Recom Engineering

Vacation Work Experience Report

Ahsanul Kabir

13549541

Department of Mechanical Engineering

Curtin University

Introduction to the Company

Recom Engineering is an Australian owned company, established in 1984 for the purpose of

remanufacturing used or faulty compressors and selling them directly to other businesses.

Remanufactured compressors often have a significant cost advantage without having any effect

on the reliability. The Company owns complete re manufacturing facilities in Melbourne,

Brisbane, Sydney and Perth. Customers of the company range from the Australian Navy, mining

and fishing industry, major hospitals to the compressor manufacturing companies themselves

such as Trane, Carrier, Bitzer and York (http://www.recom-eng.com.au/, accessed 16th June 2012).

Generalized Summary of work process

The compressors are dropped off to the warehouse workshop where first it is disassembled in

the following sequence. Initially an electrical test is performed on the rotor circuits to assess if

there were any electrical faults that may have caused the ultimate failure of the compressor.

Relief valves are checked to get rid of any compressed air inside the sump. The oil cap is then

opened to allow the oil to leak out of the sump. After all the oil is drained the heads of the

compressors are unscrewed. If it is a high priority job that needs quick assessment power tools

run on air pressure are used to dismantle it. After the heads are removed, the valve plates can

be taken off for an initial evaluation. If broken pieces of metal make its way into the cylinder

this scars the valve plate as well as the cylinder walls. Also the color of the oil can be used as an

early indicator for probable cause of failure.

The two ends are then unscrewed, one containing the rotor (not applicable to open drives) and

the other containing the oil pump. Following this the compressor is made to stand vertically on

the end containing the rotor and the sump plate is opened. The damage (if any) to the

crankshaft and con-rods is visible from here. Often shattered pieces of con-rods are found in

the sump. The caps of the connecting rods are first unscrewed and removed from the sump

side. The piston and the I beam section of the con rod usually comes out through the head side

(top of the compressor). After all the pistons and the con rods have been removed, the

crankshaft can then finally be taken out of the sump.

For compressors those are there just for routine maintenance, without any visible damage, the

crankshaft and the con rod bores are measured with micro meter screw gauge at all the

locations that held the con rods. The bores would definitely be larger, but if the difference in

readings between the bore diameter and the crankshaft diameter was found to be larger than

4/1000 of an inch, the crank was considered to be worn and needed replacement.

All the other parts, large and heavy such as the rotor or small such as relief valves are

completely disassembled leaving the empty housing of the compressor. Following this a job

card for the compressor is filed which depicts the overall condition of the compressor

subsystems as shown in the image below

Figure 1 Example job card showing damages to different parts

After the job card has been completed, orders can then be made accordingly for the parts that

need replacement. However the parts that are to be reused must be prepared for

remanufacturing. This is done by washing them and performing surface operations on them

when required.

First all the remains of the used gaskets must be removed manually. This can be a tedious

process as sometimes high working pressures and temperatures tend to stamp the gaskets into

the metal surface. In extreme cases special chemicals are used to soak the gaskets overnight so

that they can be removed the next day. After all the surfaces have been cleaned manually, with

gasket remover sand paper and or foam abrasive, they are sent off to washing. First they are

put in a synthetic kerosene wash. Inside this machine there is a circular tray made of thick steel

wires, which rotates at high speeds as a mixture of high pressure kerosene and water is sprayed

over it. This removes all the dirt and oil from the metal parts. Parts that are usually sent to the

kero wash include small nuts and bolts, pistons piston rings, connecting rods, crankshaft, valve

plates in fact everything that does not have rust on them. Rust prone parts are usually dealt

with the hot wash and acid dip. The hot wash machine operates on a similar principle except

the fact it can hold large volume of parts inside and that it uses a spray of very hot water mixed

with a caustic soda around the rotating tray. After the hot wash parts that prone to corrosion

such as the heads, piston and piston rods are dipped into an acid based solution for about 15

minutes. After the dip they are cleaned with high pressure water jet gun and put in the hot was

again to remove traces of the acid.

Figure 2 Rusted heads in the hot wash

Preparing the valve plates is probably one of the most important parts of the remanufacturing

process, since they are one of the key elements of the compressors functionality besides the

pistons and crankshaft. Whereas the pistons are replaced easily and cheaply, valve plates and

crankshafts are often re used after surface treatments. Valve plates contain several other small

parts such as discharge reeds discharge reed containers and suction reeds. All these are

manually disassembled and replaced or cleaned according to their condition. Then the plate is

fixed to a table vice with two bolts and surfaced with sand paper and abrasive foam in order to

clean it. The figure below shows the top view of the valve plates with the discharge reads

bolted down by discharge read containers.

Dischargereeds (usually2 underneath)

Dischargereedcontainer

Figure 3 Valve plate top view

The image above shows the bottom view of the same valve plate of the one in figure 3. This

side faces the pistons and contains the suction reeds. After removing these small parts,

sometimes it is found that the valve plates have been bent due to the stress of the bolts on its

edges. In such cases they are sent to the surface grinder which ensures the surface of the plates

on either side is perfectly planar and smooth.

Figure 4 Valve plate bottom view

Suctionreeds

The crankshaft is mounted on the lathe and given some sand paper treatment to make its

surface clean and smooth unless it is severely damaged by broken connecting rods. Crankshafts

are expensive to replace therefore often it might not be economical to go through with

remanufacturing compressors with damaged crankshafts.

When all the parts are ready for remanufacturing, and the new ordered parts and gaskets have

arrived the assembling process can proceed. It is done by the reverse order as disassembling.

All the parts are initially given a spray and wipe with flushing agent to get rid of any remaining

residues from the washing processes. First the housing is made to stand vertically as mentioned

Figure 6 Surface grinder Figure 5 Valve plate after operation in the surface grinder

before and the crankshaft is inserted through it. The pistons are attached with con rods with

gudgeon pins. The con rod caps are manufactured specific to the con rod I beam sections.

Hence they must be marked to avoid mix up. The piston rings are then put on the pistons. Some

pistons have a specific sequence of rings; hence care should be taken to ensure that the rings

having a light indentation saying “TOP” are facing the top side (pointing outside from the sump).

Also the openings in the rings must be facing away from the gudgeon pins and each other. The

pistons are inserted into the cylinders from the outside and with the help of a piston ring

compressor they are gently tapped inside the cylinders. From the sump side, the con rod cap is

bolted to the con rod containing the piston, sitting perpendicular on the crankshaft. Usually this

process is started at the bottom of the crankshaft, attaching the respective piston, con rod and

cap combination, the fitter gradually moving upwards covering all the cylinders.

After the pistons are in place, and it is checked that the crankshaft is moving smoothly against

the reciprocating motion of the pistons, the sump plate is screwed back on with the new gasket

oiled in between. Oiling the gaskets stops leaking air and makes the system airtight which is a

functional requirement for any compressor. The oil pump is next to be attached to the system,

and it is mounted on one of the ends of the crankshaft. The rotor is mounted on the other end.

The valve plates and the heads are screwed back on similarly with oiled gaskets where

necessary. All the bolts are tightened with a torque wrench set at a predetermined level.

CrankshaftPiston,connecting rod,con rod capalready fitted(going bottomup)

Piston andconnecting rodyet to be fitted

Figure 7 Crankshaft being assembled

The re manufactured compressor goes through two tests before making its way out of the

factory. First is a pressure test where pressure gauges are used to measure if the compressor is

producing the required suction capability. The second is an electrical test which checks if the

rotor is getting the appropriate amount of electrical power.

Journal

Week 1

The first week of work was spent mostly in observing the other professional tradesmen

disassemble or reassemble compressors and use the different machines to prepare parts for re

assembling. I was assigned a mentor, Brendon, and he showed me around the warehouse

explaining briefly what the purpose of each machine was.

Washing involved the least amount of responsibilities where the part had to be simply put

inside the designated washer and a button to be pressed so during the first few weeks I was

often carrying parts in a trolley from the work tables to the washers outside. The hot wash

required parts to be put face down as shown in fig 2 possibly because of the cleaning action of

warm steam mixed with caustic soda rising upwards inside the tray. The kero wash did not

require such preferences however parts with features on either side were often washed twice

turning it once in between washes.

Often I was also required to organize appropriate tools for a job, and this helped me get started

in knowing the names of different tools and identifying the appropriate size from a mere visual

inspection.

Week 2

I was given my first disassembling job in week 2. It was a heavy 6 cylinder 40 hp Bitzer

compressor. There were a certain set of rules that needed to be followed in sequence. First a

technician would check the electrical connectors on top for assessing whether the failure was

due to a fault in the electrical system. Then all the relief valves connected to the sump would

require to be opened in order to let the compressed air that is stuck inside to escape. Then a

small bolt shaped valve usually on the lower side of the oil filter was opened to let all the used

lubricant out of the sump. All of the work tables had a slope towards its center. These tables

also had holes in the center which allowed all the oil to pour below where it was collected in

plastic tanks and sent for recycling. It was noted that if the relief valves were not used to

release the pressure prior to letting the oil out, it would cause the oil to gush out and make a

mess of the workshop.

As the oil would be pouring out, the heads of the compressors were to be opened. Some of

these heads would contain a compressed spring underneath, so one screw was always left on

the head to first evaluate if there was a spring, and if so to remove it before taking out the head.

Following this the oil filter and the rotor was to be removed from either ends of the compressor,

and the compressor would be made to stand vertically on 4 equally spaced screws half screwed

in, on the side of rotor. From this position the sump plate was removed.

At this stage I only observed as my mentor Brendan showed me how to unscrew the con rod

caps from the con rods and remove the crankshaft. I observed that having the correct set of

tools for this job was extremely important as the sump provided a small place to maneuver the

tools in the right direction. At times the crankshaft also required to be rotated to make space

for the tools motion. This was even harder for some compact compressors.

Week 3

This week involved a lot of measurements. There were several crankshafts lying around in the

workshop. I was given the job of measuring them to check if they could be reused. This involved

finding a matching connecting rod (including the cap) for the pistons and measuring there bore

diameter against the diameter of the crankshaft. This was done with a micro meter screw gauge.

Obviously the bores would be larger in size however, for most compressors the rule was that if

the difference was found to be larger than 0.004 inches the crankshaft was considered to be

worn. For some other larger compressors this limiting number was 0.006 inches. 3

measurements were taken at the location of each connecting rods to assess the condition of

the crankshaft. If the difference at any of these locations were found to be larger than the

provided range, the crankshafts were considered worn, and were put in the scrap metal bin to

be recycled by another company.

Throughout the week, I had to disassemble other compressors, one of which was a small 2

cylinder compressor. Due to its inferior size and complexity it helped me achieve a better

understanding of how rotation of the crankshaft allows compression of air in the valve plate.

Other tasks throughout the week involved scraping gaskets from a large 6 cylinder compressor.

Due to its high compression capacity and long time use the gaskets were stamped onto the

metal valve plates’ surface which made them very difficult to scrape. Sometimes chemicals

were used.

Week 4The first few days of week four I observed Brendan modify a piston because the specific piston

required for remanufacturing a very old model compressor was not produced as a standard

part anymore. This was also made possible partially due to the fact that the head of the

required piston did not have any features such has indents for suction reeds, avoiding further

complexities in modification. A standard piston having the same diameter and number of piston

ring groves were selected from the shelf and put on the lathe. Here I observed him take of

0.066 inches from the top of the piston, starting from the outer edges.

There were also a couple of heads and housing that required scraping this week in order to

make the old compressor ready for remanufacture. The heads were rusted, so they also

required hot wash followed by acid dip and water jet spray. It did not take long for me to figure

out that the water jet spray was indeed very powerful, should be used with caution at short

ranges. But after the acid dip, the spray proved effective against rust, and the action of the high

pressure jet seemed to take the rust away with ease. Also due to the water jet, features in the

heads that were unreachable by hand such as relief valve enclosures could be sprayed clean to

remove rust. After the acid dip and the water spray, the parts needed to be put inside the hot

wash again to remove traces of the acid as this might be detrimental for the metals mechanical

properties later on.

Week 5

Not many new orders came in this week, so most of the week was spent cleaning up the

garage, organizing tool sets and making stock inventory. Some of the machines

remanufactured in the prior weeks were also tested before delivery to the customer.

First a pressure test is performed to test the suction capacity of the compressor, and

then an electrical test is performed to ensure that the wiring has been done properly

and the motor is getting the required amount of electrical power.

Other tasks involved disassembling a 6 cylinder compressor. It was a dead one, the rotor

had completely burnt out so would not be economical to remanufacture. Nevertheless I

was told to mark the pistons and connecting rods so that I could remember which

cylinder each of the pistons came from.

Week 6By week 6 I realized I have become better at identifying tools for different jobs, and I was being

trusted with more responsibilities as well. I was asked to paint a remanufactured compressor.

Brendon just showed me how the paint gun works, and how to turn the compressor on, and

how to mix the paint with thinner. It was simple enough, but one of the most exciting jobs I

have done for them so far, especially since I felt I had put my personal touch in the finished

product. By this week I also started using the power tools which saved a lot of time in

unscrewing bolts.

Other jobs during the week involved help Brendan finish assembly by putting on gaskets, oiling

them to stop air leaks and putting the heads on.

During the assembly also helped

Figure 8 oiled head gasket

connect the piston with the connecting rod with gudgeon pins. This was done manually. First

the bore of the connecting rod and piston was lined up and oiled. The gudgeon pin was also

oiled, and then gently inserted through the holes. The push had to be perfectly perpendicular

to the plane otherwise the gudgeons would get stuck.

On assembling, it was important to mark or number the pistons to avoid mix up of the

connecting rod caps. This is shown in the following picture.

Figure 9 Inserting Gudgeons

Figure 10 Figure 10 Picture showing the arrangment of the crankshaft, connecting rods andcaps inside the sump

With the help of a piston ring plier, the rings were placed on the pistons. Some pistons need a

specific sequence of rings, and have “TOP” very lightly indented on the side that requires to be

facing outside.

Week 7

I was asked to put together a damaged compressor. Probably due to the high cost of

remanufacturing as compared to the cost of purchasing a new compressor, the customer had

asked not to fix the compressor after all. However they wanted to keep the spare parts, and

this required the compressor to be bolted together only with a few screws on each side and all

the parts thrown into the sump. The crankshaft was inserted into its bearings and all the small

parts, bolts and broken pieces of the connecting rods were just put inside the sump. Some were

even put inside the cylinder bores before placing the valve plates. Only 4 screws on each side

were used just to ensure that it holds the weight of the loose parts inside.

Other tasks during this week involved the usual scraping of gaskets, and washing of parts to get

rid of rust.

Week 8Had to put together a few more broken compressors. They did not need to be in working

condition. Other responsibilities included just helping Brendan with assemblies by cleaning

parts.

A few more old compressors came in for remanufacturing. After disassembly the parts required

to be cleaned thoroughly by hot wash and acid dip. Occasionally rust was very difficult to get rid

of from some old parts. In between washes, sand paper was used to polish the surfaces free of

rust.

The gaskets associated with the old compressors were also hard to scrape. Special chemical was

often required.

Other jobs during the week involved helping Brendan with assembly. Connecting the crankshaft

and pistons seemed to be the hardest part of the whole job. After Brendan took care of that, I

was asked to put on appropriate valve plates, head gaskets and heads. They were all bolted

down and screwed on with a torque wrench set at 80 Nm.

Week 9

Quiet a few jobs had to be finished this week, so a lot of parts required washing and cleaning.

They were carried in bulk with trollies. It was observed that usually delicate parts such as the

valve plates, pistons and connecting rods that perform most of their function inside the sump

of the compressor go to the synthetic kero wash. This helps remove the dirt that has been

dissolved in the oil and stuck to metal surfaces. Larger parts with exterior features that are

prone to rust went in the hot wash. Here a mixture of caustic soda and steam helped soften the

rust and get rid of loose dirt. After the hot wash, parts were dipped in an acid solution for about

20 minutes. After this treatment the application of high pressure water jet was observed to

gently remove rust of the surface.

If this was not sufficient to get rid of the rust, the parts were sometimes sent to the kero wash.

In the presence of the synthetic kerosene based cleaning agent present in the wash, sandpaper

proved effective against rust on inner surfaces of heads and covers.

Week 10

Continued working to finish the job list from previous week. Parts needed to be perfectly clean

before manufacture. Therefore they went through several cleaning processes after disassembly.

First a manual cleaning with abrasive foam and sandpaper is preferred on some surfaces such

as the valve plate and the housing heads.

After all the jobs were finished, the rest of the week was spent on cleaning up the garage, re

organizing tools and making an inventory of the parts in stock.

Week 11

I had to take out disassemble the electrical connecting board of the compressor. Manual

cleaning was preferred on this small part. There were quiet a few tiny nuts, bolts and washers

in the whole set. As with the valve plates they were fixed to a table vice and scraped with sand

paper and abrasive foam. This seemed sufficient to get the thin layer of rust out for this part.

The small nuts, bolts and washers were cleaned with flushing agent and reassembled. Rewiring

was done according to the diagram present in the plastic box cover of the electrical system. It

was advantageous to put the gasket on before rewiring, to avoid tangling of the wires to the

gasket.

During the week also observed Brendan trying to get a rotor out of its housing by heat. The

compressor was probably old, and the press fit rotor proved difficult to detach. Eventually this

was done by hanging the housing vertically and heating the metal casing around the rotor with

Figure 11 Electrical Connections to the rotor

a blow torch so that it expands. Wires attached to the rotor could then be used to push it down

from a safe sideways distance.

Week 12

During my last week of work in Recom engineering, finally I was given the opportunity to

assemble a small compressor almost all by myself. Most of the parts were already prepared and

ready to go and I had to put in the pieces one at a time. First I had to hone the cylinder inner

walls with honing gun run on compressed air. Then the bores were cleaned with flushing agent.

Two small bolts in the crankshaft were unscrewed and cleaned. These bolts guard the

lubricating passage ways along the crankshaft stopping dirt interacting with it. Compressed air

was passed through these holes, getting rid of any dirt that may have accumulated inside over

the years.

Afterwards the crankshaft was put inside and the compressor was made to stand vertically.

Then gradually the pistons, connecting rods, valve plates, and heads were screwed on. The

rotor and the oil pump was attached at their respective ends. The compressor was tested and

passed.