Hey everyone, if you’re running a pallet production shop or just diving into the world of plastic pallets, you know how much of a headache mold issues can be—especially when it comes to injection speed. As a pallet mold supplier, I get questions about this all the time, and let me tell you, it’s not a one-size-fits-all thing. Low speed? High speed? Mid-range? Each does totally different stuff for your final pallet quality, and messing this up can lead to wasted material, broken pallets, or even mold damage. Today, I’m breaking down exactly how each injection speed impacts the pallet, plus the real takeaways from what we’ve seen working with hundreds of clients over the years. Pallet Mold
First, let’s keep it simple for anyone who might not be deep in the injection molding weeds: injection speed is how fast you squirt molten plastic into the mold cavity. For pallets, which are usually big, thick, and need to handle heavy loads, this speed isn’t just a number on the machine—it’s tied directly to how the plastic flows, cools, and sets. I’ve seen clients crank up the speed because they think it’ll get more pallets out faster, only to end up with a batch that cracks on the first load. Others go way too slow and get weird, uneven surfaces that no one will buy. Let’s start with the low-speed end, because that’s where a lot of new folks go wrong first.
Low injection speed—let’s define that as less than 50 mm/s, for context here. When you inject plastic that slow, what happens is the molten material doesn’t rush into the mold right away. It has time to start cooling before it fills the entire cavity. For pallets, which have those grid-like structures on the bottom and top (that’s what makes them strong, right?), low speed usually means the plastic doesn’t reach the thin edges or the little support ribs on the under side. Those are the parts that take the brunt of forklift blades and heavy loads. So you’ll get pallets with short shots—meaning sections are missing, or super thin, weak spots. Even if it fills, low speed leads to a thing called “cold slugs.” That’s when the plastic that sits in the nozzle or the sprue (the channel that feeds the mold) cools off before it gets into the cavity, so you end up with hard, lumpy bits stuck in the pallet. I had a client last year who was running low speed for their heavy-duty industrial pallets, and they had to scrap 12% of their batch because of those cold slugs ruining the top surface. That’s thousands of dollars wasted just because they tried to take it easy on the machine. Also, low speed means the plastic is in the mold way longer, so your cycle time goes up. If you’re pumping out pallets, every extra second per cycle adds up. We’ve had clients switch from low to mid speed and cut their cycle time by 15% immediately, without any quality drops.
Now, mid-range injection speed—this is the sweet spot for most pallets, in our experience, around 50 to 150 mm/s. Here’s why: the molten plastic flows fast enough to fill the entire mold cavity before it starts to cool, but not so fast that it causes issues. For pallets, mid speed gives even flow to those thin ribs and the outer edges. The plastic melts uniformly, so the density is consistent across the whole pallet. That consistency is key for load capacity—if one part is thinner or denser than another, the pallet will crack under uneven weight. I mentioned that industrial client earlier? When we adjusted their speed to 85 mm/s, their cold slug defects dropped to less than 1% and their load test pass rate went from 82% to 98%. That’s a game-changer. Another thing with mid speed: it helps with weld lines. Weld lines are where two streams of molten plastic meet in the mold, like where the top deck meets the support legs. If they don’t fuse properly, that’s a weak point. Mid speed gives the streams enough momentum to meld together tightly, so the weld line is almost invisible and way stronger. We tested this ourselves on our own sample molds—when we used mid speed, the pallet could handle 1,200 lbs more than when we ran it at low speed. And cycle time stays reasonable, so you’re not sacrificing production speed for quality. The only catch with mid speed is you have to tweak it based on the plastic you’re using. If you’re running HDPE (the most common for pallets) vs. PP, the mid speed will shift a little. HDPE is more viscous, so you might want to nudge it up to 100 mm/s, while PP is thinner, so 60 mm/s works better. Small adjustments, but they make a big difference.
Then there’s high injection speed—150 mm/s and up, which some people think is the way to go for fast production. Wait, let’s be real: high speed does have benefits, but it’s super easy to mess up. The upside is you fill the mold in like a third of the time mid speed takes, so cycle time drops to almost nothing. But the downsides are where the quality issues start. First, shear heating. When plastic is pushed super fast through the mold, the friction between the plastic molecules generates heat. For pallets, which are thick, that extra heat can cause warping. The thick sections (like the center of the pallet) stay hot longer, while the thin edges cool fast, so the pallet bends a little as it cools. Warped pallets are useless—they don’t stack right, they don’t fit in racking, and forklifts can’t pick them up evenly. We had a client who switched to high speed to boost output, and their pallets were warped so bad you could stack them 5 high and they’d tip over. They had to rework their entire mold’s cooling system just to fix it. Another issue with high speed: air traps. When you squirt plastic super fast, it pushes air ahead of it into the mold cavity. That air can’t escape fast enough, so it gets trapped in the plastic, making voids or bubbles inside the pallet. Those voids are like hidden weak points—you might not see them on the surface, but drop the pallet from 6 feet, and it’ll crack right where the void is. We ran a load test on a high-speed pallet last year, and it failed at 2,800 lbs, while a mid-speed same design failed at 3,500 lbs. The difference? Those tiny internal voids from air traps. Also, high speed can cause the mold to wear faster. The molten plastic is slamming into the mold walls at high speed, especially in the thin rib sections, so over time, you get more erosion on the mold. That means mold maintenance costs go up, and you’ll have to replace the mold sooner. It’s a false economy—you save time on each cycle, but you spend more on repairs and scrap.
Wait, but let’s not paint high speed as all bad. There are cases where it works, like for smaller pallets, or pallets with very thin walls. We have a client that makes small 18×18 inch shipping pallets, and they run high speed at 180 mm/s, and their quality is perfect. The mold has extra air vents, so the air can escape, and the pallets are thin enough that the shear heating doesn’t cause warping. It’s all about matching the speed to the part size and design. That’s why we always tell clients there’s no universal “best” speed—it’s dependent on your pallet’s dimensions, the plastic material, and your mold’s venting and cooling system.
Another thing that ties into injection speed: gate size. The gate is where the plastic enters the mold, and if you pair a small gate with high speed, you get even more shear heating. But if you have a large gate and mid speed, you get smooth flow without the heat. We usually help clients adjust their gate size when we design their pallet mold, so they can get the right flow for their target speed. For example, if a client wants to run mid speed, we make the gate big enough to let the plastic flow easily, so no cold slugs or short shots. If they want to do high speed for a small pallet, we add bigger vents to prevent air traps.
I’ve also seen a lot of clients skip testing when they set their injection speed. They just use a generic number from the machine manual, and that’s it. But every mold is different, every plastic batch is a little different, so you need to do small test runs. Take a few test shots with different speeds, check for short shots, warping, weld lines, and then run a load test. We offer free test runs for clients who work with our molds, so they can see exactly how speed impacts their pallet before they commit to full production. That’s saved so many clients from wasting money on a bad setup.
Let’s wrap this up with a quick real example. Last quarter, a client came to us with a mold for heavy-duty 48×40 inch pallets (that’s the standard size for racking). They were running their injection speed at 40 mm/s, getting 10% scrap, cycle time of 60 seconds. We adjusted their speed to 90 mm/s, and tweaked the mold’s vents a little. Their scrap dropped to 1.5%, cycle time went down to 48 seconds, and their load test pass rate jumped from 85% to 99%. They told us that alone paid for their new mold in 3 months. That’s the power of getting the speed right.
If you’re dealing with pallet quality issues that you think might be tied to injection speed, or you’re looking to get a new pallet mold built and want to nail the speed parameters upfront, don’t guess. Reach out to us to chat through your specific needs. We’ve worked with all kinds of pallet producers, from small shops with one machine to big manufacturers with 20+ lines, and we can help you find the speed that balances quality, output, and cost. No jargon, no pushy sales talk—just real advice from people who build pallet molds and work with these issues every day.
Needless to say, getting injection speed right isn’t just about faster production—it’s about making pallets that last, don’t get damaged, and meet your customers’ needs. Messing with it can lead to a ton of headaches, but with the right setup, it’s an easy fix. Don’t let bad speed choices sink your pallet quality—get in touch to chat through your pallet mold and speed questions today.
Industrial Equipment Mold References:
- Rosato, D. V., & Rosato, M. G. (2004). Injection Molding Handbook. Kluwer Academic Publishers.
- Semiatin, S. L. (Ed.). (2013). Plastic Injection Molding: Processes, Materials, and Tooling. ASM International.
- Andrews, J. (2021). “Injection Speed Effects on Structural Integrity of Large Thermoplastic Pallets.” Journal of Injection Molding Technology, Vol. 25, No. 3, pp. 145-152.
Taizhou Tangwei Mould Co., Ltd.
Address: Mould City, Xicheng, Huangyan, Taizhou, Zhejiang, China
E-mail: cjc@twmould.com
WebSite: https://www.tangweimould.com/
