Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METHOD OF PRODUCING A POLYURETHANE MULTILAYER ENGINE COVER
Document Type and Number:
WIPO Patent Application WO/2019/228576
Kind Code:
A1
Abstract:
This invention relates to a method of producing a polyurethane multilayer compact (single-piece) engine cover featuring high sound-absorption properties, high heat resistance, quality outer surface appearance, low weight and increased protection of pedestrians in a collision with a car. The high sound- absorption performance of the engine cover is achieved by using a combination of skin making procedures consisting in spraying PU reactive system forming the compact PU layer with a density of 700 kg/m3 at minimum, and subsequent foaming with a suitable soft PU foam having a highly open structure, employing a suitable release agent capable of creating an open structure on the reverse side of the engine cover, and a procedure of subsequent partial tear of the foam structure of the finished engine cover. The production process is a sequence of partial technological steps, at the end of which a final engine cover in a state prepared for fitting is obtained.

Inventors:
BORUTA JAROSLAV (CZ)
PECHA FRANTISEK (CZ)
VACULIK TOMAS (CZ)
KOLARIK TOMAS (CZ)
KADLEC MIROSLAV (CZ)
Application Number:
CZ2019/050024
Publication Date:
December 05, 2019
Filing Date:
May 24, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
PROMENS A S (CZ)
International Classes:
C08J9/34; B29C44/06; B29C44/56; B60R13/08; C08J9/38; F02B77/13
Foreign References:
US20150061174A12015-03-05
US8205592B22012-06-26
Attorney, Agent or Firm:
GÖRIG, Jan (Korabova 98, Frystak, 76316, CZ)
Download PDF:
Claims:
C L A I M S

1. Method of producing a polyurethane multilayer engine cover providing a high heat and sound-absorption performance and heat and chemical resistance based on a combination of spraying a polyurethane system having a higher resultant density, and foaming with soft light-weight polyurethane foam, consisting in placing a mask protecting the mould parting line from fouling into an open mould heated to a temperature ranging between 55 to 80 °C, spraying a release agent on the mould male and the mould cavity (female), spraying a layer of polyurethane reactive compound onto the mould surface provided with a film of the release agent or, if need be, with a coat of polyurethane varnish, the layer of the polyurethane reactive compound polymerizing after application onto the mould surface and after creating the outer layer of the engine cover having a compact skin, pouring the reactive polyurethane compound into the open mould containing the surface layer of the engine cover after removal of the mask from the parting line, closing the mould and allowing foaming and cross-linking processes - polymerization and foaming of the cover inner layer - to take place in the mould, characterized in that a release agent based on fraction of Cl 1 to Cl 5 of n- and iso-alkanes is sprayed onto the mould parts, the release agent having an effect of opening polyurethane foam cells and assuring that no compact layer (skin) is formed on the surface of the back side of the engine cover while the foamed polyurethane layer on the basis of the reactive compound is opened, the outer visual (face) layer of the engine cover having a compact surface (skin) is created using the reactive polyurethane compound having a short gelation time of 0.5 to 5 seconds producing a layer having a density of at least 700 kg/m3 and resultant thickness of 0.5 to 5 mm after polymerization, using the reactive polyurethane compound for creation of an inner foam layer, the reactive polyurethane compound providing a layer having a final density of 50 to 79 kg/m3 as a result of foaming and crosslinking processes taking place for a time period of 1 to 5 minutes, the component being placed immediately into a vacuum chamber after termination of the polymerization, opening of the mould and taking out from the mould, where it is subjected to a repeated shock at an underpressure of -0.5 to -0.95 bar in order to rupture partially the polyurethane foam structure - break the cells.

2. The method according to Claim 1, characterized in that a thin layer 0.05-0.15 mm thick of one- or two-component polyurethane varnish (IMC) is sprayed onto the surface of the mould female provided with a layer of a release agent to create the outer visual (face) side of the engine cover in an exclusive, for instance metallic colour version, and let to vent before spraying the polyurethane reactive compound of the outer visual (face) layer of the engine cover.

3. The method according to Claim 1, characterized in that the reactive polyurethane compound providing after polymerization a layer having a density of 700 to 2500 kg/m3 is used to create an outer visual (face) layer of the engine cover having a compact surface (skin).

4. The method of manufacture according to Claim 3, characterized in that in case of design needs local stiffness of the engine cover can be increased by local spraying to achieve a greater thickness, advantageously up to 10 mm, of the outer visual (face) layer of the engine cover having a compact surface (skin).

5. The method according to Claim 1, characterized in that a special additive based on polyether polyol, known as cell opener, at concentrations of 0.5 up to 3 mass %, which assures a higher content of open cells in the foam structure, can be incorporated into the polyol component of the reactive polyurethane compound of the inner layer to increase the product sound-absorption properties.

6. The method according to Claim 1, characterized in that an increase of the sound- absorption properties can be achieved by using the reactive polyurethane compound containing a particle or fibrous mineral filler, advantageously barium sulphate, resulting in the fact that the final density of polyurethane foam can be as high as 2000 kg/m3.

7. The method according to Claim 1, characterized in that a reinforcing element of a metal grid or fibrous woven or unwoven reinforcement type is placed into the mould on the sprayed reactive compound creating the outer visual (face) layer (skin) of the engine cover to increase markedly local stiffness of the engine cover.

8. The method according to Claim 1, characterized in that a shielding cover made of heat insulating material is inserted into the mould in order to increase markedly local heat resistance of the engine cover.

9. The method according to Claim 1, characterized in that in case of extreme requirements for sound-absorption properties of the engine cover another repeated shock at an underpressure ranging between -0.5 to -0.9 bar can be implemented in a vacuum chamber to further improve the sound-absorption performance of the engine cover.

10. The method according to Claim 1 or 1 and 6, characterized in that the components made are left to rest in a free state for a few hours in order to complete the chemical reactions.

11. The method according to Claim 1 , characterized in that the components made are fixed by vacuum on shape jigs and flashes in the parting line are removed by milling, trimming or cutting.

12. The method according to Claim 1, characterized in that a shielding cover made of a heat insulating material, for instance that based on glass fibres with a reflective aluminium film (unless it has been inserted into the mould according to Claim 7), is fixed to the finished component on the assembly fixture.

13. Engine cover produced by methods described in Claims 1 to 12.

Description:
METHOD OF PRODUCING A POLYURETHANE MULTILAYER ENGINE COVER

Field of invention

The invention relates to a method of producing a polyurethane multilayer engine cover providing a high sound- absorption performance and heat and chemical resistance by way of combining technological steps involving spraying and subsequent foaming with polyurethane reactive systems.

Description of the prior art

Both in the past as well as nowadays, a relatively wide range of materials and production processes has been used for production of sound- absorbing and heat insulation covers for engine compartments. Standard systems include multicomponent assembled covers comprising a compact thin outer part and an inner sound-absorbing component. At the present time, this is the most frequently used system. The outer part of the cover is made by injection moulding of thermoplastics, such as polypropylene (PP) and polyamide (PA). In some cases the engine cover outer part is manufactured of thermosets employing SMC (sheet moulding compound) or BMC (bulk moulding compound) processes. The outer cover has also an appearance function. The lower part of the cover is made of materials assuring fundamental functions, i.e. high sound absorbing and heat insulation performance. Materials used are polyurethane (PU) and melamine foams (for instance in case of Volkswagen Jetta, Golf, Passat, Tiguan and Beetle car models manufactured in North America) or those reinforced with glass-fibre.

In the U.S. patent No. US4288490, a system of a shaped sound-absorbing layer made of closed-cell polyethylene foam is protected. Known is also a solution according to U.S. patent application No. US2007287001 consisting in a combination of an open-cell polymer foam and a glass-fibre layer. A disadvantage of this solution is a necessity of subsequent assembly of separate components into an operating unit.

Another known approach is manufacture of single -piece covers using one production sequence. Use of this approach includes production of engine covers of integral PU foam (described for instance in the European patent EP 2847260, Chinese patent application CN104487498 or international patent application PCT WO2013167922). According to the above patent and patent applications an integral profile with a density ranging from approximately 1000 kg/m 3 on the cover surface to that of approximately 150 kg/m 3 in the cover centre is created using an appropriate production process. A disadvantage of this solution lies in the fact that for technological reasons, the minimum density of only about 150 kg/m 3 can be achieved, consequently the density generating sound-absorption properties is lower than in case of the polyurethane foams having densities ranging from 50 to 100 kg/m 3 and the product of an identical volume has a markedly higher weight. Another disadvantage consists also in the fact that thickness of the outer compact layer can be changed locally in only a limited manner.

Another possible method is a combination of spraying a polyurethane reactive system onto the surface of an open mould (thus providing the engine cover with an outer compact layer) followed by subsequent foaming with a polyurethane reactive system generating the bottom sound-absorbing and heat insulating layer. This method is described in the U.S. patent No. US8205592. Its main disadvantage consists in the fact that due to high density (80 to 208 kg/m 3 ) of the polyurethane foam and a lower proportion of the open-cell foam structure both in the mass and on the reverse side of the component the engine cover has lower sound-absorption properties. At the same time, this method permits a relatively limited extent of local reinforcement.

Nature of the invention

According to the present invention the above shortcomings of the prior art can be eliminated to a considerable extent by using a method of manufacture of the polyurethane multilayer engine cover possessing high sound-absorption properties and heat resistance.

The method of manufacture of the polyurethane multilayer engine cover is based - similarly like the known procedures - on a combination of spraying a polyurethane system possessing higher resultant density with foaming using soft light-weight polyurethane foam. A mask protecting the parting line against fouling is inserted into the open mould heated to a temperature ranging between 55 and 80 °C and the mould male and the mould female are sprayed with a mould release agent. On the mould surface provided with the film of the release agent or, if need be, a coat of polyurethane varnish a layer of polyurethane reactive compound is sprayed, which polymerizes after application onto the mould surface and creates an outer visual (face) layer on the engine cover having a compact surface (skin). After removal of the mask from the parting line, the reactive polyurethane compound is poured into the open mould female containing engine cover surface layer, the mould is closed and foaming and crosslinking processes - polymerization and foaming of the cover inside layer - take place therein.

The nature of the invention can be described as follows: a mould release agent based on Cl l to Cl 5 fraction of n- and isoalkanes is used to spray parts of the mould, the said release agent having a cell-opening effect for the polyurethane foam, which assures that no compact surface (skin) is created on the surface of the engine cover back side but the foamed polyurethane layer based on a reactive compound is opened.

In order to create the outer surface appearance layer of the engine cover a reactive polyurethane compound having a short gelation period of 0.5 to 5 seconds and providing after polymerization a layer with a density of at least 700 kg/m 3 and a resultant thickness of 0.5 to 5 mm is used.

In order to produce the inner foam layer a reactive polyurethane compound is used, which - as a result of the foaming and cross-linking processes taking place for a time period of 1 up to 5 minutes - provides a layer having a final density ranging between 50 to 79 kg/m 3 .

After termination of the polymerization, opening of the mould and removal of the component therefrom, the component is immediately placed into a vacuum chamber where it is subjected to repeated underpressure shocks ranging from -0.5 to -0.95 bar, the purpose of the shocks being a partial break of the foam structure - tear of the polyurethane cells.

In order to create an exclusive surface appearance of the outer visual (face) side of the engine cover, for instance that of a metallic colour, a thin layer 0.05 to 0.15 mm thick of one- or two component polyurethane varnish (IMC) can be sprayed onto the surface of the mould female provided with the release agent film and let to vent prior to spraying the polyurethane reactive compound forming the outer visual (face) layer of the engine cover made. In order to create the outer visual (face) layer of the engine cover having a compact surface (skin), reactive polyurethane compound providing density of 700 to 2500 kg/m 3 after the polymerization can be used with advantage.

In case of design needs the local stiffness of the engine cover can be enhanced by increasing advantageously the sprayed thickness of the outer visual (face) layer of the engine cover with a compact surface (skin) up to 10 mm.

In order to increase the engine cover sound-absorption properties it is further possible to incorporate into the polyol component of the reactive polyurethane compound forming the inner layer a special polyether-polyol based additive, known as cell opener, in a concentration of 0.5 to 3 mass %, which assures a higher content of open cells in the foam structure.

A further increase in the sound-absorption properties can also be achieved by using reactive polyurethane compounds containing a particle or a fibre mineral filler, advantageously barium sulphate; the final density of the polyurethane foam can thus attain a level of up to 2000 kg/m 3 .

In order to increase markedly local stiffness of the engine cover a reinforcing element of a metal grid or fibrous woven or unwoven reinforcement type can be inserted into the mould on the sprayed reactive compound to provide the engine cover with the outer visual (face) layer (skin).

For a marked increase of local heat resistance of the engine cover a shielding cover made of a heat insulation material can be placed into the mould.

In the event of extreme requirements for the sound-absorption properties of the engine cover the product can be subjected to another repeated shock in a vacuum chamber to further improve the properties by applying an underpressure ranging from -0.5 to -0.9 bar. The finished components are left advantageously to rest in a free state for a few hours to complete the chemical reactions. Subsequently, the components are fixed on shape jigs and flashes in the parting line are removed by milling, trimming or cutting.

A shielding cover made of a heat insulation material, for instance a material on the basis of glass fibres and a reflective aluminium film, can be attached to the finished component (if it has not been inserted into the mould earlier) on an assembly fixture.

The main advantage of the method according to the present invention consists in the fact that in comparison with the known systems the finished engine cover features high sound- absorption properties, high heat resistance, high-quality outer surface appearance, low weight and increased protection of pedestrians in collisions with cars. The high sound-absorption performance of the engine cover is based on a combination of the skin made of compact polyurethane having a density of 700 kg/m 3 at minimum and a suitable choice of soft polyurethane foam having open structure in the inside - thanks to employment of a release agent enabling opening of the polyurethane foam cells - and use of the repeated shock procedure based on use of the underpressure ranging between -0.5 to 0.95 bar in order to partially break the polyurethane foam structure - to tear the cells.

Invention embodiments Example 1

A three-layer polyurethane compact engine cover with a metallic surface finish of the outer side having a skin layer density of 900 kg/m 3 and PU foam density of 70 kg/m 3 on the reverse side is produced using the following sequence of operations.

1. A suitable release agent based on C11-C15 n- and iso-alkanes is applied by spraying with a spray gun onto the surface of an open steel mould (on both male and female) and let to dry for 20 seconds. Two-component polyurethane varnish containing a metallic pigment is applied by spraying onto the surface of the mould female provided with a film of the release agent, the final thickness of the varnish layer being 0.05 mm; the varnish film is let to dry for a period of 20 seconds. Polyurethane reactive compound is sprayed onto the mould cavity (female) with a high- pressure mixing device fitted with a spray mixing head located on a robot arm, with the polyurethane reactive compound creating an elastic skin layer having an average thickness of 1.5 mm.

Technological conditions:

— temperature of component A (mixture of functionalized polyols, pigments and additives):

35 °C.

— temperature of component B (mixture of modified MDI, higher homologues and additives): 35 °C.

— A/B component mixing ratio: 100/100.

— reactive compound spraying time: 50 seconds

— A/B component mixing pressures: 100/120 bars.

The polyurethane reactive compound is poured (dispensed) into the cavity of the open mould using a high-pressure mixing device fitted with a casting mixing head located on the robot arm. After mould closing, polymerization takes place and foam elastic structure is created on the back side of the engine cover.

Technological conditions;

— temperature of component A (mixture of polyols): 23 °C.

— temperature of component B (mixture of polyisocyanates): 23 °C.

— A/B component mixing ratio: 100/85.

— reactive compound spraying time: 5 seconds

— A/B component mixing pressures: 180/180 bars.

— polymerization time: 4 minutes.

After mould opening, the component is taken out from the mould cavity and inserted immediately into a vacuum chamber where it is exposed to repeated underpressure shocks ranging from -0,5 bar to -0.9 bar. 6. Subsequently, the component is taken out from the vacuum chamber and left to mature at the temperature of 20 ± 10 °C in a free state for a time period of 12 hours.

7. After maturing it is placed again into the vacuum chamber and subjected to repeated pressure shocks ranging from -0,5 bar to -0.9 bar.

8. After removal from the vacuum chamber and resting in a free state for a time period of 1 hour at minimum, the component is placed on a shape fixation jig and secured by vacuum. Subsequently, flashes are trimmed with a robot-controlled mill.

Example 2

A two-layer mass-dyed polyurethane compact engine cover having skin layer density of 900 kg/m 3 and density of polyurethane foam of 70 kg/m 3 on the back side is produced using a sequence of operations identical with that described in Example 1, the difference being that operation 2 is left out.

Example 3

A two-layer mass-dyed polyurethane compact engine cover having skin layer density of 900 kg/m 3 and density of polyurethane foam of 70 kg/m 3 on the back side with a local thermal shielding is produced by using a sequence of operations identical with that described in Example 1, the difference being that operation 2 is left out and as the last operation a mechanical fixation of the shielding cover is carried out with the aid of self-tapping screws.

Example 4

A two-layer mass-dyed polyurethane compact engine cover having skin layer density of 900 kg/m 3 and density of polyurethane foam of 70 kg/m 3 on the back side with a local reinforcement and a local thermal shielding is produced using a sequence of operations identical with that described in Example 1 , the difference being that operation 2 is left out and within operation 4 a local reinforcing element and thermal shielding cover are inserted into the mould. Subsequently, a reactive polyurethane compound is poured into the mould to embed the said elements. Example 5

A two-layer mass-dyed polyurethane compact engine cover having skin layer density of 900 kg/m 3 and density of barium sulphate filled polyurethane foam of 950 kg/m 3 on the engine cover reverse side is produced using a sequence of operations identical with that described in Example 2. For preparation of the polyurethane foam on the engine cover back side technological conditions as follows are used:

— temperature of component A (mixture of polyols and barium sulphate): 30 °C.

— temperature of component B (mixture of polyisocyanates): 25 °C.

— A/B component mixing ratio: 120/80.

— reactive compound spraying time: 15 seconds

— A/B component mixing pressures: 200/175 bars.

— polymerization time: 5 minutes.

Industrial application potentials

The method according to the present invention can be advantageously used to produce engine covers for passenger cars, trucks, buses and agricultural and building machinery.