DE4028031A1 - METHOD FOR COVERING GRAINY, MINERAL MATERIALS WITH SYNTHETIC RESIN - Google Patents

Abstract

The invention relates to a process for coating granular mineral materials with synthetic resin. Minerals of this type, for example quartz sand, zircon sand, chrome ore sand, fireclay and corundum, are used in coated form in foundries as a moulding material (sand) for the production of shell moulds by the Croning process. The invention has the object of providing a hot-coating process which involves adding hot-liquid synthetic resin to the mineral material to be coated, but overcomes the disadvantages of the prior art by allowing rapid change of the synthetic resin types to be processed, allowing inherently reactive synthetic resins to be employed, and generally being more practicable and less complex. This object is achieved according to the invention in that the hot-liquid synthetic resin is only formed just before its addition to the mineral material, by melting solid synthetic resin.

Description

The invention relates to a method for sheathing granular, mineral materials such as quartz sand, Zircon sand, chrome ore sand, chamotte or corundum with one curable synthetic resin cover. Such coated, granular minerals come in foundries as a molding material for the production of masks mold using the croning process.

So far, there are essentially two wrapping processes have been practiced, namely the hot and hot cladding drive.

With the so-called warm wrapping, this becomes one Solvent-dissolved synthetic resin together with a corresponding one Hot hardener fed to a mixer in which the material to be wrapped granular mineral located. It becomes warm during the mixing process air is blown into the mixer to remove the solvent from the Drive out resin solution. After a viscous, doughy twi phase, clods form, which form during the continuation Slowly dissolve the mixing process and turn into coated grains seperate.

Using this procedure is a very even umman of the granular mineral. Because of its disadvantages, in addition to the long mixing time, especially in the big air  thinning solvents and the required Expensive exhaust air cleaning (cold traps, organic laundry) shear, afterburning etc.) count, it was largely from Hot coating process replaced.

In this process, the mineral to be coated is in a heater well above the melting point of the synthetic resins warms and then fed to a mixer. Simultaneously or with the resin is fed in after a short delay. The one in the mineral amount of heat causes a slow melting of the Synthetic resin with simultaneous mixing. A wrapping of the Minerals only occurs when the synthetic resin is sufficiently low is melted viscous. Before a hot hardener is fed the temperature of the batch is reduced by one Avoid pre-curing. However, after that the distribution of the Hot hardener within the synthetic resin film no longer optimal. After adding the hot hardener, the Temperature while mixing a separation of the coated mineral reached.

In comparison to the hot wrapping, the hot wrapping comes with shorter mixing or wrapping times and the expenditure Conditions for exhaust air purification can be omitted.

In addition to these advantages, there are also disadvantages record. So the mineral material to be encased are heated relatively high, d. H. on temperatures between 130 and 170 ° C, so that to melt the mixed solid synthetic resin required amount of heat in the mineral and is available through heat transfer. A wide one The disadvantage is that they result from the high mixing temperature the long cooling times.

The aforementioned disadvantages of the hot wrapping process can ver with the method disclosed in GS-PS 15 63 686 be avoided. It is proposed to do this by implementing  Phenol and formaldehyde with the application of heat generated hot liquid Resin after distilling off the water and excess phe continue to use nols directly, d. H. the resin won't like otherwise common, converted to a solid state by cooling, but from its manufacture, be hot-melted above written hot coating process fed.

The obvious advantages of this method are total savings of the otherwise in the production of the synthetic resin expenses required to convert it into a fixed Condition, as well as the energy saving for the required how the melting of the synthetic resin in the coating process. Furthermore According to this procedure, it is sufficient to use the material to be covered to be warmed only slightly above the melting point of the synthetic resin because there is a supply of melt energy out of the material is not required. Resul from the lower mixing temperature animals advantageously shorter cooling times for the enveloped Mineral.

The advantages mentioned are relativized in that the process is only practicable if manufacturing and The place of consumption of the synthetic resin is the same. As a rule, will this condition is not met. This means that that is out its production of hot liquid synthetic resin more or less great distances to the wrapping plant trans must be ported. There are special, insulated transport bags container required, because the synthetic resin may only be minimal cool down, at least not below its melting point, you want to as intended, a higher heating of the mineral for the Avoid wrapping process.

The resin supplied cannot be used up immediately due to damage in the wrapper plant, must be stored in the transport or storage containers Resin thermal energy can be supplied to its temperature not to let it sink.  

Production takes place in modern coating plants due to the different requirements of the foundries on the coated mineral with regard to the processed synthetic resin quality and the recipes changed several times a day. That's the way it is It is not uncommon for up to 200 recipes to be produced every month to the products ordered by the foundries to be able to deliver. Did you want these practical requirements comply with the procedure according to GB-PS 15 63 686, it would be required the wrapping machine a variety of heat iso assigning storage containers, in each of which a be the right resin quality is stored. These containers should be also be heated to keep the resin at temperature.

Another disadvantage is that the Resin over considerable periods at a relatively high temperature ren is held. This is the use of self-reactive Synthetic resins, such as o-o'-novolaks and resols, in this process not possible. For the foundries, however, is the use of minerals coated with such synthetic resins is advantageous, because this means reaction and cycle times in the production of Mask shapes can be achieved.

The invention has for its object a hot to provide a wrapping process, which is also with the addition of hot liquid synthetic resin to the one to be encased mineral material works, the disadvantages of the prior art Technology removed so that there is a quick change sel of the types of synthetic resin to be processed allows that own reactive synthetic resins can be used, and that it in As a rule, it is more practicable and less complex.

According to the invention, this object is achieved in that the hot liquid synthetic resin only shortly before it is added to the mine material by melting solid synthetic resin is fathered.  

The relative term "short" is in the sense of the Er to understand the invention so that the resin after melting not for a certain period of time in advance tet, but directly, if necessary with the interposition of a condition tionation stage, the wrapping process is fed, d. H. it is only in a relatively small, for continuous continuation Production melted down the required amount.

Because of this practice, short notice can occur the different requirements of the foundries with regard to Properties of the coated mineral are reacted after Feeding the generated synthetic resin melt to the coating process another type of synthetic resin can be melted immediately.

With regard to the properties of the product produced it is also advantageous that by appropriate Temperaturfüh Depending on the need, the synthetic resin melt is low, medium, or highly viscous can be set.

Another advantage of the method according to the invention lies in the fact that self-reactive synthetic resin systems come into use men can, since the thermoset undesirable in the coating process networking due to the relatively short period in which the resin temperatures are in the critical range, only can take place on an insignificant scale.

Last but not least, the entire Expenses of the procedure according to GB-PS 15 63 686 with regard to Transport and storage of the hot liquid synthetic resin be saved.

In an advantageous embodiment of the invention the melting of the solid synthetic resin within a time Mixing cycle and in one for the next mixer batch required amount. As a result, production can be practically of one  Batch converted to another and the own when processing reactive synthetic resins by inserting the thermosetting resin critical period of time can be minimized.

The resin is in the form of pastilles, flakes, broken resin, Dust or lumpy mixed resin processed. These are to bulk goods with low density and poor thermal conductivity speed. These properties of the melt stand for one Realization of the invention required rapid melting hindering approach. To solve this problem, in further embodiment of the invention from the subclaims 3 to 7 obvious options for quick melting zen the required amount of resin proposed.

The invention is based on execution examples explained in more detail. In the accompanying drawings shows

Fig. 1 is a process flow diagram with a heated twin-screw as a melting unit,

Fig. 2 is a process flow diagram with a heated roller as a melting unit,

Fig. 3 is a process flow diagram with a micro wave melting furnace and

Fig. 4 is a process flow diagram with an autoclave as a melting unit.

In the embodiment according to Fig. 1, the resin of a metering screw 1 is, for example, in flake form, given that it promotes in a heated between 120 and 150 ° C double screw 2. There is intensive heat transfer to the melting material through forced compaction and forced transport. The liquefaction of the resin is supported by the pressure generated.

The now hot-flowing resin flows from the twin screw 2 into a downstream intermediate container 3 . This inter mediate container 3 is designed so that it can take up about four to five times the amount of resin required for a batch of resin. It serves to compensate for the fluctuating melting performance of the twin screw 2 . It makes sense to use it additionally for post-modification of the resin melt by adding additives 6 , e.g. B. hot hardener. In order to distribute the additives 6 evenly in the melt, the intermediate container 3 is equipped with an agitator 7 .

A piston pump 8 conveys the melt from the intermediate container 3 into a metering cylinder 4 which doses the amount of resin melt required for a mixer batch into the mixer 5 . In this there is already quartz sand to be coated, which was heated to a temperature between 70 and 120 ° C. in a sand heater (not shown) and was fed to the mixer 5 shortly before. After a mixing time of about 2 to 3 minutes, the batch is discharged from the mixer 5 and fed to the further, generally customary processing.

It goes without saying that all units of the system, except for the mixer 5 , and the connecting lines 9 , as shown symbolically, are heated to prevent the melt produced from cooling.

The next embodiment is shown in FIG. 2. The melting process is carried out here on a heated roller 10 . Their use is limited to smaller wrapping systems because the melting capacity is relatively low. The large surfaces have an oxidative influence on the melt and possibly also cracking. The self-cleaning properties are very low in comparison to the twin screw 2 used in the previous embodiment. The fol geaggregate correspond to the process of the flow diagram of FIG. 1st

In contrast to the two previous exemplary embodiments, the amount of resin required for a batch of mixers is weighed on a balance 12 and fed to a microwave melting furnace 11 in the embodiment according to FIG. 3, ie only the amount of resin is melted, which is required for the next coating process is. The melting of the resin takes place in the presence of a sufficient amount of water, which acts as an "energy transfer medium". The units downstream of the microwave melting furnace 11 correspond to those of the preceding examples, so that they are not explained again here.

An Er is an alternative to the microwave melt heating possible in an induction furnace. This is a mixture made of metal balls and resin through an induction reactor. After passing through the reactor, the melt produced by the Metal balls separated and fed to the coating. The Metallku gels run back into the melting process.

The process flow diagram of FIG. 4 shows the use of a heated autoclave 13 as a melting unit. Here, too, the resin required for a batch of mixers is fed via a balance 12 . By introducing saturated steam 14 at about 12 bar, the thermal energy is evenly introduced into the melting material and causes an almost instantaneous "liquidation" of the resin. An agitator 7 arranged in the autoclave 13 ensures homogenization of the melt. The melt produced can be fed to the mixer 5 directly or via a downstream metering cylinder 4 .

Claims (7)

1. A process for coating granular, mineral materials with synthetic resin, in which the synthetic resin is added to the mineral material heated slightly above the melting point of the resin in the hot liquid state and mixed with it, and the mixer batch is cooled to a temperature below the melting point of the resin and heated up Grain size is isolated, characterized in that the hot liquid synthetic resin is produced shortly before it is added to the mineral material by melting solid synthetic resin. 2. The method according to claim 1, characterized in that the melting of the solid synthetic resin within a time Mixing cycle and in one for the next mixer batch required amount. 3. The method according to claim 1 or 2, characterized in that the melting process takes place in a heated double screw ( 2 ). 4. The method according to claim 1 or 2, characterized in that the melting process takes place in a microwave melting furnace ( 11 ). 5. The method according to claim 1 or 2, characterized records that the melting process takes place in an induction reactor finds a mixture of synthetic resin and metal balls is supplied, the metal balls after passing the Reactor removed from the melt and fed to the process again will.   6. The method according to claim 1 or 2, characterized in that the melting process in a heated autoclave ( 13 ) takes place in such a way that saturated steam ( 14 ) is introduced into the resin to be melted. 7. The method according to claim 1, characterized in that the melting process is carried out on a heated roller ( 10 ).