Mould on the Bench, Press Standing Idle: What Mould Breakdowns Cost an Indian Moulding Plant (₹)

In most moulding plants the press is rarely what breaks. The mould is: a galled ejector pin, a scaled cooling line, a pinched hot-runner thermocouple. The repair itself is usually short. Most of the cost is the hours the mould spends on a trolley waiting for the toolroom, and on an illustrative 30-press plant that comes to about ₹780 per bench-hour, or nearer ₹1,400 when the press could have been selling.

By the Mama Editorial Team. Mama scopes camera and floor-visibility projects for Indian factories. For owners of Indian injection-moulding units. Every rupee figure is an assumption to replace with your own. For response time and cycle drift, see our injection-moulding camera guide. For scrap and regrind, see the regrind cost breakdown. This article is about the mould itself.

Key takeaways

• Split a mould breakdown into four parts: pulling the mould, waiting in the toolroom queue, the repair, and reloading to an approved first-off. In our worked example the queue is the biggest of the four.
• Most mould faults give a warning. Plastics Technology's tooling columnist says that if an ejector pin squeals, "stop": galling "happens quickly" and more cycles won't cure it (Plastics Technology, 2018).
• Cooling-line scale works slowly and you can't see it. Limescale conducts heat roughly a tenth as well as steel, according to figures collected in a 2025 Scientific Reports paper (Zink et al., 2025). The cost is longer cycles long before anything visibly breaks.
• Base preventive maintenance on shots, not the calendar. About 250,000 cycles is a common starting interval for cleaning an average mould (Plastics Technology, 2010). A 12-second closure mould reaches that in about five and a half weeks. A 45-second crate mould takes nearly five months.
• A shot counter and a camera answer different questions. The counter tells you when the mould stopped cycling and how many shots it has run. A camera shows where the mould went afterwards: the bench, the crane bay, or a trolley in the aisle.

Why mould breakdowns are a separate problem from press breakdowns

A press breakdown has a fault code and a maintenance fitter. A mould breakdown goes elsewhere. The mould comes off, goes to the toolroom, and the press either waits or gets a stand-in job. Because the press is now "on changeover", many Indian plants record the event under changeover rather than breakdown, and the true cost of the mould never appears as a single figure.

The three faults that fill most toolroom benches:

1. Stuck, galled or broken ejector pins. Galling is metal-to-metal adhesive wear. It gets worse with side load, for example when a pin is slightly out of line with its core hole. Plastics Technology's Jim Fattori advises setting the ejector force limit "somewhat greater than" normal running force and tying it to an alarm if the machine allows. Where force can't be monitored, ejection time is a near-equivalent check. Lubrication matters too: he notes the friction coefficient on a lubricated surface is about four times lower than on a dry one (Plastics Technology, 2018). A pin left protruding after an alarm, then closed under high pressure in manual mode, can turn a cheap pin into a damaged cavity.

2. Blocked or scaled cooling lines. Scale narrows the channel, and its low conductivity insulates the steel. A 2025 Scientific Reports simulation paper by Zink and colleagues quotes an earlier measurement of limescale from mould cooling channels at about 1.37 W/m·K, against roughly 15 W/m·K for steel. It also cites a 2007 simulation by the German firm Novoplan in which 1 mm of limescale cut cooling-circuit efficiency by 6% on a box-shaped part (Zink et al., 2025). The same paper summarises a 2018 simulation study as finding that 0.25 mm of scale made little difference to solidification time, but 1 mm lengthened it significantly (Poszwa & Szostak, 2018, as cited by Zink et al.). With hard cooling-tower or borewell water and no descaling, the result is slow cycle-time drift that the shift log calls normal running.

3. Hot-runner faults. Synventive's Bill Rousseau wrote in 2014 that when a zone overshoots, "thermocouples are the more common culprit", that "the more common failure of a thermocouple is a pinch" during reassembly, and that an overshoot "is never the result of a bad heating element" (Plastics Technology, 2014). His advice: diagnose while the tool is still in the press, before pulling it.

Where the hours go: the four stages of a mould breakdown

Most plants time only the repair, often the shortest stage. In our example the queue is 2.5 hours, the repair 1.5 hours, and pull plus reload another 1.5 hours. If the mould is sent out to a tool maker in your cluster, the queue becomes days.

The worked ₹ example: a 30-press plant

Assume a 30-press plant running PP and HDPE parts in two shifts, with 18 mould-caused stops a month, each taking the mould off the press for an average of 5.5 hours (pull 0.5 h, queue 2.5 h, repair 1.5 h, reload and first-off 1.0 h). All the inputs below are working assumptions. We don't quote state minimum wages. Use your own payroll.

Over 18 events a month, that's about ₹77,000 a month (₹9.3 lakh a year) in cash. If the plant is sold out and every lost press-hour is a lost order, it's about ₹1.37 lakh a month (₹16.4 lakh a year).

Halving the queue, from 2.5 to 1.25 hours, frees 22.5 press-hours a month. That's worth about ₹9,400 a month at A+B rates, or about ₹22,900 a month (₹2.7 lakh a year) when sold out. No equipment needed, just a rule for which mould the toolroom takes next.

The ₹375/h rate is the biggest single assumption. If you haven't built a costed rate, our machine hour rate guide shows how. Our piece on what one hour of downtime costs explains why line F belongs in the sum only when you're actually turning work away.

Preventive mould maintenance by shot count, translated into days

Plastics Technology's Steven Johnson suggests 250,000 cycles as a reasonable starting interval for cleaning an average mould. You then adjust it for resin, residue, venting, plating and condensation, and raise it in steps only after inspection shows the mould can take it. In one case, a 48-cavity cap mould was validated in 100,000-cycle steps up to 2.5 million. In another, a medical mould run "even a few hours over the maximum cycle count" showed "excess and measurable wear" (Plastics Technology, 2010).

Calendar-based maintenance ("we clean them at the Diwali shutdown") ignores how differently moulds run. Assuming a press running round the clock, about 22 hours a day (scale up for two-shift running):

The closure mould needs cleaning almost four times as often as the crate mould, and it is usually your highest-volume tool.

Spare mould, spare inserts or spare parts

Before ordering a duplicate mould, rank your moulds by the line F cost. A second mould makes sense only where a single tool supports a big customer, the plant is sold out on it, and the breakdown history is long. For everything else, the cheaper fix is a critical-spares kit per mould: ejector pins of the right length, a heater band, thermocouples of the type your hot-runner controller is set for (check the controller, not the old part's label), O-rings and a set of cooling plugs, kept in a labelled box near the toolroom. If a ₹1,500 part needs a next-day trip to the market, one lost two-shift day costs about ₹6,700 in press and operator time (16 h × ₹418/h at lines A and B). For work beyond your own toolroom, the Ministry of MSME lists 10 Tool Rooms and 8 Technology Development Centres that design and make moulds, dies and fixtures, including tool rooms at Aurangabad, Indore, Ludhiana and Jamshedpur (DC-MSME).

Shot counter versus camera: what each one actually knows

A mould-mounted monitor is the right tool for shots. Progressive Components' CVe Monitor, for example, records cycles, cycle time over the life of the tool and the last 25,000 cycles, activity versus downtime, downtime date ranges, and when maintenance was done (MoldMaking Technology, 2010). Like the press controller, it stops counting the moment the mould stops cycling.

What happens after that is a floor question, and that's where an overhead camera helps:

• the press standing with the platens open and no mould in it;
• the mould on a trolley in the aisle, and for how long;
• the mould on the toolroom bench, and whether anyone is working on it;
• the crane bay busy with another changeover while this press waits;
• the restart: when the press began cycling again and how long it took to reach steady running.

What cameras cannot tell you about a mould

• A camera can't see inside the mould. Scale, a cracked insert, a galled pin or a pinched thermocouple are invisible to it.
• It can't read the hot-runner controller, cooling-water flow or ejector force. Those come from the press, the controller and flow meters.
• It can't count shots as reliably as a mould counter, and it can't tell a good part from a short shot from a ceiling mount.

The camera shows time and location. The counter shows shots. The toolroom report gives the cause. You need all three.

On people: this is about moulds and presses, not about tracking fitters or setters. Report in aggregate by press, mould and shift, never by named individual. Tell the workforce what the cameras are for, and follow the notice requirements in our DPDP worker CCTV notice guide.

Where Mama fits

Mama reads the cameras a plant already has and sends the owner a short plain-language note each morning about where press-hours went the day before. For moulding, that means which presses stood without a mould, how long moulds waited between coming off and being worked on, and how long restarts took. Mama watches machines, moulds and flows, not individual workers, and doesn't replace your shot counter or your toolroom log. Mama can draw a camera plan covering your presses, the mould bench and the toolroom queue. Leave an email or phone in the form below.

FAQ

How often should an injection mould get preventive maintenance? Base it on shots, not the calendar. A widely used starting interval for an average mould is about 250,000 cycles. Raise it in steps only when inspection shows the mould can handle more (Plastics Technology, 2010). Convert the interval into days for each mould using its cycle time, because fast moulds reach it much sooner.

Why do ejector pins keep sticking or breaking? The usual causes are side load from misalignment, poor lubrication and hardness mismatch, all of which lead to galling. Stop the press when a pin squeals, and set an ejector force or ejection-time alarm (Plastics Technology, 2018).

How do I know if my mould cooling lines are scaled? Look for rising cycle time on an unchanged job, uneven mould surface temperatures and lower flow at the same pump setting. Measure flow and temperature drop per circuit. Simulation studies suggest a 1 mm scale layer lengthens solidification time significantly (Poszwa & Szostak, 2018, as summarised in Zink et al., 2025).

What does one hour of mould breakdown cost? In our illustrative 30-press example it's about ₹780 per hour in cash: press time, idle operator, fitter labour, restart scrap and parts. When the plant is sold out and lost press time means lost orders, it's about ₹1,380. Replace each assumption with your own figures.