JPS5946780B2 - Flexible molded product and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new method for producing flexible moldings which are particularly useful at very high temperatures, such as in rocket motors.

Material selection problems are often encountered when designing components used to protect metal surfaces from hot gases.

For example, in the field of rocket motor insulation, the he ad -end 1 insulator
The selection of materials for manufacturing parts known as .

Success or failure in igniting a rocket motor often depends on the overall quality of this part.

The head insulator is placed against the bulkhead of the rocket casing, and it protects the bulkhead from the very high temperatures generated by the rocket fuel.

Therefore, this part (head end insulator) is exposed to high temperature gas (300
sufficient thermal insulation to protect metal surfaces (i.e. bulkheads) from temperatures above 0°C, good resistance where their gases flow, good mechanical properties over a wide temperature range (-18°-71°C); It must have particularly good elasticity at low temperatures, ease of manufacture at a reasonable price, compatibility with other materials used in the insulating structure, and ease of installation in the rocket chamber. No.

Therefore, as can be seen from the foregoing, the selection of materials suitable for such specific applications is limited by the very stringent requirements imposed.

The most commonly used material is based on asbestos fibers infused with phenolic resin.

This material is suitable for high temperature (171℃) and high pressure (140ky
/cI/L) is easily formed into the desired shape and dimensions in a steel mold.

Parts molded from asbestos containing phenolic resin satisfy some of the requirements mentioned above, such as being easy to mold and providing sufficient thermal insulation.

However, since these parts are very rigid,
Inserting into a metal tube such as a rocket casing can be cumbersome, especially if the metal tube is slightly oval shaped.

Also, their rigidity prevents them from being intimately attached to the closed end of the tube.

Furthermore, these parts have very little stretchability (less than 1 percent) over the entire temperature range, which is especially problematic at low temperatures.

Furthermore, it is necessary to use cement to bond the parts to metal surfaces, and the curing period of the cement adds an extra step in manufacturing the rocket motor.

Additionally, these components can also be used with sidewall insulation based on elastomers, such as rolled butadiene.
It is also incompatible with commonly used polymeric propellants.

The present invention therefore aims to provide a method for forming molded articles based on an elastomeric polymer binder system containing asbestos fillers, which is capable of satisfying the performance requirements mentioned above. It is something.

U.S. Pat. No. 3,872,205 describes a novel insulating material for use as sidewall insulation in rocket motors comprising an elastomeric polymer binder and a refractory siliceous reinforcing filler dispersed therein. It is a sheet made of wood.

A method for forming such sheets is also described, which involves mixing a polymeric binder with a filler to form a dough and age-hardening the dough. It includes the step of curing the material sufficiently to allow it to be rolled into a sheet.

The elastomeric polymer in the specific embodiments described in the above patents is a carboxyl-terminated polybutadiene that is compatible with commonly used polybutadiene rocket propellants.

The material is therefore very suitable for the rocket chamber environment, as proven by practical use.

However, it is clear that certain components, such as head insulators, need to be molded into specific shapes, and the sheet materials of the above patents are unsuitable for such components.

It is known to heat-open mold filled compositions in order to obtain cured products with high strength.

For example, US Pat. No. 3,235,530 describes asbestos/
Methods are taught for forming high strength products by hot open molding resin binder compositions.

A large volume of asbestos paper is impregnated with a thermoset resin solution, and then the asbestos paper is passed between squeezing rollers to control the amount of solution impregnated into it.

The impregnated sheet is heated to remove volatile components and precure the sheet.

For the molding operation, the sheets so precured are cut into pieces, discs or strips, which are transferred to molds and subjected to heat and pressure.

As mentioned above, the product thus obtained has high strength and stiffness, which is contrary to the requirement of the present invention that the molded product must be highly flexible. It is.

There are two major problems with the method of US Pat. No. 3,235,530.

One is that the binder is a thermosetting resin rather than an elastomer, and the other is that heat is used in the molding process, which hardens the product to a very rigid state. This means that it will be done.

Therefore, the present invention is based on an elastomer binder/asbestos filler system and does not use heat during the actual molding.

The final product is therefore flexible and has properties that are compatible with other elastomeric polymer components and propellants as described above.

To avoid hardening of the molding material, cold-open molding methods are used.

Such a method has been found to be effective for materials formed by cutting the insulating sheet of the patent mentioned at the outset into pieces.

Such a material, apart from the difference in the binder used, is quite different from that of the aforementioned US patent, which uses sheets of asbestos paper impregnated with a resin binder.

In the present invention, the material to be molded contains 50 to 80% of the total composition.
By cutting into pieces a sheet formed of an incompletely cured powder of an elastomeric polymeric binder consisting of carboxyl-terminated polybutadiene with asbestos filler dispersed throughout in an amount of % by weight. can get.

In this case, at least 50% of the filler is in the form of fibers, and the remainder is in the form of floating particles.

The invention can thus be summarized as follows.

That is, a sheet material comprising an elastomeric polymer binder of uncured carboxyl-terminated polybutadiene and asbestos filler is first formed according to the method of U.S. Pat. No. 3,872,205, in which the asbestos filler is bonded. It is in the form of fibers and suspended matter dispersed in the material.

The sheet is then formed into multiple pieces, the multiple pieces are maintained at a temperature low enough to prevent or at least inhibit curing, and then the multiple pieces are substantially The desired molded product is formed by cold-open molding in an unhardened state.

Articles formed in the manner described above retain the excellent insulating properties of the molded composition, are flexible, and will adhere to metal surfaces with or without adhesives.

When used in a rocket motor, for example as a head end insulator, the product can be closely matched to the contours of the propellant chamber bulkhead when pressurized, and
It can be easily inserted into a casing even if the casing has a slightly oval cross-section.

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIGS. 1 and 1a, a metal rocket casing 10 includes a propellant chamber 12 and a forward compartment 13 thereof.
A partition wall 11 is provided between the two.

The casing 10 is also provided with a head end insulator 14, which abuts the partition wall 11 and the adjacent area of the inner wall.

The head end insulator is generally cup-shaped with a central protrusion 14a protruding into the propellant chamber 12 (see Figure 1).
Alternatively, a central recess 14d may be formed (see FIG. 1a).

The wall 14b of the head end insulator is attached to the inner wall of the casing 10, and the base of the insulator is attached to the partition wall 11.

The insulator 14 according to the embodiment shown in FIG. 1 is shown in a perspective view in FIG.

A side wall insulation material 15 is provided around the inner wall of the propellant chamber 12, which extends onto the wall 14b of the head end insulation 14.

This material typically consists of a matrix of asbestos fibers and suspensions in a suitable binder medium and is applied in sheet form to the inner surfaces of casing 10 and insulation 14 by means of an inflatable rubber bag.

Finally, a head-limiting split 16 is provided on a portion of the material 15 and the exposed inner surface of the insulator 14 (excluding the central protrusion 14a or central recess 14d).

Restrictor 16 functions to restrict the exposed propellant surface and is typically formed of a suitable elastomeric material that is compatible with the particular propellant being used in the rocket.

Preferably, a mold release agent is disposed between the insulator 14 and the restrictor 16 to reduce stress concentration on the head of the propellant particles during temperature cycling.

Turning now to the formation of the head insulator 14, the insulator is cold open molded from a number of pieces obtained from a preformed sheet of material.

The sheet material contains 50 to 80% by weight of asbestos filler reinforcing material, at least 50% by weight of which is in the form of fibers.
(preferably 65-75% by weight) of carboxyl-terminated polybutadiene dispersed therein.

The filler is composed of 50-80% by weight of asbestos fibers and 20-50% by weight of asbestos suspended matter.

Premixing of binder, fibers and floats takes place in a mixer.

The binder-wetted material is calendered first in a differential speed mill and then in a uniform speed mill to obtain an uncured sheet material.

Further details in this regard can be found in US Pat. No. 3,872,205.

The sheet material may be made into a number of pieces, which may be used immediately, or by preventing or at least inhibiting the curing of the polymer.
Low temperature (approximately -10℃) to maintain those molding characteristics
stored in

Of course, the sheet material itself may be stored at low temperatures and sections formed from the sheet material immediately prior to molding.

What is important here is that the molding material is in an uncured state.

A typical composition of the molding material is as follows.

Steel mold female and male sections suitable for forming the novel head insulator according to the embodiments of FIGS. 1 and 2 are shown in FIGS. 3a and 3b, respectively.

The female part 20 has a mold cavity 21 and the male part 22 has a first cylindrical part 23 that fits snugly into the mold cavity 21.
and a second cylindrical portion 24 having a slightly reduced diameter.
It has

The gap between the surface of portion 24 and the inner wall of mold cavity 21 thus constitutes a molding chamber for wall 14b of head insulator 14.

A projection (not shown in the drawing) that projects upward is provided at the bottom of the mold nest 21, and the projection is connected to the male mold portion 2.
2 cooperates with the recess 25 at the top of the cup-shaped insulator 14 to form a chamber for the base of the cup-shaped insulator 14 and the protrusion 14a.

The entire surface of the molding chamber is coated with polytetrafluoroethylene.

The shape of the mold forming the embodiment of FIG. 1a, in which the protrusion 14a is replaced by a conical recess 14d, will be apparent from consideration of FIG. 3c.

Thus, the upwardly protruding projection at the bottom of the mold cavity 21 is omitted, and the recess 25 is provided with a conical projection 26 in its center, which is connected to the recess 14d of the head end insulator.
is formed.

The molding material is metered and introduced into the mold cavity 21 of the female mold part 20.

The mold is closed and the material is compressed at a pressure of about 15 tons.
It is compressed in the mold for 4 minutes to form the head insulator 14, with molding time and pressure selected depending on the size and shape of the article to be molded.

Because the surface of the mold is coated with polytetrafluoroethylene, no other mold lubricant is required; the purpose of molding in this case is simply to compress the material into the desired shape; It should be noted that the part is not cured when it leaves the mold.

Furthermore, the parts are cohesive, need only be handled with reasonable care to avoid deformation or damage, and require no finishing.

Tests have shown that the uncured molded head end insulator formed as described above is flexible and can be easily inserted into the rocket motor propellant chamber, even if the chamber is slightly oval. was recognized.

Furthermore, the part conforms closely to the contours of the septum when pressurized and adheres to metal surfaces with or without adhesives if used within a normal shelf life.

Once cured in situ, the head insulator was found to have very good resistance and thermal insulation properties and good flexibility at low temperatures.

After the head end insulator and associated components have been placed within the casing 10 and configured as shown in FIG. 1 or FIG. 1a, the chamber 12 may be loaded with propellant.

In the embodiment of FIG. 1, the mandrel 1T is first inserted into the center of the chamber 12.

The mandrel has a recess 17a that is complementary to the protrusion 14a of the head insulator, and the mandrel is placed on the head insulator.

The propellant is then allowed to fall by gravity around the mandrel.

In the embodiment of FIG. 1a, propellant is first loaded into the chamber, and then mandrel 18 is inserted into the chamber and forced through the propellant into recess 14d.

The mandrel 18 has a conical tip 18a,
The tip is complementary to and sits neatly within the recess 14d, forming a thin film of propellant between the tip and the four walls.

[Brief explanation of the drawing]

1 and 1a are cross-sectional views showing head end insulators and rocket casings according to two embodiments of the invention; FIG. 2 shows the insertion of the head end insulator shown in FIG. 1 into the rocket casing; Figures 3a and 3b are perspective views showing the mold for forming the head end insulator in Figure 2, and Figure 3c is the same as Figure 1a. FIG. 6 shows a male mold half-cut for forming the illustrated head end insulator. 10... Metal rocket casing, 11...
...Bulkhead, 12...Propellant chamber, 13...
...Anterior compartment, 14... Head end insulator, 17.
...Mandrel, 18...Mandrel,
20...Female type part, 22...Male type part.

Claims (1)

[Scope of Claims] 1(a) An incompletely cured asbestos filler in which at least 50% by weight is in the form of fibers and the remainder is in the form of floating particles is dispersed as a reinforcing material in an amount of 50 to 80% by weight of the total composition. (b) cutting the sheet material into a number of pieces; and (C) exposing the pieces to room temperature to prevent curing thereof. 1. A method for producing a flexible molded article, comprising the steps of pressurizing the molded article at the step of applying pressure, thereby forming a molded article. 2. In the method for manufacturing a flexible molded article according to claim 1, the pressing step of the fragment at room temperature is performed for about 15 minutes.
The method is characterized in that it is carried out for about 2 to 4 minutes under a pressure of tons. 3. The method for manufacturing a flexible molded article according to claim 1 or 2, characterized in that a mold coated with polytetrafluoroethylene is used for the pressurizing step at room temperature. The said method.