A Method for Injection Molding (1.5 in. – 4 in.) or (38

mm – 101.6 mm) thick Composite Pistons for use in

Pressurized Cylinder Applications

Project Leader: Harry E. Bundy, Jr., Graduate Studies, MBA

Advisor: Associate Professor David E. Ritter, BBA, JD

ritterd@ct.tamus.edu

School of Business Administration; Texas A&M University -Central Texas, 1901 South Clear Creek Road, Killeen, TX. 76549

Phone: (254) 519-5468 Facsimile: (254) 519-5482

ABSTRACT:

The purpose of this project is to develop a cost effective injection molding method for (1.5 in. – 4 in.) or (38 mm – 101.6 mm) thick composite piston parts. The injection molded compo-site piston is designed w/the purpose of being an industrial

‘substitute’ part for the metallic piston currently used in welded hydraulic and pneumatic powered cylinder applications. It is also the purpose of this project for the composite piston to be capable of meeting ASTM Standards and the rigorous product liability standards of the Power Cylinder Industry.

In today’s advanced society engineered composite techno-logy have enabled producers, innovators, and corporate managers to increase their manufacturing outputs, increase product utility, and increase the stream of free cash flows (FCF’s). This project shall endeavor to make known to manufacturer’s, producer’s, and end-user’s of welded single acting and double acting displacement cylinders that the injection molded composite piston can form as a viable ‘substitute' for the metallic piston.

The injection molding methodology of this project utilized a non-traditional tooling method that facilitated the molding of composite pistons to the following minimum and maximum dimensions in [Table 1].

Table 1: Composite Piston Minimum and Maximum Molding Specifications.

Piston Center Bore Size

.5 in. – 2 in. 12.5 mm – 51 mm

.5 in. – 3.5 in. 12.5 mm – 89 mm

Piston Diameter

1.0 in. – 5.5 in. 25.4 mm – 139.5 mm

1.0 in. to 8 in. 25.4 mm – 203 mm

Piston Seal Grooves

.25 in. – 1.25 in. 6.35 mm – 31.8 mm

.25 in. – 2 in. 6.35 mm – 51 mm

Piston Thickness

1.5 in. – 4 in. 38 mm – 101.6 mm

1.5 in. to 4 in. 38 mm – 101.6 mm

Further, it should be noted that the traditional method or process for molding large, thick-walled composite (plastic) parts is the compression molding method because of its use of longer curing times [Charts 1 & 2] and heated molds to cure parts. Thereby, the following theories have been employed in this paper

consisting of: (1) the heat transformation and the specific heat of metals; (2) the coefficient of thermal expansion; (3) interchange-able tooling techniques; and (4) chemical engineering to scientifically define the non-traditional molding method of this project. Thus throughout this paper the heat transformation and specific heat relationship of carbon steel and aluminum metals are used to illustrate successful injection moldings of large, thick-walled composite piston parts.

Chart 1: INJECTION MOLDING CURE TIMES

180º C

ST

OC

KT

EM

PE

RA

TU

RE

Cure Time 33 Sec.

20º C

TIME Chart 2:

COMPRESSION MOLDING CURE TIMES

180º C

TIME Source: http://www.desmaindia.com

Cure Time 110 Sec.

ST

OC

KT

EM

PE

RA

TU

RE

20º C

KEYWORDS: Injection Molding, Composite Piston, Heat Transformation, Curing Times, Specific Heat, Coefficient of Thermal Expansion, Insert Tooling

INTRODUCTION:

Historically, in the US manufacturing jobs have been the mainstay of economic creation, growth, and capital investment since the industrialized revolution. However from 11990 to 2009 manufacturing jobs in the US have dwindled by nearly 40%, [Chart

3] but outputs has increased by nearly 2600%. In 2009, the increase in outputs defined US Manufacturing as the number one global manufacturer on the planet by producing nearly 19% of all global products. But in 2010, China, who was predicted to overtake the US, became the new number one global manufac-turer, by manufacturing 319.8% to the US 19.4%, of all globally consumed products.

1 U.S. Census Bureau (February 2002). Annual Survey of Manufacturers. Statistics for Industry Groups and Industries: 2000. Retrieved from: http://www.census.-gov/prod/2002-pubs/m00as-1.pdf

Chart 3:

When we compare the two economies we find that they are very different in terms of how much of the Gross Domestic Product (GDP) is made up of each countries manufac-turing output. In the US the manufactur-ing sector accounts

2 William Strauss (August 19, 2010). Is U.S. Manufacturing Disappearing? Federal Reserve Bank of Chicago. Retrieved from: http://midwest.chicagofedblogs.-org/archives/2010/08/bill_strauss_mf.html

3 Peter Marsh (March 14, 2011). Emerging economies flex manufacturing muscle. Financial Times. Retrieved From http://blogs.ft.com/beyondbrics/2011/03/14/-emerging-economies-flex-manufacturing-muscle/#axzz1fOvRaEwT

for 14% of the total GDP; while China’s output is 34% of their GDP [Chart 4]. In comparing each country manufacturing base the US manufacturing base is dominated by goods including;

Aircraft Special Industrial

Machinery Medical and Scientific

Equipment Media-Software

Industries.

In China the manufactur-ing base is skewed toward lower costs and cheaper goods including;

Textiles Apparel Appliances

Chart 4:

Manufacturing as a (%) of GDP

(%)

of

GD

P

But in the future, China is predicted and poised to have more impact on the global economy during the next 20 years than any other country. Thus assuming the current trends persist, China is predicted to become the second largest global economy and military power by 2025 (Global Trends 2025, A Transformed World, National Intelligence Council). Because of this trend and fact that the US manufacturing sector has the highest economic multiplier effect of all other sectors— every dollar in final sales of US manufactured products supports $1.40 in output from other sectors of the US economy. A necessity has been created for US manufacturing to maintain a strong presence in current markets and in new and emerging consumer markets, such as India, South America, and China. Therefore the U.S. Government recognizing the future necessity and potential negative business

by C.C. Economic blog Year

externalities issued the National Export Initiative Executive Order (NEI) to improve the conditions that directly affect the private sector’s ability to export. The objective of the NEI is to double US business export volumes over the next five -years by assisting them to overcome barriers and hurdles when entering new and emerging markets (Whitehouse.Gov, March 11, 2010).

The two primary cost that affects the private sector, particularly US Manufacturer’s and Producer’s and must be marginalized in order to meet NEI goals are material and labor costs. The Manufacturing sector is often heavier on material cost inputs and lighter on labor cost inputs. Whereas, the Production sector is often heavier on labor cost inputs and lighter on material cost intent. This project shall purport a method for US manufacturer’s, producer’s, and end-user’s of welded powered cylinders to better control their primary costs to help them achieve the goals of President Barrack O’bama’s National Export Initiative.

Thereby, US Manufacturer’s and Producer’s of welded

hydraulic and pneumatic powered cylinders can achieve the following benefits by incorporating the composite piston technology into their equipment applications:

1. Reduce material and labor costs. 2. Increase employment and productivity through

outsourcing. 3. Incorporate economic value added (EVA) and market

value added (MVA) technology to increase free cash flows (FCF’s).

4. Help protect current markets by diversifying compo-site material applications to increase product utility.

5. Meet new and emerging market demand for higher quality cylinders in extreme (dry, rainy, and tropical) environments.

INJECTION MOLDING AND TOOLING:

This project utilizes an injection molding method [Figure 1] to mold composite piston parts of varying sizes and geometry. Traditionally, the injection molding method is recommended only for molding thin-walled composite (plastic) parts because of its short cycle times, precise shot volumes, and large part outputs.

The hydraulic and pneumatic composite pistons are (1.5 in. – 4 in.) or (38 mm – 101.6 mm) thick and capable of incorporating different dimensions, volumes, and part geometries. The molding methodology used in this project for molding large, thick-walled piston parts comprised of thermal and material physics, chemical engineering, and the coefficient of thermal expansion concepts integrated into the four stages of injection molding:

Clamping Injection Cooling Ejection

Figure 1:

INJECTION MOLDING MACHINE DIAGRAM

Injection Unit

Clamping Unit

CLAMPING UNIT

This project utilized the following tooling in the injection molding process; two (2) carbon steel mold tool halves, aluminum insert tools, composite and stainless steel sleeves, and a stainless steel interchangeable center pin that was set-up inside the clamping unit of a 160 ton Sinwa Seika injection molding machine.

The specifications of the mold tooling (excluding guide pins) was, as follow: (1) right mold halve (7.50’’ l x 7.50’’ w x 4.50’’ h) incorporating a (6.00’’ dia. x .25’’ l) center bore; a (1.00’’ dia. x 2.00’’ l) stainless steel interchangeable center pin, and two sprue holes of (.50’’ dia. x 4.25’’ l) and (.25’’ dia. x 4.25’’ l; (2) left mold halve (7.50’’ l x 7.50’’ w x 4.50’’ h) incorporating a (6.00’’ dia. x 2.25’ l) center bore; (3) two aluminum insert halves (5.00’’ OD x 4.00’’ ID x 2.00’’ l); and (4) composite and stainless steel sleeves (5.95’’ OD X 4.05’’ ID X 2.00 l) [Figure 2a, 2b, & 2c].

a. Right Halve is one of the non-traditional tool-ing features of this project that facilitated the injection molding of large, thick composite pistons.

Because the specific heat of carbon steel is 480 c(J/Kg•K) and the specific heat of aluminum is 900 c(J/Kg•K). The aluminum in-sert acts as a catalyst by raising the temperature of the insert to produce a small, but measurable

Figure 2:

The tooling set-up required that the molds right halve guide pins are aligned w/the molds left halve guide pin holes (i.e. illus-trated at each mold ends corner in figure 2a & 2b) then closed for alignment. After mold alignment is achieved a sleeve and two aluminum insert halves [Figure 2c] are placed inside of the left mold halve. The aluminum inserts

Source: (Figure 2: a, b, c) C.H. Jones, Inc.

change in resin volume, elonga-tion of the fibers, and the coeffi-cient of thermal expansion.

In effect, the heat transfor-mation of the changing specific heat of the metals facilitate a long-er phase change and increased expansion and elongation of the composite fibers. In turn, the increased expansion and elong-ation of the composite fibers enabled the injection molding of large thick-walled composite piston parts.

INJECTION UNIT

This project utilized a Zytel® HTN53G50HSLRHF BK083 50% glass reinforced (PA 66) poly-amide composite resin that had improved flow and tensile strength properties. Sample specimens of the resin was tested for shrinkage pursuant to ASTM D955 – 08,

b. Left Halve

Sleeves & Aluminum c. Insert halves

“Standard Test Method of Measuring Shrinkage from Mold Dimensions of Thermoplastics” by DuPont Plastics.

The test results indicated that a (.019 in. or .5 mm.) and a (.0079 in. or .2 mm.) mold shrinkage affect in normal and parallel injection molding, respectively. This project performed a sample 20 part normal injection molding production run comprised of; ten (10) composite pistons of (1.985’’ outside diameter x .750’’ center bore x 1.50’’ height w/piston seal grooves); and ten (10) compo-site pistons of; (2.485’’ outside diameter x 1.00’’ center bore x

1.50’’ height w/piston seal grooves) produced the following results in [Table 2].

Table 2: Sample 20 Part Normal Injection Molding Results.

Insert Tool Specification Part Result Mean Shrinkage

1.985 in. OD 1.980 in. .005 in. .750 in. CB .75 in. 0 1.50 in. H 1.475 in. .021 in.

2.485 in. OD 2.480 in .005 in. 1.00 in. CB 1 in. 0 1.50 in. H 1.479 in. .02 in.

Based on the results of the normal injection molding production run there was significantly less shrinkage noted in the outside diameters and center bores of both parts than in the test specimen of (-.014 in.) and (-.019 in.), respectively [Figure 3a & 3b]. However, there was slightly more shrinkage noted in the heights of both parts than in the test specimen of (+.006 in.) [Figure 3a] and (+.002 in.) [Figure 3b], respectively. Figure 3:

a. Wt. 59.2 g (1.985’’x.750’’x1.50’’) b. Wt. 85.6 g (2.485’’x1.00’’x1.50’’)

Source: TPPHCSource: C.H. Jones, Inc.

Some of the reasons that less mold shrinkage occurred in the molded piston parts was contributed to the improved flow

properties of the resin, the molds design, and the heat transfor-mation and specific heat of aluminum and carbon steel metals. The Zytel resin used in this project is also commonly used in the Automotive Industry for engine parts because of its tensile modulus strength; flex modulus strength, high melting tempera-ture and water absorption rates. It had a dry-as-molded (DAM) tensile strength of 245 Mpa and a 50% RH (relative humidity)

tensile strength of 190 Mpa. It had a melting temperature of 300° C or 572 F (i.e. Zytel® HTNFE150004 BK083 best choice for piston w/less than a 3.00’’ diameter) and a reduced water absorption percentage rate that only exists during ambient condition of the resins phase change (DuPont Plastics 2006).

In addition, 4ASTM D5592-94(2002)e1m, “Standard Guide for Material Properties Needed in Engineering Design Using Plastics” required that the resin used in this project was able to meet current stress and engineering safety standards for pressurized cylinder parts. The stress and engineering safety standards required that the maximum rated load capacity of a powered cylinder does not exceed 25% of the strain or stress at break rating of the composite piston. This project used the following equations to calculate the following: (1) the maximum rated load capacity of a powered cylinder; and (2) the strain or stress at break load capacity rating of a composite piston comprised of a Zytel® HTN53G50-LRHF BK083 resin:

Formula: The three-step process below was used to calcu-late the maximum rated load capacity for an example (4.00 in.) or (101.6 mm) hydraulic cylinder.

Step 1: Measure the diameter of the piston of the hydraulic cylinder. If the end of the cylinder has a saddle or other

4 ASTM Standard D5592, 2002, "Standard Guide for Material Properties Needed in Engineering

Design Using Plastics," ASTM International, West Conshohocken, PA, 2002, DOI: 10.1520/D05592-94(2002)e1m, www.astm.org.

fitting, measure the actual piston diameter, and not the fitting, because the fitting could be larger than the piston.

Step 2: Calculate the cross-sectional area of the piston by squaring the diameter, multiplying the result by (π)(3.14), and then divide this result by 4. For instance, for a piston with a 4.00’’ (inch) diameter, the cross sectional area is (4.00’’ (inch) * 4.00’’ (inch) * 3.14)/4 = 12.560 sq. inches or 319.024 sq. mm.

Step 3: Calculate the cylinder’s tonnage/load by multiplying the cross sectional area as calculated above by the pressure capacity of the hydraulic pump, as listed in the pump specifications.

For instance, using the example 4.00 in. cylinder above and a 1000-psi pump, the cylinder maximum load capacity would be:

(12.560 sq. inches) *(1000 psi) = 5,697 kgs. or 12,560 lbs. To convert from kilograms to tons divide 5,697 kgs. by 907 for a 6.28 ton maximum rated load capacity @ 1000 psi. To convert pounds to tons divide 12,560 lbs. by 2000 lbs. to get 6.28 ton maximum rated load capacity @ 1000 psi.

For instance, using the example cylinder above and a 5000 psi pump, the cylinder maximum load capacity would be:

(12.560 sq. inches) *(5000 psi) = 28,486 kgs. or 62,800 lbs. To convert from kilograms to tons divide 28,486 kgs. by 907 for a 31.4 ton maximum rated load capacity @ 5000 psi. To convert pounds to tons divide 62,800 lbs. by 2,000 lbs. for a 31.4 ton maximum rated load capacity @ 5000 psi.

Thus the maximum rated load capacity for a (4.00 in.) or (101.6 mm) hydraulic cylinder is 6.28 tons or 12,560 lbs. or 5,697 kgs. at 1000 psi. and 62,800 lbs. or 24,486 kgs. at 5000 psi. Thus a (4.00 in.) or (101.6 mm) diameter composite piston must possess a stress or strain at break rated load capacity that exceeds the maximum rated load capacity of a (4.00 in.) or (101.6 mm) hydraulic cylinder at 25% of its maximum capacity.

Formula: Please review the formula below to calculate the maximum strain or stress at break capacity of a (4.00 in.) or (101.6 mm) composite piston comprised of a Zytel® HTN53G50HSLRHF BK083 resin.

F(max) = maximum force A = area of a circle formula (πr²)

π = pi (3.14) r = radius formula (½ diameter) must be in meters Te = tensile strength is the maximum stress that a material can be subjected to before failing. m(max) = the maximum mass that can be supported g = Earths gravity pull (9.81 m/s²)

F(max) = A x Te r = dia./2 = 4.00 in./2 = 2.00 in. then convert to meters F(max) = (π r²) x Te F(max) = (π) (.0508m)² (190 x 10^6 N/m²) F(max) = 1540390 Newtons

The force of 1,540,390 Newtons is the maximum weight of the mass that can be supported by a (4.00 in.) or (101.6 mm) composite piston. Next, convert 1,540,390 Newtons to mass.

m(max) = F(max) / g

m(max) = 1540390 N / 9.81 m/s² m(max) = 157,022 kg. or 346,174 lbs, or 173 tons

Thus 157,022 kg or 346,174 lbs. or 173 tons is the maximum load capacity that can be supported by a (4.00 in.) or (101.6 mm) composite piston. However the maximum strain or stress at break rated load capacity is (173 tons max. load capacity x 25% engineers safety risk) = 43.27 tons or 86,543 lbs. or 39,255 kgs. Thereby, the rated strain or stress at break load capacity for the composite piston exceeds the maximum rated load capacity of the sample (4.00 in.) or (101.6 mm) hydraulic cylinder by more than 25%.

COOLING & EJECTION

This project measured the cooling times on the following normal injection molded pistons parts [Figure 4]: (1) 1.985 in. w/piston seal grooves; (2) 2.485 in. w/piston seal grooves; (3) 4.00 in. w/piston seal grooves; and (4) 4.00 in. no/piston seal grooves [Table 3]. The cooling times varied depending on part geometry, specification, and material volume. The cooling time was defined as the time required for the molten or plasticize material to cure and take shape inside of the aluminum insert and capable of ejection.

Source: TPPHCFigure 4:

1.985 in. w/grooves

2.485 in. w/grooves 4.00 in.

w/grooves 4.00 in.

no/grooves

Table 3: Composite Piston Test Moldings.

Piston Specification Seal Grooves Weight Cooling Time

1.985’’x .750’’x1.50’’ Top: .275’’ x .30’’ bottom: .50 x .124’’

59.2 g 120 sec

2.485’’x1.00’’x1.50’’

Top: .50 x .124’’ Bottom: .275’’ x .30’’

85.6 g 140 sec.

4.00’’ x 1.00’’ x 2.00’’

Top: .375’’ x .25’’

Bottom: .375’’ x .25’’

362.4 g 300 sec.

4.00’’ x 1.00’’ x 2.00’’

Top: None Bottom: None

440 g 300 sec.

TEST METHODS AND RESULTS:

One of the chief concerns of this project was augmented at the cooling and ejection stages of the injection molding process. Previously, BASF Corporation in 5Paper Number: 2000-01-1319 noted that the tensile strength of a glass reinforced polyamide (PA 46, PA 6, PA 66) resin could be reduced because of increasing water absorption, part volumes, and temperatures ranging from -40º C to 150º C.

One of the insidious disadvantages of certain plastics, such as polyamides, is their tendency to absorb moisture in ambient conditions during phase changes that can change their properties and performance. Moisture is often absorbed during the polymerization and washing steps of the polymer processing phase and absorbed from surrounding atmosphere changes during storage and use. The moisture is known to affect a range of polymer properties that impacts the materials process-ability, dimensional stability, mechanical, acoustic, electrical, optical, and chemical properties, as well as part performance.

5 BASF Corporation (2003), Tensile Properties of Semi-Crystalline Thermoplastics –Performance

Comparison under Alternative Testing Standard. Retrieved from: http://www2.basf.us//PLASTICSWEB/-displayanyfile?id=0901a-5e180004893

Under dry-as-molded (DAM) conditions polyamide or nylon specimens usually contain 0.1% - 0.3% water. Under room temperature and 50% relative humidity (RH), type 66 polyamide non-reinforced specimens has a tendency to absorb up to 2.5% moisture [Table 4].

Table 4: Influence of RH on Non-Reinforced Polyamides.

Type of PA 30% RH 50% RH 62% RH 100% RH

PA 46 1.4 3.8 5.0 15

PA 6 1.1 2.75 3.85 9.5

PA 66 1.0 2.5 3.6 8.5

The molded composite pistons were tested based on the following testing criteria to define its fitness and intended purpose usage; a high and low altitude drop test, a hydraulic pressurize load test, and a non-destructive X-ray radioscopic test.

A high altitude drop test of (216 in. or 549 cm.) and a low altitude drop test of (72 in. or 183 cm.) were performed on the parts and produced no physical chips, mars, or visual cracks. A pressu-rized test was performed at 3250 psi.@2000 lbs. using a standard hydraulic test stand a 3.00’’ hydraulic cylinder and a test load. The test results produced better than expected results and showed no signs of part wear. A non-destructive x-ray radioscopic test was performed on the composite piston parts after performing a high and low drop test and showed no signs of voids, mars, or internal cracks.

The radioscopic x-ray images were performed by Test Equipment Distributors (TED) (i.e. http://www.tedndt.com/)

pursuant to 6ASTM E543 – 09, “Standard Specification for Agencies Performing Nondestructive Testing” and storage and transfer of radiography imagery pursuant to 7ASTM E2738 – 10, “Standard Practice for Digital Imaging and Communication Non-destructive Evaluation (DICONDE) for Computed Radiography (CR) Test Methods” [Figure 5]. Nevertheless, the x-ray images did indicate the presence and signature of a partial cold-shut on the surface of the composite piston parts. Surface cold-shuts are a common occurrence in the injection molding process that occurs on the surface of a part when the resin combines the ends and cures.

Figure 5:

Images were taken at about 90 kv on our micro-focus system.

Source: Test Equipment Distributors

Cold-Shuts

CONCLUSIONS:

This paper presented a proven methodology for injection molding large, thick-walled composite piston parts for use in powered cylinder equipments. The composite pistons presented in this paper were designed pursuant to ASTM Standard and tested in accordance to current powered cylinder manufacturing

6 ASTM E543, 2009, “Standard Specification for Agencies Performing Nondestructive Testing”

ASTM International, West Conshohocken, PA, 2009, DOI: 10.1520/E00543-09, www.astm.org. 7 ASTM E2738, 2010, “Standard Practice for Digital Imaging and Communication Nondestructive

Evaluation (DICONDE) for Computed Radiography (CR) Test Methods” ASTM International, West Conshohocken, PA, 2010, DOI: 10.1520/E02738-10, www.astm.org

standards. Although there are no current ASTM Standards that can be used to accurately determine the life expectancy of composite parts because of long-term fatigue and stress. The composite piston can offer power cylinder users a greater degree of operating seal life and operating efficiency because of its lack of heat conductivity and reduced friction.

In addition, the composite piston can offer US manufac-turer’s and producer’s a viable solution to better control the cost of production and increase their cylinders functionality in extreme cold, dry, and wet environments. Other Industries that have benefited from similar types of composite technology integrated into their manufacturing processes includes; Airline, Automotive, Transportation, and Military.

ACKNOWLEGDEMENTS:

The project leader would like to extend his gratitude and special thanks to Phil Jones of C.H. Jones, Inc. for his molding and tooling specialized support. Associate Professor, David E. Ritter of Texas A&M University - Central Texas School of Business Administration for taking out the time to mentor this project and ASTM International for choosing this project for an ASTM International Design Grant.

REFERENCE: (1) U.S. Census Bureau (February 2002). Annual Survey of Manufacturers. Statistics for Industry Groups and Industries: 2000. Retrieved from: http://www.census.-gov/prod/2002-pubs/m00as-1.pdf

(2) William Strauss (August 19, 2010). Is U.S. Manufacturing Disappearing? Federal Reserve Bank of Chicago. Retrieved from: http://midwest.chicagofedblogs.org/archives/2010/08/bill_strauss_mf.html

(3) Peter Marsh (March 14, 2011). Emerging economies flex manufacturing muscle. Financial Times. Retrieved From http://blogs.ft.com/beyondbrics/2011/03/14/-emerging-economies-flex-manufacturing-muscle/#axzz1fOvRaEwT

(4) ASTM Standard D5592, 2002, "Standard Guide for Material Properties Needed in Engineering Design Using Plastics." ASTM International, West Conshohocken, PA, DOI: 10.1520/D05592-94(2002)e1m, www.astm.org.

(5) BASF Corporation (2003), Tensile Properties of Semi-Crystalline Thermoplastics –Performance Comparison under Alternative Testing Standard. Retrieved from: http://www2.basf-.us//PLASTICSWEB/displayanyfile?id=0901a-5e180004893

(6) ASTM E543, 2009, “Standard Specification for Agencies Performing Nondestructive Testing.” ASTM International, West Conshohocken, PA, DOI: 10.1520/E00543-09, www.astm.org.

(7) ASTM E2738, 2010, “Standard Practice for Digital Imaging and Communication Nondestructive Evaluation (DICONDE) for Computed Radiography Test Methods.” ASTM International, West Conshohocken, PA, DOI: 10.1520/E02738-10, www.astm.org.

(8) Knight, Jones, and Field (2010), College Physics: A Strategic Approach (Second Edition). Pearson Education Inc., published as Addison-Wesley.

(9) Gregory N. Mania (2012, 2009), Principles of Microeconomics (Sixth Edition). South-Western CENGAGE Learning.

(10) ASTM D955 (2008), “Standard Test Method of Measuring Shrinkage from Mold Dimensions of Thermo-plastics.” ASTM International, West Conshohocken, PA, DOI: 10.1520/D00955-08, www.astm.org.

(11) Gerhardt and Brigham (2011, 2009), CORPORATE FINANCE: A Focused Approach (4th. Edition). South-Western CENGAGE Learning. (12) McMurray, Castellan, and Galantine (2007), Fundamentals of General, Organic, and Biological Chemistry (Fifth Edition). Pearson Prentice Hall. Pearson Education, Inc.