Resin dispensing

Under a Vergussanlage is defined as a procedural device to frequently pour out components of the electrical and electronics industry, with casting resin or covered. In it, the dosing, mixing and preparation of the resin and its components takes place. It is thus a subspecies of dosing.

2.1 Material Promotion
2.2 dosage 2.2.1 Gravimetric dosing
2.2.2 Volumetric dosing
2.2.3 dosage over time measurement

2.3.1 Dynamic mixing
2.3.2 Static Mixing
2.3.3 Static-dynamic mixing

2.4.1 tempering
2.4.2 drying and degassing

2.5.1 design options for potting
2.5.2 Vacuum casting
2.5.3 Automatic pressure gelation ( APG )

3.1 Encapsulation of electronic components
3.2 Preparation of LED
3.3 potting of components of the energy technology

Design and operation of a Vergussanlage

Design criteria

Depending on the purpose of application Vergussanlagen differ in structure, size and degree of automation.

There are single-component casting resins, in which the resin and hardener are mixed the product is sold, and two-component systems in which resin and hardener must be mixed in the Vergussanlage in a fixed ratio. There may be other components such as fillers, accelerators, plasticizers, or additives. The Vergussanlage must be adapted to the number and amount ratio of the components therefore.

Also, viscosity, reactivity, and abrasiveness of the casting resin and its components play a role. Some resins have only under elevated temperatures to a sufficiently low viscosity for processing, so that the whole Vegussprozess must take place under temperature. Often treatment and casting takes place (see below) under vacuum.

The Gießharzvolumen that is needed for a component can range from less than 1 ml in the electronics sector (eg in the production of LEDs) up to 100 liters or more must submit to the casting of coils for power engineering. The respective Vergussanlagen are so very different dimensions.

The level of automation ranges from fully automated, fully integrated into a production line equipment for series production to manually operated systems.

Single-line and two- line systems

Roughly speaking, divide the Vergussanlagen in single-line and two- line systems. When the components are all in Einlinienystem dosed into a mixer, mixed and prepared, so that the finished container from the potting material can be removed. A two line system in principle consists of two Einlinensystemen in which two premixes, one resin with fillers and any further components, and once with hardeners, fillers and any further components attached. The premixes are then conveyed with metering pumps to a static mixer, where it is mixed and poured.

While Einliniensysteme represent simpler and more cost -effective design, they have, compared to two- line systems have the disadvantage that, in general, the curing reaction begins with the mixing of resin and hardener and the mixture must then be used within the pot life. If the container is empty, new mass has to be set again only as long as no casting is possible. Resulting residues must be disposed of.

For two- line systems, the reactive Komponenenten come until immediately before casting into contact. The premixes can be practically stored indefinitely. Consequently, the production more flexible, thanks to sufficient stocking the premixes continuous operation is possible. Furthermore, the encapsulation is always performed without appreciable Reaktivitätsfortschritt what constant viscosities guaranteed. It is always produced only as much reactive material, as necessary for the casting, so are practically no waste.

In addition to the mixers and conveyors and metering, the system can still have containers for deployment, and pre-treatment of the components and reservoirs for premixes.

Process steps

Material promoting

In the complex, the liquid components such as resin and hardener and solid fillers need to be promoted out of the container and within the plant. Also the finished casting resin or premixes must go to the casting.

Which funding method can be applied, depends mainly on the viscosity of the material and on the abrasiveness of the fillers.

For resins of low to medium viscosity

Piston pumps
Gear pumps
Progressing Cavity Pumps
Peristaltic Pumps
Diaphragm pumps

Suitable. High viscosity resins can be promoted with follower plate pumps.

The bulk- like fillers are usually moved by vacuum or screw conveyor.

By appropriate spatial arrangement of the system components above the other, a material movement can be achieved solely by gravity.

For mixtures with fillers, the material must usually permanently or at least be moved periodically to avoid sedimentation. For material transport in pipes are therefore often recirculation lines available to pump the mass in the inlet.

Dosage

The individual components or premixes must be according to the recipe in the appropriate ratio metered to each other. Finally, the Vergussanlage must emit to the amount of resin needed exactly. For dosing, different methods are available.

Gravimetric dosing

The material is here dosed according to weight, so weighed. Weighing extended cycle times, if it also allows a very precise quantification. In most cases, the container is the material to be dosed on a weight scale, the weight loss after feeding out corresponds to the dosage amount.

This method is used mainly for filler application.

Volumetric dosing

A constant volume designed to guarantee relatively simple. Therefore, doses that are based on the definition of a constant output volume, particularly simple, less prone to interference and work reliably.

A very good option is the use of piston metering. The resin to hardener ratio in two-component system can be here by the ratio of cross sectional areas of two dosing, which can be extended at the same time, be very accurately determined. The measured quantity is determined by the fixed stop means lifting height of the piston.

Dosage over time measurement

This dosing method means that a constant outflow velocity must be ensured by suitable pumps. The flow of material is released through a valve and is interrupted after a predetermined time by the valve.

This method is particularly vulnerable, as any variation in the flow rate brings different dosages with it. To create an absolutely constant flow and monitor, requires a relatively high electronic complexity.

With flow meters can be the mass or volume flowing through a pipe, measure accurately. These sensors can also be used for metering.

Mix

After dosing, the components must be homogenized. This is particularly the mixing of the fillers with the liquid ingredients resin and hardener not entirely simple task represents the powder or fibrous fillers are sometimes very fine-grained and have a correspondingly large specific surface area which is wet by the liquid components. The particles can form clumps which must be resolved in order to achieve a low viscosity of the casting composition. Proper dispersion is primarily dependent on the mixing intensity and time.

We can distinguish the following mixing procedure:

Dynamic mixing

Making the components in a mixing chamber, usually stainless steel, each other and are homogeneously mixed by a rotating mixer. The chamber thus simultaneously serves as a reservoir. If the speed is electronically variable, the mixing intensity can be accurately controlled.

The disadvantage is that there is no continuous operation, is here only batchwise possible: the container is filled, then takes the actual mixing process, does not exist until the mixture for further processing. If a reactive mass recognized as the single-line system, the entire mixer contents must be used within the pot life. If not, there is a risk that the material cures in the mixer, which results in a complex purification or at worst a replacement of the mixer by itself. Even with proper use mostly regular, partly automated cleaning depend on the material necessary. The special cleaning agent used must be disposed of as waste or hazardous waste.

The moving parts are a possible reason for failures dar.

Static Mixing

The components are pumped into a tube of metal or plastic, where multi-divided by separation blades built rigid and recombined, resulting in a mixture. The mixing pipe is either cleaned, which can Wedendorf accomplished by flushing with a single component, or disposed upon curing.

With static mixers, a continuous process is possible without interruption. The components are mixed in a short time and go immediately to the next process step. This makes them ideal for example for the final mixture of resin and hardener -filler -filler premixes for reactive sealing compound in a two- line system. Since there are no moving parts are present, these mixers are maintenance and wear and also cost-effective and space-saving.

The disadvantage is that mixing time and intensity are difficult to influence. Static mixers are also not suitable for the incorporation of fillers.

Static-dynamic mixing

A plastic mixing tube includes a spiral of this principle, which is driven by an external motor. This method is rarely used.

Material preparation

Temperature

Many casting resins are processed at elevated temperatures to reduce the viscosity. The corresponding Vergussanlagen are equipped to with heated tanks, pipes and mixers. The heating medium such as water or oil can be passed, conversely, a cooling unit to cool the material during production interruptions. Progress of the reaction is slowed down by the increased viscosity of sedimentation is prevented.

Drying and degassing

Moisture can have undesirable effects on the material properties. In particular, the powdery and often porous fillers can absorb moisture to their large surface area, which then makes it difficult to wetting by resin and hardener. Air and other gases may be present as bubbles or in dissolved form in the liquids and negatively affect the viscosity or later lead to voids in the casting.

Therefore, the fillers are often subjected to drying prior to the processing, usually liquid components and mixtures degassed. Degassing takes place in many cases in vacuum mixers, instead of parallel to the homogenization. With Durchlaufentgasern a continuous throughput of material is possible.

Optimally, resin, hardener, filler, etc., separately heated and dried with vacuum and degassed. The other process steps such as metering and mixing also be done afterwards under vacuum to prevent a re- entry of air and moisture.

The actual casting

Design options for potting

The simplest possibility is that in a stationary workpiece by pouring into a point a certain amount of resin is poured. It is only necessary to ensure a not too rapid filling to avoid trapping air bubbles. Ideally, the mold is filled so from below.

During the casting but can also move the order unit, ie the part of the plant from which emerges the resin, or the workpiece. By appropriate control of the number of variants are possible Vergussvorganges. For example, adhesive beads or dams of different shape can be molded. With highly viscous, thixotropic material cast dams can be filled in a second step with a low-viscosity resin (dam & fill). The exit velocity of the resin can be varied during the casting or done the grouting in several portions. Here, the workpiece or the contract unit perform complex movements, which can solve difficult Vergussaufgaben.

For series production Vergussanlagen can be used with multiple application units for up to 30 potting compounds simultaneously.

Vacuum casting

Many items such as transformer windings have strong undercuts. There, the potting air can be trapped. With many components but an absolute bubble-free casting is necessary, in particular to ensure in high voltage applications to partial discharge.

Such components are cast usually under vacuum. As can be implemented technically not an absolute vacuum, but there is still a residual pressure of a few mbar, can indeed still form bubbles but then almost completely compressed when breaking the vacuum. The casting is carried out, for example, at 5 mbar, compressed bubbles possibly occurring when venting to atmospheric pressure (about 1000 mbar ) of the above-mentioned connection to a 200-fold smaller volume.

The vacuum casting is carried out in vacuum chambers or boilers, which, in order to shorten the cycle times, can be provided with an input and an output gate. There only solutions are technically feasible feasible in general, in which the workpiece is moved and the order unit is rigidly mounted.

Automatic pressure gelation ( APG )

Areas of application

The potting of electrical and electronic components to serve principally to reliable electrical insulation and prevent the ingress of moisture and dirt. On the other hand potted components are virtually no longer repairable. Typical application areas are:

Potting of electronic components

Assemblies in which individual components are placed on a circuit board, are often encapsulated in order to protect them from environmental influences and mechanical damage. In these cases, usually only one form of fill, which is a relatively simple task.

Production of LED

LEDs are manufactured in fully automatic systems. These include pouring in transparent plastic. Here it is especially on short cycle times to reduce the price of the bulbs. This is an application example of the encapsulation with Mehrfachdosierköpfen.

Shedding of components of the energy technology

The windings of electric motors, transformers (especially of cast resin ), reactors and instrument transformers are frequently shed for insulation and protection against environmental influences with casting resin. The components to be surrounded by a mold which is subsequently filled with resin. The fine structure of the spaces with their strong undercuts and the component size, the encapsulation of windings particularly high demands on the casting process. Also insulators are often made of cast resin. In serial type manufacturing the automatic pressure gelation is often used.

Mixing (process engineering) Progressive cavity pump Bar (unit) Casting defect

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