DD213878A1 - METHOD FOR THE HOT FORMING OF CORK DOME AND CORK PRESSES - Google Patents

Abstract

The invention relates to a new process for the thermal shaping of pressed parts from cork waste. The warming takes place by the use of dielectric losses in the cork or in the mold enclosing the cork by means of a high-frequency electric field a large Korngroessenverleihung be present and be mixed with various additives. Depending on the dielectric properties of the material surrounding the cork, a defined distribution of properties over the cross section of the cork products can be achieved.

Description

Method for thermoforming of cork insulation and cork materials

Field of application of the invention;

The invention relates to a method for thermoforming of Korkdämm- and Korkpreßstoffen based on cork crush and / or cork granules by heating in high-frequency .elektrisch grief.

Characteristic of the known technical solutions

It is known to form cork moldings based on cork waste or cork granules in the pressing process by heating by means of superheated steam, gas or electric heating from the outside. The cork can thereby see with diverse binders to ensure the bond strength such as polyvinyl acetate, protein, pitch, bitumen, nitrocellulose, casein, viscose _s ~ of animal and plant glues, rubber solutions or polyurethane resins mixed be. " Furthermore, the bond strength of the cork products can be achieved by the chemical conversion of the core resin suberin and the entanglement of the likewise irreversibly altered framework substance. The sequence of the individual process steps mixture of the components, heating and pressing can be varied the cork cells trapped air, for reducing the viscosity or chemical conversion of binders and for expelling low-boiling

Shares such as water, alcohols and waxes and optionally for the chemical conversion of components of the cork takes place in all known methods by heat conduction, radiation and / or convection. Thus, the power density for the heat input for the nonconductive substance cork with its cellular structure is very limited. This has a negative effect on the technological parameters in the hot deformation such as heating rate j duration of the thermal load and size of the mold volume. Among other things, this is usually counteracted only by granulated cork waste with a uniform particle size, which makes it possible to uniformly heat and thus to smoothen the cork particles contained in the molds. In the production of cork granules, up to 50 % of the cork waste is lost in the form of grinding dust and is no longer available for further processing.

For large-volume moldings such as insulation boards for floor insulation in the refrigeration and freezing industry, the cork is heated for a sufficiently long time before shaping with movement in a hot binder or in rotating drums. Due to the variation of binders and additives and of technological manufacturing parameters, the product properties important for many fields of application such as thermal conductivity, compressive strength, breaking strength, resilience, chemical and thermal resistance can be adjusted within a wide range. However, during the granulation process, the grinding process and / or or in the heat treatment by distilling off up to 75% of the initial amount of cork waste lost

Methods for producing integral structures across the cross section of the cork products are not known.

Object of the invention

The aim of the invention is to provide a method for thermoforming of Korkdämm- and Korkpreßstoffen cork waste with relatively low energy requirements and on-time thermal stress of the starting materials and with opportunities for modifying the product properties on the known variants addition, z. By the generation of integral structures in the cork products.

Explanation of the essence of the invention;

The invention has for its object to find a method for short-term heating of the starting material cork, even in the form of raw waste, and modifying components to a predetermined temperature level. The temperature distribution within the material to be heated should optionally be variable over the product cross-section constant or to achieve differentiated properties such as strength, density and thermal insulation over the cross section.

According to the invention the object is achieved in that the starting materials for Korkdämm- or Korkpreßstoffe be exposed to a high-frequency electric field in which by the specific dielectric properties of cork and modifying additives heating depending. of field strength, frequency and time in the substances enters. Since the heat arises directly in the materials in the radio frequency (RF) field, e.g. is generated between the plates of a defined dimensioned working condenser, eliminating the heat transport processes required in the known method. The equalization of the size of the cork particles to granules with defined dimensions is unnecessary and it can be assumed that cork waste with wide particle size distributions. By eliminating the heat transfer in comparison to the known technologies significantly faster heating of the starting materials

the desired temperature level, possible. Thus, the decomposition of cork constituents into gases, which is limited in known methods for the production of cork dam materials by the duration of Temperaturβinwirkung to a reduction of the initial mass up to 75 % , limited in time. This results in a further significant increase in material utilization.

The desired temperature range and its duration of action can be controlled by varying the field strength and dwell time in the RF field. »This regulates the degree of chemical conversion of constituents of the cork and the distilling off of more volatile components such as water and alcohols. Product properties such as cork cell expansion, elastic recovery, thermal conductivity, water absorption and chemical and biological resistance are also adjustable. Due to the possibility of short-term heat input remain for the mechanical properties determining structural components of the cork better preserved than in the known methods, so that higher strength of the. Products can be achieved at comparable densities ·

The Bnergieumsetzung in the material to be heated is uniform in all areas in a homogeneous alternating electric field, although the material to be heated is homogeneous in its composition, its density, its structure and thus its dielectric properties. The specific dielectric properties of the molds in which the heating of the cork products takes place in the RF field allow the generation of different temperatures and thus properties over the cross section of the molded parts, in which z. As mold materials with very low dielectric loss factor such as polytetrafluoroethylene or special ceramic can be used. The heat generated in the edge zones of the substances to be heated is then partially to the cold mold walls or to the cooled electrode plates

A temperature profile is established across the product cross-section which, for example, leads to complete chemical conversion of the cork structure, combined with high thermal insulation effect of these inner layers, while the outer, less thermally stressed Areas of the molded part largely retained their original strength and elasticity. B. Cork insulation with integral structure on completely new property level produce. On the other hand, those molding materials can be used which have the same high or higher dielectric loss behavior than the good cork to be heated. If, for example, a corresponding vitroceramic material is used as the molding material, the heat dissipation of the molding edge zones is compensated or restricted to the shape by the cork enveloping it on all sides so that the material to be treated is heated completely uniformly to the desired temperatures.

The density of the Korkdämm- or Korkpreßstoffe can be done when heating cork in the RF field as in the known methods before, during or immediately after the Warmb.ehandlung. Also, analogously to the known methods, the hot cork with the help of suitable binders or korkeigener resins except for plates and moldings such as • Hohrhalbschalen, T-profiles u. a. be pressed.

Embodiment e.

Example 1:

From Korkabf all insulating material for the Bodenisclierung is to be produced. Cork fracture with grain sizes of 1 to 30 mm is placed in a frame made of vitroceramic with a dielectric loss factor of 2.2 · 10 between the plates of a working capacitor, which is connected to a H? -Generator with a frequency of 27 _} 12 MHz. The adaptation of the G-enrator circuit and the working circuit takes place via λ / 4-line by setting resonance. From the cork filling to the electrode plates, a separating layer of paper and then also "vitroceramic plates" are symmetrically arranged, then an EF electrode with an electrode voltage of 3 kV is generated and maintained for 480 s The volatiles are released and the cork resin suberin is transferred into a viscous phase. After switching off the field, the mold is removed with the hot material. The cork closes in one direction

3 3

Densities of 100 kg / m and · 200 kg / m pressed and demolded after cooling. Table 1 compares the properties of these products to those made from cork granules by heating in an electrically heated rotating drum.

product

Loss of mass for generation of the output is indicated

Mass loss at density Thermal Conductivity Druckfestig heat treatment number at 10% compression ( % ) (k / m ³ ) (W / mK) (N / i in ² )

Backkork

(heated drum)

approx. (cork granules)

30 ... 40

30 ... 40

<0.035 0.053

> 0.2

Baking cork (HF-FeId)

0 (cork breakage)

about 15 about 15

<O, O35 0.048

> O, 25

Table 1; Properties of cork insulation panels bonded with cork-own resins according to different production methods

The performance-related properties of cork dam sheets produced with the aid of HF energy are comparable or slightly better with those of the conventional method. In this case, the same or higher compressive strengths are achieved with lower product densities. Since unprocessed cork fracture can be assumed and the mass losses are greatly reduced during the heat treatment, the starting material is used at least 50% better than in the method used for comparison.

Example 2i

Eorkbruch analogous to Example 1 with 5% polyethylene powder

2 high density (0.94-5 s / ° ^m ) u ^ 3% water mixed intensively, so that the polyethylene adheres evenly distributed on the surfaces of the cork particles. This mixture is exposed to a HF-FeId in a polytetrafluoroethylene form also analogous to Example 1 in a plate working capacitor. The upper and lower limits of the form thereby form the plate electrodes, which are separated only by paper layers of the cork mixture. The 3 kV RF field in turn operates for 480 s. While the cork in the interior of the mold is completely expanded and chemically converted at approx. 600 K, a temperature gradient sets in at the edge zones, where approx. 430 K are reached. The cork at the approximately 15 nna thick border zones is also expanded and low-boiling constituents are expelled, but the dark brown coloration typical of the chemical transformation remains lacking. The bonding of the cork particles in the surface layers is ensured by the binder polyethylene, which also supports the binding effect of the cork resins on the inside after solidification. After switching off the HF voltage, the hot cork mixture is pressed analogously to Example 1 to plates with different densities whose properties such

product

Composition Density Thermal conductivity Compressive strength Ultimate tensile strength% Immersion

OO

JLJO

(W / mK)

Imprägnierkork

Baokkork

HIi ¹ -Fe Id-K ork with PE-HD

50 cork granules 50 bitumen

100 cork granules

280

0.058

350

0.053 0.1

: 0.3

95 Korkbruch 120 0 , 033 5 polyethylene 170 0 , 042 high density 220 0 , 047

0.15 0.22

0.25

12 48 89

TABLE 2: Properties of cork-earth materials of different composition according to different production methods

ω P ^

H'CD

ti i

CD ct

ct Φ H

CD H

CD

he

CD

H H

sr *

et ta Φ ch

CD hi

CD ch

H-CD P ^- et HO

hi 4,

Γ0 ca: ⁽ rV

outside

Φ H- Cu:

Wl CD H

CD hi ö

ρ: ο o ^J hi Φ PT H I Hj ω COl ta:

H O H H,

et H ₃ ISI

for ω

First, analogous to Example 1, the advantages of high material utilization in the processing of cork waste in KF-SeId be mentioned, which are due to the processing possibility of untreated material and the relatively short-term thermal stress when working with temperature distributions over the product cross-section. In addition, by the selective adjustment of integral structures in Korkformling property combinations are possible, which are not achievable with the known methods · While thermal conductivity and compressive strength at 10 % compression provide no exceptional values, estrem high characteristics are achieved at the breaking strength, which only on the integral structure of the Products can be recycled in conjunction with a suitable binder. That the compressive strengths at 10 % compression are not higher, is due to the relatively high elastic content of chemically only slightly converted edge zones. On the other hand, this results in advantages when used as a pressure-resistant thermal insulation layer with simultaneous sound insulation effect.

The combination of known properties of thermoformed cork products with an extremely increased compressive strength to break opens up these new uses on the one hand, on the other hand in the usual applications in addition to the possibility of using molded parts lower density by the increased edge breaking strength improved storage and transport and Processing properties guaranteed.

Claims (1)

- Ί Ί ~ Process for the production of Korkdäinm- and Korkpreßstoffen by means of thermoforming, characterized in that the thermal energy for expansion of the cork cells, for drying or melting of binders and / or for the chemical conversion of cork constituents by the dielectric losses in the substance to be heated itself and / or in a shape enveloping the substance to be heated is generated as a result of the action of a high-frequency electric field. A method according to claim 1, characterized in that the binding of the cork particles to moldings takes place under heat and pressure by the use of converted into the viscous phase cork resins and / or additional binder. -Q. 3 # Process according to claim 1 and 2, characterized in that the pressure is introduced into the cork products to be molded before, during or shortly after the action of the RF field. 4 ·. A method according to claims 1 to 3, characterized in that the heating of the cork product in a mold is made of a material having lower dielectric losses than cork, and in that heat from the edge zones of the mold volume content on this molding material and / or on the Plattenelektrodan the environment is released.