The quiet enemy of profit: Waste in PU shoe production
Ever heard the saying: “a stitch in time saves nine”?
Waste is the thief that, quietly and in the shadows, robs producers of their profit. For many factories the trouble is if it’s spread around, it’s hard to notice at first, from materials to rework, rejected pairs and downtime. But over the long term, and when pieced together over a month, it’s not a small number!
If you’re in charge of production or planning a PU production line for safety shoes and rain boots, doing away with waste isn’t just about reigning in costs, it’s right at the heart of how consistent, and straightforward it will make production, and how low you can cut your selling price.
That’s a lot to cover, so we’ll take a down-to-earth approach from the factory floor up.
1. Raw materials in the first place, not the machine
We all expect a lot of waste from our foaming machines. Turns out this can be misleading because a lot of waste starts right in the mostly stable components we’re trying to foam.
The polyol and isocyanate, how it’s stored, and unstable conditions like temperature fluctuations affect frothing behavior. And all this leads to (among many):idd
- density variation
- bad adhesion
- external defects
- higher rejection rates
Simple discipline works in real factories:
keep materials at stable temperature, work with known suppliers, and keep batches separate!
2. Stabilize the mixing and metering system
In PU production a steady soul trumps hurry.
Unstable PU mixing head or poor metering will result in
- Over-pouring: waste of material
- Under-pouring: defective products
- Irregular cell structure
Regular calibration of the dosing system is not something you can skip. Many factories only check when problems become apparent, by which point, of course, it is far too late.
A well-maintained PU machine should give you repeatable results shift after shift. If this is not the case, waste will ensue.
3. Customize mold design and pouring parameters
Waste owing to poor design of the mold is one of those hidden causes. Upon examining this part of your process, chances are you’ll notice:
- Overflow; trimming waste
- Uneven filling
- Air traps
An adjustment of pouring time, shot size, or mold temperature will usually mean an uptick in yield.
In double density PU safety shoe, synchronizing shock-absorbing sole and upper injection is, for instance, critical. A lack of correct timing spells scrap.
Factory homeworkers that take the time to fine-tune this part of the process seldom fail to spot an increase in material loss.
4. Cut down on changingover loss
Where there’s an export, there’s bound to be often switching. Logically, every changeover will incur certain waste:
- Leftover material in the pipes
- Loss in cleaning
- Trial runs and sample rejection
One effective means of reducing this is factory planning: group similar product series together, pay attention to unnecessary changingover, and rationalise maturing of formulations where that is possible.
We are not talking about wiping out flexible production management, but on the contrary getting a better grip on it.
5. Educate the operator beyond that of being trained to push start buttons!
Machines do not waste; only untrained operators do.
Common symptoms include:
- Wrong parameter setting
- Late corrective measures to abnormally occurring situations
- Improper mechanism cleaning and maintenance
Operator training should be aimed to extend beyond “How to run the PU moulder.”
A little understanding of such matters as: “why the parameters are significant,” “why and how the materials behave the way they do,” and even “what the early signs of defects look like,” can go a long way.
Factories devoting precious time and money to proper operator training are almost certain to find their defective instances and variance in overall machinery output dropping.
6. Carefully maintain equipment before trouble strikes
Reactive maintenance is the costliest on the street.
A blocked mixing head, leaking seals, pneumatic pressure control problems do not only mean a downtime; defective materials going out before failure is easily detected does mean waste.
A simple preventive maintenance schedule can avoid three wasteful situations:
- Breakdowns
- Batch-level defects
- Material wastage during trouble-shooting
Take a cautious approach and to an extent teach your operators to look for signs of wear on piping and repair these before they lead to defect problems.
And where OEMs, PU equipment suppliers themselves, offer remote maintenance or fault-clearing, do take advantage of them. Not only do they mean less lost-time, they mean less blindness trial-error inefficient release of new materials.
7. Reuse where possible, but be careful
A certain amount of PU waste material is reusable, depending on the particular application concerned. For example:
- Grinding and restricting certain waste material to right properties for repeat use.
- Defects such as ‘flash’ gradually appearing where they may not seem to exist.
Whichever, however “green” a factory you are, there is a limit which you are free to go with “remix” in producing.
Too heavy on it, you can actually lower the quality of product, and particularly if talking about production of shoes.
The point seems fairly obvious—into what you can as well put as weightlessly.
Woven into the a double density PU shoe you will find that identifying lives or soles from the rest of the shoe is necessary. A matching upper then becomes terribly significant; scrape them both! Making characteristic Yu shoes in anything but find and clear form and temper indicates “waste”! Getting it right takes a bit of close education.
Tightening the system is the real solution
Reducing waste in PU shoe production means not one major sweep change but tightening up the screws.
Reducing waste in PU shoe production is not a one big swing at making a change for the better. It means tightening screws in all departments—that of materials, machines, moulds, and workers.
The factories that run at low margins are not relying on luck or on “experience,” merely on solid principles.
If you are installing another PU shoe production line or attempting to better one with some service, it will pay to review the situation in its entirety.
Some small improvements here and there are worth a whole spruce-up!And in the moonlight, factories that lead in the field control waste pieces of every description are going to prove ahead of the pack price wise.
