Formulate Your Way to Success
By Don Desrosiers, Tailwind Systems
I received an interesting telephone call today that prompted the idea for this column. It’s all about math. You probably hated math in school and never thought you’d really need it. When the pocket calculator came out in 1974, you probably became certain that even if you did need math, you wouldn’t have to struggle with formulas. Sadly, neither Casio nor Radio Shack have built-in functions for g-force or moisture retention or anything else important to you.
Picking It Up
The call was about moisture retention, so let’s start with that. The caller said he had heard a variety of different formulas, so he asked me for the definitive answer. This is a quirky statistic because it isn’t very logical. If you want, say 50% moisture retention, it sounds like what you’re looking for is an amount of fabric where half the weight is water. That would be logical; 50% moisture <retention>, 50% fabric. That’s why this formula, nay, concept, is illogical. That is not at all what 50% moisture retention is.
It is important to note: moisture retention is a critical concept in shirt laundry and linen plants these days. In my plant days, blown sleeve shirt units were merely a light bulb over some engineer’s head. We had high G-force extractors (I had one capable of 1,000 Gs and another capable of 800 Gs) to get the moisture retention down to around 20%. At that level, you need two things, without fail: Keep the shirts damp by keeping them tightly under plastic; with no way for the shirts to get exposed to the atmosphere. Secondly, you need maximum productivity. My plant processed about 465 shirt per hour. If there was a backup anywhere, the shirts would dry out. Then the pressers would need to spray the shirts and production dropped off still further as the house of cards collapsed. This didn’t happen too often, but it was more than zero times. If moisture retention was higher, say 40%, then squeeze time of the presses had to be longer and production could never be 465 shirts per hour.
These days, in order to get a beautiful finish on your blown sleeves, your moisture retention needs to be 50% at a minimum, but I usually recommend 60%. Sixty percent is much wetter than you think. It’s a degree of wetness that may cause your presser to comment. Trust me. 60%. Moisture retention is a critical number. So how do you tell? (No cheating! This is really important)
If the dry weight is 100 pounds and wet weight is 150 pounds, then you have 50% moisture retention. Easy huh? Because the wet weight is 50% more than the dry weight. The challenge is that the numbers that you will encounter will not be such beautiful, cardinal numbers. You’ll get numbers like 83 and 128. Ouch! My head hurts already.
Let’s use the numbers I grasped out of thin air above:
Subtract the dry weight from the wet weight: 128 – 83 = 45
Now divide the difference (45 pounds) by the dry weight (83 pounds) 45/83 = 54%. This is your moisture retention. Here’s another example: dry weight is 35 pounds and the weight right out of the washer is 52 pounds. The difference in weight is 17 pounds. Let’s divide 17 by the dry weight of 35 pounds. This sample’s moisture retention is almost 49%.
I will now predict the future.
You might say, “I’m pretty much right there,” and won’t do anything to alter your moisture retention. You will consider 49% to be essentially 50% and you will forget what I really recommend you attain is 60%. Admittedly, depending on how many shirts have a high polyester and other synthetic fiber content, the more the weight of a given volume of shirts will weigh. That point aside, let’s see what is involved in taking 49% to 60% — perhaps more than you think. You will probably want to make minor adjustments in your extract cycle. Perhaps you are spinning for six minutes, so you might try spinning for five minutes. It won’t make any difference. The majority of water will be extracted during the first 60-90 seconds of the extract cycle. G-force is very powerful. Reduce your extract to one minute. Reduce your extract to one minute. (I typed that twice, so it’s not an editing error.) When you weigh shirts after 60 seconds of extraction, you will probably be right at 60% moisture retention, the quality of your pressing will be inexplicably better, you will save utility costs, your polyester shirts will not need to be sprayed with water and wash time will be shortened. You will be happy.
Pieces pressed per hour is not a reflection of cost, it is strictly a planning tool — and a very important one. To use simple numbers so you don’t need to go find your trusty Texas Instrument Pocket Calculator, let’s say you have a double-buck shirt unit that regularly produces 100 shirts per hour and three drycleaning presses that, collectively, crank out 100 drycleaning pieces per hour as well.
These are PPH. Knowledge of your PPH, based on historical data, is critical here. If you have 500 drycleaning pieces — you guessed it: five hours of work. Presumably, if all of the pieces are not ready and waiting immediately in the morning, you will adjust the start time of the pressers so they never run out of work and are able to maintain the production level of 100 PPH throughout the five hours, which is, of course, critical. If you have historical data, this is not an issue because you already have data proving you do this. PPH data is also indispensable as far as employee scheduling is concerned. Simply put, if you going to do 2,000 drycleaning items this week, your production facility will only be operating for 20 hours this week. Period. How? Figure it out. The proof is in the data.
PPLH is my acronym. Another one you may have heard is PPOH. It’s the same thing but I changed it for a good reason. Pieces Per Operator Hour is misleading and has led many down the wrong path and, in my opinion, cost drycleaners millions of dollars over decades. The word “Operator” is the problem. Seriously, when was the last time you referred to the person who inspects your drycleaning quality or the person who replaces buttons on shirts an “Operator”? I’ll put $100 on never. This led many plant operators to ignore the labor hours of employees who were not “operators.” This, of course, yields bogus PPLH numbers. Someone tells you you should be getting 25 PPOH in your shirt department and then you do your math. You aren’t pleased. 100 shirts per hour with 6 “operators.” The formula is simple and non-negotiable:
Total pieces during a given time divided by the total number of “operator” hours needed to produce those pieces. More on that in a few. For this moment, 100/6 = 17.2 PPOH.
Here, you’re on the ball, and a pretty darn good operator. However, there is no way you’re running 17.2 instead of 25. No way. A wee bit of analysis and you realize the girl who scans bar codes isn’t an “operator” and neither is the guy who washes shirts. They aren’t operating anything. That leaves four employees. 100/4 = 25 PPOH. Bam!
Doing this is the mathematical equivalent to peeling the stickers off a Rubik’s Cube.
I adopted the PPLH acronym about 20 years ago with the hope that this practice would become less likely. Pieces Per Labor Hour is likely to encourage someone to bury some labor hours.
All production labor hours count. Earlier I said: Total pieces during a given time divided by the total number of “operator” hours needed to produce those pieces. I doubt you will ever see it written quite that way. Usually, you will see: “Pieces divided by hours” or “Pieces/Hours.” This is correct except it fails to remind some people what they are missing. Let me explain. In a given day, you do 600 shirts in six hours with four people. PPH is 100, which is great and as planned. 24 total hours (6 hours x 4 people = 24 hours) for a PPLH of 25 (600 shirts divided by 24 labor hours = 25 PPLH). However, the wording of my formula was as such: “…divided by the total number of <labor> hours needed to produce those pieces.” It turns out the washman comes in 30 minutes earlier than everyone else and someone stays 20 minutes after hours to fold a dozen or so shirts. Therefore, the total number of hours “…needed to produce…” is actually 24 hours and 50 minutes. So, the actual calculation is 600 shirts divided by 24.83 labor hours = 24.2 PPLH. The intention is not to split hairs, it is to count every hour. If you cut them loose in space, you are just lying to yourself.
G force – With all the talk about moisture retention, you’ve probably learned that spinning the heck out of shirts isn’t as important as you thought it might be and you’re right. However, there’s more to life than shirts. After all, these days, we are all doing wash & fold and we have all been doing comforters and there are always sheets and tablecloths. Suffice to say, spinning the heck out of fabric still has a big place in our lives. RPM does not have much to do with it. Often, you will ask an equipment salesman about G-force and he will quote you the RPM range. There’s more to it than that. You can have two machines with identical RPM numbers, but vastly different G-forces. If you want to get moisture out of fabric in a hurry, you want high G-force. Here’s the formula.
RPM2 x diameter (in inches) /70,500 = G-force
RPM squared times the drum diameter in inches divided by 70,500. Don’t ask me where 70,500 comes from.
Example: (600 x 600)=360,000; 360,000 x 30” = 10,800,000; 10,800,000/70,500 = 153g
You can use the calculator on your phone.
Don Desrosiers has been in the drycleaning and shirt laundering business since 1978. He is a workflow engineer and a management consultant who provides serves to shirt launderers and drycleaners in the United States, Mexico, and western Europe through Tailwind Systems. He is a member of the Society of Professional Consultants and the 2001 recipient of DLI’s Commitment to Professionalism Award. He can be reached at 186 Narrow Avenue, Westport, MA 02790 or at his office by fax (508) 636-8839; by cell (508) 965-3163; or e-mail at email@example.com. He has a website at www.tailwindsystems.com. The author’s views are his own and do not represent official Drycleaning & Laundry Institute positions.