About Me

Personal Compressor Model Project

Hi, welcome to my portfolio! I designed it to showcase some of my various mechanical engineering project experiences. I divided this portfolio into three main categories: Personal Engineering Experience (Samsung/School), Personal Design Projects, and Engineering Design Information. 

I offer Free CAD models of some of my Solidworks projects, various knowledge of common turbomachinery components, and even CSWA and CSWP tips (SolidWorks Certification Tests) . If you need a quick reference for CATIA Shortcuts and how to deal with common CATIA errors, then check out my CATIA Tips and Shortcuts page.

I have experience in the Turbomachinery industry and particularly with Turbo Expanders and Centrifugal Compressors. Thank you for taking a look at what I've created.

Work Experience

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I am a mechanical engineer (BSME ‘12) with six years of turbo machinery experience. I worked with Samsung Techwin, where I had the privilege of working as a design engineer. At Samsung, I helped to design integrally geared centrifugal compressors for air separation and LNG applications. I used CATIA V5 to complete models and drawings, and designed everything with attention to detail in order to minimize wasted manufacturing time in South Korea. I also had the opportunity to visit South Korea, and while there helped to assemble, modify, and test some of our LNG carrier compressors.

I also had the chance to work for a turbomachinery repair company called Sulzer, where I had the unique chance to work along-side mechanics to help assemble and disassemble various machines from small valves to large steam turbines. It was a great opportunity for me to learn through hands-on work, and apply what I was learning in school. I passed four training manual quizzes given to me by engineering with a grade of 90% or more. These quizzes were on centrifugal compressors, screw compressors, axial compressors, and steam turbines. My greatest contribution was creating seven tailor-made MS Word templates to help streamline the writing of job repair scopes in order to save time.

Skills

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• Software: CATIA V5, SolidWorks 2012-2015, AutoCAD, Microsoft Office, Teamcenter, Adobe Photoshop/After Effects/Premiere Pro
  
• Design: Drafting, GD&T ASME/ANSI Y14.5M-1994, bolted joint analysis
  
• Certifications: Certified SolidWorks Professional (CSWP)
  
• Language: Fluent in English and Spanish
  

Passion

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At Samsung, I was introduced to design engineering and have developed a strong interest for the design of machinery, and would love to continue growing in this field of mechanical engineering. I believe this field helps me utilize my best talents: my artistic ability and my engineering knowledge.

Goals

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I have worked hard to attain my SolidWorks professional certification (CSWP) and created my very own model of a two stage compressor to help solidify all that I learned at Samsung. I hope to continue learning SolidWorks and hope to take the expert certification test within the next three years. I also plan to continue learning more of design by creating more personal design projects and sharing them here and on my Youtube channel.

Spring Energized Teflon PTFE Seals

Spring Energized Teflon (PTFE) Seals are commonly used in Turbomachines where an elastomer (e.g. Buna Rubber Orings) will not meet the temperatures, friction requirements, or chemical resistance of an application. PTFE seals provide the lowest coefficient of friction of all sealing materials. You will see these types of seals in the IGV (inlet guide vane) system of a Boil-off gas Compressor. In this application, the PTFE seal will act as a rod seal under linear and reciprocating motion. Another common application, is the static face seal application where the seal is facing either internal or external pressure. There are many popular PTFE variations such as Flexiseal by Parker, Bal Seal, and Variseal by Trelleborg. 


How Do They Work?

These seals consist of a spring energized "U-shaped" jacket with different profiles and make use of different spring types and materials. These seals can meet temperature ranges from -328°F to 500°F or -200°C to 260°C. These are good candidates for cryogenic applications. 


PTFE behaves as a plastic material, so it does not have the elasticity of an elastomer, such as an Oring. They offer little or no memory after being compressed. Most seals made out of PTFE material needs to utilize an energizing element, which is commonly made of a metal spring. There are different spring materials, but they mainly come standard as 17-7ph stainless steel or a 300 series stainless steel. They can have different jacket materials, but they mainly use virgin PTFE (white color seals).

Types of Seals for Turbomachinery

In the Turbomachinery industry there are a variety of seals used to prevent a machine's process gas from leaking into the atmosphere or keep oil from going into the process gas. These types of scenarios can lead to efficiency loss or severe damage to a machine. As temperatures and pressures vary, the choice of a seal will change to meet the specific need and create a suitable seal. To meet these needs, there are a lot of different materials used such as: rubber or graphite. The first choice for a design engineer when sealing is necessary is the Oring. 

The different types of seals are listed below:

-Orings: elastomers that are stretched and compressed to create the seal. Can be used in static and dynamic applications, as well as axial or radial sealing configurations.

-Gaskets: fills the irregularities between two mating surfaces while compressed (e.g. Flanges on pipes) in order to prevent leakage.

-Spring Energized Teflon (PTFE) Seals: These seals consist of a spring energized "U-shaped" jacket with different profiles and make use of different spring types and materials. They are used when normal elastomer orings cannot meet the temperatures (e.g. cryogenic temps in the Expander side of a Turboexpander), friction requirements, or chemical resistance of an application. These seals can meet temperature ranges from -328°F to 500°F or -200°C to 260°C.

Labyrinth Seal Example

-Labyrinth Seals: used for low pressure gas applications and where low leakage could be tolerated. They have the main advantage of being low cost. These seals are non-contact and use multiple "teeth" in order to create a difficult path for the process gas to overcome. Typically these laby seals use little to no friction with very small clearances and will sometimes wear into a mating babbitted bore after a machine is first started up. The main disadvantage with this type of seal is that it can be destabilizing at high pressures.

-Floating Carbon Ring Seals: One of the most commonly used shaft seals for the rotor assembly of an integrally geared compressor. Makes use of floating carbon rings with a very tight clearance. These type of seal has a reasonable cost and also lower leakage rates than labyrinth seals. The main disadvantage is the wear that occurs on the carbon rings over time and the risk of these rings locking up due to high pressure and leading to destabilization. 

Floating Carbon Ring Seal Exploded View

-Dry Gas Seals: The most expensive and complex seal available. Can have various configurations in order to have redundancy to aid in the event of a failure. This however, will require the shaft to grow axially to account for the larger seal configuration. The main disadvantage with this seal is cost and the rotordynamics challenge due to the larger shaft.

Tilting Pad Bearing Preload Calculator

 Here is a quick reference for calculating bearing pad preload. If you want to learn more about the characteristics of bearing assembly clearance, pad clearance and preload then visit my tilting pad bearing design parameters page. A good bearing engineer will look into rotordynamics and start with industry standards, and then fine tune the bearing preload in order to meet a good balance of all factors.

Diametral Clearance and Interference Calculator

Below is a calculator that I created in order to calculate the diametral clearance encountered when trying to assemble a shaft into a part with a bore (hole). 

Tips on Diametral Clearances

This is one of the most common and simple calculations that a designer must do in order to ensure ease of assembly and control critical areas of a machine that will need precise alignment. Clearances will also control the radial tolerance stackup of parts and needs to be attended to so that there will be no assembly issues. A designer should also consider the thermal growth and shrinkage of parts based on material properties during a machine's operation. A good engineer will understand as much as he/she can about the process conditions in order to proper material selection for their parts. A close and tight fit could come apart under operating conditions and become a loose fit due to thermal effects, which may lead to complete failure of a machine.

For example, the Rotor Assemblies and Bullgear Assemblies of an Integrally Geared Centrifugal Compressor (IGC) will need to use tight radial clearances with the fluid film bearings supporting these assemblies. The Impeller/Wheel and Shroud radial clearance of a Centrifugal Compressor or a Turboexpander is one the most critical clearances that is also held to a close clearance and takes into account the axial end play of a machine. Any change to this clearance may reduce the overall machine efficiency drastically, and its effect is relative to size. Therefore, the smaller the machine is, the tighter the clearance, and thus the more effect on efficiency that a clearance has. 

Thread Standard Types and Drawing Specification

 Threads are used both in internal and external applications for fastening two parts and creating a secure mechanical joint with the appropriate hardware combination which will vary with application and process conditions. For holes you use internal threads and for shafts you use external threads. When making an engineering drawing, you have to give the thread size, thread pitch, drill size, thread and drill depths, and thread class.

There are a variety of thread standards used in the world, but the most common include: American and Metric (ISO) thread standards. The American standard is better known as the Unified National Thread which includes UNC (coarse) and UNF (fine) that distinguishes the pitch type. Metric thread which is simply known as "M" also has fine and coarse types.

There are even special threads used for special purposes such as pipe thread standards which are used to join pipes and fittings. The most commonly used pipe thread standards are NPT (National Pipe Threaded), BSPP (British Standard Pipe Parallel) and BSPT (British Standard Pipe Tapered). These are used to define both straight and tapered threads. The British pipe standard BSPP and BSPT have become obsolete recently and have changed to be known as G and R/Rp/Rc designations, respectively. 

Another common thread in industry is the SAE thread type, which uses a straight thread sealing boss. It makes use of a BUNA-N rubber O-ring to ensure sealing of fittings.

When specifying a threaded hole callout there is a common method followed in engineering drawings. Typically you first specify a counterbore depth and size first (if needed), then the drill size and depth, and finally the tap size, pitch, and depth. For example, a threaded hole that is specified in the following way: 1/4"-20 UNC  1"  DP; Indicates that a hole has a thread for a 1/4" bolt that has a Coarse thread pitch that is 20 threads per 1 inch and will be tapped to a depth of 1".

Tilting Pad Design Parameters

Journal Tilting Pad Design:

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When it comes to journal bearings in the Turbomachinery industry, the tilt pad bearing is used for the high speed rotor assemblies of centrifugal compressors because of their design flexibility. Tilting pad bearings usually come configured with 3 to 6 pads. The most commonly used configuration used in the turbomachinery industry is a 5 pad Tilt Pad Journal Bearing (TPJB). There are two main pad orientations that are used to describe how these pads are loaded by the shaft. These are load-on-pad (LOP) or load-between-pads (LBP).
 

You can easily verify which configuration is present for your rotor. Look at your TPJB and if one pad is centered with the very bottom centerline of your rotor, then you have a LOP orientation. If two pads straddle the bottom centerline of your rotor, then you have a LBP orientation.

When designing a tilt pad you have a few common design parameters such as: pad clearance (Cpad), bearing (assembly) clearance (Cbrg), journal (shaft) diameter, and preload.

Typical Tilt Pad Bearing Bores

Bearing (assembly) clearance (Cbrg)

This is equal to the diametral clearance from the assembly bore diameter minus the journal diameter. To get an approximate real life assembly clearance, a lift check can be performed using a dial indicator on the bearing and multiplying this lift by an appropriate factor based on number of pads and orientation.

Pad clearance (Cpad)

This is equal to the diametral clearance from the machined pad bore diameter minus the journal diameter.

Preload (m)

One of the most common design parameters is called preload. As the oil wedge clearance changes during operation, a bearing's damping and stiffness changes. Preload is introduced to describe these variations. Preload is the fraction of distance between the bearing clearance (when concentric) to the pad clearance. Preload can typically vary from 0 to 0.75.

*If you want to calculate your own preload, you can use my own Preload Calculator. 

Preload (m) = 1 - Cbrg/Cpad

Preload is considered positive if the pad clearance is greater than the bearing clearance. When these clearances are equal then your Preload is zero. The downside of using zero preload is that when the shaft is not centered with the bearing, only some pads will create a hydrodynamic pressure which loads the bearing against the housing. The unloaded pads or lightly loaded pads may become unstable and lead to pad "flutter". 

To find preload you must start from somewhere. You typically know the shaft journal diameter where the bearing pads will ride. From there, you will have to establish a reasonable bearing clearance (radial gap) when the shaft journal is concentric with the bearing, between the shaft journal and the pad at the pivot position. Pad clearance is chosen based on achieving either a positive or negative preload, where positive preload is typically desired. The pad clearance is the difference between radius of curvature of the pad profile and the shaft journal radius. Next, you choose a pad thickness with a desirable amount of babbitt thickness for the size of your bearing. Thereby, setting your cage bore where your bearing pad will have its pivot contact area.