KR20080103270A

KR20080103270A - A test method and a instrument for measuring the dimensional stability of polymeric products upon thermal variation

Info

Publication number: KR20080103270A
Application number: KR1020070050359A
Authority: KR
Inventors: 강신영; 홍창국
Original assignee: 전남대학교산학협력단
Priority date: 2007-05-23
Filing date: 2007-05-23
Publication date: 2008-11-27

Abstract

The present invention is to investigate the characteristics of the entropy force according to various temperature conditions and the thermal shrinkage rate, thermal expansion rate, and thermal shrinkage force, thermal expansion force change according to the expansion of molecules for measuring the volume stability of the polymer material, in particular rubber material. The present invention relates to a test method and apparatus for measuring the relationship between temperature change and strain of rubber materials, the relationship between temperature change and stress, and the relationship between strain and shrinkage or expansion force.

Description

A test method and device for measuring the volumetric stability of polymer products due to thermal changes

1 is an overall schematic view of a polymer product testing apparatus according to the present invention

2 is a partially enlarged view of FIG. 1;

3 is a schematic view of a test piece used in the present invention

4 is a schematic view of a mold of a test piece used in the present invention

5 is a graph showing the results of the length change experiment with temperature change in prestress

6 is a graph showing the results of stress change with temperature change at preliminary strain

7 is a comparison graph of stress change and length change according to heat change

8 is a correlation graph of stress change and length change due to heat

9 is a graph of the force measurement results of the test specimen by the temperature change at the preliminary pressure rate

100: test apparatus 110: upper clamp

111: lower clamp 112: upper connecting member

113: lower connecting member 114: load cell

116: lower chamber 118, 120: guide shaft

122: crosshead 124: weight

126,128: drive shaft 130: servomotor

134,140: drive pulley 136,142: belt

138,144: driven pulley 146: measuring arm

148: List 150: Measuring axis

152: LVDT 154: bracket

The present invention relates to a test method and apparatus for measuring the volume stability according to the thermal changes of polymer products, more specifically, the relationship between the temperature change and strain of the rubber material, the relationship between the temperature change and the resulting force, The present invention relates to a test method and apparatus for measuring the volume stability according to the thermal change of a polymer product that can measure the relationship between strain and shrinkage force or expansion force.

In the absence of stress, the elastic body is amorphous and consists of entangled molecular chains. The elastic strain caused by the tensile stress is the part of the tangled part that is released and stretched in the direction of stress. When the stress is removed, the chain returns to its original structure and the macroscopic form of the material restores its original shape.

The driving force of elastic restoring force is a thermodynamic factor called entropy. Entropy is the disorder of the system, which increases with disorder. As the elastic body is pulled and the chains are straightened and aligned more, the entropy of the system decreases. From this state, when the chain returns to its original entangled state, entropy increases.

Generally known as Hook's law, it is called elastic modulus or modulus. The strain in which the stress value and the strain value are proportional to each other is called elastic strain, and the stress and strain graphs have a linear relationship. The slope of this straight line corresponds to the elastic modulus E. This elastic modulus can be seen as the stiffness of the material, and indicates the degree of repulsion of the material corresponding to the elastic deformation. Elastic deformation is not a permanent deformation, and when the load is removed, the material returns to its original shape.

The elastic property, which is immediately restored to its original form when the force is removed after being deformed by force from outside, is one of the important physical properties showing the storage capacity of strain energy.

The phenomenon of returning to the original shape after deformation is an entropy force for the rubber molecular chains to return to a random coil.

When heat is applied to the stretched polymer chains, the mobility of the chain molecules is increased, and the entropy increases, that is, returns to the disordered chain form. This entropy elastic behavior is related to the heat shrinkage phenomenon, the heat shrinkage force is increased if the deformation is limited.

Rubber products may produce voids in the formulation during the blending process, and these temperatures lead to thermal expansion as the temperature increases. Such thermal contraction and thermal expansion are closely related to the volume stability and performance of polymer products.

Polymer materials, in particular rubber materials, have elastic properties and flexibility, which are widely used in the automotive, advanced medical and electrical / electronics industries, as well as in the aerospace industry.

The elastic property, which is immediately restored to its original form when the force is removed after being deformed by force from outside, is one of the important physical properties showing the storage capacity of strain energy. The phenomenon of returning to the original shape after deformation is the entropy force that the molecular chains return to the random coil.

When an external stress is applied to the polymer chain, the chain is oriented along with elongation in the stress direction. As a result, the entropy of the polymer chain is significantly reduced. When heat is added thereto, the motility of the chain molecules increases to return to the direction of increasing entropy, that is, the disordered chain form. This entropy elastic behavior is related to the heat shrinkage phenomenon, the heat shrinkage force is increased if the deformation is limited. Rubber products can also produce voids in the formulation during blending, and these temperatures cause thermal expansion when the temperature is increased. Such thermal contraction and thermal expansion may impair the volumetric stability of the product at temperature changes.

The thermal behavior of these materials is very important for the numerical stability of the products, such as sealing rubber, various parts of automobiles, and electronic materials which are widely used in the industrial field. By understanding the thermal behavior of rubber products exposed to heat, one can gauge the numerical stability of products used in industry.

However, although the volume stability due to the thermal change of the polymer product is very important for the performance of the product, the measuring method and the measuring device are not systematic.

At present, the test method for the heat shrinkage behavior of plastic tube, which is an insulation coating material for electrical / electronic products, has been limitedly applied.However, in the case of rubber products, even though the volume stability is very important, no measurement method has been proposed at home and abroad. not.

Accordingly, the present invention was invented to solve the above problems, and an object of the present invention is to expand the entropy force and the expansion of molecules according to various temperature conditions in order to measure the volume stability of the above-mentioned polymer material, especially rubber material. In order to investigate the characteristics of thermal shrinkage, thermal expansion rate, thermal contraction force and thermal expansion force, the relationship between temperature change and strain of rubber material, the relationship between temperature change and the resulting force, strain and shrinkage or expansion force It is to provide a test method and apparatus for measuring the volume stability according to the thermal change of the polymer products that can measure the.

The present invention for achieving the above object is a constant temperature chamber for maintaining a constant temperature, a temperature control chamber is provided with a temperature controller for adjusting the temperature of the constant temperature chamber, the upper clamp is installed in the constant temperature chamber to fix the test piece And an upper chamber having a lower clamp and a load cell connected to the upper clamp and the upper connecting member. A cross head connected by the lower clamp and a lower connection member and disposed to be movable up and down by a guide shaft, a drive shaft which is joined to a screw hole formed in the cross head and moves the cross head up and down, and the drive A lower chamber having drive means for rotating the shaft; And a measuring arm fixed integrally with the lower connection member, and a measuring axis integrally connected with the measuring arm and the wrist, and an LVDT fixed to the upper chamber or the lower chamber by a bracket. .

The lower connection member is characterized in that the weight is installed to impose a preliminary stress on the test piece.

The drive means may include a driven pulley integrally formed with the drive shaft, a servo motor provided in the lower chamber, a drive pulley rotating integrally with a rotation shaft of the servo motor, and the drive pulley and the driven pulley. It characterized in that it comprises a belt to connect.

Another invention, using the polymer product test apparatus, the step of applying a constant load to the test piece; And measuring a change in length of the test piece with the LVDT while maintaining a plurality of set temperatures of the test piece by adjusting the temperature of the constant temperature chamber.

Another invention, using the polymer product test apparatus, the step of maintaining the temperature of the test piece to a predetermined set temperature by adjusting the temperature of the constant temperature chamber to the test piece; And measuring the change in length of the test piece with the LVDT while changing the load imposed on the test piece by the crosshead.

Here, the set temperature is -50 ~ 300 ℃, the acting load is characterized in that less than 500N.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described. In adding reference numerals to components of the following drawings, it is determined that the same components have the same reference numerals as much as possible even if displayed on different drawings, and it is determined that they may unnecessarily obscure the subject matter of the present invention. Detailed descriptions of well-known functions and configurations will be omitted.

In the present invention, to measure the heat shrinkage force, thermal expansion force or thermal contraction rate, thermal expansion rate according to the temperature change of the rubber specimen under the external stress or strain is measured the change in force and the change in the length of the specimen.

Test apparatus 100 according to an embodiment of the present invention is as shown in FIG.

The test apparatus is largely divided into an upper chamber 102 and a lower chamber 116.

The constant temperature chamber 104 is installed in the upper chamber 102, and the upper clamp 110 and the lower clamp 111 fixing the test piece 10 in the constant temperature chamber 104 are installed.

The upper clamp 110 is connected by the load cell 114 and the upper connecting member 112 is fixed to the upper portion of the upper chamber 102, the lower clamp 111 is the lower connecting portion by the material 113 It is connected to the crosshead 122 in the lower chamber 116.

The load cell 114 serves to measure the load applied to the test piece 10 through the upper clamp 110. In the present invention, a load cell 114 having a capacity of 500N was used.

The constant temperature chamber 104 may maintain a corresponding temperature when a user sets a desired temperature through a computer program connected to the apparatus.

Therefore, the constant temperature chamber 104 is changed to -50 ~ 300 ℃, to enable the experiment for all the temperature range that the actual polymer material is used.

The lower chamber 104 may apply a load to the test piece 10 and measure an extended length of the test piece 10. In addition, preliminary stress may be imposed on the test piece 10.

The weight 124 is fixed to the lower connection member 113 to impose a prestress.

The load by the weight 124 is measured on the load cell 114.

In addition, an end of the lower connection member 113 is connected to the crosshead 122. Since the crosshead 122 is guided by two guide shafts 118 and 120, the crosshead 122 is installed to move up and down.

In addition, a screw hole is formed in the crosshead 122, and drive shafts 126 and 128 are screwed into the screw holes, thereby moving up and down due to rotation of the drive shafts 126 and 128.

Bell shaft pulleys 138 and 144 are integrally formed at the ends of the drive shafts 126 and 128, and the driven pulleys 138 and 144 are driven to rotate integrally with the rotation shaft of the servo motor 130 installed in the lower chamber 116. 134 and 140 and the belts 136 and 142 are rotated so that the drive shafts 126 and 128 are integrally rotated.

In addition, the measuring arm 146 is integrally fixed to the lower connection member 113, and the measuring arm 146 is connected to the measuring axis 150 by the wrist 148, and the measuring axis 150 is Is connected to the LVDT 152.

The LVDT 152 is installed in the lower chamber 116 by a bracket 154.

Hereinafter, the operating method according to the present invention.

The test apparatus 100 can be tested in two ways.

The first method determines the heat shrinkage rate by measuring the length of the test piece 10 according to the temperature change.

As shown in FIG. 2, the test piece 10 is fixed to the upper clamp 110 and the lower clamp 111 in the constant temperature chamber 104 capable of arbitrarily setting a temperature atmosphere.

The shape of the test piece 10, 20 may vary according to the requirements of the test as shown in FIG.

Therefore, the test piece 10 is connected to the load cell 114 at the upper side and the crosshead 122 and the measurement arm 146 at the lower side.

The weight 124 is connected to the lower connection member 113 connected to the lower clamp 111 so as to give preliminary stress to the test piece 10.

At this time, it is possible to read the pre-stress value acting on the test piece 10 in the load cell 114.

Then, the temperature of the constant temperature chamber 104 is adjusted by a computer program to change the temperature of the test piece 10.

Therefore, the deformation amount of the test piece 10 is measured by the LVDT 146 according to the temperature change of the test piece 10, wherein the upward movement distance of the LVDT 146 is proportional to the heat shrink and the downward movement is Proportional.

Next, the second method is to determine the heat shrinkage (expansion) force by measuring the force acting on the test piece by changing the length of the test piece due to the temperature change.

In the heat shrinkage force test, the test piece 10 is fixed to the upper clamp 110 and the lower clamp 111 in the constant temperature chamber 104 as shown in FIG. 2.

In addition, the crosshead 122 connected to the lower connection member 113 integrated with the lower clamp 111 is moved downward by driving the servomotor 130.

Therefore, the length of the test piece 10 is increased by the downward displacement of the crosshead 122, and the load applied to the test piece 10 can be measured by the load cell 114.

The third method is a combination of the first method and the second method, it is possible to measure the change in the length of the test piece 10 while varying the load with respect to a specific temperature of the test piece (10).

In this manner, the load change, the length change, and the current temperature change according to the load cell 114 and the LVDT 146 are recorded in real time using a computer.

EXAMPLE

The compounding design of the rubber used in the embodiment of the present invention was targeted to the natural rubber (NR), the contents are as follows.

First, natural rubber formulation is based on 100 phr of natural rubber (STR CV60 AJ2): zinc oxide (ZnO): 6 phr, sulfur (S): 3.50 phr, stearic acid 0.50 phr, Nt-butyl-benzonthiazole-2-sulfen Amides (Nt-butyl-benzonthizol-2-sulfenamide: TBBS) were respectively mixed.

The rubber specimen used in the embodiment of the present invention was produced at 150 ° C. using a mold 200 composed of two divided molds 210 and 220 shown in FIG. 4, and the thickness of the dumbbell specimen shown in FIG. The height is 120 mm.

Here, in the test for the thermal behavior of the rubber specimens, the portion held by the upper and lower clamps was set to 10 mm. In addition, the thickness of the holding part was 15 mm to prevent slipping of the specimen after connecting the clamp.

The thermal shrinkage (expansion) rate of the specimen is determined by the value in the length-time curve due to temperature change at constant prestress.

In this case, after fixing the test piece 10 with the upper clamp 110 and the lower clamp 111, the lower clamp 111 is coupled to the weight 124 using the rod connecting the lower connecting member 113 and The lower connection member 113 is connected to the LVDT 146 to measure a change in length of the test piece 10.

According to the thermal change of the constant temperature chamber 104, the upward movement distance of the LVDT 146 is proportional to thermal contraction and the downward movement is proportional to thermal expansion.

Determine the thermal shrinkage (expansion) rate by measuring the change in length caused by the temperature change of the specimen at a constant prestress. Rubber specimens that are stretched by a certain stress are subjected to heat shrinkage due to entropy elastic behavior when heat is applied, and then expand by heat.

5 shows a representative example using natural rubber, and the heat shrinkage (expansion) rate, S, is determined by the following equation.

Where L _o is the length of the initial specimen and L _s is the length contracted by the thermal change.

The thermal shrinkage (expansion) force of the specimen is determined by measuring the change in force that occurs in the specimen due to temperature changes at constant elongation or compression. In this case, the test piece is fixed with the upper and lower clamps, and the crosshead extending to the lower clamp maintains the predetermined elongation or compression. The force generated on the specimen due to temperature change at constant prestrain or precompression is measured in a load cell located above the thermostat.

Figure 6 shows a representative example for the measurement of the shrinkage force of the rubber test piece by the thermal change at a predetermined preliminary strain.

Specimens with a constant prestrain will increase entropy stress and reach their peak when temperature changes occur. In addition, the stress is relaxed in proportion to the temperature, and the stress may be reduced by thermal expansion of the specimen.

As shown in FIG. 7, the thermal contraction force (or thermal expansion force) and the thermal contraction (expansion) rate generated in the rubber test piece at a constant temperature are inversely proportional. Specimens with thermal changes at constant pressure will initially increase in stress and relieve stress over time.

FIG. 7 is again shown in FIG. 8 to show a correlation between stress change and length change due to heat of the test piece. As can be seen, the change in the force of the specimen with temperature changes can be determined to determine the change in length, ie the volumetric stability, of the specimen due to thermal changes.

For thermal expansion measurements, the specimen is placed between the upper and lower clamps, and the crosshead connected to the lower clamp maintains a predetermined precompression rate. The force generated on the specimen by thermal expansion at a constant precompression rate is measured in a load cell located above the thermostat.

Figure 9 shows a representative example for measuring the force of the rubber test piece by the temperature change at a constant preliminary pressure rate.

As described above, the present invention has been described with reference to the preferred embodiments, but those skilled in the art can variously modify the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. It will be appreciated that it can be changed.

The volume stability due to the thermal change of polymer materials widely used in various industrial fields is closely related to the performance of the product, and the present invention devises a new and simple test method and test apparatus for measuring the volume stability of such polymer products. It was. The present invention will have the effect of improving the quality and performance of the production process and products of the polymer industry.

Due to this importance, the present invention has devised a new and simple test method and test apparatus that can measure the volume stability according to the thermal behavior of the polymer product. The present invention is a polymer

It will contribute to improve the quality and performance of industrial production process and products. The measuring method and measuring device devised in the present invention are not only basic research for analyzing the thermal behavior of various polymer materials, especially rubber materials, but also for polymer products. It is expected to be useful for improving performance.

Claims

A constant temperature chamber maintaining a constant temperature, a temperature control chamber provided with a temperature controller for adjusting the temperature of the constant temperature chamber, an upper clamp and a lower clamp installed in the constant temperature chamber to fix the test piece, and an upper connection with the upper clamp. An upper chamber having a load cell connected to the member;

A cross head connected by the lower clamp and a lower connection member and disposed to be movable up and down by a guide shaft, a drive shaft which is joined to a screw hole formed in the cross head and moves the cross head up and down, and the drive A lower chamber having drive means for rotating the shaft; And

And a measuring arm integrally fixed to the lower connection member, and a measuring axis integrally connected by the measuring arm and the wrist, and comprising an LVDT fixed to the upper chamber or the lower chamber by a bracket.

The apparatus of claim 1, wherein a weight is provided on the lower connection member to impose a prestress on the test piece.

According to claim 1, wherein the drive means, the driven pulley formed integrally with the drive shaft, the servo motor provided in the lower chamber, the drive pulley to rotate integrally with the rotation shaft of the servo motor, the drive pulley And a belt for connecting the driven pulley.

Using the polymer product test apparatus of claim 1,

Applying a constant load to the test piece; And

Measuring the change in length of the test piece with the LVDT while maintaining a plurality of set temperatures of the test piece by adjusting the temperature of the constant temperature chamber.

Using the polymer product test apparatus of claim 1,

Maintaining a predetermined set temperature of the test piece by adjusting a temperature of the constant temperature chamber to the test piece; And

And measuring the change in length of the test piece with the LVDT while changing the load imposed on the test piece by the crosshead.

The method according to claim 4 or 5, wherein the set temperature is -50 ~ 300 ℃.

The method for testing polymer products according to claim 4 or 5, wherein the load acting on the load cell is 500 N or less.