CN1318000A

CN1318000A - Method for coating surface with separating agent

Info

Publication number: CN1318000A
Application number: CN99811074A
Authority: CN
Inventors: 彼得·毛杰; 汉斯－乌韦·勒林格
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 1998-09-17
Filing date: 1999-09-16
Publication date: 2001-10-17
Also published as: ES2179700T3; WO2000016931A1; CA2345922A1; PL347358A1; EP1115520A1; BR9913865A; JP2002526265A; DE59901823D1; TW475909B; DE19842660A1; EP1115520B1

Abstract

The invention relates to a method for coating a surface with a separating agent, characterised in that a BN powder is applied to the surface by means of electrostatic coating.

Description

Method with coating surface with separating agent

The present invention relates to method with coating surface with separating agent.

Based on the example of shaping aluminium the problem that occurs when being formed with non-ferrous metal has been described hereinafter.The aluminum combination block is processed into profile is normally undertaken by the method for extruding under about 450 ℃ temperature.In the method, via container, by the extruding formpiston, will press the shaping overflow mould through the aluminum combination block (Al piece) of preheating, the cross section of this Al piece is preferably circular, and the result is that it is configured as profile, is cooled off after leaving mould then.The front portion of this extruding formpiston is also referred to as stripper plate, and must finish following task: 1. it must be in the direction opposite with the direction of extrusion with this container sealing; 2. when withdrawal extruding formpiston, it must separate with aluminium easily.

In that next Al piece is moved into first being processed, residual A l extrusional slug is removed with shear-blade (extrusional slug cutting knife).

Because the common metal material is very high to the shown extent of corrosion of aluminium and other non-ferrous metal under common processing temperature, the point of contact between non-ferrous metal and the mould must be handled with so-called releasing agent, so that operate continuously becomes possibility.

Carbon black is used as conventional releasing agent to separate stripper plate and Al piece; This carbon black is to be deposited on the end face of Al piece by burning acetylene flame.To each new Al piece, this operation must be repeated.

For coating extrusional slug cutting knife, typically use and touch the oil that hot aluminium promptly evaporates thereby produce stripping result.

Releasing agent not only is used for extruding, and is used to be formed with all methods of non-ferrous metal, for example, and gravity mold casting, low pressure casting, compression moulding and continuous casting.

Usually use unpigmented formation thing based on water or mineral oil and additive.In some instances, also use the releasing agent contain pigment form thing (referring to, for example, EP 810046).Used pigment comprises the solid of whole series, for example, and graphite, MoS ₂, BN or talcum.

If the original position formation of above-mentioned carbon black is ignored as special case, the conventional key element of all known releasing agents is that they must be used with the form of liquid suspension or emulsion at present.They are applied in by being sprayed on to be warmed on the very hot surface usually.The danger of evaporating suddenly when at high temperature, having volatile components or the danger of any solvent incendiary or active compound to touch hot surface and being lost.Moreover evaporate is the heavy burden of ambient air, and the formation of degradation production further increases this burden.Usually, most of this component is to send in the water circulation system that is contained in the factory district, so the removing of this component need spend great cost.

So, the purpose of this invention is to provide a kind of method with coating surface with separating agent, this method does not have the problems referred to above of prior art.Coating is carried out evenly, fast and at low cost.

By the electrostatic applications method BN powder is applied and to realize this purpose from the teeth outwards.

Surface to be coated can be, the surface of the overflow mould that for example is shaped, for example, the surface of stripper plate or extrusional slug cutting knife.But in principle, the non-ferrous metal surface that contacts with the extruding formpiston also may be handled in this way.Owing to the surface adhesion of the release coating that applies by method of the present invention is better, the surperficial processed of the shaping overflow mould that those contact with non-ferrous metal is preferred, because this processing must be repeated after three extrusion cycle as early as possible.

Found not to be that all BN powder all are equally applicable to be coated with purpose.Particularly some powder causes highly consumption, the irregular coating on surface and the obstruction of bringing device nozzle.

Irregular coating may cause non-ferrous metal do not control in conjunction with or stick to the point of contact of non-ferrous metal and metallic substance.

Use fineness to be equivalent to specific surface area and be 10-50m ²The BN powder of/g is preferred.Particularly preferably, the specific surface area of BN powder is 10-30m ²/ g, particularly specific surface area are 10-20m ²/ g.

Moreover this powder preferably contains and is less than 5%, especially preferably is less than 0.5% boric acid and boron oxide, with B ₂O ₃Expression.As usually in the prior art, the level of various boric acid such as metaboric acid or ortho-boric acid and boron oxide is meant its B ₂O ₃Analysis on Content.

The moisture content of powder is with H ₂O content is represented, preferably is lower than 1%, particularly is lower than 0.2%.

The tap density of particularly preferred powder is to be lower than 0.5g/cm ³, particularly be lower than 0.3g/cm ³

Particularly preferred BN powder can satisfy above-mentioned all parameters.

When implementing method of the present invention, the BN powder is fluidized in storage vessel by the method for flowing gas.Flowing gas is pressurized air normally.Other rare gas elementes are as N ₂, rare gas or gaseous mixture also can be used.

Fluidizing BN powder has static charge.This for example is, as usually in powder coated, carries out in commercial powder coated spray equipment.The preferred voltage of 75-80kV that uses makes the BN powder charged.

Fluidizing BN powder is sprayed on the part that expectation was gone up and was coated on equably on the surface with charged state.This is by carrying out to the powder coated similar mode of routine.

Preferably, the throughput of BN powder is that geometrical shape (mainly being the diameter of nozzle) by air-transmitting pressure and nozzle is adjusted to and is fit to specific coating operation.So the pressure of used transmission air is the 0.5-1.5 crust preferably, the pressure of fluidizing air is the 0.3-0.8 crust.The cumulative volume of air is about 5-8m ³/ h.

This operation can be carried out by hand, and perhaps this method fully automated ground also is fully possible.Amount that is applied and adhesion can be regulated by changing voltage and pressure.

Surprisingly, need not to add any tackiness agent,, show sufficiently high its adhesion the medium (for example stripper plate) that will be coated with by the BN powder that method of the present invention applied.

So the present invention also relates to BN powder purposes as releasing agent when being formed with non-ferrous metal, and relate to releasing agent by the BN powder constituent.Preferably, these powder are to be called as preferred BN powder.

More durable by the coating that method of the present invention is carried out than conventional releasing agent coating.It made that before needs apply in addition extrusion cycle repeats for several times.

Found that this is coated on the corner and the edge also is successful, grown on trees in these zones in addition.

That coating process of the present invention is proved to be is very simple, fast and carry out easily.

The powder that is applicable to the inventive method be commercial and character various.

The BN powder that preferably is applicable to the inventive method also can make from commercial six side BN powder.

If conventional powder mesoboric acid and B ₂O ₃Level too high, make B with for example water or alcohol washing ₂O ₃Level reach the value of expectation.

Excess water content lowers by dry, for example in the baking oven of routine in the atmosphere of certain shielding gas or vacuum-drying, to reach the desired level of powder of the present invention.

If necessary, the tap density of the BN powder that the present invention requires reaches by grinding the BN powder, and this BN powder can be earlier through pre-treatment.When doing like this, do not absorb excess water during must preferably determining to grind.

Used grinding plant is a series of routines " drying " methods, for example by various forms of pin dish shredders, grindstone and ball shredder.

Test has proved that the BN powder applies easily and BN has fabulous demoulding effect to Al.The use of this powder is not limited only to Al; The BN powder static electricity coating that need not any tackiness agent and do not contain other material such as solvent of the present invention also is applicable to other non-ferrous metal of the whole series of processing, for example Cu, Zn, Mg, Pb, Sn or its alloy.

So the present invention also relates to use the inventive method coating surface when extruding non-ferrous metal.

This non-ferrous metal is Cn, Zn, Mg, Pb, Sn or its alloy preferably.

Following examples are in order to further describe the present invention:

Embodiment 1:

With the throughput of 20Kg/h, in pin dish shredder, grind by Elcktroschemlzwerk Kempten GmbH, the commercial S1 by name of Munich, it is 14.5m that fineness is equivalent to the BET specific surface area ²/ g, B ₂O ₃Content is 0.12%, and moisture is 0.25%H ₂O and tap density are 0.55g/cm ³BN powder (powder I).The powder that obtains (powder II) has 14.5m ²The BET specific surface area of/g, 0.2% B ₂O ₃Content, 0.3% moisture and 0.2g/cm ³Tap density.

By electrostatic applications (Gema Company), (80kV; Inlet end transmission air pressure is 0.8 crust, and fluidizing air pressure is 0.4 crust, and the volume of air that is used to transmit is 5m ³/ h), the powder II is applied on the stripper plate that diameter is 20cm.This powder is to be deposited on equably on this stripper plate moment.Approximately consume the BN powder of 0.5g.After three extrusion cycle, just need again coating again once again.

Embodiment 2:

In the ball shredder, it is 6m that mesh-of-grind is equivalent to specific surface area ²/ g, B ₂O ₃Content is 9% six side BN powder (powder III), and its tap density is 0.6g/cm ³, reach 15m until specific surface area ²/ g.Gained powder IV is disperseed and washed with water many times until B ₂O ₃Content reduces to 0.1%.Afterwards, dry this powder to residual water-content is 0.2% in 60 ℃ of vacuum, and grinds in grindstone to pulverize adhesive.As described in embodiment 1, (tap density is 0.19g/cm to gained powder V ³, other parameters are as previously discussed) and be used for electrostatic applications Al piece.Identical among consumption and the embodiment 1.This coating allows that the stripper plate that contacts with this layer uses three times with shaping Al piece evenly and before this coating must be upgraded.

Claims

1. A method of coating a surface with a release agent, characterized in that BN powder is applied to the surface by electrostatic coating.

2. The method according to claim 1, characterized in that the BN powder is fluidized by flowing gas in the storage container, the fluidized BN powder has an electrostatic charge, and the fluidized BN powder is sprayed on the surface to be coated with a charged state. on the surface.

3. The method according to claim 2, characterized in that the BN particles are charged with a voltage of 75-80 kV.

4. The method of claim 2, wherein the flowing gas is compressed air or an inert gas.

5. A method according to claim 1, characterized in that the conveying air pressure for coating is 0.5-1.5 bar, the flow air pressure is 0.3-0.8 bar, and the total air volume is about 5-8 ^m2 /h.

6. A method as claimed in one of claims 1 to 5, characterized in that BN powder is used having a fineness corresponding to a specific surface area of 10-50 m ² /g.

7. A method as claimed in one _of claims 1 to 6, characterized in that boric acid expressed as _B2O3 or BN powder with a boron oxide content of less than 5% is used.

8. A method as claimed in one of claims 1 to 7, characterized in that BN powder is used with a moisture content expressed as _H2O content of less than 1%.

9. A method as claimed in one of claims 1 to 8, characterized in that BN powder is used with a bulk density below 0.5 g/cm ³ .

10. Use of a method as claimed in one of claims 1 to 9 for coating surfaces when extruding non-ferrous metals.