at Hardening most disadvantaged areas just barely harden. If these limits are undershot, more and more arise Zones of uncured sand, which leads to errors that a Further use of the hardened sand bale i. Exclude R. Conversely, bales of sand that are not fully hardened can pass through Increase in dosage and flushing time can be remedied. Experience has shown that the dosage of the hardener can be increased Accelerate the curing process only to the point of time which further increases do not result in time reductions, what can be explained by the recondensation effects described. In order to obtain hardened sand bales, a larger mass must be used be used on purge air, e.g. B. by higher system pressure in the compressed air line or longer flushing times.

The third measure described here should make a contribution short curing times with low hardener dosage chen.

Condensation effects in the pipeline and in the sand bale can be avoided if pipeline, mixture, sand supply and plant  Stuff to be heated, resulting in complex and expensive facilities leads, combined with high energy costs. The temperature of the Sand supply is limited to around 25 ° C to prevent evaporation Solvents contained in the resins in favor of a longer one To achieve processing time. Tool heaters are special complex and ineffective because of the thermal inertia of the sand bale.

According to the invention, liquid hardener is made using a metering device direction z. B. via an atomizer nozzle in an internal circuit injected by a gas conveyor before the curing process pump is circulated several times. Located in the inner circulation there is also a mixture container, which is dimensioned with its contents sen is that according to Ver steaming and homogenization the dew point temperature inside Circulating volume is below room temperature.

The inner cycle consists of essential parts of the outer one Circulation, such as gas feed pump, metering device and mixture container. The tool is only flowed through in the external circuit.

B Explanation of the item numbers

• 1. 1 clamping housing on the left
• 2. 2 clamping housing on the right with partition ( 65 )
• 3. 3 tool half on the left
• 4. 4 tool half on the right
• 5. 5 gassing plate with hole for gas passage
• 6. 6 ventilation duct for outlet zone 1
• 7. 7 ventilation duct for outlet zone 2
• 8. 8 vent nozzle
• 9. 9 ejector plate in the tool
• 10. 10 ejector pin in the tool
• 11. 11 ejector plate in the clamping box
• 12. 12 ejector pin in the clamping housing
• 13. 13 actuator
• 14. 14 ventilation duct in the clamping housing without partition
• 15. 15 ventilation channel in the mold half for a clamping housing with partition ( 51 , 65 )
• 16. 16 Sealed partition wall of the clamping housing
• 17. 17 Dead space in the tool half for the clamping housing with intermediate wall
• 18. 18 Dead space in the tool half with a clamping housing without intermediate wall
• 19. 19 seal
• 20. 20 spring
• 21. 21 Air vents sand bale exit zone 2
• 22. 22 Back wall of the clamping housing
• 23. 23 bales of sand
• 24. 30 Top vent
• 25. 31 Top middle vent nozzle
• 26. 32 Bottom breather nozzle
• 27. 33 Air vent below
• 28. 36 Mixture exit core box half on the left (normal operation), exit zone 2
• 29. 37 Mixture exit core box half on the right (normal operation), exit zone 2
• 30. 42 Dead space clamping housing on the left, exit zone 1
• 31. 43 Dead space, tool half left and right, exit zone 1
• 32. 44 Wall tool for sand bales
• 33. 60 storage containers
• 34. 61 dosing device
• 35. 62 hardener valve
• 36. 63 Gas feed pump
• 37. 64 mixture container
• 38. 65 return line inner circuit
• 39. 66 Common pipes internal and external circuit
• 40. 67 valve
• 41. 68 External circuit supply line
• 42. 70 supply line with normal flow
• 43. 71 Line to and from tools
• 44. 72 Gas inlet tool (gassing) with normal flow
• 45. 73 tools
• 46. 74 Tool gas outlet (gassing) with normal flow
• 47. 75 Management from and to tools
• 48. 76 return line with normal flow
• 49. 77 valve
• 50. 78 return line external circuit
• 51. 80 valve
• 52. 81 valve
• 53. 82 valve
• 54. 83 supply line when reversing the direction of flow
• 55. 84 return line when the flow direction is reversed tung

The sand bales themselves are not shown in the figures, single Lich the cavities for the ball of sand with the help of the delimiting Walls. The flow paths shown in the tool and on clamping housings were partially interrupted for reasons of illustration chen. Arrow ends at flow paths mean that only fill these areas with gas. Continuous and from darstel flow-related reasons mean interrupted flow paths a continuous flow. Lines with dashes in the end mean closed lines.

Instead of two-part, there are also three-part or multi-part tools usable analogously, but not shown here and be were written.  

Fig. 1

The amount of hardener measured by the metering device ( 60 , 61 , 62 ) is in the line part ( 66 ) z. B. injected in front of the gas feed pump ( 64 ). The internal circulation for the evaporation of the liquid hardener takes place via ( 66 , 63 , 64 , 65 and 67 ) before the curing process. The valves ( 77 , 80 , 81 and 82 ) are closed ge.

The outer circuit for fumigation leads at normal flow direction through the tool ( 68 , 70 , 80 , 71 , 72 , 73 , 74 , 75 , 76 , 77 and 78 ), the mixture via the fumigation plate ( 5 , 72 ) Tool ( 73 ) is fed in and discharged via ( 74 ). The valves ( 81 and 82 ) remain closed, ( 77 ) and ( 80 ) are open.

The outer circuit for gassing leads to the direction of the flow through the tool via ( 68 , 83 , 81 , 75 and 74 ) to the tool ( 73 ). The mixture enters the sand bale via ventilation channels and nozzles. It leaves the tool at ( 5 , 72 ) via the gasification plate again and is returned via ( 71 , 84 , 82 , 78 and 66 ) to the suction side of the gas feed pump / compressor ( 63 ). Valves ( 77 ) and ( 80 ) are closed, ( 81 ) and ( 82 ) open.

Fig. 2

When gassing in the normal flow direction, the mixture enters at ( 5 , 72 ) and the mixture exits at ( 36 , 37 and 74 ).

( 74 ) is connected to the suction side and ( 72 ) to the pressure side of the gas feed pump / compressor ( 63 ).

Fig. 3

When gassing in the reverse direction of flow, the mixture enters at ( 74 , 36 , 37 ), the mixture exits via ( 5 , 72 ).

( 72 ) is connected to the suction side and ( 74 ) to the pressure side of the gas pump / compressor ( 63 ).

Claims (5)

1. A process for the production of resin-bonded sand bales by filling a mold cavity with sand, which is mixed with at least one resin component, and then passing hardener or catalyst gas through to solidify the sand, hardener or catalyst gas being metered with carrier gas so that it is mixed the dew point temperature of the mixture is not above room temperature, the mixture being circulated with a gas feed pump in an internal circuit and the mixture being transported for gassing through the sand bale by pressing or suction or with pressurized carrier gas, characterized in that during part of the curing time, the mixture in an external circuit in the normal flow direction through the lines ( 66 , 68 , 70 , 71 ) to the tool ( 73 ) and from there through the lines ( 75 , 76 ), the valve ( 77 ) and the line (78) flows back to the gas feed pump (63), and w the other part of the curing time, the flow direction of the sand bale is reversed while by valve control, by carrying out the mixture supply to the tool (73) via lines (66, 68, 83, 75), and the mixture recirculation through the lines (71, 84, 78). 2. The method according to claim 1, characterized in that the mixture is transported by a volumetric gas feed pump ( 63 ), the pressure side ( 66 ) with normal flow of the sand bale to ( 72 ) and the suction side ( 78 ) to ( 74 ), with reversal the direction of flow, the pressure side ( 66 ) to ( 74 ) and the suction side to ( 72 ). 3. The method according to claim 1 or / and 2 characterized in that before the hardening process after the hardening injection the evaporation and homogenization of the mixture takes place in an internal cycle. 4. The method according to any one of claims 1 to 3, characterized in that the volume of the mixture container ( 64 ) for the maximum hardener dosage is chosen so large that the dew point comes to be below the lowest operating temperature in the system. 5. Device for the production of resin-bonded sand bale with a two tool halves ( 3 , 4 ) existing tool ( 73 ) which has a cavity to be filled with sand and binder, a final fumigation plate ( 5 ) with a for connection to a supply line for Has hardener or catalyst gate mixture certain inlet ( 72 ), a discharge line ( 74 ) for hardener or catalyst mixture and devices for reversing the direction of fumigation in the sand bale ( 23 ) for performing the method according to one of claims 1 to 4, characterized characterized in that a control of the mixture path during the hardening process of the sand bale ( 23 ) from and to the gas feed pump ( 63 ) by the lines ( 66 , 68 , 70 , 71 , 75 , 76 , 78 ) and the controllable valves ( 80 , 81 , 82 , 77 ) is present.