CA1223414A - Polyurethane foam products construction - Google Patents
Polyurethane foam products constructionInfo
- Publication number
- CA1223414A CA1223414A CA000470988A CA470988A CA1223414A CA 1223414 A CA1223414 A CA 1223414A CA 000470988 A CA000470988 A CA 000470988A CA 470988 A CA470988 A CA 470988A CA 1223414 A CA1223414 A CA 1223414A
- Authority
- CA
- Canada
- Prior art keywords
- core
- mould
- skin
- density
- insert
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Casting Or Compression Moulding Of Plastics Or The Like (AREA)
Abstract
ABSTRACT
A method of producing articles from polyurethane foam which comprises forming a core of low density material, placing the core within a mould so that at least part of the core is spaced apart from the wall of the mould and injecting materials to form a skin of polyurethane foam into the space between the core and the wall of the mould, the skin having a density greater than the density of the core.
A method of producing articles from polyurethane foam which comprises forming a core of low density material, placing the core within a mould so that at least part of the core is spaced apart from the wall of the mould and injecting materials to form a skin of polyurethane foam into the space between the core and the wall of the mould, the skin having a density greater than the density of the core.
Description
3~
THIS INVENTION relates to the moulding of articles from polyurethane foam. It is particularly applicable to articles in which the weight is extremely critical, consistent with an acceptable strength, such as in the surfboard and allied industries. It is equally applicable in other fields demanding similar criteria.
It has been the practice where lightweight, polyurethane products are required to have acceptable strength and ,~mpact resistance, to either coat them with ~l~erglas~
resins as with existing surfboards, or to manufacture a variety of surface skins and then inject a light density polyurethane into the cavity so formed.
n'he disadvantages of fiberglass- coated polyurethane are 1,hat it is extremely labour intensive, it is extremely rigid an~ hence has less ability to absorb impact. It tends 1,o fracture easily, and separates9 and it is a fairly unpleasant and hazardous material to handle.
ethods by which the skin is constructed prior to filling with a polyurethane core material, have the large (~isadvantage that due to the natural shrinkage of polyurethane, separation of the skin from the core o~urs, and hence eventual breakdown.
hese problems'have been overcome by the present invention ~hich involves the manufacture of the core first, with a very low density9 lightweight materiall then covering it with a thin medium density polyurethane skin. Several types of core material may be used, including polyurethane and styrene.
Thus the present invention resides in a method of producing articles from polyurethane foam which comprises forming a core of low density material, placing the core within a ,,',.
- 3 ~ 3~
mould S(! that at least part of the core is spaced apart from the wall of the mould and injecting materials to form a skin o~ polyurethane foam into the space between the core and the wall of the mould, the skin having a density greater- than the density of the core.
Best results have been obtained using a polyurethane core over which is moulded a rigid, compatible, higher density polyurethane skin. Flexible polyurethane skins may be formed; which give a softer sur~ace as an alternative to the hard, rigid skins. The same method of construction is used.
The most critical factor in surfboard construction is ~he weight, strength being sacrificed in many instances in favour of a lower weight. It is apparent that tlie lighter the board, the weaker it is, as the only ways to lighten it are~to either reduce the density, or reduce its size.
Buoyancy is a major significant factor in that :it relakes directly to performance. The more buoyant a surfboard is, the less energy that is required to utilize it.
By utilizing a lower density core, and a medium density skin, both of which are extremely buoyant, a large range Gf combir~tions can be achieved, allowing for varying balances between light weight, strength and buoyancy.
There are many advantages in such a buoyant board. A
surfboard constructed with this method may be significantly reduced in size compared with a similar surfboard con-structed with conventional methods, resulting in increased performance, yet carrying the same person.
A major factor of this invention is the high volume production that can be achieved with relatively few rejects, resulting in extremely low cost per unit.
- 4 - ~234~
This invention preferably uses the R.I.M. ~ethod (Reaction Injection Moulding) of polyurethane construction for the formation of both the core and skin.
Moulds may be constructed from several types of material, however, aluminum moulds were found to be the most successful. The mould described in this document was highly polished on the surface to be reproduced~ with a minimum of 25mm aluminum thickness. The mould was made in two halves, a top-and bottom, joining midway around the edge, or rail, of the surfboard.
Correct clamping of the mould is essential for the - production of high quality skins. Heating of the mould is also essential.
.
It has been found that a skin thickress of between 6mm and lOmm with an average density of between 200-400 kilograms per- cubic meter moulded around a lightweight core of density between 28-50 kilograms per cubic mete~ gives the most satisfactory balan^e between weight and strength. An alternative method is to increase the density of the core, to increase the strength, and correspondingly reduce the skin thickness, thus realizing the s~me overall weight, and strength. With strict control, slcin thickness may be reduced to 2mm, however, at this thickness, a minimum - density of 250kg/c.m. was most satisfactory.
For the purpose of this description, skin thickness is 8mm with a density of 250kg/c.m. moulded around a core of density 30kg/c.m.
., Two inserts are constructed, in this case Of fiberglass however any material that can be moulded to the shape of the mould may be used. These inserts are 8mm in thickness, and made so that they fit exactly inside both the top and ., _ 5 _ ~23~4 bottom of the mould (halves)~ When the mould is closed, the void inside with the inserts is 8mm thinner all over than th~ c`osed mould without the inserts.
To construct the cores from polyurethane, the best method was found to be using the mould with the inserts inside. By initial trial and error, it can be calculated how much polyurethane must be placed inside the mould (with inserts), to exactly fill it at a density of 30kg/c.m.
When the polyurethane has cured, it may be removed from the mould. The core is now 8mm thinner all over than the finished article is to be~ The cores must be stored to minimize distortion and to cure properly. Alternatively, another mould may be made up that is exactly 8mm thinner all over than the master mould and the cores may be manufactured separately.
The demould time o~ the cores is dependent upon the thickness.
The Skinning Process.
Moulding a skin around ~he core may be done by either of two methods:
Method 1. The aluminum mould is prepared in the usual manner. Spacers are either glued or placed on both sides of the core so that when it is placed inside the mould and it is closed, an e~en ~oid of 8mm exists all around the core.
It is into this void that the higher density skinning polyurethane is to be injected and react. The spacers are positioned so that when the mould is closed, they hold the core tightly and evenly, not allowing any movement of the core when the skin material is reacting. The length oi` the spacers is 9mm so that when the mould is closedS they push - 6 - ~22~
into the core slightly, holding it tightly.
The spacers maybe of any suitable configuration. A
preferred form of spacers is forrned of nylon or other suitable plastic and comprises a disc having a central peg projecting from each face. One peg is pushed into the core until the disc bears against the surface of the core. This leaves the other peg projecting outwardly so that in position the outer end bears against the wall of the mould to hold the core spaced therefrom.
A predetermined amount of polyurethane is in~ected into the void so that the required density is reached. The entry gates where the polyurethane enters the mould must be constructed carefully to enable it to react evenly along both sides of the core. Bad design will result in more material forcing its way to one side of the core, with little or none of the other side. Each item to be moulded requires it~ own gating system. This method becomes extremely difficult where one side of the core is shaped in such a way as to allow for easier flow of the skinning material than the other. In such a case, Method 2 may be used.
Method 2. Tne mould is prepared as usual, and the bottom insert is positioned in the bottom of the mould. The core is then placed into the insert, fitting exactly as it was moulded in jt beforehand. Spacers are then placed on the top of the core, so that when the mould is closed, there will be a void of exactly 8mm around the top of` the core only. The closure of the mould will force the spacers into the core, pushing it hard against the bottom insert, so that no material can find its way around the bottom half of the core.
A predetermined amount of polyurethane is injected lnto the .. ;...
- 7 ~ 3~4 ~`
mould, which finds its way into the only void i.e. the top of the core. Af-ter the demould time, which is relatively short, the mould is opened. The skin around the top of the core adheres to the aluminum and the whole thin8 comes away from the bo-ttom of the mould. The bottom insert can now be removed. After cleaning down the mould, when it is closed -there is now an 8mm void on the bottom of the core.
Polyurethane may now be injected into the mould, filling the only void, the bottom half. Adhesion to the top half that has already ~een skinned is e~cellent. After the demould time, the mould may be opened and the product removed.
~hile Method 2 involves extra time, for more complicated ~ouldings, it is preferable to Method 1.
The amounts of material to be injected into the mould can be calculated from test shots by trial and error.
Strengthening of the product may be carried out by the insertion of various strengthening rods or by cutting grooves in the core prior to inserting it in the mould, these grooves are filled during the skinning process. These ~rooves are an ideal method of reinforcing specific sections of the product with little effort. While spacers are specifically mentioned in this description, it was found that plastic straps, equidistant from each other, and fastened each side of the bottom of the mould so that the~
span the cavity, where satisfactory. When the mould is closed the edges of the upper part of the mould bear against the ends of thestraps so that they tighten across the core and hold it sufficiently for the skinning process.
~ . .
THIS INVENTION relates to the moulding of articles from polyurethane foam. It is particularly applicable to articles in which the weight is extremely critical, consistent with an acceptable strength, such as in the surfboard and allied industries. It is equally applicable in other fields demanding similar criteria.
It has been the practice where lightweight, polyurethane products are required to have acceptable strength and ,~mpact resistance, to either coat them with ~l~erglas~
resins as with existing surfboards, or to manufacture a variety of surface skins and then inject a light density polyurethane into the cavity so formed.
n'he disadvantages of fiberglass- coated polyurethane are 1,hat it is extremely labour intensive, it is extremely rigid an~ hence has less ability to absorb impact. It tends 1,o fracture easily, and separates9 and it is a fairly unpleasant and hazardous material to handle.
ethods by which the skin is constructed prior to filling with a polyurethane core material, have the large (~isadvantage that due to the natural shrinkage of polyurethane, separation of the skin from the core o~urs, and hence eventual breakdown.
hese problems'have been overcome by the present invention ~hich involves the manufacture of the core first, with a very low density9 lightweight materiall then covering it with a thin medium density polyurethane skin. Several types of core material may be used, including polyurethane and styrene.
Thus the present invention resides in a method of producing articles from polyurethane foam which comprises forming a core of low density material, placing the core within a ,,',.
- 3 ~ 3~
mould S(! that at least part of the core is spaced apart from the wall of the mould and injecting materials to form a skin o~ polyurethane foam into the space between the core and the wall of the mould, the skin having a density greater- than the density of the core.
Best results have been obtained using a polyurethane core over which is moulded a rigid, compatible, higher density polyurethane skin. Flexible polyurethane skins may be formed; which give a softer sur~ace as an alternative to the hard, rigid skins. The same method of construction is used.
The most critical factor in surfboard construction is ~he weight, strength being sacrificed in many instances in favour of a lower weight. It is apparent that tlie lighter the board, the weaker it is, as the only ways to lighten it are~to either reduce the density, or reduce its size.
Buoyancy is a major significant factor in that :it relakes directly to performance. The more buoyant a surfboard is, the less energy that is required to utilize it.
By utilizing a lower density core, and a medium density skin, both of which are extremely buoyant, a large range Gf combir~tions can be achieved, allowing for varying balances between light weight, strength and buoyancy.
There are many advantages in such a buoyant board. A
surfboard constructed with this method may be significantly reduced in size compared with a similar surfboard con-structed with conventional methods, resulting in increased performance, yet carrying the same person.
A major factor of this invention is the high volume production that can be achieved with relatively few rejects, resulting in extremely low cost per unit.
- 4 - ~234~
This invention preferably uses the R.I.M. ~ethod (Reaction Injection Moulding) of polyurethane construction for the formation of both the core and skin.
Moulds may be constructed from several types of material, however, aluminum moulds were found to be the most successful. The mould described in this document was highly polished on the surface to be reproduced~ with a minimum of 25mm aluminum thickness. The mould was made in two halves, a top-and bottom, joining midway around the edge, or rail, of the surfboard.
Correct clamping of the mould is essential for the - production of high quality skins. Heating of the mould is also essential.
.
It has been found that a skin thickress of between 6mm and lOmm with an average density of between 200-400 kilograms per- cubic meter moulded around a lightweight core of density between 28-50 kilograms per cubic mete~ gives the most satisfactory balan^e between weight and strength. An alternative method is to increase the density of the core, to increase the strength, and correspondingly reduce the skin thickness, thus realizing the s~me overall weight, and strength. With strict control, slcin thickness may be reduced to 2mm, however, at this thickness, a minimum - density of 250kg/c.m. was most satisfactory.
For the purpose of this description, skin thickness is 8mm with a density of 250kg/c.m. moulded around a core of density 30kg/c.m.
., Two inserts are constructed, in this case Of fiberglass however any material that can be moulded to the shape of the mould may be used. These inserts are 8mm in thickness, and made so that they fit exactly inside both the top and ., _ 5 _ ~23~4 bottom of the mould (halves)~ When the mould is closed, the void inside with the inserts is 8mm thinner all over than th~ c`osed mould without the inserts.
To construct the cores from polyurethane, the best method was found to be using the mould with the inserts inside. By initial trial and error, it can be calculated how much polyurethane must be placed inside the mould (with inserts), to exactly fill it at a density of 30kg/c.m.
When the polyurethane has cured, it may be removed from the mould. The core is now 8mm thinner all over than the finished article is to be~ The cores must be stored to minimize distortion and to cure properly. Alternatively, another mould may be made up that is exactly 8mm thinner all over than the master mould and the cores may be manufactured separately.
The demould time o~ the cores is dependent upon the thickness.
The Skinning Process.
Moulding a skin around ~he core may be done by either of two methods:
Method 1. The aluminum mould is prepared in the usual manner. Spacers are either glued or placed on both sides of the core so that when it is placed inside the mould and it is closed, an e~en ~oid of 8mm exists all around the core.
It is into this void that the higher density skinning polyurethane is to be injected and react. The spacers are positioned so that when the mould is closed, they hold the core tightly and evenly, not allowing any movement of the core when the skin material is reacting. The length oi` the spacers is 9mm so that when the mould is closedS they push - 6 - ~22~
into the core slightly, holding it tightly.
The spacers maybe of any suitable configuration. A
preferred form of spacers is forrned of nylon or other suitable plastic and comprises a disc having a central peg projecting from each face. One peg is pushed into the core until the disc bears against the surface of the core. This leaves the other peg projecting outwardly so that in position the outer end bears against the wall of the mould to hold the core spaced therefrom.
A predetermined amount of polyurethane is in~ected into the void so that the required density is reached. The entry gates where the polyurethane enters the mould must be constructed carefully to enable it to react evenly along both sides of the core. Bad design will result in more material forcing its way to one side of the core, with little or none of the other side. Each item to be moulded requires it~ own gating system. This method becomes extremely difficult where one side of the core is shaped in such a way as to allow for easier flow of the skinning material than the other. In such a case, Method 2 may be used.
Method 2. Tne mould is prepared as usual, and the bottom insert is positioned in the bottom of the mould. The core is then placed into the insert, fitting exactly as it was moulded in jt beforehand. Spacers are then placed on the top of the core, so that when the mould is closed, there will be a void of exactly 8mm around the top of` the core only. The closure of the mould will force the spacers into the core, pushing it hard against the bottom insert, so that no material can find its way around the bottom half of the core.
A predetermined amount of polyurethane is injected lnto the .. ;...
- 7 ~ 3~4 ~`
mould, which finds its way into the only void i.e. the top of the core. Af-ter the demould time, which is relatively short, the mould is opened. The skin around the top of the core adheres to the aluminum and the whole thin8 comes away from the bo-ttom of the mould. The bottom insert can now be removed. After cleaning down the mould, when it is closed -there is now an 8mm void on the bottom of the core.
Polyurethane may now be injected into the mould, filling the only void, the bottom half. Adhesion to the top half that has already ~een skinned is e~cellent. After the demould time, the mould may be opened and the product removed.
~hile Method 2 involves extra time, for more complicated ~ouldings, it is preferable to Method 1.
The amounts of material to be injected into the mould can be calculated from test shots by trial and error.
Strengthening of the product may be carried out by the insertion of various strengthening rods or by cutting grooves in the core prior to inserting it in the mould, these grooves are filled during the skinning process. These ~rooves are an ideal method of reinforcing specific sections of the product with little effort. While spacers are specifically mentioned in this description, it was found that plastic straps, equidistant from each other, and fastened each side of the bottom of the mould so that the~
span the cavity, where satisfactory. When the mould is closed the edges of the upper part of the mould bear against the ends of thestraps so that they tighten across the core and hold it sufficiently for the skinning process.
~ . .
Claims (8)
1. A method of moulding an article having a core and a skin of polyurethane foam surrounding the core, comprising the steps of:
forming a core;
placing a first removable insert into a mould, the insert having a surface conforming to a part of the core;
placing the core in the mould with said part of the core received against said surface of the insert whereby the insert supports the core in position in the mould, and with the remaining part of the core spaced from the interior wall of the mould;
injecting materials into the space between the core and the wall of the mould to form part of the skin of polyurethane foam;
removing the insert; and injecting materials into the space vacated by the insert to form the remainder of the skin of polyure-thane foam.
2. The method according to claim 1, wherein said first removable insert is one of at least two removable inserts which in combination form a shell having the contour of the core, and wherein the core is formed by
forming a core;
placing a first removable insert into a mould, the insert having a surface conforming to a part of the core;
placing the core in the mould with said part of the core received against said surface of the insert whereby the insert supports the core in position in the mould, and with the remaining part of the core spaced from the interior wall of the mould;
injecting materials into the space between the core and the wall of the mould to form part of the skin of polyurethane foam;
removing the insert; and injecting materials into the space vacated by the insert to form the remainder of the skin of polyure-thane foam.
2. The method according to claim 1, wherein said first removable insert is one of at least two removable inserts which in combination form a shell having the contour of the core, and wherein the core is formed by
Claim 2 continued....
placing said at least two removable inserts into the mould and injecting materials into the shell.
placing said at least two removable inserts into the mould and injecting materials into the shell.
3. The method as claimed in claim 1, wherein the core is of low density material.
4. The method as claimed in claim 2, wherein -the core is formed of a material selected form the group consisting of polyurethane and polystyrene.
5. The method as claimed in claim 3, wherein the core has a density of between 28-50 kg/c.m.
6. The method as claimed in claim 3, wherein the skin has a density of 200-400 kg/c.m.
7. The method as claimed in claim 4, wherein the skin has a density of 200-400 kg/c.m.
8. The method as claimed in claim 5, wherein the skin has a density of 200-400 kg/c.m.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000470988A CA1223414A (en) | 1984-12-24 | 1984-12-24 | Polyurethane foam products construction |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000470988A CA1223414A (en) | 1984-12-24 | 1984-12-24 | Polyurethane foam products construction |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1223414A true CA1223414A (en) | 1987-06-30 |
Family
ID=4129454
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000470988A Expired CA1223414A (en) | 1984-12-24 | 1984-12-24 | Polyurethane foam products construction |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1223414A (en) |
-
1984
- 1984-12-24 CA CA000470988A patent/CA1223414A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |