How to Verify Whether a Supplier's "Parts Per Hour" Claim Includes Color or Mold Changeover Time

When comparing liquid silicone rubber (LSR) injection molding machines, almost every supplier quote includes a headline number: parts per hour, or cycles per hour. It looks like the easiest number to compare — until you realize it rarely means the same thing from one supplier to the next.

The gap usually hides in one place: changeover time. A machine rated at "120 cycles/hour" on paper can produce very different real output depending on whether that number assumes continuous single-color, single-cavity running, or accounts for the color purges, mold swaps, and cold-start warm-up that actually happen on a production floor.

Why This Number Is So Easy to Inflate

Most published cycle-time figures come from a best-case test run: same color, same mold, no interruptions, ideal shot weight, stable ambient temperature. In that scenario, the number is technically accurate — but it's not what a buyer will see once the order includes multiple colors, multiple part numbers, or routine maintenance stops.

Three things are almost always left out of the headline figure:

• Color/material purge time. Switching between silicone colors on a cold-runner system requires purging the barrel and runner path. Depending on the feeding system and shot size, this can range from a few minutes to well over 30 minutes per changeover.

• Mold swap and re-clamping time. Multi-cavity or family molds require re-centering, re-clamping, and often a short trial-shot cycle before stable production resumes.

• Warm-up and first-shot rejects. LSR is temperature-sensitive; the first several shots after any stop are frequently scrapped or reworked until the barrel and mold reach thermal equilibrium.

If your order profile involves frequent color changes or multiple part numbers on the same machine, the difference between "rated capacity" and "effective daily output" can be substantial.

How to Actually Verify the Number

Rather than accepting the quoted parts-per-hour figure at face value, ask the supplier for the underlying assumptions and, where possible, verify them directly.

1. Ask for the test conditions behind the number. Request the shot weight, cavity count, color, and whether the test run included any changeover at all.

2. Ask for a documented changeover time, separately, for both color change and mold change on the specific machine model and feeding system you're evaluating.

3. Request a video or live demonstration of an actual changeover, not just steady-state running. This is the single most reliable way to see real cycle behavior, including how many shots are typically scrapped after a restart.

4. Calculate your own effective output based on your real order pattern: number of colors per day, number of mold changes per week, and typical batch size. A machine that looks fastest in steady-state may not be the most productive machine for your actual production mix.

5. Compare feeding systems, not just machines. A pure electric servo feeding system generally allows faster, more repeatable purging than pneumatic or manually adjusted systems, which can meaningfully shorten changeover time across frequent color changes.

Why This Matters More Than the Sticker Price

For buyers running high-mix, low-to-mid volume production — common in medical, baby-care, and consumer electronics silicone parts — changeover time can account for a significant share of total machine downtime over a month. A machine with a slightly lower steady-state rating but a shorter, better-documented changeover process can outproduce a "faster" machine once real-world order patterns are factored in.

Before finalizing an LSR injection molding machine purchase, treat the "parts per hour" figure as a starting point for a conversation, not a final answer. A supplier willing to walk through changeover time in detail — and show it happening on camera or in a factory visit — is generally a more transparent partner for the life of the equipment.